,,the ,,inventions ,,researches ,,and ,,writings ,,of ,,nikola ,,tesla ,,to ,,his ,,countrymen ,,in ,,eastern ,,europe ,,this ,,record ,,of ,,the ,,work ,,already ,,accomplished ,,by ,,nikola ,,tesla ,,is ,,respectfully ,,dedicated ,illustration3 ,nikola ,tesla ,,the ,,inventions ,,researches ,,and ,,writings ,,of ,,nikola ,,tesla ,,with ,,special ,,reference ,,to ,,his ,,work ,,in ,,polyphase ,,currents ,,and ,,high ,,potential ,,lighting ,,by ,,thomas ,,commerford ,,martin ,editor ,,the ,,electrical ,,engineer2 ,past-,president ,american ,institute ,electrical ,engineers #ahid ,,the ,,electrical ,,engineer ,,new ,,york ,d4 ,,van ,,nostrand ,,company1 ,,new ,,york4 ,entered according to ,act of ,congress in the year #ahic by ,t4 ,c4 ,,martin in the office of the ,librarian of ,congress at ,washington ,press of ,mc,ilroy ,emmet1 #cf ,cortlandt ,st41 ,n4 ,y4 ,,preface4 ,the electrical problems of the present day lie largely in the economical transmission of power and in the radical improvement of the means and methods of illumination4 ,to many workers and thinkers in the domain of electrical invention1 the apparatus and devices that are familiar1 appear cumbrous and wasteful1 and subject to severe limitations4 ,they believe that the principles of current generation must be changed1 the area of current supply be enlarged1 and the appliances used by the consumer be at once cheapened and simplified4 ,the brilliant successes of the past justify them in every expectancy of still more generous fruition4 ,the present volume is a simple record of the pioneer work done in such departments up to date1 by ,mr4 ,nikola ,tesla1 in whom the world has already recognized one of the foremost of modern electrical investigators and inventors4 ,no attempt whatever has been made here to emphasize the importance of his researches and discoveries4 ,great ideas and real inventions win their own way1 determining their own place by intrinsic merit4 ,but with the conviction that ,mr4 ,tesla is blazing a path that electrical development must follow for many years to come1 the compiler has endeavored to bring together all that bears the impress of ,mr4 ,tesla's genius1 and is worthy of preservation4 ,aside from its value as showing the scope of his inventions1 this volume may be of service as indicating the range of his thought4 ,there is intellectual profit in studying the push and play of a vigorous and original mind4 ,although the lively interest of the public in ,mr4 ,tesla's work is perhaps of recent growth1 this volume covers the results of full ten years4 ,it includes his lectures1 miscellaneous articles and discussions1 and makes note of all his inventions thus far known1 particularly those bearing on polyphase motors and the effects obtained with currents of high potential and high frequency4 ,it will be seen that ,mr4 ,tesla has ever pressed forward1 barely pausing for an instant to work out in detail the utilizations that have at once been obvious to him of the new principles he has elucidated4 ,wherever possible his own language has been employed4 ,it may be added that this volume is issued with ,mr4 ,tesla's sanction and approval1 and that permission has been obtained for the re-publication in it of such papers as have been read before various technical societies of this country and ,europe4 ,mr4 ,tesla has kindly favored the author by looking over the proof sheets of the sections embodying his latest researches4 ,the work has also enjoyed the careful revision of the author's friend and editorial associate1 ,mr4 ,joseph ,wetzler1 through whose hands all the proofs have passed4 ,,december1 #ahic4 ,t4 ,c4 ,m4 ,,contents4 ,,part ,i4 ,,polyphase ,,currents4 ,,chapter ,i4 ,,biographical ,,and ,,introductory4 #c ,,chapter ,,ii4 ,a ,,new ,,system ,,of ,,alternating ,,current ,,motors ,,and ,,transformers4 #g ,,chapter ,,iii4 ,,the ,,tesla ,,rotating ,,magnetic ,,field4--,,motors ,,with ,,closed ,,conductors4--,,synchronizing ,,motors4--,,rotating ,,field ,,transformers4 #i ,,chapter ,,iv4 ,,modifications ,,and ,,expansions ,,of ,,the ,,tesla ,,polyphase ,,systems4 #bf ,,chapter ,v4 ,,utilizing ,,familiar ,,types ,,of ,,generators ,,of ,,the ,,continuous ,,current ,,type4 #ca ,,chapter ,,vi4 ,,method ,,of ,,obtaining ,,desired ,,speed ,,of ,,motor ,,or ,,generator4 #cf ,,chapter ,,vii4 ,,regulator ,,for ,,rotary ,,current ,,motors4 #de ,,chapter ,,viii4 ,,single ,,circuit1 ,,self-,,starting ,,synchronizing ,,motors4 #ej ,,chapter ,,ix4 ,,change ,,from ,,double ,,current ,,to ,,single ,,current ,,motors4 #ef ,,chapter ,x4 ,,motor ,,with ,,current ,,lag ,,artificially ,,secured4 #eh ,,chapter ,,xi4 ,,another ,,method ,,of ,,transformation ,,from ,a ,,torque ,,to ,a ,,synchronizing ,,motor4 #fb ,,chapter ,,xii4 ,,magnetic ,,lag ,,motor4 #fg ,,chapter ,,xiii4 ,,method ,,of ,,obtaining ,,difference ,,of ,,phase ,,by ,,magnetic ,,shielding4 #ga ,,chapter ,,xiv4 ,,type ,,of ,,tesla ,,single-,,phase ,,motor4 #gf ,,chapter ,,xv4 ,,motors ,,with ,,circuits ,,of ,,different ,,resistance4 #gi ,,chapter ,,xvi4 ,,motor ,,with ,,equal ,,magnetic ,,energies ,,in ,,field ,,and ,,armature4 #ha ,,chapter ,,xvii4 ,,motors ,,with ,,coinciding ,,maxima ,,of ,,magnetic ,,effect ,,in ,,armature ,,and ,,field4 #hc ,,chapter ,,xviii4 ,,motor ,,based ,,on ,,the ,,difference ,,of ,,phase ,,in ,,the ,,magnetization ,,of ,,the ,,inner ,,and ,,outer ,,parts ,,of ,,an ,,iron ,,core4 #hh ,,chapter ,,xix4 ,,another ,,type ,,of ,,tesla ,,induction ,,motor4 #ib ,,chapter ,,xx4 ,,combinations ,,of ,,synchronizing ,,motor ,,and ,,torque ,,motor4 #ie ,,chapter ,,xxi4 ,,motor ,,with ,a ,,condenser ,,in ,,the ,,armature ,,circuit4 #aja ,,chapter ,,xxii4 ,,motor ,,with ,,condenser ,,in ,,one ,,of ,,the ,,field ,,circuits4 #ajf ,,chapter ,,xxiii4 ,,tesla ,,polyphase ,,transformer4 #aji ,,chapter ,,xxiv4 ,a ,,constant ,,current ,,transformer ,,with ,,magnetic ,,shield ,,between ,,coils ,,of ,,primary ,,and ,,secondary4 #aac ,,part ,,ii4 ,,the ,,tesla ,,effects ,,with ,,high ,,frequency ,,and ,,high ,,potential ,,currents4 ,,chapter ,,xxv4 ,,introductory4--,,the ,,scope ,,of ,,the ,,tesla ,,lectures4 #aai ,,chapter ,,xxvi4 ,,the ,,new ,,york ,,lecture4 ,,experiments ,,with ,,alternate ,,currents ,,of ,,very ,,high ,,frequency1 ,,and ,,their ,,application ,,to ,,methods ,,of ,,artificial ,,illumination1 ,,may #bj1 #ahia4 #ade ,,chapter ,,xxvii4 ,,the ,,london ,,lecture4 ,,experiments ,,with ,,alternate ,,currents ,,of ,,high ,,potential ,,and ,,high ,,frequency1 ,,february #c1 #ahib4 #aih ,,chapter ,,xxviii4 ,,the ,,philadelphia ,,and ,,st4 ,,louis ,,lecture4 ,,on ,,light ,,and ,,other ,,high ,,frequency ,,phenomena1 ,,february ,,and ,,march1 #ahic4 #bid ,,chapter ,,xxix4 ,,tesla ,,alternating ,,current ,,generators ,,for ,,high ,,frequency4 #cgd ,,chapter ,,xxx4 ,,alternate ,,current ,,electrostatic ,,induction ,,apparatus4 #cib ,,chapter ,,xxxi4 ,,massage ,,with ,,currents ,,of ,,high ,,frequency4 #cid ,,chapter ,,xxxii4 ,,electric ,,discharge ,,in ,,vacuum ,,tubes4 #cif ,,part ,,iii4 ,,miscellaneous ,,inventions ,,and ,,writings4 ,,chapter ,,xxxiii4 ,,method ,,of ,,obtaining ,,direct ,,from ,,alternating ,,currents4 #dji ,,chapter ,,xxxiv4 ,,condensers ,,with ,,plates ,,in ,,oil4 #dah ,,chapter ,,xxxv4 ,,electrolytic ,,registering ,,meter4 #dbj ,,chapter ,,xxxvi4 ,,thermo-,,magnetic ,,motors ,,and ,,pyro-,,magnetic ,,generators4 #dbd ,,chapter ,,xxxvii4 ,,anti-,,sparking ,,dynamo ,,brush ,,and ,,commutator4 #dcb ,,chapter ,,xxxviii4 ,,auxiliary ,,brush ,,regulation ,,of ,,direct ,,current ,,dynamos4 #dch ,,chapter ,,xxxix4 ,,improvement ,,in ,,dynamo ,,and ,,motor ,,construction4 #ddh ,,chapter ,,xl4 ,,tesla ,,direct ,,current ,,arc ,,lighting ,,system4 #dea ,,chapter ,,xli4 ,,improvement ,,in ,,unipolar ,,generators4 #dfe ,,part ,,iv4 ,,appendix3 ,,early ,,phase ,,motors ,,and ,,the ,,tesla ,,oscillators4 ,,chapter ,,xlii4 ,,mr4 ,,tesla',s ,,personal ,,exhibit ,,at ,,the ,,world',s ,,fair4 #dgg ,,chapter ,,xliii4 ,,the ,,tesla ,,mechanical ,,and ,,electrical ,,oscillators4 #dhf ,,part ,i4 ,,polyphase ,,currents4 ,,chapter ,i4 ,,biographical ,,and ,,introductory4 ,as an introduction to the record contained in this volume of ,mr4 ,tesla's investigations and discoveries1 a few words of a biographical nature will1 it is deemed1 not be out of place1 nor other than welcome4 ,nikola ,tesla was born in #aheg at ,smiljan1 ,lika1 a borderland region of ,austro-,hungary1 of the ,serbian race1 which has maintained against ,turkey and all comers so unceasing a struggle for freedom4 ,his family is an old and representative one among these ,switzers of ,eastern ,europe1 and his father was an eloquent clergyman in the ,greek ,church4 ,an uncle is to-day ,metropolitan in ,bosnia4 ,his mother was a woman of inherited ingenuity1 and delighted not only in skilful work of the ordinary household character1 but in the construction of such mechanical appliances as looms and churns and other machinery required in a rural community4 ,nikola was educated at ,gospich in the public school for four years1 and then spent three years in the ,real ,schule4 ,he was then sent to ,carstatt1 ,croatia1 where he continued his studies for three years in the ,higher ,real ,schule4 ,there for the first time he saw a steam locomotive4 ,he graduated in #ahgc1 and1 surviving an attack of cholera1 devoted himself to experimentation1 especially in electricity and magnetism4 ,his father would have had him maintain the family tradition by entering the ,church1 but native genius was too strong1 and he was allowed to enter the ,polytechnic ,school at ,gratz1 to finish his studies1 and with the object of becoming a professor of mathematics and physics4 ,one of the machines there experimented with was a ,gramme dynamo1 used as a motor4 ,despite his instructor's perfect demonstration of the fact that it was impossible to operate a dynamo without commutator or brushes1 ,mr4 ,tesla could not be convinced that such accessories were necessary or desirable4 ,he had already seen with quick intuition that a way could be found to dispense with them2 and from that time he may be said to have begun work on the ideas that fructified ultimately in his rotating field motors4 ,in the second year of his ,gratz course1 ,mr4 ,tesla gave up the notion of becoming a teacher1 and took up the engineering curriculum4 ,his studies ended1 he returned home in time to see his father die1 and then went to ,prague and ,buda-,pesth to study languages1 with the object of qualifying himself broadly for the practice of the engineering profession4 ,for a short time he served as an assistant in the ,government ,telegraph ,engineering ,department1 and then became associated with ,m4 ,puskas1 a personal and family friend1 and other exploiters of the telephone in ,hungary4 ,he made a number of telephonic inventions1 but found his opportunities of benefiting by them limited in various ways4 ,to gain a wider field of action1 he pushed on to ,paris and there secured employment as an electrical engineer with one of the large companies in the new industry of electric lighting4 ,it was during this period1 and as early as #ahhb1 that he began serious and continued efforts to embody the rotating field principle in operative apparatus4 ,he was enthusiastic about it2 believed it to mark a new departure in the electrical arts1 and could think of nothing else4 ,in fact1 but for the solicitations of a few friends in commercial circles who urged him to form a company to exploit the invention1 ,mr4 ,tesla1 then a youth of little worldly experience1 would have sought an immediate opportunity to publish his ideas1 believing them to be worthy of note as a novel and radical advance in electrical theory as well as destined to have a profound influence on all dynamo electric machinery4 ,at last he determined that it would be best to try his fortunes in ,america4 ,in ,france he had met many ,americans1 and in contact with them learned the desirability of turning every new idea in electricity to practical use4 ,he learned also of the ready encouragement given in the ,united ,states to any inventor who could attain some new and valuable result4 ,the resolution was formed with characteristic quickness1 and abandoning all his prospects in ,europe1 he at once set his face westward4 ,arrived in the ,united ,states1 ,mr4 ,tesla took off his coat the day he arrived1 in the ,edison ,works4 ,that place had been a goal of his ambition1 and one can readily imagine the benefit and stimulus derived from association with ,mr4 ,edison1 for whom ,mr4 ,tesla has always had the strongest admiration4 ,it was impossible1 however1 that1 with his own ideas to carry out1 and his own inventions to develop1 ,mr4 ,tesla could long remain in even the most delightful employ2 and1 his work now attracting attention1 he left the ,edison ranks to join a company intended to make and sell an arc lighting system based on some of his inventions in that branch of the art4 ,with unceasing diligence he brought the system to perfection1 and saw it placed on the market4 ,but the thing which most occupied his time and thoughts1 however1 all through this period1 was his old discovery of the rotating field principle for alternating current work1 and the application of it in motors that have now become known the world over4 ,strong as his convictions on the subject then were1 it is a fact that he stood very much alone1 for the alternating current had no well recognized place4 ,few electrical engineers had ever used it1 and the majority were entirely unfamiliar with its value1 or even its essential features4 ,even ,mr4 ,tesla himself did not1 until after protracted effort and experimentation1 learn how to construct alternating current apparatus of fair efficiency4 ,but that he had accomplished his purpose was shown by the tests of ,prof4 ,anthony1 made in the of winter #ahhg-h1 when ,tesla motors in the hands of that distinguished expert gave an efficiency equal to that of direct current motors4 ,nothing now stood in the way of the commercial development and introduction of such motors1 except that they had to be constructed with a view to operating on the circuits then existing1 which in this country were all of high frequency4 ,the first full publication of his work in this direction--outside his patents--was a paper read before the ,american ,institute of ,electrical ,engineers in ,new ,york1 in ,may1 #ahhh 7read at the suggestion of ,prof4 ,anthony and the present writer71 when he exhibited motors that had been in operation long previous1 and with which his belief that brushes and commutators could be dispensed with1 was triumphantly proved to be correct4 ,the section of this volume devoted to ,mr4 ,tesla's inventions in the utilization of polyphase currents will show how thoroughly from the outset he had mastered the fundamental idea and applied it in the greatest variety of ways4 ,having noted for years the many advantages obtainable with alternating currents1 ,mr4 ,tesla was naturally led on to experiment with them at higher potentials and higher frequencies than were common or approved of4 ,ever pressing forward to determine in even the slightest degree the outlines of the unknown1 he was rewarded very quickly in this field with results of the most surprising nature4 ,a slight acquaintance with some of these experiments led the compiler of this volume to urge ,mr4 ,tesla to repeat them before the ,american ,institute of ,electrical ,engineers4 ,this was done in ,may1 #ahia1 in a lecture that marked1 beyond question1 a distinct departure in electrical theory and practice1 and all the results of which have not yet made themselves fully apparent4 ,the ,new ,york lecture1 and its successors1 two in number1 are also included in this volume1 with a few supplementary notes4 ,mr4 ,tesla's work ranges far beyond the vast departments of polyphase currents and high potential lighting4 ,the ,miscellaneous section of this volume includes a great many other inventions in arc lighting1 transformers1 pyro-magnetic generators1 thermo-magnetic motors1 third-brush regulation1 improvements in dynamos1 new forms of incandescent lamps1 electrical meters1 condensers1 unipolar dynamos1 the conversion of alternating into direct currents1 etc4 ,it is needless to say that at this moment ,mr4 ,tesla is engaged on a number of interesting ideas and inventions1 to be made public in due course4 ,the present volume deals simply with his work accomplished to date4 ,,chapter ,,ii4 ,a ,,new ,,system ,,of ,,alternating ,,current ,,motors ,,and ,,transformers4 ,the present section of this volume deals with polyphase currents1 and the inventions by ,mr4 ,tesla1 made known thus far1 in which he has embodied one feature or another of the broad principle of rotating field poles or resultant attraction exerted on the armature4 ,it is needless to remind electricians of the great interest aroused by the first enunciation of the rotating field principle1 or to dwell upon the importance of the advance from a single alternating current1 to methods and apparatus which deal with more than one4 ,simply prefacing the consideration here attempted of the subject1 with the remark that in nowise is the object of this volume of a polemic or controversial nature1 it may be pointed out that ,mr4 ,tesla's work has not at all been fully understood or realized up to date4 ,to many readers1 it is believed1 the analysis of what he has done in this department will be a revelation1 while it will at the same time illustrate the beautiful flexibility and range of the principles involved4 ,it will be seen that1 as just suggested1 ,mr4 ,tesla did not stop short at a mere rotating field1 but dealt broadly with the shifting of the resultant attraction of the magnets4 ,it will be seen that he went on to evolve the multiphase system with many ramifications and turns2 that he showed the broad idea of motors employing currents of differing phase in the armature with direct currents in the field2 that he first described and worked out the idea of an armature with a body of iron and coils closed upon themselves2 that he worked out both synchronizing and torque motors2 that he explained and illustrated how machines of ordinary construction might be adapted to his system2 that he employed condensers in field and armature circuits1 and went to the bottom of the fundamental principles1 testing1 approving or rejecting1 it would appear1 every detail that inventive ingenuity could hit upon4 ,now that opinion is turning so emphatically in favor of lower frequencies1 it deserves special note that ,mr4 ,tesla early recognized the importance of the low frequency feature in motor work4 ,in fact his first motors exhibited publicly--and which1 as ,prof4 ,anthony showed in his tests in the winter of #ahhg-h1 were the equal of direct current motors in efficiency1 output and starting torque--were of the low frequency type4 ,the necessity arising1 however1 to utilize these motors in connection with the existing high frequency circuits1 our survey reveals in an interesting manner ,mr4 ,tesla's fertility of resource in this direction4 ,but that1 after exhausting all the possibilities of this field1 ,mr4 ,tesla returns to low frequencies1 and insists on the superiority of his polyphase system in alternating current distribution1 need not at all surprise us1 in view of the strength of his convictions1 so often expressed1 on this subject4 ,this is1 indeed1 significant1 and may be regarded as indicative of the probable development next to be witnessed4 ,incidental reference has been made to the efficiency of rotating field motors1 a matter of much importance1 though it is not the intention to dwell upon it here4 ,prof4 ,anthony in his remarks before the ,american ,institute of ,electrical ,engineers1 in ,may1 #ahhh1 on the two small ,tesla motors then shown1 which he had tested1 stated that one gave an efficiency of about #ej per cent4 and the other a little over sixty per cent4 ,in #ahhi1 some tests were reported from ,pittsburgh1 made by ,mr4 ,tesla and ,mr4 ,albert ,schmid1 on motors up to #aj ,h4 ,p4 and weighing about #hej pounds4 ,these machines showed an efficiency of nearly #ij per cent4 ,with some larger motors it was then found practicable to obtain an efficiency1 with the three wire system1 up to as high as #id and #ie per cent4 ,these interesting figures1 which1 of course1 might be supplemented by others more elaborate and of later date1 are cited to show that the efficiency of the system has not had to wait until the present late day for any demonstration of its commercial usefulness4 ,an invention is none the less beautiful because it may lack utility1 but it must be a pleasure to any inventor to know that the ideas he is advancing are fraught with substantial benefits to the public4 ,,chapter ,,iii4 ,,the ,,tesla ,,rotating ,,magnetic ,,field4--,,motors ,,with ,,closed ,,conductors4--,,synchronizing ,,motors4--,,rotating ,,field ,,transformers4 ,the best description that can be given of what he attempted1 and succeeded in doing1 with the rotating magnetic field1 is to be found in ,mr4 ,tesla's brief paper explanatory of his rotary current1 polyphase system1 read before the ,american ,institute of ,electrical ,engineers1 in ,new ,york1 in ,may1 #ahhh1 under the title ,a ,new ,system of ,alternate ,current ,motors and ,transformers4 ,as a matter of fact1 which a perusal of the paper will establish1 ,mr4 ,tesla made no attempt in that paper to describe all his work4 ,it dealt in reality with the few topics enumerated in the caption of this chapter4 ,mr4 ,tesla's reticence was no doubt due largely to the fact that his action was governed by the wishes of others with whom he was associated1 but it may be worth mention that the compiler of this volume--who had seen the motors running1 and who was then chairman of the ,institute ,committee on ,papers and ,meetings--had great difficulty in inducing ,mr4 ,tesla to give the ,institute any paper at all4 ,mr4 ,tesla was overworked and ill1 and manifested the greatest reluctance to an exhibition of his motors1 but his objections were at last overcome4 ,the paper was written the night previous to the meeting1 in pencil1 very hastily1 and under the pressure just mentioned4 ,in this paper casual reference was made to two special forms of motors not within the group to be considered4 ,these two forms were3 #a4 ,a motor with one of its circuits in series with a transformer1 and the other in the secondary of the transformer4 #b4 ,a motor having its armature circuit connected to the generator1 and the field coils closed upon themselves4 ,the paper in its essence is as follows1 dealing with a few leading features of the ,tesla system1 namely1 the rotating magnetic field1 motors with closed conductors1 synchronizing motors1 and rotating field transformers3-- ,the subject which ,i now have the pleasure of bringing to your notice is a novel system of electric distribution and transmission of power by means of alternate currents1 affording peculiar advantages1 particularly in the way of motors1 which ,i am confident will at once establish the superior adaptability of these currents to the transmission of power and will show that many results heretofore unattainable can be reached by their use2 results which are very much desired in the practical operation of such systems1 and which cannot be accomplished by means of continuous currents4 ,before going into a detailed description of this system1 ,i think it necessary to make a few remarks with reference to certain conditions existing in continuous current generators and motors1 which1 although generally known1 are frequently disregarded4 ,in our dynamo machines1 it is well known1 we generate alternate currents which we direct by means of a commutator1 a complicated device and1 it may be justly said1 the source of most of the troubles experienced in the operation of the machines4 ,now1 the currents so directed cannot be utilized in the motor1 but they must--again by means of a similar unreliable device--be reconverted into their original state of alternate currents4 ,the function of the commutator is entirely external1 and in no way does it affect the internal working of the machines4 ,in reality1 therefore1 all machines are alternate current machines1 the currents appearing as continuous only in the external circuit during their transit from generator to motor4 ,in view simply of this fact1 alternate currents would commend themselves as a more direct application of electrical energy1 and the employment of continuous currents would only be justified if we had dynamos which would primarily generate1 and motors which would be directly actuated by1 such currents4 ,but the operation of the commutator on a motor is twofold2 first1 it reverses the currents through the motor1 and secondly1 it effects automatically1 a progressive shifting of the poles of one of its magnetic constituents4 ,assuming1 therefore1 that both of the useless operations in the systems1 that is to say1 the directing of the alternate currents on the generator and reversing the direct currents on the motor1 be eliminated1 it would still be necessary1 in order to cause a rotation of the motor1 to produce a progressive shifting of the poles of one of its elements1 and the question presented itself--,how to perform this operation by the direct action of alternate currents8 ,i will now proceed to show how this result was accomplished4 ,illustration3 ,,fig4 #a4 ,illustration3 ,,fig4 #a;a4 ,illustration3 ,,fig4 #b4 ,illustration3 ,,fig4 #b;a4 ,in the first experiment a drum-armature was provided with two coils at right angles to each other1 and the ends of these coils were connected to two pairs of insulated contact-rings as usual4 ,a ring was then made of thin insulated plates of sheet-iron and wound with four coils1 each two opposite coils being connected together so as to produce free poles on diametrically opposite sides of the ring4 ,the remaining free ends of the coils were then connected to the contact-rings of the generator armature so as to form two independent circuits1 as indicated in ,fig4 #i4 ,it may now be seen what results were secured in this combination1 and with this view ,i would refer to the diagrams1 ,figs4 #a to #h;a4 ,the field of the generator being independently excited1 the rotation of the armature sets up currents in the coils ,c ,c#a1 varying in strength and direction in the well-known manner4 ,in the position shown in ,fig4 #a1 the current in coil ,c is nil1 while coil ,c#a is traversed by its maximum current1 and the connections may be such that the ring is magnetized by the coils c#a c#a1 as indicated by the letters ,n ,s in ,fig4 #a;a1 the magnetizing effect of the coils c c being nil1 since these coils are included in the circuit of coil ,c4 ,illustration3 ,,fig4 #c4 ,illustration3 ,,fig4 #c;a4 ,in ,fig4 #b1 the armature coils are shown in a more advanced position1 one-eighth of one revolution being completed4 ,fig4 #b;a illustrates the corresponding magnetic condition of the ring4 ,at this moment the coil ,c#a generates a current of the same direction as previously1 but weaker1 producing the poles n#a s#a upon the ring2 the coil ,c also generates a current of the same direction1 and the connections may be such that the coils c c produce the poles n s1 as shown in ,fig4 #b;a4 ,the resulting polarity is indicated by the letters ,n ,s1 and it will be observed that the poles of the ring have been shifted one-eighth of the periphery of the same4 ,illustration3 ,,fig4 #d4 ,illustration3 ,,fig4 #d;a4 ,in ,fig4 #c the armature has completed one quarter of one revolution4 ,in this phase the current in coil ,c is a maximum1 and of such direction as to produce the poles ,n ,s in ,fig4 #c;a1 whereas the current in coil ,c#a is nil1 this coil being at its neutral position4 ,the poles ,n ,s in ,fig4 #c;a are thus shifted one quarter of the circumference of the ring4 ,fig4 #d shows the coils ,c ,c in a still more advanced position1 the armature having completed three-eighths of one revolution4 ,at that moment the coil ,c still generates a current of the same direction as before1 but of less strength1 producing the comparatively weaker poles n s in ,fig4 #d;a4 ,the current in the coil ,c#a is of the same strength1 but opposite direction4 ,its effect is1 therefore1 to produce upon the ring the poles n#a s#a1 as indicated1 and a polarity1 ,n ,s1 results1 the poles now being shifted three-eighths of the periphery of the ring4 ,illustration3 ,,fig4 #e4 ,illustration3 ,,fig4 #e;a4 ,in ,fig4 #e one half of one revolution of the armature is completed1 and the resulting magnetic condition of the ring is indicated in ,fig4 #e;a4 ,now the current in coil ,c is nil1 while the coil ,c#a yields its maximum current1 which is of the same direction as previously2 the magnetizing effect is1 therefore1 due to the coils1 c#a c#a alone1 and1 referring to ,fig4 #e;a1 it will be observed that the poles ,n ,s are shifted one half of the circumference of the ring4 ,during the next half revolution the operations are repeated1 as represented in the ,figs4 #f to #h;a4 ,illustration3 ,,fig4 #f4 ,illustration3 ,,fig4 #f;a4 ,a reference to the diagrams will make it clear that during one revolution of the armature the poles of the ring are shifted once around its periphery1 and1 each revolution producing like effects1 a rapid whirling of the poles in harmony with the rotation of the armature is the result4 ,if the connections of either one of the circuits in the ring are reversed1 the shifting of the poles is made to progress in the opposite direction1 but the operation is identically the same4 ,instead of using four wires1 with like result1 three wires may be used1 one forming a common return for both circuits4 ,illustration3 ,,fig4 #g4 ,illustration3 ,,fig4 #g;a4 ,this rotation or whirling of the poles manifests itself in a series of curious phenomena4 ,if a delicately pivoted disc of steel or other magnetic metal is approached to the ring it is set in rapid rotation1 the direction of rotation varying with the position of the disc4 ,for instance1 noting the direction outside of the ring it will be found that inside the ring it turns in an opposite direction1 while it is unaffected if placed in a position symmetrical to the ring4 ,this is easily explained4 ,each time that a pole approaches1 it induces an opposite pole in the nearest point on the disc1 and an attraction is produced upon that point2 owing to this1 as the pole is shifted further away from the disc a tangential pull is exerted upon the same1 and the action being constantly repeated1 a more or less rapid rotation of the disc is the result4 ,as the pull is exerted mainly upon that part which is nearest to the ring1 the rotation outside and inside1 or right and left1 respectively1 is in opposite directions1 ,fig4 #i4 ,when placed symmetrically to the ring1 the pull on the opposite sides of the disc being equal1 no rotation results4 ,the action is based on the magnetic inertia of iron2 for this reason a disc of hard steel is much more affected than a disc of soft iron1 the latter being capable of very rapid variations of magnetism4 ,such a disc has proved to be a very useful instrument in all these investigations1 as it has enabled me to detect any irregularity in the action4 ,a curious effect is also produced upon iron filings4 ,by placing some upon a paper and holding them externally quite close to the ring1 they are set in a vibrating motion1 remaining in the same place1 although the paper may be moved back and forth2 but in lifting the paper to a certain height which seems to be dependent on the intensity of the poles and the speed of rotation1 they are thrown away in a direction always opposite to the supposed movement of the poles4 ,if a paper with filings is put flat upon the ring and the current turned on suddenly1 the existence of a magnetic whirl may easily be observed4 ,to demonstrate the complete analogy between the ring and a revolving magnet1 a strongly energized electro-magnet was rotated by mechanical power1 and phenomena identical in every particular to those mentioned above were observed4 ,obviously1 the rotation of the poles produces corresponding inductive effects and may be utilized to generate currents in a closed conductor placed within the influence of the poles4 ,for this purpose it is convenient to wind a ring with two sets of superimposed coils forming respectively the primary and secondary circuits1 as shown in ,fig4 #aj4 ,in order to secure the most economical results the magnetic circuit should be completely closed1 and with this object in view the construction may be modified at will4 ,illustration3 ,,fig4 #h4 ,illustration3 ,,fig4 #h;a4 ,the inductive effect exerted upon the secondary coils will be mainly due to the shifting or movement of the magnetic action2 but there may also be currents set up in the circuits in consequence of the variations in the intensity of the poles4 ,however1 by properly designing the generator and determining the magnetizing effect of the primary coils1 the latter element may be made to disappear4 ,the intensity of the poles being maintained constant1 the action of the apparatus will be perfect1 and the same result will be secured as though the shifting were effected by means of a commutator with an infinite number of bars4 ,in such case the theoretical relation between the energizing effect of each set of primary coils and their resultant magnetizing effect may be expressed by the equation of a circle having its centre coinciding with that of an orthogonal system of axes1 and in which the radius represents the resultant and the co-ordinates both of its components4 ,these are then respectively the sine and cosine of the angle a between the radius and one of the axes 7,,ox74 ,referring to ,fig4 #aa1 we have r#b x#b y#b2 where x r cos a1 and y r sin a4 ,assuming the magnetizing effect of each set of coils in the transformer to be proportional to the current--which may be admitted for weak degrees of magnetization--then x ,kc and y ,kc#a1 where ,k is a constant and c and c#a the current in both sets of coils respectively4 ,supposing1 further1 the field of the generator to be uniform1 we have for constant speed c#a ,k#a sin a and c ,k#a sin 7#ij deg4 a7 ,k#a cos a1 where ,k#a is a constant4 ,see ,fig4 #ab4 ,therefore1 x ,kc ,k ,k#a cos a2 y ,kc#a ,k ,k#a sin a2 and ,k ,k#a r4 ,illustration3 ,,fig4 #i4 ,that is1 for a uniform field the disposition of the two coils at right angles will secure the theoretical result1 and the intensity of the shifting poles will be constant4 ,but from r#b x#b y#b it follows that for y #j1 r x2 it follows that the joint magnetizing effect of both sets of coils should be equal to the effect of one set when at its maximum action4 ,in transformers and in a certain class of motors the fluctuation of the poles is not of great importance1 but in another class of these motors it is desirable to obtain the theoretical result4 ,in applying this principle to the construction of motors1 two typical forms of motor have been developed4 ,first1 a form having a comparatively small rotary effort at the start but maintaining a perfectly uniform speed at all loads1 which motor has been termed synchronous4 ,second1 a form possessing a great rotary effort at the start1 the speed being dependent on the load4 ,these motors may be operated in three different ways3 #a4 ,by the alternate currents of the source only4 #b4 ,by a combined action of these and of induced currents4 #c4 ,by the joint action of alternate and continuous currents4 ,illustration3 ,,fig4 #aj4 ,the simplest form of a synchronous motor is obtained by winding a laminated ring provided with pole projections with four coils1 and connecting the same in the manner before indicated4 ,an iron disc having a segment cut away on each side may be used as an armature4 ,such a motor is shown in ,fig4 #i4 ,the disc being arranged to rotate freely within the ring in close proximity to the projections1 it is evident that as the poles are shifted it will1 owing to its tendency to place itself in such a position as to embrace the greatest number of the lines of force1 closely follow the movement of the poles1 and its motion will be synchronous with that of the armature of the generator2 that is1 in the peculiar disposition shown in ,fig4 #i1 in which the armature produces by one revolution two current impulses in each of the circuits4 ,it is evident that if1 by one revolution of the armature1 a greater number of impulses is produced1 the speed of the motor will be correspondingly increased4 ,considering that the attraction exerted upon the disc is greatest when the same is in close proximity to the poles1 it follows that such a motor will maintain exactly the same speed at all loads within the limits of its capacity4 ,to facilitate the starting1 the disc may be provided with a coil closed upon itself4 ,the advantage secured by such a coil is evident4 ,on the start the currents set up in the coil strongly energize the disc and increase the attraction exerted upon the same by the ring1 and currents being generated in the coil as long as the speed of the armature is inferior to that of the poles1 considerable work may be performed by such a motor even if the speed be below normal4 ,the intensity of the poles being constant1 no currents will be generated in the coil when the motor is turning at its normal speed4 ,instead of closing the coil upon itself1 its ends may be connected to two insulated sliding rings1 and a continuous current supplied to these from a suitable generator4 ,the proper way to start such a motor is to close the coil upon itself until the normal speed is reached1 or nearly so1 and then turn on the continuous current4 ,if the disc be very strongly energized by a continuous current the motor may not be able to start1 but if it be weakly energized1 or generally so that the magnetizing effect of the ring is preponderating1 it will start and reach the normal speed4 ,such a motor will maintain absolutely the same speed at all loads4 ,it has also been found that if the motive power of the generator is not excessive1 by checking the motor the speed of the generator is diminished in synchronism with that of the motor4 ,it is characteristic of this form of motor that it cannot be reversed by reversing the continuous current through the coil4 ,illustration3 ,,fig4 #aa4 ,illustration3 ,,fig4 #ab4 ,the synchronism of these motors may be demonstrated experimentally in a variety of ways4 ,for this purpose it is best to employ a motor consisting of a stationary field magnet and an armature arranged to rotate within the same1 as indicated in ,fig4 #ac4 ,in this case the shifting of the poles of the armature produces a rotation of the latter in the opposite direction4 ,it results therefrom that when the normal speed is reached1 the poles of the armature assume fixed positions relatively to the field magnet1 and the same is magnetized by induction1 exhibiting a distinct pole on each of the pole-pieces4 ,if a piece of soft iron is approached to the field magnet1 it will at the start be attracted with a rapid vibrating motion produced by the reversals of polarity of the magnet1 but as the speed of the armature increases1 the vibrations become less and less frequent and finally entirely cease4 ,then the iron is weakly but permanently attracted1 showing that synchronism is reached and the field magnet energized by induction4 ,the disc may also be used for the experiment4 ,if held quite close to the armature it will turn as long as the speed of rotation of the poles exceeds that of the armature2 but when the normal speed is reached1 or very nearly so1 it ceases to rotate and is permanently attracted4 ,illustration3 ,,fig4 #ac4 ,a crude but illustrative experiment is made with an incandescent lamp4 ,placing the lamp in circuit with the continuous current generator and in series with the magnet coil1 rapid fluctuations are observed in the light in consequence of the induced currents set up in the coil at the start2 the speed increasing1 the fluctuations occur at longer intervals1 until they entirely disappear1 showing that the motor has attained its normal speed4 ,a telephone receiver affords a most sensitive instrument2 when connected to any circuit in the motor the synchronism may be easily detected on the disappearance of the induced currents4 ,in motors of the synchronous type it is desirable to maintain the quantity of the shifting magnetism constant1 especially if the magnets are not properly subdivided4 ,to obtain a rotary effort in these motors was the subject of long thought4 ,in order to secure this result it was necessary to make such a disposition that while the poles of one element of the motor are shifted by the alternate currents of the source1 the poles produced upon the other elements should always be maintained in the proper relation to the former1 irrespective of the speed of the motor4 ,such a condition exists in a continuous current motor2 but in a synchronous motor1 such as described1 this condition is fulfilled only when the speed is normal4 ,illustration3 ,,fig4 #ad4 ,the object has been attained by placing within the ring a properly subdivided cylindrical iron core wound with several independent coils closed upon themselves4 ,two coils at right angles as in ,fig4 #ad1 are sufficient1 but a greater number may be advantageously employed4 ,it results from this disposition that when the poles of the ring are shifted1 currents are generated in the closed armature coils4 ,these currents are the most intense at or near the points of the greatest density of the lines of force1 and their effect is to produce poles upon the armature at right angles to those of the ring1 at least theoretically so2 and since this action is entirely independent of the speed--that is1 as far as the location of the poles is concerned--a continuous pull is exerted upon the periphery of the armature4 ,in many respects these motors are similar to the continuous current motors4 ,if load is put on1 the speed1 and also the resistance of the motor1 is diminished and more current is made to pass through the energizing coils1 thus increasing the effort4 ,upon the load being taken off1 the counter-electromotive force increases and less current passes through the primary or energizing coils4 ,without any load the speed is very nearly equal to that of the shifting poles of the field magnet4 ,illustration3 ,,fig4 #ae4 ,illustration3 ,,fig4 #af4 ,illustration3 ,,fig4 #ag4 ,it will be found that the rotary effort in these motors fully equals that of the continuous current motors4 ,the effort seems to be greatest when both armature and field magnet are without any projections2 but as in such dispositions the field cannot be concentrated1 probably the best results will be obtained by leaving pole projections on one of the elements only4 ,generally1 it may be stated the projections diminish the torque and produce a tendency to synchronism4 ,a characteristic feature of motors of this kind is their property of being very rapidly reversed4 ,this follows from the peculiar action of the motor4 ,suppose the armature to be rotating and the direction of rotation of the poles to be reversed4 ,the apparatus then represents a dynamo machine1 the power to drive this machine being the momentum stored up in the armature and its speed being the sum of the speeds of the armature and the poles4 ,illustration3 ,,fig4 #ah4 ,illustration3 ,,fig4 #ai4 ,illustration3 ,,fig4 #bj4 ,illustration3 ,,fig4 #ba4 ,if we now consider that the power to drive such a dynamo would be very nearly proportional to the third power of the speed1 for that reason alone the armature should be quickly reversed4 ,but simultaneously with the reversal another element is brought into action1 namely1 as the movement of the poles with respect to the armature is reversed1 the motor acts like a transformer in which the resistance of the secondary circuit would be abnormally diminished by producing in this circuit an additional electromotive force4 ,owing to these causes the reversal is instantaneous4 ,if it is desirable to secure a constant speed1 and at the same time a certain effort at the start1 this result may be easily attained in a variety of ways4 ,for instance1 two armatures1 one for torque and the other for synchronism1 may be fastened on the same shaft and any desired preponderance may be given to either one1 or an armature may be wound for rotary effort1 but a more or less pronounced tendency to synchronism may be given to it by properly constructing the iron core2 and in many other ways4 ,as a means of obtaining the required phase of the currents in both the circuits1 the disposition of the two coils at right angles is the simplest1 securing the most uniform action2 but the phase may be obtained in many other ways1 varying with the machine employed4 ,any of the dynamos at present in use may be easily adapted for this purpose by making connections to proper points of the generating coils4 ,in closed circuit armatures1 such as used in the continuous current systems1 it is best to make four derivations from equi-distant points or bars of the commutator1 and to connect the same to four insulated sliding rings on the shaft4 ,in this case each of the motor circuits is connected to two diametrically opposite bars of the commutator4 ,in such a disposition the motor may also be operated at half the potential and on the three-wire plan1 by connecting the motor circuits in the proper order to three of the contact rings4 ,in multipolar dynamo machines1 such as used in the converter systems1 the phase is conveniently obtained by winding upon the armature two series of coils in such a manner that while the coils of one set or series are at their maximum production of current1 the coils of the other will be at their neutral position1 or nearly so1 whereby both sets of coils may be subjected simultaneously or successively to the inducing action of the field magnets4 ,generally the circuits in the motor will be similarly disposed1 and various arrangements may be made to fulfill the requirements2 but the simplest and most practicable is to arrange primary circuits on stationary parts of the motor1 thereby obviating1 at least in certain forms1 the employment of sliding contacts4 ,in such a case the magnet coils are connected alternately in both the circuits2 that is1 #a1 #c1 #e 444 in one1 and #b1 #d1 #f 444 in the other1 and the coils of each set of series may be connected all in the same manner1 or alternately in opposition2 in the latter case a motor with half the number of poles will result1 and its action will be correspondingly modified4 ,the ,figs4 #ae1 #af1 and #ag1 show three different phases1 the magnet coils in each circuit being connected alternately in opposition4 ,in this case there will be always four poles1 as in ,figs4 #ae and #ag2 four pole projections will be neutral2 and in ,fig4 #af two adjacent pole projections will have the same polarity4 ,if the coils are connected in the same manner there will be eight alternating poles1 as indicated by the letters n' s' in ,fig4 #ae4 ,the employment of multipolar motors secures in this system an advantage much desired and unattainable in the continuous current system1 and that is1 that a motor may be made to run exactly at a predetermined speed irrespective of imperfections in construction1 of the load1 and1 within certain limits1 of electromotive force and current strength4 ,in a general distribution system of this kind the following plan should be adopted4 ,at the central station of supply a generator should be provided having a considerable number of poles4 ,the motors operated from this generator should be of the synchronous type1 but possessing sufficient rotary effort to insure their starting4 ,with the observance of proper rules of construction it may be admitted that the speed of each motor will be in some inverse proportion to its size1 and the number of poles should be chosen accordingly4 ,still1 exceptional demands may modify this rule4 ,in view of this1 it will be advantageous to provide each motor with a greater number of pole projections or coils1 the number being preferably a multiple of two and three4 ,by this means1 by simply changing the connections of the coils1 the motor may be adapted to any probable demands4 ,if the number of the poles in the motor is even1 the action will be harmonious and the proper result will be obtained2 if this is not the case1 the best plan to be followed is to make a motor with a double number of poles and connect the same in the manner before indicated1 so that half the number of poles result4 ,suppose1 for instance1 that the generator has twelve poles1 and it would be desired to obtain a speed equal to #ab_/g of the speed of the generator4 ,this would require a motor with seven pole projections or magnets1 and such a motor could not be properly connected in the circuits unless fourteen armature coils would be provided1 which would necessitate the employment of sliding contacts4 ,to avoid this1 the motor should be provided with fourteen magnets and seven connected in each circuit1 the magnets in each circuit alternating among themselves4 ,the armature should have fourteen closed coils4 ,the action of the motor will not be quite as perfect as in the case of an even number of poles1 but the drawback will not be of a serious nature4 ,however1 the disadvantages resulting from this unsymmetrical form will be reduced in the same proportion as the number of the poles is augmented4 ,if the generator has1 say1 n1 and the motor n#a poles1 the speed of the motor will be equal to that of the generator multiplied by n_/n#a4 ,the speed of the motor will generally be dependent on the number of the poles1 but there may be exceptions to this rule4 ,the speed may be modified by the phase of the currents in the circuit or by the character of the current impulses or by intervals between each or between groups of impulses4 ,some of the possible cases are indicated in the diagrams1 ,figs4 #ah1 #ai1 #bj and #ba1 which are self-explanatory4 ,fig4 #ah represents the condition generally existing1 and which secures the best result4 ,in such a case1 if the typical form of motor illustrated in ,fig4 #i is employed1 one complete wave in each circuit will produce one revolution of the motor4 ,in ,fig4 #ai the same result will be effected by one wave in each circuit1 the impulses being successive2 in ,fig4 #bj by four1 and in ,fig4 #ba by eight waves4 ,by such means any desired speed may be attained1 that is1 at least within the limits of practical demands4 ,this system possesses this advantage1 besides others1 resulting from simplicity4 ,at full loads the motors show an efficiency fully equal to that of the continuous current motors4 ,the transformers present an additional advantage in their capability of operating motors4 ,they are capable of similar modifications in construction1 and will facilitate the introduction of motors and their adaptation to practical demands4 ,their efficiency should be higher than that of the present transformers1 and ,i base my assertion on the following3 ,in a transformer1 as constructed at present1 we produce the currents in the secondary circuit by varying the strength of the primary or exciting currents4 ,if we admit proportionality with respect to the iron core the inductive effect exerted upon the secondary coil will be proportional to the numerical sum of the variations in the strength of the exciting current per unit of time2 whence it follows that for a given variation any prolongation of the primary current will result in a proportional loss4 ,in order to obtain rapid variations in the strength of the current1 essential to efficient induction1 a great number of undulations are employed2 from this practice various disadvantages result4 ,these are3 ,increased cost and diminished efficiency of the generator2 more waste of energy in heating the cores1 and also diminished output of the transformer1 since the core is not properly utilized1 the reversals being too rapid4 ,the inductive effect is also very small in certain phases1 as will be apparent from a graphic representation1 and there may be periods of inaction1 if there are intervals between the succeeding current impulses or waves4 ,in producing a shifting of the poles in a transformer1 and thereby inducing currents1 the induction is of the ideal character1 being always maintained at its maximum action4 ,it is also reasonable to assume that by a shifting of the poles less energy will be wasted than by reversals4 ,,chapter ,,iv4 ,,modifications ,,and ,,expansions ,,of ,,the ,,tesla ,,polyphase ,,systems4 ,in his earlier papers and patents relative to polyphase currents1 ,mr4 ,tesla devoted himself chiefly to an enunciation of the broad lines and ideas lying at the basis of this new work2 but he supplemented this immediately by a series of other striking inventions which may be regarded as modifications and expansions of certain features of the ,tesla systems4 ,these we shall now proceed to deal with4 ,in the preceding chapters we have thus shown and described the ,tesla electrical systems for the transmission of power and the conversion and distribution of electrical energy1 in which the motors and the transformers contain two or more coils or sets of coils1 which were connected up in independent circuits with corresponding coils of an alternating current generator1 the operation of the system being brought about by the co-operation of the alternating currents in the independent circuits in progressively moving or shifting the poles or points of maximum magnetic effect of the motors or converters4 ,in these systems two independent conductors are employed for each of the independent circuits connecting the generator with the devices for converting the transmitted currents into mechanical energy or into electric currents of another character4 ,this1 however1 is not always necessary4 ,the two or more circuits may have a single return path or wire in common1 with a loss1 if any1 which is so extremely slight that it may be disregarded entirely4 ,for the sake of illustration1 if the generator have two independent coils and the motor two coils or two sets of coils in corresponding relations to its operative elements one terminal of each generator coil is connected to the corresponding terminals of the motor coils through two independent conductors1 while the opposite terminals of the respective coils are both connected to one return wire4 ,the following description deals with the modification4 ,fig4 #bb is a diagrammatic illustration of a generator and single motor constructed and electrically connected in accordance with the invention4 ,fig4 #bc is a diagram of the system as it is used in operating motors or converters1 or both1 in parallel1 while ,fig4 #bd illustrates diagrammatically the manner of operating two or more motors or converters1 or both1 in series4 ,referring to ,fig4 #bb1 ,a ,a designate the poles of the field magnets of an alternating-current generator1 the armature of which1 being in this case cylindrical in form and mounted on a shaft1 ,c1 is wound longitudinally with coils ,b ,b'4 ,the shaft ,c carries three insulated contact-rings1 a b c1 to two of which1 as b c1 one terminal of each coil1 as e d1 is connected4 ,the remaining terminals1 f g1 are both connected to the third ring1 a4 ,illustration3 ,,fig4 #bb4 ,illustration3 ,,fig4 #bd4 ,a motor in this case is shown as composed of a ring1 ,h1 wound with four coils1 ,i ,i ,j ,j1 electrically connected1 so as to co-operate in pairs1 with a tendency to fix the poles of the ring at four points ninety degrees apart4 ,within the magnetic ring ,h is a disc or cylindrical core wound with two coils1 ,g ,g'1 which may be connected to form two closed circuits4 ,the terminals j k of the two sets or pairs of coils are connected1 respectively1 to the binding-posts ,e' ,f'1 and the other terminals1 h i1 are connected to a single binding-post1 ,d'4 ,to operate the motor1 three line-wires are used to connect the terminals of the generator with those of the motor4 ,illustration3 ,,fig4 #bc4 ,so far as the apparent action or mode of operation of this arrangement is concerned1 the single wire ,d1 which is1 so to speak1 a common return-wire for both circuits1 may be regarded as two independent wires4 ,in the illustration1 with the order of connection shown1 coil ,b' of the generator is producing its maximum current and coil ,b its minimum2 hence the current which passes through wire e1 ring b1 brush b'1 line-wire ,e1 terminal ,e'1 wire j1 coils ,i ,i1 wire or terminal ,d'1 line-wire ,d1 brush a'1 ring a1 and wire f1 fixes the polar line of the motor midway between the two coils ,i ,i2 but as the coil ,b' moves from the position indicated it generates less current1 while coil ,b1 moving into the field1 generates more4 ,the current from coil ,b passes through the devices and wires designated by the letters d1 c1 ,c' ,f1 ,f' k1 ,j ,j1 i1 ,d'1 ,d1 a'1 a1 and g1 and the position of the poles of the motor will be due to the resultant effect of the currents in the two sets of coils--that is1 it will be advanced in proportion to the advance or forward movement of the armature coils4 ,the movement of the generator-armature through one-quarter of a revolution will obviously bring coil ,b' into its neutral position and coil ,b into its position of maximum effect1 and this shifts the poles ninety degrees1 as they are fixed solely by coils ,b4 ,this action is repeated for each quarter of a complete revolution4 ,when more than one motor or other device is employed1 they may be run either in parallel or series4 ,in ,fig4 #bc the former arrangement is shown4 ,the electrical device is shown as a converter1 ,l1 of which the two sets of primary coils p r are connected1 respectively1 to the mains ,f ,e1 which are electrically connected with the two coils of the generator4 ,the cross-circuit wires l m1 making these connections1 are then connected to the common return-wire ,d4 ,the secondary coils p' p'' are in circuits n o1 including1 for example1 incandescent lamps4 ,only one converter is shown entire in this figure1 the others being illustrated diagrammatically4 ,when motors or converters are to be run in series1 the two wires ,e ,f are led from the generator to the coils of the first motor or converter1 then continued on to the next1 and so on through the whole series1 and are then joined to the single wire ,d1 which completes both circuits through the generator4 ,this is shown in ,fig4 #bd1 in which ,j ,i represent the two coils or sets of coils of the motors4 ,there are1 of course1 other conditions under which the same idea may be carried out4 ,for example1 in case the motor and generator each has three independent circuits1 one terminal of each circuit is connected to a line-wire1 and the other three terminals to a common return-conductor4 ,this arrangement will secure similar results to those attained with a generator and motor having but two independent circuits1 as above described4 ,when applied to such machines and motors as have three or more induced circuits with a common electrical joint1 the three or more terminals of the generator would be simply connected to those of the motor4 ,mr4 ,tesla states1 however1 that the results obtained in this manner show a lower efficiency than do the forms dwelt upon more fully above4 ,,chapter ,v4 ,,utilizing ,,familiar ,,types ,,of ,,generator ,,of ,,the ,,continuous ,,current ,,type4 ,the preceding descriptions have assumed the use of alternating current generators in which1 in order to produce the progressive movement of the magnetic poles1 or of the resultant attraction of independent field magnets1 the current generating coils are independent or separate4 ,the ordinary forms of continuous current dynamos may1 however1 be employed for the same work1 in accordance with a method of adaptation devised by ,mr4 ,tesla4 ,as will be seen1 the modification involves but slight changes in their construction1 and presents other elements of economy4 ,on the shaft of a given generator1 either in place of or in addition to the regular commutator1 are secured as many pairs of insulated collecting-rings as there are circuits to be operated4 ,now1 it will be understood that in the operation of any dynamo electric generator the currents in the coils in their movement through the field of force undergo different phases--that is to say1 at different positions of the coils the currents have certain directions and certain strengths--and that in the ,tesla motors or transformers it is necessary that the currents in the energizing coils should undergo a certain order of variations in strength and direction4 ,hence1 the further step--viz41 the connection between the induced or generating coils of the machine and the contact-rings from which the currents are to be taken off--will be determined solely by what order of variations of strength and direction in the currents is desired for producing a given result in the electrical translating device4 ,this may be accomplished in various ways2 but in the drawings we give typical instances only of the best and most practicable ways of applying the invention to three of the leading types of machines in widespread use1 in order to illustrate the principle4 ,fig4 #be is a diagram illustrative of the mode of applying the invention to the well-known type of closed or continuous circuit machines4 ,fig4 #bf is a similar diagram embodying an armature with separate coils connected diametrically1 or what is generally called an open-circuit machine4 ,fig4 #bg is a diagram showing the application of the invention to a machine the armature-coils of which have a common joint4 ,illustration3 ,,fig4 #be4 ,referring to ,fig4 #be1 let ,a represent a ,tesla motor or transformer which1 for convenience1 we will designate as a converter4 ,it consists of an annular core1 ,b1 wound with four independent coils1 ,c and ,d1 those diametrically opposite being connected together so as to co-operate in pairs in establishing free poles in the ring1 the tendency of each pair being to fix the poles at ninety degrees from the other4 ,there may be an armature1 ,e1 within the ring1 which is wound with coils closed upon themselves4 ,the object is to pass through coils ,c ,d currents of such relative strength and direction as to produce a progressive shifting or movement of the points of maximum magnetic effect around the ring1 and to thereby maintain a rotary movement of the armature4 ,there are therefore secured to the shaft ,f of the generator1 four insulated contact-rings1 a b c d1 upon which bear the collecting-brushes a' b' c' d'1 connected by wires ,g ,g ,h ,h1 respectively1 with the terminals of coils ,c and ,d4 ,assume1 for sake of illustration1 that the coils ,d ,d are to receive the maximum and coils ,c ,c at the same instant the minimum current1 so that the polar line may be midway between the coils ,d ,d4 ,the rings a b would therefore be connected to the continuous armature-coil at its neutral points with respect to the field1 or the point corresponding with that of the ordinary commutator brushes1 and between which exists the greatest difference of potential2 while rings c d would be connected to two points in the coil1 between which exists no difference of potential4 ,the best results will be obtained by making these connections at points equidistant from one another1 as shown4 ,these connections are easiest made by using wires ,l between the rings and the loops or wires ,j1 connecting the coil ,i to the segments of the commutator ,k4 ,when the converters are made in this manner1 it is evident that the phases of the currents in the sections of the generator coil will be reproduced in the converter coils4 ,for example1 after turning through an arc of ninety degrees the conductors ,l ,l1 which before conveyed the maximum current1 will receive the minimum current by reason of the change in the position of their coils1 and it is evident that for the same reason the current in these coils has gradually fallen from the maximum to the minimum in passing through the arc of ninety degrees4 ,in this special plan of connections1 the rotation of the magnetic poles of the converter will be synchronous with that of the armature coils of the generator1 and the result will be the same1 whether the energizing circuits are derivations from a continuous armature coil or from independent coils1 as in ,mr4 ,tesla's other devices4 ,in ,fig4 #be1 the brushes ,m ,m are shown in dotted lines in their proper normal position4 ,in practice these brushes may be removed from the commutator and the field of the generator excited by an external source of current2 or the brushes may be allowed to remain on the commutator and to take off a converted current to excite the field1 or to be used for other purposes4 ,in a certain well-known class of machines known as the open circuit1 the armature contains a number of coils the terminals of which connect to commutator segments1 the coils being connected across the armature in pairs4 ,this type of machine is represented in ,fig4 #bf4 ,in this machine each pair of coils goes through the same phases as the coils in some of the generators already shown1 and it is obviously only necessary to utilize them in pairs or sets to operate a ,tesla converter by extending the segments of the commutators belonging to each pair of coils and causing a collecting brush to bear on the continuous portion of each segment4 ,in this way two or more circuits may be taken off from the generator1 each including one or more pairs or sets of coils as may be desired4 ,illustration3 ,,fig4 #bf4 ,illustration3 ,,fig4 #bg4 ,in ,fig4 #bf ,i ,i represent the armature coils1 ,t ,t the poles of the field magnet1 and ,f the shaft carrying the commutators1 which are extended to form continuous portions a b c d4 ,the brushes bearing on the continuous portions for taking off the alternating currents are represented by a' b' c' d'4 ,the collecting brushes1 or those which may be used to take off the direct current1 are designated by ,m ,m4 ,two pairs of the armature coils and their commutators are shown in the figure as being utilized2 but all may be utilized in a similar manner4 ,there is another well-known type of machine in which three or more coils1 ,a' ,b' ,c'1 on the armature have a common joint1 the free ends being connected to the segments of a commutator4 ,this form of generator is illustrated in ,fig4 #bg4 ,in this case each terminal of the generator is connected directly or in derivation to a continuous ring1 a b c1 and collecting brushes1 a' b' c'1 bearing thereon1 take off the alternating currents that operate the motor4 ,it is preferable in this case to employ a motor or transformer with three energizing coils1 ,a'' ,b'' ,c''1 placed symmetrically with those of the generator1 and the circuits from the latter are connected to the terminals of such coils either directly--as when they are stationary--or by means of brushes e' and contact rings e4 ,in this1 as in the other cases1 the ordinary commutator may be used on the generator1 and the current taken from it utilized for exciting the generator field-magnets or for other purposes4 ,,chapter ,,vi4 ,,method ,,of ,,obtaining ,,desired ,,speed ,,of ,,motor ,,or ,,generator4 ,with the object of obtaining the desired speed in motors operated by means of alternating currents of differing phase1 ,mr4 ,tesla has devised various plans intended to meet the practical requirements of the case1 in adapting his system to types of multipolar alternating current machines yielding a large number of current reversals for each revolution4 ,for example1 ,mr4 ,tesla has pointed out that to adapt a given type of alternating current generator1 you may couple rigidly two complete machines1 securing them together in such a way that the requisite difference in phase will be produced2 or you may fasten two armatures to the same shaft within the influence of the same field and with the requisite angular displacement to yield the proper difference in phase between the two currents2 or two armatures may be attached to the same shaft with their coils symmetrically disposed1 but subject to the influence of two sets of field magnets duly displaced2 or the two sets of coils may be wound on the same armature alternately or in such manner that they will develop currents the phases of which differ in time sufficiently to produce the rotation of the motor4 ,another method included in the scope of the same idea1 whereby a single generator may run a number of motors either at its own rate of speed or all at different speeds1 is to construct the motors with fewer poles than the generator1 in which case their speed will be greater than that of the generator1 the rate of speed being higher as the number of their poles is relatively less4 ,this may be understood from an example1 taking a generator that has two independent generating coils which revolve between two pole pieces oppositely magnetized2 and a motor with energizing coils that produce at any given time two magnetic poles in one element that tend to set up a rotation of the motor4 ,a generator thus constructed yields four reversals1 or impulses1 in each revolution1 two in each of its independent circuits2 and the effect upon the motor is to shift the magnetic poles through three hundred and sixty degrees4 ,it is obvious that if the four reversals in the same order could be produced by each half-revolution of the generator the motor would make two revolutions to the generator's one4 ,this would be readily accomplished by adding two intermediate poles to the generator or altering it in any of the other equivalent ways above indicated4 ,the same rule applies to generators and motors with multiple poles4 ,for instance1 if a generator be constructed with two circuits1 each of which produces twelve reversals of current to a revolution1 and these currents be directed through the independent energizing-coils of a motor1 the coils of which are so applied as to produce twelve magnetic poles at all times1 the rotation of the two will be synchronous2 but if the motor-coils produce but six poles1 the movable element will be rotated twice while the generator rotates once2 or if the motor have four poles1 its rotation will be three times as fast as that of the generator4 ,illustration3 ,,fig4 #bh4 ,illustration3 ,,fig4 #bi4 ,these features1 so far as necessary to an understanding of the principle1 are here illustrated4 ,fig4 #bh is a diagrammatic illustration of a generator constructed in accordance with the invention4 ,fig4 #bi is a similar view of a correspondingly constructed motor4 ,fig4 #cj is a diagram of a generator of modified construction4 ,fig4 #ca is a diagram of a motor of corresponding character4 ,fig4 #cb is a diagram of a system containing a generator and several motors adapted to run at various speeds4 ,in ,fig4 #bh1 let ,c represent a cylindrical armature core wound longitudinally with insulated coils ,a ,a1 which are connected up in series1 the terminals of the series being connected to collecting-rings a a on the shaft ,g4 ,by means of this shaft the armature is mounted to rotate between the poles of an annular field-magnet ,d1 formed with polar projections wound with coils ,e1 that magnetize the said projections4 ,the coils ,e are included in the circuit of a generator ,f1 by means of which the field-magnet is energized4 ,if thus constructed1 the machine is a well-known form of alternating-current generator4 ,to adapt it to his system1 however1 ,mr4 ,tesla winds on armature ,c a second set of coils ,b ,b intermediate to the first1 or1 in other words1 in such positions that while the coils of one set are in the relative positions to the poles of the field-magnet to produce the maximum current1 those of the other set will be in the position in which they produce the minimum current4 ,the coils ,b are connected1 also1 in series and to two connecting-rings1 secured generally to the shaft at the opposite end of the armature4 ,illustration3 ,,fig4 #cj4 ,illustration3 ,,fig4 #ca4 ,the motor shown in ,fig4 #bi has an annular field-magnet ,h1 with four pole-pieces wound with coils ,i4 ,the armature is constructed similarly to the generator1 but with two sets of two coils in closed circuits to correspond with the reduced number of magnetic poles in the field4 ,from the foregoing it is evident that one revolution of the armature of the generator producing eight current impulses in each circuit will produce two revolutions of the motor-armature4 ,the application of the principle of this invention is not1 however1 confined to any particular form of machine4 ,in ,figs4 #cj and #ca a generator and motor of another well-known type are shown4 ,in ,fig4 #cj1 ,j ,j are magnets disposed in a circle and wound with coils ,k1 which are in circuit with a generator which supplies the current that maintains the field of force4 ,in the usual construction of these machines the armature-conductor ,l is carried by a suitable frame1 so as to be rotated in face of the magnets ,j ,j1 or between these magnets and another similar set in front of them4 ,the magnets are energized so as to be of alternately opposite polarity throughout the series1 so that as the conductor ,c is rotated the current impulses combine or are added to one another1 those produced by the conductor in any given position being all in the same direction4 ,to adapt such a machine to his system1 ,mr4 ,tesla adds a second set of induced conductors ,m1 in all respects similar to the first1 but so placed in reference to it that the currents produced in each will differ by a quarter-phase4 ,with such relations it is evident that as the current decreases in conductor ,l it increases in conductor ,m1 and conversely1 and that any of the forms of ,tesla motor invented for use in this system may be operated by such a generator4 ,fig4 #ca is intended to show a motor corresponding to the machine in ,fig4 #cj4 ,the construction of the motor is identical with that of the generator1 and if coupled thereto it will run synchronously therewith4 ,j' ,j' are the field-magnets1 and ,k' the coils thereon4 ,l' is one of the armature-conductors and ,m' the other4 ,fig4 #cb shows in diagram other forms of machine4 ,the generator ,n in this case is shown as consisting of a stationary ring ,o1 wound with twenty-four coils ,p ,p'1 alternate coils being connected in series in two circuits4 ,within this ring is a disc or drum ,q1 with projections ,q' wound with energizing-coils included in circuit with a generator ,r4 ,by driving this disc or cylinder alternating currents are produced in the coils ,p and ,p'1 which are carried off to run the several motors4 ,the motors are composed of a ring or annular field-magnet ,s1 wound with two sets of energizing-coils ,t ,t'1 and armatures ,u1 having projections ,u' wound with coils ,v1 all connected in series in a closed circuit or each closed independently on itself4 ,suppose the twelve generator-coils ,p are wound alternately in opposite directions1 so that any two adjacent coils of the same set tend to produce a free pole in the ring ,o between them and the twelve coils ,p' to be similarly wound4 ,a single revolution of the disc or cylinder ,q1 the twelve polar projections of which are of opposite polarity1 will therefore produce twelve current impulses in each of the circuits ,w ,w'4 ,hence the motor ,x1 which has sixteen coils or eight free poles1 will make one and a half turns to the generator's one4 ,the motor ,y1 with twelve coils or six poles1 will rotate with twice the speed of the generator1 and the motor ,z1 with eight coils or four poles1 will revolve three times as fast as the generator4 ,these multipolar motors have a peculiarity which may be often utilized to great advantage4 ,for example1 in the motor ,x1 ,fig4 #cb1 the eight poles may be either alternately opposite or there may be at any given time alternately two like and two opposite poles4 ,this is readily attained by making the proper electrical connections4 ,the effect of such a change1 however1 would be the same as reducing the number of poles one-half1 and thereby doubling the speed of any given motor4 ,illustration3 ,,fig4 #cb4 ,it is obvious that the ,tesla electrical transformers which have independent primary currents may be used with the generators described4 ,it may also be stated with respect to the devices we now describe that the most perfect and harmonious action of the generators and motors is obtained when the numbers of the poles of each are even and not odd4 ,if this is not the case1 there will be a certain unevenness of action which is the less appreciable as the number of poles is greater2 although this may be in a measure corrected by special provisions which it is not here necessary to explain4 ,it also follows1 as a matter of course1 that if the number of the poles of the motor be greater than that of the generator the motor will revolve at a slower speed than the generator4 ,in this chapter1 we may include a method devised by ,mr4 ,tesla for avoiding the very high speeds which would be necessary with large generators4 ,in lieu of revolving the generator armature at a high rate of speed1 he secures the desired result by a rotation of the magnetic poles of one element of the generator1 while driving the other at a different speed4 ,the effect is the same as that yielded by a very high rate of rotation4 ,in this instance1 the generator which supplies the current for operating the motors or transformers consists of a subdivided ring or annular core wound with four diametrically-opposite coils1 ,e ,e'1 ,fig4 #cc4 ,within the ring is mounted a cylindrical armature-core wound longitudinally with two independent coils1 ,f ,f'1 the ends of which lead1 respectively1 to two pairs of insulated contact or collecting rings1 ,d ,d' ,g ,g'1 on the armature shaft4 ,collecting brushes d d' g g' bear upon these rings1 respectively1 and convey the currents through the two independent line-circuits ,m ,m'4 ,in the main line there may be included one or more motors or transformers1 or both4 ,if motors be used1 they are of the usual form of ,tesla construction with independent coils or sets of coils ,j ,j'1 included1 respectively1 in the circuits ,m ,m'4 ,these energizing-coils are wound on a ring or annular field or on pole pieces thereon1 and produce by the action of the alternating currents passing through them a progressive shifting of the magnetism from pole to pole4 ,the cylindrical armature ,h of the motor is wound with two coils at right angles1 which form independent closed circuits4 ,if transformers be employed1 one set of the primary coils1 as ,n ,n1 wound on a ring or annular core is connected to one circuit1 as ,m'1 and the other primary coils1 ,n ,n'1 to the circuit ,m4 ,the secondary coils ,k ,k' may then be utilized for running groups of incandescent lamps ,p ,p'4 ,illustration3 ,,fig4 #cc4 ,with this generator an exciter is employed4 ,this consists of two poles1 ,a ,a1 of steel permanently magnetized1 or of iron excited by a battery or other generator of continuous currents1 and a cylindrical armature core mounted on a shaft1 ,b1 and wound with two longitudinal coils1 ,c ,c'4 ,one end of each of these coils is connected to the collecting-rings b c1 respectively1 while the other ends are both connected to a ring1 a4 ,collecting-brushes b' c' bear on the rings b c1 respectively1 and conductors ,l ,l convey the currents therefrom through the coils ,e and ,e of the generator4 ,l' is a common return-wire to brush a'4 ,two independent circuits are thus formed1 one including coils ,c of the exciter and ,e ,e of the generator1 the other coils ,c' of the exciter and ,e' ,e' of the generator4 ,it results from this that the operation of the exciter produces a progressive movement of the magnetic poles of the annular field-core of the generator1 the shifting or rotary movement of the poles being synchronous with the rotation of the exciter armature4 ,considering the operative conditions of a system thus established1 it will be found that when the exciter is driven so as to energize the field of the generator1 the armature of the latter1 if left free to turn1 would rotate at a speed practically the same as that of the exciter4 ,if under such conditions the coils ,f ,f' of the generator armature be closed upon themselves or short-circuited1 no currents1 at least theoretically1 will be generated in these armature coils4 ,in practice the presence of slight currents is observed1 the existence of which is attributable to more or less pronounced fluctuations in the intensity of the magnetic poles of the generator ring4 ,so1 if the armature-coils ,f ,f' be closed through the motor1 the latter will not be turned as long as the movement of the generator armature is synchronous with that of the exciter or of the magnetic poles of its field4 ,if1 on the contrary1 the speed of the generator armature be in any way checked1 so that the shifting or rotation of the poles of the field becomes relatively more rapid1 currents will be induced in the armature coils4 ,this obviously follows from the passing of the lines of force across the armature conductors4 ,the greater the speed of rotation of the magnetic poles relatively to that of the armature the more rapidly the currents developed in the coils of the latter will follow one another1 and the more rapidly the motor will revolve in response thereto1 and this continues until the armature generator is stopped entirely1 as by a brake1 when the motor1 if properly constructed1 runs at the speed with which the magnetic poles of the generator rotate4 ,the effective strength of the currents developed in the armature coils of the generator is dependent upon the strength of the currents energizing the generator and upon the number of rotations per unit of time of the magnetic poles of the generator2 hence the speed of the motor armature will depend in all cases upon the relative speeds of the armature of the generator and of its magnetic poles4 ,for example1 if the poles are turned two thousand times per unit of time and the armature is turned eight hundred1 the motor will turn twelve hundred times1 or nearly so4 ,very slight differences of speed may be indicated by a delicately balanced motor4 ,let it now be assumed that power is applied to the generator armature to turn it in a direction opposite to that in which its magnetic poles rotate4 ,in such case the result would be similar to that produced by a generator the armature and field magnets of which are rotated in opposite directions1 and by reason of these conditions the motor armature will turn at a rate of speed equal to the sum of the speeds of the armature and magnetic poles of the generator1 so that a comparatively low speed of the generator armature will produce a high speed in the motor4 ,it will be observed in connection with this system that on diminishing the resistance of the external circuit of the generator armature by checking the speed of the motor or by adding translating devices in multiple arc in the secondary circuit or circuits of the transformer the strength of the current in the armature circuit is greatly increased4 ,this is due to two causes3 first1 to the great differences in the speeds of the motor and generator1 and1 secondly1 to the fact that the apparatus follows the analogy of a transformer1 for1 in proportion as the resistance of the armature or secondary circuits is reduced1 the strength of the currents in the field or primary circuits of the generator is increased and the currents in the armature are augmented correspondingly4 ,for similar reasons the currents in the armature-coils of the generator increase very rapidly when the speed of the armature is reduced when running in the same direction as the magnetic poles or conversely4 ,it will be understood from the above description that the generator-armature may be run in the direction of the shifting of the magnetic poles1 but more rapidly1 and that in such case the speed of the motor will be equal to the difference between the two rates4 ,,chapter ,,vii4 ,,regulator ,,for ,,rotary ,,current ,,motors4 ,an interesting device for regulating and reversing has been devised by ,mr4 ,tesla for the purpose of varying the speed of polyphase motors4 ,it consists of a form of converter or transformer with one element capable of movement with respect to the other1 whereby the inductive relations may be altered1 either manually or automatically1 for the purpose of varying the strength of the induced current4 ,mr4 ,tesla prefers to construct this device in such manner that the induced or secondary element may be movable with respect to the other2 and the invention1 so far as relates merely to the construction of the device itself1 consists1 essentially1 in the combination1 with two opposite magnetic poles1 of an armature wound with an insulated coil and mounted on a shaft1 whereby it may be turned to the desired extent within the field produced by the poles4 ,the normal position of the core of the secondary element is that in which it most completely closes the magnetic circuit between the poles of the primary element1 and in this position its coil is in its most effective position for the inductive action upon it of the primary coils2 but by turning the movable core to either side1 the induced currents delivered by its coil become weaker until1 by a movement of the said core and coil through #ij deg41 there will be no current delivered4 ,fig4 #cd is a view in side elevation of the regulator4 ,fig4 #ce is a broken section on line x x of ,fig4 #cd4 ,fig4 #cf is a diagram illustrating the most convenient manner of applying the regulator to ordinary forms of motors1 and ,fig4 #cg is a similar diagram illustrating the application of the device to the ,tesla alternating-current motors4 ,the regulator may be constructed in many ways to secure the desired result2 but that which is1 perhaps1 its best form is shown in ,figs4 #cd and #ce4 ,a represents a frame of iron4 ,b ,b are the cores of the inducing or primary coils ,c ,c4 ,d is a shaft mounted on the side bars1 ,d'1 and on which is secured a sectional iron core1 ,e1 wound with an induced or secondary coil1 ,f1 the convolutions of which are parallel with the axis of the shaft4 ,the ends of the core are rounded off so as to fit closely in the space between the two poles and permit the core ,e to be turned to and held at any desired point4 ,a handle1 ,g1 secured to the projecting end of the shaft ,d1 is provided for this purpose4 ,illustration3 ,,fig4 #cd4 ,illustration3 ,,fig4 #ce4 ,in ,fig4 #cf let ,h represent an ordinary alternating current generator1 the field-magnets of which are excited by a suitable source of current1 ,i4 ,let ,j designate an ordinary form of electromagnetic motor provided with an armature1 ,k1 commutator ,l1 and field-magnets ,m4 ,it is well known that such a motor1 if its field-magnet cores be divided up into insulated sections1 may be practically operated by an alternating current2 but in using this regulator with such a motor1 ,mr4 ,tesla includes one element of the motor only--say the armature-coils--in the main circuit of the generator1 making the connections through the brushes and the commutator in the usual way4 ,he also includes one of the elements of the regulator--say the stationary coils--in the same circuit1 and in the circuit with the secondary or movable coil of the regulator he connects up the field-coils of the motor4 ,he also prefers to use flexible conductors to make the connections from the secondary coil of the regulator1 as he thereby avoids the use of sliding contacts or rings without interfering with the requisite movement of the core ,e4 ,if the regulator be in its normal position1 or that in which its magnetic circuit is most nearly closed1 it delivers its maximum induced current1 the phases of which so correspond with those of the primary current that the motor will run as though both field and armature were excited by the main current4 ,illustration3 ,,fig4 #cf4 ,to vary the speed of the motor to any rate between the minimum and maximum rates1 the core ,e and coils ,f are turned in either direction to an extent which produces the desired result1 for in its normal position the convolutions of coil ,f embrace the maximum number of lines of force1 all of which act with the same effect upon the coil2 hence it will deliver its maximum current2 but by turning the coil ,f out of its position of maximum effect the number of lines of force embraced by it is diminished4 ,the inductive effect is therefore impaired1 and the current delivered by coil ,f will continue to diminish in proportion to the angle at which the coil ,f is turned until1 after passing through an angle of ninety degrees1 the convolutions of the coil will be at right angles to those of coils ,c ,c1 and the inductive effect reduced to a minimum4 ,incidentally to certain constructions1 other causes may influence the variation in the strength of the induced currents4 ,for example1 in the present case it will be observed that by the first movement of coil ,f a certain portion of its convolutions are carried beyond the line of the direct influence of the lines of force1 and that the magnetic path or circuit for the lines is impaired2 hence the inductive effect would be reduced4 ,next1 that after moving through a certain angle1 which is obviously determined by the relative dimensions of the bobbin or coil ,f1 diagonally opposite portions of the coil will be simultaneously included in the field1 but in such positions that the lines which produce a current-impulse in one portion of the coil in a certain direction will produce in the diagonally opposite portion a corresponding impulse in the opposite direction2 hence portions of the current will neutralize one another4 ,as before stated1 the mechanical construction of the device may be greatly varied2 but the essential conditions of the principle will be fulfilled in any apparatus in which the movement of the elements with respect to one another effects the same results by varying the inductive relations of the two elements in a manner similar to that described4 ,illustration3 ,,fig4 #cg4 ,it may also be stated that the core ,e is not indispensable to the operation of the regulator2 but its presence is obviously beneficial4 ,this regulator1 however1 has another valuable property in its capability of reversing the motor1 for if the coil ,f be turned through a half-revolution1 the position of its convolutions relatively to the two coils ,c ,c and to the lines of force is reversed1 and consequently the phases of the current will be reversed4 ,this will produce a rotation of the motor in an opposite direction4 ,this form of regulator is also applied with great advantage to ,mr4 ,tesla's system of utilizing alternating currents1 in which the magnetic poles of the field of a motor are progressively shifted by means of the combined effects upon the field of magnetizing coils included in independent circuits1 through which pass alternating currents in proper order and relations to each other4 ,in ,fig4 #cg1 let ,p represent a ,tesla generator having two independent coils1 ,p' and ,p''1 on the armature1 and ,t a diagram of a motor having two independent energizing coils or sets of coils1 ,r ,r'4 ,one of the circuits from the generator1 as ,s' ,s'1 includes one set1 ,r' ,r'1 of the energizing coils of the motor1 while the other circuit1 as ,s ,s1 includes the primary coils of the regulator4 ,the secondary coil of the regulator includes the other coils1 ,r ,r1 of the motor4 ,while the secondary coil of the regulator is in its normal position1 it produces its maximum current1 and the maximum rotary effect is imparted to the motor2 but this effect will be diminished in proportion to the angle at which the coil ,f of the regulator is turned4 ,the motor will also be reversed by reversing the position of the coil with reference to the coils ,c ,c1 and thereby reversing the phases of the current produced by the generator4 ,this changes the direction of the movement of the shifting poles which the armature follows4 ,one of the main advantages of this plan of regulation is its economy of power4 ,when the induced coil is generating its maximum current1 the maximum amount of energy in the primary coils is absorbed2 but as the induced coil is turned from its normal position the self-induction of the primary-coils reduces the expenditure of energy and saves power4 ,it is obvious that in practice either coils ,c ,c or coil ,f may be used as primary or secondary1 and it is well understood that their relative proportions may be varied to produce any desired difference or similarity in the inducing and induced currents4 ,,chapter ,,viii4 ,,single ,,circuit1 ,,self-,,starting ,,synchronizing ,,motors4 ,in the first chapters of this section we have1 bearing in mind the broad underlying principle1 considered a distinct class of motors1 namely1 such as require for their operation a special generator capable of yielding currents of differing phase4 ,as a matter of course1 ,mr4 ,tesla recognizing the desirability of utilizing his motors in connection with ordinary systems of distribution1 addressed himself to the task of inventing various methods and ways of achieving this object4 ,in the succeeding chapters1 therefore1 we witness the evolution of a number of ideas bearing upon this important branch of work4 ,it must be obvious to a careful reader1 from a number of hints encountered here and there1 that even the inventions described in these chapters to follow do not represent the full scope of the work done in these lines4 ,they might1 indeed1 be regarded as exemplifications4 ,we will present these various inventions in the order which to us appears the most helpful to an understanding of the subject by the majority of readers4 ,it will be naturally perceived that in offering a series of ideas of this nature1 wherein some of the steps or links are missing1 the descriptions are not altogether sequential2 but any one who follows carefully the main drift of the thoughts now brought together will find that a satisfactory comprehension of the principles can be gained4 ,as is well known1 certain forms of alternating-current machines have the property1 when connected in circuit with an alternating current generator1 of running as a motor in synchronism therewith2 but1 while the alternating current will run the motor after it has attained a rate of speed synchronous with that of the generator1 it will not start it4 ,hence1 in all instances heretofore where these synchronizing motors1 as they are termed1 have been run1 some means have been adopted to bring the motors up to synchronism with the generator1 or approximately so1 before the alternating current of the generator is applied to drive them4 ,in some instances mechanical appliances have been utilized for this purpose4 ,in others special and complicated forms of motor have been constructed4 ,mr4 ,tesla has discovered a much more simple method or plan of operating synchronizing motors1 which requires practically no other apparatus than the motor itself4 ,in other words1 by a certain change in the circuit connections of the motor he converts it at will from a double circuit motor1 or such as have been already described1 and which will start under the action of an alternating current1 into a synchronizing motor1 or one which will be run by the generator only when it has reached a certain speed of rotation synchronous with that of the generator4 ,in this manner he is enabled to extend very greatly the applications of his system and to secure all the advantages of both forms of alternating current motor4 ,the expression synchronous with that of the generator1 is used here in its ordinary acceptation--that is to say1 a motor is said to synchronize with the generator when it preserves a certain relative speed determined by its number of poles and the number of alternations produced per revolution of the generator4 ,its actual speed1 therefore1 may be faster or slower than that of the generator2 but it is said to be synchronous so long as it preserves the same relative speed4 ,in carrying out this invention ,mr4 ,tesla constructs a motor which has a strong tendency to synchronism with the generator4 ,the construction preferred is that in which the armature is provided with polar projections4 ,the field-magnets are wound with two sets of coils1 the terminals of which are connected to a switch mechanism1 by means of which the line-current may be carried directly through these coils or indirectly through paths by which its phases are modified4 ,to start such a motor1 the switch is turned on to a set of contacts which includes in one motor circuit a dead resistance1 in the other an inductive resistance1 and1 the two circuits being in derivation1 it is obvious that the difference in phase of the current in such circuits will set up a rotation of the motor4 ,when the speed of the motor has thus been brought to the desired rate the switch is shifted to throw the main current directly through the motor-circuits1 and although the currents in both circuits will now be of the same phase the motor will continue to revolve1 becoming a true synchronous motor4 ,to secure greater efficiency1 the armature or its polar projections are wound with coils closed on themselves4 ,in the accompanying diagrams1 ,fig4 #ch illustrates the details of the plan above set forth1 and ,figs4 #ci and #dj modifications of the same4 ,illustration3 ,,figs4 #ch1 #ci and #dj4 ,referring to ,fig4 #ch1 let ,a designate the field-magnets of a motor1 the polar projections of which are wound with coils ,b ,c included in independent circuits1 and ,d the armature with polar projections wound with coils ,e closed upon themselves1 the motor in these respects being similar in construction to those described already1 but having on account of the polar projections on the armature core1 or other similar and well-known features1 the properties of a synchronizing-motor4 ,l ,l' represents the conductors of a line from an alternating current generator ,g4 ,near the motor is placed a switch the action of which is that of the one shown in the diagrams1 which is constructed as follows3 ,f ,f' are two conducting plates or arms1 pivoted at their ends and connected by an insulating cross-bar1 ,h1 so as to be shifted in parallelism4 ,in the path of the bars ,f ,f' is the contact #b1 which forms one terminal of the circuit through coils ,c1 and the contact #d1 which is one terminal of the circuit through coils ,b4 ,the opposite end of the wire of coils ,c is connected to the wire ,l or bar ,f'1 and the corresponding end of coils ,b is connected to wire ,l' and bar ,f2 hence if the bars be shifted so as to bear on contacts #b and #d both sets of coils ,b ,c will be included in the circuit ,l ,l' in multiple arc or derivation4 ,in the path of the levers ,f ,f' are two other contact terminals1 #a and #c4 ,the contact #a is connected to contact #b through an artificial resistance1 ,i1 and contact #c with contact #d through a self-induction coil1 ,j1 so that when the switch levers are shifted upon the points #a and #c the circuits of coils ,b and ,c will be connected in multiple arc or derivation to the circuit ,l ,l'1 and will include the resistance and self-induction coil respectively4 ,a third position of the switch is that in which the levers ,f and ,f' are shifted out of contact with both sets of points4 ,in this case the motor is entirely out of circuit4 ,the purpose and manner of operating the motor by these devices are as follows3 ,the normal position of the switch1 the motor being out of circuit1 is off the contact points4 ,assuming the generator to be running1 and that it is desired to start the motor1 the switch is shifted until its levers rest upon points #a and #c4 ,the two motor-circuits are thus connected with the generator circuit2 but by reason of the presence of the resistance ,i in one and the self-induction coil ,j in the other the coincidence of the phases of the current is disturbed sufficiently to produce a progression of the poles1 which starts the motor in rotation4 ,when the speed of the motor has run up to synchronism with the generator1 or approximately so1 the switch is shifted over upon the points #b and #d1 thus cutting out the coils ,i and ,j1 so that the currents in both circuits have the same phase2 but the motor now runs as a synchronous motor4 ,it will be understood that when brought up to speed the motor will run with only one of the circuits ,b or ,c connected with the main or generator circuit1 or the two circuits may be connected in series4 ,this latter plan is preferable when a current having a high number of alternations per unit of time is employed to drive the motor4 ,in such case the starting of the motor is more difficult1 and the dead and inductive resistances must take up a considerable proportion of the electromotive force of the circuits4 ,generally the conditions are so adjusted that the electromotive force used in each of the motor circuits is that which is required to operate the motor when its circuits are in series4 ,the plan followed in this case is illustrated in ,fig4 #ci4 ,in this instance the motor has twelve poles and the armature has polar projections ,d wound with closed coils ,e4 ,the switch used is of substantially the same construction as that shown in the previous figure4 ,there are1 however1 five contacts1 designated as #e1 #f1 #g1 #h1 and #i4 ,the motor-circuits ,b ,c1 which include alternate field-coils1 are connected to the terminals in the following order3 ,one end of circuit ,c is connected to contact #i and to contact #e through a dead resistance1 ,i4 ,one terminal of circuit ,b is connected to contact #g and to contact #f through a self-induction coil1 ,j4 ,the opposite terminals of both circuits are connected to contact #h4 ,one of the levers1 as ,f1 of the switch is made with an extension1 f1 or otherwise1 so as to cover both contacts #e and #f when shifted into the position to start the motor4 ,it will be observed that when in this position and with lever ,f' on contact #h the current divides between the two circuits ,b ,c1 which from their difference in electrical character produce a progression of the poles that starts the motor in rotation4 ,when the motor has attained the proper speed1 the switch is shifted so that the levers cover the contacts #g and #i1 thereby connecting circuits ,b and ,c in series4 ,it is found that by this disposition the motor is maintained in rotation in synchronism with the generator4 ,this principle of operation1 which consists in converting by a change of connections or otherwise a double-circuit motor1 or one operating by a progressive shifting of the poles1 into an ordinary synchronizing motor may be carried out in many other ways4 ,for instance1 instead of using the switch shown in the previous figures1 we may use a temporary ground circuit between the generator and motor1 in order to start the motor1 in substantially the manner indicated in ,fig4 #dj4 ,let ,g in this figure represent an ordinary alternating-current generator with1 say1 two poles1 ,m ,m'1 and an armature wound with two coils1 ,n ,n'1 at right angles and connected in series4 ,the motor has1 for example1 four poles wound with coils ,b ,c1 which are connected in series1 and an armature with polar projections ,d wound with closed coils ,e ,e4 ,from the common joint or union between the two circuits of both the generator and the motor an earth connection is established1 while the terminals or ends of these circuits are connected to the line4 ,assuming that the motor is a synchronizing motor or one that has the capability of running in synchronism with the generator1 but not of starting1 it may be started by the above-described apparatus by closing the ground connection from both generator and motor4 ,the system thus becomes one with a two-circuit generator and motor1 the ground forming a common return for the currents in the two circuits ,l and ,l'4 ,when by this arrangement of circuits the motor is brought to speed1 the ground connection is broken between the motor or generator1 or both1 ground-switches ,p ,p' being employed for this purpose4 ,the motor then runs as a synchronizing motor4 ,in describing the main features which constitute this invention illustrations have necessarily been omitted of the appliances used in conjunction with the electrical devices of similar systems--such1 for instance1 as driving-belts1 fixed and loose pulleys for the motor1 and the like2 but these are matters well understood4 ,mr4 ,tesla believes he is the first to operate electro-magnetic motors by alternating currents in any of the ways herein described--that is to say1 by producing a progressive movement or rotation of their poles or points of greatest magnetic attraction by the alternating currents until they have reached a given speed1 and then by the same currents producing a simple alternation of their poles1 or1 in other words1 by a change in the order or character of the circuit connections to convert a motor operating on one principle to one operating on another4 ,,chapter ,,ix4 ,,change ,,from ,,double ,,current ,,to ,,single ,,current ,,motor4 ,a description is given elsewhere of a method of operating alternating current motors by first rotating their magnetic poles until they have attained synchronous speed1 and then alternating the poles4 ,the motor is thus transformed1 by a simple change of circuit connections from one operated by the action of two or more independent energizing currents to one operated either by a single current or by several currents acting as one4 ,another way of doing this will now be described4 ,at the start the magnetic poles of one element or field of the motor are progressively shifted by alternating currents differing in phase and passed through independent energizing circuits1 and short circuit the coils of the other element4 ,when the motor thus started reaches or passes the limit of speed synchronous with the generator1 ,mr4 ,tesla connects up the coils previously short-circuited with a source of direct current and by a change of the circuit connections produces a simple alternation of the poles4 ,the motor then continues to run in synchronism with the generator4 ,the motor here shown in ,fig4 #da is one of the ordinary forms1 with field-cores either laminated or solid and with a cylindrical laminated armature wound1 for example1 with the coils ,a ,b at right angles4 ,the shaft of the armature carries three collecting or contact rings ,c ,d ,e4 7,shown1 for better illustration1 as of different diameters47 ,one end of coil ,a connects to one ring1 as ,c1 and one end of coil ,b connects with ring ,d4 ,the remaining ends are connected to ring ,e4 ,collecting springs or brushes ,f ,g ,h bear upon the rings and lead to the contacts of a switch1 to be presently described4 ,the field-coils have their terminals in binding-posts ,k ,k1 and may be either closed upon themselves or connected with a source of direct current ,l1 by means of a switch ,m4 ,the main or controlling switch has five contacts a b c d e and two levers f g1 pivoted and connected by an insulating cross-bar h1 so as to move in parallelism4 ,these levers are connected to the line wires from a source of alternating currents ,n4 ,contact a is connected to brush ,g and coil ,b through a dead resistance ,r and wire ,p4 ,contact b is connected with brush ,f and coil ,a through a self-induction coil ,s and wire ,o4 ,contacts c and e are connected to brushes ,g ,f1 respectively1 through the wires ,p ,o1 and contact d is directly connected with brush ,h4 ,the lever f has a widened end1 which may span the contacts a b4 ,when in such position and with lever g on contact d1 the alternating currents divide between the two motor-coils1 and by reason of their different self-induction a difference of current-phase is obtained that starts the motor in rotation4 ,in starting1 the field-coils are short circuited4 ,illustration3 ,,fig4 #da4 ,when the motor has attained the desired speed1 the switch is shifted to the position shown in dotted lines--that is to say1 with the levers f g resting on points c e4 ,this connects up the two armature coils in series1 and the motor will then run as a synchronous motor4 ,the field-coils are thrown into circuit with the direct current source when the main switch is shifted4 ,,chapter ,x4 ,,motor ,,with ,,current ,,lag ,,artificially ,,secured4 ,one of the general ways followed by ,mr4 ,tesla in developing his rotary phase motors is to produce practically independent currents differing primarily in phase and to pass these through the motor-circuits4 ,another way is to produce a single alternating current1 to divide it between the motor-circuits1 and to effect artificially a lag in one of these circuits or branches1 as by giving to the circuits different self-inductive capacity1 and in other ways4 ,in the former case1 in which the necessary difference of phase is primarily effected in the generation of currents1 in some instances1 the currents are passed through the energizing coils of both elements of the motor--the field and armature2 but a further result or modification may be obtained by doing this under the conditions hereinafter specified in the case of motors in which the lag1 as above stated1 is artificially secured4 ,figs4 #db to #dg1 inclusive1 are diagrams of different ways in which the invention is carried out2 and ,fig4 #dh1 a side view of a form of motor used by ,mr4 ,tesla for this purpose4 ,illustration3 ,,figs4 #db1 #dc and #dd4 ,a ,b in ,fig4 #db indicate the two energizing circuits of a motor1 and ,c ,d two circuits on the armature4 ,circuit or coil ,a is connected in series with circuit or coil ,c1 and the two circuits ,b ,d are similarly connected4 ,between coils ,a and ,c is a contact-ring e1 forming one terminal of the latter1 and a brush a1 forming one terminal of the former4 ,a ring d and brush c similarly connect coils ,b and ,d4 ,the opposite terminals of the field-coils connect to one binding post h of the motor1 and those of the armature coils are similarly connected to the opposite binding post i through a contact-ring f and brush g4 ,thus each motor-circuit while in derivation to the other includes one armature and one field coil4 ,these circuits are of different self-induction1 and may be made so in various ways4 ,for the sake of clearness1 an artificial resistance ,r is shown in one of these circuits1 and in the other a self-induction coil ,s4 ,when an alternating current is passed through this motor it divides between its two energizing-circuits4 ,the higher self-induction of one circuit produces a greater retardation or lag in the current therein than in the other4 ,the difference of phase between the two currents effects the rotation or shifting of the points of maximum magnetic effect that secures the rotation of the armature4 ,in certain respects this plan of including both armature and field coils in circuit is a marked improvement4 ,such a motor has a good torque at starting2 yet it has also considerable tendency to synchronism1 owing to the fact that when properly constructed the maximum magnetic effects in both armature and field coincide--a condition which in the usual construction of these motors with closed armature coils is not readily attained4 ,the motor thus constructed exhibits too1 a better regulation of current from no load to load1 and there is less difference between the apparent and real energy expended in running it4 ,the true synchronous speed of this form of motor is that of the generator when both are alike--that is to say1 if the number of the coils on the armature and on the field is x1 the motor will run normally at the same speed as a generator driving it if the number of field magnets or poles of the same be also x4 ,illustration3 ,,figs4 #de1 #df and #dg4 ,fig4 #dc shows a somewhat modified arrangement of circuits4 ,there is in this case but one armature coil ,e1 the winding of which maintains effects corresponding to the resultant poles produced by the two field-circuits4 ,fig4 #dd represents a disposition in which both armature and field are wound with two sets of coils1 all in multiple arc to the line or main circuit4 ,the armature coils are wound to correspond with the field-coils with respect to their self-induction4 ,a modification of this plan is shown in ,fig4 #de--that is to say1 the two field coils and two armature coils are in derivation to themselves and in series with one another4 ,the armature coils in this case1 as in the previous figure1 are wound for different self-induction to correspond with the field coils4 ,another modification is shown in ,fig4 #df4 ,in this case only one armature-coil1 as ,d1 is included in the line-circuit1 while the other1 as ,c1 is short-circuited4 ,in such a disposition as that shown in ,fig4 #dc1 or where only one armature-coil is employed1 the torque on the start is somewhat reduced1 while the tendency to synchronism is somewhat increased4 ,in such a disposition as shown in ,fig4 #df1 the opposite conditions would exist4 ,in both instances1 however1 there is the advantage of dispensing with one contact-ring4 ,illustration3 ,,fig4 #dh4 ,in ,fig4 #df the two field-coils and the armature-coil ,d are in multiple arc4 ,in ,fig4 #dg this disposition is modified1 coil ,d being shown in series with the two field-coils4 ,fig4 #dh is an outline of the general form of motor in which this invention is embodied4 ,the circuit connections between the armature and field coils are made1 as indicated in the previous figures1 through brushes and rings1 which are not shown4 ,,chapter ,,xi4 ,,another ,,method ,,of ,,transformation ,,from ,a ,,torque ,,to ,a ,,synchronizing ,,motor4 ,in a preceding chapter we have described a method by which ,mr4 ,tesla accomplishes the change in his type of rotating field motor from a torque to a synchronizing motor4 ,as will be observed1 the desired end is there reached by a change in the circuit connections at the proper moment4 ,we will now proceed to describe another way of bringing about the same result4 ,the principle involved in this method is as follows3-- ,if an alternating current be passed through the field coils only of a motor having two energizing circuits of different self-induction and the armature coils be short-circuited1 the motor will have a strong torque1 but little or no tendency to synchronism with the generator2 but if the same current which energizes the field be passed also through the armature coils the tendency to remain in synchronism is very considerably increased4 ,this is due to the fact that the maximum magnetic effects produced in the field and armature more nearly coincide4 ,on this principle ,mr4 ,tesla constructs a motor having independent field circuits of different self-induction1 which are joined in derivation to a source of alternating currents4 ,the armature is wound with one or more coils1 which are connected with the field coils through contact rings and brushes1 and around the armature coils a shunt is arranged with means for opening or closing the same4 ,in starting this motor the shunt is closed around the armature coils1 which will therefore be in closed circuit4 ,when the current is directed through the motor1 it divides between the two circuits1 7it is not necessary to consider any case where there are more than two circuits used71 which1 by reason of their different self-induction1 secure a difference of phase between the two currents in the two branches1 that produces a shifting or rotation of the poles4 ,by the alternations of current1 other currents are induced in the closed--or short-circuited--armature coils and the motor has a strong torque4 ,when the desired speed is reached1 the shunt around the armature-coils is opened and the current directed through both armature and field coils4 ,under these conditions the motor has a strong tendency to synchronism4 ,illustration3 ,,figs4 #di1 #ej and #ea4 ,in ,fig4 #di1 ,a and ,b designate the field coils of the motor4 ,as the circuits including these coils are of different self-induction1 this is represented by a resistance coil ,r in circuit with ,a1 and a self-induction coil ,s in circuit with ,b4 ,the same result may of course be secured by the winding of the coils4 ,c is the armature circuit1 the terminals of which are rings a b4 ,brushes c d bear on these rings and connect with the line and field circuits4 ,d is the shunt or short circuit around the armature4 ,e is the switch in the shunt4 ,it will be observed that in such a disposition as is illustrated in ,fig4 #di1 the field circuits ,a and ,b being of different self-induction1 there will always be a greater lag of the current in one than the other1 and that1 generally1 the armature phases will not correspond with either1 but with the resultant of both4 ,it is therefore important to observe the proper rule in winding the armature4 ,for instance1 if the motor have eight poles--four in each circuit--there will be four resultant poles1 and hence the armature winding should be such as to produce four poles1 in order to constitute a true synchronizing motor4 ,illustration3 ,,fig4 #eb4 ,the diagram1 ,fig4 #ej1 differs from the previous one only in respect to the order of connections4 ,in the present case the armature-coil1 instead of being in series with the field-coils1 is in multiple arc therewith4 ,the armature-winding may be similar to that of the field--that is to say1 the armature may have two or more coils wound or adapted for different self-induction and adapted1 preferably1 to produce the same difference of phase as the field-coils4 ,on starting the motor the shunt is closed around both coils4 ,this is shown in ,fig4 #ea1 in which the armature coils are ,f ,g4 ,to indicate their different electrical character1 there are shown in circuit with them1 respectively1 the resistance ,r' and the self-induction coil ,s'4 ,the two armature coils are in series with the field-coils and the same disposition of the shunt or short-circuit ,d is used4 ,it is of advantage in the operation of motors of this kind to construct or wind the armature in such manner that when short-circuited on the start it will have a tendency to reach a higher speed than that which synchronizes with the generator4 ,for example1 a given motor having1 say1 eight poles should run1 with the armature coil short-circuited1 at two thousand revolutions per minute to bring it up to synchronism4 ,it will generally happen1 however1 that this speed is not reached1 owing to the fact that the armature and field currents do not properly correspond1 so that when the current is passed through the armature 7the motor not being quite up to synchronism7 there is a liability that it will not hold on1 as it is termed4 ,it is preferable1 therefore1 to so wind or construct the motor that on the start1 when the armature coils are short-circuited1 the motor will tend to reach a speed higher than the synchronous--as for instance1 double the latter4 ,in such case the difficulty above alluded to is not felt1 for the motor will always hold up to synchronism if the synchronous speed--in the case supposed of two thousand revolutions--is reached or passed4 ,this may be accomplished in various ways2 but for all practical purposes the following will suffice3 ,on the armature are wound two sets of coils4 ,at the start only one of these is short-circuited1 thereby producing a number of poles on the armature1 which will tend to run the speed up above the synchronous limit4 ,when such limit is reached or passed1 the current is directed through the other coil1 which1 by increasing the number of armature poles1 tends to maintain synchronism4 ,illustration3 ,,fig4 #ec4 ,in ,fig4 #eb1 such a disposition is shown4 ,the motor having1 say1 eight poles contains two field-circuits ,a and ,b1 of different self-induction4 ,the armature has two coils ,f and ,g4 ,the former is closed upon itself1 the latter connected with the field and line through contact-rings a b1 brushes c d1 and a switch ,e4 ,on the start the coil ,f alone is active and the motor tends to run at a speed above the synchronous2 but when the coil ,g is connected to the circuit the number of armature poles is increased1 while the motor is made a true synchronous motor4 ,this disposition has the advantage that the closed armature-circuit imparts to the motor torque when the speed falls off1 but at the same time the conditions are such that the motor comes out of synchronism more readily4 ,to increase the tendency to synchronism1 two circuits may be used on the armature1 one of which is short-circuited on the start and both connected with the external circuit after the synchronous speed is reached or passed4 ,this disposition is shown in ,fig4 #ec4 ,there are three contact-rings a b e and three brushes c d f1 which connect the armature circuits with the external circuit4 ,on starting1 the switch ,h is turned to complete the connection between one binding-post ,p and the field-coils4 ,this short-circuits one of the armature-coils1 as ,g4 ,the other coil ,f is out of circuit and open4 ,when the motor is up to speed1 the switch ,h is turned back1 so that the connection from binding-post ,p to the field coils is through the coil ,g1 and switch ,k is closed1 thereby including coil ,f in multiple arc with the field coils4 ,both armature coils are thus active4 ,from the above-described instances it is evident that many other dispositions for carrying out the invention are possible4 ,,chapter ,,xii4 ,,magnetic ,,lag ,,motor4 ,the following description deals with another form of motor1 namely1 depending on magnetic lag or hysteresis1 its peculiarity being that in it the attractive effects or phases while lagging behind the phases of current which produce them1 are manifested simultaneously and not successively4 ,the phenomenon utilized thus at an early stage by ,mr4 ,tesla1 was not generally believed in by scientific men1 and ,prof4 ,ayrton was probably first to advocate it or to elucidate the reason of its supposed existence4 ,fig4 #ed is a side view of the motor1 in elevation4 ,fig4 #ee is a part-sectional view at right angles to ,fig4 #ed4 ,fig4 #ef is an end view in elevation and part section of a modification1 and ,fig4 #eg is a similar view of another modification4 ,in ,figs4 #ed and #ee1 ,a designates a base or stand1 and ,b ,b the supporting-frame of the motor4 ,bolted to the supporting-frame are two magnetic cores or pole-pieces ,c ,c'1 of iron or soft steel4 ,these may be subdivided or laminated1 in which case hard iron or steel plates or bars should be used1 or they should be wound with closed coils4 ,d is a circular disc armature1 built up of sections or plates of iron and mounted in the frame between the pole-pieces ,c ,c'1 curved to conform to the circular shape thereof4 ,this disc may be wound with a number of closed coils ,e4 ,f ,f are the main energizing coils1 supported by the supporting-frame1 so as to include within their magnetizing influence both the pole-pieces ,c ,c' and the armature ,d4 ,the pole-pieces ,c ,c' project out beyond the coils ,f ,f on opposite sides1 as indicated in the drawings4 ,if an alternating current be passed through the coils ,f ,f1 rotation of the armature will be produced1 and this rotation is explained by the following apparent action1 or mode of operation3 ,an impulse of current in the coils ,f ,f establishes two polarities in the motor4 ,the protruding end of pole-piece ,c1 for instance1 will be of one sign1 and the corresponding end of pole-piece ,c' will be of the opposite sign4 ,the armature also exhibits two poles at right angles to the coils ,f ,f1 like poles to those in the pole-pieces being on the same side of the coils4 ,while the current is flowing there is no appreciable tendency to rotation developed2 but after each current impulse ceases or begins to fall1 the magnetism in the armature and in the ends of the pole-pieces ,c ,c' lags or continues to manifest itself1 which produces a rotation of the armature by the repellent force between the more closely approximating points of maximum magnetic effect4 ,this effect is continued by the reversal of current1 the polarities of field and armature being simply reversed4 ,one or both of the elements--the armature or field--may be wound with closed induced coils to intensify this effect4 ,although in the illustrations but one of the fields is shown1 each element of the motor really constitutes a field1 wound with the closed coils1 the currents being induced mainly in those convolutions or coils which are parallel to the coils ,f ,f4 ,illustration3 ,,fig4 #ed4 ,illustration3 ,,fig4 #ee4 ,a modified form of this motor is shown in ,fig4 #ef4 ,in this form ,g is one of two standards that support the bearings for the armature-shaft4 ,h ,h are uprights or sides of a frame1 preferably magnetic1 the ends ,c ,c' of which are bent in the manner indicated1 to conform to the shape of the armature ,d and form field-magnet poles4 ,the construction of the armature may be the same as in the previous figure1 or it may be simply a magnetic disc or cylinder1 as shown1 and a coil or coils ,f ,f are secured in position to surround both the armature and the poles ,c ,c'4 ,the armature is detachable from its shaft1 the latter being passed through the armature after it has been inserted in position4 ,the operation of this form of motor is the same in principle as that previously described and needs no further explanation4 ,illustration3 ,,fig4 #ef4 ,illustration3 ,,fig4 #eg4 ,one of the most important features in alternating current motors is1 however1 that they should be adapted to and capable of running efficiently on the alternating circuits in present use1 in which almost without exception the generators yield a very high number of alternations4 ,such a motor1 of the type under consideration1 ,mr4 ,tesla has designed by a development of the principle of the motor shown in ,fig4 #ef1 making a multipolar motor1 which is illustrated in ,fig4 #eg4 ,in the construction of this motor he employs an annular magnetic frame ,j1 with inwardly-extending ribs or projections ,k1 the ends of which all bend or turn in one direction and are generally shaped to conform to the curved surface of the armature4 ,coils ,f ,f are wound from one part ,k to the one next adjacent1 the ends or loops of each coil or group of wires being carried over toward the shaft1 so as to form ,u-shaped groups of convolutions at each end of the armature4 ,the pole-pieces ,c ,c'1 being substantially concentric with the armature1 form ledges1 along which the coils are laid and should project to some extent beyond the the coils1 as shown4 ,the cylindrical or drum armature ,d is of the same construction as in the other motors described1 and is mounted to rotate within the annular frame ,j and between the ,u-shaped ends or bends of the coils ,f4 ,the coils ,f are connected in multiple or in series with a source of alternating currents1 and are so wound that with a current or current impulse of given direction they will make the alternate pole-pieces ,c of one polarity and the other pole-pieces ,c' of the opposite polarity4 ,the principle of the operation of this motor is the same as the other above described1 for1 considering any two pole-pieces ,c ,c'1 a current impulse passing in the coil which bridges them or is wound over both tends to establish polarities in their ends of opposite sign and to set up in the armature core between them a polarity of the same sign as that of the nearest pole-piece ,c4 ,upon the fall or cessation of the current impulse that established these polarities the magnetism which lags behind the current phase1 and which continues to manifest itself in the polar projections ,c ,c' and the armature1 produces by repulsion a rotation of the armature4 ,the effect is continued by each reversal of the current4 ,what occurs in the case of one pair of pole-pieces occurs simultaneously in all1 so that the tendency to rotation of the armature is measured by the sum of all the forces exerted by the pole-pieces1 as above described4 ,in this motor also the magnetic lag or effect is intensified by winding one or both cores with closed induced coils4 ,the armature core is shown as thus wound4 ,when closed coils are used1 the cores should be laminated4 ,it is evident that a pulsatory as well as an alternating current might be used to drive or operate the motors above described4 ,it will be understood that the degree of subdivision1 the mass of the iron in the cores1 their size and the number of alternations in the current employed to run the motor1 must be taken into consideration in order to properly construct this motor4 ,in other words1 in all such motors the proper relations between the number of alternations and the mass1 size1 or quality of the iron must be preserved in order to secure the best results4 ,,chapter ,,xiii4 ,,method ,,of ,,obtaining ,,difference ,,of ,,phase ,,by ,,magnetic ,,shielding4 ,in that class of motors in which two or more sets of energizing magnets are employed1 and in which by artificial means a certain interval of time is made to elapse between the respective maximum or minimum periods or phases of their magnetic attraction or effect1 the interval or difference in phase between the two sets of magnets is limited in extent4 ,it is desirable1 however1 for the economical working of such motors that the strength or attraction of one set of magnets should be maximum1 at the time when that of the other set is minimum1 and conversely2 but these conditions have not heretofore been realized except in cases where the two currents have been obtained from independent sources in the same or different machines4 ,mr4 ,tesla has therefore devised a motor embodying conditions that approach more nearly the theoretical requirements of perfect working1 or in other words1 he produces artificially a difference of magnetic phase by means of a current from a single primary source sufficient in extent to meet the requirements of practical and economical working4 ,he employs a motor with two sets of energizing or field magnets1 each wound with coils connected with a source of alternating or rapidly-varying currents1 but forming two separate paths or circuits4 ,the magnets of one set are protected to a certain extent from the energizing action of the current by means of a magnetic shield or screen interposed between the magnet and its energizing coil4 ,this shield is properly adapted to the conditions of particular cases1 so as to shield or protect the main core from magnetization until it has become itself saturated and no longer capable of containing all the lines of force produced by the current4 ,it will be seen that by this means the energizing action begins in the protected set of magnets a certain arbitrarily-determined period of time later than in the other1 and that by this means alone or in conjunction with other means or devices heretofore employed a practical difference of magnetic phase may readily be secured4 ,fig4 #eh is a view of a motor1 partly in section1 with a diagram illustrating the invention4 ,fig4 #ei is a similar view of a modification of the same4 ,illustration3 ,,fig4 #eh4 ,illustration3 ,,fig4 #ei4 ,in ,fig4 #eh1 which exhibits the simplest form of the invention1 ,a ,a is the field-magnet of a motor1 having1 say1 eight poles or inwardly-projecting cores ,b and ,c4 ,the cores ,b form one set of magnets and are energized by coils ,d4 ,the cores ,c1 forming the other set are energized by coils ,e1 and the coils are connected1 preferably1 in series with one another1 in two derived or branched circuits1 ,f ,g1 respectively1 from a suitable source of current4 ,each coil ,e is surrounded by a magnetic shield ,h1 which is preferably composed of an annealed1 insulated1 or oxidized iron wire wrapped or wound on the coils in the manner indicated so as to form a closed magnetic circuit around the coils and between the same and the magnetic cores ,c4 ,between the pole pieces or cores ,b ,c is mounted the armature ,k1 which1 as is usual in this type of machines1 is wound with coils ,l closed upon themselves4 ,the operation resulting from this disposition is as follows3 ,if a current impulse be directed through the two circuits of the motor1 it will quickly energize the cores ,b1 but not so the cores ,c1 for the reason that in passing through the coils ,e there is encountered the influence of the closed magnetic circuits formed by the shields ,h4 ,the first effect is to retard effectively the current impulse in circuit ,g1 while at the same time the proportion of current which does pass does not magnetize the cores ,c1 which are shielded or screened by the shields ,h4 ,as the increasing electromotive force then urges more current through the coils ,e1 the iron wire ,h becomes magnetically saturated and incapable of carrying all the lines of force1 and hence ceases to protect the cores ,c1 which becomes magnetized1 developing their maximum effect after an interval of time subsequent to the similar manifestation of strength in the other set of magnets1 the extent of which is arbitrarily determined by the thickness of the shield ,h1 and other well-understood conditions4 ,from the above it will be seen that the apparatus or device acts in two ways4 ,first1 by retarding the current1 and1 second1 by retarding the magnetization of one set of the cores1 from which its effectiveness will readily appear4 ,many modifications of the principle of this invention are possible4 ,one useful and efficient application of the invention is shown in ,fig4 #ei4 ,in this figure a motor is shown similar in all respects to that above described1 except that the iron wire ,h1 which is wrapped around the coils ,e1 is in this case connected in series with the coils ,d4 ,the iron-wire coils ,h1 are connected and wound1 so as to have little or no self-induction1 and being added to the resistance of the circuit ,f1 the action of the current in that circuit will be accelerated1 while in the other circuit ,g it will be retarded4 ,the shield ,h may be made in many forms1 as will be understood1 and used in different ways1 as appears from the foregoing description4 ,as a modification of his type of motor with shielded fields1 ,mr4 ,tesla has constructed a motor with a field-magnet having two sets of poles or inwardly-projecting cores and placed side by side1 so as practically to form two fields of force and alternately disposed--that is to say1 with the poles of one set or field opposite the spaces between the other4 ,he then connects the free ends of one set of poles by means of laminated iron bands or bridge-pieces of considerably smaller cross-section than the cores themselves1 whereby the cores will all form parts of complete magnetic circuits4 ,when the coils on each set of magnets are connected in multiple circuits or branches from a source of alternating currents1 electromotive forces are set up in or impressed upon each circuit simultaneously2 but the coils on the magnetically bridged or shunted cores will have1 by reason of the closed magnetic circuits1 a high self-induction1 which retards the current1 permitting at the beginning of each impulse but little current to pass4 ,on the other hand1 no such opposition being encountered in the other set of coils1 the current passes freely through them1 magnetizing the poles on which they are wound4 ,as soon1 however1 as the laminated bridges become saturated and incapable of carrying all the lines of force which the rising electromotive force1 and consequently increased current1 produce1 free poles are developed at the ends of the cores1 which1 acting in conjunction with the others1 produce rotation of the armature4 ,the construction in detail by which this invention is illustrated is shown in the accompanying drawings4 ,illustration3 ,,fig4 #fj4 ,illustration3 ,,fig4 #fa4 ,fig4 #fj is a view in side elevation of a motor embodying the principle4 ,fig4 #fa is a vertical cross-section of the motor4 ,a is the frame of the motor1 which should be built up of sheets of iron punched out to the desired shape and bolted together with insulation between the sheets4 ,when complete1 the frame makes a field-magnet with inwardly projecting pole-pieces ,b and ,c4 ,to adapt them to the requirements of this particular case these pole-pieces are out of line with one another1 those marked ,b surrounding one end of the armature and the others1 as ,c1 the opposite end1 and they are disposed alternately--that is to say1 the pole-pieces of one set occur in line with the spaces between those of the other sets4 ,the armature ,d is of cylindrical form1 and is also laminated in the usual way and is wound longitudinally with coils closed upon themselves4 ,the pole-pieces ,c are connected or shunted by bridge-pieces ,e4 ,these may be made independently and attached to the pole-pieces1 or they may be parts of the forms or blanks stamped or punched out of sheet-iron4 ,their size or mass is determined by various conditions1 such as the strength of the current to be employed1 the mass or size of the cores to which they are applied1 and other familiar conditions4 ,coils ,f surround the pole-pieces ,b1 and other coils ,g are wound on the pole-pieces ,c4 ,these coils are connected in series in two circuits1 which are branches of a circuit from a generator of alternating currents1 and they may be so wound1 or the respective circuits in which they are included may be so arranged1 that the circuit of coils ,g will have1 independently of the particular construction described1 a higher self-induction than the other circuit or branch4 ,the function of the shunts or bridges ,e is that they shall form with the cores ,c a closed magnetic circuit for a current up to a predetermined strength1 so that when saturated by such current and unable to carry more lines of force than such a current produces they will to no further appreciable extent interfere with the development1 by a stronger current1 of free magnetic poles at the ends of the cores ,c4 ,in such a motor the current is so retarded in the coils ,g1 and the manifestation of the free magnetism in the poles ,c is so delayed beyond the period of maximum magnetic effect in poles ,b1 that a strong torque is produced and the motor operates with approximately the power developed in a motor of this kind energized by independently generated currents differing by a full quarter phase4 ,,chapter ,,xiv4 ,,type ,,of ,,tesla ,,single-,,phase ,,motor4 ,up to this point1 two principal types of ,tesla motors have been described3 ,first1 those containing two or more energizing circuits through which are caused to pass alternating currents differing from one another in phase to an extent sufficient to produce a continuous progression or shifting of the poles or points of greatest magnetic effect1 in obedience to which the movable element of the motor is maintained in rotation2 second1 those containing poles1 or parts of different magnetic susceptibility1 which under the energizing influence of the same current or two currents coinciding in phase will exhibit differences in their magnetic periods or phases4 ,in the first class of motors the torque is due to the magnetism established in different portions of the motor by currents from the same or from independent sources1 and exhibiting time differences in phase4 ,in the second class the torque results from the energizing effects of a current upon different parts of the motor which differ in magnetic susceptibility--in other words1 parts which respond in the same relative degree to the action of a current1 not simultaneously1 but after different intervals of time4 ,in another ,tesla motor1 however1 the torque1 instead of being solely the result of a time difference in the magnetic periods or phases of the poles or attractive parts to whatever cause due1 is produced by an angular displacement of the parts which1 though movable with respect to one another1 are magnetized simultaneously1 or approximately so1 by the same currents4 ,this principle of operation has been embodied practically in a motor in which the necessary angular displacement between the points of greatest magnetic attraction in the two elements of the motor--the armature and field--is obtained by the direction of the lamination of the magnetic cores of the elements4 ,fig4 #fb is a side view of such a motor with a portion of its armature core exposed4 ,fig4 #fc is an end or edge view of the same4 ,fig4 #fd is a central cross-section of the same1 the armature being shown mainly in elevation4 ,illustration3 ,,fig4 #fb4 ,illustration3 ,,fig4 #fc4 ,illustration3 ,,fig4 #fd4 ,let ,a ,a designate two plates built up of thin sections or laminae of soft iron insulated more or less from one another and held together by bolts a and secured to a base ,b4 ,the inner faces of these plates contain recesses or grooves in which a coil or coils ,d are secured obliquely to the direction of the laminations4 ,within the coils ,d is a disc ,e1 preferably composed of a spirally-wound iron wire or ribbon or a series of concentric rings and mounted on a shaft ,f1 having bearings in the plates ,a ,a4 ,such a device when acted upon by an alternating current is capable of rotation and constitutes a motor1 the operation of which may be explained in the following manner3 ,a current or current-impulse traversing the coils ,d tends to magnetize the cores ,a ,a and ,e1 all of which are within the influence of the field of the coils4 ,the poles thus established would naturally lie in the same line at right angles to the coils ,d1 but in the plates ,a they are deflected by reason of the direction of the laminations1 and appear at or near the extremities of these plates4 ,in the disc1 however1 where these conditions are not present1 the poles or points of greatest attraction are on a line at right angles to the plane of the coils2 hence there will be a torque established by this angular displacement of the poles or magnetic lines1 which starts the disc in rotation1 the magnetic lines of the armature and field tending toward a position of parallelism4 ,this rotation is continued and maintained by the reversals of the current in coils ,d ,d1 which change alternately the polarity of the field-cores ,a ,a4 ,this rotary tendency or effect will be greatly increased by winding the disc with conductors ,g1 closed upon themselves and having a radial direction1 whereby the magnetic intensity of the poles of the disc will be greatly increased by the energizing effect of the currents induced in the coils ,g by the alternating currents in coils ,d4 ,the cores of the disc and field may or may not be of different magnetic susceptibility--that is to say1 they may both be of the same kind of iron1 so as to be magnetized at approximately the same instant by the coils ,d2 or one may be of soft iron and the other of hard1 in order that a certain time may elapse between the periods of their magnetization4 ,in either case rotation will be produced2 but unless the disc is provided with the closed energizing coils it is desirable that the above-described difference of magnetic susceptibility be utilized to assist in its rotation4 ,the cores of the field and armature may be made in various ways1 as will be well understood1 it being only requisite that the laminations in each be in such direction as to secure the necessary angular displacement of the points of greatest attraction4 ,moreover1 since the disc may be considered as made up of an infinite number of radial arms1 it is obvious that what is true of a disc holds for many other forms of armature4 ,,chapter ,,xv4 ,,motors ,,with ,,circuits ,,of ,,different ,,resistance4 ,as has been pointed out elsewhere1 the lag or retardation of the phases of an alternating current is directly proportional to the self-induction and inversely proportional to the resistance of the circuit through which the current flows4 ,hence1 in order to secure the proper differences of phase between the two motor-circuits1 it is desirable to make the self-induction in one much higher and the resistance much lower than the self-induction and resistance1 respectively1 in the other4 ,at the same time the magnetic quantities of the two poles or sets of poles which the two circuits produce should be approximately equal4 ,these requirements have led ,mr4 ,tesla to the invention of a motor having the following general characteristics3 ,the coils which are included in that energizing circuit which is to have the higher self-induction are made of coarse wire1 or a conductor of relatively low resistance1 and with the greatest possible length or number of turns4 ,in the other set of coils a comparatively few turns of finer wire are used1 or a wire of higher resistance4 ,furthermore1 in order to approximate the magnetic quantities of the poles excited by these coils1 ,mr4 ,tesla employs in the self-induction circuit cores much longer than those in the other or resistance circuit4 ,fig4 #fe is a part sectional view of the motor at right angles to the shaft4 ,fig4 #ff is a diagram of the field circuits4 ,in ,fig4 #ff1 let ,a represent the coils in one motor circuit1 and ,b those in the other4 ,the circuit ,a is to have the higher self-induction4 ,there are1 therefore1 used a long length or a large number of turns of coarse wire in forming the coils of this circuit4 ,for the circuit ,b1 a smaller conductor is employed1 or a conductor of a higher resistance than copper1 such as ,german silver or iron1 and the coils are wound with fewer turns4 ,in applying these coils to a motor1 ,mr4 ,tesla builds up a field-magnet of plates ,c1 of iron and steel1 secured together in the usual manner by bolts ,d4 ,each plate is formed with four 7more or less7 long cores ,e1 around which is a space to receive the coil and an equal number of short projections ,f to receive the coils of the resistance-circuit4 ,the plates are generally annular in shape1 having an open space in the centre for receiving the armature ,g1 which ,mr4 ,tesla prefers to wind with closed coils4 ,an alternating current divided between the two circuits is retarded as to its phases in the circuit ,a to a much greater extent than in the circuit ,b4 ,by reason of the relative sizes and disposition of the cores and coils the magnetic effect of the poles ,e and ,f upon the armature closely approximate4 ,illustration3 ,,fig4 #fe4 ,illustration3 ,,fig4 #ff4 ,an important result secured by the construction shown here is that these coils which are designed to have the higher self-induction are almost completely surrounded by iron1 and that the retardation is thus very materially increased4 ,,chapter ,,xvi4 ,,motor ,,with ,,equal ,,magnetic ,,energies ,,in ,,field ,,and ,,armature4 ,let it be assumed that the energy as represented in the magnetism in the field of a given rotating field motor is ninety and that of the armature ten4 ,the sum of these quantities1 which represents the total energy expended in driving the motor1 is one hundred2 but1 assuming that the motor be so constructed that the energy in the field is represented by fifty1 and that in the armature by fifty1 the sum is still one hundred2 but while in the first instance the product is nine hundred1 in the second it is two thousand five hundred1 and as the energy developed is in proportion to these products it is clear that those motors are the most efficient--other things being equal--in which the magnetic energies developed in the armature and field are equal4 ,these results ,mr4 ,tesla obtains by using the same amount of copper or ampere turns in both elements when the cores of both are equal1 or approximately so1 and the same current energizes both2 or in cases where the currents in one element are induced to those of the other he uses in the induced coils an excess of copper over that in the primary element or conductor4 ,illustration3 ,,fig4 #fg4 ,the conventional figure of a motor here introduced1 ,fig4 #fg1 will give an idea of the solution furnished by ,mr4 ,tesla for the specific problem4 ,referring to the drawing1 ,a is the field-magnet1 ,b the armature1 ,c the field coils1 and ,d the armature-coils of the motor4 ,generally speaking1 if the mass of the cores of armature and field be equal1 the amount of copper or ampere turns of the energizing coils on both should also be equal2 but these conditions will be modified in different forms of machine4 ,it will be understood that these results are most advantageous when existing under the conditions presented where the motor is running with its normal load1 a point to be well borne in mind4 ,,chapter ,,xvii4 ,,motors ,,with ,,coinciding ,,maxima ,,of ,,magnetic ,,effect ,,in ,,armature ,,and ,,field4 ,in this form of motor1 ,mr4 ,tesla's object is to design and build machines wherein the maxima of the magnetic effects of the armature and field will more nearly coincide than in some of the types previously under consideration4 ,these types are3 ,first1 motors having two or more energizing circuits of the same electrical character1 and in the operation of which the currents used differ primarily in phase2 second1 motors with a plurality of energizing circuits of different electrical character1 in or by means of which the difference of phase is produced artificially1 and1 third1 motors with a plurality of energizing circuits1 the currents in one being induced from currents in another4 ,considering the structural and operative conditions of any one of them--as1 for example1 that first named--the armature which is mounted to rotate in obedience to the co-operative influence or action of the energizing circuits has coils wound upon it which are closed upon themselves and in which currents are induced by the energizing-currents with the object and result of energizing the armature-core2 but under any such conditions as must exist in these motors1 it is obvious that a certain time must elapse between the manifestations of an energizing current impulse in the field coils1 and the corresponding magnetic state or phase in the armature established by the current induced thereby2 consequently a given magnetic influence or effect in the field which is the direct result of a primary current impulse will have become more or less weakened or lost before the corresponding effect in the armature indirectly produced has reached its maximum4 ,this is a condition unfavorable to efficient working in certain cases--as1 for instance1 when the progress of the resultant poles or points of maximum attraction is very great1 or when a very high number of alternations is employed--for it is apparent that a stronger tendency to rotation will be maintained if the maximum magnetic attractions or conditions in both armature and field coincide1 the energy developed by a motor being measured by the product of the magnetic quantities of the armature and field4 ,to secure this coincidence of maximum magnetic effects1 ,mr4 ,tesla has devised various means1 as explained below4 ,fig4 #fh is a diagrammatic illustration of a ,tesla motor system in which the alternating currents proceed from independent sources and differ primarily in phase4 ,illustration3 ,,fig4 #fh4 ,illustration3 ,,fig4 #fi4 ,a designates the field-magnet or magnetic frame of the motor2 ,b ,b1 oppositely located pole-pieces adapted to receive the coils of one energizing circuit2 and ,c ,c1 similar pole-pieces for the coils of the other energizing circuit4 ,these circuits are designated1 respectively1 by ,d ,e1 the conductor ,d'' forming a common return to the generator ,g4 ,between these poles is mounted an armature--for example1 a ring or annular armature1 wound with a series of coils ,f1 forming a closed circuit or circuits4 ,the action or operation of a motor thus constructed is now well understood4 ,it will be observed1 however1 that the magnetism of poles ,b1 for example1 established by a current impulse in the coils thereon1 precedes the magnetic effect set up in the armature by the induced current in coils ,f4 ,consequently the mutual attraction between the armature and field-poles is considerably reduced4 ,the same conditions will be found to exist if1 instead of assuming the poles ,b or ,c as acting independently1 we regard the ideal resultant of both acting together1 which is the real condition4 ,to remedy this1 the motor field is constructed with secondary poles ,b' ,c'1 which are situated between the others4 ,these pole-pieces are wound with coils ,d' ,e'1 the former in derivation to the coils ,d1 the latter to coils ,e4 ,the main or primary coils ,d and ,e are wound for a different self-induction from that of the coils ,d' and ,e'1 the relations being so fixed that if the currents in ,d and ,e differ1 for example1 by a quarter-phase1 the currents in each secondary coil1 as ,d' ,e'1 will differ from those in its appropriate primary ,d or ,e by1 say1 forty-five degrees1 or one-eighth of a period4 ,now1 assuming that an impulse or alternation in circuit or branch ,e is just beginning1 while in the branch ,d it is just falling from maximum1 the conditions are those of a quarter-phase difference4 ,the ideal resultant of the attractive forces of the two sets of poles ,b ,c therefore may be considered as progressing from poles ,b to poles ,c1 while the impulse in ,e is rising to maximum1 and that in ,d is falling to zero or minimum4 ,the polarity set up in the armature1 however1 lags behind the manifestations of field magnetism1 and hence the maximum points of attraction in armature and field1 instead of coinciding1 are angularly displaced4 ,this effect is counteracted by the supplemental poles ,b' ,c'4 ,the magnetic phases of these poles succeed those of poles ,b ,c by the same1 or nearly the same1 period of time as elapses between the effect of the poles ,b ,c and the corresponding induced effect in the armature2 hence the magnetic conditions of poles ,b' ,c' and of the armature more nearly coincide and a better result is obtained4 ,as poles ,b' ,c' act in conjunction with the poles in the armature established by poles ,b ,c1 so in turn poles ,c ,b act similarly with the poles set up by ,b' ,c'1 respectively4 ,under such conditions the retardation of the magnetic effect of the armature and that of the secondary poles will bring the maximum of the two more nearly into coincidence and a correspondingly stronger torque or magnetic attraction secured4 ,in such a disposition as is shown in ,fig4 #fh it will be observed that as the adjacent pole-pieces of either circuit are of like polarity they will have a certain weakening effect upon one another4 ,mr4 ,tesla therefore prefers to remove the secondary poles from the direct influence of the others4 ,this may be done by constructing a motor with two independent sets of fields1 and with either one or two armatures electrically connected1 or by using two armatures and one field4 ,these modifications are illustrated further on4 ,illustration3 ,,fig4 #gj4 ,illustration3 ,,fig4 #ga4 ,fig4 #fi is a diagrammatic illustration of a motor and system in which the difference of phase is artificially produced4 ,there are two coils ,d ,d in one branch and two coils ,e ,e in another branch of the main circuit from the generator ,g4 ,these two circuits or branches are of different self-induction1 one1 as ,d1 being higher than the other4 ,this is graphically indicated by making coils ,d much larger than coils ,e4 ,by reason of the difference in the electrical character of the two circuits1 the phases of current in one are retarded to a greater extent than the other4 ,let this difference be thirty degrees4 ,a motor thus constructed will rotate under the action of an alternating current2 but as happens in the case previously described the corresponding magnetic effects of the armature and field do not coincide owing to the time that elapses between a given magnetic effect in the armature and the condition of the field that produces it4 ,the secondary or supplemental poles ,b' ,c' are therefore availed of4 ,there being thirty degrees difference of phase between the currents in coils ,d ,e1 the magnetic effect of poles ,b' ,c' should correspond to that produced by a current differing from the current in coils ,d or ,e by fifteen degrees4 ,this we can attain by winding each supplemental pole ,b' ,c' with two coils ,h ,h'4 ,the coils ,h are included in a derived circuit having the same self-induction as circuit ,d1 and coils ,h' in a circuit having the same self-induction as circuit ,e1 so that if these circuits differ by thirty degrees the magnetism of poles ,b' ,c' will correspond to that produced by a current differing from that in either ,d or ,e by fifteen degrees4 ,this is true in all other cases4 ,for example1 if in ,fig4 #fh the coils ,d' ,e' be replaced by the coils ,h ,h' included in the derived circuits1 the magnetism of the poles ,b' ,c' will correspond in effect or phase1 if it may be so termed1 to that produced by a current differing from that in either circuit ,d or ,e by forty-five degrees1 or one-eighth of a period4 ,this invention as applied to a derived circuit motor is illustrated in ,figs4 #gj and #ga4 ,the former is an end view of the motor with the armature in section and a diagram of connections1 and ,fig4 #ga a vertical section through the field4 ,these figures are also drawn to show one of the dispositions of two fields that may be adopted in carrying out the principle4 ,the poles ,b ,b ,c ,c are in one field1 the remaining poles in the other4 ,the former are wound with primary coils ,i ,j and secondary coils ,i' ,j'1 the latter with coils ,k ,l4 ,the primary coils ,i ,j are in derived circuits1 between which1 by reason of their different self-induction1 there is a difference of phase1 say1 of thirty degrees4 ,the coils ,i' ,k are in circuit with one another1 as also are coils ,j' ,l1 and there should be a difference of phase between the currents in coils ,k and ,l and their corresponding primaries of1 say1 fifteen degrees4 ,if the poles ,b ,c are at right angles1 the armature-coils should be connected directly across1 or a single armature core wound from end to end may be used2 but if the poles ,b ,c be in line there should be an angular displacement of the armature coils1 as will be well understood4 ,the operation will be understood from the foregoing4 ,the maximum magnetic condition of a pair of poles1 as ,b' ,b'1 coincides closely with the maximum effect in the armature1 which lags behind the corresponding condition in poles ,b ,b4 ,,chapter ,,xviii4 ,,motor ,,based ,,on ,,the ,,difference ,,of ,,phase ,,in ,,the ,,magnetization ,,of ,,the ,,inner ,,and ,,outer ,,parts ,,of ,,an ,,iron ,,core4 ,it is well known that if a magnetic core1 even if laminated or subdivided1 be wound with an insulated coil and a current of electricity be directed through the coil1 the magnetization of the entire core does not immediately ensue1 the magnetizing effect not being exhibited in all parts simultaneously4 ,this may be attributed to the fact that the action of the current is to energize first those laminae or parts of the core nearest the surface and adjacent to the exciting-coil1 and from thence the action progresses toward the interior4 ,a certain interval of time therefore elapses between the manifestation of magnetism in the external and the internal sections or layers of the core4 ,if the core be thin or of small mass1 this effect may be inappreciable2 but in the case of a thick core1 or even of a comparatively thin one1 if the number of alternations or rate of change of the current strength be very great1 the time interval occurring between the manifestations of magnetism in the interior of the core and in those parts adjacent to the coil is more marked4 ,in the construction of such apparatus as motors which are designed to be run by alternating or equivalent currents--such as pulsating or undulating currents generally--,mr4 ,tesla found it desirable and even necessary to give due consideration to this phenomenon and to make special provisions in order to obviate its consequences4 ,with the specific object of taking advantage of this action or effect1 and to render it more pronounced1 he constructs a field magnet in which the parts of the core or cores that exhibit at different intervals of time the magnetic effect imparted to them by alternating or equivalent currents in an energizing coil or coils1 are so placed with relation to a rotating armature as to exert thereon their attractive effect successively in the order of their magnetization4 ,by this means he secures a result similar to that which he had previously attained in other forms or types of motor in which by means of one or more alternating currents he has produced the rotation or progression of the magnetic poles4 ,this new mode of operation will now be described4 ,fig4 #gb is a side elevation of such motor4 ,fig4 #gc is a side elevation of a more practicable and efficient embodiment of the invention4 ,fig4 #gd is a central vertical section of the same in the plane of the axis of rotation4 ,illustration3 ,,figs4 #gb and #gc4 ,referring to ,fig4 #gb1 let ,x represent a large iron core1 which may be composed of a number of sheets or laminae of soft iron or steel4 ,surrounding this core is a coil ,y1 which is connected with a source ,e of rapidly varying currents4 ,let us consider now the magnetic conditions existing in this core at any point1 as b1 at or near the centre1 and any other point1 as a1 nearer the surface4 ,when a current impulse is started in the magnetizing coil ,y1 the section or part at a1 being close to the coil1 is immediately energized1 while the section or part at b1 which1 to use a convenient expression1 is protected by the intervening sections or layers between a and b1 does not at once exhibit its magnetism4 ,however1 as the magnetization of a increases1 b becomes also affected1 reaching finally its maximum strength some time later than a4 ,upon the weakening of the current the magnetization of a first diminishes1 while b still exhibits its maximum strength2 but the continued weakening of a is attended by a subsequent weakening of b4 ,assuming the current to be an alternating one1 a will now be reversed1 while b still continues of the first imparted polarity4 ,this action continues the magnetic condition of b1 following that of a in the manner above described4 ,if an armature--for instance1 a simple disc ,f1 mounted to rotate freely on an axis--be brought into proximity to the core1 a movement of rotation will be imparted to the disc1 the direction depending upon its position relatively to the core1 the tendency being to turn the portion of the disc nearest to the core from a to b1 as indicated in ,fig4 #gb4 ,illustration3 ,,fig4 #gd4 ,this action or principle of operation has been embodied in a practicable form of motor1 which is illustrated in ,fig4 #gc4 ,let ,a in that figure represent a circular frame of iron1 from diametrically opposite points of the interior of which the cores project4 ,each core is composed of three main parts ,b1 ,b and ,c1 and they are similarly formed with a straight portion or body e1 around which the energizing coil is wound1 a curved arm or extension c1 and an inwardly projecting pole or end d4 ,each core is made up of two parts ,b ,b1 with their polar extensions reaching in one direction1 and a part ,c between the other two1 and with its polar extension reaching in the opposite direction4 ,in order to lessen in the cores the circulation of currents induced therein1 the several sections are insulated from one another in the manner usually followed in such cases4 ,these cores are wound with coils ,d1 which are connected in the same circuit1 either in parallel or series1 and supplied with an alternating or a pulsating current1 preferably the former1 by a generator ,e1 represented diagrammatically4 ,between the cores or their polar extensions is mounted a cylindrical or similar armature ,f1 wound with magnetizing coils ,g1 closed upon themselves4 ,the operation of this motor is as follows3 ,when a current impulse or alternation is directed through the coils ,d1 the sections ,b ,b of the cores1 being on the surface and in close proximity to the coils1 are immediately energized4 ,the sections ,c1 on the other hand1 are protected from the magnetizing influence of the coil by the interposed layers of iron ,b ,b4 ,as the magnetism of ,b ,b increases1 however1 the sections ,c are also energized2 but they do not attain their maximum strength until a certain time subsequent to the exhibition by the sections ,b ,b of their maximum4 ,upon the weakening of the current the magnetic strength of ,b ,b first diminishes1 while the sections ,c have still their maximum strength2 but as ,b ,b continue to weaken the interior sections are similarly weakened4 ,b ,b may then begin to exhibit an opposite polarity1 which is followed later by a similar change on ,c1 and this action continues4 ,b ,b and ,c may therefore be considered as separate field-magnets1 being extended so as to act on the armature in the most efficient positions1 and the effect is similar to that in the other forms of ,tesla motor--viz41 a rotation or progression of the maximum points of the field of force4 ,any armature--such1 for instance1 as a disc--mounted in this field would rotate from the pole first to exhibit its magnetism to that which exhibits it later4 ,it is evident that the principle here described may be carried out in conjunction with other means for securing a more favorable or efficient action of the motor4 ,for example1 the polar extensions of the sections ,c may be wound or surrounded by closed coils4 ,the effect of these coils will be to still more effectively retard the magnetization of the polar extensions of ,c4 ,,chapter ,,xix4 ,,another ,,type ,,of ,,tesla ,,induction ,,motor4 ,it will have been gathered by all who are interested in the advance of the electrical arts1 and who follow carefully1 step by step1 the work of pioneers1 that ,mr4 ,tesla has been foremost to utilize inductive effects in permanently closed circuits1 in the operation of alternating motors4 ,in this chapter one simple type of such a motor is described and illustrated1 which will serve as an exemplification of the principle4 ,let it be assumed that an ordinary alternating current generator is connected up in a circuit of practically no self-induction1 such1 for example1 as a circuit containing incandescent lamps only4 ,on the operation of the machine1 alternating currents will be developed in the circuit1 and the phases of these currents will theoretically coincide with the phases of the impressed electromotive force4 ,such currents may be regarded and designated as the unretarded currents4 ,it will be understood1 of course1 that in practice there is always more or less self-induction in the circuit1 which modifies to a corresponding extent these conditions2 but for convenience this may be disregarded in the consideration of the principle of operation1 since the same laws apply4 ,assume next that a path of currents be formed across any two points of the above circuit1 consisting1 for example1 of the primary of an induction device4 ,the phases of the currents passing through the primary1 owing to the self-induction of the same1 will not coincide with the phases of the impressed electromotive force1 but will lag behind1 such lag being directly proportional to the self-induction and inversely proportional to the resistance of the said coil4 ,the insertion of this coil will also cause a lagging or retardation of the currents traversing and delivered by the generator behind the impressed electromotive force1 such lag being the mean or resultant of the lag of the current through the primary alone and of the unretarded current in the entire working circuit4 ,next consider the conditions imposed by the association in inductive relation with the primary coil1 of a secondary coil4 ,the current generated in the secondary coil will react upon the primary current1 modifying the retardation of the same1 according to the amount of self-induction and resistance in the secondary circuit4 ,if the secondary circuit has but little self-induction--as1 for instance1 when it contains incandescent lamps only--it will increase the actual difference of phase between its own and the primary current1 first1 by diminishing the lag between the primary current and the impressed electromotive force1 and1 second1 by its own lag or retardation behind the impressed electromotive force4 ,on the other hand1 if the secondary circuit have a high self-induction1 its lag behind the current in the primary is directly increased1 while it will be still further increased if the primary have a very low self-induction4 ,the better results are obtained when the primary has a low self-induction4 ,illustration3 ,,fig4 #ge4 ,illustration3 ,,fig4 #gf4 ,fig4 #ge is a diagram of a ,tesla motor embodying this principle4 ,fig4 #gf is a similar diagram of a modification of the same4 ,in ,fig4 #ge let ,a designate the field-magnet of a motor which1 as in all these motors1 is built up of sections or plates4 ,b ,c are polar projections upon which the coils are wound4 ,upon one pair of these poles1 as ,c1 are wound primary coils ,d1 which are directly connected to the circuit of an alternating current generator ,g4 ,on the same poles are also wound secondary coils ,f1 either side by side or over or under the primary coils1 and these are connected with other coils ,e1 which surround the poles ,b ,b4 ,the currents in both primary and secondary coils in such a motor will be retarded or will lag behind the impressed electromotive force2 but to secure a proper difference in phase between the primary and secondary currents themselves1 ,mr4 ,tesla increases the resistance of the circuit of the secondary and reduces as much as practicable its self-induction4 ,this is done by using for the secondary circuit1 particularly in the coils ,e1 wire of comparatively small diameter and having but few turns around the cores2 or by using some conductor of higher specific resistance1 such as ,german silver2 or by introducing at some point in the secondary circuit an artificial resistance ,r4 ,thus the self-induction of the secondary is kept down and its resistance increased1 with the result of decreasing the lag between the impressed electro-motive force and the current in the primary coils and increasing the difference of phase between the primary and secondary currents4 ,in the disposition shown in ,fig4 #gf1 the lag in the secondary is increased by increasing the self-induction of that circuit1 while the increasing tendency of the primary to lag is counteracted by inserting therein a dead resistance4 ,the primary coils ,d in this case have a low self-induction and high resistance1 while the coils ,e ,f1 included in the secondary circuit1 have a high self-induction and low resistance4 ,this may be done by the proper winding of the coils2 or in the circuit including the secondary coils ,e ,f1 we may introduce a self-induction coil ,s1 while in the primary circuit from the generator ,g and including coils ,d1 there may be inserted a dead resistance ,r4 ,by this means the difference of phase between the primary and secondary is increased4 ,it is evident that both means of increasing the difference of phase--namely1 by the special winding as well as by the supplemental or external inductive and dead resistance--may be employed conjointly4 ,in the operation of this motor the current impulses in the primary coils induce currents in the secondary coils1 and by the conjoint action of the two the points of greatest magnetic attraction are shifted or rotated4 ,in practice it is found desirable to wind the armature with closed coils in which currents are induced by the action thereon of the primaries4 ,,chapter ,,xx4 ,,combinations ,,of ,,synchronizing ,,motor ,,and ,,torque ,,motor4 ,in the preceding descriptions relative to synchronizing motors and methods of operating them1 reference has been made to the plan adopted by ,mr4 ,tesla1 which consists broadly in winding or arranging the motor in such manner that by means of suitable switches it could be started as a multiple-circuit motor1 or one operating by a progression of its magnetic poles1 and then1 when up to speed1 or nearly so1 converted into an ordinary synchronizing motor1 or one in which the magnetic poles were simply alternated4 ,in some cases1 as when a large motor is used and when the number of alternations is very high1 there is more or less difficulty in bringing the motor to speed as a double or multiple-circuit motor1 for the plan of construction which renders the motor best adapted to run as a synchronizing motor impairs its efficiency as a torque or double-circuit motor under the assumed conditions on the start4 ,this will be readily understood1 for in a large synchronizing motor the length of the magnetic circuit of the polar projections1 and their mass1 are so great that apparently considerable time is required for magnetization and demagnetization4 ,hence with a current of a very high number of alternations the motor may not respond properly4 ,to avoid this objection and to start up a synchronizing motor in which these conditions obtain1 ,mr4 ,tesla has combined two motors1 one a synchronizing motor1 the other a multiple-circuit or torque motor1 and by the latter he brings the first-named up to speed1 and then either throws the whole current into the synchronizing motor or operates jointly both of the motors4 ,this invention involves several novel and useful features4 ,it will be observed1 in the first place1 that both motors are run1 without commutators of any kind1 and1 secondly1 that the speed of the torque motor may be higher than that of the synchronizing motor1 as will be the case when it contains a fewer number of poles or sets of poles1 so that the motor will be more readily and easily brought up to speed4 ,thirdly1 the synchronizing motor may be constructed so as to have a much more pronounced tendency to synchronism without lessening the facility with which it is started4 ,fig4 #gg is a part sectional view of the two motors2 ,fig4 #gh an end view of the synchronizing motor2 ,fig4 #gi an end view and part section of the torque or double-circuit motor2 ,fig4 #hj a diagram of the circuit connections employed2 and ,figs4 #ha1 #hb1 #hc1 #hd and #he are diagrams of modified dispositions of the two motors4 ,illustration3 ,,fig4 #gg4 ,inasmuch as neither motor is doing any work while the current is acting upon the other1 the two armatures are rigidly connected1 both being mounted upon the same shaft ,a1 the field-magnets ,b of the synchronizing and ,c of the torque motor being secured to the same base ,d4 ,the preferably larger synchronizing motor has polar projections on its armature1 which rotate in very close proximity to the poles of the field1 and in other respects it conforms to the conditions that are necessary to secure synchronous action4 ,the pole-pieces of the armature are1 however1 wound with closed coils ,e1 as this obviates the employment of sliding contacts4 ,the smaller or torque motor1 on the other hand1 has1 preferably1 a cylindrical armature ,f1 without polar projections and wound with closed coils ,g4 ,the field-coils of the torque motor are connected up in two series ,h and ,i1 and the alternating current from the generator is directed through or divided between these two circuits in any manner to produce a progression of the poles or points of maximum magnetic effect4 ,this result is secured by connecting the two motor-circuits in derivation with the circuit from the generator1 inserting in one motor circuit a dead resistance and in the other a self-induction coil1 by which means a difference in phase between the two divisions of the current is secured4 ,if both motors have the same number of field poles1 the torque motor for a given number of alternations will tend to run at double the speed of the other1 for1 assuming the connections to be such as to give the best results1 its poles are divided into two series and the number of poles is virtually reduced one-half1 which being acted upon by the same number of alternations tend to rotate the armature at twice the speed4 ,by this means the main armature is more easily brought to or above the required speed4 ,when the speed necessary for synchronism is imparted to the main motor1 the current is shifted from the torque motor into the other4 ,illustration3 ,,fig4 #gh4 ,illustration3 ,,fig4 #gi4 ,a convenient arrangement for carrying out this invention is shown in ,fig4 #hj1 in which ,j ,j are the field coils of the synchronizing1 and ,h ,i the field coils of the torque motor4 ,l ,l' are the conductors of the main line4 ,one end of1 say1 coils ,h is connected to wire ,l through a self-induction coil ,m4 ,one end of the other set of coils ,i is connected to the same wire through a dead resistance ,n4 ,the opposite ends of these two circuits are connected to the contact m of a switch1 the handle or lever of which is in connection with the line-wire ,l'4 ,one end of the field circuit of the synchronizing motor is connected to the wire ,l4 ,the other terminates in the switch-contact n4 ,from the diagram it will be readily seen that if the lever ,p be turned upon contact m1 the torque motor will start by reason of the difference of phase between the currents in its two energizing circuits4 ,then when the desired speed is attained1 if the lever ,p be shifted upon contact n the entire current will pass through the field coils of the synchronizing motor and the other will be doing no work4 ,the torque motor may be constructed and operated in various ways1 many of which have already been touched upon4 ,it is not necessary that one motor be cut out of circuit while the other is in1 for both may be acted upon by current at the same time1 and ,mr4 ,tesla has devised various dispositions or arrangements of the two motors for accomplishing this4 ,some of these arrangements are illustrated in ,figs4 #ha to #he4 ,illustration3 ,,fig4 #hj4 ,referring to ,fig4 #ha1 let ,t designate the torque or multiple circuit motor and ,s the synchronizing motor1 ,l ,l' being the line-wires from a source of alternating current4 ,the two circuits of the torque motor of different degrees of self-induction1 and designated by ,n ,m1 are connected in derivation to the wire ,l4 ,they are then joined and connected to the energizing circuit of the synchronizing motor1 the opposite terminal of which is connected to wire ,l'4 ,the two motors are thus in series4 ,to start them ,mr4 ,tesla short-circuits the synchronizing motor by a switch ,p'1 throwing the whole current through the torque motor4 ,then when the desired speed is reached the switch ,p' is opened1 so that the current passes through both motors4 ,in such an arrangement as this it is obviously desirable for economical and other reasons that a proper relation between the speeds of the two motors should be observed4 ,in ,fig4 #hb another disposition is illustrated4 ,s is the synchronizing motor and ,t the torque motor1 the circuits of both being in parallel4 ,w is a circuit also in derivation to the motor circuits and containing a switch ,p''4 ,s' is a switch in the synchronizing motor circuit4 ,on the start the switch ,s' is opened1 cutting out the motor ,s4 ,then ,p'' is opened1 throwing the entire current through the motor ,t1 giving it a very strong torque4 ,when the desired speed is reached1 switch ,s' is closed and the current divides between both motors4 ,by means of switch ,p'' both motors may be cut out4 ,illustration3 ,,figs4 #ha1 #hb1 #hc1 #hd and #he4 ,in ,fig4 #hc the arrangement is substantially the same1 except that a switch ,t' is placed in the circuit which includes the two circuits of the torque motor4 ,fig4 #hd shows the two motors in series1 with a shunt around both containing a switch ,s ,t4 ,there is also a shunt around the synchronizing motor ,s1 with a switch ,p'4 ,in ,fig4 #he the same disposition is shown2 but each motor is provided with a shunt1 in which are switches ,p' and ,t''1 as shown4 ,,chapter ,,xxi4 ,,motor ,,with ,a ,,condenser ,,in ,,the ,,armature ,,circuit4 ,we now come to a new class of motors in which resort is had to condensers for the purpose of developing the required difference of phase and neutralizing the effects of self-induction4 ,mr4 ,tesla early began to apply the condenser to alternating apparatus1 in just how many ways can only be learned from a perusal of other portions of this volume1 especially those dealing with his high frequency work4 ,certain laws govern the action or effects produced by a condenser when connected to an electric circuit through which an alternating or in general an undulating current is made to pass4 ,some of the most important of such effects are as follows3 ,first1 if the terminals or plates of a condenser be connected with two points of a circuit1 the potentials of which are made to rise and fall in rapid succession1 the condenser allows the passage1 or more strictly speaking1 the transference of a current1 although its plates or armatures may be so carefully insulated as to prevent almost completely the passage of a current of unvarying strength or direction and of moderate electromotive force4 ,second1 if a circuit1 the terminals of which are connected with the plates of the condenser1 possess a certain self-induction1 the condenser will overcome or counteract to a greater or less degree1 dependent upon well-understood conditions1 the effects of such self-induction4 ,third1 if two points of a closed or complete circuit through which a rapidly rising and falling current flows be shunted or bridged by a condenser1 a variation in the strength of the currents in the branches and also a difference of phase of the currents therein is produced4 ,these effects ,mr4 ,tesla has utilized and applied in a variety of ways in the construction and operation of his motors1 such as by producing a difference in phase in the two energizing circuits of an alternating current motor by connecting the two circuits in derivation and connecting up a condenser in series in one of the circuits4 ,a further development1 however1 possesses certain novel features of practical value and involves a knowledge of facts less generally understood4 ,it comprises the use of a condenser or condensers in connection with the induced or armature circuit of a motor and certain details of the construction of such motors4 ,in an alternating current motor of the type particularly referred to above1 or in any other which has an armature coil or circuit closed upon itself1 the latter represents not only an inductive resistance1 but one which is periodically varying in value1 both of which facts complicate and render difficult the attainment of the conditions best suited to the most efficient working conditions2 in other words1 they require1 first1 that for a given inductive effect upon the armature there should be the greatest possible current through the armature or induced coils1 and1 second1 that there should always exist between the currents in the energizing and the induced circuits a given relation of phase4 ,hence whatever tends to decrease the self-induction and increase the current in the induced circuits will1 other things being equal1 increase the output and efficiency of the motor1 and the same will be true of causes that operate to maintain the mutual attractive effect between the field magnets and armature at its maximum4 ,mr4 ,tesla secures these results by connecting with the induced circuit or circuits a condenser1 in the manner described below1 and he also1 with this purpose in view1 constructs the motor in a special manner4 ,illustration3 ,,fig4 #hf4 ,illustration3 ,,fig4 #hh4 ,illustration3 ,,fig4 #hi4 ,illustration3 ,,fig4 #hg4 ,illustration3 ,,fig4 #ij4 ,referring to the drawings1 ,fig4 #hf1 is a view1 mainly diagrammatic1 of an alternating current motor1 in which the present principle is applied4 ,fig4 #hg is a central section1 in line with the shaft1 of a special form of armature core4 ,fig4 #hh is a similar section of a modification of the same4 ,fig4 #hi is one of the sections of the core detached4 ,fig4 #ij is a diagram showing a modified disposition of the armature or induced circuits4 ,the general plan of the invention is illustrated in ,fig4 #hf4 ,a ,a in this figure represent the the frame and field magnets of an alternating current motor1 the poles or projections of which are wound with coils ,b and ,c1 forming independent energizing circuits connected either to the same or to independent sources of alternating currents1 so that the currents flowing through the circuits1 respectively1 will have a difference of phase4 ,within the influence of this field is an armature core ,d1 wound with coils ,e4 ,in motors of this description heretofore these coils have been closed upon themselves1 or connected in a closed series2 but in the present case each coil or the connected series of coils terminates in the opposite plates of a condenser ,f4 ,for this purpose the ends of the series of coils are brought out through the shaft to collecting rings ,g1 which are connected to the condenser by contact brushes ,h and suitable conductors1 the condenser being independent of the machine4 ,the armature coils are wound or connected in such manner that adjacent coils produce opposite poles4 ,the action of this motor and the effect of the plan followed in its construction are as follows3 ,the motor being started in operation and the coils of the field magnets being traversed by alternating currents1 currents are induced in the armature coils by one set of field coils1 as ,b1 and the poles thus established are acted upon by the other set1 as ,c4 ,the armature coils1 however1 have necessarily a high self-induction1 which opposes the flow of the currents thus set up4 ,the condenser ,f not only permits the passage or transference of these currents1 but also counteracts the effects of self-induction1 and by a proper adjustment of the capacity of the condenser1 the self-induction of the coils1 and the periods of the currents1 the condenser may be made to overcome entirely the effect of self-induction4 ,it is preferable on account of the undesirability of using sliding contacts of any kind1 to associate the condenser with the armature directly1 or make it a part of the armature4 ,in some cases ,mr4 ,tesla builds up the armature of annular plates ,k ,k1 held by bolts ,l between heads ,m1 which are secured to the driving shaft1 and in the hollow space thus formed he places a condenser ,f1 generally by winding the two insulated plates spirally around the shaft4 ,in other cases he utilizes the plates of the core itself as the plates of the condenser4 ,for example1 in ,figs4 #hh and #hi1 ,n is the driving shaft1 ,m ,m are the heads of the armature-core1 and ,k ,k' the iron plates of which the core is built up4 ,these plates are insulated from the shaft and from one another1 and are held together by rods or bolts ,l4 ,the bolts pass through a large hole in one plate and a small hole in the one next adjacent1 and so on1 connecting electrically all of plates ,k1 as one armature of a condenser1 and all of plates ,k' as the other4 ,to either of the condensers above described the armature coils may be connected1 as explained by reference to ,fig4 #hf4 ,in motors in which the armature coils are closed upon themselves--as1 for example1 in any form of alternating current motor in which one armature coil or set of coils is in the position of maximum induction with respect to the field coils or poles1 while the other is in the position of minimum induction--the coils are best connected in one series1 and two points of the circuit thus formed are bridged by a condenser4 ,this is illustrated in ,fig4 #ij1 in which ,e represents one set of armature coils and ,e' the other4 ,their points of union are joined through a condenser ,f4 ,it will be observed that in this disposition the self-induction of the two branches ,e and ,e' varies with their position relatively to the field magnet1 and that each branch is alternately the predominating source of the induced current4 ,hence the effect of the condenser ,f is twofold4 ,first1 it increases the current in each of the branches alternately1 and1 secondly1 it alters the phase of the currents in the branches1 this being the well-known effect which results from such a disposition of a condenser with a circuit1 as above described4 ,this effect is favorable to the proper working of the motor1 because it increases the flow of current in the armature circuits due to a given inductive effect1 and also because it brings more nearly into coincidence the maximum magnetic effects of the coacting field and armature poles4 ,it will be understood1 of course1 that the causes that contribute to the efficiency of condensers when applied to such uses as the above must be given due consideration in determining the practicability and efficiency of the motors4 ,chief among these is1 as is well known1 the periodicity of the current1 and hence the improvements described are more particularly adapted to systems in which a very high rate of alternation or change is maintained4 ,although this invention has been illustrated in connection with a special form of motor1 it will be understood that it is equally applicable to any other alternating current motor in which there is a closed armature coil wherein the currents are induced by the action of the field1 and the feature of utilizing the plates or sections of a magnetic core for forming the condenser is applicable1 generally1 to other kinds of alternating current apparatus4 ,,chapter ,,xxii4 ,,motor ,,with ,,condenser ,,in ,,one ,,of ,,the ,,field ,,circuits4 ,if the field or energizing circuits of a rotary phase motor be both derived from the same source of alternating currents and a condenser of proper capacity be included in one of the same1 approximately1 the desired difference of phase may be obtained between the currents flowing directly from the source and those flowing through the condenser2 but the great size and expense of condensers for this purpose that would meet the requirements of the ordinary systems of comparatively low potential are particularly prohibitory to their employment4 ,another1 now well-known1 method or plan of securing a difference of phase between the energizing currents of motors of this kind is to induce by the currents in one circuit those in the other circuit or circuits2 but as no means had been proposed that would secure in this way between the phases of the primary or inducing and the secondary or induced currents that difference--theoretically ninety degrees--that is best adapted for practical and economical working1 ,mr4 ,tesla devised a means which renders practicable both the above described plans or methods1 and by which he is enabled to obtain an economical and efficient alternating current motor4 ,his invention consists in placing a condenser in the secondary or induced circuit of the motor above described and raising the potential of the secondary currents to such a degree that the capacity of the condenser1 which is in part dependent on the potential1 need be quite small4 ,the value of this condenser is determined in a well-understood manner with reference to the self-induction and other conditions of the circuit1 so as to cause the currents which pass through it to differ from the primary currents by a quarter phase4 ,fig4 #ia illustrates the invention as embodied in a motor in which the inductive relation of the primary and secondary circuits is secured by winding them inside the motor partly upon the same cores2 but the invention applies1 generally1 to other forms of motor in which one of the energizing currents is induced in any way from the other4 ,let ,a ,b represent the poles of an alternating current motor1 of which ,c is the armature wound with coils ,d1 closed upon themselves1 as is now the general practice in motors of this kind4 ,the poles ,a1 which alternate with poles ,b1 are wound with coils of ordinary or coarse wire ,e in such direction as to make them of alternate north and south polarity1 as indicated in the diagram by the characters ,n ,s4 ,over these coils1 or in other inductive relation to the same1 are wound long fine-wire coils ,f ,f1 and in the same direction throughout as the coils ,e4 ,these coils are secondaries1 in which currents of very high potential are induced4 ,all the coils ,e in one series are connected1 and all the secondaries ,f in another4 ,illustration3 ,,fig4 #ia4 ,on the intermediate poles ,b are wound fine-wire energizing coils ,g1 which are connected in series with one another1 and also with the series of secondary coils ,f1 the direction of winding being such that a current-impulse induced from the primary coils ,e imparts the same magnetism to the poles ,b as that produced in poles ,a by the primary impulse4 ,this condition is indicated by the characters ,n' ,s'4 ,in the circuit formed by the two sets of coils ,f and ,g is introduced a condenser ,h2 otherwise this circuit is closed upon itself1 while the free ends of the circuit of coils ,e are connected to a source of alternating currents4 ,as the condenser capacity which is needed in any particular motor of this kind is dependent upon the rate of alternation or the potential1 or both1 its size or cost1 as before explained1 may be brought within economical limits for use with the ordinary circuits if the potential of the secondary circuit in the motor be sufficiently high4 ,by giving to the condenser proper values1 any desired difference of phase between the primary and secondary energizing circuits may be obtained4 ,,chapter ,,xxiii4 ,,tesla ,,polyphase ,,transformer4 ,applying the polyphase principle to the construction of transformers as well to the motors already noticed1 ,mr4 ,tesla has invented some very interesting forms1 which he considers free from the defects of earlier and1 at present1 more familiar forms4 ,in these transformers he provides a series of inducing coils and corresponding induced coils1 which are generally wound upon a core closed upon itself1 usually a ring of laminated iron4 ,the two sets of coils are wound side by side or superposed or otherwise placed in well-known ways to bring them into the most effective relations to one another and to the core4 ,the inducing or primary coils wound on the core are divided into pairs or sets by the proper electrical connections1 so that while the coils of one pair or set co-operate in fixing the magnetic poles of the core at two given diametrically opposite points1 the coils of the other pair or set--assuming1 for sake of illustration1 that there are but two--tend to fix the poles ninety degrees from such points4 ,with this induction device is used an alternating current generator with coils or sets of coils to correspond with those of the converter1 and the corresponding coils of the generator and converter are then connected up in independent circuits4 ,it results from this that the different electrical phases in the generator are attended by corresponding magnetic changes in the converter2 or1 in other words1 that as the generator coils revolve1 the points of greatest magnetic intensity in the converter will be progressively shifted or whirled around4 ,fig4 #ib is a diagrammatic illustration of the converter and the electrical connections of the same4 ,fig4 #ic is a horizontal central cross-section of ,fig4 #ib4 ,fig4 #id is a diagram of the circuits of the entire system1 the generator being shown in section4 ,mr4 ,tesla uses a core1 ,a1 which is closed upon itself--that is to say1 of an annular cylindrical or equivalent form--and as the efficiency of the apparatus is largely increased by the subdivision of this core1 he makes it of thin strips1 plates1 or wires of soft iron electrically insulated as far as practicable4 ,upon this core are wound1 say1 four coils1 ,b ,b ,b' ,b'1 used as primary coils1 and for which long lengths of comparatively fine wire are employed4 ,over these coils are then wound shorter coils of coarser wire1 ,c ,c ,c' ,c'1 to constitute the induced or secondary coils4 ,the construction of this or any equivalent form of converter may be carried further1 as above pointed out1 by inclosing these coils with iron--as1 for example1 by winding over the coils layers of insulated iron wire4 ,illustration3 ,,figs4 #ib and #ic4 ,illustration3 ,,fig4 #id4 ,the device is provided with suitable binding posts1 to which the ends of the coils are led4 ,the diametrically opposite coils ,b ,b and ,b' ,b' are connected1 respectively1 in series1 and the four terminals are connected to the binding posts4 ,the induced coils are connected together in any desired manner4 ,for example1 as shown in ,fig4 #id1 ,c ,c may be connected in multiple arc when a quantity current is desired--as for running a group of incandescent lamps--while ,c' ,c' may be independently connected in series in a circuit including arc lamps or the like4 ,the generator in this system will be adapted to the converter in the manner illustrated4 ,for example1 in the present case there are employed a pair of ordinary permanent or electro-magnets1 ,e ,e1 between which is mounted a cylindrical armature on a shaft1 ,f1 and wound with two coils1 ,g ,g'4 ,the terminals of these coils are connected1 respectively1 to four insulated contact or collecting rings1 ,h ,h ,h' ,h'1 and the four line circuit wires ,l connect the brushes ,k1 bearing on these rings1 to the converter in the order shown4 ,noting the results of this combination1 it will be observed that at a given point of time the coil ,g is in its neutral position and is generating little or no current1 while the other coil1 ,g'1 is in a position where it exerts its maximum effect4 ,assuming coil ,g to be connected in circuit with coils ,b ,b of the converter1 and coil ,g' with coils ,b' ,b'1 it is evident that the poles of the ring ,a will be determined by coils ,b' ,b' alone2 but as the armature of the generator revolves1 coil ,g develops more current and coil ,g' less1 until ,g reaches its maximum and ,g' its neutral position4 ,the obvious result will be to shift the poles of the ring ,a through one-quarter of its periphery4 ,the movement of the coils through the next quarter of a turn--during which coil ,g' enters a field of opposite polarity and generates a current of opposite direction and increasing strength1 while coil ,g1 in passing from its maximum to its neutral position generates a current of decreasing strength and same direction as before--causes a further shifting of the poles through the second quarter of the ring4 ,the second half-revolution will obviously be a repetition of the same action4 ,by the shifting of the poles of the ring ,a1 a powerful dynamic inductive effect on the coils ,c ,c' is produced4 ,besides the currents generated in the secondary coils by dynamo-magnetic induction1 other currents will be set up in the same coils in consequence of many variations in the intensity of the poles in the ring ,a4 ,this should be avoided by maintaining the intensity of the poles constant1 to accomplish which care should be taken in designing and proportioning the generator and in distributing the coils in the ring ,a1 and balancing their effect4 ,when this is done1 the currents are produced by dynamo-magnetic induction only1 the same result being obtained as though the poles were shifted by a commutator with an infinite number of segments4 ,the modifications which are applicable to other forms of converter are in many respects applicable to this1 such as those pertaining more particularly to the form of the core1 the relative lengths and resistances of the primary and secondary coils1 and the arrangements for running or operating the same4 ,,chapter ,,xxiv4 ,a ,,constant ,,current ,,transformer ,,with ,,magnetic ,,shield ,,between ,,coils ,,of ,,primary ,,and ,,secondary4 ,mr4 ,tesla has applied his principle of magnetic shielding of parts to the construction also of transformers1 the shield being interposed between the primary and secondary coils4 ,in transformers of the ordinary type it will be found that the wave of electromotive force of the secondary very nearly coincides with that of the primary1 being1 however1 in opposite sign4 ,at the same time the currents1 both primary and secondary1 lag behind their respective electromotive forces2 but as this lag is practically or nearly the same in the case of each it follows that the maximum and minimum of the primary and secondary currents will nearly coincide1 but differ in sign or direction1 provided the secondary be not loaded or if it contain devices having the property of self-induction4 ,on the other hand1 the lag of the primary behind the impressed electromotive force may be diminished by loading the secondary with a non-inductive or dead resistance--such as incandescent lamps--whereby the time interval between the maximum or minimum periods of the primary and secondary currents is increased4 ,this time interval1 however1 is limited1 and the results obtained by phase difference in the operation of such devices as the ,tesla alternating current motors can only be approximately realized by such means of producing or securing this difference1 as above indicated1 for it is desirable in such cases that there should exist between the primary and secondary currents1 or those which1 however produced1 pass through the two circuits of the motor1 a difference of phase of ninety degrees2 or1 in other words1 the current in one circuit should be a maximum when that in the other circuit is a minimum4 ,to attain to this condition more perfectly1 an increased retardation of the secondary current is secured in the following manner3 ,instead of bringing the primary and secondary coils or circuits of a transformer into the closest possible relations1 as has hitherto been done1 ,mr4 ,tesla protects in a measure the secondary from the inductive action or effect of the primary by surrounding either the primary or the secondary with a comparatively thin magnetic shield or screen4 ,under these modified conditions1 as long as the primary current has a small value1 the shield protects the secondary2 but as soon as the primary current has reached a certain strength1 which is arbitrarily determined1 the protecting magnetic shield becomes saturated and the inductive action upon the secondary begins4 ,it results1 therefore1 that the secondary current begins to flow at a certain fraction of a period later than it would without the interposed shield1 and since this retardation may be obtained without necessarily retarding the primary current also1 an additional lag is secured1 and the time interval between the maximum or minimum periods of the primary and secondary currents is increased4 ,such a transformer may1 by properly proportioning its several elements and determining the proper relations between the primary and secondary windings1 the thickness of the magnetic shield1 and other conditions1 be constructed to yield a constant current at all loads4 ,illustration3 ,,fig4 #ie4 ,fig4 #ie is a cross-section of a transformer embodying this improvement4 ,fig4 #if is a similar view of a modified form of transformer1 showing diagrammatically the manner of using the same4 ,a ,a is the main core of the transformer1 composed of a ring of soft annealed and insulated or oxidized iron wire4 ,upon this core is wound the secondary circuit or coil ,b ,b4 ,this latter is then covered with a layer or layers of annealed and insulated iron wires ,c ,c1 wound in a direction at right angles to the secondary coil4 ,over the whole is then wound the primary coil or wire ,d ,d4 ,from the nature of this construction it will be obvious that as long as the shield formed by the wires ,c is below magnetic saturation the secondary coil or circuit is effectually protected or shielded from the inductive influence of the primary1 although on open circuit it may exhibit some electromotive force4 ,when the strength of the primary reaches a certain value1 the shield ,c1 becoming saturated1 ceases to protect the secondary from inductive action1 and current is in consequence developed therein4 ,for similar reasons1 when the primary current weakens1 the weakening of the secondary is retarded to the same or approximately the same extent4 ,illustration3 ,,fig4 #if4 ,the specific construction of the transformer is largely immaterial4 ,in ,fig4 #if1 for example1 the core ,a is built up of thin insulated iron plates or discs4 ,the primary circuit ,d is wound next the core ,a4 ,over this is applied the shield ,c1 which in this case is made up of thin strips or plates of iron properly insulated and surrounding the primary1 forming a closed magnetic circuit4 ,the secondary ,b is wound over the shield ,c4 ,in ,fig4 #if1 also1 ,e is a source of alternating or rapidly changing currents4 ,the primary of the transformer is connected with the circuit of the generator4 ,f is a two-circuit alternating current motor1 one of the circuits being connected with the main circuit from the source ,e1 and the other being supplied with currents from the secondary of the transformer4 ,,part ,,ii4 ,,the ,,tesla ,,effects ,,with ,,high ,,frequency ,,and ,,high ,,potential ,,currents4 ,,chapter ,,xxv4 ,,introduction4--,,the ,,scope ,,of ,,the ,,tesla ,,lectures4 ,before proceeding to study the three ,tesla lectures here presented1 the reader may find it of some assistance to have his attention directed to the main points of interest and significance therein4 ,the first of these lectures was delivered in ,new ,york1 at ,columbia ,college1 before the ,american ,institute of ,electrical ,engineers1 ,may #bj1 #ahia4 ,the urgent desire expressed immediately from all parts of ,europe for an opportunity to witness the brilliant and unusual experiments with which the lecture was accompanied1 induced ,mr4 ,tesla to go to ,england early in #ahib1 when he appeared before the ,institution of ,electrical ,engineers1 and a day later1 by special request1 before the ,royal ,institution4 ,his reception was of the most enthusiastic and flattering nature on both occasions4 ,he then went1 by invitation1 to ,france1 and repeated his novel demonstrations before the ,societe ,internationale des ,electriciens1 and the ,societe ,francaise de ,physique4 ,mr4 ,tesla returned to ,america in the fall of #ahib1 and in ,february1 #ahic1 delivered his third lecture before the ,franklin ,institute of ,philadelphia1 in fulfilment of a long standing promise to ,prof4 ,houston4 ,the following week1 at the request of ,president ,james ,i4 ,ayer1 of the ,national ,electric ,light ,association1 the same lecture was re-delivered in ,st4 ,louis4 ,it had been intended to limit the invitations to members1 but the appeals from residents in the city were so numerous and pressing that it became necessary to secure a very large hall4 ,hence it came about that the lecture was listened to by an audience of over #e1jjj people1 and was in some parts of a more popular nature than either of its predecessors4 ,despite this concession to the need of the hour and occasion1 ,mr4 ,tesla did not hesitate to show many new and brilliant experiments1 and to advance the frontier of discovery far beyond any point he had theretofore marked publicly4 ,we may now proceed to a running review of the lectures themselves4 ,the ground covered by them is so vast that only the leading ideas and experiments can here be touched upon2 besides1 it is preferable that the lectures should be carefully gone over for their own sake1 it being more than likely that each student will discover a new beauty or stimulus in them4 ,taking up the course of reasoning followed by ,mr4 ,tesla in his first lecture1 it will be noted that he started out with the recognition of the fact1 which he has now experimentally demonstrated1 that for the production of light waves1 primarily1 electrostatic effects must be brought into play1 and continued study has led him to the opinion that all electrical and magnetic effects may be referred to electrostatic molecular forces4 ,this opinion finds a singular confirmation in one of the most striking experiments which he describes1 namely1 the production of a veritable flame by the agitation of electrostatically charged molecules4 ,it is of the highest interest to observe that this result points out a way of obtaining a flame which consumes no material and in which no chemical action whatever takes place4 ,it also throws a light on the nature of the ordinary flame1 which ,mr4 ,tesla believes to be due to electrostatic molecular actions1 which1 if true1 would lead directly to the idea that even chemical affinities might be electrostatic in their nature and that1 as has already been suggested1 molecular forces in general may be referable to one and the same cause4 ,this singular phenomenon accounts in a plausible manner for the unexplained fact that buildings are frequently set on fire during thunder storms without having been at all struck by lightning4 ,it may also explain the total disappearance of ships at sea4 ,one of the striking proofs of the correctness of the ideas advanced by ,mr4 ,tesla is the fact that1 notwithstanding the employment of the most powerful electromagnetic inductive effects1 but feeble luminosity is obtainable1 and this only in close proximity to the source of disturbance2 whereas1 when the electrostatic effects are intensified1 the same initial energy suffices to excite luminosity at considerable distances from the source4 ,that there are only electrostatic effects active seems to be clearly proved by ,mr4 ,tesla's experiments with an induction coil operated with alternating currents of very high frequency4 ,he shows how tubes may be made to glow brilliantly at considerable distances from any object when placed in a powerful1 rapidly alternating1 electrostatic field1 and he describes many interesting phenomena observed in such a field4 ,his experiments open up the possibility of lighting an apartment by simply creating in it such an electrostatic field1 and this1 in a certain way1 would appear to be the ideal method of lighting a room1 as it would allow the illuminating device to be freely moved about4 ,the power with which these exhausted tubes1 devoid of any electrodes1 light up is certainly remarkable4 ,that the principle propounded by ,mr4 ,tesla is a broad one is evident from the many ways in which it may be practically applied4 ,we need only refer to the variety of the devices shown or described1 all of which are novel in character and will1 without doubt1 lead to further important results at the hands of ,mr4 ,tesla and other investigators4 ,the experiment1 for instance1 of lighting up a single filament or block of refractory material with a single wire1 is in itself sufficient to give ,mr4 ,tesla's work the stamp of originality1 and the numerous other experiments and effects which may be varied at will1 are equally new and interesting4 ,thus1 the incandescent filament spinning in an unexhausted globe1 the well-known ,crookes experiment on open circuit1 and the many others suggested1 will not fail to interest the reader4 ,mr4 ,tesla has made an exhaustive study of the various forms of the discharge presented by an induction coil when operated with these rapidly alternating currents1 starting from the thread-like discharge and passing through various stages to the true electric flame4 ,a point of great importance in the introduction of high tension alternating current which ,mr4 ,tesla brings out is the necessity of carefully avoiding all gaseous matter in the high tension apparatus4 ,he shows that1 at least with very rapidly alternating currents of high potential1 the discharge may work through almost any practicable thickness of the best insulators1 if air is present4 ,in such cases the air included within the apparatus is violently agitated and by molecular bombardment the parts may be so greatly heated as to cause a rupture of the insulation4 ,the practical outcome of this is1 that1 whereas with steady currents1 any kind of insulation may be used1 with rapidly alternating currents oils will probably be the best to employ1 a fact which has been observed1 but not until now satisfactorily explained4 ,the recognition of the above fact is of special importance in the construction of the costly commercial induction coils which are often rendered useless in an unaccountable manner4 ,the truth of these views of ,mr4 ,tesla is made evident by the interesting experiments illustrative of the behavior of the air between charged surfaces1 the luminous streams formed by the charged molecules appearing even when great thicknesses of the best insulators are interposed between the charged surfaces4 ,these luminous streams afford in themselves a very interesting study for the experimenter4 ,with these rapidly alternating currents they become far more powerful and produce beautiful light effects when they issue from a wire1 pinwheel or other object attached to a terminal of the coil2 and it is interesting to note that they issue from a ball almost as freely as from a point1 when the frequency is very high4 ,from these experiments we also obtain a better idea of the importance of taking into account the capacity and self-induction in the apparatus employed and the possibilities offered by the use of condensers in conjunction with alternate currents1 the employment of currents of high frequency1 among other things1 making it possible to reduce the condenser to practicable dimensions4 ,another point of interest and practical bearing is the fact1 proved by ,mr4 ,tesla1 that for alternate currents1 especially those of high frequency1 insulators are required possessing a small specific inductive capacity1 which at the same time have a high insulating power4 ,mr4 ,tesla also makes interesting and valuable suggestion in regard to the economical utilization of iron in machines and transformers4 ,he shows how1 by maintaining by continuous magnetization a flow of lines through the iron1 the latter may be kept near its maximum permeability and a higher output and economy may be secured in such apparatus4 ,this principle may prove of considerable commercial importance in the development of alternating systems4 ,mr4 ,tesla's suggestion that the same result can be secured by heating the iron by hysteresis and eddy currents1 and increasing the permeability in this manner1 while it may appear less practical1 nevertheless opens another direction for investigation and improvement4 ,the demonstration of the fact that with alternating currents of high frequency1 sufficient energy may be transmitted under practicable conditions through the glass of an incandescent lamp by electrostatic or electromagnetic induction may lead to a departure in the construction of such devices4 ,another important experimental result achieved is the operation of lamps1 and even motors1 with the discharges of condensers1 this method affording a means of converting direct or alternating currents4 ,in this connection ,mr4 ,tesla advocates the perfecting of apparatus capable of generating electricity of high tension from heat energy1 believing this to be a better way of obtaining electrical energy for practical purposes1 particularly for the production of light4 ,while many were probably prepared to encounter curious phenomena of impedance in the use of a condenser discharged disruptively1 the experiments shown were extremely interesting on account of their paradoxical character4 ,the burning of an incandescent lamp at any candle power when connected across a heavy metal bar1 the existence of nodes on the bar and the possibility of exploring the bar by means of an ordinary ,cardew voltmeter1 are all peculiar developments1 but perhaps the most interesting observation is the phenomenon of impedance observed in the lamp with a straight filament1 which remains dark while the bulb glows4 ,mr4 ,tesla's manner of operating an induction coil by means of the disruptive discharge1 and thus obtaining enormous differences of potential from comparatively small and inexpensive coils1 will be appreciated by experimenters and will find valuable application in laboratories4 ,indeed1 his many suggestions and hints in regard to the construction and use of apparatus in these investigations will be highly valued and will aid materially in future research4 ,the ,london lecture was delivered twice4 ,in its first form1 before the ,institution of ,electrical ,engineers1 it was in some respects an amplification of several points not specially enlarged upon in the ,new ,york lecture1 but brought forward many additional discoveries and new investigations4 ,its repetition1 in another form1 at the ,royal ,institution1 was due to ,prof4 ,dewar1 who with ,lord ,rayleigh1 manifested a most lively interest in ,mr4 ,tesla's work1 and whose kindness illustrated once more the strong ,english love of scientific truth and appreciation of its votaries4 ,as an indefatigable experimenter1 ,mr4 ,tesla was certainly nowhere more at home than in the haunts of ,faraday1 and as the guest of ,faraday's successor4 ,this ,royal ,institution lecture summed up the leading points of ,mr4 ,tesla's work1 in the high potential1 high frequency field1 and we may here avail ourselves of so valuable a summarization1 in a simple form1 of a subject by no means easy of comprehension until it has been thoroughly studied4 ,in these ,london lectures1 among the many notable points made was first1 the difficulty of constructing the alternators to obtain the very high frequencies needed4 ,to obtain the high frequencies it was necessary to provide several hundred polar projections1 which were necessarily small and offered many drawbacks1 and this the more as exceedingly high peripheral speeds had to be resorted to4 ,in some of the first machines both armature and field had polar projections4 ,these machines produced a curious noise1 especially when the armature was started from the state of rest1 the field being charged4 ,the most efficient machine was found to be one with a drum armature1 the iron body of which consisted of very thin wire annealed with special care4 ,it was1 of course1 desirable to avoid the employment of iron in the armature1 and several machines of this kind1 with moving or stationary conductors were constructed1 but the results obtained were not quite satisfactory1 on account of the great mechanical and other difficulties encountered4 ,the study of the properties of the high frequency currents obtained from these machines is very interesting1 as nearly every experiment discloses something new4 ,two coils traversed by such a current attract or repel each other with a force which1 owing to the imperfection of our sense of touch1 seems continuous4 ,an interesting observation1 already noted under another form1 is that a piece of iron1 surrounded by a coil through which the current is passing appears to be continuously magnetized4 ,this apparent continuity might be ascribed to the deficiency of the sense of touch1 but there is evidence that in currents of such high frequencies one of the impulses preponderates over the other4 ,as might be expected1 conductors traversed by such currents are rapidly heated1 owing to the increase of the resistance1 and the heating effects are relatively much greater in the iron4 ,the hysteresis losses in iron are so great that an iron core1 even if finely subdivided1 is heated in an incredibly short time4 ,to give an idea of this1 an ordinary iron wire #a_/af inch in diameter inserted within a coil having #bej turns1 with a current estimated to be five amperes passing through the coil1 becomes within two seconds' time so hot as to scorch wood4 ,beyond a certain frequency1 an iron core1 no matter how finely subdivided1 exercises a dampening effect1 and it was easy to find a point at which the impedance of a coil was not affected by the presence of a core consisting of a bundle of very thin well annealed and varnished iron wires4 ,experiments with a telephone1 a conductor in a strong magnetic field1 or with a condenser or arc1 seem to afford certain proof that sounds far above the usually accepted limit of hearing would be perceived if produced with sufficient power4 ,the arc produced by these currents possesses several interesting features4 ,usually it emits a note the pitch of which corresponds to twice the frequency of the current1 but if the frequency be sufficiently high it becomes noiseless1 the limit of audition being determined principally by the linear dimensions of the arc4 ,a curious feature of the arc is its persistency1 which is due partly to the inability of the gaseous column to cool and increase considerably in resistance1 as is the case with low frequencies1 and partly to the tendency of such a high frequency machine to maintain a constant current4 ,in connection with these machines the condenser affords a particularly interesting study4 ,striking effects are produced by proper adjustments of capacity and self-induction4 ,it is easy to raise the electromotive force of the machine to many times the original value by simply adjusting the capacity of a condenser connected in the induced circuit4 ,if the condenser be at some distance from the machine1 the difference of potential on the terminals of the latter may be only a small fraction of that on the condenser4 ,but the most interesting experiences are gained when the tension of the currents from the machine is raised by means of an induction coil4 ,in consequence of the enormous rate of change obtainable in the primary current1 much higher potential differences are obtained than with coils operated in the usual ways1 and1 owing to the high frequency1 the secondary discharge possesses many striking peculiarities4 ,both the electrodes behave generally alike1 though it appears from some observations that one current impulse preponderates over the other1 as before mentioned4 ,the physiological effects of the high tension discharge are found to be so small that the shock of the coil can be supported without any inconvenience1 except perhaps a small burn produced by the discharge upon approaching the hand to one of the terminals4 ,the decidedly smaller physiological effects of these currents are thought to be due either to a different distribution through the body or to the tissues acting as condensers4 ,but in the case of an induction coil with a great many turns the harmlessness is principally due to the fact that but little energy is available in the external circuit when the same is closed through the experimenter's body1 on account of the great impedance of the coil4 ,in varying the frequency and strength of the currents through the primary of the coil1 the character of the secondary discharge is greatly varied1 and no less than five distinct forms are observed3--,a weak1 sensitive thread discharge1 a powerful flaming discharge1 and three forms of brush or streaming discharges4 ,each of these possesses certain noteworthy features1 but the most interesting to study are the latter4 ,under certain conditions the streams1 which are presumably due to the violent agitation of the air molecules1 issue freely from all points of the coil1 even through a thick insulation4 ,if there is the smallest air space between the primary and secondary1 they will form there and surely injure the coil by slowly warming the insulation4 ,as they form even with ordinary frequencies when the potential is excessive1 the air-space must be most carefully avoided4 ,these high frequency streamers differ in aspect and properties from those produced by a static machine4 ,the wind produced by them is small and should altogether cease if still considerably higher frequencies could be obtained4 ,a peculiarity is that they issue as freely from surfaces as from points4 ,owing to this1 a metallic vane1 mounted in one of the terminals of the coil so as to rotate freely1 and having one of its sides covered with insulation1 is spun rapidly around4 ,such a vane would not rotate with a steady potential1 but with a high frequency coil it will spin1 even if it be entirely covered with insulation1 provided the insulation on one side be either thicker or of a higher specific inductive capacity4 ,a ,crookes electric radiometer is also spun around when connected to one of the terminals of the coil1 but only at very high exhaustion or at ordinary pressures4 ,there is still another and more striking peculiarity of such a high frequency streamer1 namely1 it is hot4 ,the heat is easily perceptible with frequencies of about #aj1jjj1 even if the potential is not excessively high4 ,the heating effect is1 of course1 due to the molecular impacts and collisions4 ,could the frequency and potential be pushed far enough1 then a brush could be produced resembling in every particular a flame and giving light and heat1 yet without a chemical process taking place4 ,the hot brush1 when properly produced1 resembles a jet of burning gas escaping under great pressure1 and it emits an extraordinary strong smell of ozone4 ,the great ozonizing action is ascribed to the fact that the agitation of the molecules of the air is more violent in such a brush than in the ordinary streamer of a static machine4 ,but the most powerful brush discharges were produced by employing currents of much higher frequencies than it was possible to obtain by means of the alternators4 ,these currents were obtained by disruptively discharging a condenser and setting up oscillations4 ,in this manner currents of a frequency of several hundred thousand were obtained4 ,currents of this kind1 ,mr4 ,tesla pointed out1 produce striking effects4 ,at these frequencies1 the impedance of a copper bar is so great that a potential difference of several hundred volts can be maintained between two points of a short and thick bar1 and it is possible to keep an ordinary incandescent lamp burning at full candle power by attaching the terminals of the lamp to two points of the bar no more than a few inches apart4 ,when the frequency is extremely high1 nodes are found to exist on such a bar1 and it is easy to locate them by means of a lamp4 ,by converting the high tension discharges of a low frequency coil in this manner1 it was found practicable to keep a few lamps burning on the ordinary circuit in the laboratory1 and by bringing the undulation to a low pitch1 it was possible to operate small motors4 ,this plan likewise allows of converting high tension discharges of one direction into low tension unidirectional currents1 by adjusting the circuit so that there are no oscillations4 ,in passing the oscillating discharges through the primary of a specially constructed coil1 it is easy to obtain enormous potential differences with only few turns of the secondary4 ,great difficulties were at first experienced in producing a successful coil on this plan4 ,it was found necessary to keep all air1 or gaseous matter in general1 away from the charged surfaces1 and oil immersion was resorted to4 ,the wires used were heavily covered with gutta-percha and wound in oil1 or the air was pumped out by means of a ,sprengel pump4 ,the general arrangement was the following3--,an ordinary induction coil1 operated from a low frequency alternator1 was used to charge ,leyden jars4 ,the jars were made to discharge over a single or multiple gap through the primary of the second coil4 ,to insure the action of the gap1 the arc was blown out by a magnet or air blast4 ,to adjust the potential in the secondary a small oil condenser was used1 or polished brass spheres of different sizes were screwed on the terminals and their distance adjusted4 ,when the conditions were carefully determined to suit each experiment1 magnificent effects were obtained4 ,two wires1 stretched through the room1 each being connected to one of the terminals of the coil1 emitted streams so powerful that the light from them allowed distinguishing the objects in the room2 the wires became luminous even though covered with thick and most excellent insulation4 ,when two straight wires1 or two concentric circles of wire1 are connected to the terminals1 and set at the proper distance1 a uniform luminous sheet is produced between them4 ,it was possible in this way to cover an area of more than one meter square completely with the streams4 ,by attaching to one terminal a large circle of wire and to the other terminal a small sphere1 the streams are focused upon the sphere1 produce a strongly lighted spot upon the same1 and present the appearance of a luminous cone4 ,a very thin wire glued upon a plate of hard rubber of great thickness1 on the opposite side of which is fastened a tinfoil coating1 is rendered intensely luminous when the coating is connected to the other terminal of the coil4 ,such an experiment can be performed also with low frequency currents1 but much less satisfactorily4 ,when the terminals of such a coil1 even of a very small one1 are separated by a rubber or glass plate1 the discharge spreads over the plate in the form of streams1 threads or brilliant sparks1 and affords a magnificent display1 which cannot be equaled by the largest coil operated in the usual ways4 ,by a simple adjustment it is possible to produce with the coil a succession of brilliant sparks1 exactly as with a ,holtz machine4 ,under certain conditions1 when the frequency of the oscillation is very great1 white1 phantom-like streams are seen to break forth from the terminals of the coil4 ,the chief interesting feature about them is1 that they stream freely against the outstretched hand or other conducting object without producing any sensation1 and the hand may be approached very near to the terminal without a spark being induced to jump4 ,this is due presumably to the fact that a considerable portion of the energy is carried away or dissipated in the streamers1 and the difference of potential between the terminal and the hand is diminished4 ,it is found in such experiments that the frequency of the vibration and the quickness of succession of the sparks between the knobs affect to a marked degree the appearance of the streams4 ,when the frequency is very low1 the air gives way in more or less the same manner as by a steady difference of potential1 and the streams consist of distinct threads1 generally mingled with thin sparks1 which probably correspond to the successive discharges occurring between the knobs4 ,but when the frequency is very high1 and the arc of the discharge produces a sound which is loud and smooth 7which indicates both that oscillation takes place and that the sparks succeed each other with great rapidity71 then the luminous streams formed are perfectly uniform4 ,they are generally of a purplish hue1 but when the molecular vibration is increased by raising the potential1 they assume a white color4 ,the luminous intensity of the streams increases rapidly when the potential is increased2 and with frequencies of only a few hundred thousand1 could the coil be made to withstand a sufficiently high potential difference1 there is no doubt that the space around a wire could be made to emit a strong light1 merely by the agitation of the molecules of the air at ordinary pressure4 ,such discharges of very high frequency which render luminous the air at ordinary pressure we have very likely occasion to witness in the aurora borealis4 ,from many of these experiments it seems reasonable to infer that sudden cosmic disturbances1 such as eruptions on the sun1 set the electrostatic charge of the earth in an extremely rapid vibration1 and produce the glow by the violent agitation of the air in the upper and even in the lower strata4 ,it is thought that if the frequency were low1 or even more so if the charge were not at all vibrating1 the lower dense strata would break down as in a lightning discharge4 ,indications of such breaking down have been repeatedly observed1 but they can be attributed to the fundamental disturbances1 which are few in number1 for the superimposed vibration would be so rapid as not to allow a disruptive break4 ,the study of these discharge phenomena has led ,mr4 ,tesla to the recognition of some important facts4 ,it was found1 as already stated1 that gaseous matter must be most carefully excluded from any dielectric which is subjected to great1 rapidly changing electrostatic stresses4 ,since it is difficult to exclude the gas perfectly when solid insulators are used1 it is necessary to resort to liquid dielectrics4 ,when a solid dielectric is used1 it matters little how thick and how good it is2 if air be present1 streamers form1 which gradually heat the dielectric and impair its insulating power1 and the discharge finally breaks through4 ,under ordinary conditions the best insulators are those which possess the highest specific inductive capacity1 but such insulators are not the best to employ when working with these high frequency currents1 for in most cases the higher specific inductive capacity is rather a disadvantage4 ,the prime quality of the insulating medium for these currents is continuity4 ,for this reason principally it is necessary to employ liquid insulators1 such as oils4 ,if two metal plates1 connected to the terminals of the coil1 are immersed in oil and set a distance apart1 the coil may be kept working for any length of time without a break occurring1 or without the oil being warmed1 but if air bubbles are introduced1 they become luminous2 the air molecules1 by their impact against the oil1 heat it1 and after some time cause the insulation to give way4 ,if1 instead of the oil1 a solid plate of the best dielectric1 even several times thicker than the oil intervening between the metal plates1 is inserted between the latter1 the air having free access to the charged surfaces1 the dielectric invariably is warmed and breaks down4 ,the employment of oil is advisable or necessary even with low frequencies1 if the potentials are such that streamers form1 but only in such cases1 as is evident from the theory of the action4 ,if the potentials are so low that streamers do not form1 then it is even disadvantageous to employ oil1 for it may1 principally by confining the heat1 be the cause of the breaking down of the insulation4 ,the exclusion of gaseous matter is not only desirable on account of the safety of the apparatus1 but also on account of economy1 especially in a condenser1 in which considerable waste of power may occur merely owing to the presence of air1 if the electric density on the charged surfaces is great4 ,in the course of these investigations a phenomenon of special scientific interest was observed4 ,it may be ranked among the brush phenomena1 in fact it is a kind of brush which forms at1 or near1 a single terminal in high vacuum4 ,in a bulb with a conducting electrode1 even if the latter be of aluminum1 the brush has only a very short existence1 but it can be preserved for a considerable length of time in a bulb devoid of any conducting electrode4 ,to observe the phenomenon it is found best to employ a large spherical bulb having in its centre a small bulb supported on a tube sealed to the neck of the former4 ,the large bulb being exhausted to a high degree1 and the inside of the small bulb being connected to one of the terminals of the coil1 under certain conditions there appears a misty haze around the small bulb1 which1 after passing through some stages1 assumes the form of a brush1 generally at right angles to the tube supporting the small bulb4 ,when the brush assumes this form it may be brought to a state of extreme sensitiveness to electrostatic and magnetic influence4 ,the bulb hanging straight down1 and all objects being remote from it1 the approach of the observer within a few paces will cause the brush to fly to the opposite side1 and if he walks around the bulb it will always keep on the opposite side4 ,it may begin to spin around the terminal long before it reaches that sensitive stage4 ,when it begins to turn around1 principally1 but also before1 it is affected by a magnet1 and at a certain stage it is susceptible to magnetic influence to an astonishing degree4 ,a small permanent magnet1 with its poles at a distance of no more than two centimetres will affect it visibly at a distance of two metres1 slowing down or accelerating the rotation according to how it is held relatively to the brush4 ,when the bulb hangs with the globe down1 the rotation is always clockwise4 ,in the southern hemisphere it would occur in the opposite direction1 and on the 7magnetic7 equator the brush should not turn at all4 ,the rotation may be reversed by a magnet kept at some distance4 ,the brush rotates best1 seemingly1 when it is at right angles to the lines of force of the earth4 ,it very likely rotates1 when at its maximum speed1 in synchronism with the alternations1 say1 #aj1jjj times a second4 ,the rotation can be slowed down or accelerated by the approach or recession of the observer1 or any conducting body1 but it cannot be reversed by putting the bulb in any position4 ,very curious experiments may be performed with the brush when in its most sensitive state4 ,for instance1 the brush resting in one position1 the experimenter may1 by selecting a proper position1 approach the hand at a certain considerable distance to the bulb1 and he may cause the brush to pass off by merely stiffening the muscles of the arm1 the mere change of configuration of the arm and the consequent imperceptible displacement being sufficient to disturb the delicate balance4 ,when it begins to rotate slowly1 and the hands are held at a proper distance1 it is impossible to make even the slightest motion without producing a visible effect upon the brush4 ,a metal plate connected to the other terminal of the coil affects it at a great distance1 slowing down the rotation often to one turn a second4 ,mr4 ,tesla hopes that this phenomenon will prove a valuable aid in the investigation of the nature of the forces acting in an electrostatic or magnetic field4 ,if there is any motion which is measurable going on in the space1 such a brush would be apt to reveal it4 ,it is1 so to speak1 a beam of light1 frictionless1 devoid of inertia4 ,on account of its marvellous sensitiveness to electrostatic or magnetic disturbances it may be the means of sending signals through submarine cables with any speed1 and even of transmitting intelligence to a distance without wires4 ,in operating an induction coil with these rapidly alternating currents1 it is astonishing to note1 for the first time1 the great importance of the relation of capacity1 self-induction1 and frequency as bearing upon the general result4 ,the combined effect of these elements produces many curious effects4 ,for instance1 two metal plates are connected to the terminals and set at a small distance1 so that an arc is formed between them4 ,this arc prevents a strong current from flowing through the coil4 ,if the arc be interrupted by the interposition of a glass plate1 the capacity of the condenser obtained counteracts the self-induction1 and a stronger current is made to pass4 ,the effects of capacity are the most striking1 for in these experiments1 since the self-induction and frequency both are high1 the critical capacity is very small1 and need be but slightly varied to produce a very considerable change4 ,the experimenter brings his body in contact with the terminals of the secondary of the coil1 or attaches to one or both terminals insulated bodies of very small bulk1 such as exhausted bulbs1 and he produces a considerable rise or fall of potential on the secondary1 and greatly affects the flow of the current through the primary coil4 ,in many of the phenomena observed1 the presence of the air1 or1 generally speaking1 of a medium of a gaseous nature 7using this term not to imply specific properties1 but in contradistinction to homogeneity or perfect continuity7 plays an important part1 as it allows energy to be dissipated by molecular impact or bombardment4 ,the action is thus explained3--,when an insulated body connected to a terminal of the coil is suddenly charged to high potential1 it acts inductively upon the surrounding air1 or whatever gaseous medium there might be4 ,the molecules or atoms which are near it are1 of course1 more attracted1 and move through a greater distance than the further ones4 ,when the nearest molecules strike the body they are repelled1 and collisions occur at all distances within the inductive distance4 ,it is now clear that1 if the potential be steady1 but little loss of energy can be caused in this way1 for the molecules which are nearest to the body having had an additional charge imparted to them by contact1 are not attracted until they have parted1 if not with all1 at least with most of the additional charge1 which can be accomplished only after a great many collisions4 ,this is inferred from the fact that with a steady potential there is but little loss in dry air4 ,when the potential1 instead of being steady1 is alternating1 the conditions are entirely different4 ,in this case a rhythmical bombardment occurs1 no matter whether the molecules after coming in contact with the body lose the imparted charge or not1 and1 what is more1 if the charge is not lost1 the impacts are all the more violent4 ,still1 if the frequency of the impulses be very small1 the loss caused by the impacts and collisions would not be serious unless the potential was excessive4 ,but when extremely high frequencies and more or less high potentials are used1 the loss may be very great4 ,the total energy lost per unit of time is proportionate to the product of the number of impacts per second1 or the frequency and the energy lost in each impact4 ,but the energy of an impact must be proportionate to the square of the electric density of the body1 on the assumption that the charge imparted to the molecule is proportionate to that density4 ,it is concluded from this that the total energy lost must be proportionate to the product of the frequency and the square of the electric density2 but this law needs experimental confirmation4 ,assuming the preceding considerations to be true1 then1 by rapidly alternating the potential of a body immersed in an insulating gaseous medium1 any amount of energy may be dissipated into space4 ,most of that energy1 then1 is not dissipated in the form of long ether waves1 propagated to considerable distance1 as is thought most generally1 but is consumed in impact and collisional losses--that is1 heat vibrations--on the surface and in the vicinity of the body4 ,to reduce the dissipation it is necessary to work with a small electric density--the smaller1 the higher the frequency4 ,the behavior of a gaseous medium to such rapid alternations of potential makes it appear plausible that electrostatic disturbances of the earth1 produced by cosmic events1 may have great influence upon the meteorological conditions4 ,when such disturbances occur both the frequency of the vibrations of the charge and the potential are in all probability excessive1 and the energy converted into heat may be considerable4 ,since the density must be unevenly distributed1 either in consequence of the irregularity of the earth's surface1 or on account of the condition of the atmosphere in various places1 the effect produced would accordingly vary from place to place4 ,considerable variations in the temperature and pressure of the atmosphere may in this manner be caused at any point of the surface of the earth4 ,the variations may be gradual or very sudden1 according to the nature of the original disturbance1 and may produce rain and storms1 or locally modify the weather in any way4 ,from many experiences gathered in the course of these investigations it appears certain that in lightning discharges the air is an element of importance4 ,for instance1 during a storm a stream may form on a nail or pointed projection of a building4 ,if lightning strikes somewhere in the neighborhood1 the harmless static discharge may1 in consequence of the oscillations set up1 assume the character of a high-frequency streamer1 and the nail or projection may be brought to a high temperature by the violent impact of the air molecules4 ,thus1 it is thought1 a building may be set on fire without the lightning striking it4 ,in like manner small metallic objects may be fused and volatilized--as frequently occurs in lightning discharges--merely because they are surrounded by air4 ,were they immersed in a practically continuous medium1 such as oil1 they would probably be safe1 as the energy would have to spend itself elsewhere4 ,an instructive experience having a bearing on this subject is the following3--,a glass tube of an inch or so in diameter and several inches long is taken1 and a platinum wire sealed into it1 the wire running through the center of the tube from end to end4 ,the tube is exhausted to a moderate degree4 ,if a steady current is passed through the wire it is heated uniformly in all parts and the gas in the tube is of no consequence4 ,but if high frequency discharges are directed through the wire1 it is heated more on the ends than in the middle portion1 and if the frequency1 or rate of charge1 is high enough1 the wire might as well be cut in the middle as not1 for most of the heating on the ends is due to the rarefied gas4 ,here the gas might only act as a conductor of no impedance1 diverting the current from the wire as the impedance of the latter is enormously increased1 and merely heating the ends of the wire by reason of their resistance to the passage of the discharge4 ,but it is not at all necessary that the gas in the tube should be conducting2 it might be at an extremely low pressure1 still the ends of the wire would be heated2 however1 as is ascertained by experience1 only the two ends would in such case not be electrically connected through the gaseous medium4 ,now1 what with these frequencies and potentials occurs in an exhausted tube1 occurs in the lightning discharge at ordinary pressure4 ,from the facility with which any amount of energy may be carried off through a gas1 ,mr4 ,tesla infers that the best way to render harmless a lightning discharge is to afford it in some way a passage through a volume of gas4 ,the recognition of some of the above facts has a bearing upon far-reaching scientific investigations in which extremely high frequencies and potentials are used4 ,in such cases the air is an important factor to be considered4 ,so1 for instance1 if two wires are attached to the terminals of the coil1 and the streamers issue from them1 there is dissipation of energy in the form of heat and light1 and the wires behave like a condenser of larger capacity4 ,if the wires be immersed in oil1 the dissipation of energy is prevented1 or at least reduced1 and the apparent capacity is diminished4 ,the action of the air would seem to make it very difficult to tell1 from the measured or computed capacity of a condenser in which the air is acted upon1 its actual capacity or vibration period1 especially if the condenser is of very small surface and is charged to a very high potential4 ,as many important results are dependant upon the correctness of the estimation of the vibration period1 this subject demands the most careful scrutiny of investigators4 ,in ,leyden jars the loss due to the presence of air is comparatively small1 principally on account of the great surface of the coatings and the small external action1 but if there are streamers on the top1 the loss may be considerable1 and the period of vibration is affected4 ,in a resonator1 the density is small1 but the frequency is extreme1 and may introduce a considerable error4 ,it appears certain1 at any rate1 that the periods of vibration of a charged body in a gaseous and in a continuous medium1 such as oil1 are different1 on account of the action of the former1 as explained4 ,another fact recognized1 which is of some consequence1 is1 that in similar investigations the general considerations of static screening are not applicable when a gaseous medium is present4 ,this is evident from the following experiment3--,a short and wide glass tube is taken and covered with a substantial coating of bronze powder1 barely allowing the light to shine a little through4 ,the tube is highly exhausted and suspended on a metallic clasp from the end of a wire4 ,when the wire is connected with one of the terminals of the coil1 the gas inside of the tube is lighted in spite of the metal coating4 ,here the metal evidently does not screen the gas inside as it ought to1 even if it be very thin and poorly conducting4 ,yet1 in a condition of rest the metal coating1 however thin1 screens the inside perfectly4 ,one of the most interesting results arrived at in pursuing these experiments1 is the demonstration of the fact that a gaseous medium1 upon which vibration is impressed by rapid changes of electrostatic potential1 is rigid4 ,in illustration of this result an experiment made by ,mr4 ,tesla may by cited3--,a glass tube about one inch in diameter and three feet long1 with outside condenser coatings on the ends1 was exhausted to a certain point1 when1 the tube being suspended freely from a wire connecting the upper coating to one of the terminals of the coil1 the discharge appeared in the form of a luminous thread passing through the axis of the tube4 ,usually the thread was sharply defined in the upper part of the tube and lost itself in the lower part4 ,when a magnet or the finger was quickly passed near the upper part of the luminous thread1 it was brought out of position by magnetic or electrostatic influence1 and a transversal vibration like that of a suspended cord1 with one or more distinct nodes1 was set up1 which lasted for a few minutes and gradually died out4 ,by suspending from the lower condenser coating metal plates of different sizes1 the speed of the vibration was varied4 ,this vibration would seem to show beyond doubt that the thread possessed rigidity1 at least to transversal displacements4 ,many experiments were tried to demonstrate this property in air at ordinary pressure4 ,though no positive evidence has been obtained1 it is thought1 nevertheless1 that a high frequency brush or streamer1 if the frequency could be pushed far enough1 would be decidedly rigid4 ,a small sphere might then be moved within it quite freely1 but if thrown against it the sphere would rebound4 ,an ordinary flame cannot possess rigidity to a marked degree because the vibration is directionless2 but an electric arc1 it is believed1 must possess that property more or less4 ,a luminous band excited in a bulb by repeated discharges of a ,leyden jar must also possess rigidity1 and if deformed and suddenly released should vibrate4 ,from like considerations other conclusions of interest are reached4 ,the most probable medium filling the space is one consisting of independent carriers immersed in an insulating fluid4 ,if through this medium enormous electrostatic stresses are assumed to act1 which vary rapidly in intensity1 it would allow the motion of a body through it1 yet it would be rigid and elastic1 although the fluid itself might be devoid of these properties4 ,furthermore1 on the assumption that the independent carriers are of any configuration such that the fluid resistance to motion in one direction is greater than in another1 a stress of that nature would cause the carriers to arrange themselves in groups1 since they would turn to each other their sides of the greatest electric density1 in which position the fluid resistance to approach would be smaller than to receding4 ,if in a medium of the above characteristics a brush would be formed by a steady potential1 an exchange of the carriers would go on continually1 and there would be less carriers per unit of volume in the brush than in the space at some distance from the electrode1 this corresponding to rarefaction4 ,if the potential were rapidly changing1 the result would be very different2 the higher the frequency of the pulses1 the slower would be the exchange of the carriers2 finally1 the motion of translation through measurable space would cease1 and1 with a sufficiently high frequency and intensity of the stress1 the carriers would be drawn towards the electrode1 and compression would result4 ,an interesting feature of these high frequency currents is that they allow of operating all kinds of devices by connecting the device with only one leading wire to the electric source4 ,in fact1 under certain conditions it may be more economical to supply the electrical energy with one lead than with two4 ,an experiment of special interest shown by ,mr4 ,tesla1 is the running1 by the use of only one insulated line1 of a motor operating on the principle of the rotating magnetic field enunciated by ,mr4 ,tesla4 ,a simple form of such a motor is obtained by winding upon a laminated iron core a primary and close to it a secondary coil1 closing the ends of the latter and placing a freely movable metal disc within the influence of the moving field4 ,the secondary coil may1 however1 be omitted4 ,when one of the ends of the primary coil of the motor is connected to one of the terminals of the high frequency coil and the other end to an insulated metal plate1 which1 it should be stated1 is not absolutely necessary for the success of the experiment1 the disc is set in rotation4 ,experiments of this kind seem to bring it within possibility to operate a motor at any point of the earth's surface from a central source1 without any connection to the same except through the earth4 ,if1 by means of powerful machinery1 rapid variations of the earth's potential were produced1 a grounded wire reaching up to some height would be traversed by a current which could be increased by connecting the free end of the wire to a body of some size4 ,the current might be converted to low tension and used to operate a motor or other device4 ,the experiment1 which would be one of great scientific interest1 would probably best succeed on a ship at sea4 ,in this manner1 even if it were not possible to operate machinery1 intelligence might be transmitted quite certainly4 ,in the course of this experimental study special attention was devoted to the heating effects produced by these currents1 which are not only striking1 but open up the possibility of producing a more efficient illuminant4 ,it is sufficient to attach to the coil terminal a thin wire or filament1 to have the temperature of the latter perceptibly raised4 ,if the wire or filament be enclosed in a bulb1 the heating effect is increased by preventing the circulation of the air4 ,if the air in the bulb be strongly compressed1 the displacements are smaller1 the impacts less violent1 and the heating effect is diminished4 ,on the contrary1 if the air in the bulb be exhausted1 an inclosed lamp filament is brought to incandescence1 and any amount of light may thus be produced4 ,the heating of the inclosed lamp filament depends on so many things of a different nature1 that it is difficult to give a generally applicable rule under which the maximum heating occurs4 ,as regards the size of the bulb1 it is ascertained that at ordinary or only slightly differing atmospheric pressures1 when air is a good insulator1 the filament is heated more in a small bulb1 because of the better confinement of heat in this case4 ,at lower pressures1 when air becomes conducting1 the heating effect is greater in a large bulb1 but at excessively high degrees of exhaustion there seems to be1 beyond a certain and rather small size of the vessel1 no perceptible difference in the heating4 ,the shape of the vessel is also of some importance1 and it has been found of advantage for reasons of economy to employ a spherical bulb with the electrode mounted in its centre1 where the rebounding molecules collide4 ,it is desirable on account of economy that all the energy supplied to the bulb from the source should reach without loss the body to be heated4 ,the loss in conveying the energy from the source to the body may be reduced by employing thin wires heavily coated with insulation1 and by the use of electrostatic screens4 ,it is to be remarked1 that the screen cannot be connected to the ground as under ordinary conditions4 ,in the bulb itself a large portion of the energy supplied may be lost by molecular bombardment against the wire connecting the body to be heated with the source4 ,considerable improvement was effected by covering the glass stem containing the wire with a closely fitting conducting tube4 ,this tube is made to project a little above the glass1 and prevents the cracking of the latter near the heated body4 ,the effectiveness of the conducting tube is limited to very high degrees of exhaustion4 ,it diminishes the energy lost in bombardment for two reasons2 first1 the charge given up by the atoms spreads over a greater area1 and hence the electric density at any point is small1 and the atoms are repelled with less energy than if they would strike against a good insulator2 secondly1 as the tube is electrified by the atoms which first come in contact with it1 the progress of the following atoms against the tube is more or less checked by the repulsion which the electrified tube must exert upon the similarly electrified atoms4 ,this1 it is thought1 explains why the discharge through a bulb is established with much greater facility when an insulator1 than when a conductor1 is present4 ,during the investigations a great many bulbs of different construction1 with electrodes of different material1 were experimented upon1 and a number of observations of interest were made4 ,mr4 ,tesla has found that the deterioration of the electrode is the less1 the higher the frequency4 ,this was to be expected1 as then the heating is effected by many small impacts1 instead by fewer and more violent ones1 which quickly shatter the structure4 ,the deterioration is also smaller when the vibration is harmonic4 ,thus an electrode1 maintained at a certain degree of heat1 lasts much longer with currents obtained from an alternator1 than with those obtained by means of a disruptive discharge4 ,one of the most durable electrodes was obtained from strongly compressed carborundum1 which is a kind of carbon recently produced by ,mr4 ,e4 ,g4 ,acheson1 of ,monongahela ,city1 ,pa4 ,from experience1 it is inferred1 that to be most durable1 the electrode should be in the form of a sphere with a highly polished surface4 ,in some bulbs refractory bodies were mounted in a carbon cup and put under the molecular impact4 ,it was observed in such experiments that the carbon cup was heated at first1 until a higher temperature was reached2 then most of the bombardment was directed against the refractory body1 and the carbon was relieved4 ,in general1 when different bodies were mounted in the bulb1 the hardest fusible would be relieved1 and would remain at a considerably lower temperature4 ,this was necessitated by the fact that most of the energy supplied would find its way through the body which was more easily fused or evaporated4 ,curiously enough it appeared in some of the experiments made1 that a body was fused in a bulb under the molecular impact by evolution of less light than when fused by the application of heat in ordinary ways4 ,this may be ascribed to a loosening of the structure of the body under the violent impacts and changing stresses4 ,some experiments seem to indicate that under certain conditions a body1 conducting or nonconducting1 may1 when bombarded1 emit light1 which to all appearances is due to phosphorescence1 but may in reality be caused by the incandescence of an infinitesimal layer1 the mean temperature of the body being comparatively small4 ,such might be the case if each single rhythmical impact were capable of instantaneously exciting the retina1 and the rhythm were just high enough to cause a continuous impression in the eye4 ,according to this view1 a coil operated by disruptive discharge would be eminently adapted to produce such a result1 and it is found by experience that its power of exciting phosphorescence is extraordinarily great4 ,it is capable of exciting phosphorescence at comparatively low degrees of exhaustion1 and also projects shadows at pressures far greater than those at which the mean free path is comparable to the dimensions of the vessel4 ,the latter observation is of some importance1 inasmuch as it may modify the generally accepted views in regard to the radiant state phenomena4 ,a thought which early and naturally suggested itself to ,mr4 ,tesla1 was to utilize the great inductive effects of high frequency currents to produce light in a sealed glass vessel without the use of leading in wires4 ,accordingly1 many bulbs were constructed in which the energy necessary to maintain a button or filament at high incandescence1 was supplied through the glass by either electrostatic or electrodynamic induction4 ,it was easy to regulate the intensity of the light emitted by means of an externally applied condenser coating connected to an insulated plate1 or simply by means of a plate attached to the bulb which at the same time performed the function of a shade4 ,a subject of experiment1 which has been exhaustively treated in ,england by ,prof4 ,j4 ,j4 ,thomson1 has been followed up independently by ,mr4 ,tesla from the beginning of this study1 namely1 to excite by electrodynamic induction a luminous band in a closed tube or bulb4 ,in observing the behavior of gases1 and the luminous phenomena obtained1 the importance of the electrostatic effects was noted and it appeared desirable to produce enormous potential differences1 alternating with extreme rapidity4 ,experiments in this direction led to some of the most interesting results arrived at in the course of these investigations4 ,it was found that by rapid alternations of a high electrostatic potential1 exhausted tubes could be lighted at considerable distances from a conductor connected to a properly constructed coil1 and that it was practicable to establish with the coil an alternating electrostatic field1 acting through the whole room and lighting a tube wherever it was placed within the four walls4 ,phosphorescent bulbs may be excited in such a field1 and it is easy to regulate the effect by connecting to the bulb a small insulated metal plate4 ,it was likewise possible to maintain a filament or button mounted in a tube at bright incandescence1 and1 in one experiment1 a mica vane was spun by the incandescence of a platinum wire4 ,coming now to the lecture delivered in ,philadelphia and ,st4 ,louis1 it may be remarked that to the superficial reader1 ,mr4 ,tesla's introduction1 dealing with the importance of the eye1 might appear as a digression1 but the thoughtful reader will find therein much food for meditation and speculation4 ,throughout his discourse one can trace ,mr4 ,tesla's effort to present in a popular way thoughts and views on the electrical phenomena which have in recent years captivated the scientific world1 but of which the general public has even yet merely received an inkling4 ,mr4 ,tesla also dwells rather extensively on his well-known method of high-frequency conversion2 and the large amount of detail information will be gratefully received by students and experimenters in this virgin field4 ,the employment of apt analogies in explaining the fundamental principles involved makes it easy for all to gain a clear idea of their nature4 ,again1 the ease with which1 thanks to ,mr4 ,tesla's efforts1 these high-frequency currents may now be obtained from circuits carrying almost any kind of current1 cannot fail to result in an extensive broadening of this field of research1 which offers so many possibilities4 ,mr4 ,tesla1 true philosopher as he is1 does not hesitate to point out defects in some of his methods1 and indicates the lines which to him seem the most promising4 ,particular stress is laid by him upon the employment of a medium in which the discharge electrodes should be immersed in order that this method of conversion may be brought to the highest perfection4 ,he has evidently taken pains to give as much useful information as possible to those who wish to follow in his path1 as he shows in detail the circuit arrangements to be adopted in all ordinary cases met with in practice1 and although some of these methods were described by him two years before1 the additional information is still timely and welcome4 ,in his experiments he dwells first on some phenomena produced by electrostatic force1 which he considers in the light of modern theories to be the most important force in nature for us to investigate4 ,at the very outset he shows a strikingly novel experiment illustrating the effect of a rapidly varying electrostatic force in a gaseous medium1 by touching with one hand one of the terminals of a #bjj1jjj volt transformer and bringing the other hand to the opposite terminal4 ,the powerful streamers which issued from his hand and astonished his audiences formed a capital illustration of some of the views advanced1 and afforded ,mr4 ,tesla an opportunity of pointing out the true reasons why1 with these currents1 such an amount of energy can be passed through the body with impunity4 ,he then showed by experiment the difference between a steady and a rapidly varying force upon the dielectric4 ,this difference is most strikingly illustrated in the experiment in which a bulb attached to the end of a wire in connection with one of the terminals of the transformer is ruptured1 although all extraneous bodies are remote from the bulb4 ,he next illustrates how mechanical motions are produced by a varying electrostatic force acting through a gaseous medium4 ,the importance of the action of the air is particularly illustrated by an interesting experiment4 ,taking up another class of phenomena1 namely1 those of dynamic electricity1 ,mr4 ,tesla produced in a number of experiments a variety of effects by the employment of only a single wire with the evident intent of impressing upon his audience the idea that electric vibration or current can be transmitted with ease1 without any return circuit2 also how currents so transmitted can be converted and used for many practical purposes4 ,a number of experiments are then shown1 illustrating the effects of frequency1 self-induction and capacity2 then a number of ways of operating motive and other devices by the use of a single lead4 ,a number of novel impedance phenomena are also shown which cannot fail to arouse interest4 ,mr4 ,tesla next dwelt upon a subject which he thinks of great importance1 that is1 electrical resonance1 which he explained in a popular way4 ,he expressed his firm conviction that by observing proper conditions1 intelligence1 and possibly even power1 can be transmitted through the medium or through the earth2 and he considers this problem worthy of serious and immediate consideration4 ,coming now to the light phenomena in particular1 he illustrated the four distinct kinds of these phenomena in an original way1 which to many must have been a revelation4 ,mr4 ,tesla attributes these light effects to molecular or atomic impacts produced by a varying electrostatic stress in a gaseous medium4 ,he illustrated in a series of novel experiments the effect of the gas surrounding the conductor and shows beyond a doubt that with high frequency and high potential currents1 the surrounding gas is of paramount importance in the heating of the conductor4 ,he attributes the heating partially to a conduction current and partially to bombardment1 and demonstrates that in many cases the heating may be practically due to the bombardment alone4 ,he pointed out also that the skin effect is largely modified by the presence of the gas or of an atomic medium in general4 ,he showed also some interesting experiments in which the effect of convection is illustrated4 ,probably one of the most curious experiments in this connection is that in which a thin platinum wire stretched along the axis of an exhausted tube is brought to incandescence at certain points corresponding to the position of the striae1 while at others it remains dark4 ,this experiment throws an interesting light upon the nature of the striae and may lead to important revelations4 ,mr4 ,tesla also demonstrated the dissipation of energy through an atomic medium and dwelt upon the behavior of vacuous space in conveying heat1 and in this connection showed the curious behavior of an electrode stream1 from which he concludes that the molecules of a gas probably cannot be acted upon directly at measurable distances4 ,mr4 ,tesla summarized the chief results arrived at in pursuing his investigations in a manner which will serve as a valuable guide to all who may engage in this work4 ,perhaps most interest will centre on his general statements regarding the phenomena of phosphorescence1 the most important fact revealed in this direction being that when exciting a phosphorescent bulb a certain definite potential gives the most economical result4 ,the lectures will now be presented in the order of their date of delivery4 ,,chapter ,,xxvi4 ,,experiments ,,with ,,alternate ,,currents ,,of ,,very ,,high ,,frequency ,,and ,,their ,,application ,,to ,,methods ,,of ,,artificial ,,illumination4#a #a ,a lecture delivered before the ,american ,institute of ,electrical ,engineers1 at ,columbia ,college1 ,n4 ,y41 ,may #bj1 #ahia4 ,there is no subject more captivating1 more worthy of study1 than nature4 ,to understand this great mechanism1 to discover the forces which are active1 and the laws which govern them1 is the highest aim of the intellect of man4 ,nature has stored up in the universe infinite energy4 ,the eternal recipient and transmitter of this infinite energy is the ether4 ,the recognition of the existence of ether1 and of the functions it performs1 is one of the most important results of modern scientific research4 ,the mere abandoning of the idea of action at a distance1 the assumption of a medium pervading all space and connecting all gross matter1 has freed the minds of thinkers of an ever present doubt1 and1 by opening a new horizon--new and unforeseen possibilities--has given fresh interest to phenomena with which we are familiar of old4 ,it has been a great step towards the understanding of the forces of nature and their multifold manifestations to our senses4 ,it has been for the enlightened student of physics what the understanding of the mechanism of the firearm or of the steam engine is for the barbarian4 ,phenomena upon which we used to look as wonders baffling explanation1 we now see in a different light4 ,the spark of an induction coil1 the glow of an incandescent lamp1 the manifestations of the mechanical forces of currents and magnets are no longer beyond our grasp2 instead of the incomprehensible1 as before1 their observation suggests now in our minds a simple mechanism1 and although as to its precise nature all is still conjecture1 yet we know that the truth cannot be much longer hidden1 and instinctively we feel that the understanding is dawning upon us4 ,we still admire these beautiful phenomena1 these strange forces1 but we are helpless no longer2 we can in a certain measure explain them1 account for them1 and we are hopeful of finally succeeding in unraveling the mystery which surrounds them4 ,in how far we can understand the world around us is the ultimate thought of every student of nature4 ,the coarseness of our senses prevents us from recognizing the ulterior construction of matter1 and astronomy1 this grandest and most positive of natural sciences1 can only teach us something that happens1 as it were1 in our immediate neighborhood3 of the remoter portions of the boundless universe1 with its numberless stars and suns1 we know nothing4 ,but far beyond the limit of perception of our senses the spirit still can guide us1 and so we may hope that even these unknown worlds--infinitely small and great--may in a measure become known to us4 ,still1 even if this knowledge should reach us1 the searching mind will find a barrier1 perhaps forever unsurpassable1 to the true recognition of that which seems to be1 the mere appearance of which is the only and slender basis of all our philosophy4 ,of all the forms of nature's immeasurable1 all-pervading energy1 which ever and ever changing and moving1 like a soul animates the inert universe1 electricity and magnetism are perhaps the most fascinating4 ,the effects of gravitation1 of heat and light we observe daily1 and soon we get accustomed to them1 and soon they lose for us the character of the marvelous and wonderful2 but electricity and magnetism1 with their singular relationship1 with their seemingly dual character1 unique among the forces in nature1 with their phenomena of attractions1 repulsions and rotations1 strange manifestations of mysterious agents1 stimulate and excite the mind to thought and research4 ,what is electricity1 and what is magnetism8 ,these questions have been asked again and again4 ,the most able intellects have ceaselessly wrestled with the problem2 still the question has not as yet been fully answered4 ,but while we cannot even to-day state what these singular forces are1 we have made good headway towards the solution of the problem4 ,we are now confident that electric and magnetic phenomena are attributable to ether1 and we are perhaps justified in saying that the effects of static electricity are effects of ether under strain1 and those of dynamic electricity and electro-magnetism effects of ether in motion4 ,but this still leaves the question1 as to what electricity and magnetism are1 unanswered4 ,first1 we naturally inquire1 ,what is electricity1 and is there such a thing as electricity8 ,in interpreting electric phenomena1 we may speak of electricity or of an electric condition1 state or effect4 ,if we speak of electric effects we must distinguish two such effects1 opposite in character and neutralizing each other1 as observation shows that two such opposite effects exist4 ,this is unavoidable1 for in a medium of the properties of ether1 we cannot possibly exert a strain1 or produce a displacement or motion of any kind1 without causing in the surrounding medium an equivalent and opposite effect4 ,but if we speak of electricity1 meaning a thing1 we must1 ,i think1 abandon the idea of two electricities1 as the existence of two such things is highly improbable4 ,for how can we imagine that there should be two things1 equivalent in amount1 alike in their properties1 but of opposite character1 both clinging to matter1 both attracting and completely neutralizing each other8 ,such an assumption1 though suggested by many phenomena1 though most convenient for explaining them1 has little to commend it4 ,if there is such a thing as electricity1 there can be only one such thing1 and excess and want of that one thing1 possibly2 but more probably its condition determines the positive and negative character4 ,the old theory of ,franklin1 though falling short in some respects1 is1 from a certain point of view1 after all1 the most plausible one4 ,still1 in spite of this1 the theory of the two electricities is generally accepted1 as it apparently explains electric phenomena in a more satisfactory manner4 ,but a theory which better explains the facts is not necessarily true4 ,ingenious minds will invent theories to suit observation1 and almost every independent thinker has his own views on the subject4 ,it is not with the object of advancing an opinion1 but with the desire of acquainting you better with some of the results1 which ,i will describe1 to show you the reasoning ,i have followed1 the departures ,i have made--that ,i venture to express1 in a few words1 the views and convictions which have led me to these results4 ,i adhere to the idea that there is a thing which we have been in the habit of calling electricity4 ,the question is1 ,what is that thing8 or1 ,what1 of all things1 the existence of which we know1 have we the best reason to call electricity8 ,we know that it acts like an incompressible fluid2 that there must be a constant quantity of it in nature2 that it can be neither produced nor destroyed2 and1 what is more important1 the electro-magnetic theory of light and all facts observed teach us that electric and ether phenomena are identical4 ,the idea at once suggests itself1 therefore1 that electricity might be called ether4 ,in fact1 this view has in a certain sense been advanced by ,dr4 ,lodge4 ,his interesting work has been read by everyone and many have been convinced by his arguments4 ,his great ability and the interesting nature of the subject1 keep the reader spellbound2 but when the impressions fade1 one realizes that he has to deal only with ingenious explanations4 ,i must confess1 that ,i cannot believe in two electricities1 much less in a doubly-constituted ether4 ,the puzzling behavior of the ether as a solid to waves of light and heat1 and as a fluid to the motion of bodies through it1 is certainly explained in the most natural and satisfactory manner by assuming it to be in motion1 as ,sir ,william ,thomson has suggested2 but regardless of this1 there is nothing which would enable us to conclude with certainty that1 while a fluid is not capable of transmitting transverse vibrations of a few hundred or thousand per second1 it might not be capable of transmitting such vibrations when they range into hundreds of million millions per second4 ,nor can anyone prove that there are transverse ether waves emitted from an alternate current machine1 giving a small number of alternations per second2 to such slow disturbances1 the ether1 if at rest1 may behave as a true fluid4 ,returning to the subject1 and bearing in mind that the existence of two electricities is1 to say the least1 highly improbable1 we must remember1 that we have no evidence of electricity1 nor can we hope to get it1 unless gross matter is present4 ,electricity1 therefore1 cannot be called ether in the broad sense of the term2 but nothing would seem to stand in the way of calling electricity ether associated with matter1 or bound ether2 or1 in other words1 that the so-called static charge of the molecule is ether associated in some way with the molecule4 ,looking at it in that light1 we would be justified in saying1 that electricity is concerned in all molecular actions4 ,now1 precisely what the ether surrounding the molecules is1 wherein it differs from ether in general1 can only be conjectured4 ,it cannot differ in density1 ether being incompressible3 it must1 therefore1 be under some strain or in motion1 and the latter is the most probable4 ,to understand its functions1 it would be necessary to have an exact idea of the physical construction of matter1 of which1 of course1 we can only form a mental picture4 ,but of all the views on nature1 the one which assumes one matter and one force1 and a perfect uniformity throughout1 is the most scientific and most likely to be true4 ,an infinitesimal world1 with the molecules and their atoms spinning and moving in orbits1 in much the same manner as celestial bodies1 carrying with them and probably spinning with them ether1 or in other words1 carrying with them static charges1 seems to my mind the most probable view1 and one which1 in a plausible manner1 accounts for most of the phenomena observed4 ,the spinning of the molecules and their ether sets up the ether tensions or electrostatic strains2 the equalization of ether tensions sets up ether motions or electric currents1 and the orbital movements produce the effects of electro and permanent magnetism4 ,about fifteen years ago1 ,prof4 ,rowland demonstrated a most interesting and important fact1 namely1 that a static charge carried around produces the effects of an electric current4 ,leaving out of consideration the precise nature of the mechanism1 which produces the attraction and repulsion of currents1 and conceiving the electrostatically charged molecules in motion1 this experimental fact gives us a fair idea of magnetism4 ,we can conceive lines or tubes of force which physically exist1 being formed of rows of directed moving molecules2 we can see that these lines must be closed1 that they must tend to shorten and expand1 etc4 ,it likewise explains in a reasonable way1 the most puzzling phenomenon of all1 permanent magnetism1 and1 in general1 has all the beauties of the ,ampere theory without possessing the vital defect of the same1 namely1 the assumption of molecular currents4 ,without enlarging further upon the subject1 ,i would say1 that ,i look upon all electrostatic1 current and magnetic phenomena as being due to electrostatic molecular forces4 ,the preceding remarks ,i have deemed necessary to a full understanding of the subject as it presents itself to my mind4 ,of all these phenomena the most important to study are the current phenomena1 on account of the already extensive and ever-growing use of currents for industrial purposes4 ,it is now a century since the first practical source of current was produced1 and1 ever since1 the phenomena which accompany the flow of currents have been diligently studied1 and through the untiring efforts of scientific men the simple laws which govern them have been discovered4 ,but these laws are found to hold good only when the currents are of a steady character4 ,when the currents are rapidly varying in strength1 quite different phenomena1 often unexpected1 present themselves1 and quite different laws hold good1 which even now have not been determined as fully as is desirable1 though through the work1 principally1 of ,english scientists1 enough knowledge has been gained on the subject to enable us to treat simple cases which now present themselves in daily practice4 ,the phenomena which are peculiar to the changing character of the currents are greatly exalted when the rate of change is increased1 hence the study of these currents is considerably facilitated by the employment of properly constructed apparatus4 ,it was with this and other objects in view that ,i constructed alternate current machines capable of giving more than two million reversals of current per minute1 and to this circumstance it is principally due1 that ,i am able to bring to your attention some of the results thus far reached1 which ,i hope will prove to be a step in advance on account of their direct bearing upon one of the most important problems1 namely1 the production of a practical and efficient source of light4 ,the study of such rapidly alternating currents is very interesting4 ,nearly every experiment discloses something new4 ,many results may1 of course1 be predicted1 but many more are unforeseen4 ,the experimenter makes many interesting observations4 ,for instance1 we take a piece of iron and hold it against a magnet4 ,starting from low alternations and running up higher and higher we feel the impulses succeed each other faster and faster1 get weaker and weaker1 and finally disappear4 ,we then observe a continuous pull2 the pull1 of course1 is not continuous2 it only appears so to us2 our sense of touch is imperfect4 ,we may next establish an arc between the electrodes and observe1 as the alternations rise1 that the note which accompanies alternating arcs gets shriller and shriller1 gradually weakens1 and finally ceases4 ,the air vibrations1 of course1 continue1 but they are too weak to be perceived2 our sense of hearing fails us4 ,we observe the small physiological effects1 the rapid heating of the iron cores and conductors1 curious inductive effects1 interesting condenser phenomena1 and still more interesting light phenomena with a high tension induction coil4 ,all these experiments and observations would be of the greatest interest to the student1 but their description would lead me too far from the principal subject4 ,partly for this reason1 and partly on account of their vastly greater importance1 ,i will confine myself to the description of the light effects produced by these currents4 ,in the experiments to this end a high tension induction coil or equivalent apparatus for converting currents of comparatively low into currents of high tension is used4 ,if you will be sufficiently interested in the results ,i shall describe as to enter into an experimental study of this subject2 if you will be convinced of the truth of the arguments ,i shall advance--your aim will be to produce high frequencies and high potentials2 in other words1 powerful electrostatic effects4 ,you will then encounter many difficulties1 which1 if completely overcome1 would allow us to produce truly wonderful results4 ,first will be met the difficulty of obtaining the required frequencies by means of mechanical apparatus1 and1 if they be obtained otherwise1 obstacles of a different nature will present themselves4 ,next it will be found difficult to provide the requisite insulation without considerably increasing the size of the apparatus1 for the potentials required are high1 and1 owing to the rapidity of the alternations1 the insulation presents peculiar difficulties4 ,so1 for instance1 when a gas is present1 the discharge may work1 by the molecular bombardment of the gas and consequent heating1 through as much as an inch of the best solid insulating material1 such as glass1 hard rubber1 porcelain1 sealing wax1 etc42 in fact1 through any known insulating substance4 ,the chief requisite in the insulation of the apparatus is1 therefore1 the exclusion of any gaseous matter4 ,in general my experience tends to show that bodies which possess the highest specific inductive capacity1 such as glass1 afford a rather inferior insulation to others1 which1 while they are good insulators1 have a much smaller specific inductive capacity1 such as oils1 for instance1 the dielectric losses being no doubt greater in the former4 ,the difficulty of insulating1 of course1 only exists when the potentials are excessively high1 for with potentials such as a few thousand volts there is no particular difficulty encountered in conveying currents from a machine giving1 say1 #bj1jjj alternations per second1 to quite a distance4 ,this number of alternations1 however1 is by far too small for many purposes1 though quite sufficient for some practical applications4 ,this difficulty of insulating is fortunately not a vital drawback2 it affects mostly the size of the apparatus1 for1 when excessively high potentials would be used1 the light-giving devices would be located not far from the apparatus1 and often they would be quite close to it4 ,as the air-bombardment of the insulated wire is dependent on condenser action1 the loss may be reduced to a trifle by using excessively thin wires heavily insulated4 ,another difficulty will be encountered in the capacity and self-induction necessarily possessed by the coil4 ,if the coil be large1 that is1 if it contain a great length of wire1 it will be generally unsuited for excessively high frequencies2 if it be small1 it may be well adapted for such frequencies1 but the potential might then not be as high as desired4 ,a good insulator1 and preferably one possessing a small specific inductive capacity1 would afford a two-fold advantage4 ,first1 it would enable us to construct a very small coil capable of withstanding enormous differences of potential2 and secondly1 such a small coil1 by reason of its smaller capacity and self-induction1 would be capable of a quicker and more vigorous vibration4 ,the problem then of constructing a coil or induction apparatus of any kind possessing the requisite qualities ,i regard as one of no small importance1 and it has occupied me for a considerable time4 ,the investigator who desires to repeat the experiments which ,i will describe1 with an alternate current machine1 capable of supplying currents of the desired frequency1 and an induction coil1 will do well to take the primary coil out and mount the secondary in such a manner as to be able to look through the tube upon which the secondary is wound4 ,he will then be able to observe the streams which pass from the primary to the insulating tube1 and from their intensity he will know how far he can strain the coil4 ,without this precaution he is sure to injure the insulation4 ,this arrangement permits1 however1 an easy exchange of the primaries1 which is desirable in these experiments4 ,the selection of the type of machine best suited for the purpose must be left to the judgment of the experimenter4 ,there are here illustrated three distinct types of machines1 which1 besides others1 ,i have used in my experiments4 ,fig4 #ig represents the machine used in my experiments before this ,institute4 ,the field magnet consists of a ring of wrought iron with #chd pole projections4 ,the armature comprises a steel disc to which is fastened a thin1 carefully welded rim of wrought iron4 ,upon the rim are wound several layers of fine1 well annealed iron wire1 which1 when wound1 is passed through shellac4 ,the armature wires are wound around brass pins1 wrapped with silk thread4 ,the diameter of the armature wire in this type of machine should not be more than #a_/f of the thickness of the pole projections1 else the local action will be considerable4 ,illustration3 ,,fig4 #ig4 ,fig4 #ih represents a larger machine of a different type4 ,the field magnet of this machine consists of two like parts which either enclose an exciting coil1 or else are independently wound4 ,each part has #dhj pole projections1 the projections of one facing those of the other4 ,the armature consists of a wheel of hard bronze1 carrying the conductors which revolve between the projections of the field magnet4 ,to wind the armature conductors1 ,i have found it most convenient to proceed in the following manner4 ,i construct a ring of hard bronze of the required size4 ,this ring and the rim of the wheel are provided with the proper number of pins1 and both fastened upon a plate4 ,the armature conductors being wound1 the pins are cut off and the ends of the conductors fastened by two rings which screw to the bronze ring and the rim of the wheel1 respectively4 ,the whole may then be taken off and forms a solid structure4 ,the conductors in such a type of machine should consist of sheet copper1 the thickness of which1 of course1 depends on the thickness of the pole projections2 or else twisted thin wires should be employed4 ,fig4 #ii is a smaller machine1 in many respects similar to the former1 only here the armature conductors and the exciting coil are kept stationary1 while only a block of wrought iron is revolved4 ,illustration3 ,,fig4 #ih4 ,it would be uselessly lengthening this description were ,i to dwell more on the details of construction of these machines4 ,besides1 they have been described somewhat more elaborately in ,the ,electrical ,engineer1 of ,march #ah1 #ahia4 ,i deem it well1 however1 to call the attention of the investigator to two things1 the importance of which1 though self evident1 he is nevertheless apt to underestimate2 namely1 to the local action in the conductors which must be carefully avoided1 and to the clearance1 which must be small4 ,i may add1 that since it is desirable to use very high peripheral speeds1 the armature should be of very large diameter in order to avoid impracticable belt speeds4 ,of the several types of these machines which have been constructed by me1 ,i have found that the type illustrated in ,fig4 #ig caused me the least trouble in construction1 as well as in maintenance1 and on the whole1 it has been a good experimental machine4 ,in operating an induction coil with very rapidly alternating currents1 among the first luminous phenomena noticed are naturally those presented by the high-tension discharge4 ,as the number of alternations per second is increased1 or as--the number being high--the current through the primary is varied1 the discharge gradually changes in appearance4 ,it would be difficult to describe the minor changes which occur1 and the conditions which bring them about1 but one may note five distinct forms of the discharge4 ,illustration3 ,,fig4 #ii4 ,first1 one may observe a weak1 sensitive discharge in the form of a thin1 feeble-colored thread4 7,fig4 #ajj;a47 ,it always occurs when1 the number of alternations per second being high1 the current through the primary is very small4 ,in spite of the excessively small current1 the rate of change is great1 and the difference of potential at the terminals of the secondary is therefore considerable1 so that the arc is established at great distances2 but the quantity of electricity set in motion is insignificant1 barely sufficient to maintain a thin1 threadlike arc4 ,it is excessively sensitive and may be made so to such a degree that the mere act of breathing near the coil will affect it1 and unless it is perfectly well protected from currents of air1 it wriggles around constantly4 ,nevertheless1 it is in this form excessively persistent1 and when the terminals are approached to1 say1 one-third of the striking distance1 it can be blown out only with difficulty4 ,this exceptional persistency1 when short1 is largely due to the arc being excessively thin2 presenting1 therefore1 a very small surface to the blast4 ,its great sensitiveness1 when very long1 is probably due to the motion of the particles of dust suspended in the air4 ,illustration3 ,,fig4 #ajj;a4 ,illustration3 ,,fig4 #ajj;b4 ,when the current through the primary is increased1 the discharge gets broader and stronger1 and the effect of the capacity of the coil becomes visible until1 finally1 under proper conditions1 a white flaming arc1 ,fig4 #ajj ,b1 often as thick as one's finger1 and striking across the whole coil1 is produced4 ,it develops remarkable heat1 and may be further characterized by the absence of the high note which accompanies the less powerful discharges4 ,to take a shock from the coil under these conditions would not be advisable1 although under different conditions1 the potential being much higher1 a shock from the coil may be taken with impunity4 ,to produce this kind of discharge the number of alternations per second must not be too great for the coil used2 and1 generally speaking1 certain relations between capacity1 self-induction and frequency must be observed4 ,the importance of these elements in an alternate current circuit is now well-known1 and under ordinary conditions1 the general rules are applicable4 ,but in an induction coil exceptional conditions prevail4 ,first1 the self-induction is of little importance before the arc is established1 when it asserts itself1 but perhaps never as prominently as in ordinary alternate current circuits1 because the capacity is distributed all along the coil1 and by reason of the fact that the coil usually discharges through very great resistances2 hence the currents are exceptionally small4 ,secondly1 the capacity goes on increasing continually as the potential rises1 in consequence of absorption which takes place to a considerable extent4 ,owing to this there exists no critical relationship between these quantities1 and ordinary rules would not seem to be applicable4 ,as the potential is increased either in consequence of the increased frequency or of the increased current through the primary1 the amount of the energy stored becomes greater and greater1 and the capacity gains more and more in importance4 ,up to a certain point the capacity is beneficial1 but after that it begins to be an enormous drawback4 ,it follows from this that each coil gives the best result with a given frequency and primary current4 ,a very large coil1 when operated with currents of very high frequency1 may not give as much as #a_/h inch spark4 ,by adding capacity to the terminals1 the condition may be improved1 but what the coil really wants is a lower frequency4 ,when the flaming discharge occurs1 the conditions are evidently such that the greatest current is made to flow through the circuit4 ,these conditions may be attained by varying the frequency within wide limits1 but the highest frequency at which the flaming arc can still be produced1 determines1 for a given primary current1 the maximum striking distance of the coil4 ,in the flaming discharge the eclat effect of the capacity is not perceptible2 the rate at which the energy is being stored then just equals the rate at which it can be disposed of through the circuit4 ,this kind of discharge is the severest test for a coil2 the break1 when it occurs1 is of the nature of that in an overcharged ,leyden jar4 ,to give a rough approximation ,i would state that1 with an ordinary coil of1 say #aj1jjj ohms resistance1 the most powerful arc would be produced with about #ab1jjj alternations per second4 ,when the frequency is increased beyond that rate1 the potential1 of course1 rises1 but the striking distance may1 nevertheless1 diminish1 paradoxical as it may seem4 ,as the potential rises the coil attains more and more the properties of a static machine until1 finally1 one may observe the beautiful phenomenon of the streaming discharge1 ,fig4 #aja1 which may be produced across the whole length of the coil4 ,at that stage streams begin to issue freely from all points and projections4 ,these streams will also be seen to pass in abundance in the space between the primary and the insulating tube4 ,when the potential is excessively high they will always appear1 even if the frequency be low1 and even if the primary be surrounded by as much as an inch of wax1 hard rubber1 glass1 or any other insulating substance4 ,this limits greatly the output of the coil1 but ,i will later show how ,i have been able to overcome to a considerable extent this disadvantage in the ordinary coil4 ,besides the potential1 the intensity of the streams depends on the frequency2 but if the coil be very large they show themselves1 no matter how low the frequencies used4 ,for instance1 in a very large coil of a resistance of #fg1jjj ohms1 constructed by me some time ago1 they appear with as low as #ajj alternations per second and less1 the insulation of the secondary being #c_/d inch of ebonite4 ,when very intense they produce a noise similar to that produced by the charging of a ,holtz machine1 but much more powerful1 and they emit a strong smell of ozone4 ,the lower the frequency1 the more apt they are to suddenly injure the coil4 ,with excessively high frequencies they may pass freely without producing any other effect than to heat the insulation slowly and uniformly4 ,illustration3 ,,fig4 #aja4 ,illustration3 ,,fig4 #ajb4 ,the existence of these streams shows the importance of constructing an expensive coil so as to permit of one's seeing through the tube surrounding the primary1 and the latter should be easily exchangeable2 or else the space between the primary and secondary should be completely filled up with insulating material so as to exclude all air4 ,the non-observance of this simple rule in the construction of commercial coils is responsible for the destruction of many an expensive coil4 ,at the stage when the streaming discharge occurs1 or with somewhat higher frequencies1 one may1 by approaching the terminals quite nearly1 and regulating properly the effect of capacity1 produce a veritable spray of small silver-white sparks1 or a bunch of excessively thin silvery threads 7,fig4 #ajb7 amidst a powerful brush--each spark or thread possibly corresponding to one alternation4 ,this1 when produced under proper conditions1 is probably the most beautiful discharge1 and when an air blast is directed against it1 it presents a singular appearance4 ,the spray of sparks1 when received through the body1 causes some inconvenience1 whereas1 when the discharge simply streams1 nothing at all is likely to be felt if large conducting objects are held in the hands to protect them from receiving small burns4 ,if the frequency is still more increased1 then the coil refuses to give any spark unless at comparatively small distances1 and the fifth typical form of discharge may be observed 7,fig4 #ajc74 ,the tendency to stream out and dissipate is then so great that when the brush is produced at one terminal no sparking occurs1 even if1 as ,i have repeatedly tried1 the hand1 or any conducting object1 is held within the stream2 and1 what is more singular1 the luminous stream is not at all easily deflected by the approach of a conducting body4 ,illustration3 ,,fig4 #ajc4 ,illustration3 ,,fig4 #ajd4 ,at this stage the streams seemingly pass with the greatest freedom through considerable thicknesses of insulators1 and it is particularly interesting to study their behavior4 ,for this purpose it is convenient to connect to the terminals of the coil two metallic spheres which may be placed at any desired distance1 ,fig4 #ajd4 ,spheres are preferable to plates1 as the discharge can be better observed4 ,by inserting dielectric bodies between the spheres1 beautiful discharge phenomena may be observed4 ,if the spheres be quite close and a spark be playing between them1 by interposing a thin plate of ebonite between the spheres the spark instantly ceases and the discharge spreads into an intensely luminous circle several inches in diameter1 provided the spheres are sufficiently large4 ,the passage of the streams heats1 and1 after a while1 softens1 the rubber so much that two plates may be made to stick together in this manner4 ,if the spheres are so far apart that no spark occurs1 even if they are far beyond the striking distance1 by inserting a thick plate of glass the discharge is instantly induced to pass from the spheres to the glass in the form of luminous streams4 ,it appears almost as though these streams pass through the dielectric4 ,in reality this is not the case1 as the streams are due to the molecules of the air which are violently agitated in the space between the oppositely charged surfaces of the spheres4 ,when no dielectric other than air is present1 the bombardment goes on1 but is too weak to be visible2 by inserting a dielectric the inductive effect is much increased1 and besides1 the projected air molecules find an obstacle and the bombardment becomes so intense that the streams become luminous4 ,if by any mechanical means we could effect such a violent agitation of the molecules we could produce the same phenomenon4 ,a jet of air escaping through a small hole under enormous pressure and striking against an insulating substance1 such as glass1 may be luminous in the dark1 and it might be possible to produce a phosphorescence of the glass or other insulators in this manner4 ,the greater the specific inductive capacity of the interposed dielectric1 the more powerful the effect produced4 ,owing to this1 the streams show themselves with excessively high potentials even if the glass be as much as one and one-half to two inches thick4 ,but besides the heating due to bombardment1 some heating goes on undoubtedly in the dielectric1 being apparently greater in glass than in ebonite4 ,i attribute this to the greater specific inductive capacity of the glass1 in consequence of which1 with the same potential difference1 a greater amount of energy is taken up in it than in rubber4 ,it is like connecting to a battery a copper and a brass wire of the same dimensions4 ,the copper wire1 though a more perfect conductor1 would heat more by reason of its taking more current4 ,thus what is otherwise considered a virtue of the glass is here a defect4 ,glass usually gives way much quicker than ebonite2 when it is heated to a certain degree1 the discharge suddenly breaks through at one point1 assuming then the ordinary form of an arc4 ,the heating effect produced by molecular bombardment of the dielectric would1 of course1 diminish as the pressure of the air is increased1 and at enormous pressure it would be negligible1 unless the frequency would increase correspondingly4 ,it will be often observed in these experiments that when the spheres are beyond the striking distance1 the approach of a glass plate1 for instance1 may induce the spark to jump between the spheres4 ,this occurs when the capacity of the spheres is somewhat below the critical value which gives the greatest difference of potential at the terminals of the coil4 ,by approaching a dielectric1 the specific inductive capacity of the space between the spheres is increased1 producing the same effect as if the capacity of the spheres were increased4 ,the potential at the terminals may then rise so high that the air space is cracked4 ,the experiment is best performed with dense glass or mica4 ,another interesting observation is that a plate of insulating material1 when the discharge is passing through it1 is strongly attracted by either of the spheres1 that is by the nearer one1 this being obviously due to the smaller mechanical effect of the bombardment on that side1 and perhaps also to the greater electrification4 ,from the behavior of the dielectrics in these experiments1 we may conclude that the best insulator for these rapidly alternating currents would be the one possessing the smallest specific inductive capacity and at the same time one capable of withstanding the greatest differences of potential2 and thus two diametrically opposite ways of securing the required insulation are indicated1 namely1 to use either a perfect vacuum or a gas under great pressure2 but the former would be preferable4 ,unfortunately neither of these two ways is easily carried out in practice4 ,it is especially interesting to note the behavior of an excessively high vacuum in these experiments4 ,if a test tube1 provided with external electrodes and exhausted to the highest possible degree1 be connected to the terminals of the coil1 ,fig4 #aje1 the electrodes of the tube are instantly brought to a high temperature and the glass at each end of the tube is rendered intensely phosphorescent1 but the middle appears comparatively dark1 and for a while remains cool4 ,when the frequency is so high that the discharge shown in ,fig4 #ajc is observed1 considerable dissipation no doubt occurs in the coil4 ,nevertheless the coil may be worked for a long time1 as the heating is gradual4 ,in spite of the fact that the difference of potential may be enormous1 little is felt when the discharge is passed through the body1 provided the hands are armed4 ,this is to some extent due to the higher frequency1 but principally to the fact that less energy is available externally1 when the difference of potential reaches an enormous value1 owing to the circumstance that1 with the rise of potential1 the energy absorbed in the coil increases as the square of the potential4 ,up to a certain point the energy available externally increases with the rise of potential1 then it begins to fall off rapidly4 ,thus1 with the ordinary high tension induction coil1 the curious paradox exists1 that1 while with a given current through the primary the shock might be fatal1 with many times that current it might be perfectly harmless1 even if the frequency be the same4 ,with high frequencies and excessively high potentials when the terminals are not connected to bodies of some size1 practically all the energy supplied to the primary is taken up by the coil4 ,there is no breaking through1 no local injury1 but all the material1 insulating and conducting1 is uniformly heated4 ,illustration3 ,,fig4 #aje4 ,illustration3 ,,fig4 #ajf4 ,to avoid misunderstanding in regard to the physiological effect of alternating currents of very high frequency1 ,i think it necessary to state that1 while it is an undeniable fact that they are incomparably less dangerous than currents of low frequencies1 it should not be thought that they are altogether harmless4 ,what has just been said refers only to currents from an ordinary high tension induction coil1 which currents are necessarily very small2 if received directly from a machine or from a secondary of low resistance1 they produce more or less powerful effects1 and may cause serious injury1 especially when used in conjunction with condensers4 ,the streaming discharge of a high tension induction coil differs in many respects from that of a powerful static machine4 ,in color it has neither the violet of the positive1 nor the brightness of the negative1 static discharge1 but lies somewhere between1 being1 of course1 alternatively positive and negative4 ,but since the streaming is more powerful when the point or terminal is electrified positively1 than when electrified negatively1 it follows that the point of the brush is more like the positive1 and the root more like the negative1 static discharge4 ,in the dark1 when the brush is very powerful1 the root may appear almost white4 ,the wind produced by the escaping streams1 though it may be very strong--often indeed to such a degree that it may be felt quite a distance from the coil--is1 nevertheless1 considering the quantity of the discharge1 smaller than that produced by the positive brush of a static machine1 and it affects the flame much less powerfully4 ,from the nature of the phenomenon we can conclude that the higher the frequency1 the smaller must1 of course1 be the wind produced by the streams1 and with sufficiently high frequencies no wind at all would be produced at the ordinary atmospheric pressures4 ,with frequencies obtainable by means of a machine1 the mechanical effect is sufficiently great to revolve1 with considerable speed1 large pin-wheels1 which in the dark present a beautiful appearance owing to the abundance of the streams 7,fig4 #ajf74 ,illustration3 ,,fig4 #ajg4 ,illustration3 ,,fig4 #ajh4 ,in general1 most of the experiments usually performed with a static machine can be performed with an induction coil when operated with very rapidly alternating currents4 ,the effects produced1 however1 are much more striking1 being of incomparably greater power4 ,when a small length of ordinary cotton covered wire1 ,fig4 #ajg1 is attached to one terminal of the coil1 the streams issuing from all points of the wire may be so intense as to produce a considerable light effect4 ,when the potentials and frequencies are very high1 a wire insulated with gutta percha or rubber and attached to one of the terminals1 appears to be covered with a luminous film4 ,a very thin bare wire when attached to a terminal emits powerful streams and vibrates continually to and fro or spins in a circle1 producing a singular effect 7,fig4 #ajh74 ,some of these experiments have been described by me in ,the ,electrical ,world1 of ,february #ba1 #ahia4 ,another peculiarity of the rapidly alternating discharge of the induction coil is its radically different behavior with respect to points and rounded surfaces4 ,if a thick wire1 provided with a ball at one end and with a point at the other1 be attached to the positive terminal of a static machine1 practically all the charge will be lost through the point1 on account of the enormously greater tension1 dependent on the radius of curvature4 ,but if such a wire is attached to one of the terminals of the induction coil1 it will be observed that with very high frequencies streams issue from the ball almost as copiously as from the point 7,fig4 #aji74 ,it is hardly conceivable that we could produce such a condition to an equal degree in a static machine1 for the simple reason1 that the tension increases as the square of the density1 which in turn is proportional to the radius of curvature2 hence1 with a steady potential an enormous charge would be required to make streams issue from a polished ball while it is connected with a point4 ,but with an induction coil the discharge of which alternates with great rapidity it is different4 ,here we have to deal with two distinct tendencies4 ,first1 there is the tendency to escape which exists in a condition of rest1 and which depends on the radius of curvature2 second1 there is the tendency to dissipate into the surrounding air by condenser action1 which depends on the surface4 ,when one of these tendencies is a maximum1 the other is at a minimum4 ,at the point the luminous stream is principally due to the air molecules coming bodily in contact with the point2 they are attracted and repelled1 charged and discharged1 and1 their atomic charges being thus disturbed1 vibrate and emit light waves4 ,at the ball1 on the contrary1 there is no doubt that the effect is to a great extent produced inductively1 the air molecules not necessarily coming in contact with the ball1 though they undoubtedly do so4 ,to convince ourselves of this we only need to exalt the condenser action1 for instance1 by enveloping the ball1 at some distance1 by a better conductor than the surrounding medium1 the conductor being1 of course1 insulated2 or else by surrounding it with a better dielectric and approaching an insulated conductor2 in both cases the streams will break forth more copiously4 ,also1 the larger the ball with a given frequency1 or the higher the frequency1 the more will the ball have the advantage over the point4 ,but1 since a certain intensity of action is required to render the streams visible1 it is obvious that in the experiment described the ball should not be taken too large4 ,in consequence of this two-fold tendency1 it is possible to produce by means of points1 effects identical to those produced by capacity4 ,thus1 for instance1 by attaching to one terminal of the coil a small length of soiled wire1 presenting many points and offering great facility to escape1 the potential of the coil may be raised to the same value as by attaching to the terminal a polished ball of a surface many times greater than that of the wire4 ,illustration3 ,,fig4 #aji4 ,illustration3 ,,fig4 #aaj4 ,an interesting experiment1 showing the effect of the points1 may be performed in the following manner3 ,attach to one of the terminals of the coil a cotton covered wire about two feet in length1 and adjust the conditions so that streams issue from the wire4 ,in this experiment the primary coil should be preferably placed so that it extends only about half way into the secondary coil4 ,now touch the free terminal of the secondary with a conducting object held in the hand1 or else connect it to an insulated body of some size4 ,in this manner the potential on the wire may be enormously raised4 ,the effect of this will be either to increase1 or to diminish1 the streams4 ,if they increase1 the wire is too short2 if they diminish1 it is too long4 ,by adjusting the length of the wire1 a point is found where the touching of the other terminal does not at all affect the streams4 ,in this case the rise of potential is exactly counteracted by the drop through the coil4 ,it will be observed that small lengths of wire produce considerable difference in the magnitude and luminosity of the streams4 ,the primary coil is placed sidewise for two reasons3 ,first1 to increase the potential at the wire2 and1 second1 to increase the drop through the coil4 ,the sensitiveness is thus augmented4 ,there is still another and far more striking peculiarity of the brush discharge produced by very rapidly alternating currents4 ,to observe this it is best to replace the usual terminals of the coil by two metal columns insulated with a good thickness of ebonite4 ,it is also well to close all fissures and cracks with wax so that the brushes cannot form anywhere except at the tops of the columns4 ,if the conditions are carefully adjusted--which1 of course1 must be left to the skill of the experimenter--so that the potential rises to an enormous value1 one may produce two powerful brushes several inches long1 nearly white at their roots1 which in the dark bear a striking resemblance to two flames of a gas escaping under pressure 7,fig4 #aaj74 ,but they do not only resemble1 they are veritable flames1 for they are hot4 ,certainly they are not as hot as a gas burner1 but they would be so if the frequency and the potential would be sufficiently high4 ,produced with1 say1 twenty thousand alternations per second1 the heat is easily perceptible even if the potential is not excessively high4 ,the heat developed is1 of course1 due to the impact of the air molecules against the terminals and against each other4 ,as1 at the ordinary pressures1 the mean free path is excessively small1 it is possible that in spite of the enormous initial speed imparted to each molecule upon coming in contact with the terminal1 its progress--by collision with other molecules--is retarded to such an extent1 that it does not get away far from the terminal1 but may strike the same many times in succession4 ,the higher the frequency1 the less the molecule is able to get away1 and this the more so1 as for a given effect the potential required is smaller2 and a frequency is conceivable--perhaps even obtainable--at which practically the same molecules would strike the terminal4 ,under such conditions the exchange of the molecules would be very slow1 and the heat produced at1 and very near1 the terminal would be excessive4 ,but if the frequency would go on increasing constantly1 the heat produced would begin to diminish for obvious reasons4 ,in the positive brush of a static machine the exchange of the molecules is very rapid1 the stream is constantly of one direction1 and there are fewer collisions2 hence the heating effect must be very small4 ,anything that impairs the facility of exchange tends to increase the local heat produced4 ,thus1 if a bulb be held over the terminal of the coil so as to enclose the brush1 the air contained in the bulb is very quickly brought to a high temperature4 ,if a glass tube be held over the brush so as to allow the draught to carry the brush upwards1 scorching hot air escapes at the top of the tube4 ,anything held within the brush is1 of course1 rapidly heated1 and the possibility of using such heating effects for some purpose or other suggests itself4 ,when contemplating this singular phenomenon of the hot brush1 we cannot help being convinced that a similar process must take place in the ordinary flame1 and it seems strange that after all these centuries past of familiarity with the flame1 now1 in this era of electric lighting and heating1 we are finally led to recognize1 that since time immemorial we have1 after all1 always had electric light and heat at our disposal4 ,it is also of no little interest to contemplate1 that we have a possible way of producing--by other than chemical means--a veritable flame1 which would give light and heat without any material being consumed1 without any chemical process taking place1 and to accomplish this1 we only need to perfect methods of producing enormous frequencies and potentials4 ,i have no doubt that if the potential could be made to alternate with sufficient rapidity and power1 the brush formed at the end of a wire would lose its electrical characteristics and would become flamelike4 ,the flame must be due to electrostatic molecular action4 ,this phenomenon now explains in a manner which can hardly be doubted the frequent accidents occurring in storms4 ,it is well known that objects are often set on fire without the lightning striking them4 ,we shall presently see how this can happen4 ,on a nail in a roof1 for instance1 or on a projection of any kind1 more or less conducting1 or rendered so by dampness1 a powerful brush may appear4 ,if the lightning strikes somewhere in the neighborhood the enormous potential may be made to alternate or fluctuate perhaps many million times a second4 ,the air molecules are violently attracted and repelled1 and by their impact produce such a powerful heating effect that a fire is started4 ,it is conceivable that a ship at sea may1 in this manner1 catch fire at many points at once4 ,when we consider1 that even with the comparatively low frequencies obtained from a dynamo machine1 and with potentials of no more than one or two hundred thousand volts1 the heating effects are considerable1 we may imagine how much more powerful they must be with frequencies and potentials many times greater2 and the above explanation seems1 to say the least1 very probable4 ,similar explanations may have been suggested1 but ,i am not aware that1 up to the present1 the heating effects of a brush produced by a rapidly alternating potential have been experimentally demonstrated1 at least not to such a remarkable degree4 ,illustration3 ,,fig4 #aaa4 ,by preventing completely the exchange of the air molecules1 the local heating effect may be so exalted as to bring a body to incandescence4 ,thus1 for instance1 if a small button1 or preferably a very thin wire or filament be enclosed in an unexhausted globe and connected with the terminal of the coil1 it may be rendered incandescent4 ,the phenomenon is made much more interesting by the rapid spinning round in a circle of the top of the filament1 thus presenting the appearance of a luminous funnel1 ,fig4 #aaa1 which widens when the potential is increased4 ,when the potential is small the end of the filament may perform irregular motions1 suddenly changing from one to the other1 or it may describe an ellipse2 but when the potential is very high it always spins in a circle2 and so does generally a thin straight wire attached freely to the terminal of the coil4 ,these motions are1 of course1 due to the impact of the molecules1 and the irregularity in the distribution of the potential1 owing to the roughness and dissymmetry of the wire or filament4 ,with a perfectly symmetrical and polished wire such motions would probably not occur4 ,that the motion is not likely to be due to others causes is evident from the fact that it is not of a definite direction1 and that in a very highly exhausted globe it ceases altogether4 ,the possibility of bringing a body to incandescence in an exhausted globe1 or even when not at all enclosed1 would seem to afford a possible way of obtaining light effects1 which1 in perfecting methods of producing rapidly alternating potentials1 might be rendered available for useful purposes4 ,illustration3 ,,fig4 #aab;a4 ,in employing a commercial coil1 the production of very powerful brush effects is attended with considerable difficulties1 for when these high frequencies and enormous potentials are used1 the best insulation is apt to give way4 ,usually the coil is insulated well enough to stand the strain from convolution to convolution1 since two double silk covered paraffined wires will withstand a pressure of several thousand volts2 the difficulty lies principally in preventing the breaking through from the secondary to the primary1 which is greatly facilitated by the streams issuing from the latter4 ,in the coil1 of course1 the strain is greatest from section to section1 but usually in a larger coil there are so many sections that the danger of a sudden giving way is not very great4 ,no difficulty will generally be encountered in that direction1 and besides1 the liability of injuring the coil internally is very much reduced by the fact that the effect most likely to be produced is simply a gradual heating1 which1 when far enough advanced1 could not fail to be observed4 ,the principal necessity is then to prevent the streams between the primary and the tube1 not only on account of the heating and possible injury1 but also because the streams may diminish very considerably the potential difference available at the terminals4 ,a few hints as to how this may be accomplished will probably be found useful in most of these experiments with the ordinary induction coil4 ,illustration3 ,,fig4 #aab;b4 ,one of the ways is to wind a short primary1 ,fig4 #aab;a1 so that the difference of potential is not at that length great enough to cause the breaking forth of the streams through the insulating tube4 ,the length of the primary should be determined by experiment4 ,both the ends of the coil should be brought out on one end through a plug of insulating material fitting in the tube as illustrated4 ,in such a disposition one terminal of the secondary is attached to a body1 the surface of which is determined with the greatest care so as to produce the greatest rise in the potential4 ,at the other terminal a powerful brush appears1 which may be experimented upon4 ,the above plan necessitates the employment of a primary of comparatively small size1 and it is apt to heat when powerful effects are desirable for a certain length of time4 ,in such a case it is better to employ a larger coil1 ,fig4 #aab;b1 and introduce it from one side of the tube1 until the streams begin to appear4 ,in this case the nearest terminal of the secondary may be connected to the primary or to the ground1 which is practically the same thing1 if the primary is connected directly to the machine4 ,in the case of ground connections it is well to determine experimentally the frequency which is best suited under the conditions of the test4 ,another way of obviating the streams1 more or less1 is to make the primary in sections and supply it from separate1 well insulated sources4 ,in many of these experiments1 when powerful effects are wanted for a short time1 it is advantageous to use iron cores with the primaries4 ,in such case a very large primary coil may be wound and placed side by side with the secondary1 and1 the nearest terminal of the latter being connected to the primary1 a laminated iron core is introduced through the primary into the secondary as far as the streams will permit4 ,under these conditions an excessively powerful brush1 several inches long1 which may be appropriately called ,st4 ,elmo's hot fire1 may be caused to appear at the other terminal of the secondary1 producing striking effects4 ,it is a most powerful ozonizer1 so powerful indeed1 that only a few minutes are sufficient to fill the whole room with the smell of ozone1 and it undoubtedly possesses the quality of exciting chemical affinities4 ,for the production of ozone1 alternating currents of very high frequency are eminently suited1 not only on account of the advantages they offer in the way of conversion but also because of the fact1 that the ozonizing action of a discharge is dependent on the frequency as well as on the potential1 this being undoubtedly confirmed by observation4 ,in these experiments if an iron core is used it should be carefully watched1 as it is apt to get excessively hot in an incredibly short time4 ,to give an idea of the rapidity of the heating1 ,i will state1 that by passing a powerful current through a coil with many turns1 the inserting within the same of a thin iron wire for no more than one second's time is sufficient to heat the wire to something like #ajj deg4 ,c4 ,but this rapid heating need not discourage us in the use of iron cores in connection with rapidly alternating currents4 ,i have for a long time been convinced that in the industrial distribution by means of transformers1 some such plan as the following might be practicable4 ,we may use a comparatively small iron core1 subdivided1 or perhaps not even subdivided4 ,we may surround this core with a considerable thickness of material which is fire-proof and conducts the heat poorly1 and on top of that we may place the primary and secondary windings4 ,by using either higher frequencies or greater magnetizing forces1 we may by hysteresis and eddy currents heat the iron core so far as to bring it nearly to its maximum permeability1 which1 as ,hopkinson has shown1 may be as much as sixteen times greater than that at ordinary temperatures4 ,if the iron core were perfectly enclosed1 it would not be deteriorated by the heat1 and1 if the enclosure of fire-proof material would be sufficiently thick1 only a limited amount of energy could be radiated in spite of the high temperature4 ,transformers have been constructed by me on that plan1 but for lack of time1 no thorough tests have as yet been made4 ,another way of adapting the iron core to rapid alternations1 or1 generally speaking1 reducing the frictional losses1 is to produce by continuous magnetization a flow of something like seven thousand or eight thousand lines per square centimetre through the core1 and then work with weak magnetizing forces and preferably high frequencies around the point of greatest permeability4 ,a higher efficiency of conversion and greater output are obtainable in this manner4 ,i have also employed this principle in connection with machines in which there is no reversal of polarity4 ,in these types of machines1 as long as there are only few pole projections1 there is no great gain1 as the maxima and minima of magnetization are far from the point of maximum permeability2 but when the number of the pole projections is very great1 the required rate of change may be obtained1 without the magnetization varying so far as to depart greatly from the point of maximum permeability1 and the gain is considerable4 ,the above described arrangements refer only to the use of commercial coils as ordinarily constructed4 ,if it is desired to construct a coil for the express purpose of performing with it such experiments as ,i have described1 or1 generally1 rendering it capable of withstanding the greatest possible difference of potential1 then a construction as indicated in ,fig4 #aac will be found of advantage4 ,the coil in this case is formed of two independent parts which are wound oppositely1 the connection between both being made near the primary4 ,the potential in the middle being zero1 there is not much tendency to jump to the primary and not much insulation is required4 ,in some cases the middle point may1 however1 be connected to the primary or to the ground4 ,in such a coil the places of greatest difference of potential are far apart and the coil is capable of withstanding an enormous strain4 ,the two parts may be movable so as to allow a slight adjustment of the capacity effect4 ,as to the manner of insulating the coil1 it will be found convenient to proceed in the following way3 ,first1 the wire should be boiled in paraffine until all the air is out2 then the coil is wound by running the wire through melted paraffine1 merely for the purpose of fixing the wire4 ,the coil is then taken off from the spool1 immersed in a cylindrical vessel filled with pure melted wax and boiled for a long time until the bubbles cease to appear4 ,the whole is then left to cool down thoroughly1 and then the mass is taken out of the vessel and turned up in a lathe4 ,a coil made in this manner and with care is capable of withstanding enormous potential differences4 ,illustration3 ,,fig4 #aac4 ,it may be found convenient to immerse the coil in paraffine oil or some other kind of oil2 it is a most effective way of insulating1 principally on account of the perfect exclusion of air1 but it may be found that1 after all1 a vessel filled with oil is not a very convenient thing to handle in a laboratory4 ,if an ordinary coil can be dismounted1 the primary may be taken out of the tube and the latter plugged up at one end1 filled with oil1 and the primary reinserted4 ,this affords an excellent insulation and prevents the formation of the streams4 ,of all the experiments which may be performed with rapidly alternating currents the most interesting are those which concern the production of a practical illuminant4 ,it cannot be denied that the present methods1 though they were brilliant advances1 are very wasteful4 ,some better methods must be invented1 some more perfect apparatus devised4 ,modern research has opened new possibilities for the production of an efficient source of light1 and the attention of all has been turned in the direction indicated by able pioneers4 ,many have been carried away by the enthusiasm and passion to discover1 but in their zeal to reach results1 some have been misled4 ,starting with the idea of producing electro-magnetic waves1 they turned their attention1 perhaps1 too much to the study of electro-magnetic effects1 and neglected the study of electrostatic phenomena4 ,naturally1 nearly every investigator availed himself of an apparatus similar to that used in earlier experiments4 ,but in those forms of apparatus1 while the electro-magnetic inductive effects are enormous1 the electrostatic effects are excessively small4 ,in the ,hertz experiments1 for instance1 a high tension induction coil is short circuited by an arc1 the resistance of which is very small1 the smaller1 the more capacity is attached to the terminals2 and the difference of potential at these is enormously diminished4 ,on the other hand1 when the discharge is not passing between the terminals1 the static effects may be considerable1 but only qualitatively so1 not quantitatively1 since their rise and fall is very sudden1 and since their frequency is small4 ,in neither case1 therefore1 are powerful electrostatic effects perceivable4 ,similar conditions exist when1 as in some interesting experiments of ,dr4 ,lodge1 ,leyden jars are discharged disruptively4 ,it has been thought--and ,i believe asserted--that in such cases most of the energy is radiated into space4 ,in the light of the experiments which ,i have described above1 it will now not be thought so4 ,i feel safe in asserting that in such cases most of the energy is partly taken up and converted into heat in the arc of the discharge and in the conducting and insulating material of the jar1 some energy being1 of course1 given off by electrification of the air2 but the amount of the directly radiated energy is very small4 ,when a high tension induction coil1 operated by currents alternating only #bj1jjj times a second1 has its terminals closed through even a very small jar1 practically all the energy passes through the dielectric of the jar1 which is heated1 and the electrostatic effects manifest themselves outwardly only to a very weak degree4 ,now the external circuit of a ,leyden jar1 that is1 the arc and the connections of the coatings1 may be looked upon as a circuit generating alternating currents of excessively high frequency and fairly high potential1 which is closed through the coatings and the dielectric between them1 and from the above it is evident that the external electrostatic effects must be very small1 even if a recoil circuit be used4 ,these conditions make it appear that with the apparatus usually at hand1 the observation of powerful electrostatic effects was impossible1 and what experience has been gained in that direction is only due to the great ability of the investigators4 ,but powerful electrostatic effects are a sine qua non of light production on the lines indicated by theory4 ,electro-magnetic effects are primarily unavailable1 for the reason that to produce the required effects we would have to pass current impulses through a conductor1 which1 long before the required frequency of the impulses could be reached1 would cease to transmit them4 ,on the other hand1 electro-magnetic waves many times longer than those of light1 and producible by sudden discharge of a condenser1 could not be utilized1 it would seem1 except we avail ourselves of their effect upon conductors as in the present methods1 which are wasteful4 ,we could not affect by means of such waves the static molecular or atomic charges of a gas1 cause them to vibrate and to emit light4 ,long transverse waves cannot1 apparently1 produce such effects1 since excessively small electro-magnetic disturbances may pass readily through miles of air4 ,such dark waves1 unless they are of the length of true light waves1 cannot1 it would seem1 excite luminous radiation in a ,geissler tube1 and the luminous effects1 which are producible by induction in a tube devoid of electrodes1 ,i am inclined to consider as being of an electrostatic nature4 ,to produce such luminous effects1 straight electrostatic thrusts are required2 these1 whatever be their frequency1 may disturb the molecular charges and produce light4 ,since current impulses of the required frequency cannot pass through a conductor of measurable dimensions1 we must work with a gas1 and then the production of powerful electrostatic effects becomes an imperative necessity4 ,it has occurred to me1 however1 that electrostatic effects are in many ways available for the production of light4 ,for instance1 we may place a body of some refractory material in a closed1 and preferably more or less exhausted1 globe1 connect it to a source of high1 rapidly alternating potential1 causing the molecules of the gas to strike it many times a second at enormous speeds1 and in this manner1 with trillions of invisible hammers1 pound it until it gets incandescent2 or we may place a body in a very highly exhausted globe1 in a non-striking vacuum1 and1 by employing very high frequencies and potentials1 transfer sufficient energy from it to other bodies in the vicinity1 or in general to the surroundings1 to maintain it at any degree of incandescence2 or we may1 by means of such rapidly alternating high potentials1 disturb the ether carried by the molecules of a gas or their static charges1 causing them to vibrate and to emit light4 ,but1 electrostatic effects being dependent upon the potential and frequency1 to produce the most powerful action it is desirable to increase both as far as practicable4 ,it may be possible to obtain quite fair results by keeping either of these factors small1 provided the other is sufficiently great2 but we are limited in both directions4 ,my experience demonstrates that we cannot go below a certain frequency1 for1 first1 the potential then becomes so great that it is dangerous2 and1 secondly1 the light production is less efficient4 ,i have found that1 by using the ordinary low frequencies1 the physiological effect of the current required to maintain at a certain degree of brightness a tube four feet long1 provided at the ends with outside and inside condenser coatings1 is so powerful that1 ,i think1 it might produce serious injury to those not accustomed to such shocks2 whereas1 with twenty thousand alternations per second1 the tube may be maintained at the same degree of brightness without any effect being felt4 ,this is due principally to the fact that a much smaller potential is required to produce the same light effect1 and also to the higher efficiency in the light production4 ,it is evident that the efficiency in such cases is the greater1 the higher the frequency1 for the quicker the process of charging and discharging the molecules1 the less energy will be lost in the form of dark radiation4 ,but1 unfortunately1 we cannot go beyond a certain frequency on account of the difficulty of producing and conveying the effects4 ,i have stated above that a body inclosed in an unexhausted bulb may be intensely heated by simply connecting it with a source of rapidly alternating potential4 ,the heating in such a case is1 in all probability1 due mostly to the bombardment of the molecules of the gas contained in the bulb4 ,when the bulb is exhausted1 the heating of the body is much more rapid1 and there is no difficulty whatever in bringing a wire or filament to any degree of incandescence by simply connecting it to one terminal of a coil of the proper dimensions4 ,thus1 if the well-known apparatus of ,prof4 ,crookes1 consisting of a bent platinum wire with vanes mounted over it 7,fig4 #aad71 be connected to one terminal of the coil--either one or both ends of the platinum wire being connected--the wire is rendered almost instantly incandescent1 and the mica vanes are rotated as though a current from a battery were used4 ,a thin carbon filament1 or1 preferably1 a button of some refractory material 7,fig4 #aae71 even if it be a comparatively poor conductor1 inclosed in an exhausted globe1 may be rendered highly incandescent2 and in this manner a simple lamp capable of giving any desired candle power is provided4 ,the success of lamps of this kind would depend largely on the selection of the light-giving bodies contained within the bulb4 ,since1 under the conditions described1 refractory bodies--which are very poor conductors and capable of withstanding for a long time excessively high degrees of temperature--may be used1 such illuminating devices may be rendered successful4 ,illustration3 ,,fig4 #aad4 ,illustration3 ,,fig4 #aae4 ,it might be thought at first that if the bulb1 containing the filament or button of refractory material1 be perfectly well exhausted--that is1 as far as it can be done by the use of the best apparatus--the heating would be much less intense1 and that in a perfect vacuum it could not occur at all4 ,this is not confirmed by my experience2 quite the contrary1 the better the vacuum the more easily the bodies are brought to incandescence4 ,this result is interesting for many reasons4 ,at the outset of this work the idea presented itself to me1 whether two bodies of refractory material enclosed in a bulb exhausted to such a degree that the discharge of a large induction coil1 operated in the usual manner1 cannot pass through1 could be rendered incandescent by mere condenser action4 ,obviously1 to reach this result enormous potential differences and very high frequencies are required1 as is evident from a simple calculation4 ,but such a lamp would possess a vast advantage over an ordinary incandescent lamp in regard to efficiency4 ,it is well-known that the efficiency of a lamp is to some extent a function of the degree of incandescence1 and that1 could we but work a filament at many times higher degrees of incandescence1 the efficiency would be much greater4 ,in an ordinary lamp this is impracticable on account of the destruction of the filament1 and it has been determined by experience how far it is advisable to push the incandescence4 ,it is impossible to tell how much higher efficiency could be obtained if the filament could withstand indefinitely1 as the investigation to this end obviously cannot be carried beyond a certain stage2 but there are reasons for believing that it would be very considerably higher4 ,an improvement might be made in the ordinary lamp by employing a short and thick carbon2 but then the leading-in wires would have to be thick1 and1 besides1 there are many other considerations which render such a modification entirely impracticable4 ,but in a lamp as above described1 the leading in wires may be very small1 the incandescent refractory material may be in the shape of blocks offering a very small radiating surface1 so that less energy would be required to keep them at the desired incandescence2 and in addition to this1 the refractory material need not be carbon1 but may be manufactured from mixtures of oxides1 for instance1 with carbon or other material1 or may be selected from bodies which are practically non-conductors1 and capable of withstanding enormous degrees of temperature4 ,all this would point to the possibility of obtaining a much higher efficiency with such a lamp than is obtainable in ordinary lamps4 ,in my experience it has been demonstrated that the blocks are brought to high degrees of incandescence with much lower potentials than those determined by calculation1 and the blocks may be set at greater distances from each other4 ,we may freely assume1 and it is probable1 that the molecular bombardment is an important element in the heating1 even if the globe be exhausted with the utmost care1 as ,i have done2 for although the number of the molecules is1 comparatively speaking1 insignificant1 yet on account of the mean free path being very great1 there are fewer collisions1 and the molecules may reach much higher speeds1 so that the heating effect due to this cause may be considerable1 as in the ,crookes experiments with radiant matter4 ,but it is likewise possible that we have to deal here with an increased facility of losing the charge in very high vacuum1 when the potential is rapidly alternating1 in which case most of the heating would be directly due to the surging of the charges in the heated bodies4 ,or else the observed fact may be largely attributable to the effect of the points which ,i have mentioned above1 in consequence of which the blocks or filaments contained in the vacuum are equivalent to condensers of many times greater surface than that calculated from their geometrical dimensions4 ,scientific men still differ in opinion as to whether a charge should1 or should not1 be lost in a perfect vacuum1 or in other words1 whether ether is1 or is not1 a conductor4 ,if the former were the case1 then a thin filament enclosed in a perfectly exhausted globe1 and connected to a source of enormous1 steady potential1 would be brought to incandescence4 ,illustration3 ,,fig4 #aaf4 ,illustration3 ,,fig4 #aag4 ,various forms of lamps on the above described principle1 with the refractory bodies in the form of filaments1 ,fig4 #aaf1 or blocks1 ,fig4 #aag1 have been constructed and operated by me1 and investigations are being carried on in this line4 ,there is no difficulty in reaching such high degrees of incandescence that ordinary carbon is to all appearance melted and volatilized4 ,if the vacuum could be made absolutely perfect1 such a lamp1 although inoperative with apparatus ordinarily used1 would1 if operated with currents of the required character1 afford an illuminant which would never be destroyed1 and which would be far more efficient than an ordinary incandescent lamp4 ,this perfection can1 of course1 never be reached1 and a very slow destruction and gradual diminution in size always occurs1 as in incandescent filaments2 but there is no possibility of a sudden and premature disabling which occurs in the latter by the breaking of the filament1 especially when the incandescent bodies are in the shape of blocks4 ,with these rapidly alternating potentials there is1 however1 no necessity of enclosing two blocks in a globe1 but a single block1 as in ,fig4 #aae1 or filament1 ,fig4 #aah1 may be used4 ,the potential in this case must of course be higher1 but is easily obtainable1 and besides it is not necessarily dangerous4 ,illustration3 ,,fig4 #aah4 ,the facility with which the button or filament in such a lamp is brought to incandescence1 other things being equal1 depends on the size of the globe4 ,if a perfect vacuum could be obtained1 the size of the globe would not be of importance1 for then the heating would be wholly due to the surging of the charges1 and all the energy would be given off to the surroundings by radiation4 ,but this can never occur in practice4 ,there is always some gas left in the globe1 and although the exhaustion may be carried to the highest degree1 still the space inside of the bulb must be considered as conducting when such high potentials are used1 and ,i assume that1 in estimating the energy that may be given off from the filament to the surroundings1 we may consider the inside surface of the bulb as one coating of a condenser1 the air and other objects surrounding the bulb forming the other coating4 ,when the alternations are very low there is no doubt that a considerable portion of the energy is given off by the electrification of the surrounding air4 ,in order to study this subject better1 ,i carried on some experiments with excessively high potentials and low frequencies4 ,i then observed that when the hand is approached to the bulb1--the filament being connected with one terminal of the coil1--a powerful vibration is felt1 being due to the attraction and repulsion of the molecules of the air which are electrified by induction through the glass4 ,in some cases when the action is very intense ,i have been able to hear a sound1 which must be due to the same cause4 ,illustration3 ,,fig4 #aai4 ,illustration3 ,,fig4 #abj4 ,when the alternations are low1 one is apt to get an excessively powerful shock from the bulb4 ,in general1 when one attaches bulbs or objects of some size to the terminals of the coil1 one should look out for the rise of potential1 for it may happen that by merely connecting a bulb or plate to the terminal1 the potential may rise to many times its original value4 ,when lamps are attached to the terminals1 as illustrated in ,fig4 #aai1 then the capacity of the bulbs should be such as to give the maximum rise of potential under the existing conditions4 ,in this manner one may obtain the required potential with fewer turns of wire4 ,the life of such lamps as described above depends1 of course1 largely on the degree of exhaustion1 but to some extent also on the shape of the block of refractory material4 ,theoretically it would seem that a small sphere of carbon enclosed in a sphere of glass would not suffer deterioration from molecular bombardment1 for1 the matter in the globe being radiant1 the molecules would move in straight lines1 and would seldom strike the sphere obliquely4 ,an interesting thought in connection with such a lamp is1 that in it electricity and electrical energy apparently must move in the same lines4 ,illustration3 ,,fig4 #aba;a4 ,illustration3 ,,fig4 #aba;b4 ,the use of alternating currents of very high frequency makes it possible to transfer1 by electrostatic or electromagnetic induction through the glass of a lamp1 sufficient energy to keep a filament at incandescence and so do away with the leading-in wires4 ,such lamps have been proposed1 but for want of proper apparatus they have not been successfully operated4 ,many forms of lamps on this principle with continuous and broken filaments have been constructed by me and experimented upon4 ,when using a secondary enclosed within the lamp1 a condenser is advantageously combined with the secondary4 ,when the transference is effected by electrostatic induction1 the potentials used are1 of course1 very high with frequencies obtainable from a machine4 ,for instance1 with a condenser surface of forty square centimetres1 which is not impracticably large1 and with glass of good quality #a mm4 thick1 using currents alternating twenty thousand times a second1 the potential required is approximately #i1jjj volts4 ,this may seem large1 but since each lamp may be included in the secondary of a transformer of very small dimensions1 it would not be inconvenient1 and1 moreover1 it would not produce fatal injury4 ,the transformers would all be preferably in series4 ,the regulation would offer no difficulties1 as with currents of such frequencies it is very easy to maintain a constant current4 ,in the accompanying engravings some of the types of lamps of this kind are shown4 ,fig4 #abj is such a lamp with a broken filament1 and ,figs4 #aba ,a and #aba ,b one with a single outside and inside coating and a single filament4 ,i have also made lamps with two outside and inside coatings and a continuous loop connecting the latter4 ,such lamps have been operated by me with current impulses of the enormous frequencies obtainable by the disruptive discharge of condensers4 ,the disruptive discharge of a condenser is especially suited for operating such lamps--with no outward electrical connections--by means of electromagnetic induction1 the electromagnetic inductive effects being excessively high2 and ,i have been able to produce the desired incandescence with only a few short turns of wire4 ,incandescence may also be produced in this manner in a simple closed filament4 ,leaving now out of consideration the practicability of such lamps1 ,i would only say that they possess a beautiful and desirable feature1 namely1 that they can be rendered1 at will1 more or less brilliant simply by altering the relative position of the outside and inside condenser coatings1 or inducing and induced circuits4 ,when a lamp is lighted by connecting it to one terminal only of the source1 this may be facilitated by providing the globe with an outside condenser coating1 which serves at the same time as a reflector1 and connecting this to an insulated body of some size4 ,lamps of this kind are illustrated in ,fig4 #abb and ,fig4 #abc4 ,fig4 #abd shows the plan of connection4 ,the brilliancy of the lamp may1 in this case1 be regulated within wide limits by varying the size of the insulated metal plate to which the coating is connected4 ,it is likewise practicable to light with one leading wire lamps such as illustrated in ,fig4 #aaf and ,fig4 #aag1 by connecting one terminal of the lamp to one terminal of the source1 and the other to an insulated body of the required size4 ,in all cases the insulated body serves to give off the energy into the surrounding space1 and is equivalent to a return wire4 ,obviously1 in the two last-named cases1 instead of connecting the wires to an insulated body1 connections may be made to the ground4 ,the experiments which will prove most suggestive and of most interest to the investigator are probably those performed with exhausted tubes4 ,as might be anticipated1 a source of such rapidly alternating potentials is capable of exciting the tubes at a considerable distance1 and the light effects produced are remarkable4 ,illustration3 ,,fig4 #abb4 ,illustration3 ,,fig4 #abc4 ,during my investigations in this line ,i endeavored to excite tubes1 devoid of any electrodes1 by electromagnetic induction1 making the tube the secondary of the induction device1 and passing through the primary the discharges of a ,leyden jar4 ,these tubes were made of many shapes1 and ,i was able to obtain luminous effects which ,i then thought were due wholly to electromagnetic induction4 ,but on carefully investigating the phenomena ,i found that the effects produced were more of an electrostatic nature4 ,it may be attributed to this circumstance that this mode of exciting tubes is very wasteful1 namely1 the primary circuit being closed1 the potential1 and consequently the electrostatic inductive effect1 is much diminished4 ,when an induction coil1 operated as above described1 is used1 there is no doubt that the tubes are excited by electrostatic induction1 and that electromagnetic induction has little1 if anything1 to do with the phenomena4 ,illustration3 ,,fig4 #abd4 ,this is evident from many experiments4 ,for instance1 if a tube be taken in one hand1 the observer being near the coil1 it is brilliantly lighted and remains so no matter in what position it is held relatively to the observer's body4 ,were the action electromagnetic1 the tube could not be lighted when the observer's body is interposed between it and the coil1 or at least its luminosity should be considerably diminished4 ,when the tube is held exactly over the centre of the coil--the latter being wound in sections and the primary placed symmetrically to the secondary--it may remain completely dark1 whereas it is rendered intensely luminous by moving it slightly to the right or left from the centre of the coil4 ,it does not light because in the middle both halves of the coil neutralize each other1 and the electric potential is zero4 ,if the action were electromagnetic1 the tube should light best in the plane through the centre of the coil1 since the electromagnetic effect there should be a maximum4 ,when an arc is established between the terminals1 the tubes and lamps in the vicinity of the coil go out1 but light up again when the arc is broken1 on account of the rise of potential4 ,yet the electromagnetic effect should be practically the same in both cases4 ,by placing a tube at some distance from the coil1 and nearer to one terminal--preferably at a point on the axis of the coil--one may light it by touching the remote terminal with an insulated body of some size or with the hand1 thereby raising the potential at that terminal nearer to the tube4 ,if the tube is shifted nearer to the coil so that it is lighted by the action of the nearer terminal1 it may be made to go out by holding1 on an insulated support1 the end of a wire connected to the remote terminal1 in the vicinity of the nearer terminal1 by this means counteracting the action of the latter upon the tube4 ,these effects are evidently electrostatic4 ,likewise1 when a tube is placed at a considerable distance from the coil1 the observer may1 standing upon an insulated support between coil and tube1 light the latter by approaching the hand to it2 or he may even render it luminous by simply stepping between it and the coil4 ,this would be impossible with electro-magnetic induction1 for the body of the observer would act as a screen4 ,when the coil is energized by excessively weak currents1 the experimenter may1 by touching one terminal of the coil with the tube1 extinguish the latter1 and may again light it by bringing it out of contact with the terminal and allowing a small arc to form4 ,this is clearly due to the respective lowering and raising of the potential at that terminal4 ,in the above experiment1 when the tube is lighted through a small arc1 it may go out when the arc is broken1 because the electrostatic inductive effect alone is too weak1 though the potential may be much higher2 but when the arc is established1 the electrification of the end of the tube is much greater1 and it consequently lights4 ,if a tube is lighted by holding it near to the coil1 and in the hand which is remote1 by grasping the tube anywhere with the other hand1 the part between the hands is rendered dark1 and the singular effect of wiping out the light of the tube may be produced by passing the hand quickly along the tube and at the same time withdrawing it gently from the coil1 judging properly the distance so that the tube remains dark afterwards4 ,if the primary coil is placed sidewise1 as in ,fig4 #aab ,b for instance1 and an exhausted tube be introduced from the other side in the hollow space1 the tube is lighted most intensely because of the increased condenser action1 and in this position the striae are most sharply defined4 ,in all these experiments described1 and in many others1 the action is clearly electrostatic4 ,the effects of screening also indicate the electrostatic nature of the phenomena and show something of the nature of electrification through the air4 ,for instance1 if a tube is placed in the direction of the axis of the coil1 and an insulated metal plate be interposed1 the tube will generally increase in brilliancy1 or if it be too far from the coil to light1 it may even be rendered luminous by interposing an insulated metal plate4 ,the magnitude of the effects depends to some extent on the size of the plate4 ,but if the metal plate be connected by a wire to the ground1 its interposition will always make the tube go out even if it be very near the coil4 ,in general1 the interposition of a body between the coil and tube1 increases or diminishes the brilliancy of the tube1 or its facility to light up1 according to whether it increases or diminishes the electrification4 ,when experimenting with an insulated plate1 the plate should not be taken too large1 else it will generally produce a weakening effect by reason of its great facility for giving off energy to the surroundings4 ,if a tube be lighted at some distance from the coil1 and a plate of hard rubber or other insulating substance be interposed1 the tube may be made to go out4 ,the interposition of the dielectric in this case only slightly increases the inductive effect1 but diminishes considerably the electrification through the air4 ,in all cases1 then1 when we excite luminosity in exhausted tubes by means of such a coil1 the effect is due to the rapidly alternating electrostatic potential2 and1 furthermore1 it must be attributed to the harmonic alternation produced directly by the machine1 and not to any superimposed vibration which might be thought to exist4 ,such superimposed vibrations are impossible when we work with an alternate current machine4 ,if a spring be gradually tightened and released1 it does not perform independent vibrations2 for this a sudden release is necessary4 ,so with the alternate currents from a dynamo machine2 the medium is harmonically strained and released1 this giving rise to only one kind of waves2 a sudden contact or break1 or a sudden giving way of the dielectric1 as in the disruptive discharge of a ,leyden jar1 are essential for the production of superimposed waves4 ,in all the last described experiments1 tubes devoid of any electrodes may be used1 and there is no difficulty in producing by their means sufficient light to read by4 ,the light effect is1 however1 considerably increased by the use of phosphorescent bodies such as yttria1 uranium glass1 etc4 ,a difficulty will be found when the phosphorescent material is used1 for with these powerful effects1 it is carried gradually away1 and it is preferable to use material in the form of a solid4 ,instead of depending on induction at a distance to light the tube1 the same may be provided with an external--and1 if desired1 also with an internal--condenser coating1 and it may then be suspended anywhere in the room from a conductor connected to one terminal of the coil1 and in this manner a soft illumination may be provided4 ,illustration3 ,,fig4 #abe4 ,the ideal way of lighting a hall or room would1 however1 be to produce such a condition in it that an illuminating device could be moved and put anywhere1 and that it is lighted1 no matter where it is put and without being electrically connected to anything4 ,i have been able to produce such a condition by creating in the room a powerful1 rapidly alternating electrostatic field4 ,for this purpose ,i suspend a sheet of metal a distance from the ceiling on insulating cords and connect it to one terminal of the induction coil1 the other terminal being preferably connected to the ground4 ,or else ,i suspend two sheets as illustrated in ,fig4 #abe1 each sheet being connected with one of the terminals of the coil1 and their size being carefully determined4 ,an exhausted tube may then be carried in the hand anywhere between the sheets or placed anywhere1 even a certain distance beyond them2 it remains always luminous4 ,in such an electrostatic field interesting phenomena may be observed1 especially if the alternations are kept low and the potentials excessively high4 ,in addition to the luminous phenomena mentioned1 one may observe that any insulated conductor gives sparks when the hand or another object is approached to it1 and the sparks may often be powerful4 ,when a large conducting object is fastened on an insulating support1 and the hand approached to it1 a vibration1 due to the rythmical motion of the air molecules is felt1 and luminous streams may be perceived when the hand is held near a pointed projection4 ,when a telephone receiver is made to touch with one or both of its terminals an insulated conductor of some size1 the telephone emits a loud sound2 it also emits a sound when a length of wire is attached to one or both terminals1 and with very powerful fields a sound may be perceived even without any wire4 ,how far this principle is capable of practical application1 the future will tell4 ,it might be thought that electrostatic effects are unsuited for such action at a distance4 ,electromagnetic inductive effects1 if available for the production of light1 might be thought better suited4 ,it is true the electrostatic effects diminish nearly with the cube of the distance from the coil1 whereas the electromagnetic inductive effects diminish simply with the distance4 ,but when we establish an electrostatic field of force1 the condition is very different1 for then1 instead of the differential effect of both the terminals1 we get their conjoint effect4 ,besides1 ,i would call attention to the effect1 that in an alternating electrostatic field1 a conductor1 such as an exhausted tube1 for instance1 tends to take up most of the energy1 whereas in an electromagnetic alternating field the conductor tends to take up the least energy1 the waves being reflected with but little loss4 ,this is one reason why it is difficult to excite an exhausted tube1 at a distance1 by electromagnetic induction4 ,i have wound coils of very large diameter and of many turns of wire1 and connected a ,geissler tube to the ends of the coil with the object of exciting the tube at a distance2 but even with the powerful inductive effects producible by ,leyden jar discharges1 the tube could not be excited unless at a very small distance1 although some judgment was used as to the dimensions of the coil4 ,i have also found that even the most powerful ,leyden jar discharges are capable of exciting only feeble luminous effects in a closed exhausted tube1 and even these effects upon thorough examination ,i have been forced to consider of an electrostatic nature4 ,how then can we hope to produce the required effects at a distance by means of electromagnetic action1 when even in the closest proximity to the source of disturbance1 under the most advantageous conditions1 we can excite but faint luminosity8 ,it is true that when acting at a distance we have the resonance to help us out4 ,we can connect an exhausted tube1 or whatever the illuminating device may be1 with an insulated system of the proper capacity1 and so it may be possible to increase the effect qualitatively1 and only qualitatively1 for we would not get more energy through the device4 ,so we may1 by resonance effect1 obtain the required electromotive force in an exhausted tube1 and excite faint luminous effects1 but we cannot get enough energy to render the light practically available1 and a simple calculation1 based on experimental results1 shows that even if all the energy which a tube would receive at a certain distance from the source should be wholly converted into light1 it would hardly satisfy the practical requirements4 ,hence the necessity of directing1 by means of a conducting circuit1 the energy to the place of transformation4 ,but in so doing we cannot very sensibly depart from present methods1 and all we could do would be to improve the apparatus4 ,from these considerations it would seem that if this ideal way of lighting is to be rendered practicable it will be only by the use of electrostatic effects4 ,in such a case the most powerful electrostatic inductive effects are needed2 the apparatus employed must1 therefore1 be capable of producing high electrostatic potentials changing in value with extreme rapidity4 ,high frequencies are especially wanted1 for practical considerations make it desirable to keep down the potential4 ,by the employment of machines1 or1 generally speaking1 of any mechanical apparatus1 but low frequencies can be reached2 recourse must1 therefore1 be had to some other means4 ,the discharge of a condenser affords us a means of obtaining frequencies by far higher than are obtainable mechanically1 and ,i have accordingly employed condensers in the experiments to the above end4 ,when the terminals of a high tension induction coil1 ,fig4 #abf1 are connected to a ,leyden jar1 and the latter is discharging disruptively into a circuit1 we may look upon the arc playing between the knobs as being a source of alternating1 or generally speaking1 undulating currents1 and then we have to deal with the familiar system of a generator of such currents1 a circuit connected to it1 and a condenser bridging the circuit4 ,the condenser in such case is a veritable transformer1 and since the frequency is excessive1 almost any ratio in the strength of the currents in both the branches may be obtained4 ,in reality the analogy is not quite complete1 for in the disruptive discharge we have most generally a fundamental instantaneous variation of comparatively low frequency1 and a superimposed harmonic vibration1 and the laws governing the flow of currents are not the same for both4 ,in converting in this manner1 the ratio of conversion should not be too great1 for the loss in the arc between the knobs increases with the square of the current1 and if the jar be discharged through very thick and short conductors1 with the view of obtaining a very rapid oscillation1 a very considerable portion of the energy stored is lost4 ,on the other hand1 too small ratios are not practicable for many obvious reasons4 ,as the converted currents flow in a practically closed circuit1 the electrostatic effects are necessarily small1 and ,i therefore convert them into currents or effects of the required character4 ,i have effected such conversions in several ways4 ,the preferred plan of connections is illustrated in ,fig4 #abg4 ,the manner of operating renders it easy to obtain by means of a small and inexpensive apparatus enormous differences of potential which have been usually obtained by means of large and expensive coils4 ,for this it is only necessary to take an ordinary small coil1 adjust to it a condenser and discharging circuit1 forming the primary of an auxiliary small coil1 and convert upward4 ,as the inductive effect of the primary currents is excessively great1 the second coil need have comparatively but very few turns4 ,by properly adjusting the elements1 remarkable results may be secured4 ,in endeavoring to obtain the required electrostatic effects in this manner1 ,i have1 as might be expected1 encountered many difficulties which ,i have been gradually overcoming1 but ,i am not as yet prepared to dwell upon my experiences in this direction4 ,i believe that the disruptive discharge of a condenser will play an important part in the future1 for it offers vast possibilities1 not only in the way of producing light in a more efficient manner and in the line indicated by theory1 but also in many other respects4 ,illustration3 ,,fig4 #abf4 ,for years the efforts of inventors have been directed towards obtaining electrical energy from heat by means of the thermopile4 ,it might seem invidious to remark that but few know what is the real trouble with the thermopile4 ,it is not the inefficiency or small output--though these are great drawbacks--but the fact that the thermopile has its phylloxera1 that is1 that by constant use it is deteriorated1 which has thus far prevented its introduction on an industrial scale4 ,now that all modern research seems to point with certainty to the use of electricity of excessively high tension1 the question must present itself to many whether it is not possible to obtain in a practicable manner this form of energy from heat4 ,we have been used to look upon an electrostatic machine as a plaything1 and somehow we couple with it the idea of the inefficient and impractical4 ,but now we must think differently1 for now we know that everywhere we have to deal with the same forces1 and that it is a mere question of inventing proper methods or apparatus for rendering them available4 ,in the present systems of electrical distribution1 the employment of the iron with its wonderful magnetic properties allows us to reduce considerably the size of the apparatus2 but1 in spite of this1 it is still very cumbersome4 ,the more we progress in the study of electric and magnetic phenomena1 the more we become convinced that the present methods will be short-lived4 ,for the production of light1 at least1 such heavy machinery would seem to be unnecessary4 ,the energy required is very small1 and if light can be obtained as efficiently as1 theoretically1 it appears possible1 the apparatus need have but a very small output4 ,there being a strong probability that the illuminating methods of the future will involve the use of very high potentials1 it seems very desirable to perfect a contrivance capable of converting the energy of heat into energy of the requisite form4 ,nothing to speak of has been done towards this end1 for the thought that electricity of some #ej1jjj or #ajj1jjj volts pressure or more1 even if obtained1 would be unavailable for practical purposes1 has deterred inventors from working in this direction4 ,illustration3 ,,fig4 #abg4 ,in ,fig4 #abf a plan of connections is shown for converting currents of high1 into currents of low1 tension by means of the disruptive discharge of a condenser4 ,this plan has been used by me frequently for operating a few incandescent lamps required in the laboratory4 ,some difficulties have been encountered in the arc of the discharge which ,i have been able to overcome to a great extent2 besides this1 and the adjustment necessary for the proper working1 no other difficulties have been met with1 and it was easy to operate ordinary lamps1 and even motors1 in this manner4 ,the line being connected to the ground1 all the wires could be handled with perfect impunity1 no matter how high the potential at the terminals of the condenser4 ,in these experiments a high tension induction coil1 operated from a battery or from an alternate current machine1 was employed to charge the condenser2 but the induction coil might be replaced by an apparatus of a different kind1 capable of giving electricity of such high tension4 ,in this manner1 direct or alternating currents may be converted1 and in both cases the current-impulses may be of any desired frequency4 ,when the currents charging the condenser are of the same direction1 and it is desired that the converted currents should also be of one direction1 the resistance of the discharging circuit should1 of course1 be so chosen that there are no oscillations4 ,illustration3 ,,fig4 #abh4 ,in operating devices on the above plan ,i have observed curious phenomena of impedance which are of interest4 ,for instance if a thick copper bar be bent1 as indicated in ,fig4 #abh1 and shunted by ordinary incandescent lamps1 then1 by passing the discharge between the knobs1 the lamps may be brought to incandescence although they are short-circuited4 ,when a large induction coil is employed it is easy to obtain nodes on the bar1 which are rendered evident by the different degree of brilliancy of the lamps1 as shown roughly in ,fig4 #abh4 ,the nodes are never clearly defined1 but they are simply maxima and minima of potentials along the bar4 ,this is probably due to the irregularity of the arc between the knobs4 ,in general when the above-described plan of conversion from high to low tension is used1 the behavior of the disruptive discharge may be closely studied4 ,the nodes may also be investigated by means of an ordinary ,cardew voltmeter which should be well insulated4 ,geissler tubes may also be lighted across the points of the bent bar2 in this case1 of course1 it is better to employ smaller capacities4 ,i have found it practicable to light up in this manner a lamp1 and even a ,geissler tube1 shunted by a short1 heavy block of metal1 and this result seems at first very curious4 ,in fact1 the thicker the copper bar in ,fig4 #abh1 the better it is for the success of the experiments1 as they appear more striking4 ,when lamps with long slender filaments are used it will be often noted that the filaments are from time to time violently vibrated1 the vibration being smallest at the nodal points4 ,this vibration seems to be due to an electrostatic action between the filament and the glass of the bulb4 ,illustration3 ,,fig4 #abi4 ,in some of the above experiments it is preferable to use special lamps having a straight filament as shown in ,fig4 #abi4 ,when such a lamp is used a still more curious phenomenon than those described may be observed4 ,the lamp may be placed across the copper bar and lighted1 and by using somewhat larger capacities1 or1 in other words1 smaller frequencies or smaller impulsive impedances1 the filament may be brought to any desired degree of incandescence4 ,but when the impedance is increased1 a point is reached when comparatively little current passes through the carbon1 and most of it through the rarefied gas2 or perhaps it may be more correct to state that the current divides nearly evenly through both1 in spite of the enormous difference in the resistance1 and this would be true unless the gas and the filament behave differently4 ,it is then noted that the whole bulb is brilliantly illuminated1 and the ends of the leading-in wires become incandescent and often throw off sparks in consequence of the violent bombardment1 but the carbon filament remains dark4 ,this is illustrated in ,fig4 #abi4 ,instead of the filament a single wire extending through the whole bulb may be used1 and in this case the phenomenon would seem to be still more interesting4 ,from the above experiment it will be evident1 that when ordinary lamps are operated by the converted currents1 those should be preferably taken in which the platinum wires are far apart1 and the frequencies used should not be too great1 else the discharge will occur at the ends of the filament or in the base of the lamp between the leading-in wires1 and the lamp might then be damaged4 ,in presenting to you these results of my investigation on the subject under consideration1 ,i have paid only a passing notice to facts upon which ,i could have dwelt at length1 and among many observations ,i have selected only those which ,i thought most likely to interest you4 ,the field is wide and completely unexplored1 and at every step a new truth is gleaned1 a novel fact observed4 ,how far the results here borne out are capable of practical applications will be decided in the future4 ,as regards the production of light1 some results already reached are encouraging and make me confident in asserting that the practical solution of the problem lies in the direction ,i have endeavored to indicate4 ,still1 whatever may be the immediate outcome of these experiments ,i am hopeful that they will only prove a step in further development towards the ideal and final perfection4 ,the possibilities which are opened by modern research are so vast that even the most reserved must feel sanguine of the future4 ,eminent scientists consider the problem of utilizing one kind of radiation without the others a rational one4 ,in an apparatus designed for the production of light by conversion from any form of energy into that of light1 such a result can never be reached1 for no matter what the process of producing the required vibrations1 be it electrical1 chemical or any other1 it will not be possible to obtain the higher light vibrations without going through the lower heat vibrations4 ,it is the problem of imparting to a body a certain velocity without passing through all lower velocities4 ,but there is a possibility of obtaining energy not only in the form of light1 but motive power1 and energy of any other form1 in some more direct way from the medium4 ,the time will be when this will be accomplished1 and the time has come when one may utter such words before an enlightened audience without being considered a visionary4 ,we are whirling through endless space with an inconceivable speed1 all around us everything is spinning1 everything is moving1 everywhere is energy4 ,there must be some way of availing ourselves of this energy more directly4 ,then1 with the light obtained from the medium1 with the power derived from it1 with every form of energy obtained without effort1 from the store forever inexhaustible1 humanity will advance with giant strides4 ,the mere contemplation of these magnificent possibilities expands our minds1 strengthens our hopes and fills our hearts with supreme delight4 ,,chapter ,,xxvii4 ,,experiments ,,with ,,alternate ,,currents ,,of ,,high ,,potential ,,and ,,high ,,frequency4#b #b ,lecture delivered before the ,institution of ,electrical ,engineers1 ,london1 ,february1 #ahib4 ,i cannot find words to express how deeply ,i feel the honor of addressing some of the foremost thinkers of the present time1 and so many able scientific men1 engineers and electricians1 of the country greatest in scientific achievements4 ,the results which ,i have the honor to present before such a gathering ,i cannot call my own4 ,there are among you not a few who can lay better claim than myself on any feature of merit which this work may contain4 ,i need not mention many names which are world-known--names of those among you who are recognized as the leaders in this enchanting science2 but one1 at least1 ,i must mention--a name which could not be omitted in a demonstration of this kind4 ,it is a name associated with the most beautiful invention ever made3 it is ,crookes6 ,when ,i was at college1 a good while ago1 ,i read1 in a translation 7for then ,i was not familiar with your magnificent language71 the description of his experiments on radiant matter4 ,i read it only once in my life--that time--yet every detail about that charming work ,i can remember to this day4 ,few are the books1 let me say1 which can make such an impression upon the mind of a student4 ,but if1 on the present occasion1 ,i mention this name as one of many your ,institution can boast of1 it is because ,i have more than one reason to do so4 ,for what ,i have to tell you and to show you this evening concerns1 in a large measure1 that same vague world which ,professor ,crookes has so ably explored2 and1 more than this1 when ,i trace back the mental process which led me to these advances--which even by myself cannot be considered trifling1 since they are so appreciated by you--,i believe that their real origin1 that which started me to work in this direction1 and brought me to them1 after a long period of constant thought1 was that fascinating little book which ,i read many years ago4 ,and now that ,i have made a feeble effort to express my homage and acknowledge my indebtedness to him and others among you1 ,i will make a second effort1 which ,i hope you will not find so feeble as the first1 to entertain you4 ,give me leave to introduce the subject in a few words4 ,a short time ago ,i had the honor to bring before our ,american ,institute of ,electrical ,engineers some results then arrived at by me in a novel line of work4 ,i need not assure you that the many evidences which ,i have received that ,english scientific men and engineers were interested in this work have been for me a great reward and encouragement4 ,i will not dwell upon the experiments already described1 except with the view of completing1 or more clearly expressing1 some ideas advanced by me before1 and also with the view of rendering the study here presented self-contained1 and my remarks on the subject of this evening's lecture consistent4 ,this investigation1 then1 it goes without saying1 deals with alternating currents1 and to be more precise1 with alternating currents of high potential and high frequency4 ,just in how much a very high frequency is essential for the production of the results presented is a question which1 even with my present experience1 would embarrass me to answer4 ,some of the experiments may be performed with low frequencies2 but very high frequencies are desirable1 not only on account of the many effects secured by their use1 but also as a convenient means of obtaining1 in the induction apparatus employed1 the high potentials1 which in their turn are necessary to the demonstration of most of the experiments here contemplated4 ,of the various branches of electrical investigation1 perhaps the most interesting and the most immediately promising is that dealing with alternating currents4 ,the progress in this branch of applied science has been so great in recent years that it justifies the most sanguine hopes4 ,hardly have we become familiar with one fact1 when novel experiences are met and new avenues of research are opened4 ,even at this hour possibilities not dreamed of before are1 by the use of these currents1 partly realized4 ,as in nature all is ebb and tide1 all is wave motion1 so it seems that in all branches of industry alternating currents--electric wave motion--will have the sway4 ,one reason1 perhaps1 why this branch of science is being so rapidly developed is to be found in the interest which is attached to its experimental study4 ,we wind a simple ring of iron with coils2 we establish the connections to the generator1 and with wonder and delight we note the effects of strange forces which we bring into play1 which allow us to transform1 to transmit and direct energy at will4 ,we arrange the circuits properly1 and we see the mass of iron and wires behave as though it were endowed with life1 spinning a heavy armature1 through invisible connections1 with great speed and power--with the energy possibly conveyed from a great distance4 ,we observe how the energy of an alternating current traversing the wire manifests itself--not so much in the wire as in the surrounding space--in the most surprising manner1 taking the forms of heat1 light1 mechanical energy1 and1 most surprising of all1 even chemical affinity4 ,all these observations fascinate us1 and fill us with an intense desire to know more about the nature of these phenomena4 ,each day we go to our work in the hope of discovering1--in the hope that some one1 no matter who1 may find a solution of one of the pending great problems1--and each succeeding day we return to our task with renewed ardor2 and even if we are unsuccessful1 our work has not been in vain1 for in these strivings1 in these efforts1 we have found hours of untold pleasure1 and we have directed our energies to the benefit of mankind4 ,we may take--at random1 if you choose--any of the many experiments which may be performed with alternating currents2 a few of which only1 and by no means the most striking1 form the subject of this evening's demonstration2 they are all equally interesting1 equally inciting to thought4 ,here is a simple glass tube from which the air has been partially exhausted4 ,i take hold of it2 ,i bring my body in contact with a wire conveying alternating currents of high potential1 and the tube in my hand is brilliantly lighted4 ,in whatever position ,i may put it1 wherever ,i move it in space1 as far as ,i can reach1 its soft1 pleasing light persists with undiminished brightness4 ,here is an exhausted bulb suspended from a single wire4 ,standing on an insulated support1 ,i grasp it1 and a platinum button mounted in it is brought to vivid incandescence4 ,here1 attached to a leading wire1 is another bulb1 which1 as ,i touch its metallic socket1 is filled with magnificent colors of phosphorescent light4 ,here still another1 which by my fingers' touch casts a shadow--the ,crookes shadow--of the stem inside of it4 ,here1 again1 insulated as ,i stand on this platform1 ,i bring my body in contact with one of the terminals of the secondary of this induction coil--with the end of a wire many miles long--and you see streams of light break forth from its distant end1 which is set in violent vibration4 ,here1 once more1 ,i attach these two plates of wire gauze to the terminals of the coil2 ,i set them a distance apart1 and ,i set the coil to work4 ,you may see a small spark pass between the plates4 ,i insert a thick plate of one of the best dielectrics between them1 and instead of rendering altogether impossible1 as we are used to expect1 ,i aid the passage of the discharge1 which1 as ,i insert the plate1 merely changes in appearance and assumes the form of luminous streams4 ,is there1 ,i ask1 can there be1 a more interesting study than that of alternating currents8 ,in all these investigations1 in all these experiments1 which are so very1 very interesting1 for many years past--ever since the greatest experimenter who lectured in this hall discovered its principle--we have had a steady companion1 an appliance familiar to every one1 a plaything once1 a thing of momentous importance now--the induction coil4 ,there is no dearer appliance to the electrician4 ,from the ablest among you1 ,i dare say1 down to the inexperienced student1 to your lecturer1 we all have passed many delightful hours in experimenting with the induction coil4 ,we have watched its play1 and thought and pondered over the beautiful phenomena which it disclosed to our ravished eyes4 ,so well known is this apparatus1 so familiar are these phenomena to every one1 that my courage nearly fails me when ,i think that ,i have ventured to address so able an audience1 that ,i have ventured to entertain you with that same old subject4 ,here in reality is the same apparatus1 and here are the same phenomena1 only the apparatus is operated somewhat differently1 the phenomena are presented in a different aspect4 ,some of the results we find as expected1 others surprise us1 but all captivate our attention1 for in scientific investigation each novel result achieved may be the centre of a new departure1 each novel fact learned may lead to important developments4 ,usually in operating an induction coil we have set up a vibration of moderate frequency in the primary1 either by means of an interrupter or break1 or by the use of an alternator4 ,earlier ,english investigators1 to mention only ,spottiswoode and ,j4 ,e4 ,h4 ,gordon1 have used a rapid break in connection with the coil4 ,our knowledge and experience of to-day enables us to see clearly why these coils under the conditions of the test did not disclose any remarkable phenomena1 and why able experimenters failed to perceive many of the curious effects which have since been observed4 ,in the experiments such as performed this evening1 we operate the coil either from a specially constructed alternator capable of giving many thousands of reversals of current per second1 or1 by disruptively discharging a condenser through the primary1 we set up a vibration in the secondary circuit of a frequency of many hundred thousand or millions per second1 if we so desire2 and in using either of these means we enter a field as yet unexplored4 ,it is impossible to pursue an investigation in any novel line without finally making some interesting observation or learning some useful fact4 ,that this statement is applicable to the subject of this lecture the many curious and unexpected phenomena which we observe afford a convincing proof4 ,by way of illustration1 take for instance the most obvious phenomena1 those of the discharge of the induction coil4 ,here is a coil which is operated by currents vibrating with extreme rapidity1 obtained by disruptively discharging a ,leyden jar4 ,it would not surprise a student were the lecturer to say that the secondary of this coil consists of a small length of comparatively stout wire2 it would not surprise him were the lecturer to state that1 in spite of this1 the coil is capable of giving any potential which the best insulation of the turns is able to withstand2 but although he may be prepared1 and even be indifferent as to the anticipated result1 yet the aspect of the discharge of the coil will surprise and interest him4 ,every one is familiar with the discharge of an ordinary coil2 it need not be reproduced here4 ,but1 by way of contrast1 here is a form of discharge of a coil1 the primary current of which is vibrating several hundred thousand times per second4 ,the discharge of an ordinary coil appears as a simple line or band of light4 ,the discharge of this coil appears in the form of powerful brushes and luminous streams issuing from all points of the two straight wires attached to the terminals of the secondary4 7,fig4 #acj47 ,illustration3 ,,fig4 #acj4 ,illustration3 ,,fig4 #aca4 ,now compare this phenomenon which you have just witnessed with the discharge of a ,holtz or ,wimshurst machine--that other interesting appliance so dear to the experimenter4 ,what a difference there is between these phenomena6 ,and yet1 had ,i made the necessary arrangements--which could have been made easily1 were it not that they would interfere with other experiments--,i could have produced with this coil sparks which1 had ,i the coil hidden from your view and only two knobs exposed1 even the keenest observer among you would find it difficult1 if not impossible1 to distinguish from those of an influence or friction machine4 ,this may be done in many ways--for instance1 by operating the induction coil which charges the condenser from an alternating-current machine of very low frequency1 and preferably adjusting the discharge circuit so that there are no oscillations set up in it4 ,we then obtain in the secondary circuit1 if the knobs are of the required size and properly set1 a more or less rapid succession of sparks of great intensity and small quantity1 which possess the same brilliancy1 and are accompanied by the same sharp crackling sound1 as those obtained from a friction or influence machine4 ,another way is to pass through two primary circuits1 having a common secondary1 two currents of a slightly different period1 which produce in the secondary circuit sparks occurring at comparatively long intervals4 ,but1 even with the means at hand this evening1 ,i may succeed in imitating the spark of a ,holtz machine4 ,for this purpose ,i establish between the terminals of the coil which charges the condenser a long1 unsteady arc1 which is periodically interrupted by the upward current of air produced by it4 ,to increase the current of air ,i place on each side of the arc1 and close to it1 a large plate of mica4 ,the condenser charged from this coil discharges into the primary circuit of a second coil through a small air gap1 which is necessary to produce a sudden rush of current through the primary4 ,the scheme of connections in the present experiment is indicated in ,fig4 #aca4 ,g is an ordinarily constructed alternator1 supplying the primary ,p of an induction coil1 the secondary ,s of which charges the condensers or jars ,c ,c4 ,the terminals of the secondary are connected to the inside coatings of the jars1 the outer coatings being connected to the ends of the primary p p of a second induction coil4 ,this primary p p has a small air gap a b4 ,the secondary s of this coil is provided with knobs or spheres ,k ,k of the proper size and set at a distance suitable for the experiment4 ,a long arc is established between the terminals ,a ,b of the first induction coil4 ,m ,m are the mica plates4 ,each time the arc is broken between ,a and ,b the jars are quickly charged and discharged through the primary p p1 producing a snapping spark between the knobs ,k ,k4 ,upon the arc forming between ,a and ,b the potential falls1 and the jars cannot be charged to such high potential as to break through the air gap a b until the arc is again broken by the draught4 ,in this manner sudden impulses1 at long intervals1 are produced in the primary p p1 which in the secondary s give a corresponding number of impulses of great intensity4 ,if the secondary knobs or spheres1 ,k ,k1 are of the proper size1 the sparks show much resemblance to those of a ,holtz machine4 ,but these two effects1 which to the eye appear so very different1 are only two of the many discharge phenomena4 ,we only need to change the conditions of the test1 and again we make other observations of interest4 ,when1 instead of operating the induction coil as in the last two experiments1 we operate it from a high frequency alternator1 as in the next experiment1 a systematic study of the phenomena is rendered much more easy4 ,in such case1 in varying the strength and frequency of the currents through the primary1 we may observe five distinct forms of discharge1 which ,i have described in my former paper on the subject before the ,american ,institute of ,electrical ,engineers1 ,may #bj1 #ahia4 ,it would take too much time1 and it would lead us too far from the subject presented this evening1 to reproduce all these forms1 but it seems to me desirable to show you one of them4 ,it is a brush discharge1 which is interesting in more than one respect4 ,viewed from a near position it resembles much a jet of gas escaping under great pressure4 ,we know that the phenomenon is due to the agitation of the molecules near the terminal1 and we anticipate that some heat must be developed by the impact of the molecules against the terminal or against each other4 ,indeed1 we find that the brush is hot1 and only a little thought leads us to the conclusion that1 could we but reach sufficiently high frequencies1 we could produce a brush which would give intense light and heat1 and which would resemble in every particular an ordinary flame1 save1 perhaps1 that both phenomena might not be due to the same agent--save1 perhaps1 that chemical affinity might not be electrical in its nature4 ,as the production of heat and light is here due to the impact of the molecules1 or atoms of air1 or something else besides1 and1 as we can augment the energy simply by raising the potential1 we might1 even with frequencies obtained from a dynamo machine1 intensify the action to such a degree as to bring the terminal to melting heat4 ,but with such low frequencies we would have to deal always with something of the nature of an electric current4 ,if ,i approach a conducting object to the brush1 a thin little spark passes1 yet1 even with the frequencies used this evening1 the tendency to spark is not very great4 ,so1 for instance1 if ,i hold a metallic sphere at some distance above the terminal1 you may see the whole space between the terminal and sphere illuminated by the streams without the spark passing2 and with the much higher frequencies obtainable by the disruptive discharge of a condenser1 were it not for the sudden impulses1 which are comparatively few in number1 sparking would not occur even at very small distances4 ,however1 with incomparably higher frequencies1 which we may yet find means to produce efficiently1 and provided that electric impulses of such high frequencies could be transmitted through a conductor1 the electrical characteristics of the brush discharge would completely vanish--no spark would pass1 no shock would be felt--yet we would still have to deal with an electric phenomenon1 but in the broad1 modern interpretation of the word4 ,in my first paper1 before referred to1 ,i have pointed out the curious properties of the brush1 and described the best manner of producing it1 but ,i have thought it worth while to endeavor to express myself more clearly in regard to this phenomenon1 because of its absorbing interest4 ,when a coil is operated with currents of very high frequency1 beautiful brush effects may be produced1 even if the coil be of comparatively small dimensions4 ,the experimenter may vary them in many ways1 and1 if it were for nothing else1 they afford a pleasing sight4 ,what adds to their interest is that they may be produced with one single terminal as well as with two--in fact1 often better with one than with two4 ,but of all the discharge phenomena observed1 the most pleasing to the eye1 and the most instructive1 are those observed with a coil which is operated by means of the disruptive discharge of a condenser4 ,the power of the brushes1 the abundance of the sparks1 when the conditions are patiently adjusted1 is often amazing4 ,with even a very small coil1 if it be so well insulated as to stand a difference of potential of several thousand volts per turn1 the sparks may be so abundant that the whole coil may appear a complete mass of fire4 ,curiously enough the sparks1 when the terminals of the coil are set at a considerable distance1 seem to dart in every possible direction as though the terminals were perfectly independent of each other4 ,as the sparks would soon destroy the insulation1 it is necessary to prevent them4 ,this is best done by immersing the coil in a good liquid insulator1 such as boiled-out oil4 ,immersion in a liquid may be considered almost an absolute necessity for the continued and successful working of such a coil4 ,it is1 of course1 out of the question1 in an experimental lecture1 with only a few minutes at disposal for the performance of each experiment1 to show these discharge phenomena to advantage1 as1 to produce each phenomenon at its best1 a very careful adjustment is required4 ,but even if imperfectly produced1 as they are likely to be this evening1 they are sufficiently striking to interest an intelligent audience4 ,before showing some of these curious effects ,i must1 for the sake of completeness1 give a short description of the coil and other apparatus used in the experiments with the disruptive discharge this evening4 ,illustration3 ,,fig4 #acb4 ,it is contained in a box ,b 7,fig4 #acb7 of thick boards of hard wood1 covered on the outside with a zinc sheet ,z1 which is carefully soldered all around4 ,it might be advisable1 in a strictly scientific investigation1 when accuracy is of great importance1 to do away with the metal cover1 as it might introduce many errors1 principally on account of its complex action upon the coil1 as a condenser of very small capacity and as an electrostatic and electromagnetic screen4 ,when the coil is used for such experiments as are here contemplated1 the employment of the metal cover offers some practical advantages1 but these are not of sufficient importance to be dwelt upon4 ,the coil should be placed symmetrically to the metal cover1 and the space between should1 of course1 not be too small1 certainly not less than1 say1 five centimetres1 but much more if possible2 especially the two sides of the zinc box1 which are at right angles to the axis of the coil1 should be sufficiently remote from the latter1 as otherwise they might impair its action and be a source of loss4 ,the coil consists of two spools of hard rubber ,r ,r1 held apart at a distance of #aj centimetres by bolts ,c and nuts n1 likewise of hard rubber4 ,each spool comprises a tube ,t of approximately #h centimetres inside diameter1 and #c millimetres thick1 upon which are screwed two flanges ,f ,f1 #bd centimetres square1 the space between the flanges being about #c centimetres4 ,the secondary1 ,s ,s1 of the best gutta percha-covered wire1 has #bf layers1 #aj turns in each1 giving for each half a total of #bfj turns4 ,the two halves are wound oppositely and connected in series1 the connection between both being made over the primary4 ,this disposition1 besides being convenient1 has the advantage that when the coil is well balanced--that is1 when both of its terminals ,t#a1 ,t#a1 are connected to bodies or devices of equal capacity--there is not much danger of breaking through to the primary1 and the insulation between the primary and the secondary need not be thick4 ,in using the coil it is advisable to attach to both terminals devices of nearly equal capacity1 as1 when the capacity of the terminals is not equal1 sparks will be apt to pass to the primary4 ,to avoid this1 the middle point of the secondary may be connected to the primary1 but this is not always practicable4 ,the primary ,p ,p is wound in two parts1 and oppositely1 upon a wooden spool w1 and the four ends are led out of the oil through hard rubber tubes t t4 ,the ends of the secondary ,t#a ,t#a1 are also led out of the oil through rubber tubes t#a t#a of great thickness4 ,the primary and secondary layers are insulated by cotton cloth1 the thickness of the insulation1 of course1 bearing some proportion to the difference of potential between the turns of the different layers4 ,each half of the primary has four layers1 #bd turns in each1 this giving a total of #if turns4 ,when both the parts are connected in series1 this gives a ratio of conversion of about #a3b4g1 and with the primaries in multiple1 #a3e4d2 but in operating with very rapidly alternating currents this ratio does not convey even an approximate idea of the ratio of the ,e4 ,m4 ,f's4 in the primary and secondary circuits4 ,the coil is held in position in the oil on wooden supports1 there being about #e centimetres thickness of oil all round4 ,where the oil is not specially needed1 the space is filled with pieces of wood1 and for this purpose principally the wooden box ,b surrounding the whole is used4 ,the construction here shown is1 of course1 not the best on general principles1 but ,i believe it is a good and convenient one for the production of effects in which an excessive potential and a very small current are needed4 ,in connection with the coil ,i use either the ordinary form of discharger or a modified form4 ,in the former ,i have introduced two changes which secure some advantages1 and which are obvious4 ,if they are mentioned1 it is only in the hope that some experimenter may find them of use4 ,one of the changes is that the adjustable knobs ,a and ,b 7,fig4 #acc71 of the discharger are held in jaws of brass1 ,j ,j1 by spring pressure1 this allowing of turning them successively into different positions1 and so doing away with the tedious process of frequent polishing up4 ,illustration3 ,,fig4 #acc4 ,the other change consists in the employment of a strong electromagnet ,n ,s1 which is placed with its axis at right angles to the line joining the knobs ,a and ,b1 and produces a strong magnetic field between them4 ,the pole pieces of the magnet are movable and properly formed so as to protrude between the brass knobs1 in order to make the field as intense as possible2 but to prevent the discharge from jumping to the magnet the pole pieces are protected by a layer of mica1 ,m ,m1 of sufficient thickness2 s#a s#a and s#b s#b are screws for fastening the wires4 ,on each side one of the screws is for large and the other for small wires4 ,l ,l are screws for fixing in position the rods ,r ,r1 which support the knobs4 ,in another arrangement with the magnet ,i take the discharge between the rounded pole pieces themselves1 which in such case are insulated and preferably provided with polished brass caps4 ,the employment of an intense magnetic field is of advantage principally when the induction coil or transformer which charges the condenser is operated by currents of very low frequency4 ,in such a case the number of the fundamental discharges between the knobs may be so small as to render the currents produced in the secondary unsuitable for many experiments4 ,the intense magnetic field then serves to blow out the arc between the knobs as soon as it is formed1 and the fundamental discharges occur in quicker succession4 ,illustration3 ,,fig4 #acd4 ,instead of the magnet1 a draught or blast of air may be employed with some advantage4 ,in this case the arc is preferably established between the knobs ,a ,b1 in ,fig4 #aca 7the knobs a b being generally joined1 or entirely done away with71 as in this disposition the arc is long and unsteady1 and is easily affected by the draught4 ,when a magnet is employed to break the arc1 it is better to choose the connection indicated diagrammatically in ,fig4 #acd1 as in this case the currents forming the arc are much more powerful1 and the magnetic field exercises a greater influence4 ,the use of the magnet permits1 however1 of the arc being replaced by a vacuum tube1 but ,i have encountered great difficulties in working with an exhausted tube4 ,the other form of discharger used in these and similar experiments is indicated in ,figs4 #ace and #acf4 ,it consists of a number of brass pieces c c 7,fig4 #ace71 each of which comprises a spherical middle portion m with an extension e below--which is merely used to fasten the piece in a lathe when polishing up the discharging surface--and a column above1 which consists of a knurled flange f surmounted by a threaded stem l carrying a nut n1 by means of which a wire is fastened to the column4 ,the flange f conveniently serves for holding the brass piece when fastening the wire1 and also for turning it in any position when it becomes necessary to present a fresh discharging surface4 ,two stout strips of hard rubber ,r ,r1 with planed grooves g g 7,fig4 #acf7 to fit the middle portion of the pieces c c1 serve to clamp the latter and hold them firmly in position by means of two bolts ,c ,c 7of which only one is shown7 passing through the ends of the strips4 ,illustration3 ,,fig4 #ace4 ,illustration3 ,,fig4 #acf4 ,in the use of this kind of discharger ,i have found three principal advantages over the ordinary form4 ,first1 the dielectric strength of a given total width of air space is greater when a great many small air gaps are used instead of one1 which permits of working with a smaller length of air gap1 and that means smaller loss and less deterioration of the metal2 secondly1 by reason of splitting the arc up into smaller arcs1 the polished surfaces are made to last much longer2 and1 thirdly1 the apparatus affords some gauge in the experiments4 ,i usually set the pieces by putting between them sheets of uniform thickness at a certain very small distance which is known from the experiments of ,sir ,william ,thomson to require a certain electromotive force to be bridged by the spark4 ,it should1 of course1 be remembered that the sparking distance is much diminished as the frequency is increased4 ,by taking any number of spaces the experimenter has a rough idea of the electromotive force1 and he finds it easier to repeat an experiment1 as he has not the trouble of setting the knobs again and again4 ,with this kind of discharger ,i have been able to maintain an oscillating motion without any spark being visible with the naked eye between the knobs1 and they would not show a very appreciable rise in temperature4 ,this form of discharge also lends itself to many arrangements of condensers and circuits which are often very convenient and time-saving4 ,i have used it preferably in a disposition similar to that indicated in ,fig4 #aca1 when the currents forming the arc are small4 ,i may here mention that ,i have also used dischargers with single or multiple air gaps1 in which the discharge surfaces were rotated with great speed4 ,no particular advantage was1 however1 gained by this method1 except in cases where the currents from the condenser were large and the keeping cool of the surfaces was necessary1 and in cases when1 the discharge not being oscillating of itself1 the arc as soon as established was broken by the air current1 thus starting the vibration at intervals in rapid succession4 ,i have also used mechanical interrupters in many ways4 ,to avoid the difficulties with frictional contacts1 the preferred plan adopted was to establish the arc and rotate through it at great speed a rim of mica provided with many holes and fastened to a steel plate4 ,it is understood1 of course1 that the employment of a magnet1 air current1 or other interrupter1 produces no effect worth noticing1 unless the self-induction1 capacity and resistance are so related that there are oscillations set up upon each interruption4 ,i will now endeavor to show you some of the most noteworthy of these discharge phenomena4 ,i have stretched across the room two ordinary cotton covered wires1 each about seven metres in length4 ,they are supported on insulating cords at a distance of about thirty centimetres4 ,i attach now to each of the terminals of the coil one of the wires1 and set the coil in action4 ,upon turning the lights off in the room you see the wires strongly illuminated by the streams issuing abundantly from their whole surface in spite of the cotton covering1 which may even be very thick4 ,when the experiment is performed under good conditions1 the light from the wires is sufficiently intense to allow distinguishing the objects in a room4 ,to produce the best result it is1 of course1 necessary to adjust carefully the capacity of the jars1 the arc between the knobs and the length of the wires4 ,my experience is that calculation of the length of the wires leads1 in such case1 to no result whatever4 ,the experimenter will do best to take the wires at the start very long1 and then adjust by cutting off first long pieces1 and then smaller and smaller ones as he approaches the right length4 ,a convenient way is to use an oil condenser of very small capacity1 consisting of two small adjustable metal plates1 in connection with this and similar experiments4 ,in such case ,i take wires rather short and at the beginning set the condenser plates at maximum distance4 ,if the streams from the wires increase by approach of the plates1 the length of the wires is about right2 if they diminish1 the wires are too long for that frequency and potential4 ,when a condenser is used in connection with experiments with such a coil1 it should be an oil condenser by all means1 as in using an air condenser considerable energy might be wasted4 ,the wires leading to the plates in the oil should be very thin1 heavily coated with some insulating compound1 and provided with a conducting covering--this preferably extending under the surface of the oil4 ,the conducting cover should not be too near the terminals1 or ends1 of the wire1 as a spark would be apt to jump from the wire to it4 ,the conducting coating is used to diminish the air losses1 in virtue of its action as an electrostatic screen4 ,as to the size of the vessel containing the oil1 and the size of the plates1 the experimenter gains at once an idea from a rough trial4 ,the size of the plates in oil is1 however1 calculable1 as the dielectric losses are very small4 ,in the preceding experiment it is of considerable interest to know what relation the quantity of the light emitted bears to the frequency and potential of the electric impulses4 ,my opinion is that the heat as well as light effects produced should be proportionate1 under otherwise equal conditions of test1 to the product of frequency and square of potential1 but the experimental verification of the law1 whatever it may be1 would be exceedingly difficult4 ,one thing is certain1 at any rate1 and that is1 that in augmenting the potential and frequency we rapidly intensify the streams2 and1 though it may be very sanguine1 it is surely not altogether hopeless to expect that we may succeed in producing a practical illuminant on these lines4 ,we would then be simply using burners or flames1 in which there would be no chemical process1 no consumption of material1 but merely a transfer of energy1 and which would1 in all probability1 emit more light and less heat than ordinary flames4 ,illustration3 ,,fig4 #acg4 ,the luminous intensity of the streams is1 of course1 considerably increased when they are focused upon a small surface4 ,this may be shown by the following experiment3 ,i attach to one of the terminals of the coil a wire w 7,fig4 #acg71 bent in a circle of about #cj centimetres in diameter1 and to the other terminal ,i fasten a small brass sphere s1 the surface of the wire being preferably equal to the surface of the sphere1 and the centre of the latter being in a line at right angles to the plane of the wire circle and passing through its centre4 ,when the discharge is established under proper conditions1 a luminous hollow cone is formed1 and in the dark one-half of the brass sphere is strongly illuminated1 as shown in the cut4 ,by some artifice or other it is easy to concentrate the streams upon small surfaces and to produce very strong light effects4 ,two thin wires may thus be rendered intensely luminous4 ,in order to intensify the streams the wires should be very thin and short2 but as in this case their capacity would be generally too small for the coil--at least for such a one as the present--it is necessary to augment the capacity to the required value1 while1 at the same time1 the surface of the wires remains very small4 ,this may be done in many ways4 ,illustration3 ,,fig4 #ach4 ,here1 for instance1 ,i have two plates1 ,r ,r1 of hard rubber 7,fig4 #ach71 upon which ,i have glued two very thin wires w w1 so as to form a name4 ,the wires may be bare or covered with the best insulation--it is immaterial for the success of the experiment4 ,well insulated wires1 if anything1 are preferable4 ,on the back of each plate1 indicated by the shaded portion1 is a tinfoil coating t t4 ,the plates are placed in line at a sufficient distance to prevent a spark passing from one wire to the other4 ,the two tinfoil coatings ,i have joined by a conductor ,c1 and the two wires ,i presently connect to the terminals of the coil4 ,it is now easy1 by varying the strength and frequency of the currents through the primary1 to find a point at which the capacity of the system is best suited to the conditions1 and the wires become so strongly luminous that1 when the light in the room is turned off the name formed by them appears in brilliant letters4 ,it is perhaps preferable to perform this experiment with a coil operated from an alternator of high frequency1 as then1 owing to the harmonic rise and fall1 the streams are very uniform1 though they are less abundant than when produced with such a coil as the present one4 ,this experiment1 however1 may be performed with low frequencies1 but much less satisfactorily4 ,illustration3 ,,fig4 #aci4 ,when two wires1 attached to the terminals of the coil1 are set at the proper distance1 the streams between them may be so intense as to produce a continuous luminous sheet4 ,to show this phenomenon ,i have here two circles1 ,c and c 7,fig4 #aci71 of rather stout wire1 one being about #hj centimetres and the other #cj centimetres in diameter4 ,to each of the terminals of the coil ,i attach one of the circles4 ,the supporting wires are so bent that the circles may be placed in the same plane1 coinciding as nearly as possible4 ,when the light in the room is turned off and the coil set to work1 you see the whole space between the wires uniformly filled with streams1 forming a luminous disc1 which could be seen from a considerable distance1 such is the intensity of the streams4 ,the outer circle could have been much larger than the present one2 in fact1 with this coil ,i have used much larger circles1 and ,i have been able to produce a strongly luminous sheet1 covering an area of more than one square metre1 which is a remarkable effect with this very small coil4 ,to avoid uncertainty1 the circle has been taken smaller1 and the area is now about #j4dc square metre4 ,the frequency of the vibration1 and the quickness of succession of the sparks between the knobs1 affect to a marked degree the appearance of the streams4 ,when the frequency is very low1 the air gives way in more or less the same manner1 as by a steady difference of potential1 and the streams consist of distinct threads1 generally mingled with thin sparks1 which probably correspond to the successive discharges occurring between the knobs4 ,but when the frequency is extremely high1 and the arc of the discharge produces a very loud and smooth sound--showing both that oscillation takes place and that the sparks succeed each other with great rapidity--then the luminous streams formed are perfectly uniform4 ,to reach this result very small coils and jars of small capacity should be used4 ,i take two tubes of thick ,bohemian glass1 about #e centimetres in diameter and #bj centimetres long4 ,in each of the tubes ,i slip a primary of very thick copper wire4 ,on the top of each tube ,i wind a secondary of much thinner gutta-percha covered wire4 ,the two secondaries ,i connect in series1 the primaries preferably in multiple arc4 ,the tubes are then placed in a large glass vessel1 at a distance of #aj to #ae centimetres from each other1 on insulating supports1 and the vessel is filled with boiled-out oil1 the oil reaching about an inch above the tubes4 ,the free ends of the secondary are lifted out of the coil and placed parallel to each other at a distance of about ten centimetres4 ,the ends which are scraped should be dipped in the oil4 ,two four-pint jars joined in series may be used to discharge through the primary4 ,when the necessary adjustments in the length and distance of the wires above the oil and in the arc of discharge are made1 a luminous sheet is produced between the wires which is perfectly smooth and textureless1 like the ordinary discharge through a moderately exhausted tube4 ,i have purposely dwelt upon this apparently insignificant experiment4 ,in trials of this kind the experimenter arrives at the startling conclusion that1 to pass ordinary luminous discharges through gases1 no particular degree of exhaustion is needed1 but that the gas may be at ordinary or even greater pressure4 ,to accomplish this1 a very high frequency is essential2 a high potential is likewise required1 but this is merely an incidental necessity4 ,these experiments teach us that1 in endeavoring to discover novel methods of producing light by the agitation of atoms1 or molecules1 of a gas1 we need not limit our research to the vacuum tube1 but may look forward quite seriously to the possibility of obtaining the light effects without the use of any vessel whatever1 with air at ordinary pressure4 ,such discharges of very high frequency1 which render luminous the air at ordinary pressures1 we have probably occasion often to witness in ,nature4 ,i have no doubt that if1 as many believe1 the aurora borealis is produced by sudden cosmic disturbances1 such as eruptions at the sun's surface1 which set the electrostatic charge of the earth in an extremely rapid vibration1 the red glow observed is not confined to the upper rarefied strata of the air1 but the discharge traverses1 by reason of its very high frequency1 also the dense atmosphere in the form of a glow1 such as we ordinarily produce in a slightly exhausted tube4 ,if the frequency were very low1 or even more so1 if the charge were not at all vibrating1 the dense air would break down as in a lightning discharge4 ,indications of such breaking down of the lower dense strata of the air have been repeatedly observed at the occurrence of this marvelous phenomenon2 but if it does occur1 it can only be attributed to the fundamental disturbances1 which are few in number1 for the vibration produced by them would be far too rapid to allow a disruptive break4 ,it is the original and irregular impulses which affect the instruments2 the superimposed vibrations probably pass unnoticed4 ,when an ordinary low frequency discharge is passed through moderately rarefied air1 the air assumes a purplish hue4 ,if by some means or other we increase the intensity of the molecular1 or atomic1 vibration1 the gas changes to a white color4 ,a similar change occurs at ordinary pressures with electric impulses of very high frequency4 ,if the molecules of the air around a wire are moderately agitated1 the brush formed is reddish or violet2 if the vibration is rendered sufficiently intense1 the streams become white4 ,we may accomplish this in various ways4 ,in the experiment before shown with the two wires across the room1 ,i have endeavored to secure the result by pushing to a high value both the frequency and potential2 in the experiment with the thin wires glued on the rubber plate ,i have concentrated the action upon a very small surface--in other words1 ,i have worked with a great electric density4 ,illustration3 ,,fig4 #adj4 ,a most curious form of discharge is observed with such a coil when the frequency and potential are pushed to the extreme limit4 ,to perform the experiment1 every part of the coil should be heavily insulated1 and only two small spheres--or1 better still1 two sharp-edged metal discs 7d d1 ,fig4 #adj7 of no more than a few centimetres in diameter--should be exposed to the air4 ,the coil here used is immersed in oil1 and the ends of the secondary reaching out of the oil are covered with an air-tight cover of hard rubber of great thickness4 ,all cracks1 if there are any1 should be carefully stopped up1 so that the brush discharge cannot form anywhere except on the small spheres or plates which are exposed to the air4 ,in this case1 since there are no large plates or other bodies of capacity attached to the terminals1 the coil is capable of an extremely rapid vibration4 ,the potential may be raised by increasing1 as far as the experimenter judges proper1 the rate of change of the primary current4 ,with a coil not widely differing from the present1 it is best to connect the two primaries in multiple arc2 but if the secondary should have a much greater number of turns the primaries should preferably be used in series1 as otherwise the vibration might be too fast for the secondary4 ,it occurs under these conditions that misty white streams break forth from the edges of the discs and spread out phantom-like into space4 ,with this coil1 when fairly well produced1 they are about #be to #cj centimetres long4 ,when the hand is held against them no sensation is produced1 and a spark1 causing a shock1 jumps from the terminal only upon the hand being brought much nearer4 ,if the oscillation of the primary current is rendered intermittent by some means or other1 there is a corresponding throbbing of the streams1 and now the hand or other conducting object may be brought in still greater proximity to the terminal without a spark being caused to jump4 ,among the many beautiful phenomena which may be produced with such a coil1 ,i have here selected only those which appear to possess some features of novelty1 and lead us to some conclusions of interest4 ,one will not find it at all difficult to produce in the laboratory1 by means of it1 many other phenomena which appeal to the eye even more than these here shown1 but present no particular feature of novelty4 ,early experimenters describe the display of sparks produced by an ordinary large induction coil upon an insulating plate separating the terminals4 ,quite recently ,siemens performed some experiments in which fine effects were obtained1 which were seen by many with interest4 ,no doubt large coils1 even if operated with currents of low frequencies1 are capable of producing beautiful effects4 ,but the largest coil ever made could not1 by far1 equal the magnificent display of streams and sparks obtained from such a disruptive discharge coil when properly adjusted4 ,to give an idea1 a coil such as the present one will cover easily a plate of one metre in diameter completely with the streams4 ,the best way to perform such experiments is to take a very thin rubber or a glass plate and glue on one side of it a narrow ring of tinfoil of very large diameter1 and on the other a circular washer1 the centre of the latter coinciding with that of the ring1 and the surfaces of both being preferably equal1 so as to keep the coil well balanced4 ,the washer and ring should be connected to the terminals by heavily insulated thin wires4 ,it is easy in observing the effect of the capacity to produce a sheet of uniform streams1 or a fine network of thin silvery threads1 or a mass of loud brilliant sparks1 which completely cover the plate4 ,since ,i have advanced the idea of the conversion by means of the disruptive discharge1 in my paper before the ,american ,institute of ,electrical ,engineers at the beginning of the past year1 the interest excited in it has been considerable4 ,it affords us a means for producing any potentials by the aid of inexpensive coils operated from ordinary systems of distribution1 and--what is perhaps more appreciated--it enables us to convert currents of any frequency into currents of any other lower or higher frequency4 ,but its chief value will perhaps be found in the help which it will afford us in the investigations of the phenomena of phosphorescence1 which a disruptive discharge coil is capable of exciting in innumerable cases where ordinary coils1 even the largest1 would utterly fail4 ,considering its probable uses for many practical purposes1 and its possible introduction into laboratories for scientific research1 a few additional remarks as to the construction of such a coil will perhaps not be found superfluous4 ,it is1 of course1 absolutely necessary to employ in such a coil wires provided with the best insulation4 ,good coils may be produced by employing wires covered with several layers of cotton1 boiling the coil a long time in pure wax1 and cooling under moderate pressure4 ,the advantage of such a coil is that it can be easily handled1 but it cannot probably give as satisfactory results as a coil immersed in pure oil4 ,besides1 it seems that the presence of a large body of wax affects the coil disadvantageously1 whereas this does not seem to be the case with oil4 ,perhaps it is because the dielectric losses in the liquid are smaller4 ,i have tried at first silk and cotton covered wires with oil immersions1 but ,i have been gradually led to use gutta-percha covered wires1 which proved most satisfactory4 ,gutta-percha insulation adds1 of course1 to the capacity of the coil1 and this1 especially if the coil be large1 is a great disadvantage when extreme frequencies are desired2 but1 on the other hand1 gutta-percha will withstand much more than an equal thickness of oil1 and this advantage should be secured at any price4 ,once the coil has been immersed1 it should never be taken out of the oil for more than a few hours1 else the gutta-percha will crack up and the coil will not be worth half as much as before4 ,gutta-percha is probably slowly attacked by the oil1 but after an immersion of eight to nine months ,i have found no ill effects4 ,i have obtained two kinds of gutta-percha wire known in commerce3 in one the insulation sticks tightly to the metal1 in the other it does not4 ,unless a special method is followed to expel all air1 it is much safer to use the first kind4 ,i wind the coil within an oil tank so that all interstices are filled up with the oil4 ,between the layers ,i use cloth boiled out thoroughly in oil1 calculating the thickness according to the difference of potential between the turns4 ,there seems not to be a very great difference whatever kind of oil is used2 ,i use paraffine or linseed oil4 ,to exclude more perfectly the air1 an excellent way to proceed1 and easily practicable with small coils1 is the following3 ,construct a box of hardwood of very thick boards which have been for a long time boiled in oil4 ,the boards should be so joined as to safely withstand the external air pressure4 ,the coil being placed and fastened in position within the box1 the latter is closed with a strong lid1 and covered with closely fitting metal sheets1 the joints of which are soldered very carefully4 ,on the top two small holes are drilled1 passing through the metal sheet and the wood1 and in these holes two small glass tubes are inserted and the joints made air-tight4 ,one of the tubes is connected to a vacuum pump1 and the other with a vessel containing a sufficient quantity of boiled-out oil4 ,the latter tube has a very small hole at the bottom1 and is provided with a stopcock4 ,when a fairly good vacuum has been obtained1 the stopcock is opened and the oil slowly fed in4 ,proceeding in this manner1 it is impossible that any big bubbles1 which are the principal danger1 should remain between the turns4 ,the air is most completely excluded1 probably better than by boiling out1 which1 however1 when gutta-percha coated wires are used1 is not practicable4 ,for the primaries ,i use ordinary line wire with a thick cotton coating4 ,strands of very thin insulated wires properly interlaced would1 of course1 be the best to employ for the primaries1 but they are not to be had4 ,in an experimental coil the size of the wires is not of great importance4 ,in the coil here used the primary is ,no4 #ab and the secondary ,no4 #bd ,brown ,sharpe gauge wire2 but the sections may be varied considerably4 ,it would only imply different adjustments2 the results aimed at would not be materially affected4 ,i have dwelt at some length upon the various forms of brush discharge because1 in studying them1 we not only observe phenomena which please our eye1 but also afford us food for thought1 and lead us to conclusions of practical importance4 ,in the use of alternating currents of very high tension1 too much precaution cannot be taken to prevent the brush discharge4 ,in a main conveying such currents1 in an induction coil or transformer1 or in a condenser1 the brush discharge is a source of great danger to the insulation4 ,in a condenser1 especially1 the gaseous matter must be most carefully expelled1 for in it the charged surfaces are near each other1 and if the potentials are high1 just as sure as a weight will fall if let go1 so the insulation will give way if a single gaseous bubble of some size be present1 whereas1 if all gaseous matter were carefully excluded1 the condenser would safely withstand a much higher difference of potential4 ,a main conveying alternating currents of very high tension may be injured merely by a blow hole or small crack in the insulation1 the more so as a blowhole is apt to contain gas at low pressure2 and as it appears almost impossible to completely obviate such little imperfections1 ,i am led to believe that in our future distribution of electrical energy by currents of very high tension1 liquid insulation will be used4 ,the cost is a great drawback1 but if we employ an oil as an insulator the distribution of electrical energy with something like #ajj1jjj volts1 and even more1 becomes1 at least with higher frequencies1 so easy that it could be hardly called an engineering feat4 ,with oil insulation and alternate current motors1 transmissions of power can be affected with safety and upon an industrial basis at distances of as much as a thousand miles4 ,a peculiar property of oils1 and liquid insulation in general1 when subjected to rapidly changing electric stresses1 is to disperse any gaseous bubbles which may be present1 and diffuse them through its mass1 generally long before any injurious break can occur4 ,this feature may be easily observed with an ordinary induction coil by taking the primary out1 plugging up the end of the tube upon which the secondary is wound1 and filling it with some fairly transparent insulator1 such as paraffine oil4 ,a primary of a diameter something like six millimetres smaller than the inside of the tube may be inserted in the oil4 ,when the coil is set to work one may see1 looking from the top through the oil1 many luminous points--air bubbles which are caught by inserting the primary1 and which are rendered luminous in consequence of the violent bombardment4 ,the occluded air1 by its impact against the oil1 heats it2 the oil begins to circulate1 carrying some of the air along with it1 until the bubbles are dispersed and the luminous points disappear4 ,in this manner1 unless large bubbles are occluded in such way that circulation is rendered impossible1 a damaging break is averted1 the only effect being a moderate warming up of the oil4 ,if1 instead of the liquid1 a solid insulation1 no matter how thick1 were used1 a breaking through and injury of the apparatus would be inevitable4 ,the exclusion of gaseous matter from any apparatus in which the dielectric is subjected to more or less rapidly changing electric forces is1 however1 not only desirable in order to avoid a possible injury of the apparatus1 but also on account of economy4 ,in a condenser1 for instance1 as long as only a solid or only a liquid dielectric is used1 the loss is small2 but if a gas under ordinary or small pressure be present the loss may be very great4 ,whatever the nature of the force acting in the dielectric may be1 it seems that in a solid or liquid the molecular displacement produced by the force is small3 hence the product of force and displacement is insignificant1 unless the force be very great2 but in a gas the displacement1 and therefore this product1 is considerable2 the molecules are free to move1 they reach high speeds1 and the energy of their impact is lost in heat or otherwise4 ,if the gas be strongly compressed1 the displacement due to the force is made smaller1 and the losses are reduced4 ,in most of the succeeding experiments ,i prefer1 chiefly on account of the regular and positive action1 to employ the alternator before referred to4 ,this is one of the several machines constructed by me for the purpose of these investigations4 ,it has #chd pole projections1 and is capable of giving currents of a frequency of about #aj1jjj per second4 ,this machine has been illustrated and briefly described in my first paper before the ,american ,institute of ,electrical ,engineers1 ,may #bjth1 #ahia1 to which ,i have already referred4 ,a more detailed description1 sufficient to enable any engineer to build a similar machine1 will be found in several electrical journals of that period4 ,the induction coils operated from the machine are rather small1 containing from #e1jjj to #ae1jjj turns in the secondary4 ,they are immersed in boiled-out linseed oil1 contained in wooden boxes covered with zinc sheet4 ,i have found it advantageous to reverse the usual position of the wires1 and to wind1 in these coils1 the primaries on the top2 thus allowing the use of a much larger primary1 which1 of course1 reduces the danger of overheating and increases the output of the coil4 ,i make the primary on each side at least one centimetre shorter than the secondary1 to prevent the breaking through on the ends1 which would surely occur unless the insulation on the top of the secondary be very thick1 and this1 of course1 would be disadvantageous4 ,when the primary is made movable1 which is necessary in some experiments1 and many times convenient for the purposes of adjustment1 ,i cover the secondary with wax1 and turn it off in a lathe to a diameter slightly smaller than the inside of the primary coil4 ,the latter ,i provide with a handle reaching out of the oil1 which serves to shift it in any position along the secondary4 ,i will now venture to make1 in regard to the general manipulation of induction coils1 a few observations bearing upon points which have not been fully appreciated in earlier experiments with such coils1 and are even now often overlooked4 ,the secondary of the coil possesses usually such a high self-induction that the current through the wire is inappreciable1 and may be so even when the terminals are joined by a conductor of small resistance4 ,if capacity is added to the terminals1 the self-induction is counteracted1 and a stronger current is made to flow through the secondary1 though its terminals are insulated from each other4 ,to one entirely unacquainted with the properties of alternating currents nothing will look more puzzling4 ,this feature was illustrated in the experiment performed at the beginning with the top plates of wire gauze attached to the terminals and the rubber plate4 ,when the plates of wire gauze were close together1 and a small arc passed between them1 the arc prevented a strong current from passing through the secondary1 because it did away with the capacity on the terminals2 when the rubber plate was inserted between1 the capacity of the condenser formed counteracted the self-induction of the secondary1 a stronger current passed now1 the coil performed more work1 and the discharge was by far more powerful4 ,the first thing1 then1 in operating the induction coil is to combine capacity with the secondary to overcome the self-induction4 ,if the frequencies and potentials are very high1 gaseous matter should be carefully kept away from the charged surfaces4 ,if ,leyden jars are used1 they should be immersed in oil1 as otherwise considerable dissipation may occur if the jars are greatly strained4 ,when high frequencies are used1 it is of equal importance to combine a condenser with the primary4 ,one may use a condenser connected to the ends of the primary or to the terminals of the alternator1 but the latter is not to be recommended1 as the machine might be injured4 ,the best way is undoubtedly to use the condenser in series with the primary and with the alternator1 and to adjust its capacity so as to annul the self-induction of both the latter4 ,the condenser should be adjustable by very small steps1 and for a finer adjustment a small oil condenser with movable plates may be used conveniently4 ,i think it best at this juncture to bring before you a phenomenon1 observed by me some time ago1 which to the purely scientific investigator may perhaps appear more interesting than any of the results which ,i have the privilege to present to you this evening4 ,it may be quite properly ranked among the brush phenomena--in fact1 it is a brush1 formed at1 or near1 a single terminal in high vacuum4 ,illustration3 ,,fig4 #ada4 ,illustration3 ,,fig4 #adb4 ,in bulbs provided with a conducting terminal1 though it be of aluminum1 the brush has but an ephemeral existence1 and cannot1 unfortunately1 be indefinitely preserved in its most sensitive state1 even in a bulb devoid of any conducting electrode4 ,in studying the phenomenon1 by all means a bulb having no leading-in wire should be used4 ,i have found it best to use bulbs constructed as indicated in ,figs4 #ada and #adb4 ,in ,fig4 #ada the bulb comprises an incandescent lamp globe ,l1 in the neck of which is sealed a barometer tube b1 the end of which is blown out to form a small sphere s4 ,this sphere should be sealed as closely as possible in the centre of the large globe4 ,before sealing1 a thin tube t1 of aluminum sheet1 may be slipped in the barometer tube1 but it is not important to employ it4 ,the small hollow sphere s is filled with some conducting powder1 and a wire w is cemented in the neck for the purpose of connecting the conducting powder with the generator4 ,the construction shown in ,fig4 #adb was chosen in order to remove from the brush any conducting body which might possibly affect it4 ,the bulb consists in this case of a lamp globe ,l1 which has a neck n1 provided with a tube b and small sphere s1 sealed to it1 so that two entirely independent compartments are formed1 as indicated in the drawing4 ,when the bulb is in use the neck n is provided with a tinfoil coating1 which is connected to the generator and acts inductively upon the moderately rarefied and highly conducted gas inclosed in the neck4 ,from there the current passes through the tube b into the small sphere s1 to act by induction upon the gas contained in the globe ,l4 ,it is of advantage to make the tube t very thick1 the hole through it very small1 and to blow the sphere s very thin4 ,it is of the greatest importance that the sphere s be placed in the centre of the globe ,l4 ,illustration3 ,,fig4 #adc4 ,figs4 #adc1 #add and #ade indicate different forms1 or stages1 of the brush4 ,fig4 #adc shows the brush as it first appears in a bulb provided with a conducting terminal2 but1 as in such a bulb it very soon disappears--often after a few minutes--,i will confine myself to the description of the phenomenon as seen in a bulb without conducting electrode4 ,it is observed under the following conditions3 ,when the globe ,l 7,figs4 #ada and #adb7 is exhausted to a very high degree1 generally the bulb is not excited upon connecting the wire w 7,fig4 #ada7 or the tinfoil coating of the bulb 7,fig4 #adb7 to the terminal of the induction coil4 ,to excite it1 it is usually sufficient to grasp the globe ,l with the hand4 ,an intense phosphorescence then spreads at first over the globe1 but soon gives place to a white1 misty light4 ,shortly afterward one may notice that the luminosity is unevenly distributed in the globe1 and after passing the current for some time the bulb appears as in ,fig4 #add4 ,from this stage the phenomenon will gradually pass to that indicated in ,fig4 #ade1 after some minutes1 hours1 days or weeks1 according as the bulb is worked4 ,warming the bulb or increasing the potential hastens the transit4 ,illustration3 ,,fig4 #add4 ,illustration3 ,,fig4 #ade4 ,when the brush assumes the form indicated in ,fig4 #ade1 it may be brought to a state of extreme sensitiveness to electrostatic and magnetic influence4 ,the bulb hanging straight down from a wire1 and all objects being remote from it1 the approach of the observer at a few paces from the bulb will cause the brush to fly to the opposite side1 and if he walks around the bulb it will always keep on the opposite side4 ,it may begin to spin around the terminal long before it reaches that sensitive stage4 ,when it begins to turn around1 principally1 but also before1 it is affected by a magnet1 and at a certain stage it is susceptible to magnetic influence to an astonishing degree4 ,a small permanent magnet1 with its poles at a distance of no more than two centimetres1 will affect it visibly at a distance of two metres1 slowing down or accelerating the rotation according to how it is held relatively to the brush4 ,i think ,i have observed that at the stage when it is most sensitive to magnetic1 it is not most sensitive to electrostatic1 influence4 ,my explanation is1 that the electrostatic attraction between the brush and the glass of the bulb1 which retards the rotation1 grows much quicker than the magnetic influence when the intensity of the stream is increased4 ,when the bulb hangs with the globe ,l down1 the rotation is always clockwise4 ,in the southern hemisphere it would occur in the opposite direction and on the equator the brush should not turn at all4 ,the rotation may be reversed by a magnet kept at some distance4 ,the brush rotates best1 seemingly1 when it is at right angles to the lines of force of the earth4 ,it very likely rotates1 when at its maximum speed1 in synchronism with the alternations1 say1 #aj1jjj times a second4 ,the rotation can be slowed down or accelerated by the approach or receding of the observer1 or any conducting body1 but it cannot be reversed by putting the bulb in any position4 ,when it is in the state of the highest sensitiveness and the potential or frequency be varied1 the sensitiveness is rapidly diminished4 ,changing either of these but little will generally stop the rotation4 ,the sensitiveness is likewise affected by the variations of temperature4 ,to attain great sensitiveness it is necessary to have the small sphere s in the centre of the globe ,l1 as otherwise the electrostatic action of the glass of the globe will tend to stop the rotation4 ,the sphere s should be small and of uniform thickness2 any dissymmetry of course has the effect to diminish the sensitiveness4 ,the fact that the brush rotates in a definite direction in a permanent magnetic field seems to show that in alternating currents of very high frequency the positive and negative impulses are not equal1 but that one always preponderates over the other4 ,of course1 this rotation in one direction may be due to the action of the two elements of the same current upon each other1 or to the action of the field produced by one of the elements upon the other1 as in a series motor1 without necessarily one impulse being stronger than the other4 ,the fact that the brush turns1 as far as ,i could observe1 in any position1 would speak for this view4 ,in such case it would turn at any point of the earth's surface4 ,but1 on the other hand1 it is then hard to explain why a permanent magnet should reverse the rotation1 and one must assume the preponderance of impulses of one kind4 ,as to the causes of the formation of the brush or stream1 ,i think it is due to the electrostatic action of the globe and the dissymmetry of the parts4 ,if the small bulb s and the globe ,l were perfect concentric spheres1 and the glass throughout of the same thickness and quality1 ,i think the brush would not form1 as the tendency to pass would be equal on all sides4 ,that the formation of the stream is due to an irregularity is apparent from the fact that it has the tendency to remain in one position1 and rotation occurs most generally only when it is brought out of this position by electrostatic or magnetic influence4 ,when in an extremely sensitive state it rests in one position1 most curious experiments may be performed with it4 ,for instance1 the experimenter may1 by selecting a proper position1 approach the hand at a certain considerable distance to the bulb1 and he may cause the brush to pass off by merely stiffening the muscles of the arm4 ,when it begins to rotate slowly1 and the hands are held at a proper distance1 it is impossible to make even the slightest motion without producing a visible effect upon the brush4 ,a metal plate connected to the other terminal of the coil affects it at a great distance1 slowing down the rotation often to one turn a second4 ,i am firmly convinced that such a brush1 when we learn how to produce it properly1 will prove a valuable aid in the investigation of the nature of the forces acting in an electrostatic or magnetic field4 ,if there is any motion which is measurable going on in the space1 such a brush ought to reveal it4 ,it is1 so to speak1 a beam of light1 frictionless1 devoid of inertia4 ,i think that it may find practical applications in telegraphy4 ,with such a brush it would be possible to send dispatches across the ,atlantic1 for instance1 with any speed1 since its sensitiveness may be so great that the slightest changes will affect it4 ,if it were possible to make the stream more intense and very narrow1 its deflections could be easily photographed4 ,i have been interested to find whether there is a rotation of the stream itself1 or whether there is simply a stress traveling around the bulb4 ,for this purpose ,i mounted a light mica fan so that its vanes were in the path of the brush4 ,if the stream itself was rotating the fan would be spun around4 ,i could produce no distinct rotation of the fan1 although ,i tried the experiment repeatedly2 but as the fan exerted a noticeable influence on the stream1 and the apparent rotation of the latter was1 in this case1 never quite satisfactory1 the experiment did not appear to be conclusive4 ,i have been unable to produce the phenomenon with the disruptive discharge coil1 although every other of these phenomena can be well produced by it--many1 in fact1 much better than with coils operated from an alternator4 ,it may be possible to produce the brush by impulses of one direction1 or even by a steady potential1 in which case it would be still more sensitive to magnetic influence4 ,in operating an induction coil with rapidly alternating currents1 we realize with astonishment1 for the first time1 the great importance of the relation of capacity1 self-induction and frequency as regards the general results4 ,the effects of capacity are the most striking1 for in these experiments1 since the self-induction and frequency both are high1 the critical capacity is very small1 and need be but slightly varied to produce a very considerable change4 ,the experimenter may bring his body in contact with the terminals of the secondary of the coil1 or attach to one or both terminals insulated bodies of very small bulk1 such as bulbs1 and he may produce a considerable rise or fall of potential1 and greatly affect the flow of the current through the primary4 ,in the experiment before shown1 in which a brush appears at a wire attached to one terminal1 and the wire is vibrated when the experimenter brings his insulated body in contact with the other terminal of the coil1 the sudden rise of potential was made evident4 ,i may show you the behavior of the coil in another manner which possesses a feature of some interest4 ,i have here a little light fan of aluminum sheet1 fastened to a needle and arranged to rotate freely in a metal piece screwed to one of the terminals of the coil4 ,when the coil is set to work1 the molecules of the air are rhythmically attracted and repelled4 ,as the force with which they are repelled is greater than that with which they are attracted1 it results that there is a repulsion exerted on the surfaces of the fan4 ,if the fan were made simply of a metal sheet1 the repulsion would be equal on the opposite sides1 and would produce no effect4 ,but if one of the opposing surfaces is screened1 or if1 generally speaking1 the bombardment on this side is weakened in some way or other1 there remains the repulsion exerted upon the other1 and the fan is set in rotation4 ,the screening is best effected by fastening upon one of the opposing sides of the fan insulated conducting coatings1 or1 if the fan is made in the shape of an ordinary propeller screw1 by fastening on one side1 and close to it1 an insulated metal plate4 ,the static screen may1 however1 be omitted1 and simply a thickness of insulating material fastened to one of the sides of the fan4 ,to show the behavior of the coil1 the fan may be placed upon the terminal and it will readily rotate when the coil is operated by currents of very high frequency4 ,with a steady potential1 of course1 and even with alternating currents of very low frequency1 it would not turn1 because of the very slow exchange of air and1 consequently1 smaller bombardment2 but in the latter case it might turn if the potential were excessive4 ,with a pin wheel1 quite the opposite rule holds good2 it rotates best with a steady potential1 and the effort is the smaller the higher the frequency4 ,now1 it is very easy to adjust the conditions so that the potential is normally not sufficient to turn the fan1 but that by connecting the other terminal of the coil with an insulated body it rises to a much greater value1 so as to rotate the fan1 and it is likewise possible to stop the rotation by connecting to the terminal a body of different size1 thereby diminishing the potential4 ,instead of using the fan in this experiment1 we may use the electric radiometer with similar effect4 ,but in this case it will be found that the vanes will rotate only at high exhaustion or at ordinary pressures2 they will not rotate at moderate pressures1 when the air is highly conducting4 ,this curious observation was made conjointly by ,professor ,crookes and myself4 ,i attribute the result to the high conductivity of the air1 the molecules of which then do not act as independent carriers of electric charges1 but act all together as a single conducting body4 ,in such case1 of course1 if there is any repulsion at all of the molecules from the vanes1 it must be very small4 ,it is possible1 however1 that the result is in part due to the fact that the greater part of the discharge passes from the leading-in wire through the highly conducting gas1 instead of passing off from the conducting vanes4 ,in trying the preceding experiment with the electric radiometer the potential should not exceed a certain limit1 as then the electrostatic attraction between the vanes and the glass of the bulb may be so great as to stop the rotation4 ,a most curious feature of alternate currents of high frequencies and potentials is that they enable us to perform many experiments by the use of one wire only4 ,in many respects this feature is of great interest4 ,in a type of alternate current motor invented by me some years ago ,i produced rotation by inducing1 by means of a single alternating current passed through a motor circuit1 in the mass or other circuits of the motor1 secondary currents1 which1 jointly with the primary or inducing current1 created a moving field of force4 ,a simple but crude form of such a motor is obtained by winding upon an iron core a primary1 and close to it a secondary coil1 joining the ends of the latter and placing a freely movable metal disc within the influence of the field produced by both4 ,the iron core is employed for obvious reasons1 but it is not essential to the operation4 ,to improve the motor1 the iron core is made to encircle the armature4 ,again to improve1 the secondary coil is made to partly overlap the primary1 so that it cannot free itself from a strong inductive action of the latter1 repel its lines as it may4 ,once more to improve1 the proper difference of phase is obtained between the primary and secondary currents by a condenser1 self-induction1 resistance or equivalent windings4 ,i had discovered1 however1 that rotation is produced by means of a single coil and core2 my explanation of the phenomenon1 and leading thought in trying the experiment1 being that there must be a true time lag in the magnetization of the core4 ,i remember the pleasure ,i had when1 in the writings of ,professor ,ayrton1 which came later to my hand1 ,i found the idea of the time lag advocated4 ,whether there is a true time lag1 or whether the retardation is due to eddy currents circulating in minute paths1 must remain an open question1 but the fact is that a coil wound upon an iron core and traversed by an alternating current creates a moving field of force1 capable of setting an armature in rotation4 ,it is of some interest1 in conjunction with the historical ,arago experiment1 to mention that in lag or phase motors ,i have produced rotation in the opposite direction to the moving field1 which means that in that experiment the magnet may not rotate1 or may even rotate in the opposite direction to the moving disc4 ,here1 then1 is a motor 7diagrammatically illustrated in ,fig4 #adf71 comprising a coil and iron core1 and a freely movable copper disc in proximity to the latter4 ,illustration3 ,,fig4 #adf4 ,to demonstrate a novel and interesting feature1 ,i have1 for a reason which ,i will explain1 selected this type of motor4 ,when the ends of the coil are connected to the terminals of an alternator the disc is set in rotation4 ,but it is not this experiment1 now well known1 which ,i desire to perform4 ,what ,i wish to show you is that this motor rotates with one single connection between it and the generator2 that is to say1 one terminal of the motor is connected to one terminal of the generator--in this case the secondary of a high-tension induction coil--the other terminals of motor and generator being insulated in space4 ,to produce rotation it is generally 7but not absolutely7 necessary to connect the free end of the motor coil to an insulated body of some size4 ,the experimenter's body is more than sufficient4 ,if he touches the free terminal with an object held in the hand1 a current passes through the coil and the copper disc is set in rotation4 ,if an exhausted tube is put in series with the coil1 the tube lights brilliantly1 showing the passage of a strong current4 ,instead of the experimenter's body1 a small metal sheet suspended on a cord may be used with the same result4 ,in this case the plate acts as a condenser in series with the coil4 ,it counteracts the self-induction of the latter and allows a strong current to pass4 ,in such a combination1 the greater the self-induction of the coil the smaller need be the plate1 and this means that a lower frequency1 or eventually a lower potential1 is required to operate the motor4 ,a single coil wound upon a core has a high self-induction2 for this reason1 principally1 this type of motor was chosen to perform the experiment4 ,were a secondary closed coil wound upon the core1 it would tend to diminish the self-induction1 and then it would be necessary to employ a much higher frequency and potential4 ,neither would be advisable1 for a higher potential would endanger the insulation of the small primary coil1 and a higher frequency would result in a materially diminished torque4 ,it should be remarked that when such a motor with a closed secondary is used1 it is not at all easy to obtain rotation with excessive frequencies1 as the secondary cuts off almost completely the lines of the primary--and this1 of course1 the more1 the higher the frequency--and allows the passage of but a minute current4 ,in such a case1 unless the secondary is closed through a condenser1 it is almost essential1 in order to produce rotation1 to make the primary and secondary coils overlap each other more or less4 ,but there is an additional feature of interest about this motor1 namely1 it is not necessary to have even a single connection between the motor and generator1 except1 perhaps1 through the ground2 for not only is an insulated plate capable of giving off energy into space1 but it is likewise capable of deriving it from an alternating electrostatic field1 though in the latter case the available energy is much smaller4 ,in this instance one of the motor terminals is connected to the insulated plate or body located within the alternating electrostatic field1 and the other terminal preferably to the ground4 ,it is quite possible1 however1 that such no wire motors1 as they might be called1 could be operated by conduction through the rarefied air at considerable distances4 ,alternate currents1 especially of high frequencies1 pass with astonishing freedom through even slightly rarefied gases4 ,the upper strata of the air are rarefied4 ,to reach a number of miles out into space requires the overcoming of difficulties of a merely mechanical nature4 ,there is no doubt that with the enormous potentials obtainable by the use of high frequencies and oil insulation1 luminous discharges might be passed through many miles of rarefied air1 and that1 by thus directing the energy of many hundreds or thousands of horse-power1 motors or lamps might be operated at considerable distances from stationary sources4 ,but such schemes are mentioned merely as possibilities4 ,we shall have no need to transmit power in this way4 ,we shall have no need to transmit power at all4 ,ere many generations pass1 our machinery will be driven by a power obtainable at any point of the universe4 ,this idea is not novel4 ,men have been led to it long ago by instinct or reason4 ,it has been expressed in many ways1 and in many places1 in the history of old and new4 ,we find it in the delightful myth of ,antheus1 who derives power from the earth2 we find it among the subtle speculations of one of your splendid mathematicians1 and in many hints and statements of thinkers of the present time4 ,throughout space there is energy4 ,is this energy static or kinetic8 ,if static our hopes are in vain2 if kinetic--and this we know it is1 for certain--then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature4 ,of all1 living or dead1 ,crookes came nearest to doing it4 ,his radiometer will turn in the light of day and in the darkness of the night2 it will turn everywhere where there is heat1 and heat is everywhere4 ,but1 unfortunately1 this beautiful little machine1 while it goes down to posterity as the most interesting1 must likewise be put on record as the most inefficient machine ever invented6 ,the preceding experiment is only one of many equally interesting experiments which may be performed by the use of only one wire with alternations of high potential and frequency4 ,we may connect an insulated line to a source of such currents1 we may pass an inappreciable current over the line1 and on any point of the same we are able to obtain a heavy current1 capable of fusing a thick copper wire4 ,or we may1 by the help of some artifice1 decompose a solution in any electrolytic cell by connecting only one pole of the cell to the line or source of energy4 ,or we may1 by attaching to the line1 or only bringing into its vicinity1 light up an incandescent lamp1 an exhausted tube1 or a phosphorescent bulb4 ,however impracticable this plan of working may appear in many cases1 it certainly seems practicable1 and even recommendable1 in the production of light4 ,a perfected lamp would require but little energy1 and if wires were used at all we ought to be able to supply that energy without a return wire4 ,it is now a fact that a body may be rendered incandescent or phosphorescent by bringing it either in single contact or merely in the vicinity of a source of electric impulses of the proper character1 and that in this manner a quantity of light sufficient to afford a practical illuminant may be produced4 ,it is1 therefore1 to say the least1 worth while to attempt to determine the best conditions and to invent the best appliances for attaining this object4 ,some experiences have already been gained in this direction1 and ,i will dwell on them briefly1 in the hope that they might prove useful4 ,the heating of a conducting body inclosed in a bulb1 and connected to a source of rapidly alternating electric impulses1 is dependent on so many things of a different nature1 that it would be difficult to give a generally applicable rule under which the maximum heating occurs4 ,as regards the size of the vessel1 ,i have lately found that at ordinary or only slightly differing atmospheric pressures1 when air is a good insulator1 and hence practically the same amount of energy by a certain potential and frequency is given off from the body1 whether the bulb be small or large1 the body is brought to a higher temperature if enclosed in a small bulb1 because of the better confinement of heat in this case4 ,at lower pressures1 when air becomes more or less conducting1 or if the air be sufficiently warmed to become conducting1 the body is rendered more intensely incandescent in a large bulb1 obviously because1 under otherwise equal conditions of test1 more energy may be given off from the body when the bulb is large4 ,at very high degrees of exhaustion1 when the matter in the bulb becomes radiant1 a large bulb has still an advantage1 but a comparatively slight one1 over the small bulb4 ,finally1 at excessively high degrees of exhaustion1 which cannot be reached except by the employment of special means1 there seems to be1 beyond a certain and rather small size of vessel1 no perceptible difference in the heating4 ,these observations were the result of a number of experiments1 of which one1 showing the effect of the size of the bulb at a high degree of exhaustion1 may be described and shown here1 as it presents a feature of interest4 ,three spherical bulbs of #b inches1 #c inches and #d inches diameter were taken1 and in the centre of each was mounted an equal length of an ordinary incandescent lamp filament of uniform thickness4 ,in each bulb the piece of filament was fastened to the leading-in wire of platinum1 contained in a glass stem sealed in the bulb2 care being taken1 of course1 to make everything as nearly alike as possible4 ,on each glass stem in the inside of the bulb was slipped a highly polished tube made of aluminum sheet1 which fitted the stem and was held on it by spring pressure4 ,the function of this aluminum tube will be explained subsequently4 ,in each bulb an equal length of filament protruded above the metal tube4 ,it is sufficient to say now that under these conditions equal lengths of filament of the same thickness--in other words1 bodies of equal bulk--were brought to incandescence4 ,the three bulbs were sealed to a glass tube1 which was connected to a ,sprengel pump4 ,when a high vacuum had been reached1 the glass tube carrying the bulbs was sealed off4 ,a current was then turned on successively on each bulb1 and it was found that the filaments came to about the same brightness1 and1 if anything1 the smallest bulb1 which was placed midway between the two larger ones1 may have been slightly brighter4 ,this result was expected1 for when either of the bulbs was connected to the coil the luminosity spread through the other two1 hence the three bulbs constituted really one vessel4 ,when all the three bulbs were connected in multiple arc to the coil1 in the largest of them the filament glowed brightest1 in the next smaller it was a little less bright1 and in the smallest it only came to redness4 ,the bulbs were then sealed off and separately tried4 ,the brightness of the filaments was now such as would have been expected on the supposition that the energy given off was proportionate to the surface of the bulb1 this surface in each case representing one of the coatings of a condenser4 ,accordingly1 there was less difference between the largest and the middle sized than between the latter and the smallest bulb4 ,an interesting observation was made in this experiment4 ,the three bulbs were suspended from a straight bare wire connected to a terminal of a coil1 the largest bulb being placed at the end of the wire1 at some distance from it the smallest bulb1 and at an equal distance from the latter the middle-sized one4 ,the carbons glowed then in both the larger bulbs about as expected1 but the smallest did not get its share by far4 ,this observation led me to exchange the position of the bulbs1 and ,i then observed that whichever of the bulbs was in the middle was by far less bright than it was in any other position4 ,this mystifying result was1 of course1 found to be due to the electrostatic action between the bulbs4 ,when they were placed at a considerable distance1 or when they were attached to the corners of an equilateral triangle of copper wire1 they glowed in about the order determined by their surfaces4 ,as to the shape of the vessel1 it is also of some importance1 especially at high degrees of exhaustion4 ,of all the possible constructions1 it seems that a spherical globe with the refractory body mounted in its centre is the best to employ4 ,by experience it has been demonstrated that in such a globe a refractory body of a given bulk is more easily brought to incandescence than when differently shaped bulbs are used4 ,there is also an advantage in giving to the incandescent body the shape of a sphere1 for self-evident reasons4 ,in any case the body should be mounted in the centre1 where the atoms rebounding from the glass collide4 ,this object is best attained in the spherical bulb2 but it is also attained in a cylindrical vessel with one or two straight filaments coinciding with its axis1 and possibly also in parabolical or spherical bulbs with refractory body or bodies placed in the focus or foci of the same2 though the latter is not probable1 as the electrified atoms should in all cases rebound normally from the surface they strike1 unless the speed were excessive1 in which case they would probably follow the general law of reflection4 ,no matter what shape the vessel may have1 if the exhaustion be low1 a filament mounted in the globe is brought to the same degree of incandescence in all parts2 but if the exhaustion be high and the bulb be spherical or pear-shaped1 as usual1 focal points form and the filament is heated to a higher degree at or near such points4 ,to illustrate the effect1 ,i have here two small bulbs which are alike1 only one is exhausted to a low and the other to a very high degree4 ,when connected to the coil1 the filament in the former glows uniformly throughout all its length2 whereas in the latter1 that portion of the filament which is in the centre of the bulb glows far more intensely than the rest4 ,a curious point is that the phenomenon occurs even if two filaments are mounted in a bulb1 each being connected to one terminal of the coil1 and1 what is still more curious1 if they be very near together1 provided the vacuum be very high4 ,i noted in experiments with such bulbs that the filaments would give way usually at a certain point1 and in the first trials ,i attributed it to a defect in the carbon4 ,but when the phenomenon occurred many times in succession ,i recognized its real cause4 ,in order to bring a refractory body inclosed in a bulb to incandescence1 it is desirable1 on account of economy1 that all the energy supplied to the bulb from the source should reach without loss the body to be heated2 from there1 and from nowhere else1 it should be radiated4 ,it is1 of course1 out of the question to reach this theoretical result1 but it is possible by a proper construction of the illuminating device to approximate it more or less4 ,for many reasons1 the refractory body is placed in the centre of the bulb1 and it is usually supported on a glass stem containing the leading-in wire4 ,as the potential of this wire is alternated1 the rarefied gas surrounding the stem is acted upon inductively1 and the glass stem is violently bombarded and heated4 ,in this manner by far the greater portion of the energy supplied to the bulb--especially when exceedingly high frequencies are used--may be lost for the purpose contemplated4 ,to obviate this loss1 or at least to reduce it to a minimum1 ,i usually screen the rarefied gas surrounding the stem from the inductive action of the leading-in wire by providing the stem with a tube or coating of conducting material4 ,it seems beyond doubt that the best among metals to employ for this purpose is aluminum1 on account of its many remarkable properties4 ,its only fault is that it is easily fusible1 and1 therefore1 its distance from the incandescing body should be properly estimated4 ,usually1 a thin tube1 of a diameter somewhat smaller than that of the glass stem1 is made of the finest aluminum sheet1 and slipped on the stem4 ,the tube is conveniently prepared by wrapping around a rod fastened in a lathe a piece of aluminum sheet of proper size1 grasping the sheet firmly with clean chamois leather or blotting paper1 and spinning the rod very fast4 ,the sheet is wound tightly around the rod1 and a highly polished tube of one or three layers of the sheet is obtained4 ,when slipped on the stem1 the pressure is generally sufficient to prevent it from slipping off1 but1 for safety1 the lower edge of the sheet may be turned inside4 ,the upper inside corner of the sheet--that is1 the one which is nearest to the refractory incandescent body--should be cut out diagonally1 as it often happens that1 in consequence of the intense heat1 this corner turns toward the inside and comes very near to1 or in contact with1 the wire1 or filament1 supporting the refractory body4 ,the greater part of the energy supplied to the bulb is then used up in heating the metal tube1 and the bulb is rendered useless for the purpose4 ,the aluminum sheet should project above the glass stem more or less--one inch or so--or else1 if the glass be too close to the incandescing body1 it may be strongly heated and become more or less conducting1 whereupon it may be ruptured1 or may1 by its conductivity1 establish a good electrical connection between the metal tube and the leading-in wire1 in which case1 again1 most of the energy will be lost in heating the former4 ,perhaps the best way is to make the top of the glass tube1 for about an inch1 of a much smaller diameter4 ,to still further reduce the danger arising from the heating of the glass stem1 and also with the view of preventing an electrical connection between the metal tube and the electrode1 ,i preferably wrap the stem with several layers of thin mica1 which extends at least as far as the metal tube4 ,in some bulbs ,i have also used an outside insulating cover4 ,the preceding remarks are only made to aid the experimenter in the first trials1 for the difficulties which he encounters he may soon find means to overcome in his own way4 ,to illustrate the effect of the screen1 and the advantage of using it1 ,i have here two bulbs of the same size1 with their stems1 leading-in wires and incandescent lamp filaments tied to the latter1 as nearly alike as possible4 ,the stem of one bulb is provided with an aluminum tube1 the stem of the other has none4 ,originally the two bulbs were joined by a tube which was connected to a ,sprengel pump4 ,when a high vacuum had been reached1 first the connecting tube1 and then the bulbs1 were sealed off2 they are therefore of the same degree of exhaustion4 ,when they are separately connected to the coil giving a certain potential1 the carbon filament in the bulb provided with the aluminum screen is rendered highly incandescent1 while the filament in the other bulb may1 with the same potential1 not even come to redness1 although in reality the latter bulb takes generally more energy than the former4 ,when they are both connected together to the terminal1 the difference is even more apparent1 showing the importance of the screening4 ,the metal tube placed on the stem containing the leading-in wire performs really two distinct functions3 ,first1 it acts more or less as an electrostatic screen1 thus economizing the energy supplied to the bulb2 and1 second1 to whatever extent it may fail to act electrostatically1 it acts mechanically1 preventing the bombardment1 and consequently intense heating and possible deterioration of the slender support of the refractory incandescent body1 or of the glass stem containing the leading-in wire4 ,i say slender support1 for it is evident that in order to confine the heat more completely to the incandescing body its support should be very thin1 so as to carry away the smallest possible amount of heat by conduction4 ,of all the supports used ,i have found an ordinary incandescent lamp filament to be the best1 principally because among conductors it can withstand the highest degree of heat4 ,the effectiveness of the metal tube as an electrostatic screen depends largely on the degree of exhaustion4 ,at excessively high degrees of exhaustion--which are reached by using great care and special means in connection with the ,sprengel pump--when the matter in the globe is in the ultra-radiant state1 it acts most perfectly4 ,the shadow of the upper edge of the tube is then sharply defined upon the bulb4 ,at a somewhat lower degree of exhaustion1 which is about the ordinary non-striking vacuum1 and generally as long as the matter moves predominantly in straight lines1 the screen still does well4 ,in elucidation of the preceding remark it is necessary to state that what is a non-striking vacuum for a coil operated as ordinarily1 by impulses1 or currents1 of low frequency1 is not so1 by far1 when the coil is operated by currents of very high frequency4 ,in such case the discharge may pass with great freedom through the rarefied gas through which a low frequency discharge may not pass1 even though the potential be much higher4 ,at ordinary atmospheric pressures just the reverse rule holds good3 the higher the frequency1 the less the spark discharge is able to jump between the terminals1 especially if they are knobs or spheres of some size4 ,finally1 at very low degrees of exhaustion1 when the gas is well conducting1 the metal tube not only does not act as an electrostatic screen1 but even is a drawback1 aiding to a considerable extent the dissipation of the energy laterally from the leading-in wire4 ,this1 of course1 is to be expected4 ,in this case1 namely1 the metal tube is in good electrical connection with the leading-in wire1 and most of the bombardment is directed upon the tube4 ,as long as the electrical connection is not good1 the conducting tube is always of some advantage1 for although it may not greatly economize energy1 still it protects the support of the refractory button1 and is the means of concentrating more energy upon the same4 ,to whatever extent the aluminum tube performs the function of a screen1 its usefulness is therefore limited to very high degrees of exhaustion when it is insulated from the electrode--that is1 when the gas as a whole is non-conducting1 and the molecules1 or atoms1 act as independent carriers of electric charges4 ,in addition to acting as a more or less effective screen1 in the true meaning of the word1 the conducting tube or coating may also act1 by reason of its conductivity1 as a sort of equalizer or dampener of the bombardment against the stem4 ,to be explicit1 ,i assume the action to be as follows3 ,suppose a rhythmical bombardment to occur against the conducting tube by reason of its imperfect action as a screen1 it certainly must happen that some molecules1 or atoms1 strike the tube sooner than others4 ,those which come first in contact with it give up their superfluous charge1 and the tube is electrified1 the electrification instantly spreading over its surface4 ,but this must diminish the energy lost in the bombardment1 for two reasons3 first1 the charge given up by the atoms spreads over a great area1 and hence the electric density at any point is small1 and the atoms are repelled with less energy than they would be if they struck against a good insulator2 secondly1 as the tube is electrified by the atoms which first come in contact with it1 the progress of the following atoms against the tube is more or less checked by the repulsion which the electrified tube must exert upon the similarly electrified atoms4 ,this repulsion may perhaps be sufficient to prevent a large portion of the atoms from striking the tube1 but at any rate it must diminish the energy of their impact4 ,it is clear that when the exhaustion is very low1 and the rarefied gas well conducting1 neither of the above effects can occur1 and1 on the other hand1 the fewer the atoms1 with the greater freedom they move2 in other words1 the higher the degree of exhaustion1 up to a limit1 the more telling will be both the effects4 ,illustration3 ,,fig4 #adg4 ,illustration3 ,,fig4 #adh4 ,what ,i have just said may afford an explanation of the phenomenon observed by ,prof4 ,crookes1 namely1 that a discharge through a bulb is established with much greater facility when an insulator than when a conductor is present in the same4 ,in my opinion1 the conductor acts as a dampener of the motion of the atoms in the two ways pointed out2 hence1 to cause a visible discharge to pass through the bulb1 a much higher potential is needed if a conductor1 especially of much surface1 be present4 ,for the sake of elucidating of some of the remarks before made1 ,i must now refer to ,figs4 #adg1 #adh and #adi1 which illustrate various arrangements with a type of bulb most generally used4 ,fig4 #adg is a section through a spherical bulb ,l1 with the glass stem s1 contains the leading-in wire w1 which has a lamp filament l fastened to it1 serving to support the refractory button m in the centre4 ,m is a sheet of thin mica wound in several layers around the stem s1 and a is the aluminum tube4 ,fig4 #adh illustrates such a bulb in a somewhat more advanced stage of perfection4 ,a metallic tube ,s is fastened by means of some cement to the neck of the tube4 ,in the tube is screwed a plug ,p1 of insulating material1 in the centre of which is fastened a metallic terminal t1 for the connection to the leading-in wire w4 ,this terminal must be well insulated from the metal tube ,s2 therefore1 if the cement used is conducting--and most generally it is sufficiently so--the space between the plug ,p and the neck of the bulb should be filled with some good insulating material1 such as mica powder4 ,fig4 #adi shows a bulb made for experimental purposes4 ,in this bulb the aluminum tube is provided with an external connection1 which serves to investigate the effect of the tube under various conditions4 ,it is referred to chiefly to suggest a line of experiment followed4 ,since the bombardment against the stem containing the leading-in wire is due to the inductive action of the latter upon the rarefied gas1 it is of advantage to reduce this action as far as practicable by employing a very thin wire1 surrounded by a very thick insulation of glass or other material1 and by making the wire passing through the rarefied gas as short as practicable4 ,to combine these features ,i employ a large tube ,t 7,fig4 #aej71 which protrudes into the bulb to some distance1 and carries on the top a very short glass stem s1 into which is sealed the leading-in wire w1 and ,i protect the top of the glass stem against the heat by a small aluminum tube a and a layer of mica underneath the same1 as usual4 ,the wire w1 passing through the large tube to the outside of the bulb1 should be well insulated--with a glass tube1 for instance--and the space between ought to be filled out with some excellent insulator4 ,among many insulating powders ,i have found that mica powder is the best to employ4 ,if this precaution is not taken1 the tube ,t1 protruding into the bulb1 will surely be cracked in consequence of the heating by the brushes which are apt to form in the upper part of the tube1 near the exhausted globe1 especially if the vacuum be excellent1 and therefore the potential necessary to operate the lamp be very high4 ,illustration3 ,,fig4 #adi4 ,illustration3 ,,fig4 #aej4 ,fig4 #aea illustrates a similar arrangement1 with a large tube ,t protruding into the part of the bulb containing the refractory button m4 ,in this case the wire leading from the outside into the bulb is omitted1 the energy required being supplied through condenser coatings ,c ,c4 ,the insulating packing ,p should in this construction be tightly fitting to the glass1 and rather wide1 or otherwise the discharge might avoid passing through the wire w1 which connects the inside condenser coating to the incandescent button m4 ,the molecular bombardment against the glass stem in the bulb is a source of great trouble4 ,as an illustration ,i will cite a phenomenon only too frequently and unwillingly observed4 ,a bulb1 preferably a large one1 may be taken1 and a good conducting body1 such as a piece of carbon1 may be mounted in it upon a platinum wire sealed in the glass stem4 ,the bulb may be exhausted to a fairly high degree1 nearly to the point when phosphorescence begins to appear4 ,when the bulb is connected with the coil1 the piece of carbon1 if small1 may become highly incandescent at first1 but its brightness immediately diminishes1 and then the discharge may break through the glass somewhere in the middle of the stem1 in the form of bright sparks1 in spite of the fact that the platinum wire is in good electrical connection with the rarefied gas through the piece of carbon or metal at the top4 ,the first sparks are singularly bright1 recalling those drawn from a clear surface of mercury4 ,but1 as they heat the glass rapidly1 they1 of course1 lose their brightness1 and cease when the glass at the ruptured place becomes incandescent1 or generally sufficiently hot to conduct4 ,when observed for the first time the phenomenon must appear very curious1 and shows in a striking manner how radically different alternate currents1 or impulses1 of high frequency behave1 as compared with steady currents1 or currents of low frequency4 ,with such currents--namely1 the latter--the phenomenon would of course not occur4 ,when frequencies such as are obtained by mechanical means are used1 ,i think that the rupture of the glass is more or less the consequence of the bombardment1 which warms it up and impairs its insulating power2 but with frequencies obtainable with condensers ,i have no doubt that the glass may give way without previous heating4 ,although this appears most singular at first1 it is in reality what we might expect to occur4 ,the energy supplied to the wire leading into the bulb is given off partly by direct action through the carbon button1 and partly by inductive action through the glass surrounding the wire4 ,the case is thus analogous to that in which a condenser shunted by a conductor of low resistance is connected to a source of alternating current4 ,as long as the frequencies are low1 the conductor gets the most and the condenser is perfectly safe2 but when the frequency becomes excessive1 the role of the conductor may become quite insignificant4 ,in the latter case the difference of potential at the terminals of the condenser may become so great as to rupture the dielectric1 notwithstanding the fact that the terminals are joined by a conductor of low resistance4 ,it is1 of course1 not necessary1 when it is desired to produce the incandescence of a body inclosed in a bulb by means of these currents1 that the body should be a conductor1 for even a perfect non-conductor may be quite as readily heated4 ,for this purpose it is sufficient to surround a conducting electrode with a non-conducting material1 as1 for instance1 in the bulb described before in ,fig4 #aej1 in which a thin incandescent lamp filament is coated with a non-conductor1 and supports a button of the same material on the top4 ,at the start the bombardment goes on by inductive action through the non-conductor1 until the same is sufficiently heated to become conducting1 when the bombardment continues in the ordinary way4 ,illustration3 ,,fig4 #aea4 ,illustration3 ,,fig4 #aeb4 ,a different arrangement used in some of the bulbs constructed is illustrated in ,fig4 #aeb4 ,in this instance a non-conductor m is mounted in a piece of common arc light carbon so as to project some small distance above the latter4 ,the carbon piece is connected to the leading-in wire passing through a glass stem1 which is wrapped with several layers of mica4 ,an aluminum tube a is employed as usual for screening4 ,it is so arranged that it reaches very nearly as high as the carbon and only the non-conductor m projects a little above it4 ,the bombardment goes at first against the upper surface of carbon1 the lower parts being protected by the aluminum tube4 ,as soon1 however1 as the non-conductor m is heated it is rendered good conducting1 and then it becomes the centre of the bombardment1 being most exposed to the same4 ,i have also constructed during these experiments many such single-wire bulbs with or without internal electrode1 in which the radiant matter was projected against1 or focused upon1 the body to be rendered incandescent4 ,fig4 #aec 7page #bfc7 illustrates one of the bulbs used4 ,it consists of a spherical globe ,l1 provided with a long neck n1 on top1 for increasing the action in some cases by the application of an external conducting coating4 ,the globe ,l is blown out on the bottom into a very small bulb b1 which serves to hold it firmly in a socket ,s of insulating material into which it is cemented4 ,a fine lamp filament f1 supported on a wire w1 passes through the centre of the globe ,l4 ,the filament is rendered incandescent in the middle portion1 where the bombardment proceeding from the lower inside surface of the globe is most intense4 ,the lower portion of the globe1 as far as the socket ,s reaches1 is rendered conducting1 either by a tinfoil coating or otherwise1 and the external electrode is connected to a terminal of the coil4 ,the arrangement diagrammatically indicated in ,fig4 #aec was found to be an inferior one when it was desired to render incandescent a filament or button supported in the centre of the globe1 but it was convenient when the object was to excite phosphorescence4 ,in many experiments in which bodies of different kind were mounted in the bulb as1 for instance1 indicated in ,fig4 #aeb1 some observations of interest were made4 ,it was found1 among other things1 that in such cases1 no matter where the bombardment began1 just as soon as a high temperature was reached there was generally one of the bodies which seemed to take most of the bombardment upon itself1 the other1 or others1 being thereby relieved4 ,the quality appeared to depend principally on the point of fusion1 and on the facility with which the body was evaporated1 or1 generally speaking1 disintegrated--meaning by the latter term not only the throwing off of atoms1 but likewise of large lumps4 ,the observation made was in accordance with generally accepted notions4 ,in a highly exhausted bulb1 electricity is carried off from the electrode by independent carriers1 which are partly the atoms1 or molecules1 of the residual atmosphere1 and partly the atoms1 molecules1 or lumps thrown off from the electrode4 ,if the electrode is composed of bodies of different character1 and if one of these is more easily disintegrated than the other1 most of the electricity supplied is carried off from that body1 which is then brought to a higher temperature than the others1 and this the more1 as upon an increase of the temperature the body is still more easily disintegrated4 ,it seems to me quite probable that a similar process takes place in the bulb even with a homogeneous electrode1 and ,i think it to be the principal cause of the disintegration4 ,there is bound to be some irregularity1 even if the surface is highly polished1 which1 of course1 is impossible with most of the refractory bodies employed as electrodes4 ,assume that a point of the electrode gets hotter2 instantly most of the discharge passes through that point1 and a minute patch it probably fused and evaporated4 ,it is now possible that in consequence of the violent disintegration the spot attacked sinks in temperature1 or that a counter force is created1 as in an arc2 at any rate1 the local tearing off meets with the limitations incident to the experiment1 whereupon the same process occurs on another place4 ,to the eye the electrode appears uniformly brilliant1 but there are upon it points constantly shifting and wandering around1 of a temperature far above the mean1 and this materially hastens the process of deterioration4 ,that some such thing occurs1 at least when the electrode is at a lower temperature1 sufficient experimental evidence can be obtained in the following manner3 ,exhaust a bulb to a very high degree1 so that with a fairly high potential the discharge cannot pass--that is1 not a luminous one1 for a weak invisible discharge occurs always1 in all probability4 ,now raise slowly and carefully the potential1 leaving the primary current on no more than for an instant4 ,at a certain point1 two1 three1 or half a dozen phosphorescent spots will appear on the globe4 ,these places of the glass are evidently more violently bombarded than others1 this being due to the unevenly distributed electric density1 necessitated1 of course1 by sharp projections1 or1 generally speaking1 irregularities of the electrode4 ,but the luminous patches are constantly changing in position1 which is especially well observable if one manages to produce very few1 and this indicates that the configuration of the electrode is rapidly changing4 ,from experiences of this kind ,i am led to infer that1 in order to be most durable1 the refractory button in the bulb should be in the form of a sphere with a highly polished surface4 ,such a small sphere could be manufactured from a diamond or some other crystal1 but a better way would be to fuse1 by the employment of extreme degrees of temperature1 some oxide--as1 for instance1 zirconia--into a small drop1 and then keep it in the bulb at a temperature somewhat below its point of fusion4 ,interesting and useful results can1 no doubt1 be reached in the direction of extreme degrees of heat4 ,how can such high temperatures be arrived at8 ,how are the highest degrees of heat reached in nature8 ,by the impact of stars1 by high speeds and collisions4 ,in a collision any rate of heat generation may be attained4 ,in a chemical process we are limited4 ,when oxygen and hydrogen combine1 they fall1 metaphorically speaking1 from a definite height4 ,we cannot go very far with a blast1 nor by confining heat in a furnace1 but in an exhausted bulb we can concentrate any amount of energy upon a minute button4 ,leaving practicability out of consideration1 this1 then1 would be the means which1 in my opinion1 would enable us to reach the highest temperature4 ,but a great difficulty when proceeding in this way is encountered1 namely1 in most cases the body is carried off before it can fuse and form a drop4 ,this difficulty exists principally with an oxide1 such as zirconia1 because it cannot be compressed in so hard a cake that it would not be carried off quickly4 ,i have endeavored repeatedly to fuse zirconia1 placing it in a cup of arc light carbon1 as indicated in ,fig4 #aeb4 ,it glowed with a most intense light1 and the stream of the particles projected out of the carbon cup was of a vivid white2 but whether it was compressed in a cake or made into a paste with carbon1 it was carried off before it could be fused4 ,the carbon cup1 containing zirconia1 had to be mounted very low in the neck of a large bulb1 as the heating of the glass by the projected particles of the oxide was so rapid that in the first trial the bulb was cracked almost in an instant1 when the current was turned on4 ,the heating of the glass by the projected particles was found to be always greater when the carbon cup contained a body which was rapidly carried off--,i presume1 because in such cases1 with the same potential1 higher speeds were reached1 and also because1 per unit of time1 more matter was projected--that is1 more particles would strike the glass4 ,the before-mentioned difficulty did not exist1 however1 when the body mounted in the carbon cup offered great resistance to deterioration4 ,for instance1 when an oxide was first fused in an oxygen blast1 and then mounted in the bulb1 it melted very readily into a drop4 ,generally1 during the process of fusion1 magnificent light effects were noted1 of which it would be difficult to give an adequate idea4 ,fig4 #aeb is intended to illustrate the effect observed with a ruby drop4 ,at first one may see a narrow funnel of white light projected against the top of the globe1 where it produces an irregularly outlined phosphorescent patch4 ,when the point of the ruby fuses1 the phosphorescence becomes very powerful2 but as the atoms are projected with much greater speed from the surface of the drop1 soon the glass gets hot and tired1 and now only the outer edge of the patch glows4 ,in this manner an intensely phosphorescent1 sharply defined line1 l1 corresponding to the outline of the drop1 is produced1 which spreads slowly over the globe as the drop gets larger4 ,when the mass begins to boil1 small bubbles and cavities are formed1 which cause dark colored spots to sweep across the globe4 ,the bulb may be turned downward without fear of the drop falling off1 as the mass possesses considerable viscosity4 ,i may mention here another feature of some interest1 which ,i believe to have noted in the course of these experiments1 though the observations do not amount to a certitude4 ,it appeared that under the molecular impact caused by the rapidly alternating potential1 the body was fused and maintained in that state at a lower temperature in a highly exhausted bulb than was the case at normal pressure and application of heat in the ordinary way--that is1 at least1 judging from the quantity of the light emitted4 ,one of the experiments performed may be mentioned here by way of illustration4 ,a small piece of pumice stone was stuck on a platinum wire1 and first melted to it in a gas burner4 ,the wire was next placed between two pieces of charcoal1 and a burner applied1 so as to produce an intense heat1 sufficient to melt down the pumice stone into a small glass-like button4 ,the platinum wire had to be taken of sufficient thickness1 to prevent its melting in the fire4 ,while in the charcoal fire1 or when held in a burner to get a better idea of the degree of heat1 the button glowed with great brilliancy4 ,the wire with the button was then mounted in a bulb1 and upon exhausting the same to a high degree1 the current was turned on slowly1 so as to prevent the cracking of the button4 ,the button was heated to the point of fusion1 and when it melted1 it did not1 apparently1 glow with the same brilliancy as before1 and this would indicate a lower temperature4 ,leaving out of consideration the observer's possible1 and even probable1 error1 the question is1 can a body under these conditions be brought from a solid to a liquid state with the evolution of less light8 ,when the potential of a body is rapidly alternated1 it is certain that the structure is jarred4 ,when the potential is very high1 although the vibrations may be few--say #bj1jjj per second--the effect upon the structure may be considerable4 ,suppose1 for example1 that a ruby is melted into a drop by a steady application of energy4 ,when it forms a drop1 it will emit visible and invisible waves1 which will be in a definite ratio1 and to the eye the drop will appear to be of a certain brilliancy4 ,next1 suppose we diminish to any degree we choose the energy steadily supplied1 and1 instead1 supply energy which rises and falls according to a certain law4 ,now1 when the drop is formed1 there will be emitted from it three different kinds of vibrations--the ordinary visible1 and two kinds of invisible waves3 that is1 the ordinary dark waves of all lengths1 and1 in addition1 waves of a well defined character4 ,the latter would not exist by a steady supply of the energy2 still they help to jar and loosen the structure4 ,if this really be the case1 then the ruby drop will emit relatively less visible and more invisible waves than before4 ,thus it would seem that when a platinum wire1 for instance1 is fused by currents alternating with extreme rapidity1 it emits at the point of fusion less light and more visible radiation than it does when melted by a steady current1 though the total energy used up in the process of fusion is the same in both cases4 ,or1 to cite another example1 a lamp filament is not capable of withstanding as long with currents of extreme frequency as it does with steady currents1 assuming that it be worked at the same luminous intensity4 ,this means that for rapidly alternating currents the filament should be shorter and thicker4 ,the higher the frequency--that is1 the greater the departure from the steady flow--the worse it would be for the filament4 ,but if the truth of this remark were demonstrated1 it would be erroneous to conclude that such a refractory button as used in these bulbs would be deteriorated quicker by currents of extremely high frequency than by steady or low frequency currents4 ,from experience ,i may say that just the opposite holds good3 the button withstands the bombardment better with currents of very high frequency4 ,but this is due to the fact that a high frequency discharge passes through a rarefied gas with much greater freedom than a steady or low frequency discharge1 and this will mean that with the former we can work with a lower potential or with a less violent impact4 ,as long1 then1 as the gas is of no consequence1 a steady or low frequency current is better2 but as soon as the action of the gas is desired and important1 high frequencies are preferable4 ,in the course of these experiments a great many trials were made with all kinds of carbon buttons4 ,electrodes made of ordinary carbon buttons were decidedly more durable when the buttons were obtained by the application of enormous pressure4 ,electrodes prepared by depositing carbon in well known ways did not show up well2 they blackened the globe very quickly4 ,from many experiences ,i conclude that lamp filaments obtained in this manner can be advantageously used only with low potentials and low frequency currents4 ,some kinds of carbon withstand so well that1 in order to bring them to the point of fusion1 it is necessary to employ very small buttons4 ,in this case the observation is rendered very difficult on account of the intense heat produced4 ,nevertheless there can be no doubt that all kinds of carbon are fused under the molecular bombardment1 but the liquid state must be one of great instability4 ,of all the bodies tried there were two which withstood best--diamond and carborundum4 ,these two showed up about equally1 but the latter was preferable for many reasons4 ,as it is more than likely that this body is not yet generally known1 ,i will venture to call your attention to it4 ,it has been recently produced by ,mr4 ,e4 ,g4 ,acheson1 of ,monongahela ,city1 ,pa41 ,u4 ,s4 ,a4 ,it is intended to replace ordinary diamond powder for polishing precious stones1 etc41 and ,i have been informed that it accomplishes this object quite successfully4 ,i do not know why the name carborundum has been given to it1 unless there is something in the process of its manufacture which justifies this selection4 ,through the kindness of the inventor1 ,i obtained a short while ago some samples which ,i desired to test in regard to their qualities of phosphorescence and capability of withstanding high degrees of heat4 ,carborundum can be obtained in two forms--in the form of crystals and of powder4 ,the former appear to the naked eye dark colored1 but are very brilliant2 the latter is of nearly the same color as ordinary diamond powder1 but very much finer4 ,when viewed under a microscope the samples of crystals given to me did not appear to have any definite form1 but rather resembled pieces of broken up egg coal of fine quality4 ,the majority were opaque1 but there were some which were transparent and colored4 ,the crystals are a kind of carbon containing some impurities2 they are extremely hard1 and withstand for a long time even an oxygen blast4 ,when the blast is directed against them they at first form a cake of some compactness1 probably in consequence of the fusion of impurities they contain4 ,the mass withstands for a very long time the blast without further fusion2 but a slow carrying off1 or burning1 occurs1 and1 finally1 a small quantity of a glass-like residue is left1 which1 ,i suppose1 is melted alumina4 ,when compressed strongly they conduct very well1 but not as well as ordinary carbon4 ,the powder1 which is obtained from the crystals in some way1 is practically non-conducting4 ,it affords a magnificent polishing material for stones4 ,the time has been too short to make a satisfactory study of the properties of this product1 but enough experience has been gained in a few weeks ,i have experimented upon it to say that it does possess some remarkable properties in many respects4 ,it withstands excessively high degrees of heat1 it is little deteriorated by molecular bombardment1 and it does not blacken the globe as ordinary carbon does4 ,the only difficulty which ,i have experienced in its use in connection with these experiments was to find some binding material which would resist the heat and the effect of the bombardment as successfully as carborundum itself does4 ,i have here a number of bulbs which ,i have provided with buttons of carborundum4 ,to make such a button of carborundum crystals ,i proceed in the following manner3 ,i take an ordinary lamp filament and dip its point in tar1 or some other thick substance or paint which may be readily carbonized4 ,i next pass the point of the filament through the crystals1 and then hold it vertically over a hot plate4 ,the tar softens and forms a drop on the point of the filament1 the crystals adhering to the surface of the drop4 ,by regulating the distance from the plate the tar is slowly dried out and the button becomes solid4 ,i then once more dip the button in tar and hold it again over a plate until the tar is evaporated1 leaving only a hard mass which firmly binds the crystals4 ,when a larger button is required ,i repeat the process several times1 and ,i generally also cover the filament a certain distance below the button with crystals4 ,the button being mounted in a bulb1 when a good vacuum has been reached1 first a weak and then a strong discharge is passed through the bulb to carbonize the tar and expel all gases1 and later it is brought to a very intense incandescence4 ,when the powder is used ,i have found it best to proceed as follows3 ,i make a thick paint of carborundum and tar1 and pass a lamp filament through the paint4 ,taking then most of the paint off by rubbing the filament against a piece of chamois leather1 ,i hold it over a hot plate until the tar evaporates and the coating becomes firm4 ,i repeat this process as many times as it is necessary to obtain a certain thickness of coating4 ,on the point of the coated filament ,i form a button in the same manner4 ,there is no doubt that such a button--properly prepared under great pressure--of carborundum1 especially of powder of the best quality1 will withstand the effect of the bombardment fully as well as anything we know4 ,the difficulty is that the binding material gives way1 and the carborundum is slowly thrown off after some time4 ,as it does not seem to blacken the globe in the least1 it might be found useful for coating the filaments of ordinary incandescent lamps1 and ,i think that it is even possible to produce thin threads or sticks of carborundum which will replace the ordinary filaments in an incandescent lamp4 ,a carborundum coating seems to be more durable than other coatings1 not only because the carborundum can withstand high degrees of heat1 but also because it seems to unite with the carbon better than any other material ,i have tried4 ,a coating of zirconia or any other oxide1 for instance1 is far more quickly destroyed4 ,i prepared buttons of diamond dust in the same manner as of carborundum1 and these came in durability nearest to those prepared of carborundum1 but the binding paste gave way much more quickly in the diamond buttons2 this1 however1 ,i attributed to the size and irregularity of the grains of the diamond4 ,it was of interest to find whether carborundum possesses the quality of phosphorescence4 ,one is1 of course1 prepared to encounter two difficulties3 first1 as regards the rough product1 the crystals1 they are good conducting1 and it is a fact that conductors do not phosphoresce2 second1 the powder1 being exceedingly fine1 would not be apt to exhibit very prominently this quality1 since we know that when crystals1 even such as diamond or ruby1 are finely powdered1 they lose the property of phosphorescence to a considerable degree4 ,the question presents itself here1 can a conductor phosphoresce8 ,what is there in such a body as a metal1 for instance1 that would deprive it of the quality of phosphoresence1 unless it is that property which characterizes it as a conductor8 ,for it is a fact that most of the phosphorescent bodies lose that quality when they are sufficiently heated to become more or less conducting4 ,then1 if a metal be in a large measure1 or perhaps entirely1 deprived of that property1 it should be capable of phosphoresence4 ,therefore it is quite possible that at some extremely high frequency1 when behaving practically as a non-conductor1 a metal or any other conductor might exhibit the quality of phosphoresence1 even though it be entirely incapable of phosphorescing under the impact of a low-frequency discharge4 ,there is1 however1 another possible way how a conductor might at least appear to phosphoresce4 ,considerable doubt still exists as to what really is phosphorescence1 and as to whether the various phenomena comprised under this head are due to the same causes4 ,suppose that in an exhausted bulb1 under the molecular impact1 the surface of a piece of metal or other conductor is rendered strongly luminous1 but at the same time it is found that it remains comparatively cool1 would not this luminosity be called phosphorescence8 ,now such a result1 theoretically at least1 is possible1 for it is a mere question of potential or speed4 ,assume the potential of the electrode1 and consequently the speed of the projected atoms1 to be sufficiently high1 the surface of the metal piece1 against which the atoms are projected1 would be rendered highly incandescent1 since the process of heat generation would be incomparably faster than that of radiating or conducting away from the surface of the collision4 ,in the eye of the observer a single impact of the atoms would cause an instantaneous flash1 but if the impacts were repeated with sufficient rapidity1 they would produce a continuous impression upon his retina4 ,to him then the surface of the metal would appear continuously incandescent and of constant luminous intensity1 while in reality the light would be either intermittent1 or at least changing periodically in intensity4 ,the metal piece would rise in temperature until equilibrium was attained--that is1 until the energy continuously radiated would equal that intermittently supplied4 ,but the supplied energy might under such conditions not be sufficient to bring the body to any more than a very moderate mean temperature1 especially if the frequency of the atomic impacts be very low--just enough that the fluctuation of the intensity of the light emitted could not be detected by the eye4 ,the body would now1 owing to the manner in which the energy is supplied1 emit a strong light1 and yet be at a comparatively very low mean temperature4 ,how should the observer name the luminosity thus produced8 ,even if the analysis of the light would teach him something definite1 still he would probably rank it under the phenomena of phosphorescence4 ,it is conceivable that in such a way both conducting and non-conducting bodies may be maintained at a certain luminous intensity1 but the energy required would very greatly vary with the nature and properties of the bodies4 ,these and some foregoing remarks of a speculative nature were made merely to bring out curious features of alternate currents or electric impulses4 ,by their help we may cause a body to emit more light1 while at a certain mean temperature1 than it would emit if brought to that temperature by a steady supply2 and1 again1 we may bring a body to the point of fusion1 and cause it to emit less light than when fused by the application of energy in ordinary ways4 ,it all depends on how we supply the energy1 and what kind of vibrations we set up2 in one case the vibrations are more1 in the other less1 adapted to affect our sense of vision4 ,some effects1 which ,i had not observed before1 obtained with carborundum in the first trials1 ,i attributed to phosphorescence1 but in subsequent experiments it appeared that it was devoid of that quality4 ,the crystals possess a noteworthy feature4 ,in a bulb provided with a single electrode in the shape of a small circular metal disc1 for instance1 at a certain degree of exhaustion the electrode is covered with a milky film1 which is separated by a dark space from the glow filling the bulb4 ,when the metal disc is covered with carborundum crystals1 the film is far more intense1 and snow-white4 ,this ,i found later to be merely an effect of the bright surface of the crystals1 for when an aluminum electrode was highly polished1 it exhibited more or less the same phenomenon4 ,i made a number of experiments with the samples of crystals obtained1 principally because it would have been of special interest to find that they are capable of phosphorescence1 on account of their being conducting4 ,i could not produce phosphorescence distinctly1 but ,i must remark that a decisive opinion cannot be formed until other experimenters have gone over the same ground4 ,the powder behaved in some experiments as though it contained alumina1 but it did not exhibit with sufficient distinctness the red of the latter4 ,its dead color brightens considerably under the molecular impact1 but ,i am now convinced it does not phosphoresce4 ,still1 the tests with the powder are not conclusive1 because powdered carborundum probably does not behave like a phosphorescent sulphide1 for example1 which could be finely powdered without impairing the phosphorescence1 but rather like powdered ruby or diamond1 and therefore it would be necessary1 in order to make a decisive test1 to obtain it in a large lump and polish up the surface4 ,if the carborundum proves useful in connection with these and similar experiments1 its chief value will be found in the production of coatings1 thin conductors1 buttons1 or other electrodes capable of withstanding extremely high degrees of heat4 ,the production of a small electrode1 capable of withstanding enormous temperatures1 ,i regard as of the greatest importance in the manufacture of light4 ,it would enable us to obtain1 by means of currents of very high frequencies1 certainly #bj times1 if not more1 the quantity of light which is obtained in the present incandescent lamp by the same expenditure of energy4 ,this estimate may appear to many exaggerated1 but in reality ,i think it is far from being so4 ,as this statement might be misunderstood1 ,i think it is necessary to expose clearly the problem with which1 in this line of work1 we are confronted1 and the manner in which1 in my opinion1 a solution will be arrived at4 ,any one who begins a study of the problem will be apt to think that what is wanted in a lamp with an electrode is a very high degree of incandescence of the electrode4 ,there he will be mistaken4 ,the high incandescence of the button is a necessary evil1 but what is really wanted is the high incandescence of the gas surrounding the button4 ,in other words1 the problem in such a lamp is to bring a mass of gas to the highest possible incandescence4 ,the higher the incandescence1 the quicker the mean vibration1 the greater is the economy of the light production4 ,but to maintain a mass of gas at a high degree of incandescence in a glass vessel1 it will always be necessary to keep the incandescent mass away from the glass2 that is1 to confine it as much as possible to the central portion of the globe4 ,in one of the experiments this evening a brush was produced at the end of a wire4 ,the brush was a flame1 a source of heat and light4 ,it did not emit much perceptible heat1 nor did it glow with an intense light2 but is it the less a flame because it does not scorch my hand8 ,is it the less a flame because it does not hurt my eyes by its brilliancy8 ,the problem is precisely to produce in the bulb such a flame1 much smaller in size1 but incomparably more powerful4 ,were there means at hand for producing electric impulses of a sufficiently high frequency1 and for transmitting them1 the bulb could be done away with1 unless it were used to protect the electrode1 or to economize the energy by confining the heat4 ,but as such means are not at disposal1 it becomes necessary to place the terminal in the bulb and rarefy the air in the same4 ,this is done merely to enable the apparatus to perform the work which it is not capable of performing at ordinary air pressure4 ,in the bulb we are able to intensify the action to any degree--so far that the brush emits a powerful light4 ,the intensity of the light emitted depends principally on the frequency and potential of the impulses1 and on the electric density on the surface of the electrode4 ,it is of the greatest importance to employ the smallest possible button1 in order to push the density very far4 ,under the violent impact of the molecules of the gas surrounding it1 the small electrode is of course brought to an extremely high temperature1 but around it is a mass of highly incandescent gas1 a flame photosphere1 many hundred times the volume of the electrode4 ,with a diamond1 carborundum or zirconia button the photosphere can be as much as one thousand times the volume of the button4 ,without much reflection one would think that in pushing so far the incandescence of the electrode it would be instantly volatilized4 ,but after a careful consideration one would find that1 theoretically1 it should not occur1 and in this fact--which1 moreover1 is experimentally demonstrated--lies principally the future value of such a lamp4 ,at first1 when the bombardment begins1 most of the work is performed on the surface of the button1 but when a highly conducting photosphere is formed the button is comparatively relieved4 ,the higher the incandescence of the photosphere1 the more it approaches in conductivity to that of the electrode1 and the more1 therefore1 the solid and the gas form one conducting body4 ,the consequence is that the further the incandescence is forced the more work1 comparatively1 is performed on the gas1 and the less on the electrode4 ,the formation of a powerful photosphere is consequently the very means for protecting the electrode4 ,this protection1 of course1 is a relative one1 and it should not be thought that by pushing the incandescence higher the electrode is actually less deteriorated4 ,still1 theoretically1 with extreme frequencies1 this result must be reached1 but probably at a temperature too high for most of the refractory bodies known4 ,given1 then1 an electrode which can withstand to a very high limit the effect of the bombardment and outward strain1 it would be safe1 no matter how much it was forced beyond that limit4 ,in an incandescent lamp quite different considerations apply4 ,there the gas is not at all concerned2 the whole of the work is performed on the filament2 and the life of the lamp diminishes so rapidly with the increase of the degree of incandescence that economical reasons compel us to work it at a low incandescence4 ,but if an incandescent lamp is operated with currents of very high frequency1 the action of the gas cannot be neglected1 and the rules for the most economical working must be considerably modified4 ,in order to bring such a lamp with one or two electrodes to a great perfection1 it is necessary to employ impulses of very high frequency4 ,the high frequency secures1 among others1 two chief advantages1 which have a most important bearing upon the economy of the light production4 ,first1 the deterioration of the electrode is reduced by reason of the fact that we employ a great many small impacts1 instead of a few violent ones1 which quickly shatter the structure2 secondly1 the formation of a large photosphere is facilitated4 ,in order to reduce the deterioration of the electrode to the minimum1 it is desirable that the vibration be harmonic1 for any suddenness hastens the process of destruction4 ,an electrode lasts much longer when kept at incandescence by currents1 or impulses1 obtained from a high frequency alternator1 which rise and fall more or less harmonically1 than by impulses obtained from a disruptive discharge coil4 ,in the latter case there is no doubt that most of the damage is done by the fundamental sudden discharges4 ,one of the elements of loss in such a lamp is the bombardment of the globe4 ,as the potential is very high1 the molecules are projected with great speed2 they strike the glass1 and usually excite a strong phosphorescence4 ,the effect produced is very pretty1 but for economical reasons it would be perhaps preferable to prevent1 or at least reduce to a minimum1 the bombardment against the globe1 as in such case it is1 as a rule1 not the object to excite phosphorescence1 and as some loss of energy results from the bombardment4 ,this loss in the bulb is principally dependent on the potential of the impulses and on the electric density on the surface of the electrode4 ,in employing very high frequencies the loss of energy by the bombardment is greatly reduced1 for1 first1 the potential needed to perform a given amount of work is much smaller2 and1 secondly1 by producing a highly conducting photosphere around the electrode1 the same result is obtained as though the electrode were much larger1 which is equivalent to a smaller electric density4 ,but be it by the diminution of the maximum potential or of the density1 the gain is effected in the same manner1 namely1 by avoiding violent shocks1 which strain the glass much beyond its limit of elasticity4 ,if the frequency could be brought high enough1 the loss due to the imperfect elasticity of the glass would be entirely negligible4 ,the loss due to bombardment of the globe may1 however1 be reduced by using two electrodes instead of one4 ,in such case each of the electrodes may be connected to one of the terminals2 or else1 if it is preferable to use only one wire1 one electrode may be connected to one terminal and the other to the ground or to an insulated body of some surface1 as1 for instance1 a shade on the lamp4 ,in the latter case1 unless some judgment is used1 one of the electrodes might glow more intensely than the other4 ,but on the whole ,i find it preferable1 when using such high frequencies1 to employ only one electrode and one connecting wire4 ,i am convinced that the illuminating device of the near future will not require for its operation more than one lead1 and1 at any rate1 it will have no leading-in wire1 since the energy required can be as well transmitted through the glass4 ,in experimental bulbs the leading-in wire is not generally used on account of convenience1 as in employing condenser coatings in the manner indicated in ,fig4 #aea1 for example1 there is some difficulty in fitting the parts1 but these difficulties would not exist if a great many bulbs were manufactured2 otherwise the energy can be conveyed through the glass as well as through a wire1 and with these high frequencies the losses are very small4 ,such illustrating devices will necessarily involve the use of very high potentials1 and this1 in the eyes of practical men1 might be an objectionable feature4 ,yet1 in reality1 high potentials are not objectionable--certainly not in the least so far as the safety of the devices is concerned4 ,there are two ways of rendering an electric appliance safe4 ,one is to use low potentials1 the other is to determine the dimensions of the apparatus so that it is safe1 no matter how high a potential is used4 ,of the two1 the latter seems to me the better way1 for then the safety is absolute1 unaffected by any possible combination of circumstances which might render even a low-potential appliance dangerous to life and property4 ,but the practical conditions require not only the judicious determination of the dimensions of the apparatus2 they likewise necessitate the employment of energy of the proper kind4 ,it is easy1 for instance1 to construct a transformer capable of giving1 when operated from an ordinary alternate current machine of low tension1 say #ej1jjj volts1 which might be required to light a highly exhausted phosphorescent tube1 so that1 in spite of the high potential1 it is perfectly safe1 the shock from it producing no inconvenience4 ,still such a transformer would be expensive1 and in itself inefficient2 and1 besides1 what energy was obtained from it would not be economically used for the production of light4 ,the economy demands the employment of energy in the form of extremely rapid vibrations4 ,the problem of producing light has been likened to that of maintaining a certain high-pitch note by means of a bell4 ,it should be said a barely audible note2 and even these words would not express it1 so wonderful is the sensitiveness of the eye4 ,we may deliver powerful blows at long intervals1 waste a good deal of energy1 and still not get what we want2 or we may keep up the note by delivering frequent taps1 and get nearer to the object sought by the expenditure of much less energy4 ,in the production of light1 as far as the illuminating device is concerned1 there can be only one rule--that is1 to use as high frequencies as can be obtained2 but the means for the production and conveyance of impulses of such character impose1 at present at least1 great limitations4 ,once it is decided to use very high frequencies1 the return wire becomes unnecessary1 and all the appliances are simplified4 ,by the use of obvious means the same result is obtained as though the return wire were used4 ,it is sufficient for this purpose to bring in contact with the bulb1 or merely in the vicinity of the same1 an insulated body of some surface4 ,the surface need1 of course1 be the smaller1 the higher the frequency and potential used1 and necessarily1 also1 the higher the economy of the lamp or other device4 ,this plan of working has been resorted to on several occasions this evening4 ,so1 for instance1 when the incandescence of a button was produced by grasping the bulb with the hand1 the body of the experimenter merely served to intensify the action4 ,the bulb used was similar to that illustrated in ,fig4 #adh1 and the coil was excited to a small potential1 not sufficient to bring the button to incandescence when the bulb was hanging from the wire2 and incidentally1 in order to perform the experiment in a more suitable manner1 the button was taken so large that a perceptible time had to elapse before1 upon grasping the bulb1 it could be rendered incandescent4 ,the contact with the bulb was1 of course1 quite unnecessary4 ,it is easy1 by using a rather large bulb with an exceedingly small electrode1 to adjust the conditions so that the latter is brought to bright incandescence by the mere approach of the experimenter within a few feet of the bulb1 and that the incandescence subsides upon his receding4 ,illustration3 ,,fig4 #aec4 ,illustration3 ,,fig4 #aed4 ,in another experiment1 when phosphorescence was excited1 a similar bulb was used4 ,here again1 originally1 the potential was not sufficient to excite phosphorescence until the action was intensified--in this case1 however1 to present a different feature1 by touching the socket with a metallic object held in the hand4 ,the electrode in the bulb was a carbon button so large that it could not be brought to incandescence1 and thereby spoil the effect produced by phosphorescence4 ,again1 in another of the early experiments1 a bulb was used1 as illustrated in ,fig4 #ada4 ,in this instance1 by touching the bulb with one or two fingers1 one or two shadows of the stem inside were projected against the glass1 the touch of the finger producing the same results as the application of an external negative electrode under ordinary circumstances4 ,in all these experiments the action was intensified by augmenting the capacity at the end of the lead connected to the terminal4 ,as a rule1 it is not necessary to resort to such means1 and would be quite unnecessary with still higher frequencies2 but when it is desired1 the bulb1 or tube1 can be easily adapted to the purpose4 ,in ,fig4 #aec1 for example1 an experimental bulb1 ,l1 is shown1 which is provided with a neck1 n1 on the top1 for the application of an external tinfoil coating1 which may be connected to a body of larger surface4 ,such a lamp as illustrated in ,fig4 #aed may also be lighted by connecting the tinfoil coating on the neck n to the terminal1 and the leading-in wire1 w1 to an insulated plate4 ,if the bulb stands in a socket upright1 as shown in the cut1 a shade of conducting material may be slipped in the neck1 n1 and the action thus magnified4 ,a more perfected arrangement used in some of these bulbs is illustrated in ,fig4 #aee4 ,in this case the construction of the bulb is as shown and described before1 when reference was made to ,fig4 #adh4 ,a zinc sheet1 ,z1 with a tubular extension1 ,t1 is applied over the metallic socket1 ,s4 ,the bulb hangs downward from the terminal1 t1 the zinc sheet1 ,z1 performing the double office of intensifier and reflector4 ,the reflector is separated from the terminal1 t1 by an extension of the insulating plug1 ,p4 ,a similar disposition with a phosphorescent tube is illustrated in ,fig4 #aef4 ,the tube1 ,t1 is prepared from two short tubes of different diameter1 which are sealed on the ends4 ,on the lower end is placed an inside conducting coating1 ,c1 which connects to the wire w4 ,the wire has a hook on the upper end for suspension1 and passes through the centre of the inside tube1 which is filled with some good and tightly packed insulator4 ,on the outside of the upper end of the tube1 ,t1 is another conducting coating1 ,c#a1 upon which is slipped a metallic reflector ,z1 which should be separated by a thick insulation from the end of wire w4 ,the economical use of such a reflector or intensifier would require that all energy supplied to an air condenser should be recoverable1 or1 in other words1 that there should not be any losses1 neither in the gaseous medium nor through its action elsewhere4 ,this is far from being so1 but1 fortunately1 the losses may be reduced to anything desired4 ,a few remarks are necessary on this subject1 in order to make the experiences gathered in the course of these investigations perfectly clear4 ,illustration3 ,,fig4 #aee4 ,suppose a small helix with many well insulated turns1 as in experiment ,fig4 #adf1 has one of its ends connected to one of the terminals of the induction coil1 and the other to a metal plate1 or1 for the sake of simplicity1 a sphere1 insulated in space4 ,when the coil is set to work1 the potential of the sphere is alternated1 and a small helix now behaves as though its free end were connected to the other terminal of the induction coil4 ,if an iron rod be held within a small helix1 it is quickly brought to a high temperature1 indicating the passage of a strong current through the helix4 ,how does the insulated sphere act in this case8 ,it can be a condenser1 storing and returning the energy supplied to it1 or it can be a mere sink of energy1 and the conditions of the experiment determine whether it is rather one than the other4 ,the sphere being charged to a high potential1 it acts inductively upon the surrounding air1 or whatever gaseous medium there might be4 ,the molecules1 or atoms1 which are near the sphere1 are of course more attracted1 and move through a greater distance than the farther ones4 ,when the nearest molecules strike the sphere1 they are repelled1 and collisions occur at all distances within the inductive action of the sphere4 ,it is now clear that1 if the potential be steady1 but little loss of energy can be caused in this way1 for the molecules which are nearest to the sphere1 having had an additional charge imparted to them by contact1 are not attracted until they have parted1 if not with all1 at least with most of the additional charge1 which can be accomplished only after a great many collisions4 ,from the fact1 that with a steady potential there is but little loss in dry air1 one must come to such a conclusion4 ,when the potential of a sphere1 instead of being steady1 is alternating1 the conditions are entirely different4 ,in this case a rhythmical bombardment occurs1 no matter whether the molecules1 after coming in contact with the sphere1 lose the imparted charge or not2 what is more1 if the charge is not lost1 the impacts are only the more violent4 ,still1 if the frequency of the impulses be very small1 the loss caused by the impacts and collisions would not be serious1 unless the potential were excessive4 ,but when extremely high frequencies and more or less high potentials are used1 the loss may very great4 ,the total energy lost per unit of time is proportionate to the product of the number of impacts per second1 or the frequency and the energy lost in each impact4 ,but the energy of an impact must be proportionate to the square of the electric density of the sphere1 since the charge imparted to the molecule is proportionate to that density4 ,i conclude from this that the total energy lost must be proportionate to the product of the frequency and the square of the electric density2 but this law needs experimental confirmation4 ,assuming the preceding considerations to be true1 then1 by rapidly alternating the potential of a body immersed in an insulating gaseous medium1 any amount of energy may be dissipated into space4 ,most of that energy then1 ,i believe1 is not dissipated in the form of long ether waves1 propagated to considerable distance1 as is thought most generally1 but is consumed--in the case of an insulated sphere1 for example--in impact and collisional losses--that is1 heat vibrations--on the surface and in the vicinity of the sphere4 ,to reduce the dissipation1 it is necessary to work with a small electric density--the smaller1 the higher the frequency4 ,illustration3 ,,fig4 #aef4 ,but since1 on the assumption before made1 the loss is diminished with the square of the density1 and since currents of very high frequencies involve considerable waste when transmitted through conductors1 it follows that1 on the whole1 it is better to employ one wire than two4 ,therefore1 if motors1 lamps1 or devices of any kind are perfected1 capable of being advantageously operated by currents of extremely high frequency1 economical reasons will make it advisable to use only one wire1 especially if the distances are great4 ,when energy is absorbed in a condenser1 the same behaves as though its capacity were increased4 ,absorption always exists more or less1 but generally it is small and of no consequence as long as the frequencies are not very great4 ,in using extremely high frequencies1 and1 necessarily in such case1 also high potentials1 the absorption--or1 what is here meant more particularly by this term1 the loss of energy due to the presence of a gaseous medium--is an important factor to be considered1 as the energy absorbed in the air condenser may be any fraction of the supplied energy4 ,this would seem to make it very difficult to tell from the measured or computed capacity of an air condenser its actual capacity or vibration period1 especially if the condenser is of very small surface and is charged to a very high potential4 ,as many important results are dependent upon the correctness of the estimation of the vibration period1 this subject demands the most careful scrutiny of other investigators4 ,to reduce the probable error as much as possible in experiments of the kind alluded to1 it is advisable to use spheres or plates of large surface1 so as to make the density exceedingly small4 ,otherwise1 when it is practicable1 an oil condenser should be used in preference4 ,in oil or other liquid dielectrics there are seemingly no such losses as in gaseous media4 ,it being impossible to exclude entirely the gas in condensers with solid dielectrics1 such condensers should be immersed in oil1 for economical reasons1 if nothing else2 they can then be strained to the utmost1 and will remain cool4 ,in ,leyden jars the loss due to air is comparatively small1 as the tinfoil coatings are large1 close together1 and the charged surfaces not directly exposed2 but when the potentials are very high1 the loss may be more or less considerable at1 or near1 the upper edge of the foil1 where the air is principally acted upon4 ,if the jar be immersed in boiled-out oil1 it will be capable of performing four times the amount of work which it can for any length of time when used in the ordinary way1 and the loss will be inappreciable4 ,it should not be thought that the loss in heat in an air condenser is necessarily associated with the formation of visible streams or brushes4 ,if a small electrode1 inclosed in an unexhausted bulb1 is connected to one of the terminals of the coil1 streams can be seen to issue from the electrode1 and the air in the bulb is heated2 if instead of a small electrode a large sphere is inclosed in the bulb1 no streams are observed1 still the air is heated4 ,nor should it be thought that the temperature of an air condenser would give even an approximate idea of the loss in heat incurred1 as in such case heat must be given off much more quickly1 since there is1 in addition to the ordinary radiation1 a very active carrying away of heat by independent carriers going on1 and since not only the apparatus1 but the air at some distance from it is heated in consequence of the collisions which must occur4 ,owing to this1 in experiments with such a coil1 a rise of temperature can be distinctly observed only when the body connected to the coil is very small4 ,but with apparatus on a larger scale1 even a body of considerable bulk would be heated1 as1 for instance1 the body of a person2 and ,i think that skilled physicians might make observations of utility in such experiments1 which1 if the apparatus were judiciously designed1 would not present the slightest danger4 ,a question of some interest1 principally to meteorologists1 presents itself here4 ,how does the earth behave8 ,the earth is an air condenser1 but is it a perfect or a very imperfect one--a mere sink of energy8 ,there can be little doubt that to such small disturbance as might be caused in an experiment1 the earth behaves as an almost perfect condenser4 ,but it might be different when its charge is set in vibration by some sudden disturbance occurring in the heavens4 ,in such case1 as before stated1 probably only little of the energy of the vibrations set up would be lost into space in the form of long ether radiations1 but most of the energy1 ,i think1 would spend itself in molecular impacts and collisions1 and pass off into space in the form of short heat1 and possibly light1 waves4 ,as both the frequency of the vibrations of the charge and the potential are in all probability excessive1 the energy converted into heat may be considerable4 ,since the density must be unevenly distributed1 either in consequence of the irregularity of the earth's surface1 or on account of the condition of the atmosphere in various places1 the effect produced would accordingly vary from place to place4 ,considerable variations in the temperature and pressure of the atmosphere may in this manner be caused at any point of the surface of the earth4 ,the variations may be gradual or very sudden1 according to the nature of the general disturbance1 and may produce rain and storms1 or locally modify the weather in any way4 ,from the remarks before made1 one may see what an important factor of loss the air in the neighborhood of a charged surface becomes when the electric density is great and the frequency of the impulses excessive4 ,but the action1 as explained1 implies that the air is insulating--that is1 that it is composed of independent carriers immersed in an insulating medium4 ,this is the case only when the air is at something like ordinary or greater1 or at extremely small1 pressure4 ,when the air is slightly rarefied and conducting1 then true conduction losses occur also4 ,in such case1 of course1 considerable energy may be dissipated into space even with a steady potential1 or with impulses of low frequency1 if the density is very great4 ,when the gas is at very low pressure1 an electrode is heated more because higher speeds can be reached4 ,if the gas around the electrode is strongly compressed1 the displacements1 and consequently the speeds1 are very small1 and the heating is insignificant4 ,but if in such case the frequency could be sufficiently increased1 the electrode would be brought to a high temperature as well as if the gas were at very low pressure2 in fact1 exhausting the bulb is only necessary because we cannot produce1 7and possibly not convey7 currents of the required frequency4 ,returning to the subject of electrode lamps1 it is obviously of advantage in such a lamp to confine as much as possible the heat to the electrode by preventing the circulation of the gas in the bulb4 ,if a very small bulb be taken1 it would confine the heat better than a large one1 but it might not be of sufficient capacity to be operated from the coil1 or1 if so1 the glass might get too hot4 ,a simple way to improve in this direction is to employ a globe of the required size1 but to place a small bulb1 the diameter of which is properly estimated1 over the refractory button contained in the globe4 ,this arrangement is illustrated in ,fig4 #aeg4 ,illustration3 ,,fig4 #aeg4 ,illustration3 ,,fig4 #aeh4 ,the globe ,l has in this case a large neck n1 allowing the small bulb b to slip through4 ,otherwise the construction is the same as shown in ,fig4 #adg1 for example4 ,the small bulb is conveniently supported upon the stem s1 carrying the refractory button m4 ,it is separated from the aluminum tube a by several layers of mica ,m1 in order to prevent the cracking of the neck by the rapid heating of the aluminum tube upon a sudden turning on of the current4 ,the inside bulb should be as small as possible when it is desired to obtain light only by incandescence of the electrode4 ,if it is desired to produce phosphorescence1 the bulb should be larger1 else it would be apt to get too hot1 and the phosphorescence would cease4 ,in this arrangement usually only the small bulb shows phosphorescence1 as there is practically no bombardment against the outer globe4 ,in some of these bulbs constructed as illustrated in ,fig4 #aeg1 the small tube was coated with phosphorescent paint1 and beautiful effects were obtained4 ,instead of making the inside bulb large1 in order to avoid undue heating1 it answers the purpose to make the electrode m larger4 ,in this case the bombardment is weakened by reason of the smaller electric density4 ,many bulbs were constructed on the plan illustrated in ,fig4 #aeh4 ,here a small bulb b1 containing the refractory button m1 upon being exhausted to a very high degree was sealed in a large globe ,l1 which was then moderately exhausted and sealed off4 ,the principal advantage of this construction was that it allowed of reaching extremely high vacua1 and1 at the same time of using a large bulb4 ,it was found1 in the course of experiments with bulbs such as illustrated in ,fig4 #aeh1 that it was well to make the stem s1 near the seal at e1 very thick1 and the leading-in wire w thin1 as it occurred sometimes that the stem at e was heated and the bulb was cracked4 ,often the outer globe ,l was exhausted only just enough to allow the discharge to pass through1 and the space between the bulbs appeared crimson1 producing a curious effect4 ,in some cases1 when the exhaustion in globe ,l was very low1 and the air good conducting1 it was found necessary1 in order to bring the button m to high incandescence1 to place1 preferably on the upper part of the neck of the globe1 a tinfoil coating which was connected to an insulated body1 to the ground1 or to the other terminal of the coil1 as the highly conducting air weakened the effect somewhat1 probably by being acted upon inductively from the wire w1 where it entered the bulb at e4 ,another difficulty--which1 however1 is always present when the refractory button is mounted in a very small bulb--existed in the construction illustrated in ,fig4 #aeh1 namely1 the vacuum in the bulb b would be impaired in a comparatively short time4 ,the chief idea in the two last described constructions was to confine the heat to the central portion of the globe by preventing the exchange of air4 ,an advantage is secured1 but owing to the heating of the inside bulb and slow evaporation of the glass1 the vacuum is hard to maintain1 even if the construction illustrated in ,fig4 #aeg be chosen1 in which both bulbs communicate4 ,but by far the better way--the ideal way--would be to reach sufficiently high frequencies4 ,the higher the frequency1 the slower would be the exchange of the air1 and ,i think that a frequency may be reached1 at which there would be no exchange whatever of the air molecules around the terminal4 ,we would then produce a flame in which there would be no carrying away of material1 and a queer flame it would be1 for it would be rigid6 ,with such high frequencies the inertia of the particles would come into play4 ,as the brush1 or flame1 would gain rigidity in virtue of the inertia of the particles1 the exchange of the latter would be prevented4 ,this would necessarily occur1 for1 the number of impulses being augmented1 the potential energy of each would diminish1 so that finally only atomic vibrations could be set up1 and the motion of translation through measurable space would cease4 ,thus an ordinary gas burner connected to a source of rapidly alternating potential might have its efficiency augmented to a certain limit1 and this for two reasons--because of the additional vibration imparted1 and because of a slowing down of the process of carrying off4 ,but the renewal being rendered difficult1 a renewal being necessary to maintain the burner1 a continued increase of the frequency of the impulses1 assuming they could be transmitted to and impressed upon the flame1 would result in the extinction of the latter1 meaning by this term only the cessation of the chemical process4 ,i think1 however1 that in the case of an electrode immersed in a fluid insulating medium1 and surrounded by independent carriers of electric charges1 which can be acted upon inductively1 a sufficient high frequency of the impulses would probably result in a gravitation of the gas all around toward the electrode4 ,for this it would be only necessary to assume that the independent bodies are irregularly shaped2 they would then turn toward the electrode their side of the greatest electric density1 and this would be a position in which the fluid resistance to approach would be smaller than that offered to the receding4 ,the general opinion1 ,i do not doubt1 is that it is out of the question to reach any such frequencies as might--assuming some of the views before expressed to be true--produce any of the results which ,i have pointed out as mere possibilities4 ,this may be so1 but in the course of these investigations1 from the observation of many phenomena1 ,i have gained the conviction that these frequencies would be much lower than one is apt to estimate at first4 ,in a flame we set up light vibrations by causing molecules1 or atoms1 to collide4 ,but what is the ratio of the frequency of the collisions and that of the vibrations set up8 ,certainly it must be incomparably smaller than that of the strokes of the bell and the sound vibrations1 or that of the discharges and the oscillations of the condenser4 ,we may cause the molecules of the gas to collide by the use of alternate electric impulses of high frequency1 and so we may imitate the process in a flame2 and from experiments with frequencies which we are now able to obtain1 ,i think that the result is producible with impulses which are transmissible through a conductor4 ,in connection with thoughts of a similar nature1 it appeared to me of great interest to demonstrate the rigidity of a vibrating gaseous column4 ,although with such low frequencies as1 say #aj1jjj per second1 which ,i was able to obtain without difficulty from a specially constructed alternator1 the task looked discouraging at first1 ,i made a series of experiments4 ,the trials with air at ordinary pressure led to no result1 but with air moderately rarefied ,i obtain what ,i think to be an unmistakable experimental evidence of the property sought for4 ,as a result of this kind might lead able investigators to conclusions of importance1 ,i will describe one of the experiments performed4 ,it is well known that when a tube is slightly exhausted1 the discharge may be passed through it in the form of a thin luminous thread4 ,when produced with currents of low frequency1 obtained from a coil operated as usual1 this thread is inert4 ,if a magnet be approached to it1 the part near the same is attracted or repelled1 according to the direction of the lines of force of the magnet4 ,it occurred to me that if such a thread would be produced with currents of very high frequency1 it should be more or less rigid1 and as it was visible it could be easily studied4 ,accordingly ,i prepared a tube about one inch in diameter and one metre long1 with outside coating at each end4 ,the tube was exhausted to a point at which1 by a little working1 the thread discharge could be obtained4 ,it must be remarked here that the general aspect of the tube1 and the degree of exhaustion1 are quite other than when ordinary low frequency currents are used4 ,as it was found preferable to work with one terminal1 the tube prepared was suspended from the end of a wire connected to the terminal1 the tinfoil coating being connected to the wire1 and to the lower coating sometimes a small insulated plate was attached4 ,when the thread was formed1 it extended through the upper part of the tube and lost itself in the lower end4 ,if it possessed rigidity it resembled1 not exactly an elastic cord stretched tight between two supports1 but a cord suspended from a height with a small weight attached at the end4 ,when the finger or a small magnet was approached to the upper end of the luminous thread1 it could be brought locally out of position by electrostatic or magnetic action2 and when the disturbing object was very quickly removed1 an analogous result was produced1 as though a suspended cord would be displaced and quickly released near the point of suspension4 ,in doing this the luminous thread was set in vibration1 and two very sharply marked nodes1 and a third indistinct one1 were formed4 ,the vibration1 once set up1 continued for fully eight minutes1 dying gradually out4 ,the speed of the vibration often varied perceptibly1 and it could be observed that the electrostatic attraction of the glass affected the vibrating thread2 but it was clear that the electrostatic action was not the cause of the vibration1 for the thread was most generally stationary1 and could always be set in vibration by passing the finger quickly near the upper part of the tube4 ,with a magnet the thread could be split in two and both parts vibrated4 ,by approaching the hand to the lower coating of the tube1 or insulation plate if attached1 the vibration was quickened2 also1 as far as ,i could see1 by raising the potential or frequency4 ,thus1 either increasing the frequency or passing a stronger discharge of the same frequency corresponded to a tightening of the cord4 ,i did not obtain any experimental evidence with condenser discharges4 ,a luminous band excited in the bulb by repeated discharges of a ,leyden jar must possess rigidity1 and if deformed and suddenly released1 should vibrate4 ,but probably the amount of vibrating matter is so small that in spite of the extreme speed1 the inertia cannot prominently assert itself4 ,besides1 the observation in such a case is rendered extremely difficult on account of the fundamental vibration4 ,the demonstration of the fact--which still needs better experimental confirmation--that a vibrating gaseous column possesses rigidity1 might greatly modify the views of thinkers4 ,when with low frequencies and insignificant potentials indications of that property may be noted1 how must a gaseous medium behave under the influence of enormous electrostatic stresses which may be active in the interstellar space1 and which may alternate with inconceivable rapidity8 ,the existence of such an electrostatic1 rhythmically throbbing force--of a vibrating electrostatic field--would show a possible way how solids might have formed from the ultra-gaseous uterus1 and how transverse and all kinds of vibrations may be transmitted through a gaseous medium filling all space4 ,then1 ether might be a true fluid1 devoid of rigidity1 and at rest1 it being merely necessary as a connecting link to enable interaction4 ,what determines the rigidity of a body8 ,it must be the speed and the amount of motive matter4 ,in a gas the speed maybe considerable1 but the density is exceedingly small2 in a liquid the speed would be likely to be small1 though the density may be considerable2 and in both cases the inertia resistance offered to displacement is practically nil4 ,but place a gaseous 7or liquid7 column in an intense1 rapidly alternating electrostatic field1 set the particles vibrating with enormous speeds1 then the inertia resistance asserts itself4 ,a body might move with more or less freedom through the vibrating mass1 but as a whole it would be rigid4 ,there is a subject which ,i must mention in connection with these experiments3 it is that of high vacua4 ,this is a subject1 the study of which is not only interesting1 but useful1 for it may lead to results of great practical importance4 ,in commercial apparatus1 such as incandescent lamps1 operated from ordinary systems of distribution1 a much higher vacuum than is obtained at present would not secure a very great advantage4 ,in such a case the work is performed on the filament1 and the gas is little concerned2 the improvement1 therefore1 would be but trifling4 ,but when we begin to use very high frequencies and potentials1 the action of the gas becomes all important1 and the degree of exhaustion materially modifies the results4 ,as long as ordinary coils1 even very large ones1 were used1 the study of the subject was limited1 because just at a point when it became most interesting it had to be interrupted on account of the non-striking vacuum being reached4 ,but at present we are able to obtain from a small disruptive discharge coil potentials much higher than even the largest coil was capable of giving1 and1 what is more1 we can make the potential alternate with great rapidity4 ,both of these results enable us now to pass a luminous discharge through almost any vacua obtainable1 and the field of our investigations is greatly extended4 ,think we as we may1 of all the possible directions to develop a practical illuminant1 the line of high vacua seems to be the most promising at present4 ,but to reach extreme vacua the appliances must be much more improved1 and ultimate perfection will not be attained until we shall have discharged the mechanical and perfected an electrical vacuum pump4 ,molecules and atoms can be thrown out of a bulb under the action of an enormous potential3 this will be the principle of the vacuum pump of the future4 ,for the present1 we must secure the best results we can with mechanical appliances4 ,in this respect1 it might not be out of the way to say a few words about the method of1 and apparatus for1 producing excessively high degrees of exhaustion of which ,i have availed myself in the course of these investigations4 ,it is very probable that other experimenters have used similar arrangements2 but as it is possible that there may be an item of interest in their description1 a few remarks1 which will render this investigation more complete1 might be permitted4 ,illustration3 ,,fig4 #aei4 ,the apparatus is illustrated in a drawing shown in ,fig4 #aei4 ,s represents a ,sprengel pump1 which has been specially constructed to better suit the work required4 ,the stop-cock which is usually employed has been omitted1 and instead of it a hollow stopper s has been fitted in the neck of the reservoir ,r4 ,this stopper has a small hole h1 through which the mercury descends2 the size of the outlet o being properly determined with respect to the section of the fall tube t1 which is sealed to the reservoir instead of being connected to it in the usual manner4 ,this arrangement overcomes the imperfections and troubles which often arise from the use of the stopcock on the reservoir and the connections of the latter with the fall tube4 ,the pump is connected through a ,u-shaped tube t to a very large reservoir ,r#a4 ,especial care was taken in fitting the grinding surfaces of the stoppers p and p#a1 and both of these and the mercury caps above them were made exceptionally long4 ,after the ,u-shaped tube was fitted and put in place1 it was heated1 so as to soften and take off the strain resulting from imperfect fitting4 ,the ,u-shaped tube was provided with a stopcock ,c1 and two ground connections g and g#a1--one for a small bulb b1 usually containing caustic potash1 and the other for the receiver r1 to be exhausted4 ,the reservoir ,r#a1 was connected by means of a rubber tube to a slightly larger reservoir ,r#b1 each of the two reservoirs being provided with a stopcock ,c#a and ,c#b1 respectively4 ,the reservoir ,r#b could be raised and lowered by a wheel and rack1 and the range of its motion was so determined that when it was filled with mercury and the stopcock ,c#b closed1 so as to form a ,torricellian vacuum in it when raised1 it could be lifted so high that the reservoir ,r#a would stand a little above stopcock ,c#a2 and when this stopcock was closed and the reservoir ,r#b descended1 so as to form a ,torricellian vacuum in reservoir ,r#a1 it could be lowered so far as to completely empty the latter1 the mercury filling the reservoir ,r#b up to a little above stopcock ,c#b4 ,the capacity of the pump and of the connections was taken as small as possible relatively to the volume of reservoir1 ,r#a1 since1 of course1 the degree of exhaustion depended upon the ratio of these quantities4 ,with this apparatus ,i combined the usual means indicated by former experiments for the production of very high vacua4 ,in most of the experiments it was most convenient to use caustic potash4 ,i may venture to say1 in regard to its use1 that much time is saved and a more perfect action of the pump insured by fusing and boiling the potash as soon as1 or even before1 the pump settles down4 ,if this course is not followed1 the sticks1 as ordinarily employed1 may give off moisture at a certain very slow rate1 and the pump may work for many hours without reaching a very high vacuum4 ,the potash was heated either by a spirit lamp or by passing a discharge through it1 or by passing a current through a wire contained in it4 ,the advantage in the latter case was that the heating could be more rapidly repeated4 ,generally the process of exhaustion was the following3--,at the start1 the stop-cocks ,c and ,c#a being open1 and all other connections closed1 the reservoir ,r#b was raised so far that the mercury filled the reservoir ,r#a and a part of the narrow connecting ,u-shaped tube4 ,when the pump was set to work1 the mercury would1 of course1 quickly rise in the tube1 and reservoir ,r#b was lowered1 the experimenter keeping the mercury at about the same level4 ,the reservoir ,r#b was balanced by a long spring which facilitated the operation1 and the friction of the parts was generally sufficient to keep it in almost any position4 ,when the ,sprengel pump had done its work1 the reservoir ,r#b was further lowered and the mercury descended in ,r#a and filled ,r#b1 whereupon stopcock ,c#b was closed4 ,the air adhering to the walls of ,r#a and that absorbed by the mercury was carried off1 and to free the mercury of all air the reservoir ,r#b was for a long time worked up and down4 ,during this process some air1 which would gather below stopcock ,c#b1 was expelled from ,r#b by lowering it far enough and opening the stopcock1 closing the latter again before raising the reservoir4 ,when all the air had been expelled from the mercury1 and no air would gather in ,r#b when it was lowered1 the caustic potash was resorted to4 ,the reservoir ,r#b was now again raised until the mercury in ,r#a1 stood above stopcock ,c#a4 ,the caustic potash was fused and boiled1 and moisture partly carried off by the pump and partly re-absorbed2 and this process of heating and cooling was repeated many times1 and each time1 upon the moisture being absorbed or carried off1 the reservoir ,r#b was for a long time raised and lowered4 ,in this manner all the moisture was carried off from the mercury1 and both the reservoirs were in proper condition to be used4 ,the reservoir ,r#b was then again raised to the top1 and the pump was kept working for a long time4 ,when the highest vacuum obtainable with the pump had been reached1 the potash bulb was usually wrapped with cotton which was sprinkled with ether so as to keep the potash at a very low temperature1 then the reservoir ,r#b was lowered1 and upon reservoir ,r#a being emptied the receiver was quickly sealed up4 ,when a new bulb was put on1 the mercury was always raised above stopcock ,c#a1 which was closed1 so as to always keep the mercury and both the reservoirs in fine condition1 and the mercury was never withdrawn from ,r#a except when the pump had reached the highest degree of exhaustion4 ,it is necessary to observe this rule if it is desired to use the apparatus to advantage4 ,by means of this arrangement ,i was able to proceed very quickly1 and when the apparatus was in perfect order it was possible to reach the phosphorescent stage in a small bulb in less than fifteen minutes1 which is certainly very quick work for a small laboratory arrangement requiring all in all about #ajj pounds of mercury4 ,with ordinary small bulbs the ratio of the capacity of the pump1 receiver1 and connections1 and that of reservoir ,r was about #a to #bj1 and the degrees of exhaustion reached were necessarily very high1 though ,i am unable to make a precise and reliable statement how far the exhaustion was carried4 ,what impresses the investigator most in the course of these experiences is the behavior of gases when subjected to great rapidly alternating electrostatic stresses4 ,but he must remain in doubt as to whether the effects observed are due wholly to the molecules1 or atoms1 of the gas which chemical analysis discloses to us1 or whether there enters into play another medium of a gaseous nature1 comprising atoms1 or molecules1 immersed in a fluid pervading the space4 ,such a medium surely must exist1 and ,i am convinced that1 for instance1 even if air were absent1 the surface and neighborhood of a body in space would be heated by rapidly alternating the potential of the body2 but no such heating of the surface or neighborhood could occur if all free atoms were removed and only a homogeneous1 incompressible1 and elastic fluid--such as ether is supposed to be--would remain1 for then there would be no impacts1 no collisions4 ,in such a case1 as far as the body itself is concerned1 only frictional losses in the inside could occur4 ,it is a striking fact that the discharge through a gas is established with ever-increasing freedom as the frequency of the impulses is augmented4 ,it behaves in this respect quite contrarily to a metallic conductor4 ,in the latter the impedance enters prominently into play as the frequency is increased1 but the gas acts much as a series of condensers would2 the facility with which the discharge passes through1 seems to depend on the rate of change of potential4 ,if it acts so1 then in a vacuum tube even of great length1 and no matter how strong the current1 self-induction could not assert itself to any appreciable degree4 ,we have1 then1 as far as we can now see1 in the gas a conductor which is capable of transmitting electric impulses of any frequency which we may be able to produce4 ,could the frequency be brought high enough1 then a queer system of electric distribution1 which would be likely to interest gas companies1 might be realized3 metal pipes filled with gas--the metal being the insulator1 the gas the conductor--supplying phosphorescent bulbs1 or perhaps devices as yet uninvented4 ,it is certainly possible to take a hollow core of copper1 rarefy the gas in the same1 and by passing impulses of sufficiently high frequency through a circuit around it1 bring the gas inside to a high degree of incandescence2 but as to the nature of the forces there would be considerable uncertainty1 for it would be doubtful whether with such impulses the copper core would act as a static screen4 ,such paradoxes and apparent impossibilities we encounter at every step in this line of work1 and therein lies1 to a great extent1 the charm of the study4 ,i have here a short and wide tube which is exhausted to a high degree and covered with a substantial coating of bronze1 the coating barely allowing the light to shine through4 ,a metallic cap1 with a hook for suspending the tube1 is fastened around the middle portion of the latter1 the clasp being in contact with the bronze coating4 ,i now want to light the gas inside by suspending the tube on a wire connected to the coil4 ,any one who would try the experiment for the first time1 not having any previous experience1 would probably take care to be quite alone when making the trial1 for fear that he might become the joke of his assistants4 ,still1 the bulb lights in spite of the metal coating1 and the light can be distinctly perceived through the latter4 ,a long tube covered with aluminum bronze lights when held in one hand--the other touching the terminal of the coil--quite powerfully4 ,it might be objected that the coatings are not sufficiently conducting2 still1 even if they were highly resistant1 they ought to screen the gas4 ,they certainly screen it perfectly in a condition of rest1 but far from perfectly when the charge is surging in the coating4 ,but the loss of energy which occurs within the tube1 notwithstanding the screen1 is occasioned principally by the presence of the gas4 ,were we to take a large hollow metallic sphere and fill it with a perfect1 incompressible1 fluid dielectric1 there would be no loss inside of the sphere1 and consequently the inside might be considered as perfectly screened1 though the potential be very rapidly alternating4 ,even were the sphere filled with oil1 the loss would be incomparably smaller than when the fluid is replaced by a gas1 for in the latter case the force produces displacements2 that means impact and collisions in the inside4 ,no matter what the pressure of the gas may be1 it becomes an important factor in the heating of a conductor when the electric density is great and the frequency very high4 ,that in the heating of conductors by lightning discharges1 air is an element of great importance1 is almost as certain as an experimental fact4 ,i may illustrate the action of the air by the following experiment3 ,i take a short tube which is exhausted to a moderate degree and has a platinum wire running through the middle from one end to the other4 ,i pass a steady or low frequency current through the wire1 and it is heated uniformly in all parts4 ,the heating here is due to conduction1 or frictional losses1 and the gas around the wire has--as far as we can see--no function to perform4 ,but now let me pass sudden discharges1 or high frequency currents1 through the wire4 ,again the wire is heated1 this time principally on the ends and least in the middle portion2 and if the frequency of the impulses1 or the rate of change1 is high enough1 the wire might as well be cut in the middle as not1 for practically all heating is due to the rarefied gas4 ,here the gas might only act as a conductor of no impedance diverting the current from the wire as the impedance of the latter is enormously increased1 and merely heating the ends of the wire by reason of their resistance to the passage of the discharge4 ,but it is not at all necessary that the gas in the tube should be conducting2 it might be at an extremely low pressure1 still the ends of the wire would be heated--as1 however1 is ascertained by experience--only the two ends would in such case not be electrically connected through the gaseous medium4 ,now what with these frequencies and potentials occurs in an exhausted tube1 occurs in the lightning discharges at ordinary pressure4 ,we only need remember one of the facts arrived at in the course of these investigations1 namely1 that to impulses of very high frequency the gas at ordinary pressure behaves much in the same manner as though it were at moderately low pressure4 ,i think that in lightning discharges frequently wires or conducting objects are volatilized merely because air is present1 and that1 were the conductor immersed in an insulating liquid1 it would be safe1 for then the energy would have to spend itself somewhere else4 ,from the behavior of gases under sudden impulses of high potential1 ,i am led to conclude that there can be no surer way of diverting a lightning discharge than by affording it a passage through a volume of gas1 if such a thing can be done in a practical manner4 ,there are two more features upon which ,i think it necessary to dwell in connection with these experiments--the radiant state and the non-striking vacuum4 ,any one who has studied ,crookes' work must have received the impression that the radiant state is a property of the gas inseparably connected with an extremely high degree of exhaustion4 ,but it should be remembered that the phenomena observed in an exhausted vessel are limited to the character and capacity of the apparatus which is made use of4 ,i think that in a bulb a molecule1 or atom1 does not precisely move in a straight line because it meets no obstacle1 but because the velocity imparted to it is sufficient to propel it in a sensibly straight line4 ,the mean free path is one thing1 but the velocity--the energy associated with the moving body--is another1 and under ordinary circumstances ,i believe that it is a mere question of potential or speed4 ,a disruptive discharge coil1 when the potential is pushed very far1 excites phosphorescence and projects shadows1 at comparatively low degrees of exhaustion4 ,in a lightning discharge1 matter moves in straight lines at ordinary pressure when the mean free path is exceedingly small1 and frequently images of wires or other metallic objects have been produced by the particles thrown off in straight lines4 ,i have prepared a bulb to illustrate by an experiment the correctness of these assertions4 ,in a globe ,l1 ,fig4 #afj1 ,i have mounted upon a lamp filament f a piece of lime l4 ,the lamp filament is connected with a wire which leads into the bulb1 and the general construction of the latter is as indicated in ,fig4 #adh1 before described4 ,the bulb being suspended from a wire connected to the terminal of the coil1 and the latter being set to work1 the lime piece l and the projecting parts of the filament f are bombarded4 ,the degree of exhaustion is just such that with the potential the coil is capable of giving1 phosphorescence of the glass is produced1 but disappears as soon as the vacuum is impaired4 ,the lime containing moisture1 and moisture being given off as soon as heating occurs1 the phosphorescence lasts only for a few moments4 ,when the lime has been sufficiently heated1 enough moisture has been given off to impair materially the vacuum of the bulb4 ,as the bombardment goes on1 one point of the lime piece is more heated than other points1 and the result is that finally practically all the discharge passes through that point which is intensely heated1 and a white stream of lime particles 7,fig4 #afj7 then breaks forth from that point4 ,this stream is composed of radiant matter1 yet the degree of exhaustion is low4 ,but the particles move in straight lines because the velocity imparted to them is great1 and this is due to three causes--to the great electric density1 the high temperature of the small point1 and the fact that the particles of the lime are easily torn and thrown off--far more easily than those of carbon4 ,with frequencies such as we are able to obtain1 the particles are bodily thrown off and projected to a considerable distance2 but with sufficiently high frequencies no such thing would occur2 in such case only a stress would spread or a vibration would be propagated through the bulb4 ,it would be out of the question to reach any such frequency on the assumption that the atoms move with the speed of light2 but ,i believe that such a thing is impossible2 for this an enormous potential would be required4 ,with potentials which we are able to obtain1 even with a disruptive discharge coil1 the speed must be quite insignificant4 ,illustration3 ,,fig4 #afj4 ,as to the non-striking vacuum1 the point to be noted is1 that it can occur only with low frequency impulses1 and it is necessitated by the impossibility of carrying off enough energy with such impulses in high vacuum1 since the few atoms which are around the terminal upon coming in contact with the same1 are repelled and kept at a distance for a comparatively long period of time1 and not enough work can be performed to render the effect perceptible to the eye4 ,if the difference of potential between the terminals is raised1 the dielectric breaks down4 ,but with very high frequency impulses there is no necessity for such breaking down1 since any amount of work can be performed by continually agitating the atoms in the exhausted vessel1 provided the frequency is high enough4 ,it is easy to reach--even with frequencies obtained from an alternator as here used--a stage at which the discharge does not pass between two electrodes in a narrow tube1 each of these being connected to one of the terminals of the coil1 but it is difficult to reach a point at which a luminous discharge would not occur around each electrode4 ,illustration3 ,,fig4 #afa4 ,illustration3 ,,fig4 #afb4 ,a thought which naturally presents itself in connection with high frequency currents1 is to make use of their powerful electrodynamic inductive action to produce light effects in a sealed glass globe4 ,the leading-in wire is one of the defects of the present incandescent lamp1 and if no other improvement were made1 that imperfection at least should be done away with4 ,following this thought1 ,i have carried on experiments in various directions1 of which some were indicated in my former paper4 ,i may here mention one or two more lines of experiment which have been followed up4 ,many bulbs were constructed as shown in ,fig4 #afa and ,fig4 #afb4 ,in ,fig4 #afa1 a wide tube1 ,t1 was sealed to a smaller ,w shaped tube ,u1 of phosphorescent glass4 ,in the tube ,t1 was placed a coil ,c1 of aluminum wire1 the ends of which were provided with small spheres1 t and t#a1 of aluminum1 and reached into the ,u tube4 ,the tube ,t was slipped into a socket containing a primary coil1 through which usually the discharges of ,leyden jars were directed1 and the rarefied gas in the small ,u tube was excited to strong luminosity by the high-tension current induced in the coil ,c4 ,when ,leyden jar discharges were used to induce currents in the coil ,c1 it was found necessary to pack the tube ,t tightly with insulating powder1 as a discharge would occur frequently between the turns of the coil1 especially when the primary was thick and the air gap1 through which the jars discharged1 large1 and no little trouble was experienced in this way4 ,in ,fig4 #afb is illustrated another form of the bulb constructed4 ,in this case a tube ,t is sealed to a globe ,l4 ,the tube contains a coil ,c1 the ends of which pass through two small glass tubes t and t#a1 which are sealed to the tube ,t4 ,two refractory buttons m and m#a1 are mounted on lamp filaments which are fastened to the ends of the wires passing through the glass tubes t and t#a4 ,generally in bulbs made on this plan the globe ,l communicated with the tube ,t4 ,for this purpose the ends of the small tubes t and t#a were heated just a trifle in the burner1 merely to hold the wires1 but not to interfere with the communication4 ,the tube ,t1 with the small tubes1 wires through the same1 and the refractory buttons m and m#a1 were first prepared1 and then sealed to globe ,l1 whereupon the coil ,c was slipped in and the connections made to its ends4 ,the tube was then packed with insulating powder1 jamming the latter as tight as possible up to very nearly the end2 then it was closed and only a small hole left through which the remainder of the powder was introduced1 and finally the end of the tube was closed4 ,usually in bulbs constructed as shown in ,fig4 #afb an aluminum tube a was fastened to the upper end s of each of the tubes t and t#a in order to protect that end against the heat4 ,the buttons m and m#a could be brought to any degree of incandescence by passing the discharges of ,leyden jars around the coil ,c4 ,in such bulbs with two buttons a very curious effect is produced by the formation of the shadows of each of the two buttons4 ,another line of experiment1 which has been assiduously followed1 was to induce by electro-dynamic induction a current or luminous discharge in an exhausted tube or bulb4 ,this matter has received such able treatment at the hands of ,prof4 ,j4 ,j4 ,thomson1 that ,i could add but little to what he has made known1 even had ,i made it the special subject of this lecture4 ,still1 since experiments in this line have gradually led me to the present views and results1 a few words must be devoted here to this subject4 ,it has occurred1 no doubt1 to many that as a vacuum tube is made longer1 the electromotive force per unit length of the tube1 necessary to pass a luminous discharge through the latter1 becomes continually smaller2 therefore1 if the exhausted tube be made long enough1 even with low frequencies a luminous discharge could be induced in such a tube closed upon itself4 ,such a tube might be placed around a hall or on a ceiling1 and at once a simple appliance capable of giving considerable light would be obtained4 ,but this would be an appliance hard to manufacture and extremely unmanageable4 ,it would not do to make the tube up of small lengths1 because there would be with ordinary frequencies considerable loss in the coatings1 and besides1 if coatings were used1 it would be better to supply the current directly to the tube by connecting the coatings to a transformer4 ,but even if all objections of such nature were removed1 with low frequencies the light conversion itself would be inefficient1 as ,i have before stated4 ,in using extremely high frequencies the length of the secondary--in other words1 the size of the vessel--can be reduced as much as desired1 and the efficiency of the light conversion is increased1 provided that means are invented for efficiently obtaining such high frequencies4 ,thus one is led1 from theoretical and practical considerations1 to the use of high frequencies1 and this means high electromotive forces and small currents in the primary4 ,when one works with condenser charges--and they are the only means up to the present known for reaching these extreme frequencies--one gets to electromotive forces of several thousands of volts per turn of the primary4 ,we cannot multiply the electro-dynamic inductive effect by taking more turns in the primary1 for we arrive at the conclusion that the best way is to work with one single turn--though we must sometimes depart from this rule--and we must get along with whatever inductive effect we can obtain with one turn4 ,but before one has long experimented with the extreme frequencies required to set up in a small bulb an electromotive force of several thousands of volts1 one realizes the great importance of electrostatic effects1 and these effects grow relatively to the electro-dynamic in significance as the frequency is increased4 ,now1 if anything is desirable in this case1 it is to increase the frequency1 and this would make it still worse for the electrodynamic effects4 ,on the other hand1 it is easy to exalt the electrostatic action as far as one likes by taking more turns on the secondary1 or combining self-induction and capacity to raise the potential4 ,it should also be remembered that1 in reducing the current to the smallest value and increasing the potential1 the electric impulses of high frequency can be more easily transmitted through a conductor4 ,these and similar thoughts determined me to devote more attention to the electrostatic phenomena1 and to endeavor to produce potentials as high as possible1 and alternating as fast as they could be made to alternate4 ,i then found that ,i could excite vacuum tubes at considerable distance from a conductor connected to a properly constructed coil1 and that ,i could1 by converting the oscillatory current of a conductor to a higher potential1 establish electrostatic alternating fields which acted through the whole extent of the room1 lighting up a tube no matter where it was held in space4 ,i thought ,i recognized that ,i had made a step in advance1 and ,i have persevered in this line2 but ,i wish to say that ,i share with all lovers of science and progress the one and only desire--to reach a result of utility to men in any direction to which thought or experiment may lead me4 ,i think that this departure is the right one1 for ,i cannot see1 from the observation of the phenomena which manifest themselves as the frequency is increased1 what there would remain to act between two circuits conveying1 for instance1 impulses of several hundred millions per second1 except electrostatic forces4 ,even with such trifling frequencies the energy would be practically all potential1 and my conviction has grown strong that1 to whatever kind of motion light may be due1 it is produced by tremendous electrostatic stresses vibrating with extreme rapidity4 ,illustration3 ,,fig4 #afc4 ,illustration3 ,,fig4 #afd4 ,of all these phenomena observed with currents1 or electric impulses1 of high frequency1 the most fascinating for an audience are certainly those which are noted in an electrostatic field acting through considerable distance2 and the best an unskilled lecturer can do is to begin and finish with the exhibition of these singular effects4 ,i take a tube in my hand and move it about1 and it is lighted wherever ,i may hold it2 throughout space the invisible forces act4 ,but ,i may take another tube and it might not light1 the vacuum being very high4 ,i excite it by means of a disruptive discharge coil1 and now it will light in the electrostatic field4 ,i may put it away for a few weeks or months1 still it retains the faculty of being excited4 ,what change have ,i produced in the tube in the act of exciting it8 ,if a motion imparted to atoms1 it is difficult to perceive how it can persist so long without being arrested by frictional losses2 and if a strain exerted in the dielectric1 such as a simple electrification would produce1 it is easy to see how it may persist indefinitely1 but very difficult to understand why such a condition should aid the excitation when we have to deal with potentials which are rapidly alternating4 ,since ,i have exhibited these phenomena for the first time1 ,i have obtained some other interesting effects4 ,for instance1 ,i have produced the incandescence of a button1 filament1 or wire enclosed in a tube4 ,to get to this result it was necessary to economize the energy which is obtained from the field1 and direct most of it on the small body to be rendered incandescent4 ,at the beginning the task appeared difficult1 but the experiences gathered permitted me to reach the result easily4 ,in ,fig4 #afc and ,fig4 #afd1 two such tubes are illustrated1 which are prepared for the occasion4 ,in ,fig4 #afc a short tube ,t#a1 sealed to another long tube ,t1 is provided with a stem s1 with a platinum wire sealed in the latter4 ,a very thin lamp filament l1 is fastened to this wire and connection to the outside is made through a thin copper wire w4 ,the tube is provided with outside and inside coatings1 ,c and ,c#a1 respectively1 and is filled as far as the coatings reach with conducting1 and the space above with insulating1 powder4 ,these coatings are merely used to enable me to perform two experiments with the tube--namely1 to produce the effect desired either by direct connection of the body of the experimenter or of another body to the wire w1 or by acting inductively through the glass4 ,the stem s is provided with an aluminum tube a1 for purposes before explained1 and only a small part of the filament reaches out of this tube4 ,by holding the tube ,t#a anywhere in the electrostatic field1 the filament is rendered incandescent4 ,a more interesting piece of apparatus is illustrated in ,fig4 #afd4 ,the construction is the same as before1 only instead of the lamp filament a small platinum wire p1 sealed in a stem s1 and bent above it in a circle1 is connected to the copper wire w1 which is joined to an inside coating ,c4 ,a small stem s#a is provided with a needle1 on the point of which is arranged1 to rotate very freely1 a very light fan of mica v4 ,to prevent the fan from falling out1 a thin stem of glass g1 is bent properly and fastened to the aluminum tube4 ,when the glass tube is held anywhere in the electrostatic field the platinum wire becomes incandescent1 and the mica vanes are rotated very fast4 ,intense phosphorescence may be excited in a bulb by merely connecting it to a plate within the field1 and the plate need not be any larger than an ordinary lamp shade4 ,the phosphorescence excited with these currents is incomparably more powerful than with ordinary apparatus4 ,a small phosphorescent bulb1 when attached to a wire connected to a coil1 emits sufficient light to allow reading ordinary print at a distance of five to six paces4 ,it was of interest to see how some of the phosphorescent bulbs of ,professor ,crookes would behave with these currents1 and he has had the kindness to lend me a few for the occasion4 ,the effects produced are magnificent1 especially by the sulphide of calcium and sulphide of zinc4 ,with the disruptive discharge coil they glow intensely merely by holding them in the hand and connecting the body to the terminal of the coil4 ,to whatever results investigations of this kind may lead1 the chief interest lies1 for the present1 in the possibilities they offer for the production of an efficient illuminating device4 ,in no branch of electric industry is an advance more desired than in the manufacture of light4 ,every thinker1 when considering the barbarous methods employed1 the deplorable losses incurred in our best systems of light production1 must have asked himself1 ,what is likely to be the light of the future8 ,is it to be an incandescent solid1 as in the present lamp1 or an incandescent gas1 or a phosphorescent body1 or something like a burner1 but incomparably more efficient8 ,there is little chance to perfect a gas burner2 not1 perhaps1 because human ingenuity has been bent upon that problem for centuries without a radical departure having been made--though the argument is not devoid of force--but because in a burner the highest vibrations can never be reached1 except by passing through all the low ones4 ,for how is a flame to proceed unless by a fall of lifted weights8 ,such process cannot be maintained without renewal1 and renewal is repeated passing from low to high vibrations4 ,one way only seems to be open to improve a burner1 and that is by trying to reach higher degrees of incandescence4 ,higher incandescence is equivalent to a quicker vibration3 that means more light from the same material1 and that again1 means more economy4 ,in this direction some improvements have been made1 but the progress is hampered by many limitations4 ,discarding1 then1 the burner1 there remains the three ways first mentioned1 which are essentially electrical4 ,suppose the light of the immediate future to be a solid1 rendered incandescent by electricity4 ,would it not seem that it is better to employ a small button than a frail filament8 ,from many considerations it certainly must be concluded that a button is capable of a higher economy1 assuming1 of course1 the difficulties connected with the operation of such a lamp to be effectively overcome4 ,but to light such a lamp we require a high potential2 and to get this economically1 we must use high frequencies4 ,such considerations apply even more to the production of light by the incandescence of a gas1 or by phosphorescence4 ,in all cases we require high frequencies and high potentials4 ,these thoughts occurred to me a long time ago4 ,incidentally we gain1 by the use of high frequencies1 many advantages1 such as higher economy in the light production1 the possibility of working with one lead1 the possibility of doing away with the leading-in wire1 etc4 ,the question is1 how far can we go with frequencies8 ,ordinary conductors rapidly lose the facility of transmitting electric impulses when the frequency is greatly increased4 ,assume the means for the production of impulses of very great frequency brought to the utmost perfection1 every one will naturally ask how to transmit them when the necessity arises4 ,in transmitting such impulses through conductors we must remember that we have to deal with pressure and flow1 in the ordinary interpretation of these terms4 ,let the pressure increase to an enormous value1 and let the flow correspondingly diminish1 then such impulses--variations merely of pressure1 as it were--can no doubt be transmitted through a wire even if their frequency be many hundreds of millions per second4 ,it would1 of course1 be out of question to transmit such impulses through a wire immersed in a gaseous medium1 even if the wire were provided with a thick and excellent insulation1 for most of the energy would be lost in molecular bombardment and consequent heating4 ,the end of the wire connected to the source would be heated1 and the remote end would receive but a trifling part of the energy supplied4 ,the prime necessity1 then1 if such electric impulses are to be used1 is to find means to reduce as much as possible the dissipation4 ,the first thought is1 to employ the thinnest possible wire surrounded by the thickest practicable insulation4 ,the next thought is to employ electrostatic screens4 ,the insulation of the wire may be covered with a thin conducting coating and the latter connected to the ground4 ,but this would not do1 as then all the energy would pass through the conducting coating to the ground and nothing would get to the end of the wire4 ,if a ground connection is made it can only be made through a conductor offering an enormous impedance1 or through a condenser of extremely small capacity4 ,this1 however1 does not do away with other difficulties4 ,if the wave length of the impulses is much smaller than the length of the wire1 then corresponding short waves will be set up in the conducting coating1 and it will be more or less the same as though the coating were directly connected to earth4 ,it is therefore necessary to cut up the coating in sections much shorter than the wave length4 ,such an arrangement does not still afford a perfect screen1 but it is ten thousand times better than none4 ,i think it preferable to cut up the conducting coating in small sections1 even if the current waves be much longer than the coating4 ,if a wire were provided with a perfect electrostatic screen1 it would be the same as though all objects were removed from it at infinite distance4 ,the capacity would then be reduced to the capacity of the wire itself1 which would be very small4 ,it would then be possible to send over the wire current vibrations of very high frequencies at enormous distances1 without affecting greatly the character of the vibrations4 ,a perfect screen is of course out of the question1 but ,i believe that with a screen such as ,i have just described telephony could be rendered practicable across the ,atlantic4 ,according to my ideas1 the gutta-percha covered wire should be provided with a third conducting coating subdivided in sections4 ,on the top of this should be again placed a layer of gutta-percha and other insulation1 and on the top of the whole the armor4 ,but such cables will not be constructed1 for ere long intelligence--transmitted without wires--will throb through the earth like a pulse through a living organism4 ,the wonder is that1 with the present state of knowledge and the experiences gained1 no attempt is being made to disturb the electrostatic or magnetic condition of the earth1 and transmit1 if nothing else1 intelligence4 ,it has been my chief aim in presenting these results to point out phenomena or features of novelty1 and to advance ideas which ,i am hopeful will serve as starting points of new departures4 ,it has been my chief desire this evening to entertain you with some novel experiments4 ,your applause1 so frequently and generously accorded1 has told me that ,i have succeeded4 ,in conclusion1 let me thank you most heartily for your kindness and attention1 and assure you that the honor ,i have had in addressing such a distinguished audience1 the pleasure ,i have had in presenting these results to a gathering of so many able men--and among them also some of those in whose work for many years past ,i have found enlightenment and constant pleasure--,i shall never forget4 ,,chapter ,,xxviii4 ,,on ,,light ,,and ,,other ,,high ,,frequency ,,phenomena4#c #c ,a lecture delivered before the ,franklin ,institute1 ,philadelphia1 ,february1 #ahic1 and before the ,national ,electric ,light ,association1 ,st4 ,louis1 ,march1 #ahic4 ,,introductory4--,,some ,,thoughts ,,on ,,the ,,eye4 ,when we look at the world around us1 on ,nature1 we are impressed with its beauty and grandeur4 ,each thing we perceive1 though it may be vanishingly small1 is in itself a world1 that is1 like the whole of the universe1 matter and force governed by law1--a world1 the contemplation of which fills us with feelings of wonder and irresistibly urges us to ceaseless thought and inquiry4 ,but in all this vast world1 of all objects our senses reveal to us1 the most marvellous1 the most appealing to our imagination1 appears no doubt a highly developed organism1 a thinking being4 ,if there is anything fitted to make us admire ,nature's handiwork1 it is certainly this inconceivable structure1 which performs its innumerable motions of obedience to external influence4 ,to understand its workings1 to get a deeper insight into this ,nature's masterpiece1 has ever been for thinkers a fascinating aim1 and after many centuries of arduous research men have arrived at a fair understanding of the functions of its organs and senses4 ,again1 in all the perfect harmony of its parts1 of the parts which constitute the material or tangible of our being1 of all its organs and senses1 the eye is the most wonderful4 ,it is the most precious1 the most indispensable of our perceptive or directive organs1 it is the great gateway through which all knowledge enters the mind4 ,of all our organs1 it is the one1 which is in the most intimate relation with that which we call intellect4 ,so intimate is this relation1 that it is often said1 the very soul shows itself in the eye4 ,it can be taken as a fact1 which the theory of the action of the eye implies1 that for each external impression1 that is1 for each image produced upon the retina1 the ends of the visual nerves1 concerned in the conveyance of the impression to the mind1 must be under a peculiar stress or in a vibratory state4 ,it now does not seem improbable that1 when by the power of thought an image is evoked1 a distinct reflex action1 no matter how weak1 is exerted upon certain ends of the visual nerves1 and therefore upon the retina4 ,will it ever be within human power to analyze the condition of the retina when disturbed by thought or reflex action1 by the help of some optical or other means of such sensitiveness1 that a clear idea of its state might be gained at any time8 ,if this were possible1 then the problem of reading one's thoughts with precision1 like the characters of an open book1 might be much easier to solve than many problems belonging to the domain of positive physical science1 in the solution of which many1 if not the majority1 of scientific men implicitly believe4 ,helmholtz1 has shown that the fundi of the eye are themselves1 luminous1 and he was able to see1 in total darkness1 the movement of his arm by the light of his own eyes4 ,this is one of the most remarkable experiments recorded in the history of science1 and probably only a few men could satisfactorily repeat it1 for it is very likely1 that the luminosity of the eyes is associated with uncommon activity of the brain and great imaginative power4 ,it is fluorescence of brain action1 as it were4 ,another fact having a bearing on this subject which has probably been noted by many1 since it is stated in popular expressions1 but which ,i cannot recollect to have found chronicled as a positive result of observation is1 that at times1 when a sudden idea or image presents itself to the intellect1 there is a distinct and sometimes painful sensation of luminosity produced in the eye1 observable even in broad daylight4 ,the saying then1 that the soul shows itself in the eye1 is deeply founded1 and we feel that it expresses a great truth4 ,it has a profound meaning even for one who1 like a poet or artist1 only following his inborn instinct or love for ,nature1 finds delight in aimless thoughts and in the mere contemplation of natural phenomena1 but a still more profound meaning for one who1 in the spirit of positive scientific investigation1 seeks to ascertain the causes of the effects4 ,it is principally the natural philosopher1 the physicist1 for whom the eye is the subject of the most intense admiration4 ,two facts about the eye must forcibly impress the mind of the physicist1 notwithstanding he may think or say that it is an imperfect optical instrument1 forgetting1 that the very conception of that which is perfect or seems so to him1 has been gained through this same instrument4 ,first1 the eye is1 as far as our positive knowledge goes1 the only organ which is directly affected by that subtile medium1 which as science teaches us1 must fill all space2 secondly1 it is the most sensitive of our organs1 incomparably more sensitive to external impressions than any other4 ,the organ of hearing implies the impact of ponderable bodies1 the organ of smell the transference of detached material particles1 and the organs of taste1 and of touch or force1 the direct contact1 or at least some interference of ponderable matter1 and this is true even in those instances of animal organisms1 in which some of these organs are developed to a degree of truly marvelous perfection4 ,this being so1 it seems wonderful that the organ of sight solely should be capable of being stirred by that1 which all our other organs are powerless to detect1 yet which plays an essential part in all natural phenomena1 which transmits all energy and sustains all motion and1 that most intricate of all1 life1 but which has properties such that even a scientifically trained mind cannot help drawing a distinction between it and all that is called matter4 ,considering merely this1 and the fact that the eye1 by its marvelous power1 widens our otherwise very narrow range of perception far beyond the limits of the small world which is our own1 to embrace myriads of other worlds1 suns and stars in the infinite depths of the universe1 would make it justifiable to assert1 that it is an organ of a higher order4 ,its performances are beyond comprehension4 ,nature as far as we know never produced anything more wonderful4 ,we can get barely a faint idea of its prodigious power by analyzing what it does and by comparing4 ,when ether waves impinge upon the human body1 they produce the sensations of warmth or cold1 pleasure or pain1 or perhaps other sensations of which we are not aware1 and any degree or intensity of these sensations1 which degrees are infinite in number1 hence an infinite number of distinct sensations4 ,but our sense of touch1 or our sense of force1 cannot reveal to us these differences in degree or intensity1 unless they are very great4 ,now we can readily conceive how an organism1 such as the human1 in the eternal process of evolution1 or more philosophically speaking1 adaptation to ,nature1 being constrained to the use of only the sense of touch or force1 for instance1 might develop this sense to such a degree of sensitiveness or perfection1 that it would be capable of distinguishing the minutest differences in the temperature of a body even at some distance1 to a hundredth1 or thousandth1 or millionth part of a degree4 ,yet1 even this apparently impossible performance would not begin to compare with that of the eye1 which is capable of distinguishing and conveying to the mind in a single instant innumerable peculiarities of the body1 be it in form1 or color1 or other respects4 ,this power of the eye rests upon two things1 namely1 the rectilinear propagation of the disturbance by which it is effected1 and upon its sensitiveness4 ,to say that the eye is sensitive is not saying anything4 ,compared with it1 all other organs are monstrously crude4 ,the organ of smell which guides a dog on the trail of a deer1 the organ of touch or force which guides an insect in its wanderings1 the organ of hearing1 which is affected by the slightest disturbances of the air1 are sensitive organs1 to be sure1 but what are they compared with the human eye6 ,no doubt it responds to the faintest echoes or reverberations of the medium2 no doubt1 it brings us tidings from other worlds1 infinitely remote1 but in a language we cannot as yet always understand4 ,and why not8 ,because we live in a medium filled with air and other gases1 vapors and a dense mass of solid particles flying about4 ,these play an important part in many phenomena2 they fritter away the energy of the vibrations before they can reach the eye2 they too1 are the carriers of germs of destruction1 they get into our lungs and other organs1 clog up the channels and imperceptibly1 yet inevitably1 arrest the stream of life4 ,could we but do away with all ponderable matter in the line of sight of the telescope1 it would reveal to us undreamt of marvels4 ,even the unaided eye1 ,i think1 would be capable of distinguishing in the pure medium1 small objects at distances measured probably by hundreds or perhaps thousands of miles4 ,but there is something else about the eye which impresses us still more than these wonderful features which we observed1 viewing it from the standpoint of a physicist1 merely as an optical instrument1--something which appeals to us more than its marvelous faculty of being directly affected by the vibrations of the medium1 without interference of gross matter1 and more than its inconceivable sensitiveness and discerning power4 ,it is its significance in the processes of life4 ,no matter what one's views on nature and life may be1 he must stand amazed when1 for the first time in his thoughts1 he realizes the importance of the eye in the physical processes and mental performances of the human organism4 ,and how could it be otherwise1 when he realizes1 that the eye is the means through which the human race has acquired the entire knowledge it possesses1 that it controls all our motions1 more still1 all our actions4 ,there is no way of acquiring knowledge except through the eye4 ,what is the foundation of all philosophical systems of ancient and modern times1 in fact1 of all the philosophy of man8 ,i am1 ,i think2 ,i think1 therefore ,i am4 ,but how could ,i think and how would ,i know that ,i exist1 if ,i had not the eye8 ,for knowledge involves consciousness2 consciousness involves ideas1 conceptions2 conceptions involve pictures or images1 and images the sense of vision1 and therefore the organ of sight4 ,but how about blind men1 will be asked8 ,yes1 a blind man may depict in magnificent poems1 forms and scenes from real life1 from a world he physically does not see4 ,a blind man may touch the keys of an instrument with unerring precision1 may model the fastest boat1 may discover and invent1 calculate and construct1 may do still greater wonders--but all the blind men who have done such things have descended from those who had seeing eyes4 ,nature may reach the same result in many ways4 ,like a wave in the physical world1 in the infinite ocean of the medium which pervades all1 so in the world of organisms1 in life1 an impulse started proceeds onward1 at times1 may be1 with the speed of light1 at times1 again1 so slowly that for ages and ages it seems to stay1 passing through processes of a complexity inconceivable to men1 but in all its forms1 in all its stages1 its energy ever and ever integrally present4 ,a single ray of light from a distant star falling upon the eye of a tyrant in bygone times1 may have altered the course of his life1 may have changed the destiny of nations1 may have transformed the surface of the globe1 so intricate1 so inconceivably complex are the processes in ,nature4 ,in no way can we get such an overwhelming idea of the grandeur of ,nature1 as when we consider1 that in accordance with the law of the conservation of energy1 throughout the infinite1 the forces are in a perfect balance1 and hence the energy of a single thought may determine the motion of a ,universe4 ,it is not necessary that every individual1 not even that every generation or many generations1 should have the physical instrument of sight1 in order to be able to form images and to think1 that is1 form ideas or conceptions2 but sometime or other1 during the process of evolution1 the eye certainly must have existed1 else thought1 as we understand it1 would be impossible2 else conceptions1 like spirit1 intellect1 mind1 call it as you may1 could not exist4 ,it is conceivable1 that in some other world1 in some other beings1 the eye is replaced by a different organ1 equally or more perfect1 but these beings cannot be men4 ,now what prompts us all to voluntary motions and actions of any kind8 ,again the eye4 ,if ,i am conscious of the motion1 ,i must have an idea or conception1 that is1 an image1 therefore the eye4 ,if ,i am not precisely conscious of the motion1 it is1 because the images are vague or indistinct1 being blurred by the superimposition of many4 ,but when ,i perform the motion1 does the impulse which prompts me to the action come from within or from without8 ,the greatest physicists have not disdained to endeavor to answer this and similar questions and have at times abandoned themselves to the delights of pure and unrestrained thought4 ,such questions are generally considered not to belong to the realm of positive physical science1 but will before long be annexed to its domain4 ,helmholtz has probably thought more on life than any modern scientist4 ,lord ,kelvin expressed his belief that life's process is electrical and that there is a force inherent to the organism and determining its motions4 ,just as much as ,i am convinced of any physical truth ,i am convinced that the motive impulse must come from the outside4 ,for1 consider the lowest organism we know--and there are probably many lower ones--an aggregation of a few cells only4 ,if it is capable of voluntary motion it can perform an infinite number of motions1 all definite and precise4 ,but now a mechanism consisting of a finite number of parts and few at that1 cannot perform an infinite number of definite motions1 hence the impulses which govern its movements must come from the environment4 ,so1 the atom1 the ulterior element of the ,universe's structure1 is tossed about in space1 eternally1 a play to external influences1 like a boat in a troubled sea4 ,were it to stop its motion it would die4 ,matter at rest1 if such a thing could exist1 would be matter dead4 ,death of matter6 ,never has a sentence of deeper philosophical meaning been uttered4 ,this is the way in which ,prof4 ,dewar forcibly expresses it in the description of his admirable experiments1 in which liquid oxygen is handled as one handles water1 and air at ordinary pressure is made to condense and even to solidify by the intense cold4 ,experiments1 which serve to illustrate1 in his language1 the last feeble manifestations of life1 the last quiverings of matter about to die4 ,but human eyes shall not witness such death4 ,there is no death of matter1 for throughout the infinite universe1 all has to move1 to vibrate1 that is1 to live4 ,i have made the preceding statements at the peril of treading upon metaphysical ground1 in my desire to introduce the subject of this lecture in a manner not altogether uninteresting1 ,i may hope1 to an audience such as ,i have the honor to address4 ,but now1 then1 returning to the subject1 this divine organ of sight1 this indispensable instrument for thought and all intellectual enjoyment1 which lays open to us the marvels of this universe1 through which we have acquired what knowledge we possess1 and which prompts us to1 and controls1 all our physical and mental activity4 ,by what is it affected8 ,by light6 ,what is light8 ,we have witnessed the great strides which have been made in all departments of science in recent years4 ,so great have been the advances that we cannot refrain from asking ourselves1 ,is this all true1 or is it but a dream8 ,centuries ago men have lived1 have thought1 discovered1 invented1 and have believed that they were soaring1 while they were merely proceeding at a snail's pace4 ,so we too may be mistaken4 ,but taking the truth of the observed events as one of the implied facts of science1 we must rejoice in the immense progress already made and still more in the anticipation of what must come1 judging from the possibilities opened up by modern research4 ,there is1 however1 an advance which we have been witnessing1 which must be particularly gratifying to every lover of progress4 ,it is not a discovery1 or an invention1 or an achievement in any particular direction4 ,it is an advance in all directions of scientific thought and experiment4 ,i mean the generalization of the natural forces and phenomena1 the looming up of a certain broad idea on the scientific horizon4 ,it is this idea which has1 however1 long ago taken possession of the most advanced minds1 to which ,i desire to call your attention1 and which ,i intend to illustrate in a general way1 in these experiments1 as the first step in answering the question ,what is light8 and to realize the modern meaning of this word4 ,it is beyond the scope of my lecture to dwell upon the subject of light in general1 my object being merely to bring presently to your notice a certain class of light effects and a number of phenomena observed in pursuing the study of these effects4 ,but to be consistent in my remarks it is necessary to state that1 according to that idea1 now accepted by the majority of scientific men as a positive result of theoretical and experimental investigation1 the various forms or manifestations of energy which were generally designated as electric or more precisely electromagnetic are energy manifestations of the same nature as those of radiant heat and light4 ,therefore the phenomena of light and heat and others besides these1 may be called electrical phenomena4 ,thus electrical science has become the mother science of all and its study has become all important4 ,the day when we shall know exactly what electricity is1 will chronicle an event probably greater1 more important than any other recorded in the history of the human race4 ,the time will come when the comfort1 the very existence1 perhaps1 of man will depend upon that wonderful agent4 ,for our existence and comfort we require heat1 light and mechanical power4 ,how do we now get all these8 ,we get them from fuel1 we get them by consuming material4 ,what will man do when the forests disappear1 when the coal fields are exhausted8 ,only one thing1 according to our present knowledge will remain2 that is1 to transmit power at great distances4 ,men will go to the waterfalls1 to the tides1 which are the stores of an infinitesimal part of ,nature's immeasurable energy4 ,there will they harness the energy and transmit the same to their settlements1 to warm their homes by1 to give them light1 and to keep their obedient slaves1 the machines1 toiling4 ,but how will they transmit this energy if not by electricity8 ,judge then1 if the comfort1 nay1 the very existence1 of man will not depend on electricity4 ,i am aware that this view is not that of a practical engineer1 but neither is it that of an illusionist1 for it is certain1 that power transmission1 which at present is merely a stimulus to enterprise1 will some day be a dire necessity4 ,it is more important for the student1 who takes up the study of light phenomena1 to make himself thoroughly acquainted with certain modern views1 than to peruse entire books on the subject of light itself1 as disconnected from these views4 ,were ,i therefore to make these demonstrations before students seeking information--and for the sake of the few of those who may be present1 give me leave to so assume--it would be my principal endeavor to impress these views upon their minds in this series of experiments4 ,it might be sufficient for this purpose to perform a simple and well-known experiment4 ,i might take a familiar appliance1 a ,leyden jar1 charge it from a frictional machine1 and then discharge it4 ,in explaining to you its permanent state when charged1 and its transitory condition when discharging1 calling your attention to the forces which enter into play and to the various phenomena they produce1 and pointing out the relation of the forces and phenomena1 ,i might fully succeed in illustrating that modern idea4 ,no doubt1 to the thinker1 this simple experiment would appeal as much as the most magnificent display4 ,but this is to be an experimental demonstration1 and one which should possess1 besides instructive1 also entertaining features and as such1 a simple experiment1 such as the one cited1 would not go very far towards the attainment of the lecturer's aim4 ,i must therefore choose another way of illustrating1 more spectacular certainly1 but perhaps also more instructive4 ,instead of the frictional machine and ,leyden jar1 ,i shall avail myself in these experiments1 of an induction coil of peculiar properties1 which was described in detail by me in a lecture before the ,london ,institution of ,electrical ,engineers1 in ,feb41 #ahib4 ,this induction coil is capable of yielding currents of enormous potential differences1 alternating with extreme rapidity4 ,with this apparatus ,i shall endeavor to show you three distinct classes of effects1 or phenomena1 and it is my desire that each experiment1 while serving for the purposes of illustration1 should at the same time teach us some novel truth1 or show us some novel aspect of this fascinating science4 ,but before doing this1 it seems proper and useful to dwell upon the apparatus employed1 and method of obtaining the high potentials and high-frequency currents which are made use of in these experiments4 ,illustration3 ,,fig4 #afe4 ,,on ,,the ,,apparatus ,,and ,,method ,,of ,,conversion4 ,these high-frequency currents are obtained in a peculiar manner4 ,the method employed was advanced by me about two years ago in an experimental lecture before the ,american ,institute of ,electrical ,engineers4 ,a number of ways1 as practiced in the laboratory1 of obtaining these currents either from continuous or low frequency alternating currents1 is diagramatically indicated in ,fig4 #afe1 which will be later described in detail4 ,the general plan is to charge condensers1 from a direct or alternate-current source1 preferably of high-tension1 and to discharge them disruptively while observing well-known conditions necessary to maintain the oscillations of the current4 ,in view of the general interest taken in high-frequency currents and effects producible by them1 it seems to me advisable to dwell at some length upon this method of conversion4 ,in order to give you a clear idea of the action1 ,i will suppose that a continuous-current generator is employed1 which is often very convenient4 ,it is desirable that the generator should possess such high tension as to be able to break through a small air space4 ,if this is not the case1 then auxiliary means have to be resorted to1 some of which will be indicated subsequently4 ,when the condensers are charged to a certain potential1 the air1 or insulating space1 gives way and a disruptive discharge occurs4 ,there is then a sudden rush of current and generally a large portion of accumulated electrical energy spends itself4 ,the condensers are thereupon quickly charged and the same process is repeated in more or less rapid succession4 ,to produce such sudden rushes of current it is necessary to observe certain conditions4 ,if the rate at which the condensers are discharged is the same as that at which they are charged1 then1 clearly1 in the assumed case the condensers do not come into play4 ,if the rate of discharge be smaller than the rate of charging1 then1 again1 the condensers cannot play an important part4 ,but if1 on the contrary1 the rate of discharging is greater than that of charging1 then a succession of rushes of current is obtained4 ,it is evident that1 if the rate at which the energy is dissipated by the discharge is very much greater than the rate of supply to the condensers1 the sudden rushes will be comparatively few1 with long-time intervals between4 ,this always occurs when a condenser of considerable capacity is charged by means of a comparatively small machine4 ,if the rates of supply and dissipation are not widely different1 then the rushes of current will be in quicker succession1 and this the more1 the more nearly equal both the rates are1 until limitations incident to each case and depending upon a number of causes are reached4 ,thus we are able to obtain from a continuous-current generator as rapid a succession of discharges as we like4 ,of course1 the higher the tension of the generator1 the smaller need be the capacity of the condensers1 and for this reason1 principally1 it is of advantage to employ a generator of very high tension4 ,besides1 such a generator permits the attaining of greater rates of vibration4 ,the rushes of current may be of the same direction under the conditions before assumed1 but most generally there is an oscillation superimposed upon the fundamental vibration of the current4 ,when the conditions are so determined that there are no oscillations1 the current impulses are unidirectional and thus a means is provided of transforming a continuous current of high tension1 into a direct current of lower tension1 which ,i think may find employment in the arts4 ,this method of conversion is exceedingly interesting and ,i was much impressed by its beauty when ,i first conceived it4 ,it is ideal in certain respects4 ,it involves the employment of no mechanical devices of any kind1 and it allows of obtaining currents of any desired frequency from an ordinary circuit1 direct or alternating4 ,the frequency of the fundamental discharges depending on the relative rates of supply and dissipation can be readily varied within wide limits1 by simple adjustments of these quantities1 and the frequency of the superimposed vibration by the determination of the capacity1 self-induction and resistance of the circuit4 ,the potential of the currents1 again1 may be raised as high as any insulation is capable of withstanding safely by combining capacity and self-induction or by induction in a secondary1 which need have but comparatively few turns4 ,as the conditions are often such that the intermittence or oscillation does not readily establish itself1 especially when a direct current source is employed1 it is of advantage to associate an interrupter with the arc1 as ,i have1 some time ago1 indicated the use of an air-blast or magnet1 or other such device readily at hand4 ,the magnet is employed with special advantage in the conversion of direct currents1 as it is then very effective4 ,if the primary source is an alternate current generator1 it is desirable1 as ,i have stated on another occasion1 that the frequency should be low1 and that the current forming the arc be large1 in order to render the magnet more effective4 ,a form of such discharger with a magnet which has been found convenient1 and adopted after some trials1 in the conversion of direct currents particularly1 is illustrated in ,fig4 #aff4 ,n ,s are the pole pieces of a very strong magnet which is excited by a coil ,c4 ,the pole pieces are slotted for adjustment and can be fastened in any position by screws s s#a4 ,the discharge rods d d#a1 thinned down on the ends in order to allow a closer approach of the magnetic pole pieces1 pass through the columns of brass b b#a and are fastened in position by screws s#b s#b4 ,springs r r#a and collars c c#a are slipped on the rods1 the latter serving to set the points of the rods at a certain suitable distance by means of screws s#c s#c1 and the former to draw the points apart4 ,when it is desired to start the arc1 one of the large rubber handles h h#a is tapped quickly with the hand1 whereby the points of the rods are brought in contact but are instantly separated by the springs r r#a4 ,such an arrangement has been found to be often necessary1 namely in cases when the ,e4 ,m4 ,f4 was not large enough to cause the discharge to break through the gap1 and also when it was desirable to avoid short circuiting of the generator by the metallic contact of the rods4 ,the rapidity of the interruptions of the current with a magnet depends on the intensity of the magnetic field and on the potential difference at the end of the arc4 ,the interruptions are generally in such quick succession as to produce a musical sound4 ,years ago it was observed that when a powerful induction coil is discharged between the poles of a strong magnet1 the discharge produces a loud noise1 not unlike a small pistol shot4 ,it was vaguely stated that the spark was intensified by the presence of the magnetic field4 ,it is now clear that the discharge current1 flowing for some time1 was interrupted a great number of times by the magnet1 thus producing the sound4 ,the phenomenon is especially marked when the field circuit of a large magnet or dynamo is broken in a powerful magnetic field4 ,illustration3 ,,fig4 #aff4 ,when the current through the gap is comparatively large1 it is of advantage to slip on the points of the discharge rods pieces of very hard carbon and let the arc play between the carbon pieces4 ,this preserves the rods1 and besides has the advantage of keeping the air space hotter1 as the heat is not conducted away as quickly through the carbons1 and the result is that a smaller ,e4 ,m4 ,f4 in the arc gap is required to maintain a succession of discharges4 ,illustration3 ,,fig4 #afg4 ,another form of discharger1 which may be employed with advantage in some cases1 is illustrated in ,fig4 #afg4 ,in this form the discharge rods d d#a pass through perforations in a wooden box ,b1 which is thickly coated with mica on the inside1 as indicated by the heavy lines4 ,the perforations are provided with mica tubes m m#a of some thickness1 which are preferably not in contact with the rods d d#a4 ,the box has a cover ,c which is a little larger and descends on the outside of the box4 ,the spark gap is warmed by a small lamp l contained in the box4 ,a plate p above the lamp allows the draught to pass only through the chimney e of the lamp1 the air entering through holes o o in or near the bottom of the box and following the path indicated by the arrows4 ,when the discharger is in operation1 the door of the box is closed so that the light of the arc is not visible outside4 ,it is desirable to exclude the light as perfectly as possible1 as it interferes with some experiments4 ,this form of discharger is simple and very effective when properly manipulated4 ,the air being warmed to a certain temperature1 has its insulating power impaired2 it becomes dielectrically weak1 as it were1 and the consequence is that the arc can be established at much greater distance4 ,the arc should1 of course1 be sufficiently insulating to allow the discharge to pass through the gap disruptively4 ,the arc formed under such conditions1 when long1 may be made extremely sensitive1 and the weak draught through the lamp chimney c is quite sufficient to produce rapid interruptions4 ,the adjustment is made by regulating the temperature and velocity of the draught4 ,instead of using the lamp1 it answers the purpose to provide for a draught of warm air in other ways4 ,a very simple way which has been practiced is to enclose the arc in a long vertical tube1 with plates on the top and bottom for regulating the temperature and velocity of the air current4 ,some provision had to be made for deadening the sound4 ,the air may be rendered dielectrically weak also by rarefaction4 ,dischargers of this kind have likewise been used by me in connection with a magnet4 ,a large tube is for this purpose provided with heavy electrodes of carbon or metal1 between which the discharge is made to pass1 the tube being placed in a powerful magnetic field4 ,the exhaustion of the tube is carried to a point at which the discharge breaks through easily1 but the pressure should be more than #ge millimetres1 at which the ordinary thread discharge occurs4 ,in another form of discharger1 combining the features before mentioned1 the discharge was made to pass between two adjustable magnetic pole pieces1 the space between them being kept at an elevated temperature4 ,it should be remarked here that when such1 or interrupting devices of any kind1 are used and the currents are passed through the primary of a disruptive discharge coil1 it is not1 as a rule1 of advantage to produce a number of interruptions of the current per second greater than the natural frequency of vibration of the dynamo supply circuit1 which is ordinarily small4 ,it should also be pointed out here1 that while the devices mentioned in connection with the disruptive discharge are advantageous under certain conditions1 they may be sometimes a source of trouble1 as they produce intermittences and other irregularities in the vibration which it would be very desirable to overcome4 ,there is1 ,i regret to say1 in this beautiful method of conversion a defect1 which fortunately is not vital1 and which ,i have been gradually overcoming4 ,i will best call attention to this defect and indicate a fruitful line of work1 by comparing the electrical process with its mechanical analogue4 ,the process may be illustrated in this manner4 ,imagine a tank with a wide opening at the bottom1 which is kept closed by spring pressure1 but so that it snaps off suddenly when the liquid in the tank has reached a certain height4 ,let the fluid be supplied to the tank by means of a pipe feeding at a certain rate4 ,when the critical height of the liquid is reached1 the spring gives way and the bottom of the tank drops out4 ,instantly the liquid falls through the wide opening1 and the spring1 reasserting itself1 closes the bottom again4 ,the tank is now filled1 and after a certain time interval the same process is repeated4 ,it is clear1 that if the pipe feeds the fluid quicker than the bottom outlet is capable of letting it pass through1 the bottom will remain off and the tank will still overflow4 ,if the rates of supply are exactly equal1 then the bottom lid will remain partially open and no vibration of the same and of the liquid column will generally occur1 though it might1 if started by some means4 ,but if the inlet pipe does not feed the fluid fast enough for the outlet1 then there will be always vibration4 ,again1 in such case1 each time the bottom flaps up or down1 the spring and the liquid column1 if the pliability of the spring and the inertia of the moving parts are properly chosen1 will perform independent vibrations4 ,in this analogue the fluid may be likened to electricity or electrical energy1 the tank to the condenser1 the spring to the dielectric1 and the pipe to the conductor through which electricity is supplied to the condenser4 ,to make this analogy quite complete it is necessary to make the assumption1 that the bottom1 each time it gives way1 is knocked violently against a non-elastic stop1 this impact involving some loss of energy2 and that1 besides1 some dissipation of energy results due to frictional losses4 ,in the preceding analogue the liquid is supposed to be under a steady pressure4 ,if the presence of the fluid be assumed to vary rhythmically1 this may be taken as corresponding to the case of an alternating current4 ,the process is then not quite as simple to consider1 but the action is the same in principle4 ,it is desirable1 in order to maintain the vibration economically1 to reduce the impact and frictional losses as much as possible4 ,as regards the latter1 which in the electrical analogue correspond to the losses due to the resistance of the circuits1 it is impossible to obviate them entirely1 but they can be reduced to a minimum by a proper selection of the dimensions of the circuits and by the employment of thin conductors in the form of strands4 ,but the loss of energy caused by the first breaking through of the dielectric--which in the above example corresponds to the violent knock of the bottom against the inelastic stop--would be more important to overcome4 ,at the moment of the breaking through1 the air space has a very high resistance1 which is probably reduced to a very small value when the current has reached some strength1 and the space is brought to a high temperature4 ,it would materially diminish the loss of energy if the space were always kept at an extremely high temperature1 but then there would be no disruptive break4 ,by warming the space moderately by means of a lamp or otherwise1 the economy as far as the arc is concerned is sensibly increased4 ,but the magnet or other interrupting device does not diminish the loss in the arc4 ,likewise1 a jet of air only facilitates the carrying off of the energy4 ,air1 or a gas in general1 behaves curiously in this respect4 ,when two bodies charged to a very high potential1 discharge disruptively through an air space1 any amount of energy may be carried off by the air4 ,this energy is evidently dissipated by bodily carriers1 in impact and collisional losses of the molecules4 ,the exchange of the molecules in the space occurs with inconceivable rapidity4 ,a powerful discharge taking place between two electrodes1 they may remain entirely cool1 and yet the loss in the air may represent any amount of energy4 ,it is perfectly practicable1 with very great potential differences in the gap1 to dissipate several horse-power in the arc of the discharge without even noticing a small increase in the temperature of the electrodes4 ,all the frictional losses occur then practically in the air4 ,if the exchange of the air molecules is prevented1 as by enclosing the air hermetically1 the gas inside of the vessel is brought quickly to a high temperature1 even with a very small discharge4 ,it is difficult to estimate how much of the energy is lost in sound waves1 audible or not1 in a powerful discharge4 ,when the currents through the gap are large1 the electrodes may become rapidly heated1 but this is not a reliable measure of the energy wasted in the arc1 as the loss through the gap itself may be comparatively small4 ,the air or a gas in general is1 at ordinary pressure at least1 clearly not the best medium through which a disruptive discharge should occur4 ,air or other gas under great pressure is of course a much more suitable medium for the discharge gap4 ,i have carried on long-continued experiments in this direction1 unfortunately less practicable on account of the difficulties and expense in getting air under great pressure4 ,but even if the medium in the discharge space is solid or liquid1 still the same losses take place1 though they are generally smaller1 for just as soon as the arc is established1 the solid or liquid is volatilized4 ,indeed1 there is no body known which would not be disintegrated by the arc1 and it is an open question among scientific men1 whether an arc discharge could occur at all in the air itself without the particles of the electrodes being torn off4 ,when the current through the gap is very small and the arc very long1 ,i believe that a relatively considerable amount of heat is taken up in the disintegration of the electrodes1 which partially on this account may remain quite cold4 ,the ideal medium for a discharge gap should only crack1 and the ideal electrode should be of some material which cannot be disintegrated4 ,with small currents through the gap it is best to employ aluminum1 but not when the currents are large4 ,the disruptive break in the air1 or more or less in any ordinary medium1 is not of the nature of a crack1 but it is rather comparable to the piercing of innumerable bullets through a mass offering great frictional resistances to the motion of the bullets1 this involving considerable loss of energy4 ,a medium which would merely crack when strained electrostatically--and this possibly might be the case with a perfect vacuum1 that is1 pure ether--would involve a very small loss in the gap1 so small as to be entirely negligible1 at least theoretically1 because a crack may be produced by an infinitely small displacement4 ,in exhausting an oblong bulb provided with two aluminum terminals1 with the greatest care1 ,i have succeeded in producing such a vacuum that the secondary discharge of a disruptive discharge coil would break disruptively through the bulb in the form of fine spark streams4 ,the curious point was that the discharge would completely ignore the terminals and start far behind the two aluminum plates which served as electrodes4 ,this extraordinary high vacuum could only be maintained for a very short while4 ,to return to the ideal medium1 think1 for the sake of illustration1 of a piece of glass or similar body clamped in a vice1 and the latter tightened more and more4 ,at a certain point a minute increase of the pressure will cause the glass to crack4 ,the loss of energy involved in splitting the glass may be practically nothing1 for though the force is great1 the displacement need be but extremely small4 ,now imagine that the glass would possess the property of closing again perfectly the crack upon a minute diminution of the pressure4 ,this is the way the dielectric in the discharge space should behave4 ,but inasmuch as there would be always some loss in the gap1 the medium1 which should be continuous1 should exchange through the gap at a rapid rate4 ,in the preceding example1 the glass being perfectly closed1 it would mean that the dielectric in the discharge space possesses a great insulating power2 the glass being cracked1 it would signify that the medium in the space is a good conductor4 ,the dielectric should vary enormously in resistance by minute variations of the ,e4 ,m4 ,f4 across the discharge space4 ,this condition is attained1 but in an extremely imperfect manner1 by warming the air space to a certain critical temperature1 dependent on the ,e4 ,m4 ,f4 across the gap1 or by otherwise impairing the insulating power of the air4 ,but as a matter of fact the air does never break down disruptively1 if this term be rigorously interpreted1 for before the sudden rush of the current occurs1 there is always a weak current preceding it1 which rises first gradually and then with comparative suddenness4 ,that is the reason why the rate of change is very much greater when glass1 for instance1 is broken through1 than when the break takes place through an air space of equivalent dielectric strength4 ,as a medium for the discharge space1 a solid1 or even a liquid1 would be preferable therefor4 ,it is somewhat difficult to conceive of a solid body which would possess the property of closing instantly after it has been cracked4 ,but a liquid1 especially under great pressure1 behaves practically like a solid1 while it possesses the property of closing the crack4 ,hence it was thought that a liquid insulator might be more suitable as a dielectric than air4 ,following out this idea1 a number of different forms of dischargers in which a variety of such insulators1 sometimes under great pressure1 were employed1 have been experimented upon4 ,it is thought sufficient to dwell in a few words upon one of the forms experimented upon4 ,one of these dischargers is illustrated in ,figs4 #afh;a and #afh;b4 ,illustration3 ,,fig4 #afh;a4 ,illustration3 ,,fig4 #afh;b4 ,a hollow metal pulley ,p 7,fig4 #afh;a71 was fastened upon an arbor a1 which by suitable means was rotated at a considerable speed4 ,on the inside of the pulley1 but disconnected from the same1 was supported a thin disc h 7which is shown thick for the sake of clearness71 of hard rubber in which there were embedded two metal segments s s with metallic extensions e e into which were screwed conducting terminals t t covered with thick tubes of hard rubber t t4 ,the rubber disc h with its metallic segments s s1 was finished in a lathe1 and its entire surface highly polished so as to offer the smallest possible frictional resistance to the motion through a fluid4 ,in the hollow of the pulley an insulating liquid such as a thin oil was poured so as to reach very nearly to the opening left in the flange f1 which was screwed tightly on the front side of the pulley4 ,the terminals t t1 were connected to the opposite coatings of a battery of condensers so that the discharge occurred through the liquid4 ,when the pulley was rotated1 the liquid was forced against the rim of the pulley and considerable fluid pressure resulted4 ,in this simple way the discharge gap was filled with a medium which behaved practically like a solid1 which possessed the quality of closing instantly upon the occurrence of the break1 and which moreover was circulating through the gap at a rapid rate4 ,very powerful effects were produced by discharges of this kind with liquid interrupters1 of which a number of different forms were made4 ,it was found that1 as expected1 a longer spark for a given length of wire was obtainable in this way than by using air as an interrupting device4 ,generally the speed1 and therefore also the fluid pressure1 was limited by reason of the fluid friction1 in the form of discharger described1 but the practically obtainable speed was more than sufficient to produce a number of breaks suitable for the circuits ordinarily used4 ,in such instances the metal pulley ,p was provided with a few projections inwardly1 and a definite number of breaks was then produced which could be computed from the speed of rotation of the pulley4 ,experiments were also carried on with liquids of different insulating power with the view of reducing the loss in the arc4 ,when an insulating liquid is moderately warmed1 the loss in the arc is diminished4 ,a point of some importance was noted in experiments with various discharges of this kind4 ,it was found1 for instance1 that whereas the conditions maintained in these forms were favorable for the production of a great spark length1 the current so obtained was not best suited to the production of light effects4 ,experience undoubtedly has shown1 that for such purposes a harmonic rise and fall of the potential is preferable4 ,be it that a solid is rendered incandescent1 or phosphorescent1 or be it that energy is transmitted by condenser coating through the glass1 it is quite certain that a harmonically rising and falling potential produces less destructive action1 and that the vacuum is more permanently maintained4 ,this would be easily explained if it were ascertained that the process going on in an exhausted vessel is of an electrolytic nature4 ,in the diagrammatical sketch1 ,fig4 #afe1 which has been already referred to1 the cases which are most likely to be met with in practice are illustrated4 ,one has at his disposal either direct or alternating currents from a supply station4 ,it is convenient for an experimenter in an isolated laboratory to employ a machine ,g1 such as illustrated1 capable of giving both kinds of currents4 ,in such case it is also preferable to use a machine with multiple circuits1 as in many experiments it is useful and convenient to have at one's disposal currents of different phases4 ,in the sketch1 ,d represents the direct and ,a the alternating circuit4 ,in each of these1 three branch circuits are shown1 all of which are provided with double line switches s s s s s s4 ,consider first the direct current conversion2 ,ia represents the simplest case4 ,if the ,e4 ,m4 ,f4 of the generator is sufficient to break through a small air space1 at least when the latter is warmed or otherwise rendered poorly insulating1 there is no difficulty in maintaining a vibration with fair economy by judicious adjustment of the capacity1 self-induction and resistance of the circuit ,l containing the devices l l m4 ,the magnet ,n1 ,s1 can be in this case advantageously combined with the air space4 ,the discharger d d with the magnet may be placed either way1 as indicated by the full or by the dotted lines4 ,the circuit ,ia with the connections and devices is supposed to possess dimensions such as are suitable for the maintenance of a vibration4 ,but usually the ,e4 ,m4 ,f4 on the circuit or branch ,ia will be something like a #ajj volts or so1 and in this case it is not sufficient to break through the gap4 ,many different means may be used to remedy this by raising the ,e4 ,m4 ,f4 across the gap4 ,the simplest is probably to insert a large self-induction coil in series with the circuit ,l4 ,when the arc is established1 as by the discharger illustrated in ,fig4 #aff1 the magnet blows the arc out the instant it is formed4 ,now the extra current of the break1 being of high ,e4 ,m4 ,f41 breaks through the gap1 and a path of low resistance for the dynamo current being again provided1 there is a sudden rush of current from the dynamo upon the weakening or subsidence of the extra current4 ,this process is repeated in rapid succession1 and in this manner ,i have maintained oscillation with as low as #ej volts1 or even less1 across the gap4 ,but conversion on this plan is not to be recommended on account of the too heavy currents through the gap and consequent heating of the electrodes2 besides1 the frequencies obtained in this way are low1 owing to the high self-induction necessarily associated with the circuit4 ,it is very desirable to have the ,e4 ,m4 ,f4 as high as possible1 first1 in order to increase the economy of the conversion1 and1 secondly1 to obtain high frequencies4 ,the difference of potential in this electric oscillation is1 of course1 the equivalent of the stretching force in the mechanical vibration of the spring4 ,to obtain very rapid vibration in a circuit of some inertia1 a great stretching force or difference of potential is necessary4 ,incidentally1 when the ,e4 ,m4 ,f4 is very great1 the condenser which is usually employed in connection with the circuit need but have a small capacity1 and many other advantages are gained4 ,with a view of raising the ,e4 ,m4 ,f4 to a many times greater value than obtainable from ordinary distribution circuits1 a rotating transformer g is used1 as indicated at ,,iia1 ,fig4 #afe1 or else a separate high potential machine is driven by means of a motor operated from the generator ,g4 ,the latter plan is in fact preferable1 as changes are easier made4 ,the connections from the high tension winding are quite similar to those in branch ,ia with the exception that a condenser ,c1 which should be adjustable1 is connected to the high tension circuit4 ,usually1 also1 an adjustable self-induction coil in series with the circuit has been employed in these experiments4 ,when the tension of the currents is very high1 the magnet ordinarily used in connection with the discharger is of comparatively small value1 as it is quite easy to adjust the dimensions of the circuit so that oscillation is maintained4 ,the employment of a steady ,e4 ,m4 ,f4 in the high frequency conversion affords some advantages over the employment of alternating ,e4 ,m4 ,f41 as the adjustments are much simpler and the action can be easier controlled4 ,but unfortunately one is limited by the obtainable potential difference4 ,the winding also breaks down easily in consequence of the sparks which form between the sections of the armature or commutator when a vigorous oscillation takes place4 ,besides1 these transformers are expensive to build4 ,it has been found by experience that it is best to follow the plan illustrated at ,,iiia4 ,in this arrangement a rotating transformer g1 is employed to convert the low tension direct currents into low frequency alternating currents1 preferably also of small tension4 ,the tension of the currents is then raised in a stationary transformer ,t4 ,the secondary ,s of this transformer is connected to an adjustable condenser ,c which discharges through the gap or discharger d d1 placed in either of the ways indicated1 through the primary ,p of a disruptive discharge coil1 the high frequency current being obtained from the secondary ,s of this coil1 as described on previous occasions4 ,this will undoubtedly be found the cheapest and most convenient way of converting direct currents4 ,the three branches of the circuit ,a represent the usual cases met in practice when alternating currents are converted4 ,in ,fig4 #a;b a condenser ,c1 generally of large capacity1 is connected to the circuit ,l containing the devices l l1 m m4 ,the devices m m are supposed to be of high self-induction so as to bring the frequency of the circuit more or less to that of the dynamo4 ,in this instance the discharger d d should best have a number of makes and breaks per second equal to twice the frequency of the dynamo4 ,if not so1 then it should have at least a number equal to a multiple or even fraction of the dynamo frequency4 ,it should be observed1 referring to ,ib1 that the conversion to a high potential is also effected when the discharger d d1 which is shown in the sketch1 is omitted4 ,but the effects which are produced by currents which rise instantly to high values1 as in a disruptive discharge1 are entirely different from those produced by dynamo currents which rise and fall harmonically4 ,so1 for instance1 there might be in a given case a number of makes and breaks at d d equal to just twice the frequency of the dynamo1 or in other words1 there may be the same number of fundamental oscillations as would be produced without the discharge gap1 and there might even not be any quicker superimposed vibration2 yet the differences of potential at the various points of the circuit1 the impedance and other phenomena1 dependent upon the rate of change1 will bear no similarity in the two cases4 ,thus1 when working with currents discharging disruptively1 the element chiefly to be considered is not the frequency1 as a student might be apt to believe1 but the rate of change per unit of time4 ,with low frequencies in a certain measure the same effects may be obtained as with high frequencies1 provided the rate of change is sufficiently great4 ,so if a low frequency current is raised to a potential of1 say1 #ge1jjj volts1 and the high tension current passed through a series of high resistance lamp filaments1 the importance of the rarefied gas surrounding the filament is clearly noted1 as will be seen later2 or1 if a low frequency current of several thousand amperes is passed through a metal bar1 striking phenomena of impedance are observed1 just as with currents of high frequencies4 ,but it is1 of course1 evident that with low frequency currents it is impossible to obtain such rates of change per unit of time as with high frequencies1 hence the effects produced by the latter are much more prominent4 ,it is deemed advisable to make the preceding remarks1 inasmuch as many more recently described effects have been unwittingly identified with high frequencies4 ,frequency alone in reality does not mean anything1 except when an undisturbed harmonic oscillation is considered4 ,in the branch ,,iiib a similar disposition to that in ,ib is illustrated1 with the difference that the currents discharging through the gap d d are used to induce currents in the secondary ,s of a transformer ,t4 ,in such case the secondary should be provided with an adjustable condenser for the purpose of tuning it to the primary4 ,,iib illustrates a plan of alternate current high frequency conversion which is most frequently used and which is found to be most convenient4 ,this plan has been dwelt upon in detail on previous occasions and need not be described here4 ,some of these results were obtained by the use of a high frequency alternator4 ,a description of such machines will be found in my original paper before the ,american ,institute of ,electrical ,engineers1 and in periodicals of that period1 notably in ,,the ,,electrical ,,engineer of ,march #ah1 #ahia4 ,i will now proceed with the experiments4 ,,on ,,phenomena ,,produced ,,by ,,electrostatic ,,force4 ,the first class of effects ,i intend to show you are effects produced by electrostatic force4 ,it is the force which governs the the motion of the atoms1 which causes them to collide and develop the life-sustaining energy of heat and light1 and which causes them to aggregate in an infinite variety of ways1 according to ,nature's fanciful designs1 and to form all these wondrous structures we perceive around us2 it is1 in fact1 if our present views be true1 the most important force for us to consider in ,nature4 ,as the term electrostatic might imply a steady electric condition1 it should be remarked1 that in these experiments the force is not constant1 but varies at a rate which may be considered moderate1 about one million times a second1 or thereabouts4 ,this enables me to produce many effects which are not producible with an unvarying force4 ,when two conducting bodies are insulated and electrified1 we say that an electrostatic force is acting between them4 ,this force manifests itself in attractions1 repulsions and stresses in the bodies and space or medium without4 ,so great may be the strain exerted in the air1 or whatever separates the two conducting bodies1 that it may break down1 and we observe sparks or bundles of light or streamers1 as they are called4 ,these streamers form abundantly when the force through the air is rapidly varying4 ,i will illustrate this action of electrostatic force in a novel experiment in which ,i will employ the induction coil before referred to4 ,the coil is contained in a trough filled with oil1 and placed under the table4 ,the two ends of the secondary wire pass through the two thick columns of hard rubber which protrude to some height above the table4 ,it is necessary to insulate the ends or terminals of the secondary heavily with hard rubber1 because even dry wood is by far too poor an insulator for these currents of enormous potential differences4 ,on one of the terminals of the coil1 ,i have placed a large sphere of sheet brass1 which is connected to a larger insulated brass plate1 in order to enable me to perform the experiments under conditions1 which1 as you will see1 are more suitable for this experiment4 ,i now set the coil to work and approach the free terminal with a metallic object held in my hand1 this simply to avoid burns4 ,as ,i approach the metallic object to a distance of eight or ten inches1 a torrent of furious sparks breaks forth from the end of the secondary wire1 which passes through the rubber column4 ,the sparks cease when the metal in my hand touches the wire4 ,my arm is now traversed by a powerful electric current1 vibrating at about the rate of one million times a second4 ,all around me the electrostatic force makes itself felt1 and the air molecules and particles of dust flying about are acted upon and are hammering violently against my body4 ,so great is this agitation of the particles1 that when the lights are turned out you may see streams of feeble light appear on some parts of my body4 ,when such a streamer breaks out on any part of the body1 it produces a sensation like the pricking of a needle4 ,were the potentials sufficiently high and the frequency of the vibration rather low1 the skin would probably be ruptured under the tremendous strain1 and the blood would rush out with great force in the form of fine spray or jet so thin as to be invisible1 just as oil will when placed on the positive terminal of a ,holtz machine4 ,the breaking through of the skin though it may seem impossible at first1 would perhaps occur1 by reason of the tissues under the skin being incomparably better conducting4 ,this1 at least1 appears plausible1 judging from some observations4 ,illustration3 ,,fig4 #afi4 ,i can make these streams of light visible to all1 by touching with the metallic object one of the terminals as before1 and approaching my free hand to the brass sphere1 which is connected to the second terminal of the coil4 ,as the hand is approached1 the air between it and the sphere1 or in the immediate neighborhood1 is more violently agitated1 and you see streams of light now break forth from my finger tips and from the whole hand 7,fig4 #afi74 ,were ,i to approach the hand closer1 powerful sparks would jump from the brass sphere to my hand1 which might be injurious4 ,the streamers offer no particular inconvenience1 except that in the ends of the finger tips a burning sensation is felt4 ,they should not be confounded with those produced by an influence machine1 because in many respects they behave differently4 ,i have attached the brass sphere and plate to one of the terminals in order to prevent the formation of visible streamers on that terminal1 also in order to prevent sparks from jumping at a considerable distance4 ,besides1 the attachment is favorable for the working of the coil4 ,the streams of light which you have observed issuing from my hand are due to a potential of about #bjj1jjj volts1 alternating in rather irregular intervals1 sometimes like a million times a second4 ,a vibration of the same amplitude1 but four times as fast1 to maintain which over #c1jjj1jjj volts would be required1 would be more than sufficient to envelop my body in a complete sheet of flame4 ,but this flame would not burn me up2 quite contrarily1 the probability is that ,i would not be injured in the least4 ,yet a hundredth part of that energy1 otherwise directed1 would be amply sufficient to kill a person4 ,the amount of energy which may thus be passed into the body of a person depends on the frequency and potential of the currents1 and by making both of these very great1 a vast amount of energy may be passed into the body without causing any discomfort1 except perhaps1 in the arm1 which is traversed by a true conduction current4 ,the reason why no pain in the body is felt1 and no injurious effect noted1 is that everywhere1 if a current be imagined to flow through the body1 the direction of its flow would be at right angles to the surface2 hence the body of the experimenter offers an enormous section to the current1 and the density is very small1 with the exception of the arm1 perhaps1 where the density may be considerable4 ,but if only a small fraction of that energy would be applied in such a way that a current would traverse the body in the same manner as a low frequency current1 a shock would be received which might be fatal4 ,a direct or low frequency alternating current is fatal1 ,i think1 principally because its distribution through the body is not uniform1 as it must divide itself in minute streamlets of great density1 whereby some organs are vitally injured4 ,that such a process occurs ,i have not the least doubt1 though no evidence might apparently exist1 or be found upon examination4 ,the surest to injure and destroy life1 is a continuous current1 but the most painful is an alternating current of very low frequency4 ,the expression of these views1 which are the result of long continued experiment and observation1 both with steady and varying currents1 is elicited by the interest which is at present taken in this subject1 and by the manifestly erroneous ideas which are daily propounded in journals on this subject4 ,i may illustrate an effect of the electrostatic force by another striking experiment1 but before1 ,i must call your attention to one or two facts4 ,i have said before1 that when the medium between two oppositely electrified bodies is strained beyond a certain limit it gives way and1 stated in popular language1 the opposite electric charges unite and neutralize each other4 ,this breaking down of the medium occurs principally when the force acting between the bodies is steady1 or varies at a moderate rate4 ,were the variation sufficiently rapid1 such a destructive break would not occur1 no matter how great the force1 for all the energy would be spent in radiation1 convection and mechanical and chemical action4 ,thus the spark length1 or greatest distance which a spark will jump between the electrified bodies is the smaller1 the greater the variation or time rate of change4 ,but this rule may be taken to be true only in a general way1 when comparing rates which are widely different4 ,illustration3 ,,fig4 #agj;a4 ,illustration3 ,,fig4 #agj;b4 ,i will show you by an experiment the difference in the effect produced by a rapidly varying and a steady or moderately varying force4 ,i have here two large circular brass plates p p 7,fig4 #agj;a and ,fig4 #agj;b71 supported on movable insulating stands on the table1 connected to the ends of the secondary of a coil similar to the one used before4 ,i place the plates ten or twelve inches apart and set the coil to work4 ,you see the whole space between the plates1 nearly two cubic feet1 filled with uniform light1 ,fig4 #agj;a4 ,this light is due to the streamers you have seen in the first experiment1 which are now much more intense4 ,i have already pointed out the importance of these streamers in commercial apparatus and their still greater importance in some purely scientific investigations4 ,often they are too weak to be visible1 but they always exist1 consuming energy and modifying the action of the apparatus4 ,when intense1 as they are at present1 they produce ozone in great quantity1 and also1 as ,professor ,crookes has pointed out1 nitrous acid4 ,so quick is the chemical action that if a coil1 such as this one1 is worked for a very long time it will make the atmosphere of a small room unbearable1 for the eyes and throat are attacked4 ,but when moderately produced1 the streamers refresh the atmosphere wonderfully1 like a thunder-storm1 and exercises unquestionably a beneficial effect4 ,in this experiment the force acting between the plates changes in intensity and direction at a very rapid rate4 ,i will now make the rate of change per unit time much smaller4 ,this ,i effect by rendering the discharges through the primary of the induction coil less frequent1 and also by diminishing the rapidity of the vibration in the secondary4 ,the former result is conveniently secured by lowering the ,e4 ,m4 ,f4 over the air gap in the primary circuit1 the latter by approaching the two brass plates to a distance of about three or four inches4 ,when the coil is set to work1 you see no streamers or light between the plates1 yet the medium between them is under a tremendous strain4 ,i still further augment the strain by raising the ,e4 ,m4 ,f4 in the primary circuit1 and soon you see the air give way and the hall is illuminated by a shower of brilliant and noisy sparks1 ,fig4 #agj;b4 ,these sparks could be produced also with unvarying force2 they have been for many years a familiar phenomenon1 though they were usually obtained from an entirely different apparatus4 ,in describing these two phenomena so radically different in appearance1 ,i have advisedly spoken of a force acting between the plates4 ,it would be in accordance with accepted views to say1 that there was an alternating ,e4 ,m4 ,f1 acting between the plates4 ,this term is quite proper and applicable in all cases where there is evidence of at least a possibility of an essential inter-dependence of the electric state of the plates1 or electric action in their neighborhood4 ,but if the plates were removed to an infinite distance1 or if at a finite distance1 there is no probability or necessity whatever for such dependence4 ,i prefer to use the term electrostatic force1 and to say that such a force is acting around each plate or electrified insulated body in general4 ,there is an inconvenience in using this expression as the term incidentally means a steady electric condition2 but a proper nomenclature will eventually settle this difficulty4 ,i now return to the experiment to which ,i have already alluded1 and with which ,i desire to illustrate a striking effect produced by a rapidly varying electrostatic force4 ,i attach to the end of the wire1 l 7,fig4 #aga71 which is in connection with one of the terminals of the secondary of the induction coil1 an exhausted bulb b4 ,this bulb contains a thin carbon filament f1 which is fastened to a platinum wire w1 sealed in the glass and leading outside of the bulb1 where it connects to the wire l4 ,the bulb may be exhausted to any degree attainable with ordinary apparatus4 ,just a moment before1 you have witnessed the breaking down of the air between the charged brass plates4 ,you know that a plate of glass1 or any other insulating material1 would break down in like manner4 ,had ,i therefore a metallic coating attached to the outside of the bulb1 or placed near the same1 and were this coating connected to the other terminal of the coil1 you would be prepared to see the glass give way if the strain were sufficiently increased4 ,even were the coating not connected to the other terminal1 but to an insulated plate1 still1 if you have followed recent developments1 you would naturally expect a rupture of the glass4 ,illustration3 ,,fig4 #aga4 ,illustration3 ,,fig4 #agb;a4 ,illustration3 ,,fig4 #agb;b4 ,but it will certainly surprise you to note that under the action of the varying electrostatic force1 the glass gives way when all other bodies are removed from the bulb4 ,in fact1 all the surrounding bodies we perceive might be removed to an infinite distance without affecting the result in the slightest4 ,when the coil is set to work1 the glass is invariably broken through at the seal1 or other narrow channel1 and the vacuum is quickly impaired4 ,such a damaging break would not occur with a steady force1 even if the same were many times greater4 ,the break is due to the agitation of the molecules of the gas within the bulb1 and outside of the same4 ,this agitation1 which is generally most violent in the narrow pointed channel near the seal1 causes a heating and rupture of the glass4 ,this rupture1 would1 however1 not occur1 not even with a varying force1 if the medium filling the inside of the bulb1 and that surrounding it1 were perfectly homogeneous4 ,the break occurs much quicker if the top of the bulb is drawn out into a fine fibre4 ,in bulbs used with these coils such narrow1 pointed channels must therefore be avoided4 ,when a conducting body is immersed in air1 or similar insulating medium1 consisting of1 or containing1 small freely movable particles capable of being electrified1 and when the electrification of the body is made to undergo a very rapid change--which is equivalent to saying that the electrostatic force acting around the body is varying in intensity1--the small particles are attracted and repelled1 and their violent impacts against the body may cause a mechanical motion of the latter4 ,phenomena of this kind are noteworthy1 inasmuch as they have not been observed before with apparatus such as has been commonly in use4 ,if a very light conducting sphere be suspended on an exceedingly fine wire1 and charged to a steady potential1 however high1 the sphere will remain at rest4 ,even if the potential would be rapidly varying1 provided that the small particles of matter1 molecules or atoms1 are evenly distributed1 no motion of the sphere should result4 ,but if one side of the conducting sphere is covered with a thick insulating layer1 the impacts of the particles will cause the sphere to move about1 generally in irregular curves1 ,fig4 #agb;a4 ,in like manner1 as ,i have shown on a previous occasion1 a fan of sheet metal1 ,fig4 #agb;b1 covered partially with insulating material as indicated1 and placed upon the terminal of the coil so as to turn freely on it1 is spun around4 ,all these phenomena you have witnessed and others which will be shown later1 are due to the presence of a medium like air1 and would not occur in a continuous medium4 ,the action of the air may be illustrated still better by the following experiment4 ,i take a glass tube t1 ,fig4 #agc1 of about an inch in diameter1 which has a platinum wire w sealed in the lower end1 and to which is attached a thin lamp filament f4 ,i connect the wire with the terminal of the coil and set the coil to work4 ,the platinum wire is now electrified positively and negatively in rapid succession and the wire and air inside of the tube is rapidly heated by the impacts of the particles1 which may be so violent as to render the filament incandescent4 ,but if ,i pour oil in the tube1 just as soon as the wire is covered with the oil1 all action apparently ceases and there is no marked evidence of heating4 ,the reason of this is that the oil is a practically continuous medium4 ,the displacements in such a continuous medium are1 with these frequencies1 to all appearance incomparably smaller than in air1 hence the work performed in such a medium is insignificant4 ,but oil would behave very differently with frequencies many times as great1 for even though the displacements be small1 if the frequency were much greater1 considerable work might be performed in the oil4 ,illustration3 ,,fig4 #agc4 ,illustration3 ,,fig4 #agd4 ,the electrostatic attractions and repulsions between bodies of measurable dimensions are1 of all the manifestations of this force1 the first so-called electrical phenomena noted4 ,but though they have been known to us for many centuries1 the precise nature of the mechanism concerned in these actions is still unknown to us1 and has not been even quite satisfactorily explained4 ,what kind of mechanism must that be8 ,we cannot help wondering when we observe two magnets attracting and repelling each other with a force of hundreds of pounds with apparently nothing between them4 ,we have in our commercial dynamos magnets capable of sustaining in mid-air tons of weight4 ,but what are even these forces acting between magnets when compared with the tremendous attractions and repulsions produced by electrostatic force1 to which there is apparently no limit as to intensity4 ,in lightning discharges bodies are often charged to so high a potential that they are thrown away with inconceivable force and torn asunder or shattered into fragments4 ,still even such effects cannot compare with the attractions and repulsions which exist between charged molecules or atoms1 and which are sufficient to project them with speeds of many kilometres a second1 so that under their violent impact bodies are rendered highly incandescent and are volatilized4 ,it is of special interest for the thinker who inquires into the nature of these forces to note that whereas the actions between individual molecules or atoms occur seemingly under any conditions1 the attractions and repulsions of bodies of measurable dimensions imply a medium possessing insulating properties4 ,so1 if air1 either by being rarefied or heated1 is rendered more or less conducting1 these actions between two electrified bodies practically cease1 while the actions between the individual atoms continue to manifest themselves4 ,an experiment may serve as an illustration and as a means of bringing out other features of interest4 ,some time ago ,i showed that a lamp filament or wire mounted in a bulb and connected to one of the terminals of a high tension secondary coil is set spinning1 the top of the filament generally describing a circle4 ,this vibration was very energetic when the air in the bulb was at ordinary pressure and became less energetic when the air in the bulb was strongly compressed4 ,it ceased altogether when the air was exhausted so as to become comparatively good conducting4 ,i found at that time that no vibration took place when the bulb was very highly exhausted4 ,but ,i conjectured that the vibration which ,i ascribed to the electrostatic action between the walls of the bulb and the filament should take place also in a highly exhausted bulb4 ,to test this under conditions which were more favorable1 a bulb like the one in ,fig4 #agd1 was constructed4 ,it comprised a globe b1 in the neck of which was sealed a platinum wire w carrying a thin lamp filament f4 ,in the lower part of the globe a tube t was sealed so as to surround the filament4 ,the exhaustion was carried as far as it was practicable with the apparatus employed4 ,this bulb verified my expectation1 for the filament was set spinning when the current was turned on1 and became incandescent4 ,it also showed another interesting feature1 bearing upon the preceding remarks1 namely1 when the filament had been kept incandescent some time1 the narrow tube and the space inside were brought to an elevated temperature1 and as the gas in the tube then became conducting1 the electrostatic attraction between the glass and the filament became very weak or ceased1 and the filament came to rest4 ,when it came to rest it would glow far more intensely4 ,this was probably due to its assuming the position in the centre of the tube where the molecular bombardment was most intense1 and also partly to the fact that the individual impacts were more violent and that no part of the supplied energy was converted into mechanical movement4 ,since1 in accordance with accepted views1 in this experiment the incandescence must be attributed to the impacts of the particles1 molecules or atoms in the heated space1 these particles must therefore1 in order to explain such action1 be assumed to behave as independent carriers of electric charges immersed in an insulating medium2 yet there is no attractive force between the glass tube and the filament because the space in the tube is1 as a whole1 conducting4 ,it is of some interest to observe in this connection that whereas the attraction between two electrified bodies may cease owing to the impairing of the insulating power of the medium in which they are immersed1 the repulsion between the bodies may still be observed4 ,this may be explained in a plausible way4 ,when the bodies are placed at some distance in a poorly conducting medium1 such as slightly warmed or rarefied air1 and are suddenly electrified1 opposite electric charges being imparted to them1 these charges equalize more or less by leakage through the air4 ,but if the bodies are similarly electrified1 there is less opportunity afforded for such dissipation1 hence the repulsion observed in such case is greater than the attraction4 ,repulsive actions in a gaseous medium are however1 as ,prof4 ,crookes has shown1 enhanced by molecular bombardment4 ,,on ,,current ,,or ,,dynamic ,,electricity ,,phenomena4 ,so far1 ,i have considered principally effects produced by a varying electrostatic force in an insulating medium1 such as air4 ,when such a force is acting upon a conducting body of measurable dimensions1 it causes within the same1 or on its surface1 displacements of the electricity and gives rise to electric currents1 and these produce another kind of phenomena1 some of which ,i shall presently endeavor to illustrate4 ,in presenting this second class of electrical effects1 ,i will avail myself principally of such as are producible without any return circuit1 hoping to interest you the more by presenting these phenomena in a more or less novel aspect4 ,it has been a long time customary1 owing to the limited experience with vibratory currents1 to consider an electric current as something circulating in a closed conducting path4 ,it was astonishing at first to realize that a current may flow through the conducting path even if the latter be interrupted1 and it was still more surprising to learn1 that sometimes it may be even easier to make a current flow under such conditions than through a closed path4 ,but that old idea is gradually disappearing1 even among practical men1 and will soon be entirely forgotten4 ,illustration3 ,,fig4 #age4 ,if ,i connect an insulated metal plate ,p1 ,fig4 #age1 to one of the terminals ,t of the induction coil by means of a wire1 though this plate be very well insulated1 a current passes through the wire when the coil is set to work4 ,first ,i wish to give you evidence that there is a current passing through the connecting wire4 ,an obvious way of demonstrating this is to insert between the terminal of the coil and the insulated plate a very thin platinum or german silver wire w and bring the latter to incandescence or fusion by the current4 ,this requires a rather large plate or else current impulses of very high potential and frequency4 ,another way is to take a coil ,c1 ,fig4 #age1 containing many turns of thin insulated wire and to insert the same in the path of the current to the plate4 ,when ,i connect one of the ends of the coil to the wire leading to another insulated plate ,p#a1 and its other end to the terminal ,t#a of the induction coil1 and set the latter to work1 a current passes through the inserted coil ,c and the existence of the current may be made manifest in various ways4 ,for instance1 ,i insert an iron core i within the coil4 ,the current being one of very high frequency1 will1 if it be of some strength1 soon bring the iron core to a noticeably higher temperature1 as the hysteresis and current losses are great with such high frequencies4 ,one might take a core of some size1 laminated or not1 it would matter little2 but ordinary iron wire #a_/afth or #a_/hth of an inch thick is suitable for the purpose4 ,while the induction coil is working1 a current traverses the inserted coil and only a few moments are sufficient to bring the iron wire i to an elevated temperature sufficient to soften the sealing-wax s1 and cause a paper washer p fastened by it to the iron wire to fall off4 ,but with the apparatus such as ,i have here1 other1 much more interesting1 demonstrations of this kind can be made4 ,i have a secondary ,s1 ,fig #agf1 of coarse wire1 wound upon a coil similar to the first4 ,in the preceding experiment the current through the coil ,c1 ,fig4 #age1 was very small1 but there being many turns a strong heating effect was1 nevertheless1 produced in the iron wire4 ,had ,i passed that current through a conductor in order to show the heating of the latter1 the current might have been too small to produce the effect desired4 ,but with this coil provided with a secondary winding1 ,i can now transform the feeble current of high tension which passes through the primary ,p into a strong secondary current of low tension1 and this current will quite certainly do what ,i expect4 ,in a small glass tube 7t1 ,fig4 #agf71 ,i have enclosed a coiled platinum wire1 w1 this merely in order to protect the wire4 ,on each end of the glass tube is sealed a terminal of stout wire to which one of the ends of the platinum wire w1 is connected4 ,i join the terminals of the secondary coil to these terminals and insert the primary p1 between the insulated plate ,p#a1 and the terminal ,t#a1 of the induction coil as before4 ,the latter being set to work1 instantly the platinum wire w is rendered incandescent and can be fused1 even if it be very thick4 ,illustration3 ,,fig4 #agf4 ,instead of the platinum wire ,i now take an ordinary #ej-volt #af ,c4 ,p4 lamp4 ,when ,i set the induction coil in operation the lamp filament is brought to high incandescence4 ,it is1 however1 not necessary to use the insulated plate1 for the lamp 7l1 ,fig4 #agg7 is rendered incandescent even if the plate ,p#a be disconnected4 ,the secondary may also be connected to the primary as indicated by the dotted line in ,fig4 #agg1 to do away more or less with the electrostatic induction or to modify the action otherwise4 ,illustration3 ,,fig4 #agg4 ,i may here call attention to a number of interesting observations with the lamp4 ,first1 ,i disconnect one of the terminals of the lamp from the secondary ,s4 ,when the induction coil plays1 a glow is noted which fills the whole bulb4 ,this glow is due to electrostatic induction4 ,it increases when the bulb is grasped with the hand1 and the capacity of the experimenter's body thus added to the secondary circuit4 ,the secondary1 in effect1 is equivalent to a metallic coating1 which would be placed near the primary4 ,if the secondary1 or its equivalent1 the coating1 were placed symmetrically to the primary1 the electrostatic induction would be nil under ordinary conditions1 that is1 when a primary return circuit is used1 as both halves would neutralize each other4 ,the secondary is in fact placed symmetrically to the primary1 but the action of both halves of the latter1 when only one of its ends is connected to the induction coil1 is not exactly equal2 hence electrostatic induction takes place1 and hence the glow in the bulb4 ,i can nearly equalize the action of both halves of the primary by connecting the other1 free end of the same to the insulated plate1 as in the preceding experiment4 ,when the plate is connected1 the glow disappears4 ,with a smaller plate it would not entirely disappear and then it would contribute to the brightness of the filament when the secondary is closed1 by warming the air in the bulb4 ,illustration3 ,,fig4 #agh;a4 ,illustration3 ,,fig4 #agh;b4 ,illustration3 ,,fig4 #agi;a4 ,illustration3 ,,fig4 #agi;b4 ,to demonstrate another interesting feature1 ,i have adjusted the coils used in a certain way4 ,i first connect both the terminals of the lamp to the secondary1 one end of the primary being connected to the terminal ,t#a of the induction coil and the other to the insulated plate ,p#a as before4 ,when the current is turned on1 the lamp glows brightly1 as shown in ,fig4 #agh;b1 in which ,c is a fine wire coil and ,s a coarse wire secondary wound upon it4 ,if the insulated plate ,p#a is disconnected1 leaving one of the ends a of the primary insulated1 the filament becomes dark or generally it diminishes in brightness 7,fig4 #agh;a74 ,connecting again the plate ,p#a and raising the frequency of the current1 ,i make the filament quite dark or barely red 7,fig4 #agi;b74 ,once more ,i will disconnect the plate4 ,one will of course infer that when the plate is disconnected1 the current through the primary will be weakened1 that therefore the ,e4 ,m4 ,f4 will fall in the secondary ,s1 and that the brightness of the lamp will diminish4 ,this might be the case and the result can be secured by an easy adjustment of the coils2 also by varying the frequency and potential of the currents4 ,but it is perhaps of greater interest to note1 that the lamp increases in brightness when the plate is disconnected 7,fig4 #agi;a74 ,in this case all the energy the primary receives is now sunk into it1 like the charge of a battery in an ocean cable1 but most of that energy is recovered through the secondary and used to light the lamp4 ,the current traversing the primary is strongest at the end b which is connected to the terminal ,t#a of the induction coil1 and diminishes in strength towards the remote end a4 ,but the dynamic inductive effect exerted upon the secondary ,s is now greater than before1 when the suspended plate was connected to the primary4 ,these results might have been produced by a number of causes4 ,for instance1 the plate ,p#a being connected1 the reaction from the coil ,c may be such as to diminish the potential at the terminal ,t#a of the induction coil1 and therefore weaken the current through the primary of the coil ,c4 ,or the disconnecting of the plate may diminish the capacity effect with relation to the primary of the latter coil to such an extent that the current through it is diminished1 though the potential at the terminal ,t#a of the induction coil may be the same or even higher4 ,or the result might have been produced by the change of phase of the primary and secondary currents and consequent reaction4 ,but the chief determining factor is the relation of the self-induction and capacity of coil ,c and plate ,p#a and the frequency of the currents4 ,the greater brightness of the filament in ,fig4 #agi;a1 is1 however1 in part due to the heating of the rarefied gas in the lamp by electrostatic induction1 which1 as before remarked1 is greater when the suspended plate is disconnected4 ,still another feature of some interest ,i may here bring to your attention4 ,when the insulated plate is disconnected and the secondary of the coil opened1 by approaching a small object to the secondary1 but very small sparks can be drawn from it1 showing that the electrostatic induction is small in this case4 ,but upon the secondary being closed upon itself or through the lamp1 the filament glowing brightly1 strong sparks are obtained from the secondary4 ,the electrostatic induction is now much greater1 because the closed secondary determines a greater flow of current through the primary and principally through that half of it which is connected to the induction coil4 ,if now the bulb be grasped with the hand1 the capacity of the secondary with reference to the primary is augmented by the experimenter's body and the luminosity of the filament is increased1 the incandescence now being due partly to the flow of current through the filament and partly to the molecular bombardment of the rarefied gas in the bulb4 ,the preceding experiments will have prepared one for the next following results of interest1 obtained in the course of these investigations4 ,since ,i can pass a current through an insulated wire merely by connecting one of its ends to the source of electrical energy1 since ,i can induce by it another current1 magnetize an iron core1 and1 in short1 perform all operations as though a return circuit were used1 clearly ,i can also drive a motor by the aid of only one wire4 ,on a former occasion ,i have described a simple form of motor comprising a single exciting coil1 an iron core and disc4 ,fig4 #ahj illustrates a modified way of operating such an alternate current motor by currents induced in a transformer connected to one lead1 and several other arrangements of circuits for operating a certain class of alternating motors founded on the action of currents of differing phase4 ,in view of the present state of the art it is thought sufficient to describe these arrangements in a few words only4 ,the diagram1 ,fig4 #ahj ,,ii41 shows a primary coil ,p1 connected with one of its ends to the line ,l leading from a high tension transformer terminal ,t#a4 ,in inductive relation to this primary ,p is a secondary ,s of coarse wire in the circuit of which is a coil c4 ,the currents induced in the secondary energize the iron core i1 which is preferably1 but not necessarily1 subdivided1 and set the metal disc d in rotation4 ,such a motor ,m#b as diagramatically shown in ,fig4 #ahj ,,ii41 has been called a magnetic lag motor1 but this expression may be objected to by those who attribute the rotation of the disc to eddy currents circulating in minute paths when the core i is finally subdivided4 ,in order to operate such a motor effectively on the plan indicated1 the frequencies should not be too high1 not more than four or five thousand1 though the rotation is produced even with ten thousand per second1 or more4 ,in ,fig4 #ahj ,i41 a motor ,m#a having two energizing circuits1 ,a and ,b1 is diagrammatically indicated4 ,the circuit ,a is connected to the line ,l and in series with it is a primary ,p1 which may have its free end connected to an insulated plate ,p#a1 such connection being indicated by the dotted lines4 ,the other motor circuit ,b is connected to the secondary ,s which is in inductive relation to the primary ,p4 ,when the transformer terminal ,t#a is alternately electrified1 currents traverse the open line ,l and also circuit ,a and primary ,p4 ,the currents through the latter induce secondary currents in the circuit ,s1 which pass through the energizing coil ,b of the motor4 ,the currents through the secondary ,s and those through the primary ,p differ in phase #ij degrees1 or nearly so1 and are capable of rotating an armature placed in inductive relation to the circuits ,a and ,b4 ,in ,fig4 #ahj ,,iii41 a similar motor ,m#c with two energizing circuits ,a#a and ,b#a is illustrated4 ,a primary ,p1 connected with one of its ends to the line ,l has a secondary ,s1 which is preferably wound for a tolerably high ,e4 ,m4 ,f41 and to which the two energizing circuits of the motor are connected1 one directly to the ends of the secondary and the other through a condenser ,c1 by the action of which the currents traversing the circuit ,a#a and ,b#a are made to differ in phase4 ,illustration3 ,,fig4 #ahj4 ,illustration3 ,,fig4 #aha4 ,illustration3 ,,fig4 #ahb4 ,in ,fig4 #ahj ,,iv41 still another arrangement is shown4 ,in this case two primaries ,p#a and ,p#b are connected to the line ,l1 one through a condenser ,c of small capacity1 and the other directly4 ,the primaries are provided with secondaries ,s#a and ,s#b which are in series with the energizing circuits1 ,a#b and ,b#b and a motor ,m#c1 the condenser ,c again serving to produce the requisite difference in the phase of the currents traversing the motor circuits4 ,as such phase motors with two or more circuits are now well known in the art1 they have been here illustrated diagrammatically4 ,no difficulty whatever is found in operating a motor in the manner indicated1 or in similar ways2 and although such experiments up to this day present only scientific interest1 they may at a period not far distant1 be carried out with practical objects in view4 ,it is thought useful to devote here a few remarks to the subject of operating devices of all kinds by means of only one leading wire4 ,it is quite obvious1 that when high-frequency currents are made use of1 ground connections are--at least when the ,e4 ,m4 ,f4 of the currents is great--better than a return wire4 ,such ground connections are objectionable with steady or low frequency currents on account of destructive chemical actions of the former and disturbing influences exerted by both on the neighboring circuits2 but with high frequencies these actions practically do not exist4 ,still1 even ground connections become superfluous when the ,e4 ,m4 ,f4 is very high1 for soon a condition is reached1 when the current may be passed more economically through open1 than through closed1 conductors4 ,remote as might seem an industrial application of such single wire transmission of energy to one not experienced in such lines of experiment1 it will not seem so to anyone who for some time has carried on investigations of such nature4 ,indeed ,i cannot see why such a plan should not be practicable4 ,nor should it be thought that for carrying out such a plan currents of very high frequency are expressly required1 for just as soon as potentials of say #cj1jjj volts are used1 the single wire transmission may be effected with low frequencies1 and experiments have been made by me from which these inferences are made4 ,when the frequencies are very high it has been found in laboratory practice quite easy to regulate the effects in the manner shown in diagram ,fig4 #aha4 ,here two primaries ,p and ,p#a are shown1 each connected with one of its ends to the line ,l and with the other end to the condenser plates ,c and ,c1 respectively4 ,near these are placed other condenser plates ,c#a and ,c#a1 the former being connected to the line ,l and the latter to an insulated larger plate ,p#b4 ,on the primaries are wound secondaries ,s and ,s#a1 of coarse wire1 connected to the devices d and l respectively4 ,by varying the distances of the condenser plates ,c and ,c#a1 and ,c and ,c#a the currents through the secondaries ,s and ,s#a are varied in intensity4 ,the curious feature is the great sensitiveness1 the slightest change in the distance of the plates producing considerable variations in the intensity or strength of the currents4 ,the sensitiveness may be rendered extreme by making the frequency such1 that the primary itself1 without any plate attached to its free end1 satisfies1 in conjunction with the closed secondary1 the condition of resonance4 ,in such condition an extremely small change in the capacity of the free terminal produces great variations4 ,for instance1 ,i have been able to adjust the conditions so that the mere approach of a person to the coil produces a considerable change in the brightness of the lamps attached to the secondary4 ,such observations and experiments possess1 of course1 at present1 chiefly scientific interest1 but they may soon become of practical importance4 ,very high frequencies are of course not practicable with motors on account of the necessity of employing iron cores4 ,but one may use sudden discharges of low frequency and thus obtain certain advantages of high-frequency currents without rendering the iron core entirely incapable of following the changes and without entailing a very great expenditure of energy in the core4 ,i have found it quite practicable to operate with such low frequency disruptive discharges of condensers1 alternating-current motors4 ,a certain class of such motors which ,i advanced a few years ago1 which contain closed secondary circuits1 will rotate quite vigorously when the discharges are directed through the exciting coils4 ,one reason that such a motor operates so well with these discharges is that the difference of phase between the primary and secondary currents is #ij degrees1 which is generally not the case with harmonically rising and falling currents of low frequency4 ,it might not be without interest to show an experiment with a simple motor of this kind1 inasmuch as it is commonly thought that disruptive discharges are unsuitable for such purposes4 ,the motor is illustrated in ,fig4 #ahb4 ,it comprises a rather large iron core i with slots on the top into which are embedded thick copper washers c c4 ,in proximity to the core is a freely-movable metal disc ,d4 ,the core is provided with a primary exciting coil ,c#a the ends a and b of which are connected to the terminals of the secondary ,s of an ordinary transformer1 the primary ,p of the latter being connected to an alternating distribution circuit or generator ,g of low or moderate frequency4 ,the terminals of the secondary ,s are attached to a condenser ,c which discharges through an air gap d d which may be placed in series or shunt to the coil ,c#a4 ,when the conditions are properly chosen the disc ,d rotates with considerable effort and the iron core i does not get very perceptibly hot4 ,with currents from a high-frequency alternator1 on the contrary1 the core gets rapidly hot and the disc rotates with a much smaller effort4 ,to perform the experiment properly it should be first ascertained that the disc ,d is not set in rotation when the discharge is not occurring at d d4 ,it is preferable to use a large iron core and a condenser of large capacity so as to bring the superimposed quicker oscillation to a very low pitch or to do away with it entirely4 ,by observing certain elementary rules ,i have also found it practicable to operate ordinary series or shunt direct-current motors with such disruptive discharges1 and this can be done with or without a return wire4 ,,impedance ,,phenomena4 ,among the various current phenomena observed1 perhaps the most interesting are those of impedance presented by conductors to currents varying at a rapid rate4 ,in my first paper before the ,american ,institute of ,electrical ,engineers1 ,i have described a few striking observations of this kind4 ,thus ,i showed that when such currents or sudden discharges are passed through a thick metal bar there may be points on the bar only a few inches apart1 which have a sufficient potential difference between them to maintain at bright incandescence an ordinary filament lamp4 ,i have also described the curious behavior of rarefied gas surrounding a conductor1 due to such sudden rushes of current4 ,these phenomena have since been more carefully studied and one or two novel experiments of this kind are deemed of sufficient interest to be described here4 ,referring to ,fig4 #ahc;a1 ,b and ,b#a are very stout copper bars connected at their lower ends to plates ,c and ,c#a1 respectively1 of a condenser1 the opposite plates of the latter being connected to the terminals of the secondary ,s of a high-tension transformer1 the primary ,p of which is supplied with alternating currents from an ordinary low-frequency dynamo ,g or distribution circuit4 ,the condenser discharges through an adjustable gap d d as usual4 ,by establishing a rapid vibration it was found quite easy to perform the following curious experiment4 ,the bars ,b and ,b#a were joined at the top by a low-voltage lamp l#c2 a little lower was placed by means of clamps c c1 a #ej-volt lamp l#b2 and still lower another #ajj-volt lamp l#a2 and finally1 at a certain distance below the latter lamp1 an exhausted tube ,t4 ,by carefully determining the positions of these devices it was found practicable to maintain them all at their proper illuminating power4 ,yet they were all connected in multiple arc to the two stout copper bars and required widely different pressures4 ,this experiment requires of course some time for adjustment but is quite easily performed4 ,illustration3 ,,figs4 #ahc;a1 #ahc;b and #ahc;c4 ,in ,figs4 #ahc;b and #ahc;c1 two other experiments are illustrated which1 unlike the previous experiment1 do not require very careful adjustments4 ,in ,fig4 #ahc;b1 two lamps1 l#a and l#b1 the former a #ajj-volt and the latter a #ej-volt are placed in certain positions as indicated1 the #ajj-volt lamp being below the #ej-volt lamp4 ,when the arc is playing at d d and the sudden discharges are passed through the bars ,b ,b#a1 the #ej-volt lamp will1 as a rule1 burn brightly1 or at least this result is easily secured1 while the #ajj-volt lamp will burn very low or remain quite dark1 ,fig4 #ahc;b4 ,now the bars ,b ,b#a may be joined at the top by a thick cross bar ,b#b and it is quite easy to maintain the #ajj-volt lamp at full candle-power while the #ej-volt lamp remains dark1 ,fig4 #ahc;c4 ,these results1 as ,i have pointed out previously1 should not be considered to be due exactly to frequency but rather to the time rate of change which may be great1 even with low frequencies4 ,a great many other results of the same kind1 equally interesting1 especially to those who are only used to manipulate steady currents1 may be obtained and they afford precious clues in investigating the nature of electric currents4 ,in the preceding experiments ,i have already had occasion to show some light phenomena and it would now be proper to study these in particular2 but to make this investigation more complete ,i think it necessary to make first a few remarks on the subject of electrical resonance which has to be always observed in carrying out these experiments4 ,,on ,,electrical ,,resonance4 ,the effects of resonance are being more and more noted by engineers and are becoming of great importance in the practical operation of apparatus of all kinds with alternating currents4 ,a few general remarks may therefore be made concerning these effects4 ,it is clear1 that if we succeed in employing the effects of resonance practically in the operation of electric devices the return wire will1 as a matter of course1 become unnecessary1 for the electric vibration may be conveyed with one wire just as well as1 and sometimes even better than1 with two4 ,the question first to answer is1 then1 whether pure resonance effects are producible4 ,theory and experiment both show that such is impossible in ,nature1 for as the oscillation becomes more and more vigorous1 the losses in the vibrating bodies and environing media rapidly increase and necessarily check the vibration which otherwise would go on increasing forever4 ,it is a fortunate circumstance that pure resonance is not producible1 for if it were there is no telling what dangers might not lie in wait for the innocent experimenter4 ,but to a certain degree resonance is producible1 the magnitude of the effects being limited by the imperfect conductivity and imperfect elasticity of the media or1 generally stated1 by frictional losses4 ,the smaller these losses1 the more striking are the effects4 ,the same is the case in mechanical vibration4 ,a stout steel bar may be set in vibration by drops of water falling upon it at proper intervals2 and with glass1 which is more perfectly elastic1 the resonance effect is still more remarkable1 for a goblet may be burst by singing into it a note of the proper pitch4 ,the electrical resonance is the more perfectly attained1 the smaller the resistance or the impedance of the conducting path and the more perfect the dielectric4 ,in a ,leyden jar discharging through a short stranded cable of thin wires these requirements are probably best fulfilled1 and the resonance effects are therefore very prominent4 ,such is not the case with dynamo machines1 transformers and their circuits1 or with commercial apparatus in general in which the presence of iron cores complicates the action or renders it impossible4 ,in regard to ,leyden jars with which resonance effects are frequently demonstrated1 ,i would say that the effects observed are often attributed but are seldom due to true resonance1 for an error is quite easily made in this respect4 ,this may be undoubtedly demonstrated by the following experiment4 ,take1 for instance1 two large insulated metallic plates or spheres which ,i shall designate ,a and ,b2 place them at a certain small distance apart and charge them from a frictional or influence machine to a potential so high that just a slight increase of the difference of potential between them will cause the small air or insulating space to break down4 ,this is easily reached by making a few preliminary trials4 ,if now another plate--fastened on an insulating handle and connected by a wire to one of the terminals of a high tension secondary of an induction coil1 which is maintained in action by an alternator 7preferably high frequency7--is approached to one of the charged bodies ,a or ,b1 so as to be nearer to either one of them1 the discharge will invariably occur between them2 at least it will1 if the potential of the coil in connection with the plate is sufficiently high4 ,but the explanation of this will soon be found in the fact that the approached plate acts inductively upon the bodies ,a and ,b and causes a spark to pass between them4 ,when this spark occurs1 the charges which were previously imparted to these bodies from the influence machine1 must needs be lost1 since the bodies are brought in electrical connection through the arc formed4 ,now this arc is formed whether there be resonance or not4 ,but even if the spark would not be produced1 still there is an alternating ,e4 ,m4 ,f4 set up between the bodies when the plate is brought near one of them2 therefore the approach of the plate1 if it does not always actually1 will1 at any rate1 tend to break down the air space by inductive action4 ,instead of the spheres or plates ,a and ,b we may take the coatings of a ,leyden jar with the same result1 and in place of the machine1--which is a high frequency alternator preferably1 because it is more suitable for the experiment and also for the argument1--we may take another ,leyden jar or battery of jars4 ,when such jars are discharging through a circuit of low resistance the same is traversed by currents of very high frequency4 ,the plate may now be connected to one of the coatings of the second jar1 and when it is brought near to the first jar just previously charged to a high potential from an influence machine1 the result is the same as before1 and the first jar will discharge through a small air space upon the second being caused to discharge4 ,but both jars and their circuits need not be tuned any closer than a basso profundo is to the note produced by a mosquito1 as small sparks will be produced through the air space1 or at least the latter will be considerably more strained owing to the setting up of an alternating ,e4 ,m4 ,f4 by induction1 which takes place when one of the jars begins to discharge4 ,again another error of a similar nature is quite easily made4 ,if the circuits of the two jars are run parallel and close together1 and the experiment has been performed of discharging one by the other1 and now a coil of wire be added to one of the circuits whereupon the experiment does not succeed1 the conclusion that this is due to the fact that the circuits are now not tuned1 would be far from being safe4 ,for the two circuits act as condenser coatings and the addition of the coil to one of them is equivalent to bridging them1 at the point where the coil is placed1 by a small condenser1 and the effect of the latter might be to prevent the spark from jumping through the discharge space by diminishing the alternating ,e4 ,m4 ,f4 acting across the same4 ,all these remarks1 and many more which might be added but for fear of wandering too far from the subject1 are made with the pardonable intention of cautioning the unsuspecting student1 who might gain an entirely unwarranted opinion of his skill at seeing every experiment succeed2 but they are in no way thrust upon the experienced as novel observations4 ,in order to make reliable observations of electric resonance effects it is very desirable1 if not necessary1 to employ an alternator giving currents which rise and fall harmonically1 as in working with make and break currents the observations are not always trustworthy1 since many phenomena1 which depend on the rate of change1 may be produced with widely different frequencies4 ,even when making such observations with an alternator one is apt to be mistaken4 ,when a circuit is connected to an alternator there are an indefinite number of values for capacity and self-induction which1 in conjunction1 will satisfy the condition of resonance4 ,so there are in mechanics an infinite number of tuning forks which will respond to a note of a certain pitch1 or loaded springs which have a definite period of vibration4 ,but the resonance will be most perfectly attained in that case in which the motion is effected with the greatest freedom4 ,now in mechanics1 considering the vibration in the common medium--that is1 air--it is of comparatively little importance whether one tuning fork be somewhat larger than another1 because the losses in the air are not very considerable4 ,one may1 of course1 enclose a tuning fork in an exhausted vessel and by thus reducing the air resistance to a minimum obtain better resonant action4 ,still the difference would not be very great4 ,but it would make a great difference if the tuning fork were immersed in mercury4 ,in the electrical vibration it is of enormous importance to arrange the conditions so that the vibration is effected with the greatest freedom4 ,the magnitude of the resonance effect depends1 under otherwise equal conditions1 on the quantity of electricity set in motion or on the strength of the current driven through the circuit4 ,but the circuit opposes the passage of the currents by reason of its impedance and therefore1 to secure the best action it is necessary to reduce the impedance to a minimum4 ,it is impossible to overcome it entirely1 but merely in part1 for the ohmic resistance cannot be overcome4 ,but when the frequency of the impulses is very great1 the flow of the current is practically determined by self-induction4 ,now self-induction can be overcome by combining it with capacity4 ,if the relation between these is such1 that at the frequency used they annul each other1 that is1 have such values as to satisfy the condition of resonance1 and the greatest quantity of electricity is made to flow through the external circuit1 then the best result is obtained4 ,it is simpler and safer to join the condenser in series with the self-induction4 ,it is clear that in such combinations there will be1 for a given frequency1 and considering only the fundamental vibration1 values which will give the best result1 with the condenser in shunt to the self-induction coil2 of course more such values than with the condenser in series4 ,but practical conditions determine the selection4 ,in the latter case in performing the experiments one may take a small self-induction and a large capacity or a small capacity and a large self-induction1 but the latter is preferable1 because it is inconvenient to adjust a large capacity by small steps4 ,by taking a coil with a very large self-induction the critical capacity is reduced to a very small value1 and the capacity of the coil itself may be sufficient4 ,it is easy1 especially by observing certain artifices1 to wind a coil through which the impedance will be reduced to the value of the ohmic resistance only2 and for any coil there is1 of course1 a frequency at which the maximum current will be made to pass through the coil4 ,the observation of the relation between self-induction1 capacity and frequency is becoming important in the operation of alternate current apparatus1 such as transformers or motors1 because by a judicious determination of the elements the employment of an expensive condenser becomes unnecessary4 ,thus it is possible to pass through the coils of an alternating current motor under the normal working conditions the required current with a low ,e4 ,m4 ,f4 and do away entirely with the false current1 and the larger the motor1 the easier such a plan becomes practicable2 but it is necessary for this to employ currents of very high potential or high frequency4 ,illustration3 ,,fig4 #ahd4 ,in ,fig4 #ahd ,i4 is shown a plan which has been followed in the study of the resonance effects by means of a high frequency alternator4 ,c#a is a coil of many turns1 which is divided into small separate sections for the purpose of adjustment4 ,the final adjustment was made sometimes with a few thin iron wires 7though this is not always advisable7 or with a closed secondary4 ,the coil ,c#a is connected with one of its ends to the line ,l from the alternator ,g and with the other end to one of the plates c of a condenser c c#a1 the plate 7c#a7 of the latter being connected to a much larger plate ,p#a4 ,in this manner both capacity and self-induction were adjusted to suit the dynamo frequency4 ,as regards the rise of potential through resonant action1 of course1 theoretically1 it may amount to anything since it depends on self-induction and resistance and since these may have any value4 ,but in practice one is limited in the selection of these values and besides these1 there are other limiting causes4 ,one may start with1 say1 #a1jjj volts and raise the ,e4 ,m4 ,f4 to #ej times that value1 but one cannot start with #ajj1jjj and raise it to ten times that value because of the losses in the media which are great1 especially if the frequency is high4 ,it should be possible to start with1 for instance1 two volts from a high or low frequency circuit of a dynamo and raise the ,e4 ,m4 ,f4 to many hundred times that value4 ,thus coils of the proper dimensions might be connected each with only one of its ends to the mains from a machine of low ,e4 ,m4 ,f41 and though the circuit of the machine would not be closed in the ordinary acceptance of the term1 yet the machine might be burned out if a proper resonance effect would be obtained4 ,i have not been able to produce1 nor have ,i observed with currents from a dynamo machine1 such great rises of potential4 ,it is possible1 if not probable1 that with currents obtained from apparatus containing iron the disturbing influence of the latter is the cause that these theoretical possibilities cannot be realized4 ,but if such is the case ,i attribute it solely to the hysteresis and ,foucault current losses in the core4 ,generally it was necessary to transform upward1 when the ,e4 ,m4 ,f4 was very low1 and usually an ordinary form of induction coil was employed1 but sometimes the arrangement illustrated in ,fig4 #ahd ,,ii41 has been found to be convenient4 ,in this case a coil ,c is made in a great many sections1 a few of these being used as a primary4 ,in this manner both primary and secondary are adjustable4 ,one end of the coil is connected to the line ,l#a from the alternator1 and the other line ,l is connected to the intermediate point of the coil4 ,such a coil with adjustable primary and secondary will be found also convenient in experiments with the disruptive discharge4 ,when true resonance is obtained the top of the wave must of course be on the free end of the coil as1 for instance1 at the terminal of the phosphorescence bulb ,b4 ,this is easily recognized by observing the potential of a point on the wire w near to the coil4 ,in connection with resonance effects and the problem of transmission of energy over a single conductor which was previously considered1 ,i would say a few words on a subject which constantly fills my thoughts and which concerns the welfare of all4 ,i mean the transmission of intelligible signals or perhaps even power to any distance without the use of wires4 ,i am becoming daily more convinced of the practicability of the scheme2 and though ,i know full well that the great majority of scientific men will not believe that such results can be practically and immediately realized1 yet ,i think that all consider the developments in recent years by a number of workers to have been such as to encourage thought and experiment in this direction4 ,my conviction has grown so strong1 that ,i no longer look upon this plan of energy or intelligence transmission as a mere theoretical possibility1 but as a serious problem in electrical engineering1 which must be carried out some day4 ,the idea of transmitting intelligence without wires is the natural outcome of the most recent results of electrical investigations4 ,some enthusiasts have expressed their belief that telephony to any distance by induction through the air is possible4 ,i cannot stretch my imagination so far1 but ,i do firmly believe that it is practicable to disturb by means of powerful machines the electrostatic condition of the earth and thus transmit intelligible signals and perhaps power4 ,in fact1 what is there against the carrying out of such a scheme8 ,we now know that electric vibration may be transmitted through a single conductor4 ,why then not try to avail ourselves of the earth for this purpose8 ,we need not be frightened by the idea of distance4 ,to the weary wanderer counting the mile-posts the earth may appear very large1 but to that happiest of all men1 the astronomer1 who gazes at the heavens and by their standard judges the magnitude of our globe1 it appears very small4 ,and so ,i think it must seem to the electrician1 for when he considers the speed with which an electric disturbance is propagated through the earth all his ideas of distance must completely vanish4 ,a point of great importance would be first to know what is the capacity of the earth8 and what charge does it contain if electrified8 ,though we have no positive evidence of a charged body existing in space without other oppositely electrified bodies being near1 there is a fair probability that the earth is such a body1 for by whatever process it was separated from other bodies--and this is the accepted view of its origin--it must have retained a charge1 as occurs in all processes of mechanical separation4 ,if it be a charged body insulated in space its capacity should be extremely small1 less than one-thousandth of a farad4 ,but the upper strata of the air are conducting1 and so1 perhaps1 is the medium in free space beyond the atmosphere1 and these may contain an opposite charge4 ,then the capacity might be incomparably greater4 ,in any case it is of the greatest importance to get an idea of what quantity of electricity the earth contains4 ,it is difficult to say whether we shall ever acquire this necessary knowledge1 but there is hope that we may1 and that is1 by means of electrical resonance4 ,if ever we can ascertain at what period the earth's charge1 when disturbed1 oscillates with respect to an oppositely electrified system or known circuit1 we shall know a fact possibly of the greatest importance to the welfare of the human race4 ,i propose to seek for the period by means of an electrical oscillator1 or a source of alternating electric currents4 ,one of the terminals of the source would be connected to earth as1 for instance1 to the city water mains1 the other to an insulated body of large surface4 ,it is possible that the outer conducting air strata1 or free space1 contain an opposite charge and that1 together with the earth1 they form a condenser of very large capacity4 ,in such case the period of vibration may be very low and an alternating dynamo machine might serve for the purpose of the experiment4 ,i would then transform the current to a potential as high as it would be found possible and connect the ends of the high tension secondary to the ground and to the insulated body4 ,by varying the frequency of the currents and carefully observing the potential of the insulated body and watching for the disturbance at various neighboring points of the earth's surface resonance might be detected4 ,should1 as the majority of scientific men in all probability believe1 the period be extremely small1 then a dynamo machine would not do and a proper electrical oscillator would have to be produced and perhaps it might not be possible to obtain such rapid vibrations4 ,but whether this be possible or not1 and whether the earth contains a charge or not1 and whatever may be its period of vibration1 it certainly is possible--for of this we have daily evidence--to produce some electrical disturbance sufficiently powerful to be perceptible by suitable instruments at any point of the earth's surface4 ,illustration3 ,,fig4 #ahe4 ,assume that a source of alternating current ,s be connected1 as in ,fig4 #ahe1 with one of its terminals to earth 7conveniently to the water mains7 and with the other to a body of large surface ,p4 ,when the electric oscillation is set up there will be a movement of electricity in and out of ,p1 and alternating currents will pass through the earth1 converging to1 or diverging from1 the point ,c where the ground connection is made4 ,in this manner neighboring points on the earth's surface within a certain radius will be disturbed4 ,but the disturbance will diminish with the distance1 and the distance at which the effect will still be perceptible will depend on the quantity of electricity set in motion4 ,since the body ,p is insulated1 in order to displace a considerable quantity1 the potential of the source must be excessive1 since there would be limitations as to the surface of ,p4 ,the conditions might be adjusted so that the generator or source ,s will set up the same electrical movement as though its circuit were closed4 ,thus it is certainly practicable to impress an electric vibration at least of a certain low period upon the earth by means of proper machinery4 ,at what distance such a vibration might be made perceptible can only be conjectured4 ,i have on another occasion considered the question how the earth might behave to electric disturbances4 ,there is no doubt that1 since in such an experiment the electrical density at the surface could be but extremely small considering the size of the earth1 the air would not act as a very disturbing factor1 and there would be not much energy lost through the action of the air1 which would be the case if the density were great4 ,theoretically1 then1 it could not require a great amount of energy to produce a disturbance perceptible at great distance1 or even all over the surface of the globe4 ,now1 it is quite certain that at any point within a certain radius of the source ,s a properly adjusted self-induction and capacity device can be set in action by resonance4 ,but not only can this be done1 but another source ,s#a1 ,fig4 #ahe1 similar to ,s1 or any number of such sources1 can be set to work in synchronism with the latter1 and the vibration thus intensified and spread over a large area1 or a flow of electricity produced to or from the source ,s#a if the same be of opposite phase to the source ,s4 ,i think that beyond doubt it is possible to operate electrical devices in a city through the ground or pipe system by resonance from an electrical oscillator located at a central point4 ,but the practical solution of this problem would be of incomparably smaller benefit to man than the realization of the scheme of transmitting intelligence1 or perhaps power1 to any distance through the earth or environing medium4 ,if this is at all possible1 distance does not mean anything4 ,proper apparatus must first be produced by means of which the problem can be attacked and ,i have devoted much thought to this subject4 ,i am firmly convinced that it can be done and hope that we shall live to see it done4 ,,on ,,the ,,light ,,phenomena ,,produced ,,by ,,high-,,frequency ,,currents ,,of ,,high ,,potential ,,and ,,general ,,remarks ,,relating ,,to ,,the ,,subject4 ,returning now to the light effects which it has been the chief object to investigate1 it is thought proper to divide these effects into four classes3 #a4 ,incandescence of a solid4 #b4 ,phosphorescence4 #c4 ,incandescence or phosphorescence of a rarefied gas2 and #d4 ,luminosity produced in a gas at ordinary pressure4 ,the first question is3 ,how are these luminous effects produced8 ,in order to answer this question as satisfactorily as ,i am able to do in the light of accepted views and with the experience acquired1 and to add some interest to this demonstration1 ,i shall dwell here upon a feature which ,i consider of great importance1 inasmuch as it promises1 besides1 to throw a better light upon the nature of most of the phenomena produced by high-frequency electric currents4 ,i have on other occasions pointed out the great importance of the presence of the rarefied gas1 or atomic medium in general1 around the conductor through which alternate currents of high frequency are passed1 as regards the heating of the conductor by the currents4 ,my experiments1 described some time ago1 have shown that1 the higher the frequency and potential difference of the currents1 the more important becomes the rarefied gas in which the conductor is immersed1 as a factor of the heating4 ,the potential difference1 however1 is1 as ,i then pointed out1 a more important element than the frequency4 ,when both of these are sufficiently high1 the heating may be almost entirely due to the presence of the rarefied gas4 ,the experiments to follow will show the importance of the rarefied gas1 or1 generally1 of gas at ordinary or other pressure as regards the incandescence or other luminous effects produced by currents of this kind4 ,i take two ordinary #ej-volt #af ,c4 ,p4 lamps which are in every respect alike1 with the exception1 that one has been opened at the top and the air has filled the bulb1 while the other is at the ordinary degree of exhaustion of commercial lamps4 ,when ,i attach the lamp which is exhausted to the terminal of the secondary of the coil1 which ,i have already used1 as in experiments illustrated in ,fig4 #agi;a for instance1 and turn on the current1 the filament1 as you have before seen1 comes to high incandescence4 ,when ,i attach the second lamp1 which is filled with air1 instead of the former1 the filament still glows1 but much less brightly4 ,this experiment illustrates only in part the truth of the statements before made4 ,the importance of the filament's being immersed in rarefied gas is plainly noticeable but not to such a degree as might be desirable4 ,the reason is that the secondary of this coil is wound for low tension1 having only #aej turns1 and the potential difference at the terminals of the lamp is therefore small4 ,were ,i to take another coil with many more turns in the secondary1 the effect would be increased1 since it depends partially on the potential difference1 as before remarked4 ,but since the effect likewise depends on the frequency1 it maybe properly stated that it depends on the time rate of the variation of the potential difference4 ,the greater this variation1 the more important becomes the gas as an element of heating4 ,i can produce a much greater rate of variation in another way1 which1 besides1 has the advantage of doing away with the objections1 which might be made in the experiment just shown1 even if both the lamps were connected in series or multiple arc to the coil1 namely1 that in consequence of the reactions existing between the primary and secondary coil the conclusions are rendered uncertain4 ,this result ,i secure by charging1 from an ordinary transformer which is fed from the alternating current supply station1 a battery of condensers1 and discharging the latter directly through a circuit of small self-induction1 as before illustrated in ,figs4 #ahc;a1 #ahc;b1 and #ahc;c4 ,illustration3 ,,fig4 #ahf;a4 ,illustration3 ,,fig4 #ahf;b4 ,illustration3 ,,fig4 #ahf;c4 ,in ,figs4 #ahf;a1 #ahf;b and #ahf;c1 the heavy copper bars ,b ,b#a1 are connected to the opposite coatings of a battery of condensers1 or generally in such way1 that the high frequency or sudden discharges are made to traverse them4 ,i connect first an ordinary #ej-volt incandescent lamp to the bars by means of the clamps c c4 ,the discharges being passed through the lamp1 the filament is rendered incandescent1 though the current through it is very small1 and would not be nearly sufficient to produce a visible effect under the conditions of ordinary use of the lamp4 ,instead of this ,i now attach to the bars another lamp exactly like the first1 but with the seal broken off1 the bulb being therefore filled with air at ordinary pressure4 ,when the discharges are directed through the filament1 as before1 it does not become incandescent4 ,but the result might still be attributed to one of the many possible reactions4 ,i therefore connect both the lamps in multiple arc as illustrated in ,fig4 #ahf;a4 ,passing the discharges through both the lamps1 again the filament in the exhausted lamp l glows very brightly while that in the non-exhausted lamp l#a remains dark1 as previously4 ,but it should not be thought that the latter lamp is taking only a small fraction of the energy supplied to both the lamps2 on the contrary1 it may consume a considerable portion of the energy and it may become even hotter than the one which burns brightly4 ,in this experiment the potential difference at the terminals of the lamps varies in sign theoretically three to four million times a second4 ,the ends of the filaments are correspondingly electrified1 and the gas in the bulbs is violently agitated and a large portion of the supplied energy is thus converted into heat4 ,in the non-exhausted bulb1 there being a few million times more gas molecules than in the exhausted one1 the bombardment1 which is most violent at the ends of the filament1 in the neck of the bulb1 consumes a large portion of the energy without producing any visible effect4 ,the reason is that1 there being many molecules1 the bombardment is quantitatively considerable1 but the individual impacts are not very violent1 as the speeds of the molecules are comparatively small owing to the small free path4 ,in the exhausted bulb1 on the contrary1 the speeds are very great1 and the individual impacts are violent and therefore better adapted to produce a visible effect4 ,besides1 the convection of heat is greater in the former bulb4 ,in both the bulbs the current traversing the filaments is very small1 incomparably smaller than that which they require on an ordinary low-frequency circuit4 ,the potential difference1 however1 at the ends of the filaments is very great and might be possibly #bj1jjj volts or more1 if the filaments were straight and their ends far apart4 ,in the ordinary lamp a spark generally occurs between the ends of the filament or between the platinum wires outside1 before such a difference of potential can be reached4 ,it might be objected that in the experiment before shown the lamps1 being in multiple arc1 the exhausted lamp might take a much larger current and that the effect observed might not be exactly attributable to the action of the gas in the bulbs4 ,such objections will lose much weight if ,i connect the lamps in series1 with the same result4 ,when this is done and the discharges are directed through the filaments1 it is again noted that the filament in the non-exhausted bulb l#a1 remains dark1 while that in the exhausted one 7l7 glows even more intensely than under its normal conditions of working1 ,fig4 #ahf;b4 ,according to general ideas the current through the filaments should now be the same1 were it not modified by the presence of the gas around the filaments4 ,at this juncture ,i may point out another interesting feature1 which illustrates the effect of the rate of change of potential of the currents4 ,i will leave the two lamps connected in series to the bars ,b ,b#a1 as in the previous experiment1 ,fig4 #ahf;b1 but will presently reduce considerably the frequency of the currents1 which was excessive in the experiment just before shown4 ,this ,i may do by inserting a self-induction coil in the path of the discharges1 or by augmenting the capacity of the condensers4 ,when ,i now pass these low-frequency discharges through the lamps1 the exhausted lamp l again is as bright as before1 but it is noted also that the non-exhausted lamp l#a glows1 though not quite as intensely as the other4 ,reducing the current through the lamps1 ,i may bring the filament in the latter lamp to redness1 and1 though the filament in the exhausted lamp l is bright1 ,fig4 #ahf;c1 the degree of its incandescence is much smaller than in ,fig4 #ahf;b1 when the currents were of a much higher frequency4 ,in these experiments the gas acts in two opposite ways in determining the degree of the incandescence of the filaments1 that is1 by convection and bombardment4 ,the higher the frequency and potential of the currents1 the more important becomes the bombardment4 ,the convection on the contrary should be the smaller1 the higher the frequency4 ,when the currents are steady there is practically no bombardment1 and convection may therefore with such currents also considerably modify the degree of incandescence and produce results similar to those just before shown4 ,thus1 if two lamps exactly alike1 one exhausted and one not exhausted1 are connected in multiple arc or series to a direct-current machine1 the filament in the non-exhausted lamp will require a considerably greater current to be rendered incandescent4 ,this result is entirely due to convection1 and the effect is the more prominent the thinner the filament4 ,professor ,ayrton and ,mr4 ,kilgour some time ago published quantitative results concerning the thermal emissivity by radiation and convection in which the effect with thin wires was clearly shown4 ,this effect may be strikingly illustrated by preparing a number of small1 short1 glass tubes1 each containing through its axis the thinnest obtainable platinum wire4 ,if these tubes be highly exhausted1 a number of them may be connected in multiple arc to a direct-current machine and all of the wires may be kept at incandescence with a smaller current than that required to render incandescent a single one of the wires if the tube be not exhausted4 ,could the tubes be so highly exhausted that convection would be nil1 then the relative amounts of heat given off by convection and radiation could be determined without the difficulties attending thermal quantitative measurements4 ,if a source of electric impulses of high frequency and very high potential is employed1 a still greater number of the tubes may be taken and the wires rendered incandescent by a current not capable of warming perceptibly a wire of the same size immersed in air at ordinary pressure1 and conveying the energy to all of them4 ,i may here describe a result which is still more interesting1 and to which ,i have been led by the observation of these phenomena4 ,i noted that small differences in the density of the air produced a considerable difference in the degree of incandescence of the wires1 and ,i thought that1 since in a tube1 through which a luminous discharge is passed1 the gas is generally not of uniform density1 a very thin wire contained in the tube might be rendered incandescent at certain places of smaller density of the gas1 while it would remain dark at the places of greater density1 where the convection would be greater and the bombardment less intense4 ,accordingly a tube t was prepared1 as illustrated in ,fig4 #ahg1 which contained through the middle a very fine platinum wire w4 ,the tube was exhausted to a moderate degree and it was found that when it was attached to the terminal of a high-frequency coil the platinum wire w would indeed1 become incandescent in patches1 as illustrated in ,fig4 #ahg4 ,later a number of these tubes with one or more wires were prepared1 each showing this result4 ,the effect was best noted when the striated discharge occurred in the tube1 but was also produced when the striae were not visible1 showing that1 even then1 the gas in the tube was not of uniform density4 ,the position of the striae was generally such1 that the rarefactions corresponded to the places of incandescence or greater brightness on the wire w4 ,but in a few instances it was noted1 that the bright spots on the wire were covered by the dense parts of the striated discharge as indicated by l in ,fig4 #ahg1 though the effect was barely perceptible4 ,this was explained in a plausible way by assuming that the convection was not widely different in the dense and rarefied places1 and that the bombardment was greater on the dense places of the striated discharge4 ,it is1 in fact1 often observed in bulbs1 that under certain conditions a thin wire is brought to higher incandescence when the air is not too highly rarefied4 ,this is the case when the potential of the coil is not high enough for the vacuum1 but the result may be attributed to many different causes4 ,in all cases this curious phenomenon of incandescence disappears when the tube1 or rather the wire1 acquires throughout a uniform temperature4 ,illustration3 ,,fig4 #ahg4 ,illustration3 ,,fig4 #ahh4 ,disregarding now the modifying effect of convection there are then two distinct causes which determine the incandescence of a wire or filament with varying currents1 that is1 conduction current and bombardment4 ,with steady currents we have to deal only with the former of these two causes1 and the heating effect is a minimum1 since the resistance is least to steady flow4 ,when the current is a varying one the resistance is greater1 and hence the heating effect is increased4 ,thus if the rate of change of the current is very great1 the resistance may increase to such an extent that the filament is brought to incandescence with inappreciable currents1 and we are able to take a short and thick block of carbon or other material and bring it to bright incandescence with a current incomparably smaller than that required to bring to the same degree of incandescence an ordinary thin lamp filament with a steady or low frequency current4 ,this result is important1 and illustrates how rapidly our views on these subjects are changing1 and how quickly our field of knowledge is extending4 ,in the art of incandescent lighting1 to view this result in one aspect only1 it has been commonly considered as an essential requirement for practical success1 that the lamp filament should be thin and of high resistance4 ,but now we know that the resistance of the filament to the steady flow does not mean anything2 the filament might as well be short and thick2 for if it be immersed in rarefied gas it will become incandescent by the passage of a small current4 ,it all depends on the frequency and potential of the currents4 ,we may conclude from this1 that it would be of advantage1 so far as the lamp is considered1 to employ high frequencies for lighting1 as they allow the use of short and thick filaments and smaller currents4 ,if a wire or filament be immersed in a homogeneous medium1 all the heating is due to true conduction current1 but if it be enclosed in an exhausted vessel the conditions are entirely different4 ,here the gas begins to act and the heating effect of the conduction current1 as is shown in many experiments1 may be very small compared with that of the bombardment4 ,this is especially the case if the circuit is not closed and the potentials are of course very high4 ,suppose that a fine filament enclosed in an exhausted vessel be connected with one of its ends to the terminal of a high tension coil and with its other end to a large insulated plate4 ,though the circuit is not closed1 the filament1 as ,i have before shown1 is brought to incandescence4 ,if the frequency and potential be comparatively low1 the filament is heated by the current passing through it4 ,if the frequency and potential1 and principally the latter1 be increased1 the insulated plate need be but very small1 or may be done away with entirely2 still the filament will become incandescent1 practically all the heating being then due to the bombardment4 ,a practical way of combining both the effects of conduction currents and bombardment is illustrated in ,fig4 #ahh1 in which an ordinary lamp is shown provided with a very thin filament which has one of the ends of the latter connected to a shade serving the purpose of the insulated plate1 and the other end to the terminal of a high tension source4 ,it should not be thought that only rarefied gas is an important factor in the heating of a conductor by varying currents1 but gas at ordinary pressure may become important1 if the potential difference and frequency of the currents is excessive4 ,on this subject ,i have already stated1 that when a conductor is fused by a stroke of lightning1 the current through it may be exceedingly small1 not even sufficient to heat the conductor perceptibly1 were the latter immersed in a homogeneous medium4 ,from the preceding it is clear that when a conductor of high resistance is connected to the terminals of a source of high frequency currents of high potential1 there may occur considerable dissipation of energy1 principally at the ends of the conductor1 in consequence of the action of the gas surrounding the conductor4 ,owing to this1 the current through a section of the conductor at a point midway between its ends may be much smaller than through a section near the ends4 ,furthermore1 the current passes principally through the outer portions of the conductor1 but this effect is to be distinguished from the skin effect as ordinarily interpreted1 for the latter would1 or should1 occur also in a continuous incompressible medium4 ,if a great many incandescent lamps are connected in series to a source of such currents1 the lamps at the ends may burn brightly1 whereas those in the middle may remain entirely dark4 ,this is due principally to bombardment1 as before stated4 ,but even if the currents be steady1 provided the difference of potential is very great1 the lamps at the end will burn more brightly than those in the middle4 ,in such case there is no rhythmical bombardment1 and the result is produced entirely by leakage4 ,this leakage or dissipation into space when the tension is high1 is considerable when incandescent lamps are used1 and still more considerable with arcs1 for the latter act like flames4 ,generally1 of course1 the dissipation is much smaller with steady1 than with varying1 currents4 ,i have contrived an experiment which illustrates in an interesting manner the effect of lateral diffusion4 ,if a very long tube is attached to the terminal of a high frequency coil1 the luminosity is greatest near the terminal and falls off gradually towards the remote end4 ,this is more marked if the tube is narrow4 ,a small tube about one-half inch in diameter and twelve inches long 7,fig4 #ahi71 has one of its ends drawn out into a fine fibre f nearly three feet long4 ,the tube is placed in a brass socket ,t which can be screwed on the terminal ,t#a of the induction coil4 ,the discharge passing through the tube first illuminates the bottom of the same1 which is of comparatively large section2 but through the long glass fibre the discharge cannot pass4 ,but gradually the rarefied gas inside becomes warmed and more conducting and the discharge spreads into the glass fibre4 ,this spreading is so slow1 that it may take half a minute or more until the discharge has worked through up to the top of the glass fibre1 then presenting the appearance of a strongly luminous thin thread4 ,by adjusting the potential at the terminal the light may be made to travel upwards at any speed4 ,once1 however1 the glass fibre is heated1 the discharge breaks through its entire length instantly4 ,the interesting point to be noted is that1 the higher the frequency of the currents1 or in other words1 the greater relatively the lateral dissipation1 at a slower rate may the light be made to propagate through the fibre4 ,this experiment is best performed with a highly exhausted and freshly made tube4 ,when the tube has been used for some time the experiment often fails4 ,it is possible that the gradual and slow impairment of the vacuum is the cause4 ,this slow propagation of the discharge through a very narrow glass tube corresponds exactly to the propagation of heat through a bar warmed at one end4 ,the quicker the heat is carried away laterally the longer time it will take for the heat to warm the remote end4 ,when the current of a low frequency coil is passed through the fibre from end to end1 then the lateral dissipation is small and the discharge instantly breaks through almost without exception4 ,illustration3 ,,fig4 #ahi4 ,illustration3 ,,fig4 #aij4 ,after these experiments and observations which have shown the importance of the discontinuity or atomic structure of the medium and which will serve to explain1 in a measure at least1 the nature of the four kinds of light effects producible with these currents1 ,i may now give you an illustration of these effects4 ,for the sake of interest ,i may do this in a manner which to many of you might be novel4 ,you have seen before that we may now convey the electric vibration to a body by means of a single wire or conductor of any kind4 ,since the human frame is conducting ,i may convey the vibration through my body4 ,first1 as in some previous experiments1 ,i connect my body with one of the terminals of a high-tension transformer and take in my hand an exhausted bulb which contains a small carbon button mounted upon a platinum wire leading to the outside of the bulb1 and the button is rendered incandescent as soon as the transformer is set to work 7,fig4 #aij74 ,i may place a conducting shade on the bulb which serves to intensify the action1 but is not necessary4 ,nor is it required that the button should be in conducting connection with the hand through a wire leading through the glass1 for sufficient energy may be transmitted through the glass itself by inductive action to render the button incandescent4 ,illustration3 ,,fig4 #aia4 ,illustration3 ,,fig4 #aib4 ,next ,i take a highly exhausted bulb containing a strongly phosphorescent body1 above which is mounted a small plate of aluminum on a platinum wire leading to the outside1 and the currents flowing through my body excite intense phosphorescence in the bulb 7,fig4 #aia74 ,next again ,i take in my hand a simple exhausted tube1 and in the same manner the gas inside the tube is rendered highly incandescent or phosphorescent 7,fig4 #aib74 ,finally1 ,i may take in my hand a wire1 bare or covered with thick insulation1 it is quite immaterial2 the electrical vibration is so intense as to cover the wire with a luminous film 7,fig4 #aic74 ,illustration3 ,,fig4 #aic4 ,illustration3 ,,fig4 #aid4 ,illustration3 ,,fig4 #aie4 ,a few words must now be devoted to each of these phenomena4 ,in the first place1 ,i will consider the incandescence of a button or of a solid in general1 and dwell upon some facts which apply equally to all these phenomena4 ,it was pointed out before that when a thin conductor1 such as a lamp filament1 for instance1 is connected with one of its ends to the terminal of a transformer of high tension the filament is brought to incandescence partly by a conduction current and partly by bombardment4 ,the shorter and thicker the filament the more important becomes the latter1 and finally1 reducing the filament to a mere button1 all the heating must practically be attributed to the bombardment4 ,so in the experiment before shown1 the button is rendered incandescent by the rhythmical impact of freely movable small bodies in the bulb4 ,these bodies may be the molecules of the residual gas1 particles of dust or lumps torn from the electrode2 whatever they are1 it is certain that the heating of the button is essentially connected with the pressure of such freely movable particles1 or of atomic matter in general in the bulb4 ,the heating is the more intense the greater the number of impacts per second and the greater the energy of each impact4 ,yet the button would be heated also if it were connected to a source of a steady potential4 ,in such a case electricity would be carried away from the button by the freely movable carriers or particles flying about1 and the quantity of electricity thus carried away might be sufficient to bring the button to incandescence by its passage through the latter4 ,but the bombardment could not be of great importance in such case4 ,for this reason it would require a comparatively very great supply of energy to the button to maintain it at incandescence with a steady potential4 ,the higher the frequency of the electric impulses the more economically can the button be maintained at incandescence4 ,one of the chief reasons why this is so1 is1 ,i believe1 that with impulses of very high frequency there is less exchange of the freely movable carriers around the electrode and this means1 that in the bulb the heated matter is better confined to the neighborhood of the button4 ,if a double bulb1 as illustrated in ,fig4 #aid be made1 comprising a large globe ,b and a small one b1 each containing as usual a filament f mounted on a platinum wire w and w#a1 it is found1 that if the filaments f f be exactly alike1 it requires less energy to keep the filament in the globe b at a certain degree of incandescence1 than that in the globe ,b4 ,this is due to the confinement of the movable particles around the button4 ,in this case it is also ascertained1 that the filament in the small globe b is less deteriorated when maintained a certain length of time at incandescence4 ,this is a necessary consequence of the fact that the gas in the small bulb becomes strongly heated and therefore a very good conductor1 and less work is then performed on the button1 since the bombardment becomes less intense as the conductivity of the gas increases4 ,in this construction1 of course1 the small bulb becomes very hot and when it reaches an elevated temperature the convection and radiation on the outside increase4 ,on another occasion ,i have shown bulbs in which this drawback was largely avoided4 ,in these instances a very small bulb1 containing a refractory button1 was mounted in a large globe and the space between the walls of both was highly exhausted4 ,the outer large globe remained comparatively cool in such constructions4 ,when the large globe was on the pump and the vacuum between the walls maintained permanent by the continuous action of the pump1 the outer globe would remain quite cold1 while the button in the small bulb was kept at incandescence4 ,but when the seal was made1 and the button in the small bulb maintained incandescent some length of time1 the large globe too would become warmed4 ,from this ,i conjecture that if vacuous space 7as ,prof4 ,dewar finds7 cannot convey heat1 it is so merely in virtue of our rapid motion through space or1 generally speaking1 by the motion of the medium relatively to us1 for a permanent condition could not be maintained without the medium being constantly renewed4 ,a vacuum cannot1 according to all evidence1 be permanently maintained around a hot body4 ,in these constructions1 before mentioned1 the small bulb inside would1 at least in the first stages1 prevent all bombardment against the outer large globe4 ,it occurred to me then to ascertain how a metal sieve would behave in this respect1 and several bulbs1 as illustrated in ,fig4 #aie1 were prepared for this purpose4 ,in a globe b1 was mounted a thin filament f 7or button7 upon a platinum wire w passing through a glass stem and leading to the outside of the globe4 ,the filament f was surrounded by a metal sieve s4 ,it was found in experiments with such bulbs that a sieve with wide meshes apparently did not in the slightest affect the bombardment against the globe b4 ,when the vacuum was high1 the shadow of the sieve was clearly projected against the globe and the latter would get hot in a short while4 ,in some bulbs the sieve s was connected to a platinum wire sealed in the glass4 ,when this wire was connected to the other terminal of the induction coil 7the ,e4 ,m4 ,f4 being kept low in this case71 or to an insulated plate1 the bombardment against the outer globe b was diminished4 ,by taking a sieve with fine meshes the bombardment against the globe b was always diminished1 but even then if the exhaustion was carried very far1 and when the potential of the transformer was very high1 the globe b would be bombarded and heated quickly1 though no shadow of the sieve was visible1 owing to the smallness of the meshes4 ,but a glass tube or other continuous body mounted so as to surround the filament1 did entirely cut off the bombardment and for a while the outer globe b would remain perfectly cold4 ,of course when the glass tube was sufficiently heated the bombardment against the outer globe could be noted at once4 ,the experiments with these bulbs seemed to show that the speeds of the projected molecules or particles must be considerable 7though quite insignificant when compared with that of light71 otherwise it would be difficult to understand how they could traverse a fine metal sieve without being affected1 unless it were found that such small particles or atoms cannot be acted upon directly at measurable distances4 ,in regard to the speed of the projected atoms1 ,lord ,kelvin has recently estimated it at about one kilometre a second or thereabouts in an ordinary ,crookes bulb4 ,as the potentials obtainable with a disruptive discharge coil are much higher than with ordinary coils1 the speeds must1 of course1 be much greater when the bulbs are lighted from such a coil4 ,assuming the speed to be as high as five kilometres and uniform through the whole trajectory1 as it should be in a very highly exhausted vessel1 then if the alternate electrifications of the electrode would be of a frequency of five million1 the greatest distance a particle could get away from the electrode would be one millimetre1 and if it could be acted upon directly at that distance1 the exchange of electrode matter or of the atoms would be very slow and there would be practically no bombardment against the bulb4 ,this at least should be so1 if the action of an electrode upon the atoms of the residual gas would be such as upon electrified bodies which we can perceive4 ,a hot body enclosed in an exhausted bulb produces always atomic bombardment1 but a hot body has no definite rhythm1 for its molecules perform vibrations of all kinds4 ,if a bulb containing a button or filament be exhausted as high as is possible with the greatest care and by the use of the best artifices1 it is often observed that the discharge cannot1 at first1 break through1 but after some time1 probably in consequence of some changes within the bulb1 the discharge finally passes through and the button is rendered incandescent4 ,in fact1 it appears that the higher the degree of exhaustion the easier is the incandescence produced4 ,there seem to be no other causes to which the incandescence might be attributed in such case except to the bombardment or similar action of the residual gas1 or of particles of matter in general4 ,but if the bulb be exhausted with the greatest care can these play an important part8 ,assume the vacuum in the bulb to be tolerably perfect1 the great interest then centres in the question3 ,is the medium which pervades all space continuous or atomic8 ,if atomic1 then the heating of a conducting button or filament in an exhausted vessel might be due largely to ether bombardment1 and then the heating of a conductor in general through which currents of high frequency or high potential are passed must be modified by the behavior of such medium2 then also the skin effect1 the apparent increase of the ohmic resistance1 etc41 admit1 partially at least1 of a different explanation4 ,it is certainly more in accordance with many phenomena observed with high-frequency currents to hold that all space is pervaded with free atoms1 rather than to assume that it is devoid of these1 and dark and cold1 for so it must be1 if filled with a continuous medium1 since in such there can be neither heat nor light4 ,is then energy transmitted by independent carriers or by the vibration of a continuous medium8 ,this important question is by no means as yet positively answered4 ,but most of the effects which are here considered1 especially the light effects1 incandescence1 or phosphorescence1 involve the presence of free atoms and would be impossible without these4 ,in regard to the incandescence of a refractory button 7or filament7 in an exhausted receiver1 which has been one of the subjects of this investigation1 the chief experiences1 which may serve as a guide in constructing such bulbs1 may be summed up as follows3 #a4 ,the button should be as small as possible1 spherical1 of a smooth or polished surface1 and of refractory material which withstands evaporation best4 #b4 ,the support of the button should be very thin and screened by an aluminum and mica sheet1 as ,i have described on another occasion4 #c4 ,the exhaustion of the bulb should be as high as possible4 #d4 ,the frequency of the currents should be as high as practicable4 #e4 ,the currents should be of a harmonic rise and fall1 without sudden interruptions4 #f4 ,the heat should be confined to the button by inclosing the same in a small bulb or otherwise4 #g4 ,the space between the walls of the small bulb and the outer globe should be highly exhausted4 ,most of the considerations which apply to the incandescence of a solid just considered may likewise be applied to phosphorescence4 ,indeed1 in an exhausted vessel the phosphorescence is1 as a rule1 primarily excited by the powerful beating of the electrode stream of atoms against the phosphorescent body4 ,even in many cases1 where there is no evidence of such a bombardment1 ,i think that phosphorescence is excited by violent impacts of atoms1 which are not necessarily thrown off from the electrode but are acted upon from the same inductively through the medium or through chains of other atoms4 ,that mechanical shocks play an important part in exciting phosphorescence in a bulb may be seen from the following experiment4 ,if a bulb1 constructed as that illustrated in ,fig4 #agd1 be taken and exhausted with the greatest care so that the discharge cannot pass1 the filament f acts by electrostatic induction upon the tube t and the latter is set in vibration4 ,if the tube o be rather wide1 about an inch or so1 the filament may be so powerfully vibrated that whenever it hits the glass tube it excites phosphorescence4 ,but the phosphorescence ceases when the filament comes to rest4 ,the vibration can be arrested and again started by varying the frequency of the currents4 ,now the filament has its own period of vibration1 and if the frequency of the currents is such that there is resonance1 it is easily set vibrating1 though the potential of the currents be small4 ,i have often observed that the filament in the bulb is destroyed by such mechanical resonance4 ,the filament vibrates as a rule so rapidly that it cannot be seen and the experimenter may at first be mystified4 ,when such an experiment as the one described is carefully performed1 the potential of the currents need be extremely small1 and for this reason ,i infer that the phosphorescence is then due to the mechanical shock of the filament against the glass1 just as it is produced by striking a loaf of sugar with a knife4 ,the mechanical shock produced by the projected atoms is easily noted when a bulb containing a button is grasped in the hand and the current turned on suddenly4 ,i believe that a bulb could be shattered by observing the conditions of resonance4 ,in the experiment before cited it is1 of course1 open to say1 that the glass tube1 upon coming in contact with the filament1 retains a charge of a certain sign upon the point of contact4 ,if now the filament again touches the glass at the same point while it is oppositely charged1 the charges equalize under evolution of light4 ,but nothing of importance would be gained by such an explanation4 ,it is unquestionable that the initial charges given to the atoms or to the glass play some part in exciting phosphorescence4 ,so1 for instance1 if a phosphorescent bulb be first excited by a high frequency coil by connecting it to one of the terminals of the latter and the degree of luminosity be noted1 and then the bulb be highly charged from a ,holtz machine by attaching it preferably to the positive terminal of the machine1 it is found that when the bulb is again connected to the terminal of the high frequency coil1 the phosphorescence is far more intense4 ,on another occasion ,i have considered the possibility of some phosphorescent phenomena in bulbs being produced by the incandescence of an infinitesimal layer on the surface of the phosphorescent body4 ,certainly the impact of the atoms is powerful enough to produce intense incandescence by the collisions1 since they bring quickly to a high temperature a body of considerable bulk4 ,if any such effect exists1 then the best appliance for producing phosphorescence in a bulb1 which we know so far1 is a disruptive discharge coil giving an enormous potential with but few fundamental discharges1 say #be-cj per second1 just enough to produce a continuous impression upon the eye4 ,it is a fact that such a coil excites phosphorescence under almost any condition and at all degrees of exhaustion1 and ,i have observed effects which appear to be due to phosphorescence even at ordinary pressures of the atmosphere1 when the potentials are extremely high4 ,but if phosphorescent light is produced by the equalization of charges of electrified atoms 7whatever this may mean ultimately71 then the higher the frequency of the impulses or alternate electrifications1 the more economical will be the light production4 ,it is a long known and noteworthy fact that all the phosphorescent bodies are poor conductors of electricity and heat1 and that all bodies cease to emit phosphorescent light when they are brought to a certain temperature4 ,conductors on the contrary do not possess this quality4 ,there are but few exceptions to the rule4 ,carbon is one of them4 ,becquerel noted that carbon phosphoresces at a certain elevated temperature preceding the dark red4 ,this phenomenon may be easily observed in bulbs provided with a rather large carbon electrode 7say1 a sphere of six millimetres diameter74 ,if the current is turned on after a few seconds1 a snow white film covers the electrode1 just before it gets dark red4 ,similar effects are noted with other conducting bodies1 but many scientific men will probably not attribute them to true phosphorescence4 ,whether true incandescence has anything to do with phosphorescence excited by atomic impact or mechanical shocks still remains to be decided1 but it is a fact that all conditions1 which tend to localize and increase the heating effect at the point of impact1 are almost invariably the most favorable for the production of phosphorescence4 ,so1 if the electrode be very small1 which is equivalent to saying in general1 that the electric density is great2 if the potential be high1 and if the gas be highly rarefied1 all of which things imply high speed of the projected atoms1 or matter1 and consequently violent impacts--the phosphorescence is very intense4 ,if a bulb provided with a large and small electrode be attached to the terminal of an induction coil1 the small electrode excites phosphorescence while the large one may not do so1 because of the smaller electric density and hence smaller speed of the atoms4 ,a bulb provided with a large electrode may be grasped with the hand while the electrode is connected to the terminal of the coil and it may not phosphoresce2 but if instead of grasping the bulb with the hand1 the same be touched with a pointed wire1 the phosphorescence at once spreads through the bulb1 because of the great density at the point of contact4 ,with low frequencies it seems that gases of great atomic weight excite more intense phosphorescence than those of smaller weight1 as for instance1 hydrogen4 ,with high frequencies the observations are not sufficiently reliable to draw a conclusion4 ,oxygen1 as is well-known1 produces exceptionally strong effects1 which may be in part due to chemical action4 ,a bulb with hydrogen residue seems to be most easily excited4 ,electrodes which are most easily deteriorated produce more intense phosphorescence in bulbs1 but the condition is not permanent because of the impairment of the vacuum and the deposition of the electrode matter upon the phosphorescent surfaces4 ,some liquids1 as oils1 for instance1 produce magnificent effects of phosphorescence 7or fluorescence871 but they last only a few seconds4 ,so if a bulb has a trace of oil on the walls and the current is turned on1 the phosphorescence only persists for a few moments until the oil is carried away4 ,of all bodies so far tried1 sulphide of zinc seems to be the most susceptible to phosphorescence4 ,some samples1 obtained through the kindness of ,prof4 ,henry in ,paris1 were employed in many of these bulbs4 ,one of the defects of this sulphide is1 that it loses its quality of emitting light when brought to a temperature which is by no means high4 ,it can therefore1 be used only for feeble intensities4 ,an observation which might deserve notice is1 that when violently bombarded from an aluminum electrode it assumes a black color1 but singularly enough1 it returns to the original condition when it cools down4 ,the most important fact arrived at in pursuing investigations in this direction is1 that in all cases it is necessary1 in order to excite phosphorescence with a minimum amount of energy1 to observe certain conditions4 ,namely1 there is always1 no matter what the frequency of the currents1 degree of exhaustion and character of the bodies in the bulb1 a certain potential 7assuming the bulb excited from one terminal7 or potential difference 7assuming the bulb to be excited with both terminals7 which produces the most economical result4 ,if the potential be increased1 considerable energy may be wasted without producing any more light1 and if it be diminished1 then again the light production is not as economical4 ,the exact condition under which the best result is obtained seems to depend on many things of a different nature1 and it is to be yet investigated by other experimenters1 but it will certainly have to be observed when such phosphorescent bulbs are operated1 if the best results are to be obtained4 ,coming now to the most interesting of these phenomena1 the incandescence or phosphorescence of gases1 at low pressures or at the ordinary pressure of the atmosphere1 we must seek the explanation of these phenomena in the same primary causes1 that is1 in shocks or impacts of the atoms4 ,just as molecules or atoms beating upon a solid body excite phosphorescence in the same or render it incandescent1 so when colliding among themselves they produce similar phenomena4 ,but this is a very insufficient explanation and concerns only the crude mechanism4 ,light is produced by vibrations which go on at a rate almost inconceivable4 ,if we compute1 from the energy contained in the form of known radiations in a definite space the force which is necessary to set up such rapid vibrations1 we find1 that though the density of the ether be incomparably smaller than that of any body we know1 even hydrogen1 the force is something surpassing comprehension4 ,what is this force1 which in mechanical measure may amount to thousands of tons per square inch8 ,it is electrostatic force in the light of modern views4 ,it is impossible to conceive how a body of measurable dimensions could be charged to so high a potential that the force would be sufficient to produce these vibrations4 ,long before any such charge could be imparted to the body it would be shattered into atoms4 ,the sun emits light and heat1 and so does an ordinary flame or incandescent filament1 but in neither of these can the force be accounted for if it be assumed that it is associated with the body as a whole4 ,only in one way may we account for it1 namely1 by identifying it with the atom4 ,an atom is so small1 that if it be charged by coming in contact with an electrified body and the charge be assumed to follow the same law as in the case of bodies of measurable dimensions1 it must retain a quantity of electricity which is fully capable of accounting for these forces and tremendous rates of vibration4 ,but the atom behaves singularly in this respect--it always takes the same charge4 ,it is very likely that resonant vibration plays a most important part in all manifestations of energy in nature4 ,throughout space all matter is vibrating1 and all rates of vibration are represented1 from the lowest musical note to the highest pitch of the chemical rays1 hence an atom1 or complex of atoms1 no matter what its period1 must find a vibration with which it is in resonance4 ,when we consider the enormous rapidity of the light vibrations1 we realize the impossibility of producing such vibrations directly with any apparatus of measurable dimensions1 and we are driven to the only possible means of attaining the object of setting up waves of light by electrical means and economically1 that is1 to affect the molecules or atoms of a gas1 to cause them to collide and vibrate4 ,we then must ask ourselves--,how can free molecules or atoms be affected8 ,illustration3 ,,fig4 #aif4 ,illustration3 ,,fig4 #aig4 ,it is a fact that they can be affected by electrostatic force1 as is apparent in many of these experiments4 ,by varying the electrostatic force we can agitate the atoms1 and cause them to collide accompanied by evolution of heat and light4 ,it is not demonstrated beyond doubt that we can affect them otherwise4 ,if a luminous discharge is produced in a closed exhausted tube1 do the atoms arrange themselves in obedience to any other but to electrostatic force acting in straight lines from atom to atom8 ,only recently ,i investigated the mutual action between two circuits with extreme rates of vibration4 ,when a battery of a few jars 7c c c c1 ,fig4 #aif7 is discharged through a primary ,p of low resistance 7the connections being as illustrated in ,figs4 #ahc;a1 #ahc;b and #ahc;c71 and the frequency of vibration is many millions there are great differences of potential between points on the primary not more than a few inches apart4 ,these differences may be #aj1jjj volts per inch1 if not more1 taking the maximum value of the ,e4 ,m4 ,f4 ,the secondary s is therefore acted upon by electrostatic induction1 which is in such extreme cases of much greater importance than the electro-dynamic4 ,to such sudden impulses the primary as well as the secondary are poor conductors1 and therefore great differences of potential may be produced by electrostatic induction between adjacent points on the secondary4 ,then sparks may jump between the wires and streamers become visible in the dark if the light of the discharge through the spark gap d d be carefully excluded4 ,if now we substitute a closed vacuum tube for the metallic secondary s1 the differences of potential produced in the tube by electrostatic induction from the primary are fully sufficient to excite portions of it2 but as the points of certain differences of potential on the primary are not fixed1 but are generally constantly changing in position1 a luminous band is produced in the tube1 apparently not touching the glass1 as it should1 if the points of maximum and minimum differences of potential were fixed on the primary4 ,i do not exclude the possibility of such a tube being excited only by electro-dynamic induction1 for very able physicists hold this view2 but in my opinion1 there is as yet no positive proof given that atoms of a gas in a closed tube may arrange themselves in chains under the action of an electromotive impulse produced by electro-dynamic induction in the tube4 ,i have been unable so far to produce striae in a tube1 however long1 and at whatever degree of exhaustion1 that is1 striae at right angles to the supposed direction of the discharge or the axis of the tube2 but ,i have distinctly observed in a large bulb1 in which a wide luminous band was produced by passing a discharge of a battery through a wire surrounding the bulb1 a circle of feeble luminosity between two luminous bands1 one of which was more intense than the other4 ,furthermore1 with my present experience ,i do not think that such a gas discharge in a closed tube can vibrate1 that is1 vibrate as a whole4 ,i am convinced that no discharge through a gas can vibrate4 ,the atoms of a gas behave very curiously in respect to sudden electric impulses4 ,the gas does not seem to possess any appreciable inertia to such impulses1 for it is a fact1 that the higher the frequency of the impulses1 with the greater freedom does the discharge pass through the gas4 ,if the gas possesses no inertia then it cannot vibrate1 for some inertia is necessary for the free vibration4 ,i conclude from this that if a lightning discharge occurs between two clouds1 there can be no oscillation1 such as would be expected1 considering the capacity of the clouds4 ,but if the lightning discharge strike the earth1 there is always vibration--in the earth1 but not in the cloud4 ,in a gas discharge each atom vibrates at its own rate1 but there is no vibration of the conducting gaseous mass as a whole4 ,this is an important consideration in the great problem of producing light economically1 for it teaches us that to reach this result we must use impulses of very high frequency and necessarily also of high potential4 ,it is a fact that oxygen produces a more intense light in a tube4 ,is it because oxygen atoms possess some inertia and the vibration does not die out instantly8 ,but then nitrogen should be as good1 and chlorine and vapors of many other bodies much better than oxygen1 unless the magnetic properties of the latter enter prominently into play4 ,or1 is the process in the tube of an electrolytic nature8 ,many observations certainly speak for it1 the most important being that matter is always carried away from the electrodes and the vacuum in a bulb cannot be permanently maintained4 ,if such process takes place in reality1 then again must we take refuge in high frequencies1 for1 with such1 electrolytic action should be reduced to a minimum1 if not rendered entirely impossible4 ,it is an undeniable fact that with very high frequencies1 provided the impulses be of harmonic nature1 like those obtained from an alternator1 there is less deterioration and the vacua are more permanent4 ,with disruptive discharge coils there are sudden rises of potential and the vacua are more quickly impaired1 for the electrodes are deteriorated in a very short time4 ,it was observed in some large tubes1 which were provided with heavy carbon blocks ,b ,b#a1 connected to platinum wires w w#a 7as illustrated in ,fig4 #aig71 and which were employed in experiments with the disruptive discharge instead of the ordinary air gap1 that the carbon particles under the action of the powerful magnetic field in which the tube was placed1 were deposited in regular fine lines in the middle of the tube1 as illustrated4 ,these lines were attributed to the deflection or distortion of the discharge by the magnetic field1 but why the deposit occurred principally where the field was most intense did not appear quite clear4 ,a fact of interest1 likewise noted1 was that the presence of a strong magnetic field increases the deterioration of the electrodes1 probably by reason of the rapid interruptions it produces1 whereby there is actually a higher ,e4 ,m4 ,f4 maintained between the electrodes4 ,much would remain to be said about the luminous effects produced in gases at low or ordinary pressures4 ,with the present experiences before us we cannot say that the essential nature of these charming phenomena is sufficiently known4 ,but investigations in this direction are being pushed with exceptional ardor4 ,every line of scientific pursuit has its fascinations1 but electrical investigation appears to possess a peculiar attraction1 for there is no experiment or observation of any kind in the domain of this wonderful science which would not forcibly appeal to us4 ,yet to me it seems1 that of all the many marvelous things we observe1 a vacuum tube1 excited by an electric impulse from a distant source1 bursting forth out of the darkness and illuminating the room with its beautiful light1 is as lovely a phenomenon as can greet our eyes4 ,more interesting still it appears when1 reducing the fundamental discharges across the gap to a very small number and waving the tube about we produce all kinds of designs in luminous lines4 ,so by way of amusement ,i take a straight long tube1 or a square one1 or a square attached to a straight tube1 and by whirling them about in the hand1 ,i imitate the spokes of a wheel1 a ,gramme winding1 a drum winding1 an alternate current motor winding1 etc4 7,fig4 #aih74 ,viewed from a distance the effect is weak and much of its beauty is lost1 but being near or holding the tube in the hand1 one cannot resist its charm4 ,illustration3 ,,fig4 #aih4 ,in presenting these insignificant results ,i have not attempted to arrange and co-ordinate them1 as would be proper in a strictly scientific investigation1 in which every succeeding result should be a logical sequence of the preceding1 so that it might be guessed in advance by the careful reader or attentive listener4 ,i have preferred to concentrate my energies chiefly upon advancing novel facts or ideas which might serve as suggestions to others1 and this may serve as an excuse for the lack of harmony4 ,the explanations of the phenomena have been given in good faith and in the spirit of a student prepared to find that they admit of a better interpretation4 ,there can be no great harm in a student taking an erroneous view1 but when great minds err1 the world must dearly pay for their mistakes4 ,,chapter ,,xxix4 ,,tesla ,,alternating ,,current ,,generators ,,for ,,high ,,frequency1 ,,in ,,detail4 ,it has become a common practice to operate arc lamps by alternating or pulsating1 as distinguished from continuous1 currents2 but an objection which has been raised to such systems exists in the fact that the arcs emit a pronounced sound1 varying with the rate of the alternations or pulsations of current4 ,this noise is due to the rapidly alternating heating and cooling1 and consequent expansion and contraction1 of the gaseous matter forming the arc1 which corresponds with the periods or impulses of the current4 ,another disadvantageous feature is found in the difficulty of maintaining an alternating current arc in consequence of the periodical increase in resistance corresponding to the periodical working of the current4 ,this feature entails a further disadvantage1 namely1 that small arcs are impracticable4 ,theoretical considerations have led ,mr4 ,tesla to the belief that these disadvantageous features could be obviated by employing currents of a sufficiently high number of alternations1 and his anticipations have been confirmed in practice4 ,these rapidly alternating currents render it possible to maintain small arcs which1 besides1 possess the advantages of silence and persistency4 ,the latter quality is due to the necessarily rapid alternations1 in consequence of which the arc has no time to cool1 and is always maintained at a high temperature and low resistance4 ,at the outset of his experiments ,mr4 ,tesla encountered great difficulties in the construction of high frequency machines4 ,a generator of this kind is described here1 which1 though constructed quite some time ago1 is well worthy of a detailed description4 ,it may be mentioned1 in passing1 that dynamos of this type have been used by ,mr4 ,tesla in his lighting researches and experiments with currents of high potential and high frequency1 and reference to them will be found in his lectures elsewhere printed in this volume4#d #d ,see pages #aec-d #e4 ,in the accompanying engravings1 ,figs4 #aii and #bjj show the machine1 respectively1 in side elevation and vertical cross-section2 ,figs4 #bja1 #bjb and #bjc showing enlarged details of construction4 ,as will be seen1 ,a is an annular magnetic frame1 the interior of which is provided with a large number of pole-pieces ,d4 ,owing to the very large number and small size of the poles and the spaces between them1 the field coils are applied by winding an insulated conductor ,f zigzag through the grooves1 as shown in ,fig4 #bjc1 carrying the wire around the annulus to form as many layers as is desired4 ,in this way the pole-pieces ,d will be energized with alternately opposite polarity around the entire ring4 ,for the armature1 ,mr4 ,tesla employs a spider carrying a ring ,j1 turned down1 except at its edges1 to form a trough-like receptacle for a mass of fine annealed iron wires ,k1 which are wound in the groove to form the core proper for the armature-coils4 ,pins ,l are set in the sides of the ring ,j and the coils ,m are wound over the periphery of the armature-structure and around the pins4 ,the coils ,m are connected together in series1 and these terminals ,n carried through the hollow shaft ,h to contact-rings ,p ,p1 from which the currents are taken off by brushes ,o4 ,illustration3 ,,fig4 #aii4 ,in this way a machine with a very large number of poles may be constructed4 ,it is easy1 for instance1 to obtain in this manner three hundred and seventy-five to four hundred poles in a machine that may be safely driven at a speed of fifteen hundred or sixteen hundred revolutions per minute1 which will produce ten thousand or eleven thousand alternations of current per second4 ,arc lamps ,r ,r are shown in the diagram as connected up in series with the machine in ,fig4 #bjj4 ,if such a current be applied to running arc lamps1 the sound produced by or in the arc becomes practically inaudible1 for1 by increasing the rate of change in the current1 and consequently the number of vibrations per unit of time of the gaseous material of the arc up to1 or beyond1 ten thousand or eleven thousand per second1 or to what is regarded as the limit of audition1 the sound due to such vibrations will not be audible4 ,the exact number of changes or undulations necessary to produce this result will vary somewhat according to the size of the arc--that is to say1 the smaller the arc1 the greater the number of changes that will be required to render it inaudible within certain limits4 ,it should also be stated that the arc should not exceed a certain length4 ,illustration3 ,,figs4 #bjj1 #bja1 #bjb and #bjc4 ,the difficulties encountered in the construction of these machines are of a mechanical as well as an electrical nature4 ,the machines may be designed on two plans3 the field may be formed either of alternating poles1 or of polar projections of the same polarity4 ,up to about #ae1jjj alternations per second in an experimental machine1 the former plan may be followed1 but a more efficient machine is obtained on the second plan4 ,in the machine above described1 which was capable of running two arcs of normal candle power1 the field was composed of a ring of wrought iron #cb inches outside diameter1 and about #a inch thick4 ,the inside diameter was #cj inches4 ,there were #chd polar projections4 ,the wire was wound in zigzag form1 but two wires were wound so as to completely envelop the projections4 ,the distance between the projections is about #c_/af inch1 and they are a little over #a_/af inch thick4 ,the field magnet was made relatively small so as to adapt the machine for a constant current4 ,there are #chd coils connected in two series4 ,it was found impracticable to use any wire much thicker than ,no4 #bf ,b4 and ,s4 gauge on account of the local effects4 ,in such a machine the clearance should be as small as possible2 for this reason the machine was made only #a-a_/d inch wide1 so that the binding wires might be obviated4 ,the armature wires must be wound with great care1 as they are apt to fly off in consequence of the great peripheral speed4 ,in various experiments this machine has been run as high as #c1jjj revolutions per minute4 ,owing to the great speed it was possible to obtain as high as #aj amperes out of the machine4 ,the electromotive force was regulated by means of an adjustable condenser within very wide limits1 the limits being the greater1 the greater the speed4 ,this machine was frequently used to run ,mr4 ,tesla's laboratory lights4 ,illustration3 ,,fig4 #bjd4 ,the machine above described was only one of many such types constructed4 ,it serves well for an experimental machine1 but if still higher alternations are required and higher efficiency is necessary1 then a machine on a plan shown in ,figs4 #bjd to #bjg1 is preferable4 ,the principal advantage of this type of machine is that there is not much magnetic leakage1 and that a field may be produced1 varying greatly in intensity in places not much distant from each other4 ,in these engravings1 ,figs4 #bjd and #bje illustrate a machine in which the armature conductor and field coils are stationary1 while the field magnet core revolves4 ,fig4 #bjf shows a machine embodying the same plan of construction1 but having a stationary field magnet and rotary armature4 ,the conductor in which the currents are induced may be arranged in various ways2 but ,mr4 ,tesla prefers the following method3 ,he employs an annular plate of copper ,d1 and by means of a saw cuts in it radial slots from one edge nearly through to the other1 beginning alternately from opposite edges4 ,in this way a continuous zigzag conductor is formed4 ,when the polar projections are #a_/h inch wide1 the width of the conductor should not1 under any circumstances1 be more than #a_/cb inch wide2 even then the eddy effect is considerable4 ,illustration3 ,,fig4 #bje4 ,to the inner edge of this plate are secured two rings of non-magnetic metal ,e1 which are insulated from the copper conductor1 but held firmly thereto by means of the bolts ,f4 ,within the rings ,e is then placed an annular coil ,g1 which is the energizing coil for the field magnet4 ,the conductor ,d and the parts attached thereto are supported by means of the cylindrical shell or casting ,a ,a1 the two parts of which are brought together and clamped to the outer edge of the conductor ,d4 ,illustration3 ,,fig4 #bjf4 ,the core for the field magnet is built up of two circular parts ,h ,h1 formed with annular grooves ,i1 which1 when the two parts are brought together1 form a space for the reception of the energizing coil ,g4 ,the hubs of the cores are trued off1 so as to fit closely against one another1 while the outer portions or flanges which form the polar faces ,j ,j1 are reduced somewhat in thickness to make room for the conductor ,d1 and are serrated on their faces4 ,the number of serrations in the polar faces is arbitrary2 but there must exist between them and the radial portions of the conductor ,d certain relation1 which will be understood by reference to ,fig4 #bjg in which ,n ,n represent the projections or points on one face of the core of the field1 and ,s ,s the points of the other face4 ,the conductor ,d is shown in this figure in section a a' designating the radial portions of the conductor1 and b the insulating divisions between them4 ,the relative width of the parts a a' and the space between any two adjacent points ,n ,n or ,s ,s is such that when the radial portions a of the conductor are passing between the opposite points ,n ,s where the field is strongest1 the intermediate radial portions a' are passing through the widest spaces midway between such points and where the field is weakest4 ,since the core on one side is of opposite polarity to the part facing it1 all the projections of one polar face will be of opposite polarity to those of the other face4 ,hence1 although the space between any two adjacent points on the same face may be extremely small1 there will be no leakage of the magnetic lines between any two points of the same name1 but the lines of force will pass across from one set of points to the other4 ,the construction followed obviates to a great degree the distortion of the magnetic lines by the action of the current in the conductor ,d1 in which it will be observed the current is flowing at any given time from the centre toward the periphery in one set of radial parts a and in the opposite direction in the adjacent parts a'4 ,in order to connect the energizing coil ,g1 ,fig4 #bjd1 with a source of continuous current1 ,mr4 ,tesla utilizes two adjacent radial portions of the conductor ,d for connecting the terminals of the coil ,g with two binding posts ,m4 ,for this purpose the plate ,d is cut entirely through1 as shown1 and the break thus made is bridged over by a short conductor ,c4 ,the plate ,d is cut through to form two terminals d1 which are connected to binding posts ,n4 ,the core ,h ,h1 when rotated by the driving pulley1 generates in the conductors ,d an alternating current1 which is taken off from the binding posts ,n4 ,illustration3 ,,fig4 #bjg4 ,when it is desired to rotate the conductor between the faces of a stationary field magnet1 the construction shown in ,fig4 #bjf1 is adopted4 ,the conductor ,d in this case is or may be made in substantially the same manner as above described by slotting an annular conducting-plate and supporting it between two heads ,o1 held together by bolts o and fixed to the driving-shaft ,k4 ,the inner edge of the plate or conductor ,d is preferably flanged to secure a firmer union between it and the heads ,o4 ,it is insulated from the head4 ,the field-magnet in this case consists of two annular parts ,h ,h1 provided with annular grooves ,i for the reception of the coils4 ,the flanges or faces surrounding the annular groove are brought together1 while the inner flanges are serrated1 as in the previous case1 and form the polar faces4 ,the two parts ,h ,h are formed with a base ,r1 upon which the machine rests4 ,s ,s are non-magnetic bushings secured or set in the central opening of the cores4 ,the conductor ,d is cut entirely through at one point to form terminals1 from which insulated conductors ,t are led through the shaft to collecting-rings ,v4 ,in one type of machine of this kind constructed by ,mr4 ,tesla1 the field had #dhj polar projections on each side1 and from this machine it was possible to obtain #cj1jjj alternations per second4 ,as the polar projections must necessarily be very narrow1 very thin wires or sheets must be used to avoid the eddy current effects4 ,mr4 ,tesla has thus constructed machines with a stationary armature and rotating field1 in which case also the field-coil was supported so that the revolving part consisted only of a wrought iron body devoid of any wire and also machines with a rotating armature and stationary field4 ,the machines may be either drum or disc1 but ,mr4 ,tesla's experience shows the latter to be preferable4 99 99 99 99 99 ,in the course of a very interesting article contributed to the ,electrical ,world in ,february1 #ahia1 ,mr4 ,tesla makes some suggestive remarks on these high frequency machines and his experiences with them1 as well as with other parts of the high frequency apparatus4 ,part of it is quoted here and is as follows3-- ,the writer will incidentally mention that any one who attempts for the first time to construct such a machine will have a tale of woe to tell4 ,he will first start out1 as a matter of course1 by making an armature with the required number of polar projections4 ,he will then get the satisfaction of having produced an apparatus which is fit to accompany a thoroughly ,wagnerian opera4 ,it may besides possess the virtue of converting mechanical energy into heat in a nearly perfect manner4 ,if there is a reversal in the polarity of the projections1 he will get heat out of the machine2 if there is no reversal1 the heating will be less1 but the output will be next to nothing4 ,he will then abandon the iron in the armature1 and he will get from the ,scylla to the ,charybdis4 ,he will look for one difficulty and will find another1 but1 after a few trials1 he may get nearly what he wanted4 ,among the many experiments which may be performed with such a machine1 of not the least interest are those performed with a high-tension induction coil4 ,the character of the discharge is completely changed4 ,the arc is established at much greater distances1 and it is so easily affected by the slightest current of air that it often wriggles around in the most singular manner4 ,it usually emits the rhythmical sound peculiar to the alternate current arcs1 but the curious point is that the sound may be heard with a number of alternations far above ten thousand per second1 which by many is considered to be about the limit of audition4 ,in many respects the coil behaves like a static machine4 ,points impair considerably the sparking interval1 electricity escaping from them freely1 and from a wire attached to one of the terminals streams of light issue1 as though it were connected to a pole of a powerful ,toepler machine4 ,all these phenomena are1 of course1 mostly due to the enormous differences of potential obtained4 ,as a consequence of the self-induction of the coil and the high frequency1 the current is minute while there is a corresponding rise of pressure4 ,a current impulse of some strength started in such a coil should persist to flow no less than four ten-thousandths of a second4 ,as this time is greater than half the period1 it occurs that an opposing electromotive force begins to act while the current is still flowing4 ,as a consequence1 the pressure rises as in a tube filled with liquid and vibrated rapidly around its axis4 ,the current is so small that1 in the opinion and involuntary experience of the writer1 the discharge of even a very large coil cannot produce seriously injurious effects1 whereas1 if the same coil were operated with a current of lower frequency1 though the electromotive force would be much smaller1 the discharge would be most certainly injurious4 ,this result1 however1 is due in part to the high frequency4 ,the writer's experiences tend to show that the higher the frequency the greater the amount of electrical energy which may be passed through the body without serious discomfort2 whence it seems certain that human tissues act as condensers4 ,one is not quite prepared for the behavior of the coil when connected to a ,leyden jar4 ,one1 of course1 anticipates that since the frequency is high the capacity of the jar should be small4 ,he therefore takes a very small jar1 about the size of a small wine glass1 but he finds that even with this jar the coil is practically short-circuited4 ,he then reduces the capacity until he comes to about the capacity of two spheres1 say1 ten centimetres in diameter and two to four centimetres apart4 ,the discharge then assumes the form of a serrated band exactly like a succession of sparks viewed in a rapidly revolving mirror2 the serrations1 of course1 corresponding to the condenser discharges4 ,in this case one may observe a queer phenomenon4 ,the discharge starts at the nearest points1 works gradually up1 breaks somewhere near the top of the spheres1 begins again at the bottom1 and so on4 ,this goes on so fast that several serrated bands are seen at once4 ,one may be puzzled for a few minutes1 but the explanation is simple enough4 ,the discharge begins at the nearest points1 the air is heated and carries the arc upward until it breaks1 when it is re-established at the nearest points1 etc4 ,since the current passes easily through a condenser of even small capacity1 it will be found quite natural that connecting only one terminal to a body of the same size1 no matter how well insulated1 impairs considerably the striking distance of the arc4 ,experiments with ,geissler tubes are of special interest4 ,an exhausted tube1 devoid of electrodes of any kind1 will light up at some distance from the coil4 ,if a tube from a vacuum pump is near the coil the whole of the pump is brilliantly lighted4 ,an incandescent lamp approached to the coil lights up and gets perceptibly hot4 ,if a lamp have the terminals connected to one of the binding posts of the coil and the hand is approached to the bulb1 a very curious and rather unpleasant discharge from the glass to the hand takes place1 and the filament may become incandescent4 ,the discharge resembles to some extent the stream issuing from the plates of a powerful ,toepler machine1 but is of incomparably greater quantity4 ,the lamp in this case acts as a condenser1 the rarefied gas being one coating1 the operator's hand the other4 ,by taking the globe of a lamp in the hand1 and by bringing the metallic terminals near to or in contact with a conductor connected to the coil1 the carbon is brought to bright incandescence and the glass is rapidly heated4 ,with a #ajj-volt #aj ,c4 ,p4 lamp one may without great discomfort stand as much current as will bring the lamp to a considerable brilliancy2 but it can be held in the hand only for a few minutes1 as the glass is heated in an incredibly short time4 ,when a tube is lighted by bringing it near to the coil it may be made to go out by interposing a metal plate on the hand between the coil and tube2 but if the metal plate be fastened to a glass rod or otherwise insulated1 the tube may remain lighted if the plate be interposed1 or may even increase in luminosity4 ,the effect depends on the position of the plate and tube relatively to the coil1 and may be always easily foretold by assuming that conduction takes place from one terminal of the coil to the other4 ,according to the position of the plate1 it may either divert from or direct the current to the tube4 ,in another line of work the writer has in frequent experiments maintained incandescent lamps of #ej or #ajj volts burning at any desired candle power with both the terminals of each lamp connected to a stout copper wire of no more than a few feet in length4 ,these experiments seem interesting enough1 but they are not more so than the queer experiment of ,faraday1 which has been revived and made much of by recent investigators1 and in which a discharge is made to jump between two points of a bent copper wire4 ,an experiment may be cited here which may seem equally interesting4 ,if a ,geissler tube1 the terminals of which are joined by a copper wire1 be approached to the coil1 certainly no one would be prepared to see the tube light up4 ,curiously enough1 it does light up1 and1 what is more1 the wire does not seem to make much difference4 ,now one is apt to think in the first moment that the impedance of the wire might have something to do with the phenomenon4 ,but this is of course immediately rejected1 as for this an enormous frequency would be required4 ,this result1 however1 seems puzzling only at first2 for upon reflection it is quite clear that the wire can make but little difference4 ,it may be explained in more than one way1 but it agrees perhaps best with observation to assume that conduction takes place from the terminals of the coil through the space4 ,on this assumption1 if the tube with the wire be held in any position1 the wire can divert little more than the current which passes through the space occupied by the wire and the metallic terminals of the tube2 through the adjacent space the current passes practically undisturbed4 ,for this reason1 if the tube be held in any position at right angles to the line joining the binding posts of the coil1 the wire makes hardly any difference1 but in a position more or less parallel with that line it impairs to a certain extent the brilliancy of the tube and its facility to light up4 ,numerous other phenomena may be explained on the same assumption4 ,for instance1 if the ends of the tube be provided with washers of sufficient size and held in the line joining the terminals of the coil1 it will not light up1 and then nearly the whole of the current1 which would otherwise pass uniformly through the space between the washers1 is diverted through the wire4 ,but if the tube be inclined sufficiently to that line1 it will light up in spite of the washers4 ,also1 if a metal plate be fastened upon a glass rod and held at right angles to the line joining the binding posts1 and nearer to one of them1 a tube held more or less parallel with the line will light up instantly when one of the terminals touches the plate1 and will go out when separated from the plate4 ,the greater the surface of the plate1 up to a certain limit1 the easier the tube will light up4 ,when a tube is placed at right angles to the straight line joining the binding posts1 and then rotated1 its luminosity steadily increases until it is parallel with that line4 ,the writer must state1 however1 that he does not favor the idea of a leakage or current through the space any more than as a suitable explanation1 for he is convinced that all these experiments could not be performed with a static machine yielding a constant difference of potential1 and that condenser action is largely concerned in these phenomena4 ,it is well to take certain precautions when operating a ,ruhmkorff coil with very rapidly alternating currents4 ,the primary current should not be turned on too long1 else the core may get so hot as to melt the gutta-percha or paraffin1 or otherwise injure the insulation1 and this may occur in a surprisingly short time1 considering the current's strength4 ,the primary current being turned on1 the fine wire terminals may be joined without great risk1 the impedance being so great that it is difficult to force enough current through the fine wire so as to injure it1 and in fact the coil may be on the whole much safer when the terminals of the fine wire are connected than when they are insulated2 but special care should be taken when the terminals are connected to the coatings of a ,leyden jar1 for with anywhere near the critical capacity1 which just counteracts the self-induction at the existing frequency1 the coil might meet the fate of ,st4 ,polycarpus4 ,if an expensive vacuum pump is lighted up by being near to the coil or touched with a wire connected to one of the terminals1 the current should be left on no more than a few moments1 else the glass will be cracked by the heating of the rarefied gas in one of the narrow passages--in the writer's own experience quod erat demonstrandum4#e #e ,it is thought necessary to remark that1 although the induction coil may give quite a good result when operated with such rapidly alternating currents1 yet its construction1 quite irrespective of the iron core1 makes it very unfit for such high frequencies1 and to obtain the best results the construction should be greatly modified4 ,there are a good many other points of interest which may be observed in connection with such a machine4 ,experiments with the telephone1 a conductor in a strong field or with a condenser or arc1 seem to afford certain proof that sounds far above the usual accepted limit of hearing would be perceived4 ,a telephone will emit notes of twelve to thirteen thousand vibrations per second2 then the inability of the core to follow such rapid alternations begins to tell4 ,if1 however1 the magnet and core be replaced by a condenser and the terminals connected to the high-tension secondary of a transformer1 higher notes may still be heard4 ,if the current be sent around a finely laminated core and a small piece of thin sheet iron be held gently against the core1 a sound may be still heard with thirteen to fourteen thousand alternations per second1 provided the current is sufficiently strong4 ,a small coil1 however1 tightly packed between the poles of a powerful magnet1 will emit a sound with the above number of alternations1 and arcs may be audible with a still higher frequency4 ,the limit of audition is variously estimated4 ,in ,sir ,william ,thomson's writings it is stated somewhere that ten thousand per second1 or nearly so1 is the limit4 ,other1 but less reliable1 sources give it as high as twenty-four thousand per second4 ,the above experiments have convinced the writer that notes of an incomparably higher number of vibrations per second would be perceived provided they could be produced with sufficient power4 ,there is no reason why it should not be so4 ,the condensations and rarefactions of the air would necessarily set the diaphragm in a corresponding vibration and some sensation would be produced1 whatever--within certain limits--the velocity of transmission to their nerve centres1 though it is probable that for want of exercise the ear would not be able to distinguish any such high note4 ,with the eye it is different2 if the sense of vision is based upon some resonance effect1 as many believe1 no amount of increase in the intensity of the ethereal vibration could extend our range of vision on either side of the visible spectrum4 ,the limit of audition of an arc depends on its size4 ,the greater the surface by a given heating effect in the arc1 the higher the limit of audition4 ,the highest notes are emitted by the high-tension discharges of an induction coil in which the arc is1 so to speak1 all surface4 ,if ,r be the resistance of an arc1 and ,c the current1 and the linear dimensions be n times increased1 then the resistance is ,r_/n1 and with the same current density the current would be n#b;,c2 hence the heating effect is n#c times greater1 while the surface is only n#b times as great4 ,for this reason very large arcs would not emit any rhythmical sound even with a very low frequency4 ,it must be observed1 however1 that the sound emitted depends to some extent also on the composition of the carbon4 ,if the carbon contain highly refractory material1 this1 when heated1 tends to maintain the temperature of the arc uniform and the sound is lessened2 for this reason it would seem that an alternating arc requires such carbons4 ,with currents of such high frequencies it is possible to obtain noiseless arcs1 but the regulation of the lamp is rendered extremely difficult on account of the excessively small attractions or repulsions between conductors conveying these currents4 ,an interesting feature of the arc produced by these rapidly alternating currents is its persistency4 ,there are two causes for it1 one of which is always present1 the other sometimes only4 ,one is due to the character of the current and the other to a property of the machine4 ,the first cause is the more important one1 and is due directly to the rapidity of the alternations4 ,when an arc is formed by a periodically undulating current1 there is a corresponding undulation in the temperature of the gaseous column1 and1 therefore1 a corresponding undulation in the resistance of the arc4 ,but the resistance of the arc varies enormously with the temperature of the gaseous column1 being practically infinite when the gas between the electrodes is cold4 ,the persistence of the arc1 therefore1 depends on the inability of the column to cool4 ,it is for this reason impossible to maintain an arc with the current alternating only a few times a second4 ,on the other hand1 with a practically continuous current1 the arc is easily maintained1 the column being constantly kept at a high temperature and low resistance4 ,the higher the frequency the smaller the time interval during which the arc may cool and increase considerably in resistance4 ,with a frequency of #aj1jjj per second or more in an arc of equal size excessively small variations of temperature are superimposed upon a steady temperature1 like ripples on the surface of a deep sea4 ,the heating effect is practically continuous and the arc behaves like one produced by a continuous current1 with the exception1 however1 that it may not be quite as easily started1 and that the electrodes are equally consumed2 though the writer has observed some irregularities in this respect4 ,the second cause alluded to1 which possibly may not be present1 is due to the tendency of a machine of such high frequency to maintain a practically constant current4 ,when the arc is lengthened1 the electromotive force rises in proportion and the arc appears to be more persistent4 ,such a machine is eminently adapted to maintain a constant current1 but it is very unfit for a constant potential4 ,as a matter of fact1 in certain types of such machines a nearly constant current is an almost unavoidable result4 ,as the number of poles or polar projections is greatly increased1 the clearance becomes of great importance4 ,one has really to do with a great number of very small machines4 ,then there is the impedance in the armature1 enormously augmented by the high frequency4 ,then1 again1 the magnetic leakage is facilitated4 ,if there are three or four hundred alternate poles1 the leakage is so great that it is virtually the same as connecting1 in a two-pole machine1 the poles by a piece of iron4 ,this disadvantage1 it is true1 may be obviated more or less by using a field throughout of the same polarity1 but then one encounters difficulties of a different nature4 ,all these things tend to maintain a constant current in the armature circuit4 ,in this connection it is interesting to notice that even to-day engineers are astonished at the performance of a constant current machine1 just as1 some years ago1 they used to consider it an extraordinary performance if a machine was capable of maintaining a constant potential difference between the terminals4 ,yet one result is just as easily secured as the other4 ,it must only be remembered that in an inductive apparatus of any kind1 if constant potential is required1 the inductive relation between the primary or exciting and secondary or armature circuit must be the closest possible2 whereas1 in an apparatus for constant current just the opposite is required4 ,furthermore1 the opposition to the current's flow in the induced circuit must be as small as possible in the former and as great as possible in the latter case4 ,but opposition to a current's flow may be caused in more than one way4 ,it may be caused by ohmic resistance or self-induction4 ,one may make the induced circuit of a dynamo machine or transformer of such high resistance that when operating devices of considerably smaller resistance within very wide limits a nearly constant current is maintained4 ,but such high resistance involves a great loss in power1 hence it is not practicable4 ,not so self-induction4 ,self-induction does not necessarily mean loss of power4 ,the moral is1 use self-induction instead of resistance4 ,there is1 however1 a circumstance which favors the adoption of this plan1 and this is1 that a very high self-induction may be obtained cheaply by surrounding a comparatively small length of wire more or less completely with iron1 and1 furthermore1 the effect may be exalted at will by causing a rapid undulation of the current4 ,to sum up1 the requirements for constant current are3 ,weak magnetic connection between the induced and inducing circuits1 greatest possible self-induction with the least resistance1 greatest practicable rate of change of the current4 ,constant potential1 on the other hand1 requires3 ,closest magnetic connection between the circuits1 steady induced current1 and1 if possible1 no reaction4 ,if the latter conditions could be fully satisfied in a constant potential machine1 its output would surpass many times that of a machine primarily designed to give constant current4 ,unfortunately1 the type of machine in which these conditions may be satisfied is of little practical value1 owing to the small electromotive force obtainable and the difficulties in taking off the current4 ,with their keen inventor's instinct1 the now successful arc-light men have early recognized the desiderata of a constant current machine4 ,their arc light machines have weak fields1 large armatures1 with a great length of copper wire and few commutator segments to produce great variations in the current's strength and to bring self-induction into play4 ,such machines may maintain within considerable limits of variation in the resistance of the circuit a practically constant current4 ,their output is of course correspondingly diminished1 and1 perhaps with the object in view not to cut down the output too much1 a simple device compensating exceptional variations is employed4 ,the undulation of the current is almost essential to the commercial success of an arc-light system4 ,it introduces in the circuit a steadying element taking the place of a large ohmic resistance1 without involving a great loss in power1 and1 what is more important1 it allows the use of simple clutch lamps1 which with a current of a certain number of impulses per second1 best suitable for each particular lamp1 will1 if properly attended to1 regulate even better than the finest clock-work lamps4 ,this discovery has been made by the writer--several years too late4 ,it has been asserted by competent ,english electricians that in a constant-current machine or transformer the regulation is effected by varying the phase of the secondary current4 ,that this view is erroneous may be easily proved by using1 instead of lamps1 devices each possessing self-induction and capacity or self-induction and resistance--that is1 retarding and accelerating components--in such proportions as to not affect materially the phase of the secondary current4 ,any number of such devices may be inserted or cut out1 still it will be found that the regulation occurs1 a constant current being maintained1 while the electromotive force is varied with the number of the devices4 ,the change of phase of the secondary current is simply a result following from the changes in resistance1 and1 though secondary reaction is always of more or less importance1 yet the real cause of the regulation lies in the existence of the conditions above enumerated4 ,it should be stated1 however1 that in the case of a machine the above remarks are to be restricted to the cases in which the machine is independently excited4 ,if the excitation be effected by commutating the armature current1 then the fixed position of the brushes makes any shifting of the neutral line of the utmost importance1 and it may not be thought immodest of the writer to mention that1 as far as records go1 he seems to have been the first who has successfully regulated machines by providing a bridge connection between a point of the external circuit and the commutator by means of a third brush4 ,the armature and field being properly proportioned and the brushes placed in their determined positions1 a constant current or constant potential resulted from the shifting of the diameter of commutation by the varying loads4 ,in connection with machines of such high frequencies1 the condenser affords an especially interesting study4 ,it is easy to raise the electromotive force of such a machine to four or five times the value by simply connecting the condenser to the circuit1 and the writer has continually used the condenser for the the purposes of regulation1 as suggested by ,blakesley in his book on alternate currents1 in which he has treated the most frequently occurring condenser problems with exquisite simplicity and clearness4 ,the high frequency allows the use of small capacities and renders investigation easy4 ,but1 although in most of the experiments the result may be foretold1 some phenomena observed seem at first curious4 ,one experiment performed three or four months ago with such a machine and a condenser may serve as an illustration4 ,a machine was used giving about #bj1jjj alternations per second4 ,two bare wires about twenty feet long and two millimetres in diameter1 in close proximity to each other1 were connected to the terminals of the machine at the one end1 and to a condenser at the other4 ,a small transformer without an iron core1 of course1 was used to bring the reading within range of a ,cardew voltmeter by connecting the voltmeter to the secondary4 ,on the terminals of the condenser the electromotive force was about #abj volts1 and from there inch by inch it gradually fell until at the terminals of the machine it was about #fe volts4 ,it was virtually as though the condenser were a generator1 and the line and armature circuit simply a resistance connected to it4 ,the writer looked for a case of resonance1 but he was unable to augment the effect by varying the capacity very carefully and gradually or by changing the speed of the machine4 ,a case of pure resonance he was unable to obtain4 ,when a condenser was connected to the terminals of the machine--the self-induction of the armature being first determined in the maximum and minimum position and the mean value taken--the capacity which gave the highest electromotive force corresponded most nearly to that which just counteracted the self-induction with the existing frequency4 ,if the capacity was increased or diminished1 the electromotive force fell as expected4 ,with frequencies as high as the above mentioned1 the condenser effects are of enormous importance4 ,the condenser becomes a highly efficient apparatus capable of transferring considerable energy4 99 99 99 99 99 ,in an appendix to this book will be found a description of the ,tesla oscillator1 which its inventor believes will among other great advantages give him the necessary high frequency conditions1 while relieving him of the inconveniences that attach to generators of the type described at the beginning of this chapter4 ,,chapter ,,xxx4 ,,alternate ,,current ,,electrostatic ,,induction ,,apparatus4#f #f ,article by ,mr4 ,tesla in ,the ,electrical ,engineer1 ,n4 ,y41 ,may #f1 #ahia4 ,about a year and a half ago while engaged in the study of alternate currents of short period1 it occurred to me that such currents could be obtained by rotating charged surfaces in close proximity to conductors4 ,accordingly ,i devised various forms of experimental apparatus of which two are illustrated in the accompanying engravings4 ,illustration3 ,,fig4 #bjh4 ,in the apparatus shown in ,fig4 #bjh1 ,a is a ring of dry shellacked hard wood provided on its inside with two sets of tin-foil coatings1 a and b1 all the a coatings and all the b coatings being connected together1 respectively1 but independent from each other4 ,these two sets of coatings are connected to two terminals1 ,t4 ,for the sake of clearness only a few coatings are shown4 ,inside of the ring ,a1 and in close proximity to it there is arranged to rotate a cylinder ,b1 likewise of dry1 shellacked hard wood1 and provided with two similar sets of coatings1 a#a and b#a1 all the coatings a#a being connected to one ring and all the others1 b#a1 to another marked and -4 ,these two sets1 a#a and b#a are charged to a high potential by a ,holtz or ,wimshurst machine1 and may be connected to a jar of some capacity4 ,the inside of ring ,a is coated with mica in order to increase the induction and also to allow higher potentials to be used4 ,illustration3 ,,fig4 #bji4 ,when the cylinder ,b with the charged coatings is rotated1 a circuit connected to the terminals ,t is traversed by alternating currents4 ,another form of apparatus is illustrated in ,fig4 #bji4 ,in this apparatus the two sets of tin-foil coatings are glued on a plate of ebonite1 and a similar plate which is rotated1 and the coatings of which are charged as in ,fig4 #bjh1 is provided4 ,the output of such an apparatus is very small1 but some of the effects peculiar to alternating currents of short periods may be observed4 ,the effects1 however1 cannot be compared with those obtainable with an induction coil which is operated by an alternate current machine of high frequency1 some of which were described by me a short while ago4 ,,chapter ,,xxxi4 ,,massage ,,with ,,currents ,,of ,,high ,,frequency4#g #g ,article by ,mr4 ,tesla in ,the ,electrical ,engineer of ,dec4 #bc;d1 #ahia4 ,i trust that the present brief communication will not be interpreted as an effort on my part to put myself on record as a patent medicine man1 for a serious worker cannot despise anything more than the misuse and abuse of electricity which we have frequent occasion to witness4 ,my remarks are elicited by the lively interest which prominent medical practitioners evince at every real advance in electrical investigation4 ,the progress in recent years has been so great that every electrician and electrical engineer is confident that electricity will become the means of accomplishing many things that have been heretofore1 with our existing knowledge1 deemed impossible4 ,no wonder then that progressive physicians also should expect to find in it a powerful tool and help in new curative processes4 ,since ,i had the honor to bring before the ,american ,institute of ,electrical ,engineers some results in utilizing alternating currents of high tension1 ,i have received many letters from noted physicians inquiring as to the physical effects of such currents of high frequency4 ,it may be remembered that ,i then demonstrated that a body perfectly well insulated in air can be heated by simply connecting it with a source of rapidly alternating high potential4 ,the heating in this case is due in all probability to the bombardment of the body by air1 or possibly by some other medium1 which is molecular or atomic in construction1 and the presence of which has so far escaped our analysis--for according to my ideas1 the true ether radiation with such frequencies as even a few millions per second must be very small4 ,this body may be a good conductor or it may be a very poor conductor of electricity with little change in the result4 ,the human body is1 in such a case1 a fine conductor1 and if a person insulated in a room1 or no matter where1 is brought into contact with such a source of rapidly alternating high potential1 the skin is heated by bombardment4 ,it is a mere question of the dimensions and character of the apparatus to produce any degree of heating desired4 ,it has occurred to me whether1 with such apparatus properly prepared1 it would not be possible for a skilled physician to find in it a means for the effective treatment of various types of disease4 ,the heating will1 of course1 be superficial1 that is1 on the skin1 and would result1 whether the person operated on were in bed or walking around a room1 whether dressed in thick clothes or whether reduced to nakedness4 ,in fact1 to put it broadly1 it is conceivable that a person entirely nude at the ,north ,pole might keep himself comfortably warm in this manner4 ,without vouching for all the results1 which must1 of course1 be determined by experience and observation1 ,i can at least warrant the fact that heating would occur by the use of this method of subjecting the human body to bombardment by alternating currents of high potential and frequency such ,i have long worked with4 ,it is only reasonable to expect that some of the novel effects will be wholly different from those obtainable with the old familiar therapeutic methods generally used4 ,whether they would all be beneficial or not remains to be proved4 ,,chapter ,,xxxii4 ,,electric ,,discharge ,,in ,,vacuum ,,tubes4#h #h ,article by ,mr4 ,tesla in ,the ,electrical ,engineer4 ,n4 ,y41 ,july #a1 #ahia4 ,in ,the ,electrical ,engineer of ,june #aj ,i have noted the description of some experiments of ,prof4 ,j4 ,j4 ,thomson1 on the ,electric ,discharge in ,vacuum ,tubes1 and in your issue of ,june #bd ,prof4 ,elihu ,thomson describes an experiment of the same kind4 ,the fundamental idea in these experiments is to set up an electromotive force in a vacuum tube---preferably devoid of any electrodes--by means of electro-magnetic induction1 and to excite the tube in this manner4 ,as ,i view the subject ,i should1 think that to any experimenter who had carefully studied the problem confronting us and who attempted to find a solution of it1 this idea must present itself as naturally as1 for instance1 the idea of replacing the tinfoil coatings of a ,leyden jar by rarefied gas and exciting luminosity in the condenser thus obtained by repeatedly charging and discharging it4 ,the idea being obvious1 whatever merit there is in this line of investigation must depend upon the completeness of the study of the subject and the correctness of the observations4 ,the following lines are not penned with any desire on my part to put myself on record as one who has performed similar experiments1 but with a desire to assist other experimenters by pointing out certain peculiarities of the phenomena observed1 which1 to all appearances1 have not been noted by ,prof4 ,j4 ,j4 ,thomson1 who1 however1 seems to have gone about systematically in his investigations1 and who has been the first to make his results known4 ,these peculiarities noted by me would seem to be at variance with the views of ,prof4 ,j4 ,j4 ,thomson1 and present the phenomena in a different light4 ,my investigations in this line occupied me principally during the winter and spring of the past year4 ,during this time many different experiments were performed1 and in my exchanges of ideas on this subject with ,mr4 ,alfred ,s4 ,brown1 of the ,western ,union ,telegraph ,company1 various different dispositions were suggested which were carried out by me in practice4 ,fig4 #baj may serve as an example of one of the many forms of apparatus used4 ,this consisted of a large glass tube sealed at one end and projecting into an ordinary incandescent lamp bulb4 ,the primary1 usually consisting of a few turns of thick1 well-insulated copper sheet was inserted within the tube1 the inside space of the bulb furnishing the secondary4 ,this form of apparatus was arrived at after some experimenting1 and was used principally with the view of enabling me to place a polished reflecting surface on the inside of the tube1 and for this purpose the last turn of the primary was covered with a thin silver sheet4 ,in all forms of apparatus used there was no special difficulty in exciting a luminous circle or cylinder in proximity to the primary4 ,illustration3 ,,fig4 #baj4 ,as to the number of turns1 ,i cannot quite understand why ,prof4 ,j4 ,j4 ,thomson should think that a few turns were quite sufficient1 but lest ,i should impute to him an opinion he may not have1 ,i will add that ,i have gained this impression from the reading of the published abstracts of his lecture4 ,clearly1 the number of turns which gives the best result in any case1 is dependent on the dimensions of the apparatus1 and1 were it not for various considerations1 one turn would always give the best result4 ,i have found that it is preferable to use in these experiments an alternate current machine giving a moderate number of alternations per second to excite the induction coil for charging the ,leyden jar which discharges through the primary--shown diagrammatically in ,fig4 #baa1--;as in such case1 before the disruptive discharge takes place1 the tube or bulb is slightly excited and the formation of the luminous circle is decidedly facilitated4 ,but ,i have also used a ,wimshurst machine in some experiments4 ,illustration3 ,,fig4 #baa4 ,prof4 ,j4 ,j4 ,thomson's view of the phenomena under consideration seems to be that they are wholly due to electro-magnetic action4 ,i was1 at one time1 of the same opinion1 but upon carefully investigating the subject ,i was led to the conviction that they are more of an electrostatic nature4 ,it must be remembered that in these experiments we have to deal with primary currents of an enormous frequency or rate of change and of high potential1 and that the secondary conductor consists of a rarefied gas1 and that under such conditions electrostatic effects must play an important part4 ,illustration3 ,,fig4 #bab4 ,in support of my view ,i will describe a few experiments made by me4 ,to excite luminosity in the tube it is not absolutely necessary that the conductor should be closed4 ,for instance1 if an ordinary exhausted tube 7preferably of large diameter7 be surrounded by a spiral of thick copper wire serving as the primary1 a feebly luminous spiral may be induced in the tube1 roughly shown in ,fig4 #bab4 ,in one of these experiments a curious phenomenon was observed2 namely1 two intensely luminous circles1 each of them close to a turn of the primary spiral1 were formed inside of the tube1 and ,i attributed this phenomenon to the existence of nodes on the primary4 ,the circles were connected by a faint luminous spiral parallel to the primary and in close proximity to it4 ,to produce this effect ,i have found it necessary to strain the jar to the utmost4 ,the turns of the spiral tend to close and form circles1 but this1 of course1 would be expected1 and does not necessarily indicate an electro-magnetic effect2 ,whereas the fact that a glow can be produced along the primary in the form of an open spiral argues for an electrostatic effect4 ,illustration3 ,,fig4 #bac4 ,in using ,dr4 ,lodge's recoil circuit1 the electrostatic action is likewise apparent4 ,the arrangement is illustrated in ,fig4 #bac4 ,in his experiment two hollow exhausted tubes ,h ,h were slipped over the wires of the recoil circuit and upon discharging the jar in the usual manner luminosity was excited in the tubes4 ,another experiment performed is illustrated in ,fig4 #bad4 ,in this case an ordinary lamp-bulb was surrounded by one or two turns of thick copper wire ,p and the luminous circle ,l excited in the bulb by discharging the jar through the primary4 ,the lamp-bulb was provided with a tinfoil coating on the side opposite to the primary and each time the tinfoil coating was connected to the ground or to a large object the luminosity of the circle was considerably increased4 ,this was evidently due to electrostatic action4 ,in other experiments ,i have noted that when the primary touches the glass the luminous circle is easier produced and is more sharply defined2 but ,i have not noted that1 generally speaking1 the circles induced were very sharply defined1 as ,prof4 ,j4 ,j4 ,thomson has observed2 on the contrary1 in my experiments they were broad and often the whole of the bulb or tube was illuminated2 and in one case ,i have observed an intensely purplish glow1 to which ,prof4 ,j4 ,j4 ,thomson refers4 ,but the circles were always in close proximity to the primary and were considerably easier produced when the latter was very close to the glass1 much more so than would be expected assuming the action to be electromagnetic and considering the distance2 and these facts speak for an electrostatic effect4 ,illustration3 ,,fig4 #bad4 ,illustration3 ,,fig4 #bae4 ,furthermore ,i have observed that there is a molecular bombardment in the plane of the luminous circle at right angles to the glass--supposing the circle to be in the plane of the primary--this bombardment being evident from the rapid heating of the glass near the primary4 ,were the bombardment not at right angles to the glass the heating could not be so rapid4 ,if there is a circumferential movement of the molecules constituting the luminous circle1 ,i have thought that it might be rendered manifest by placing within the tube or bulb1 radially to the circle1 a thin plate of mica coated with some phosphorescent material and another such plate tangentially to the circle4 ,if the molecules would move circumferentially1 the former plate would be rendered more intensely phosphorescent4 ,for want of time ,i have1 however1 not been able to perform the experiment4 ,another observation made by me was that when the specific inductive capacity of the medium between the primary and secondary is increased1 the inductive effect is augmented4 ,this is roughly illustrated in ,fig4 #bae4 ,in this case luminosity was excited in an exhausted tube or bulb ,b and a glass tube ,t slipped between the primary and the bulb1 when the effect pointed out was noted4 ,were the action wholly electromagnetic no change could possibly have been observed4 ,i have likewise noted that when a bulb is surrounded by a wire closed upon itself and in the plane of the primary1 the formation of the luminous circle within the bulb is not prevented4 ,but if instead of the wire a broad strip of tinfoil is glued upon the bulb1 the formation of the luminous band was prevented1 because then the action was distributed over a greater surface4 ,the effect of the closed tinfoil was no doubt of an electrostatic nature1 for it presented a much greater resistance than the closed wire and produced therefore a much smaller electromagnetic effect4 ,some of the experiments of ,prof4 ,j4 ,j4 ,thomson also would seem to show some electrostatic action4 ,for instance1 in the experiment with the bulb enclosed in a bell jar1 ,i should think that when the latter is exhausted so far that the gas enclosed reaches the maximum conductivity1 the formation of the circle in the bulb and jar is prevented because of the space surrounding the primary being highly conducting2 when the jar is further exhausted1 the conductivity of the space around the primary diminishes and the circles appear necessarily first in the bell jar1 as the rarefied gas is nearer to the primary4 ,but were the inductive effect very powerful1 they would probably appear in the bulb also4 ,if1 however1 the bell jar were exhausted to the highest degree they would very likely show themselves in the bulb only1 that is1 supposing the vacuous space to be non-conducting4 ,on the assumption that in these phenomena electrostatic actions are concerned we find it easily explicable why the introduction of mercury or the heating of the bulb prevents the formation of the luminous band or shortens the after-glow2 and also why in some cases a platinum wire may prevent the excitation of the tube4 ,nevertheless some of the experiments of ,prof4 ,j4 ,j4 ,thomson would seem to indicate an electromagnetic effect4 ,i may add that in one of my experiments in which a vacuum was produced by the ,torricellian method1 ,i was unable to produce the luminous band1 but this may have been due to the weak exciting current employed4 ,my principal argument is the following3 ,i have experimentally proved that if the same discharge which is barely sufficient to excite a luminous band in the bulb when passed through the primary circuit be so directed as to exalt the electrostatic inductive effect--namely1 by converting upwards--an exhausted tube1 devoid of electrodes1 may be excited at a distance of several feet4 ,,some ,,experiments ,,on ,,the ,,electric ,,discharge ,,in ,,vacuum ,,tubes4#i ,,by ,,prof4 ,j4 ,j4 ,,thomson1 ,m4,a41 ,f4,r4,s4 #i ,abstract of a paper read before ,physical ,society of ,london4 ,illustration3 ,,fig4 #baf4 ,illustration3 ,,fig4 #bag4 ,illustration3 ,,fig4 #bah4 ,illustration3 ,,fig4 #bai4 ,the phenomena of vacuum discharges were1 ,prof4 ,thomson said1 greatly simplified when their path was wholly gaseous1 the complication of the dark space surrounding the negative electrode1 and the stratifications so commonly observed in ordinary vacuum tubes1 being absent4 ,to produce discharges in tubes devoid of electrodes was1 however1 not easy to accomplish1 for the only available means of producing an electromotive force in the discharge circuit was by electro-magnetic induction4 ,ordinary methods of producing variable induction were valueless1 and recourse was had to the oscillatory discharge of a ,leyden jar1 which combines the two essentials of a current whose maximum value is enormous1 and whose rapidity of alternation is immensely great4 ,the discharge circuits1 which may take the shape of bulbs1 or of tubes bent in the form of coils1 were placed in close proximity to glass tubes filled with mercury1 which formed the path of the oscillatory discharge4 ,the parts thus corresponded to the windings of an induction coil1 the vacuum tubes being the secondary1 and the tubes filled with mercury the primary4 ,in such an apparatus the ,leyden jar need not be large1 and neither primary nor secondary need have many turns1 for this would increase the self-induction of the former1 and lengthen the discharge path in the latter4 ,increasing the self-induction of the primary reduces the ,e4 ,m4 ,f4 induced in the secondary1 whilst lengthening the secondary does not increase the ,e4 ,m4 ,f4 per unit length4 ,the two or three turns1 as shown in ,fig4 #baf1 in each1 were found to be quite sufficient1 and1 on discharging the ,leyden jar between two highly polished knobs in the primary circuit1 a plain uniform band of light was seen to pass round the secondary4 ,an exhausted bulb1 ,fig4 #bag1 containing traces of oxygen was placed within a primary spiral of three turns1 and1 on passing the jar discharge1 a circle of light was seen within the bulb in close proximity to the primary circuit1 accompanied by a purplish glow1 which lasted for a second or more4 ,on heating the bulb1 the duration of the glow was greatly diminished1 and it could be instantly extinguished by the presence of an electro-magnet4 ,another exhausted bulb1 ,fig4 #bah1 surrounded by a primary spiral1 was contained in a bell-jar1 and when the pressure of air in the jar was about that of the atmosphere1 the secondary discharge occurred in the bulb1 as is ordinarily the case4 ,on exhausting the jar1 however1 the luminous discharge grew fainter1 and a point was reached at which no secondary discharge was visible4 ,further exhaustion of the jar caused the secondary discharge to appear outside of the bulb4 ,the fact of obtaining no luminous discharge1 either in the bulb or jar1 the author could only explain on two suppositions1 viz43 that under the conditions then existing the specific inductive capacity of the gas was very great1 or that a discharge could pass without being luminous4 ,the author had also observed that the conductivity of a vacuum tube without electrodes increased as the pressure diminished1 until a certain point was reached1 and afterwards diminished again1 thus showing that the high resistance of a nearly perfect vacuum is in no way due to the presence of the electrodes4 ,one peculiarity of the discharges was their local nature1 the rings of light being much more sharply defined than was to be expected4 ,they were also found to be most easily produced when the chain of molecules in the discharge were all of the same kind4 ,for example1 a discharge could be easily sent through a tube many feet long1 but the introduction of a small pellet of mercury in the tube stopped the discharge1 although the conductivity of the mercury was much greater than that of the vacuum4 ,in some cases he had noticed that a very fine wire placed within a tube1 on the side remote from the primary circuit1 would prevent a luminous discharge in that tube4 ,fig4 #bai shows an exhausted secondary coil of one loop containing bulbs2 the discharge passed along the inner side of the bulbs1 the primary coils being placed within the secondary4 #i;,in ,the ,electrical ,engineer of ,august #ab1 ,i find some remarks of ,prof4 ,j4 ,j4 ,thomson1 which appeared originally in the ,london ,electrician and which have a bearing upon some experiments described by me in your issue of ,july #a4 #i ,article by ,mr4 ,tesla in ,the ,electrical ,engineer1 ,n4 ,y41 ,august #bf1 #ahia4 ,i did not1 as ,prof4 ,j4 ,j4 ,thomson seems to believe1 misunderstand his position in regard to the cause of the phenomena considered1 but ,i thought that in his experiments1 as well as in my own1 electrostatic effects were of great importance4 ,it did not appear1 from the meagre description of his experiments1 that all possible precautions had been taken to exclude these effects4 ,i did not doubt that luminosity could be excited in a closed tube when electrostatic action is completely excluded4 ,in fact1 at the outset1 ,i myself looked for a purely electrodynamic effect and believed that ,i had obtained it4 ,but many experiments performed at that time proved to me that the electrostatic effects were generally of far greater importance1 and admitted of a more satisfactory explanation of most of the phenomena observed4 ,in using the term electrostatic ,i had reference rather to the nature of the action than to a stationary condition1 which is the usual acceptance of the term4 ,to express myself more clearly1 ,i will suppose that near a closed exhausted tube be placed a small sphere charged to a very high potential4 ,the sphere would act inductively upon the tube1 and by distributing electricity over the same would undoubtedly produce luminosity 7if the potential be sufficiently high71 until a permanent condition would be reached4 ,assuming the tube to be perfectly well insulated1 there would be only one instantaneous flash during the act of distribution4 ,this would be due to the electrostatic action simply4 ,but now1 suppose the charged sphere to be moved at short intervals with great speed along the exhausted tube4 ,the tube would now be permanently excited1 as the moving sphere would cause a constant redistribution of electricity and collisions of the molecules of the rarefied gas4 ,we would still have to deal with an electrostatic effect1 and in addition an electrodynamic effect would be observed4 ,but if it were found that1 for instance1 the effect produced depended more on the specific inductive capacity than on the magnetic permeability of the medium--which would certainly be the case for speeds incomparably lower than that of light--then ,i believe ,i would be justified in saying that the effect produced was more of an electrostatic nature4 ,i do not mean to say1 however1 that any similar condition prevails in the case of the discharge of a ,leyden jar through the primary1 but ,i think that such an action would be desirable4 ,it is in the spirit of the above example that ,i used the terms more of an electrostatic nature1 and have investigated the influence of bodies of high specific inductive capacity1 and observed1 for instance1 the importance of the quality of glass of which the tube is made4 ,i also endeavored to ascertain the influence of a medium of high permeability by using oxygen4 ,it appeared from rough estimation that an oxygen tube when excited under similar conditions--that is1 as far as could be determined--gives more light2 but this1 of course1 may be due to many causes4 ,without doubting in the least that1 with the care and precautions taken by ,prof4 ,j4 ,j4 ,thomson1 the luminosity excited was due solely to electrodynamic action1 ,i would say that in many experiments ,i have observed curious instances of the ineffectiveness of the screening1 and ,i have also found that the electrification through the air is often of very great importance1 and may1 in some cases1 determine the excitation of the tube4 ,in his original communication to the ,electrician1 ,prof4 ,j4 ,j4 ,thomson refers to the fact that the luminosity in a tube near a wire through which a ,leyden jar was discharged was noted by ,hittorf4 ,i think that the feeble luminous effect referred to has been noted by many experimenters1 but in my experiments the effects were much more powerful than those usually noted4 ,the following is the communication#aj referred to3-- #aj ,note by ,prof4 ,j4 ,j4 ,thomson in the ,london ,electrician1 ,july #bd1 #ahia4 ,mr4 ,tesla seems to ascribe the effects he observed to electrostatic action1 and ,i have no doubt1 from the description he gives of his method of conducting his experiments1 that in them electrostatic action plays a very important part4 ,he seems1 however1 to have misunderstood my position with respect to the cause of these discharges1 which is not1 as he implies1 that luminosity in tubes without electrodes cannot be produced by electrostatic action1 but that it can also be produced when this action is excluded4 ,as a matter of fact1 it is very much easier to get the luminosity when these electrostatic effects are operative than when they are not4 ,as an illustration of this ,i may mention that the first experiment ,i tried with the discharge of a ,leyden jar produced luminosity in the tube1 but it was not until after six weeks' continuous experimenting that ,i was able to get a discharge in the exhausted tube which ,i was satisfied was due to what is ordinarily called electrodynamic action4 ,it is advisable to have a clear idea of what we mean by electrostatic action4 ,if1 previous to the discharge of the jar1 the primary coil is raised to a high potential1 it will induce over the glass of the tube a distribution of electricity4 ,when the potential of the primary suddenly falls1 this electrification will redistribute itself1 and may pass through the rarefied gas and produce luminosity in doing so4 ,whilst the discharge of the jar is going on1 it is difficult1 and1 from a theoretical point of view1 undesirable1 to separate the effect into parts1 one of which is called electrostatic1 the other electromagnetic2 what we can prove is that in this case the discharge is not such as would be produced by electromotive forces derived from a potential function4 ,in my experiments the primary coil was connected to earth1 and1 as a further precaution1 the primary was separated from the discharge tube by a screen of blotting paper1 moistened with dilute sulphuric acid1 and connected to earth4 ,wet blotting paper is a sufficiently good conductor to screen off a stationary electrostatic effect1 though it is not a good enough one to stop waves of alternating electromotive intensity4 ,when showing the experiments to the ,physical ,society ,i could not1 of course1 keep the tubes covered up1 but1 unless my memory deceives me1 ,i stated the precautions which had been taken against the electrostatic effect4 ,to correct misapprehension ,i may state that ,i did not read a formal paper to the ,society1 my object being to exhibit a few of the most typical experiments4 ,the account of the experiments in the ,electrician was from a reporter's note1 and was not written1 or even read1 by me4 ,i have now almost finished writing out1 and hope very shortly to publish1 an account of these and a large number of allied experiments1 including some analogous to those mentioned by ,mr4 ,tesla on the effect of conductors placed near the discharge tube1 which ,i find1 in some cases1 to produce a diminution1 in others an increase1 in the brightness of the discharge1 as well as some on the effect of the presence of substances of large specific inductive capacity4 ,these seem to me to admit of a satisfactory explanation1 for which1 however1 ,i must refer to my paper4 ,,part ,,iii4 ,,miscellaneous ,,inventions ,,and ,,writings4 ,,chapter ,,xxxiii4 ,,method ,,of ,,obtaining ,,driect ,,from ,,alternating ,,currents4 ,this method consists in obtaining direct from alternating currents1 or in directing the waves of an alternating current so as to produce direct or substantially direct currents by developing or producing in the branches of a circuit including a source of alternating currents1 either permanently or periodically1 and by electric1 electro-magnetic1 or magnetic agencies1 manifestations of energy1 or what may be termed active resistances of opposite electrical character1 whereby the currents or current waves of opposite sign will be diverted through different circuits1 those of one sign passing over one branch and those of opposite sign over the other4 ,we may consider herein only the case of a circuit divided into two paths1 inasmuch as any further subdivision involves merely an extension of the general principle4 ,selecting1 then1 any circuit through which is flowing an alternating current1 ,mr4 ,tesla divides such circuit at any desired point into two branches or paths4 ,in one of these paths he inserts some device to create an electromotive force counter to the waves or impulses of current of one sign and a similar device in the other branch which opposes the waves of opposite sign4 ,assume1 for example1 that these devices are batteries1 primary or secondary1 or continuous current dynamo machines4 ,the waves or impulses of opposite direction composing the main current have a natural tendency to divide between the two branches2 but by reason of the opposite electrical character or effect of the two branches1 one will offer an easy passage to a current of a certain direction1 while the other will offer a relatively high resistance to the passage of the same current4 ,the result of this disposition is1 that the waves of current of one sign will1 partly or wholly1 pass over one of the paths or branches1 while those of the opposite sign pass over the other4 ,there may thus be obtained from an alternating current two or more direct currents without the employment of any commutator such as it has been heretofore regarded as necessary to use4 ,the current in either branch may be used in the same way and for the same purposes as any other direct current--that is1 it may be made to charge secondary batteries1 energize electro-magnets1 or for any other analogous purpose4 ,fig4 #bbj represents a plan of directing the alternating currents by means of devices purely electrical in character4 ,figs4 #bba1 #bbb1 #bbc1 #bbd1 #bbe1 and #bbf are diagrams illustrative of other ways of carrying out the invention4 ,illustration3 ,,fig4 #bbj4 ,in ,fig4 #bbj1 ,a designates a generator of alternating currents1 and ,b ,b the main or line circuit therefrom4 ,at any given point in this circuit at or near which it is desired to obtain direct currents1 the circuit ,b is divided into two paths or branches ,c ,d4 ,in each of these branches is placed an electrical generator1 which for the present we will assume produces direct or continuous currents4 ,the direction of the current thus produced is opposite in one branch to that of the current in the other branch1 or1 considering the two branches as forming a closed circuit1 the generators ,e ,f are connected up in series therein1 one generator in each part or half of the circuit4 ,the electromotive force of the current sources ,e and ,f may be equal to or higher or lower than the electromotive forces in the branches ,c ,d1 or between the points ,x and ,y of the circuit ,b ,b4 ,if equal1 it is evident that current waves of one sign will be opposed in one branch and assisted in the other to such an extent that all the waves of one sign will pass over one branch and those of opposite sign over the other4 ,if1 on the other hand1 the electromotive force of the sources ,e ,f be lower than that between ,x and ,y1 the currents in both branches will be alternating1 but the waves of one sign will preponderate4 ,one of the generators or sources of current ,e or ,f may be dispensed with2 but it is preferable to employ both1 if they offer an appreciable resistance1 as the two branches will be thereby better balanced4 ,the translating or other devices to be acted upon by the current are designated by the letters ,g1 and they are inserted in the branches ,c ,d in any desired manner2 but in order to better preserve an even balance between the branches due regard should1 of course1 be had to the number and character of the devices4 ,illustration3 ,,fig4 #bba4 ,figs4 #bba1 #bbb1 #bbc1 and #bbd illustrate what may termed electro-magnetic devices for accomplishing a similar result--that is to say1 instead of producing directly by a generator an electromotive force in each branch of the circuit1 ,mr4 ,tesla establishes a field or fields of force and leads the branches through the same in such manner that an active opposition of opposite effect or direction will be developed therein by the passage1 or tendency to pass1 of the alternations of current4 ,in ,fig4 #bba1 for example1 ,a is the generator of alternating currents1 ,b ,b the line circuit1 and ,c ,d the branches over which the alternating currents are directed4 ,in each branch is included the secondary of a transformer or induction coil1 which1 since they correspond in their functions to the batteries of the previous figure1 are designated by the letters ,e ,f4 ,the primaries ,h ,h' of the induction coils or transformers are connected either in parallel or series with a source of direct or continuous currents ,i1 and the number of convolutions is so calculated for the strength of the current from ,i that the cores ,j ,j' will be saturated4 ,the connections are such that the conditions in the two transformers are of opposite character--that is to say1 the arrangement is such that a current wave or impulse corresponding in direction with that of the direct current in one primary1 as ,h1 is of opposite direction to that in the other primary ,h'4 ,it thus results that while one secondary offers a resistance or opposition to the passage through it of a wave of one sign1 the other secondary similarly opposes a wave of opposite sign4 ,in consequence1 the waves of one sign will1 to a greater or less extent1 pass by way of one branch1 while those of opposite sign in like manner pass over the other branch4 ,in lieu of saturating the primaries by a source of continuous current1 we may include the primaries in the branches ,c ,d1 respectively1 and periodically short-circuit by any suitable mechanical devices--such as an ordinary revolving commutator--their secondaries4 ,it will be understood1 of course1 that the rotation and action of the commutator must be in synchronism or in proper accord with the periods of the alternations in order to secure the desired results4 ,such a disposition is represented diagrammatically in ,fig4 #bbb4 ,corresponding to the previous figures1 ,a is the generator of alternating currents1 ,b ,b the line1 and ,c ,d the two branches for the direct currents4 ,in branch ,c are included two primary coils ,e ,e'1 and in branch ,d are two similar primaries ,f ,f' ,the corresponding secondaries for these coils and which are on the same subdivided cores ,j or ,j'1 are in circuits the terminals of which connect to opposite segments ,k ,k'1 and ,l ,l'1 respectively1 of a commutator4 ,brushes b b bear upon the commutator and alternately short-circuit the plates ,k and ,k'1 and ,l and ,l'1 through a connection c4 ,it is obvious that either the magnets and commutator1 or the brushes1 may revolve4 ,illustration3 ,,fig4 #bbb4 ,the operation will be understood from a consideration of the effects of closing or short-circuiting the secondaries4 ,for example1 if at the instant when a given wave of current passes1 one set of secondaries be short-circuited1 nearly all the current flows through the corresponding primaries2 but the secondaries of the other branch being open-circuited1 the self-induction in the primaries is highest1 and hence little or no current will pass through that branch4 ,if1 as the current alternates1 the secondaries of the two branches are alternately short-circuited1 the result will be that the currents of one sign pass over one branch and those of the opposite sign over the other4 ,the disadvantages of this arrangement1 which would seem to result from the employment of sliding contacts1 are in reality very slight1 inasmuch as the electromotive force of the secondaries may be made exceedingly low1 so that sparking at the brushes is avoided4 ,illustration3 ,,fig4 #bbc4 ,fig4 #bbc is a diagram1 partly in section1 of another plan of carrying out the invention4 ,the circuit ,b in this case is divided1 as before1 and each branch includes the coils of both the fields and revolving armatures of two induction devices4 ,the armatures ,o ,p are preferably mounted on the same shaft1 and are adjusted relatively to one another in such manner that when the self-induction in one branch1 as ,c1 is maximum1 in the other branch ,d it is minimum4 ,the armatures are rotated in synchronism with the alternations from the source ,a4 ,the winding or position of the armature coils is such that a current in a given direction passed through both armatures would establish in one1 poles similar to those in the adjacent poles of the field1 and in the other1 poles unlike the adjacent field poles1 as indicated by n n s s in the diagram4 ,if the like poles are presented1 as shown in circuit ,d1 the condition is that of a closed secondary upon a primary1 or the position of least inductive resistance2 hence a given alternation of current will pass mainly through ,d4 ,a half revolution of the armatures produces an opposite effect and the succeeding current impulse passes through ,c4 ,using this figure as an illustration1 it is evident that the fields ,n ,m may be permanent magnets or independently excited and the armatures ,o ,p driven1 as in the present case1 so as to produce alternate currents1 which will set up alternately impulses of opposite direction in the two branches ,d ,c1 which in such case would include the armature circuits and translating devices only4 ,in ,fig4 #bbd a plan alternative with that shown in ,fig4 #bbb is illustrated4 ,in the previous case illustrated1 each branch ,c and ,d contained one or more primary coils1 the secondaries of which were periodically short circuited in synchronism with the alternations of current from the main source ,a1 and for this purpose a commutator was employed4 ,the latter may1 however1 be dispensed with and an armature with a closed coil substituted4 ,illustration3 ,,fig4 #bbd4 ,referring to ,fig4 #bbd in one of the branches1 as ,c1 are two coils ,m'1 wound on laminated cores1 and in the other branches ,d are similar coils ,n'4 ,a subdivided or laminated armature ,o'1 carrying a closed coil ,r'1 is rotatably supported between the coils ,m' ,n'1 as shown4 ,in the position shown--that is1 with the coil ,r' parallel with the convolutions of the primaries ,n' ,m'--practically the whole current will pass through branch ,d1 because the self-induction in coils ,m' ,m' is maximum4 ,if1 therefore1 the armature and coil be rotated at a proper speed relatively to the periods or alternations of the source ,a1 the same results are obtained as in the case of ,fig4 #bbb4 ,fig4 #bbe is an instance of what may be called1 in distinction to the others1 a magnetic means of securing the result4 ,v and ,w are two strong permanent magnets provided with armatures ,v' ,w'1 respectively4 ,the armatures are made of thin laminae of soft iron or steel1 and the amount of magnetic metal which they contain is so calculated that they will be fully or nearly saturated by the magnets4 ,around the armatures are coils ,e ,f1 contained1 respectively1 in the circuits ,c and ,d4 ,the connections and electrical conditions in this case are similar to those in ,fig4 #bba1 except that the current source of ,i1 ,fig4 #bba1 is dispensed with and the saturation of the core of coils ,e ,f obtained from the permanent magnets4 ,illustration3 ,,fig4 #bbe4 ,the previous illustrations have all shown the two branches or paths containing the translating or induction devices as in derivation one to the other2 but this is not always necessary4 ,for example1 in ,fig4 #bbf1 ,a is an alternating-current generator2 ,b ,b1 the line wires or circuit4 ,at any given point in the circuit let us form two paths1 as ,d ,d'1 and at another point two paths1 as ,c ,c'4 ,either pair or group of paths is similar to the previous dispositions with the electrical source or induction device in one branch only1 while the two groups taken together form the obvious equivalent of the cases in which an induction device or generator is included in both branches4 ,in one of the paths1 as ,d1 are included the devices to be operated by the current4 ,in the other branch1 as ,d'1 is an induction device that opposes the current impulses of one direction and directs them through the branch ,d4 ,so1 also1 in branch ,c are translating devices ,g1 and in branch ,c' an induction device or its equivalent that diverts through ,c impulses of opposite direction to those diverted by the device in branch ,d'4 ,the diagram shows a special form of induction device for this purpose4 ,j ,j' are the cores1 formed with pole-pieces1 upon which are wound the coils ,m ,n4 ,between these pole-pieces are mounted at right angles to one another the magnetic armatures ,o ,p1 preferably mounted on the same shaft and designed to be rotated in synchronism with the alternations of current4 ,when one of the armatures is in line with the poles or in the position occupied by armature ,p1 the magnetic circuit of the induction device is practically closed2 hence there will be the greatest opposition to the passage of a current through coils ,n ,n4 ,the alternation will therefore pass by way of branch ,d4 ,at the same time1 the magnetic circuit of the other induction device being broken by the position of the armature ,o1 there will be less opposition to the current in coils ,m1 which will shunt the current from branch ,c4 ,a reversal of the current being attended by a shifting of the armatures1 the opposite effect is produced4 ,illustration3 ,,fig4 #bbf4 ,other modifications of these methods are possible1 but need not be pointed out4 ,in all these plans1 it will be observed1 there is developed in one or all of these branches of a circuit from a source of alternating currents1 an active 7as distinguished from a dead7 resistance or opposition to the currents of one sign1 for the purpose of diverting the currents of that sign through the other or another path1 but permitting the currents of opposite sign to pass without substantial opposition4 ,whether the division of the currents or waves of current of opposite sign be effected with absolute precision or not is immaterial1 since it will be sufficient if the waves are only partially diverted or directed1 for in such case the preponderating influence in each branch of the circuit of the waves of one sign secures the same practical results in many if not all respects as though the current were direct and continuous4 ,an alternating and a direct current have been combined so that the waves of one direction or sign were partially or wholly overcome by the direct current2 but by this plan only one set of alternations are utilized1 whereas by the system just described the entire current is rendered available4 ,by obvious applications of this discovery ,mr4 ,tesla is enabled to produce a self-exciting alternating dynamo1 or to operate direct current meters on alternating-current circuits or to run various devices--such as arc lamps--by direct currents in the same circuit with incandescent lamps or other devices operated by alternating currents4 ,it will be observed that if an intermittent counter or opposing force be developed in the branches of the circuit and of higher electromotive force than that of the generator1 an alternating current will result in each branch1 with the waves of one sign preponderating1 while a constantly or uniformly acting opposition in the branches of higher electromotive force than the generator would produce a pulsating current1 which conditions would be1 under some circumstances1 the equivalent of those described4 ,,chapter ,,xxxiv4 ,,condensers ,,with ,,plates ,,in ,,oil4 ,illustration3 ,,fig4 #bbg4 ,illustration3 ,,fig4 #bbh4 ,in experimenting with currents of high frequency and high potential1 ,mr4 ,tesla has found that insulating materials such as glass1 mica1 and in general those bodies which possess the highest specific inductive capacity1 are inferior as insulators in such devices when currents of the kind described are employed compared with those possessing high insulating power1 together with a smaller specific inductive capacity2 and he has also found that it is very desirable to exclude all gaseous matter from the apparatus1 or any access of the same to the electrified surfaces1 in order to prevent heating by molecular bombardment and the loss or injury consequent thereon4 ,he has therefore devised a method to accomplish these results and produce highly efficient and reliable condensers1 by using oil as the dielectric#aa4 ,the plan admits of a particular construction of condenser1 in which the distance between the plates is adjustable1 and of which he takes advantage4 #aa ,mr4 ,tesla's experiments1 as the careful reader of his three lectures will perceive1 have revealed a very important fact which is taken advantage of in this invention4 ,namely1 he has shown that in a condenser a considerable amount of energy may be wasted1 and the condenser may break down merely because gaseous matter is present between the surfaces4 ,a number of experiments are described in the lectures1 which bring out this fact forcibly and serve as a guide in the operation of high tension apparatus4 ,but besides bearing upon this point1 these experiments also throw a light upon investigations of a purely scientific nature and explain now the lack of harmony among the observations of various investigators4 ,mr4 ,tesla shows that in a fluid such as oil the losses are very small as compared with those incurred in a gas4 ,in the accompanying illustrations1 ,fig4 #bbg is a section of a condenser constructed in accordance with this principle and having stationary plates2 and ,fig4 #bbh is a similar view of a condenser with adjustable plates4 ,any suitable box or receptacle ,a may be used to contain the plates or armatures4 ,these latter are designated by ,b and ,c and are connected1 respectively1 to terminals ,d and ,e1 which pass out through the sides of the case4 ,the plates ordinarily are separated by strips of porous insulating material ,f1 which are used merely for the purpose of maintaining them in position4 ,the space within the can is filled with oil ,g4 ,such a condenser will prove highly efficient and will not become heated or permanently injured4 ,in many cases it is desirable to vary or adjust the capacity of a condenser1 and this is provided for by securing the plates to adjustable supports--as1 for example1 to rods ,h--passing through stuffing boxes ,k in the sides of case ,a and furnished with nuts ,l1 the ends of the rods being threaded for engagement with the nuts4 ,it is well known that oils possess insulating properties1 and it has been a common practice to interpose a body of oil between two conductors for purposes of insulation2 but ,mr4 ,tesla believes he has discovered peculiar properties in oils which render them very valuable in this particular form of device4 ,,chapter ,,xxxv4 ,,electrolytic ,,registering ,,meter4 ,an ingenious form of electrolytic meter attributable to ,mr4 ,tesla is one in which a conductor is immersed in a solution1 so arranged that metal may be deposited from the solution or taken away in such a manner that the electrical resistance of the conductor is varied in a definite proportion to the strength of the current the energy of which is to be computed1 whereby this variation in resistance serves as a measure of the energy and also may actuate registering mechanism1 whenever the resistance rises above or falls below certain limits4 ,in carrying out this idea ,mr4 ,tesla employs an electrolytic cell1 through which extend two conductors parallel and in close proximity to each other4 ,these conductors he connects in series through a resistance1 but in such manner that there is an equal difference of potential between them throughout their entire extent4 ,the free ends or terminals of the conductors are connected either in series in the circuit supplying the current to the lamps or other devices1 or in parallel to a resistance in the circuit and in series with the current consuming devices4 ,under such circumstances a current passing through the conductors establishes a difference of potential between them which is proportional to the strength of the current1 in consequence of which there is a leakage of current from one conductor to the other across the solution4 ,the strength of this leakage current is proportional to the difference of potential1 and1 therefore1 in proportion to the strength of the current passing through the conductors4 ,moreover1 as there is a constant difference of potential between the two conductors throughout the entire extent that is exposed to the solution1 the current density through such solution is the same at all corresponding points1 and hence the deposit is uniform along the whole of one of the conductors1 while the metal is taken away uniformly from the other4 ,the resistance of one conductor is by this means diminished1 while that of the other is increased1 both in proportion to the strength of the current passing through the conductors4 ,from such variation in the resistance of either or both of the conductors forming the positive and negative electrodes of the cell1 the current energy expended may be readily computed4 ,figs4 #bbi and #bcj illustrate two forms of such a meter4 ,illustration3 ,,fig4 #bbi4 ,in ,fig4 #bbi ,g designates a direct-current generator4 ,l ,l are the conductors of the circuit extending therefrom4 ,a is a tube of glass1 the ends of which are sealed1 as by means of insulating plugs or caps ,b ,b4 ,c ,c' are two conductors extending through the tube ,a1 their ends passing out through the plugs ,b to terminals thereon4 ,these conductors may be corrugated or formed in other proper ways to offer the desired electrical resistance4 ,r is a resistance connected in series with the two conductors ,c ,c'1 which by their free terminals are connected up in circuit with one of the conductors ,l4 ,the method of using this device and computing by means thereof the energy of the current will be readily understood4 ,first1 the resistances of the two conductors ,c ,c'1 respectively1 are accurately measured and noted4 ,then a known current is passed through the instrument for a given time1 and by a second measurement the increase and diminution of the resistances of the two conductors are respectively taken4 ,from these data the constant is obtained--that is to say1 for example1 the increase of resistance of one conductor or the diminution of the resistance of the other per lamp hour4 ,these two measurements evidently serve as a check1 since the gain of one conductor should equal the loss of the other4 ,a further check is afforded by measuring both wires in series with the resistance1 in which case the resistance of the whole should remain constant4 ,illustration3 ,,fig4 #bcj4 ,in ,fig4 #bcj the conductors ,c ,c' are connected in parallel1 the current device at ,x passing in one branch first through a resistance ,r' and then through conductor ,c1 while on the other branch it passes first through conductor ,c'1 and then through resistance ,r''4 ,the resistances ,r' ,r'' are equal1 as also are the resistances of the conductors ,c ,c'4 ,it is1 moreover1 preferable that the respective resistances of the conductors ,c ,c' should be a known and convenient fraction of the coils or resistances ,r' ,r''4 ,it will be observed that in the arrangement shown in ,fig4 #bcj there is a constant potential difference between the two conductors ,c ,c' throughout their entire length4 ,it will be seen that in both cases illustrated1 the proportionality of the increase or decrease of resistance to the current strength will always be preserved1 for what one conductor gains the other loses1 and the resistances of the conductors ,c ,c' being small as compared with the resistances in series with them4 ,it will be understood that after each measurement or registration of a given variation of resistance in one or both conductors1 the direction of the current should be changed or the instrument reversed1 so that the deposit will be taken from the conductor which has gained and added to that which has lost4 ,this principle is capable of many modifications4 ,for instance1 since there is a section of the circuit--to wit1 the conductor ,c or ,c'--that varies in resistance in proportion to the current strength1 such variation may be utilized1 as is done in many analogous cases1 to effect the operation of various automatic devices1 such as registers4 ,it is better1 however1 for the sake of simplicity to compute the energy by measurements of resistance4 ,the chief advantages of this arrangement are1 first1 that it is possible to read off directly the amount of the energy expended by means of a properly constructed ohm-meter and without resorting to weighing the deposit2 secondly it is not necessary to employ shunts1 for the whole of the current to be measured may be passed through the instrument2 third1 the accuracy of the instrument and correctness of the indications are but slightly affected by changes in temperature4 ,it is also said that such meters have the merit of superior economy and compactness1 as well as of cheapness in construction4 ,electrolytic meters seem to need every auxiliary advantage to make them permanently popular and successful1 no matter how much ingenuity may be shown in their design4 ,,chapter ,,xxxvi4 ,,thermo-,,magnetic ,,motors ,,and ,,pyro-,,magnetic ,,generators4 ,no electrical inventor of the present day dealing with the problems of light and power considers that he has done himself or his opportunities justice until he has attacked the subject of thermo-magnetism4 ,as far back as the beginning of the seventeenth century it was shown by ,dr4 ,william ,gilbert1 the father of modern electricity1 that a loadstone or iron bar when heated to redness loses its magnetism2 and since that time the influence of heat on the magnetic metals has been investigated frequently1 though not with any material or practical result4 ,for a man of ,mr4 ,tesla's inventive ability1 the problems in this field have naturally had no small fascination1 and though he has but glanced at them1 it is to be hoped he may find time to pursue the study deeper and further4 ,for such as he1 the investigation must undoubtedly bear fruit4 ,meanwhile he has worked out one or two operative devices worthy of note4#ab ,he obtains mechanical power by a reciprocating action resulting from the joint operations of heat1 magnetism1 and a spring or weight or other force--that is to say he subjects a body magnetized by induction or otherwise to the action of heat until the magnetism is sufficiently neutralized to allow a weight or spring to give motion to the body and lessen the action of the heat1 so that the magnetism may be sufficiently restored to move the body in the opposite direction1 and again subject the same to the demagnetizing power of the heat4 #ab ,it will1 of course1 be inferred from the nature of these devices that the vibration obtained in this manner is very slow owing to the inability of the iron to follow rapid changes in temperature4 ,in an interview with ,mr4 ,tesla on this subject1 the compiler learned of an experiment which will interest students4 ,a simple horseshoe magnet is taken and a piece of sheet iron bent in the form of an ,l is brought in contact with one of the poles and placed in such a position that it is kept in the attraction of the opposite pole delicately suspended4 ,a spirit lamp is placed under the sheet iron piece and when the iron is heated to a certain temperature it is easily set in vibration oscillating as rapidly as #djj to #ejj times a minute4 ,the experiment is very easily performed and is interesting principally on account of the very rapid rate of vibration4 ,use is made of either an electro-magnet or a permanent magnet1 and the heat is directed against a body that is magnetized by induction1 rather than directly against a permanent magnet1 thereby avoiding the loss of magnetism that might result in the permanent magnet by the action of heat4 ,mr4 ,tesla also provides for lessening the volume of the heat or for intercepting the same during that portion of the reciprocation in which the cooling action takes place4 ,in the diagrams are shown some of the numerous arrangements that may be made use of in carrying out this idea4 ,in all of these figures the magnet-poles are marked ,n ,s1 the armature ,a1 the ,bunsen burner or other source of heat ,h1 the axis of motion ,m1 and the spring or the equivalent thereof--namely1 a weight--is marked ,w4 ,illustration3 ,,fig4 #bcb4 ,illustration3 ,,fig4 #bca4 ,illustration3 ,,fig4 #bcc4 ,in ,fig4 #bca the permanent magnet ,n is connected with a frame1 ,f1 supporting the axis ,m1 from which the arm ,p hangs1 and at the lower end of which the armature ,a is supported4 ,the stops #b and #c limit the extent of motion1 and the spring ,w tends to draw the armature ,a away from the magnet ,n4 ,it will now be understood that the magnetism of ,n is sufficient to overcome the spring ,w and draw the armature ,a toward the magnet ,n4 ,the heat acting upon the armature ,a neutralizes its induced magnetism sufficiently for the spring ,w to draw the armature ,a away from the magnet ,n and also from the heat at ,h4 ,the armature now cools1 and the attraction of the magnet ,n overcomes the spring ,w and draws the armature ,a back again above the burner ,h1 so that the same is again heated and the operations are repeated4 ,the reciprocating movements thus obtained are employed as a source of mechanical power in any desired manner4 ,usually a connecting-rod to a crank upon a fly-wheel shaft would be made use of1 as indicated in ,fig4 #bdj4 ,illustration3 ,,fig4 #bcd4 ,illustration3 ,,fig4 #bcf4 ,illustration3 ,,fig4 #bce4 ,fig4 #bcb represents the same parts as before described2 but an electro-magnet is illustrated in place of a permanent magnet4 ,the operations1 however1 are the same4 ,in ,fig4 #bcc are shown the same parts as in ,figs4 #bca and #bcb1 but they are differently arranged4 ,the armature ,a1 instead of swinging1 is stationary and held by arm ,p'1 and the core ,n ,s of the electro-magnet is made to swing within the helix ,q1 the core being suspended by the arm ,p from the pivot ,m4 ,a shield1 ,r1 is connected with the magnet-core and swings with it1 so that after the heat has demagnetized the armature ,a to such an extent that the spring ,w draws the core ,n ,s away from the armature ,a1 the shield ,r comes between the flame ,h and armature ,a1 thereby intercepting the action of the heat and allowing the armature to cool1 so that the magnetism1 again preponderating1 causes the movement of the core ,n ,s toward the armature ,a and the removal of the shield ,r from above the flame1 so that the heat again acts to lessen or neutralize the magnetism4 ,a rotary or other movement may be obtained from this reciprocation4 ,fig4 #bcd corresponds in every respect with ,fig4 #bcc1 except that a permanent horseshoe-magnet1 ,n ,s is represented as taking the place of the electro-magnet in ,fig4 #bcc4 ,in ,fig4 #bce is shown a helix1 ,q1 with an armature adapted to swing toward or from the helix4 ,in this case there may be a soft-iron core in the helix1 or the armature may assume the form of a solenoid core1 there being no permanent core within the helix4 ,illustration3 ,,fig4 #bcg4 ,illustration3 ,,fig4 #bch4 ,illustration3 ,,fig4 #bci4 ,fig4 #bcf is an end view1 and ,fig4 #bcg a plan view1 illustrating the method as applied to a swinging armature1 ,a1 and a stationary permanent magnet1 ,n ,s4 ,in this instance ,mr4 ,tesla applies the heat to an auxiliary armature or keeper1 ,t1 which is adjacent to and preferably in direct contact with the magnet4 ,this armature ,t1 in the form of a plate of sheet-iron1 extends across from one pole to the other and is of sufficient section to practically form a keeper for the magnet1 so that when the armature ,t is cool nearly all the lines of force pass over the same and very little free magnetism is exhibited4 ,then the armature ,a1 which swings freely on the pivots ,m in front of the poles ,n ,s1 is very little attracted and the spring ,w pulls the same way from the poles into the position indicated in the diagram4 ,the heat is directed upon the iron plate ,t at some distance from the magnet1 so as to allow the magnet to keep comparatively cool4 ,this heat is applied beneath the plate by means of the burners ,h1 and there is a connection from the armature ,a or its pivot to the gas-cock #f1 or other device for regulating the heat4 ,the heat acting upon the middle portion of the plate ,t1 the magnetic conductivity of the heated portion is diminished or destroyed1 and a great number of the lines of force are deflected over the armature ,a1 which is now powerfully attracted and drawn into line1 or nearly so1 with the poles ,n ,s4 ,in so doing the cock #f is nearly closed and the plate ,t cools1 the lines of force are again deflected over the same1 the attraction exerted upon the armature ,a is diminished1 and the spring ,w pulls the same away from the magnet into the position shown by full lines1 and the operations are repeated4 ,the arrangement shown in ,fig4 #bcf has the advantages that the magnet and armature are kept cool and the strength of the permanent magnet is better preserved1 as the magnetic circuit is constantly closed4 ,in the plan view1 ,fig4 #bch1 is shown a permanent magnet and keeper plate1 ,t1 similar to those in ,figs4 #bcf and #bcg1 with the burners ,h for the gas beneath the same2 but the armature is pivoted at one end to one pole of the magnet and the other end swings toward and from the other pole of the magnet4 ,the spring ,w acts against a lever arm that projects from the armature1 and the supply of heat has to be partly cut off by a connection to the swinging armature1 so as to lessen the heat acting upon the keeper plate when the armature ,a has been attracted4 ,illustration3 ,,fig4 #bdj4 ,illustration3 ,,fig4 #bda4 ,fig4 #bci is similar to ,fig4 #bch1 except that the keeper ,t is not made use of and the armature itself swings into and out of the range of the intense action of the heat from the burner ,h4 ,fig4 #bdj is a diagram similar to ,fig4 #bca1 except that in place of using a spring and stops1 the armature is shown as connected by a link1 to the crank of a fly-wheel1 so that the fly-wheel will be revolved as rapidly as the armature can be heated and cooled to the necessary extent4 ,a spring may be used in addition1 as in ,fig4 #bca4 ,in ,fig4 #bda the armatures ,a ,a are connected by a link1 so that one will be heating while the other is cooling1 and the attraction exerted to move the cooled armature is availed of to draw away the heated armature instead of using a spring4 ,mr4 ,tesla has also devoted his attention to the development of a pyromagnetic generator of electricity#ac based upon the following laws3 ,first1 that electricity or electrical energy is developed in any conducting body by subjecting such body to a varying magnetic influence2 and second1 that the magnetic properties of iron or other magnetic substance may be partially or entirely destroyed or caused to disappear by raising it to a certain temperature1 but restored and caused to reappear by again lowering its temperature to a certain degree4 ,these laws may be applied in the production of electrical currents in many ways1 the principle of which is in all cases the same1 viz41 to subject a conductor to a varying magnetic influence1 producing such variations by the application of heat1 or1 more strictly speaking1 by the application or action of a varying temperature upon the source of the magnetism4 ,this principle of operation may be illustrated by a simple experiment3 ,place end to end1 and preferably in actual contact1 a permanently magnetized steel bar and a strip or bar of soft iron4 ,around the end of the iron bar or plate wind a coil of insulated wire4 ,then apply to the iron between the coil and the steel bar a flame or other source of heat which will be capable of raising that portion of the iron to an orange red1 or a temperature of about #fjj deg4 centigrade4 ,when this condition is reached1 the iron somewhat suddenly loses its magnetic properties1 if it be very thin1 and the same effect is produced as though the iron had been moved away from the magnet or the heated section had been removed4 ,this change of position1 however1 is accompanied by a shifting of the magnetic lines1 or1 in other words1 by a variation in the magnetic influence to which the coil is exposed1 and a current in the coil is the result4 ,then remove the flame or in any other way reduce the temperature of the iron4 ,the lowering of its temperature is accompanied by a return of its magnetic properties1 and another change of magnetic conditions occurs1 accompanied by a current in an opposite direction in the coil4 ,the same operation may be repeated indefinitely1 the effect upon the coil being similar to that which would follow from moving the magnetized bar to and from the end of the iron bar or plate4 #ac ,the chief point to be noted is that ,mr4 ,tesla attacked this problem in a way which was1 from the standpoint of theory1 and that of an engineer1 far better than that from which some earlier trials in this direction started4 ,the enlargement of these ideas will be found in ,mr4 ,tesla's work on the pyromagnetic generator1 treated in this chapter4 ,the chief effort of the inventor was to economize the heat1 which was accomplished by inclosing the iron in a source of heat well insulated1 and by cooling the iron by means of steam1 utilizing the steam over again4 ,the construction also permits of more rapid magnetic changes per unit of time1 meaning larger output4 ,the device illustrated below is a means of obtaining this result1 the features of novelty in the invention being1 first1 the employment of an artificial cooling device1 and1 second1 inclosing the source of heat and that portion of the magnetic circuit exposed to the heat and artificially cooling the heated part4 ,these improvements are applicable generally to the generators constructed on the plan above described--that is to say1 we may use an artificial cooling device in conjunction with a variable or varied or uniform source of heat4 ,illustration3 ,,fig4 #bdb4 ,illustration3 ,,fig4 #bdc4 ,fig4 #bdb is a central vertical longitudinal section of the complete apparatus and ,fig4 #bdc is a cross-section of the magnetic armature-core of the generator4 ,let ,a represent a magnetized core or permanent magnet the poles of which are bridged by an armature-core composed of a casing or shell ,b inclosing a number of hollow iron tubes ,c4 ,around this core are wound the conductors ,e ,e'1 to form the coils in which the currents are developed4 ,in the circuits of these coils are current-consuming devices1 as ,f ,f'4 ,d is a furnace or closed fire-box1 through which the central portion of the core ,b extends4 ,above the fire is a boiler ,k1 containing water4 ,the flue ,l from the fire-box may extend up through the boiler4 ,g is a water-supply pipe1 and ,h is the steam-exhaust pipe1 which communicates with all the tubes ,c in the armature ,b1 so that steam escaping from the boiler will pass through the tubes4 ,in the steam-exhaust pipe ,h is a valve ,v1 to which is connected the lever ,i1 by the movement of which the valve is opened or closed4 ,in such a case as this the heat of the fire may be utilized for other purposes after as much of it as may be needed has been applied to heating the core ,b4 ,there are special advantages in the employment of a cooling device1 in that the metal of the core ,b is not so quickly oxidized4 ,moreover1 the difference between the temperature of the applied heat and of the steam1 air1 or whatever gas or fluid be applied as the cooling medium1 may be increased or decreased at will1 whereby the rapidity of the magnetic changes or fluctuations may be regulated4 ,,chapter ,,xxxvii4 ,,anti-,,sparking ,,dynamo ,,brush ,,and ,,commutator4 ,in direct current dynamos of great electromotive force--such1 for instance1 as those used for arc lighting--when one commutator bar or plate comes out of contact with the collecting-brush a spark is apt to appear on the commutator4 ,this spark may be due to the break of the complete circuit1 or to a shunt of low resistance formed by the brush between two or more commutator-bars4 ,in the first case the spark is more apparent1 as there is at the moment when the circuit is broken a discharge of the magnets through the field helices1 producing a great spark or flash which causes an unsteady current1 rapid wear of the commutator bars and brushes1 and waste of power4 ,the sparking may be reduced by various devices1 such as providing a path for the current at the moment when the commutator segment or bar leaves the brush1 by short-circuiting the field-helices1 by increasing the number of the commutator-bars1 or by other similar means2 but all these devices are expensive or not fully available1 and seldom attain the object desired4 ,to prevent this sparking in a simple manner1 ,mr4 ,tesla some years ago employed with the commutator-bars and intervening insulating material1 mica1 asbestos paper or other insulating and incombustible material1 arranged to bear on the surface of the commutator1 near to and behind the brush4 ,in the drawings1 ,fig4 #bdd is a section of a commutator with an asbestos insulating device2 and ,fig4 #bde is a similar view1 representing two plates of mica upon the back of the brush4 ,in #bdd1 ,c represents the commutator and intervening insulating material2 ,b ,b1 the brushes4 d d are sheets of asbestos paper or other suitable non-conducting material4 f f are springs1 the pressure of which may be adjusted by means of the screws g g4 ,in ,fig4 #bde a simple arrangement is shown with two plates of mica or other material4 ,it will be seen that whenever one commutator segment passes out of contact with the brush1 the formation of the arc will be prevented by the intervening insulating material coming in contact with the insulating material on the brush4 ,illustration3 ,,fig4 #bdd4 ,illustration3 ,,fig4 #bde4 ,asbestos paper or cloth impregnated with zinc-oxide1 magnesia1 zirconia1 or other suitable material1 may be used1 as the paper and cloth are soft1 and serve at the same time to wipe and polish the commutator2 but mica or any other suitable material can be employed1 provided the material be an insulator or a bad conductor of electricity4 ,a few years later ,mr4 ,tesla turned his attention again to the same subject1 as1 perhaps1 was very natural in view of the fact that the commutator had always been prominent in his thoughts1 and that so much of his work was even aimed at dispensing with it entirely as an objectionable and unnecessary part of dynamos and motors4 ,in these later efforts to remedy commutator troubles1 ,mr4 ,tesla constructs a commutator and the collectors therefor in two parts mutually adapted to one another1 and1 so far as the essential features are concerned1 alike in mechanical structure4 ,selecting as an illustration a commutator of two segments adapted for use with an armature the coils or coil of which have but two free ends1 connected respectively to the segments1 the bearing-surface is the face of a disc1 and is formed of two metallic quadrant segments and two insulating segments of the same dimensions1 and the face of the disc is smoothed off1 so that the metal and insulating segments are flush4 ,the part which takes the place of the usual brushes1 or the collector1 is a disc of the same character as the commutator and has a surface similarly formed with two insulating and two metallic segments4 ,these two parts are mounted with their faces in contact and in such manner that the rotation of the armature causes the commutator to turn upon the collector1 whereby the currents induced in the coils are taken off by the collector segments and thence conveyed off by suitable conductors leading from the collector segments4 ,this is the general plan of the construction adopted4 ,aside from certain adjuncts1 the nature and functions of which are set forth later1 this means of commutation will be seen to possess many important advantages4 ,in the first place the short-circuiting and the breaking of the armature coil connected to the commutator-segments occur at the same instant1 and from the nature of the construction this will be done with the greatest precision2 secondly1 the duration of both the break and of the short circuit will be reduced to a minimum4 ,the first results in a reduction which amounts practically to a suppression of the spark1 since the break and the short circuit produce opposite effects in the armature-coil4 ,the second has the effect of diminishing the destructive effect of a spark1 since this would be in a measure proportional to the duration of the spark2 while lessening the duration of the short circuit obviously increases the efficiency of the machine4 ,illustration3 ,,fig4 #bdf4 ,illustration3 ,,fig4 #bdg4 ,the mechanical advantages will be better understood by referring to the accompanying diagrams1 in which ,fig4 #bdf is a central longitudinal section of the end of a shaft with the improved commutator carried thereon4 ,fig4 #bdg is a view of the inner or bearing face of the collector4 ,fig4 #bdh is an end view from the armature side of a modified form of commutator4 ,figs4 #bdi and #bej are views of details of ,fig4 #bdh4 ,fig4 #bea is a longitudinal central section of another modification1 and ,fig4 #beb is a sectional view of the same4 ,a is the end of the armature-shaft of a dynamo-electric machine or motor4 ,a' is a sleeve of insulating material around the shaft1 secured in place by a screw1 a'4 ,illustration3 ,,fig4 #bdh4 ,illustration3 ,,fig4 #bdi4 ,illustration3 ,,fig4 #bej4 ,the commutator proper is in the form of a disc which is made up of four segments ,d ,d' ,g ,g'1 similar to those shown in ,fig4 #bdh4 ,two of these segments1 as ,d ,d'1 are of metal and are in electrical connection with the ends of the coils on the armature4 ,the other two segments are of insulating material4 ,the segments are held in place by a band1 ,b1 of insulating material4 ,the disc is held in place by friction or by screws1 g' g'1 ,fig4 #bdh1 which secure the disc firmly to the sleeve ,a'4 ,the collector is made in the same form as the commutator4 ,it is composed of the two metallic segments ,e ,e' and the two insulating segments ,f ,f'1 bound together by a band1 ,c4 ,the metallic segments ,e ,e' are of the same or practically the same width or extent as the insulating segments or spaces of the commutator4 ,the collector is secured to a sleeve1 ,b'1 by screws g g1 and the sleeve is arranged to turn freely on the shaft ,a4 ,the end of the sleeve ,b' is closed by a plate1 f1 upon which presses a pivot-pointed screw1 h1 adjustable in a spring1 ,h1 which acts to maintain the collector in close contact with the commutator and to compensate for the play of the shaft4 ,the collector is so fixed that it cannot turn with the shaft4 ,for example1 the diagram shows a slotted plate1 ,k1 which is designed to be attached to a stationary support1 and an arm extending from the collector and carrying a clamping screw1 ,l1 by which the collector may be adjusted and set to the desired position4 ,mr4 ,tesla prefers the form shown in ,figs4 #bdf and #bdg to fit the insulating segments of both commutator and collector loosely and to provide some means--as1 for example1 light springs1 e e1 secured to the bands ,a' ,b'1 respectively1 and bearing against the segments--to exert a light pressure upon them and keep them in close contact and to compensate for wear4 ,the metal segments of the commutator may be moved forward by loosening the screw a'4 ,the line wires are fed from the metal segments of the collector1 being secured thereto in any convenient manner1 the plan of connections being shown as applied to a modified form of the commutator in ,fig4 #bea4 ,the commutator and the collector in thus presenting two flat and smooth bearing surfaces prevent most effectually by mechanical action the occurrence of sparks4 ,the insulating segments are made of some hard material capable of being polished and formed with sharp edges4 ,such materials as glass1 marble1 or soapstone may be advantageously used4 ,the metal segments are preferably of copper or brass2 but they may have a facing or edge of durable material--such as platinum or the like--where the sparks are liable to occur4 ,illustration3 ,,fig4 #bea4 ,illustration3 ,,fig4 #beb4 ,in ,fig4 #bdh a somewhat modified form of the invention is shown1 a form designed to facilitate the construction and replacing of the parts4 ,in this modification the commutator and collector are made in substantially the same manner as previously described1 except that the bands ,b ,c are omitted4 ,the four segments of each part1 however1 are secured to their respective sleeves by screws g' g'1 and one edge of each segment is cut away1 so that small plates a b may be slipped into the spaces thus formed4 ,of these plates a a are of metal1 and are in contact with the metal segments ,d ,d'1 respectively4 ,the other two1 b b1 are of glass or marble1 and they are all better square1 as shown in ,figs4 #bdi and #bej1 so that they may be turned to present new edges should any edge become worn by use4 ,light springs d bear upon these plates and press those in the commutator toward those in the collector1 and insulating strips c c are secured to the periphery of the discs to prevent the blocks from being thrown out by centrifugal action4 ,these plates are1 of course1 useful at those edges of the segments only where sparks are liable to occur1 and1 as they are easily replaced1 they are of great advantage4 ,it is considered best to coat them with platinum or silver4 ,in ,figs4 #bea and #beb is shown a construction where1 instead of solid segments1 a fluid is employed4 ,in this case the commutator and collector are made of two insulating discs1 ,s ,t1 and in lieu of the metal segments a space is cut out of each part1 as at ,r ,r'1 corresponding in shape and size to a metal segment4 ,the two parts are fitted smoothly and the collector ,t held by the screw h and spring ,h against the commutator ,s4 ,as in the other cases1 the commutator revolves while the collector remains stationary4 ,the ends of the coils are connected to binding-posts s s1 which are in electrical connection with metal plates t t within the recesses in the two parts ,s ,t4 ,these chambers or recesses are filled with mercury1 and in the collector part are tubes ,w ,w1 with screws w w1 carrying springs ,x and pistons ,x'1 which compensate for the expansion and contraction of the mercury under varying temperatures1 but which are sufficiently strong not to yield to the pressure of the fluid due to centrifugal action1 and which serve as binding-posts4 ,in all the above cases the commutators are adapted for a single coil1 and the device is particularly suited to such purposes4 ,the number of segments may be increased1 however1 or more than one commutator used with a single armature4 ,although the bearing-surfaces are shown as planes at right angles to the shaft or axis1 it is evident that in this particular the construction may be very greatly modified4 ,,chapter ,,xxxviii4 ,,auxiliary ,,brush ,,regulation ,,of ,,direct ,,current ,,dynamos4 ,an interesting method devised by ,mr4 ,tesla for the regulation of direct current dynamos1 is that which has come to be known as the third brush method4 ,in machines of this type1 devised by him as far back as #ahhe1 he makes use of two main brushes to which the ends of the field magnet coils are connected1 an auxiliary brush1 and a branch or shunt connection from an intermediate point of the field wire to the auxiliary brush4#ad #ad ,the compiler has learned partially from statements made on several occasions in journals and partially by personal inquiry of ,mr4 ,tesla1 that a great deal of work in this interesting line is unpublished4 ,in these inventions as will be seen1 the brushes are automatically shifted1 but in the broad method barely suggested here the regulation is effected without any change in the position of the brushes4 ,this auxiliary brush invention1 it will be remembered1 was very much discussed a few years ago1 and it may be of interest that this work of ,mr4 ,tesla1 then unknown in this field1 is now brought to light4 ,the relative positions of the respective brushes are varied1 either automatically or by hand1 so that the shunt becomes inoperative when the auxiliary brush has a certain position upon the commutator2 but when the auxiliary brush is moved in its relation to the main brushes1 or the latter are moved in their relation to the auxiliary brush1 the electric condition is disturbed and more or less of the current through the field-helices is diverted through the shunt or a current is passed over the shunt to the field-helices4 ,by varying the relative position upon the commutator of the respective brushes automatically in proportion to the varying electrical conditions of the working-circuit1 the current developed can be regulated in proportion to the demands in the working-circuit4 ,fig4 #bec is a diagram illustrating the invention1 showing one core of the field-magnets with one helix wound in the same direction throughout4 ,figs4 #bed and #bee are diagrams showing one core of the field-magnets with a portion of the helices wound in opposite directions4 ,figs4 #bef and #beg are diagrams illustrating the electric devices that may be employed for automatically adjusting the brushes1 and ,fig4 #beh is a diagram illustrating the positions of the brushes when the machine is being energized at the start4 a and b are the positive and negative brushes of the main or working-circuit1 and c the auxiliary brush4 ,the working-circuit ,d extends from the brushes a and b1 as usual1 and contains electric lamps or other devices1 ,d'1 either in series or in multiple arc4 ,m ,m' represent the field-helices1 the ends of which are connected to the main brushes a and b4 ,the branch or shunt wire c' extends from the auxiliary brush c to the circuit of the field-helices1 and is connected to the same at an intermediate point1 x4 ,illustration3 ,,fig4 #bec4 ,h represents the commutator1 with the plates of ordinary construction4 ,when the auxiliary brush c occupies such a position upon the commutator that the electro-motive force between the brushes a and c is to the electro-motive force between the brushes c and b as the resistance of the circuit a ,m c' c ,a is to the resistance of the circuit b ,m' c' c ,b1 the potentials of the points x and ,y will be equal1 and no current will flow over the auxiliary brush2 but when the brush c occupies a different position the potentials of the points x and ,y will be different1 and a current will flow over the auxiliary brush to and from the commutator1 according to the relative position of the brushes4 ,if1 for instance1 the commutator-space between the brushes a and c1 when the latter is at the neutral point1 is diminished1 a current will flow from the point ,y over the shunt c to the brush b1 thus strengthening the current in the part ,m'1 and partly neutralizing the current in part ,m2 but if the space between the brushes a and c is increased1 the current will flow over the auxiliary brush in an opposite direction1 and the current in ,m will be strengthened1 and in ,m'1 partly neutralized4 ,by combining with the brushes a1 b1 and c any usual automatic regulating mechanism1 the current developed can be regulated in proportion to the demands in the working circuit4 ,the parts ,m and ,m' of the field wire may be wound in the same direction4 ,in this case they are arranged as shown in ,fig4 #bec2 or the part ,m may be wound in the opposite direction1 as shown in ,figs4 #bed and #bee4 ,illustration3 ,,fig4 #bed4 ,it will be apparent that the respective cores of the field-magnets are subjected to neutralizing or intensifying effects of the current in the shunt through c'1 and the magnetism of the cores will be partially neutralized1 or the points of greatest magnetism shifted1 so that it will be more or less remote from or approaching to the armature1 and hence the aggregate energizing actions of the field magnets on the armature will be correspondingly varied4 ,in the form indicated in ,fig4 #bec the regulation is effected by shifting the point of greatest magnetism1 and in ,figs4 #bed and #bee the same effect is produced by the action of the current in the shunt passing through the neutralizing helix4 ,the relative positions of the respective brushes may be varied by moving the auxiliary brush1 or the brush c may remain stationary and the core ,p be connected to the main-brush holder ,a1 so as to adjust the brushes a b in their relation to the brush c4 ,if1 however1 an adjustment is applied to all the brushes1 as seen in ,fig4 #beg1 the solenoid should be connected to both a and c1 so as to move them toward or away from each other4 ,there are several known devices for giving motion in proportion to an electric current4 ,in ,figs4 #bef and #beg the moving cores are shown as convenient devices for obtaining the required extent of motion with very slight changes in the current passing through the helices4 ,it is understood that the adjustment of the main brushes causes variations in the strength of the current independently of the relative position of those brushes to the auxiliary brush4 ,in all cases the adjustment should be such that no current flows over the auxiliary brush when the dynamo is running with its normal load4 ,in ,figs4 #bef and #beg ,a ,a indicate the main-brush holder1 carrying the main brushes1 and ,c the auxiliary-brush holder1 carrying the auxiliary brush4 ,these brush-holders are movable in arcs concentric with the centre of the commutator-shaft4 ,an iron piston1 ,p1 of the solenoid ,s1 ,fig4 #bef1 is attached to the auxiliary-brush holder ,c4 ,the adjustment is effected by means of a spring and screw or tightener4 ,in ,fig4 #beg instead of a solenoid1 an iron tube inclosing a coil is shown4 ,the piston of the coil is attached to both brush-holders ,a ,a and ,c4 ,when the brushes are moved directly by electrical devices1 as shown in ,figs4 #bef and #beg1 these are so constructed that the force exerted for adjusting is practically uniform through the whole length of motion4 ,illustration3 ,,fig4 #bee4 ,it is true that auxiliary brushes have been used in connection with the helices of the field-wire2 but in these instances the helices receive the entire current through the auxiliary brush or brushes1 and these brushes could not be taken off without breaking the circuit through the field4 ,these brushes cause1 moreover1 heavy sparking at the commutator4 ,in the present case the auxiliary brush causes very little or no sparking1 and can be taken off without breaking the circuit through the field-helices4 ,the arrangement has1 besides1 the advantage of facilitating the self-excitation of the machine in all cases where the resistance of the field-wire is very great comparatively to the resistance of the main circuit at the start--for instance1 on arc-light machines4 ,in this case the auxiliary brush c is placed near to1 or better still in contact with1 the brush b1 as shown in ,fig4 #beh4 ,in this manner the part ,m' is completely cut out1 and as the part ,m has a considerably smaller resistance than the whole length of the field-wire the machine excites itself1 whereupon the auxiliary brush is shifted automatically to its normal position4 ,illustration3 ,,fig4 #bef4 ,illustration3 ,,fig4 #beg4 ,in a further method devised by ,mr4 ,tesla1 one or more auxiliary brushes are employed1 by means of which a portion or the whole of the field coils is shunted4 ,according to the relative position upon the commutator of the respective brushes more or less current is caused to pass through the helices of the field1 and the current developed by the machine can be varied at will by varying the relative positions of the brushes4 ,illustration3 ,,fig4 #beh4 ,in ,fig4 #bei1 a and b are the positive and negative brushes of the main circuit1 and c an auxiliary brush4 ,the main circuit ,d extends from the brushes a and b1 as usual1 and contains the helices ,m of the field wire and the electric lamps or other working devices4 ,the auxiliary brush c is connected to the point x of the main circuit by means of the wire c'4 ,h is a commutator of ordinary construction4 ,it will have been seen from what was said already that when the electro-motive force between the brushes a and c is to the electromotive force between the brushes c and b as the resistance of the circuit a ,m c' c ,a is to the resistance of the circuit b ,c ,b c c' ,d1 the potentials of the points x and y will be equal1 and no current will pass over the auxiliary brush c2 but if that brush occupies a different position relatively to the main brushes the electric condition is disturbed1 and current will flow either from y to x or from x to y1 according to the relative position of the brushes4 ,in the first case the current through the field-helices will be partly neutralized and the magnetism of the field magnets will be diminished4 ,in the second case the current will be increased and the magnets gain strength4 ,by combining with the brushes at a b c any automatic regulating mechanism1 the current developed can be regulated automatically in proportion to the demands of the working circuit4 ,in ,figs4 #bfd and #bfe some of the automatic means are represented that maybe used for moving the brushes4 ,the core ,p1 ,fig4 #bfd1 of the solenoid-helix ,s is connected with the brush a to move the same1 and in ,fig4 #bfe the core ,p is shown as within the helix ,s1 and connected with brushes a and c1 so as to move the same toward or from each other1 according to the strength of the current in the helix1 the helix being within an iron tube1 ,s'1 that becomes magnetized and increases the action of the solenoid4 ,in practice it is sufficient to move only the auxiliary brush1 as shown in ,fig4 #bfd1 as the regulation is very sensitive to the slightest changes2 but the relative position of the auxiliary brush to the main brushes may be varied by moving the main brushes1 or both main and auxiliary brushes may be moved1 as illustrated in ,fig4 #bfe4 ,in the latter two cases1 it will be understood1 the motion of the main brushes relatively to the neutral line of the machine causes variations in the strength of the current independently of their relative position to the auxiliary brush4 ,in all cases the adjustment may be such that when the machine is running with the ordinary load1 no current flows over the auxiliary brush4 ,the field helices may be connected1 as shown in ,fig4 #bei1 or a part of the field helices may be in the outgoing and the other part in the return circuit1 and two auxiliary brushes may be employed as shown in ,figs4 #bfa and #bfb4 ,instead of shunting the whole of the field helices1 a portion only of such helices may be shunted1 as shown in ,figs4 #bfj and #bfb4 ,the arrangement shown in ,fig4 #bfb is advantageous1 as it diminishes the sparking upon the commutator1 the main circuit being closed through the auxiliary brushes at the moment of the break of the circuit at the main brushes4 ,illustration3 ,,fig4 #bei4 ,illustration3 ,,fig4 #bfj4 ,illustration3 ,,fig4 #bfa4 ,illustration3 ,,fig4 #bfb4 ,illustration3 ,,fig4 #bfc4 ,the field helices may be wound in the same direction1 or a part may be wound in opposite directions4 ,the connection between the helices and the auxiliary brush or brushes may be made by a wire of small resistance1 or a resistance may be interposed 7,r1 ,fig4 #bfc17 between the point x and the auxiliary brush or brushes to divide the sensitiveness when the brushes are adjusted4 ,illustration3 ,,fig4 #bfd4 ,illustration3 ,,fig4 #bfe4 ,the accompanying sketches also illustrate improvements made by ,mr4 ,tesla in the mechanical devices used to effect the shifting of the brushes1 in the use of an auxiliary brush4 ,fig4 #bff is an elevation of the regulator with the frame partly in section2 and ,fig4 #bfg is a section at the line x x1 ,fig4 #bff4 ,c is the commutator2 ,b and ,b'1 the brush-holders1 ,b carrying the main brushes a a'1 and ,b' the auxiliary or shunt brushes b b4 ,the axis of the brush-holder ,b is supported by two pivot-screws1 p p4 ,the other brush-holder1 ,b'1 has a sleeve1 d1 and is movable around the axis of the brush-holder ,b4 ,in this way both brush-holders can turn very freely1 the friction of the parts being reduced to a minimum4 ,over the brush-holders is mounted the solenoid ,s1 which rests upon a forked column1 c4 ,this column also affords a support for the pivots p p1 and is fastened upon a solid bracket or projection1 ,p1 which extends from the base of the machine1 and is cast in one piece with the same4 ,the brush-holders ,b ,b' are connected by means of the links e e and the cross-piece ,f to the iron core ,i1 which slides freely in the tube ,t of the solenoid4 ,the iron core ,i has a screw1 s1 by means of which it can be raised and adjusted in its position relatively to the solenoid1 so that the pull exerted upon it by the solenoid is practically uniform through the whole length of motion which is required to effect the regulation4 ,in order to effect the adjustment with greater precision1 the core ,i is provided with a small iron screw1 s'4 ,the core being first brought very nearly in the required position relatively to the solenoid by means of the screw s1 the small screw s' is then adjusted until the magnetic attraction upon the core is the same when the core is in any position4 ,a convenient stop1 t1 serves to limit the upward movement of the iron core4 ,to check somewhat the movement of the core ,i1 a dash-pot1 ,k1 is used4 ,the piston ,l of the dash-pot is provided with a valve1 ,v1 which opens by a downward pressure and allows an easy downward movement of the iron core ,i1 but closes and checks the movement of the core when it is pulled up by the action of the solenoid4 ,to balance the opposing forces1 the weight of the moving parts1 and the pull exerted by the solenoid upon the iron core1 the weights ,w ,w may be used4 ,the adjustment is such that when the solenoid is traversed by the normal current it is just strong enough to balance the downward pull of the parts4 ,illustration3 ,,fig4 #bff4 ,illustration3 ,,fig4 #bfg4 ,the electrical circuit-connections are substantially the same as indicated in the previous diagrams1 the solenoid being in series with the circuit when the translating devices are in series1 and in shunt when the devices are in multiple arc4 ,the operation of the device is as follows3 ,when upon a decrease of the resistance of the circuit or for some other reason1 the current is increased1 the solenoid ,s gains in strength and pulls up the iron core ,i1 thus shifting the main brushes in the direction of rotation and the auxiliary brushes in the opposite way4 ,this diminishes the strength of the current until the opposing forces are balanced and the solenoid is traversed by the normal current2 but if from any cause the current in the circuit is diminished1 then the weight of the moving parts overcomes the pull of the solenoid1 the iron core ,i descends1 thus shifting the brushes the opposite way and increasing the current to the normal strength4 ,the dash-pot connected to the iron core ,i may be of ordinary construction2 but it is better1 especially in machines for arc lights1 to provide the piston of the dash-pot with a valve1 as indicated in the diagrams4 ,this valve permits a comparatively easy downward movement of the iron core1 but checks its movement when it is drawn up by the solenoid4 ,such an arrangement has the advantage that a great number of lights may be put on without diminishing the light-power of the lamps in the circuit1 as the brushes assume at once the proper position4 ,when lights are cut out1 the dash-pot acts to retard the movement2 but if the current is considerably increased the solenoid gets abnormally strong and the brushes are shifted instantly4 ,the regulator being properly adjusted1 lights or other devices may be put on or out with scarcely any perceptible difference4 ,it is obvious that instead of the dash-pot any other retarding device may be used4 ,,chapter ,,xxxix4 ,,improvement ,,in ,,the ,,construction ,,of ,,dynamos ,,and ,,motors4 ,this invention of ,mr4 ,tesla is an improvement in the construction of dynamo or magneto electric machines or motors1 consisting in a novel form of frame and field magnet which renders the machine more solid and compact as a structure1 which requires fewer parts1 and which involves less trouble and expense in its manufacture4 ,it is applicable to generators and motors generally1 not only to those which have independent circuits adapted for use in the ,tesla alternating current system1 but to other continuous or alternating current machines of the ordinary type generally used4 ,fig4 #bfh shows the machine in side elevation4 ,fig4 #bfi is a vertical sectional view of the field magnets and frame and an end view of the armature2 and ,fig4 #bgj is a plan view of one of the parts of the frame and the armature1 a portion of the latter being cut away4 ,the field magnets and frame are cast in two parts4 ,these parts are identical in size and shape1 and each consists of the solid plates or ends ,a ,b1 from which project inwardly the cores ,c ,d and the side bars or bridge pieces1 ,e ,f4 ,the precise shape of these parts is largely a matter of choice--that is to say1 each casting1 as shown1 forms an approximately rectangular frame2 but it might obviously be more or less oval1 round1 or square1 without departure from the invention4 ,it is also desirable to reduce the width of the side bars1 ,e ,f1 at the center and to so proportion the parts that when the frame is put together the spaces between the pole pieces will be practically equal to the arcs which the surfaces of the poles occupy4 ,the bearings ,g for the armature shaft are cast in the side bars ,e ,f4 ,the field coils are either wound on the pole pieces or on a form and then slipped on over the ends of the pole pieces4 ,the lower part or casting is secured to the base after being finished off4 ,the armature ,k on its shaft is then mounted in the bearings of the lower casting and the other part of the frame placed in position1 dowel pins ,l or any other means being used to secure the two parts in proper position4 ,illustration3 ,,fig4 #bfh4 ,illustration3 ,,fig4 #bfi4 ,illustration3 ,,fig4 #bgj4 ,in order to secure an easier fit1 the side bars ,e ,f1 and end pieces1 ,a ,b1 are so cast that slots ,m are formed when the two parts are put together4 ,this machine possesses several advantages4 ,for example1 if we magnetize the cores alternately1 as indicated by the characters ,n ,s1 it will be seen that the magnetic circuit between the poles of each part of a casting is completed through the solid iron side bars4 ,the bearings for the shaft are located at the neutral points of the field1 so that the armature core is not affected by the magnetic condition of the field4 ,the improvement is not restricted to the use of four pole pieces1 as it is evident that each pole piece could be divided or more than four formed by the shape of the casting4 ,,chapter ,,xl4 ,,tesla ,,direct ,,current ,,arc ,,lighting ,,system4 ,at one time1 soon after his arrival in ,america1 ,mr4 ,tesla was greatly interested in the subject of arc lighting1 which then occupied public attention and readily enlisted the support of capital4 ,he therefore worked out a system which was confided to a company formed for its exploitation1 and then proceeded to devote his energies to the perfection of the details of his more celebrated rotary field motor system4 ,the ,tesla arc lighting apparatus appeared at a time when a great many other lamps and machines were in the market1 but it commanded notice by its ingenuity4 ,its chief purpose was to lessen the manufacturing cost and simplify the processes of operation4 ,we will take up the dynamo first4 ,fig4 #bga is a longitudinal section1 and ,fig4 #bgb a cross section of the machine4 ,fig4 #bgc is a top view1 and ,fig4 #bgd a side view of the magnetic frame4 ,fig4 #bge is an end view of the commutator bars1 and ,fig4 #bgf is a section of the shaft and commutator bars4 ,fig4 #bgg is a diagram illustrating the coils of the armature and the connections to the commutator plates4 ,the cores c c c c of the field-magnets are tapering in both directions1 as shown1 for the purposes of concentrating the magnetism upon the middle of the pole-pieces4 ,the connecting-frame ,f ,f of the field-magnets is in the form indicated in the side view1 ,fig4 #bgd1 the lower part being provided with the spreading curved cast legs e e1 so that the machine will rest firmly upon two base-bars1 r r4 ,to the lower pole1 ,s1 of the field-magnet ,m is fastened1 by means of babbitt or other fusible diamagnetic material1 the base ,b1 which is provided with bearings b for the armature-shaft ,h4 ,the base ,b has a projection1 ,p1 which supports the brush-holders and the regulating devices1 which are of a special character devised by ,mr4 ,tesla4 ,the armature is constructed with the view to reduce to a minimum the loss of power due to ,foucault currents and to the change of polarity1 and also to shorten as much as possible the length of the inactive wire wound upon the armature core4 ,illustration3 ,,fig4 #bga4 ,it is well known that when the armature is revolved between the poles of the field-magnets1 currents are generated in the iron body of the armature which develop heat1 and consequently cause a waste of power4 ,owing to the mutual action of the lines of force1 the magnetic properties of iron1 and the speed of the different portions of the armature core1 these currents are generated principally on and near the surface of the armature core1 diminishing in strength gradually toward the centre of the core4 ,their quantity is under some conditions proportional to the length of the iron body in the direction in which these currents are generated4 ,by subdividing the iron core electrically in this direction1 the generation of these currents can be reduced to a great extent4 ,for instance1 if the length of the armature-core is twelve inches1 and by a suitable construction it is subdivided electrically1 so that there are in the generating direction six inches of iron and six inches of intervening air-spaces or insulating material1 the waste currents will be reduced to fifty per cent4 ,as shown in the diagrams1 the armature is constructed of thin iron discs ,d ,d ,d1 of various diameters1 fastened upon the armature-shaft in a suitable manner and arranged according to their sizes1 so that a series of iron bodies1 i i i1 is formed1 each of which diminishes in thickness from the centre toward the periphery4 ,at both ends of the armature the inwardly curved discs d d1 of cast iron1 are fastened to the armature shaft4 ,the armature core being constructed as shown1 it will be easily seen that on those portions of the armature that are the most remote from the axis1 and where the currents are principally developed1 the length of iron in the generating direction is only a small fraction of the total length of the armature core1 and besides this the iron body is subdivided in the generating direction1 and therefore the ,foucault currents are greatly reduced4 ,another cause of heating is the shifting of the poles of the armature core4 ,in consequence of the subdivision of the iron in the armature and the increased surface for radiation1 the risk of heating is lessened4 ,the iron discs ,d ,d ,d are insulated or coated with some insulating-paint1 a very careful insulation being unnecessary1 as an electrical contact between several discs can only occur at places where the generated currents are comparatively weak4 ,an armature core constructed in the manner described may be revolved between the poles of the field magnets without showing the slightest increase of temperature4 ,illustration3 ,,fig4 #bgb4 ,illustration3 ,,fig4 #bgc4 ,the end discs1 d d1 which are of sufficient thickness and1 for the sake of cheapness1 of cast-iron1 are curved inwardly1 as indicated in the drawings4 ,the extent of the curve is dependent on the amount of wire to be wound upon the armatures4 ,in this machine the wire is wound upon the armature in two superimposed parts1 and the curve of the end discs1 d d1 is so calculated that the first part--that is1 practically half of the wire--just fills up the hollow space to the line x x2 or1 if the wire is wound in any other manner1 the curve is such that when the whole of the wire is wound1 the outside mass of wires1 w1 and the inside mass of wires1 w'1 are equal at each side of the plane x x4 ,in this case the passive or electrically-inactive wires are of the smallest length practicable4 ,the arrangement has further the advantage that the total lengths of the crossing wires at the two sides of the plane x x are practically equal4 ,illustration3 ,,fig4 #bgd4 ,to equalize further the armature coils at both sides of the plates that are in contact with the brushes1 the winding and connecting up is effected in the following manner3 ,the whole wire is wound upon the armature-core in two superimposed parts1 which are thoroughly insulated from each other4 ,each of these two parts is composed of three separated groups of coils4 ,the first group of coils of the first part of wire being wound and connected to the commutator-bars in the usual manner1 this group is insulated and the second group wound2 but the coils of this second group1 instead of being connected to the next following commutator bars1 are connected to the directly opposite bars of the commutator4 ,the second group is then insulated and the third group wound1 the coils of this group being connected to those bars to which they would be connected in the usual way4 ,the wires are then thoroughly insulated and the second part of wire is wound and connected in the same manner4 ,suppose1 for instance1 that there are twenty-four coils--that is1 twelve in each part--and consequently twenty-four commutator plates4 ,there will be in each part three groups1 each containing four coils1 and the coils will be connected as follows3 ,groups4 ,commutator ,bars4 ,first #a--e ,first part of wire ,second #ag--ba ,third #i--ac ,first #ac--ag ,second part of wire ,second #e--i ,third #ba--a ,in constructing the armature core and winding and connecting the coils in the manner indicated1 the passive or electrically inactive wire is reduced to a minimum1 and the coils at each side of the plates that are in contact with the brushes are practically equal4 ,in this way the electrical efficiency of the machine is increased4 ,illustration3 ,,fig4 #bge4 ,illustration3 ,,fig4 #bgf4 ,the commutator plates t are shown as outside the bearing b of the armature shaft4 ,the shaft ,h is tubular and split at the end portion1 and the wires are carried through the same in the usual manner and connected to the respective commutator plates4 ,the commutator plates are upon a cylinder1 u1 and insulated1 and this cylinder is properly placed and then secured by expanding the split end of the shaft by a tapering screw plug1 v4 ,illustration3 ,,fig4 #bgg4 ,the arc lamps invented by ,mr4 ,tesla for use on the circuits from the above described dynamo are those in which the separation and feed of the carbon electrodes or their equivalents is accomplished by means of electro-magnets or solenoids in connection with suitable clutch mechanism1 and were designed for the purpose of remedying certain faults common to arc lamps4 ,he proposed to prevent the frequent vibrations of the movable carbon point and flickering of the light arising therefrom2 to prevent the falling into contact of the carbons2 to dispense with the dash pot1 clock work1 or gearing and similar devices2 to render the lamp extremely sensitive1 and to feed the carbon almost imperceptibly1 and thereby obtain a very steady and uniform light4 ,in that class of lamps where the regulation of the arc is effected by forces acting in opposition on a free1 movable rod or lever directly connected with the electrode1 all or some of the forces being dependent on the strength of the current1 any change in the electrical condition of the circuit causes a vibration and a corresponding flicker in the light4 ,this difficulty is most apparent when there are only a few lamps in circuit4 ,to lessen this difficulty lamps have been constructed in which the lever or armature1 after the establishing of the arc1 is kept in a fixed position and cannot vibrate during the feed operation1 the feed mechanism acting independently2 but in these lamps1 when a clamp is employed1 it frequently occurs that the carbons come into contact and the light is momentarily extinguished1 and frequently parts of the circuit are injured4 ,in both these classes of lamps it has been customary to use dash pot1 clock work1 or equivalent retarding devices2 but these are often unreliable and objectionable1 and increase the cost of construction4 ,mr4 ,tesla combines two electro-magnets--one of low resistance in the main or lamp circuit1 and the other of comparatively high resistance in a shunt around the arc--a movable armature lever1 and a special feed mechanism1 the parts being arranged so that in the normal working position of the armature lever the same is kept almost rigidly in one position1 and is not affected even by considerable changes in the electric circuit2 but if the carbons fall into contact the armature will be actuated by the magnets so as to move the lever and start the arc1 and hold the carbons until the arc lengthens and the armature lever returns to the normal position4 ,after this the carbon rod holder is released by the action of the feed mechanism1 so as to feed the carbon and restore the arc to its normal length4 ,fig4 #bgh is an elevation of the mechanism made use of in this arc lamp4 ,fig4 #bgi is a plan view4 ,fig4 #bhj is an elevation of the balancing lever and spring2 ,fig4 #bha is a detached plan view of the pole pieces and armatures upon the friction clamp1 and ,fig4 #bhb is a section of the clamping tube4 ,m is a helix of coarse wire in a circuit from the lower carbon holder to the negative binding screw -4 ,n is a helix of fine wire in a shunt between the positive binding screw and the negative binding screw -4 ,the upper carbon holder ,s is a parallel rod sliding through the plates ,s' ,s#b of the frame of the lamp1 and hence the electric current passes from the positive binding post through the plate ,s#b1 carbon holder ,s1 and upper carbon to the lower carbon1 and thence by the holder and a metallic connection to the helix ,m4 ,illustration3 ,,fig4 #bgh4 ,illustration3 ,,fig4 #bgi4 ,illustration3 ,,fig4 #bhj4 ,illustration3 ,,fig4 #bha4 ,illustration3 ,,fig4 #bhb4 ,the carbon holders are of the usual character1 and to insure electric connections the springs l are made use of to grasp the upper carbon holding rod ,s1 but to allow the rod to slide freely through the same4 ,these springs l may be adjusted in their pressure by the screw m1 and the spring l maybe sustained upon any suitable support4 ,they are shown as connected with the upper end of the core of the magnet ,n4 ,around the carbon-holding rod ,s1 between the plates ,s' ,s#b1 there is a tube1 ,r1 which forms a clamp4 ,this tube is counter-bored1 as seen in the section ,fig4 #bhb1 so that it bears upon the rod ,s at its upper end and near the middle1 and at the lower end of this tubular clamp ,r there are armature segments r of soft iron4 ,a frame or arm1 n1 extending1 preferably1 from the core ,n#b1 supports the lever ,a by a fulcrum-pin1 o4 ,this lever ,a has a hole1 through which the upper end of the tubular clamp ,r passes freely1 and from the lever ,a is a link1 q1 to the lever t1 which lever is pivoted at y to a ring upon one of the columns ,s#c4 ,this lever t has an opening or bow surrounding the tubular clamp ,r1 and there are pins or pivotal connections w between the lever t and this clamp ,r1 and a spring1 r#b1 serves to support or suspend the weight of the parts and balance them1 or nearly so4 ,this spring is adjustable4 ,at one end of the lever ,a is a soft-iron armature block1 a1 over the core ,m' of the helix ,m1 and there is a limiting screw1 c1 passing through this armature block a1 and at the other end of the lever ,a is a soft iron armature block1 b1 with the end tapering or wedge shaped1 and the same comes close to and in line with the lateral projection e on the core ,n#b4 ,the lower ends of the cores ,m' ,n#b are made with laterally projecting pole-pieces ,m#c ,n#c1 respectively1 and these pole-pieces are concave at their outer ends1 and are at opposite sides of the armature segments r at the lower end of the tubular clamp ,r4 ,the operation of these devices is as follows3 ,in the condition of inaction1 the upper carbon rests upon the lower one1 and when the electric current is turned on it passes freely1 by the frame and spring l1 through the rods and carbons to the coarse wire and helix ,m1 and to the negative binding post ,v and the core ,m' thereby is energized4 ,the pole piece ,m#c attracts the armature r1 and by the lateral pressure causes the clamp ,r to grasp the rod ,s'1 and the lever ,a is simultaneously moved from the position shown by dotted lines1 ,fig4 #bgh1 to the normal position shown in full lines1 and in so doing the link q and lever t are raised1 lifting the clamp ,r and ,s1 separating the carbons and forming the arc4 ,the magnetism of the pole piece e tends to hold the lever ,a level1 or nearly so1 the core ,n#b being energized by the current in the shunt which contains the helix ,n4 ,in this position the lever ,a is not moved by any ordinary variation in the current1 because the armature b is strongly attracted by the magnetism of e1 and these parts are close to each other1 and the magnetism of e acts at right angles to the magnetism of the core ,m'4 ,if1 now1 the arc becomes too long1 the current through the helix ,m is lessened1 and the magnetism of the core ,n#c is increased by the greater current passing through the shunt1 and this core ,n#c1 attracting the segmental armature r1 lessens the hold of the clamp ,r upon the rod ,s1 allowing the latter to slide and lessen the length of the arc1 which instantly restores the magnetic equilibrium and causes the clamp ,r to hold the rod ,s4 ,if it happens that the carbons fall into contact1 then the magnetism of ,n#b is lessened so much that the attraction of the magnet ,m will be sufficient to move the armature a and lever ,a so that the armature b passes above the normal position1 so as to separate the carbons instantly2 but when the carbons burn away1 a greater amount of current will pass through the shunt until the attraction of the core ,n#b will overcome the attraction of the core ,m' and bring the armature lever ,a again into the normal horizontal position1 and this occurs before the feed can take place4 ,the segmental armature pieces r are shown as nearly semicircular4 ,they are square or of any other desired shape1 the ends of the pole pieces ,m#c1 ,n#c being made to correspond in shape4 ,in a modification of this lamp1 ,mr4 ,tesla provided means for automatically withdrawing a lamp from the circuit1 or cutting it out when1 from a failure of the feed1 the arc reached an abnormal length2 and also means for automatically reinserting such lamp in the circuit when the rod drops and the carbons come into contact4 ,fig4 #bhc is an elevation of the lamp with the case in section4 ,fig4 #bhd is a sectional plan at the line x x4 ,fig4 #bhe is an elevation1 partly in section1 of the lamp at right angles to ,fig4 #bhc4 ,fig4 #bhf is a sectional plan at the line y y of ,fig4 #bhc4 ,fig4 #bhg is a section of the clamp in about full size4 ,fig4 #bhh is a detached section illustrating the connection of the spring to the lever that carries the pivots of the clamp1 and ,fig4 #bhi is a diagram showing the circuit-connections of the lamp4 ,in ,fig4 #bhc1 ,m represents the main and ,n the shunt magnet1 both securely fastened to the base ,a1 which with its side columns1 ,s ,s1 are cast in one piece of brass or other diamagnetic material4 ,to the magnets are soldered or otherwise fastened the brass washers or discs a a a a4 ,similar washers1 b b1 of fibre or other insulating material1 serve to insulate the wires from the brass washers4 ,the magnets ,m and ,n are made very flat1 so that their width exceeds three times their thickness1 or even more4 ,in this way a comparatively small number of convolutions is sufficient to produce the required magnetism1 while a greater surface is offered for cooling off the wires4 ,illustration3 ,,fig4 #bhf4 ,illustration3 ,,fig4 #bhc4 ,illustration3 ,,fig4 #bhe4 ,illustration3 ,,fig4 #bhd4 ,illustration3 ,,fig4 #bhg4 ,illustration3 ,,fig4 #bhh4 ,the upper pole pieces1 m n1 of the magnets are curved1 as indicated in the drawings1 ,fig4 #bhc4 ,the lower pole pieces m' n'1 are brought near together1 tapering toward the armature g1 as shown in ,figs4 #bhd and #bhf4 ,the object of this taper is to concentrate the greatest amount of the developed magnetism upon the armature1 and also to allow the pull to be exerted always upon the middle of the armature g4 ,this armature g is a piece of iron in the shape of a hollow cylinder1 having on each side a segment cut away1 the width of which is equal to the width of the pole pieces m' n'4 ,the armature is soldered or otherwise fastened to the clamp r1 which is formed of a brass tube1 provided with gripping-jaws e e1 ,fig4 #bhg4 ,these jaws are arcs of a circle of the diameter of the rod ,r1 and are made of hardened ,german silver4 ,the guides f f1 through which the carbon-holding rod ,r slides1 are made of the same material4 ,this has the advantage of reducing greatly the wear and corrosion of the parts coming in frictional contact with the rod1 which frequently causes trouble4 ,the jaws e e are fastened to the inside of the tube r1 so that one is a little lower than the other4 ,the object of this is to provide a greater opening for the passage of the rod when the same is released by the clamp4 ,the clamp r is supported on bearings w w1 ,figs4 #bhc1 #bhe and #bhg1 which are just in the middle between the jaws e e4 ,the bearings w w are carried by a lever1 t1 one end of which rests upon an adjustable support1 q1 of the side columns1 ,s1 the other end being connected by means of the link e' to the armature-lever ,l4 ,the armature-lever ,l is a flat piece of iron in ,n shape1 having its ends curved so as to correspond to the form of the upper pole-pieces of the magnets ,m and ,n4 ,it is hung upon the pivots v v1 ,fig4 #bhd1 which are in the jaw x of the top plate ,b4 ,this plate ,b1 with the jaw1 is cast in one piece and screwed to the side columns1 ,s ,s1 that extend up from the base ,a4 ,to partly balance the overweight of the moving parts1 a spring1 s'1 ,figs4 #bhd and #bhh1 is fastened to the top plate1 ,b1 and hooked to the lever t4 ,the hook o is toward one side of the lever or bent a little sidewise1 as seen in ,fig4 #bhh4 ,by this means a slight tendency is given to swing the armature toward the pole-piece m' of the main magnet4 ,the binding-posts ,k ,k' are screwed to the base ,a4 ,a manual switch1 for short-circuiting the lamp when the carbons are renewed1 is also fastened to the base4 ,this switch is of ordinary character1 and is not shown in the drawings4 ,the rod ,r is electrically connected to the lamp-frame by means of a flexible conductor or otherwise4 ,the lamp-case receives a removable cover1 s#b1 to inclose the parts4 ,the electrical connections are as indicated diagrammatically in ,fig4 #bhi4 ,the wire in the main magnet consists of two parts1 x' and p'4 ,these two parts may be in two separated coils or in one single helix1 as shown in the drawings4 ,the part x' being normally in circuit1 is1 with the fine wire upon the shunt-magnet1 wound and traversed by the current in the same direction1 so as to tend to produce similar poles1 ,n ,n or ,s ,s1 on the corresponding pole-pieces of the magnets ,m and ,n4 ,the part p' is only in circuit when the lamp is cut out1 and then the current being in the opposite direction produces in the main magnet1 magnetism of the opposite polarity4 ,the operation is as follows3 ,at the start the carbons are to be in contact1 and the current passes from the positive binding-post ,k to the lamp-frame1 carbon-holder1 upper and lower carbon1 insulated return-wire in one of the side rods1 and from there through the part x' of the wire on the main magnet to the negative binding-post4 ,upon the passage of the current the main magnet is energized and attracts the clamping-armature g1 swinging the clamp and gripping the rod by means of the gripping jaws e e4 ,at the same time the armature lever ,l is pulled down and the carbons are separated4 ,in pulling down the armature lever ,l the main magnet is assisted by the shunt-magnet ,n1 the latter being magnetized by magnetic induction from the magnet ,m4 ,illustration3 ,,fig4 #bhi4 ,it will be seen that the armatures ,l and g are practically the keepers for the magnets ,m and ,n1 and owing to this fact both magnets with either one of the armatures ,l and g may be considered as one horseshoe magnet1 which we might term a compound magnet4 ,the whole of the soft-iron parts ,m1 m'1 g1 n'1 ,n and ,l form a compound magnet4 ,the carbons being separated1 the fine wire receives a portion of the current4 ,now1 the magnetic induction from the magnet ,m is such as to produce opposite poles on the corresponding ends of the magnet ,n2 but the current traversing the helices tends to produce similar poles on the corresponding ends of both magnets1 and therefore as soon as the fine wire is traversed by sufficient current the magnetism of the whole compound magnet is diminished4 ,with regard to the armature g and the operation of the lamp1 the pole m' may be considered as the clamping and the pole n' as the releasing pole4 ,as the carbons burn away1 the fine wire receives more current and the magnetism diminishes in proportion4 ,this causes the armature lever ,l to swing and the armature g to descend gradually under the weight of the moving parts until the end p1 ,fig4 #bhc1 strikes a stop on the top plate1 ,b4 ,the adjustment is such that when this takes place the rod ,r is yet gripped securely by the jaws e e4 ,the further downward movement of the armature lever being prevented1 the arc becomes longer as the carbons are consumed1 and the compound magnet is weakened more and more until the clamping armature g releases the hold of the gripping-jaws e e upon the rod ,r1 and the rod is allowed to drop a little1 thus shortening the arc4 ,the fine wire now receiving less current1 the magnetism increases1 and the rod is clamped again and slightly raised1 if necessary4 ,this clamping and releasing of the rod continues until the carbons are consumed4 ,in practice the feed is so sensitive that for the greatest part of the time the movement of the rod cannot be detected without some actual measurement4 ,during the normal operation of the lamp the armature lever ,l remains practically stationary1 in the position shown in ,fig4 #bhc4 ,should it happen that1 owing to an imperfection in it1 the rod and the carbons drop too far1 so as to make the arc too short1 or even bring the carbons in contact1 a very small amount of current passes through the fine wire1 and the compound magnet becomes sufficiently strong to act as at the start in pulling the armature lever ,l down and separating the carbons to a greater distance4 ,it occurs often in practical work that the rod sticks in the guides4 ,in this case the are reaches a great length1 until it finally breaks4 ,then the light goes out1 and frequently the fine wire is injured4 ,to prevent such an accident ,mr4 ,tesla provides this lamp with an automatic cut-out which operates as follows3 ,when1 upon a failure of the feed1 the arc reaches a certain predetermined length1 such an amount of current is diverted through the fine wire that the polarity of the compound magnet is reversed4 ,the clamping armature g is now moved against the shunt magnet ,n until it strikes the releasing pole n'4 ,as soon as the contact is established1 the current passes from the positive binding post over the clamp r1 armature g1 insulated shunt magnet1 and the helix p' upon the main magnet ,m to the negative binding post4 ,in this case the current passes in the opposite direction and changes the polarity of the magnet ,m1 at the same time maintaining by magnetic induction in the core of the shunt magnet the required magnetism without reversal of polarity1 and the armature g remains against the shunt magnet pole n'4 ,the lamp is thus cut out as long as the carbons are separated4 ,the cut out may be used in this form without any further improvement2 but ,mr4 ,tesla arranges it so that if the rod drops and the carbons come in contact the arc is started again4 ,for this purpose he proportions the resistance of part p' and the number of the convolutions of the wire upon the main magnet so that when the carbons come in contact a sufficient amount of current is diverted through the carbons and the part x' to destroy or neutralize the magnetism of the compound magnet4 ,then the armature g1 having a slight tendency to approach to the clamping pole m'1 comes out of contact with the releasing pole n'4 ,as soon as this happens1 the current through the part p' is interrupted1 and the whole current passes through the part x4 ,the magnet ,m is now strongly magnetized1 the armature g is attracted1 and the rod clamped4 ,at the same time the armature lever ,l is pulled down out of its normal position and the arc started4 ,in this way the lamp cuts itself out automatically when the arc gets too long1 and reinserts itself automatically in the circuit if the carbons drop together4 ,,chapter ,,xli4 ,,improvement ,,in ,,unipolar ,,generators4 ,another interesting class of apparatus to which ,mr4 ,tesla has directed his attention1 is that of unipolar generators1 in which a disc or a cylindrical conductor is mounted between magnetic poles adapted to produce an approximately uniform field4 ,in the disc armature machines the currents induced in the rotating conductor flow from the centre to the periphery1 or conversely1 according to the direction of rotation or the lines of force as determined by the signs of the magnetic poles1 and these currents are taken off usually by connections or brushes applied to the disc at points on its periphery and near its centre4 ,in the case of the cylindrical armature machine1 the currents developed in the cylinder are taken off by brushes applied to the sides of the cylinder at its ends4 ,in order to develop economically an electromotive force available for practicable purposes1 it is necessary either to rotate the conductor at a very high rate of speed or to use a disc of large diameter or a cylinder of great length2 but in either case it becomes difficult to secure and maintain a good electrical connection between the collecting brushes and the conductor1 owing to the high peripheral speed4 ,it has been proposed to couple two or more discs together in series1 with the object of obtaining a higher electro-motive force2 but with the connections heretofore used and using other conditions of speed and dimension of disc necessary to securing good practicable results1 this difficulty is still felt to be a serious obstacle to the use of this kind of generator4 ,these objections ,mr4 ,tesla has sought to avoid by constructing a machine with two fields1 each having a rotary conductor mounted between its poles4 ,the same principle is involved in the case of both forms of machine above described1 but the description now given is confined to the disc type1 which ,mr4 ,tesla is inclined to favor for that machine4 ,the discs are formed with flanges1 after the manner of pulleys1 and are connected together by flexible conducting bands or belts4 ,the machine is built in such manner that the direction of magnetism or order of the poles in one field of force is opposite to that in the other1 so that rotation of the discs in the same direction develops a current in one from centre to circumference and in the other from circumference to centre4 ,contacts applied therefore to the shafts upon which the discs are mounted form the terminals of a circuit the electro-motive force in which is the sum of the electro-motive forces of the two discs4 ,it will be obvious that if the direction of magnetism in both fields be the same1 the same result as above will be obtained by driving the discs in opposite directions and crossing the connecting belts4 ,in this way the difficulty of securing and maintaining good contact with the peripheries of the discs is avoided and a cheap and durable machine made which is useful for many purposes--such as for an exciter for alternating current generators1 for a motor1 and for any other purpose for which dynamo machines are used4 ,illustration3 ,,fig4 #bij4 ,illustration3 ,,fig4 #bia4 ,fig4 #bij is a side view1 partly in section1 of this machine4 ,fig4 #bia is a vertical section of the same at right angles to the shafts4 ,in order to form a frame with two fields of force1 a support1 ,a1 is cast with two pole pieces ,b ,b' integral with it4 ,to this are joined by bolts ,e a casting ,d1 with two similar and corresponding pole pieces ,c ,c'4 ,the pole pieces ,b ,b' are wound and connected to produce a field of force of given polarity1 and the pole pieces ,c ,c' are wound so as to produce a field of opposite polarity4 ,the driving shafts ,f ,g pass through the poles and are journaled in insulating bearings in the casting ,a ,d1 as shown4 ,h ,k are the discs or generating conductors4 ,they are composed of copper1 brass1 or iron and are keyed or secured to their respective shafts4 ,they are provided with broad peripheral flanges ,j4 ,it is of course obvious that the discs may be insulated from their shafts1 if so desired4 ,a flexible metallic belt ,l is passed over the flanges of the two discs1 and1 if desired1 may be used to drive one of the discs4 ,it is better1 however1 to use this belt merely as a conductor1 and for this purpose sheet steel1 copper1 or other suitable metal is used4 ,each shaft is provided with a driving pulley ,m1 by which power is imparted from a driving shaft4 ,n ,n are the terminals4 ,for the sake of clearness they are shown as provided with springs ,p1 that bear upon the ends of the shafts4 ,this machine1 if self-exciting1 would have copper bands around its poles2 or conductors of any kind--such as wires shown in the drawings--may be used4 99 99 99 99 99 ,it is thought appropriate by the compiler to append here some notes on unipolar dynamos1 written by ,mr4 ,tesla1 on a recent occasion4 ,,notes ,,on ,a ,,unipolar ,,dynamo4#ae #ae ,article by ,mr4 ,tesla1 contributed to ,the ,electrical ,engineer1 ,n4 ,y41 ,sept4 #b1 #ahia4 ,it is characteristic of fundamental discoveries1 of great achievements of intellect1 that they retain an undiminished power upon the imagination of the thinker4 ,the memorable experiment of ,faraday with a disc rotating between the two poles of a magnet1 which has borne such magnificent fruit1 has long passed into every-day experience2 yet there are certain features about this embryo of the present dynamos and motors which even to-day appear to us striking1 and are worthy of the most careful study4 ,consider1 for instance1 the case of a disc of iron or other metal revolving between the two opposite poles of a magnet1 and the polar surfaces completely covering both sides of the disc1 and assume the current to be taken off or conveyed to the same by contacts uniformly from all points of the periphery of the disc4 ,take first the case of a motor4 ,in all ordinary motors the operation is dependent upon some shifting or change of the resultant of the magnetic attraction exerted upon the armature1 this process being effected either by some mechanical contrivance on the motor or by the action of currents of the proper character4 ,we may explain the operation of such a motor just as we can that of a water-wheel4 ,but in the above example of the disc surrounded completely by the polar surfaces1 there is no shifting of the magnetic action1 no change whatever1 as far as we know1 and yet rotation ensues4 ,here1 then1 ordinary considerations do not apply2 we cannot even give a superficial explanation1 as in ordinary motors1 and the operation will be clear to us only when we shall have recognized the very nature of the forces concerned1 and fathomed the mystery of the invisible connecting mechanism4 ,considered as a dynamo machine1 the disc is an equally interesting object of study4 ,in addition to its peculiarity of giving currents of one direction without the employment of commutating devices1 such a machine differs from ordinary dynamos in that there is no reaction between armature and field4 ,the armature current tends to set up a magnetization at right angles to that of the field current1 but since the current is taken off uniformly from all points of the periphery1 and since1 to be exact1 the external circuit may also be arranged perfectly symmetrical to the field magnet1 no reaction can occur4 ,this1 however1 is true only as long as the magnets are weakly energized1 for when the magnets are more or less saturated1 both magnetizations at right angles seemingly interfere with each other4 ,for the above reason alone it would appear that the output of such a machine should1 for the same weight1 be much greater than that of any other machine in which the armature current tends to demagnetize the field4 ,the extraordinary output of the ,forbes unipolar dynamo and the experience of the writer confirm this view4 ,again1 the facility with which such a machine may be made to excite itself is striking1 but this may be due--besides to the absence of armature reaction--to the perfect smoothness of the current and non-existence of self-induction4 ,if the poles do not cover the disc completely on both sides1 then1 of course1 unless the disc be properly subdivided1 the machine will be very inefficient4 ,again1 in this case there are points worthy of notice4 ,if the disc be rotated and the field current interrupted1 the current through the armature will continue to flow and the field magnets will lose their strength comparatively slowly4 ,the reason for this will at once appear when we consider the direction of the currents set up in the disc4 ,illustration3 ,,fig4 #bib4 ,referring to the diagram ,fig4 #bib1 d represents the disc with the sliding contacts ,b ,b' on the shaft and periphery4 ,n and ,s represent the two poles of a magnet4 ,if the pole ,n be above1 as indicated in the diagram1 the disc being supposed to be in the plane of the paper1 and rotating in the direction of the arrow ,d1 the current set up in the disc will flow from the centre to the periphery1 as indicated by the arrow ,a4 ,since the magnetic action is more or less confined to the space between the poles ,n ,s1 the other portions of the disc may be considered inactive4 ,the current set up will therefore not wholly pass through the external circuit ,f1 but will close through the disc itself1 and generally1 if the disposition be in any way similar to the one illustrated1 by far the greater portion of the current generated will not appear externally1 as the circuit ,f is practically short-circuited by the inactive portions of the disc4 ,the direction of the resulting currents in the latter may be assumed to be as indicated by the dotted lines and arrows m and n2 and the direction of the energizing field current being indicated by the arrows a b c d1 an inspection of the figure shows that one of the two branches of the eddy current1 that is1 ,a ,b' m ,b1 will tend to demagnetize the field1 while the other branch1 that is1 ,a ,b' n ,b1 will have the opposite effect4 ,therefore1 the branch ,a ,b' m ,b1 that is1 the one which is approaching the field1 will repel the lines of the same1 while branch ,a ,b' n ,b1 that is1 the one leaving the field1 will gather the lines of force upon itself4 ,in consequence of this there will be a constant tendency to reduce the current flow in the path ,a ,b' m ,b1 while on the other hand no such opposition will exist in path ,a ,b' n ,b1 and the effect of the latter branch or path will be more or less preponderating over that of the former4 ,the joint effect of both the assumed branch currents might be represented by that of one single current of the same direction as that energizing the field4 ,in other words1 the eddy currents circulating in the disc will energize the field magnet4 ,this is a result quite contrary to what we might be led to suppose at first1 for we would naturally expect that the resulting effect of the armature currents would be such as to oppose the field current1 as generally occurs when a primary and secondary conductor are placed in inductive relations to each other4 ,but it must be remembered that this results from the peculiar disposition in this case1 namely1 two paths being afforded to the current1 and the latter selecting that path which offers the least opposition to its flow4 ,from this we see that the eddy currents flowing in the disc partly energize the field1 and for this reason when the field current is interrupted the currents in the disc will continue to flow1 and the field magnet will lose its strength with comparative slowness and may even retain a certain strength as long as the rotation of the disc is continued4 ,the result will1 of course1 largely depend on the resistance and geometrical dimensions of the path of the resulting eddy current and on the speed of rotation2 these elements1 namely1 determine the retardation of this current and its position relative to the field4 ,for a certain speed there would be a maximum energizing action2 then at higher speeds1 it would gradually fall off to zero and finally reverse1 that is1 the resultant eddy current effect would be to weaken the field4 ,the reaction would be best demonstrated experimentally by arranging the fields ,n ,s1 ,n' ,s'1 freely movable on an axis concentric with the shaft of the disc4 ,if the latter were rotated as before in the direction of the arrow ,d1 the field would be dragged in the same direction with a torque1 which1 up to a certain point1 would go on increasing with the speed of rotation1 then fall off1 and1 passing through zero1 finally become negative2 that is1 the field would begin to rotate in opposite direction to the disc4 ,in experiments with alternate current motors in which the field was shifted by currents of differing phase1 this interesting result was observed4 ,for very low speeds of rotation of the field the motor would show a torque of #ijj lbs4 or more1 measured on a pulley #ab inches in diameter4 ,when the speed of rotation of the poles was increased1 the torque would diminish1 would finally go down to zero1 become negative1 and then the armature would begin to rotate in opposite direction to the field4 ,to return to the principal subject2 assume the conditions to be such that the eddy currents generated by the rotation of the disc strengthen the field1 and suppose the latter gradually removed while the disc is kept rotating at an increased rate4 ,the current1 once started1 may then be sufficient to maintain itself and even increase in strength1 and then we have the case of ,sir ,william ,thomson's current accumulator4 ,but from the above considerations it would seem that for the success of the experiment the employment of a disc not subdivided#af would be essential1 for if there should be a radial subdivision1 the eddy currents could not form and the self-exciting action would cease4 ,if such a radially subdivided disc were used it would be necessary to connect the spokes by a conducting rim or in any proper manner so as to form a symmetrical system of closed circuits4 #af ,mr4 ,tesla here refers to an interesting article which appeared in ,july1 #ahfe1 in the ,phil4 ,magazine1 by ,sir ,w4 ,thomson1 in which ,sir ,william1 speaking of his uniform electric current accumulator1 assumes that for self-excitation it is desirable to subdivide the disc into an infinite number of infinitely thin spokes1 in order to prevent diffusion of the current4 ,mr4 ,tesla shows that diffusion is absolutely necessary for the excitation and that when the disc is subdivided no excitation can occur4 ,the action of the eddy currents may be utilized to excite a machine of any construction4 ,for instance1 in ,figs4 #bic and #bid an arrangement is shown by which a machine with a disc armature might be excited4 ,here a number of magnets1 ,n ,s1 ,n ,s1 are placed radially on each side of a metal disc ,d carrying on its rim a set of insulated coils1 ,c ,c4 ,the magnets form two separate fields1 an internal and an external one1 the solid disc rotating in the field nearest the axis1 and the coils in the field further from it4 ,assume the magnets slightly energized at the start2 they could be strengthened by the action of the eddy currents in the solid disc so as to afford a stronger field for the peripheral coils4 ,although there is no doubt that under proper conditions a machine might be excited in this or a similar manner1 there being sufficient experimental evidence to warrant such an assertion1 such a mode of excitation would be wasteful4 ,but a unipolar dynamo or motor1 such as shown in ,fig4 #bib1 may be excited in an efficient manner by simply properly subdividing the disc or cylinder in which the currents are set up1 and it is practicable to do away with the field coils which are usually employed4 ,such a plan is illustrated in ,fig4 #bie4 ,the disc or cylinder ,d is supposed to be arranged to rotate between the two poles ,n and ,s of a magnet1 which completely cover it on both sides1 the contours of the disc and poles being represented by the circles d and d#a respectively1 the upper pole being omitted for the sake of clearness4 ,the cores of the magnet are supposed to be hollow1 the shaft ,c of the disc passing through them4 ,if the unmarked pole be below1 and the disc be rotated screw fashion1 the current will be1 as before1 from the centre to the periphery1 and may be taken off by suitable sliding contacts1 ,b ,b'1 on the shaft and periphery respectively4 ,in this arrangement the current flowing through the disc and external circuit will have no appreciable effect on the field magnet4 ,illustration3 ,,fig4 #bic4 ,illustration3 ,,fig4 #bid4 ,but let us now suppose the disc to be subdivided spirally1 as indicated by the full or dotted lines1 ,fig4 #bie4 ,the difference of potential between a point on the shaft and a point on the periphery will remain unchanged1 in sign as well as in amount4 ,the only difference will be that the resistance of the disc will be augmented and that there will be a greater fall of potential from a point on the shaft to a point on the periphery when the same current is traversing the external circuit4 ,but since the current is forced to follow the lines of subdivision1 we see that it will tend either to energize or de-energize the field1 and this will depend1 other things being equal1 upon the direction of the lines of subdivision4 ,if the subdivision be as indicated by the full lines in ,fig4 #bie1 it is evident that if the current is of the same direction as before1 that is1 from centre to periphery1 its effect will be to strengthen the field magnet2 ,whereas1 if the subdivision be as indicated by the dotted lines1 the current generated will tend to weaken the magnet4 ,in the former case the machine will be capable of exciting itself when the disc is rotated in the direction of arrow ,d2 in the latter case the direction of rotation must be reversed4 ,two such discs may be combined1 however1 as indicated1 the two discs rotating in opposite fields1 and in the same or opposite direction4 ,illustration3 ,,fig4 #bie4 ,illustration3 ,,fig4 #bif4 ,similar disposition may1 of course1 be made in a type of machine in which1 instead of a disc1 a cylinder is rotated4 ,in such unipolar machines1 in the manner indicated1 the usual field coils and poles may be omitted and the machine may be made to consist only of a cylinder or of two discs enveloped by a metal casting4 ,instead of subdividing the disc or cylinder spirally1 as indicated in ,fig4 #bie1 it is more convenient to interpose one or more turns between the disc and the contact ring on the periphery1 as illustrated in ,fig4 #bif4 ,a ,forbes dynamo may1 for instance1 be excited in such a manner4 ,in the experience of the writer it has been found that instead of taking the current from two such discs by sliding contacts1 as usual1 a flexible conducting belt may be employed to advantage4 ,the discs are in such case provided with large flanges1 affording a very great contact surface4 ,the belt should be made to bear on the flanges with spring pressure to take up the expansion4 ,several machines with belt contact were constructed by the writer two years ago1 and worked satisfactorily2 but for want of time the work in that direction has been temporarily suspended4 ,a number of features pointed out above have also been used by the writer in connection with some types of alternating current motors4 ,,part ,,iv4 ,,appendix4--,,early ,,phase ,,motors ,,and ,,the ,,tesla ,,mechanical ,,and ,,electrical ,,oscillator4 ,,chapter ,,xlii4 ,,mr4 ,,tesla',s ,,personal ,,exhibit ,,at ,,the ,,world',s ,,fair4 ,while the exhibits of firms engaged in the manufacture of electrical apparatus of every description at the ,chicago ,world's ,fair1 afforded the visitor ample opportunity for gaining an excellent knowledge of the state of the art1 there were also numbers of exhibits which brought out in strong relief the work of the individual inventor1 which lies at the foundation of much1 if not all1 industrial or mechanical achievement4 ,prominent among such personal exhibits was that of ,mr4 ,tesla1 whose apparatus occupied part of the space of the ,westinghouse ,company1 in ,electricity ,building4 ,this apparatus represented the results of work and thought covering a period of ten years4 ,it embraced a large number of different alternating motors and ,mr4 ,tesla's earlier high frequency apparatus4 ,the motor exhibit consisted of a variety of fields and armatures for two1 three and multiphase circuits1 and gave a fair idea of the gradual evolution of the fundamental idea of the rotating magnetic field4 ,the high frequency exhibit included ,mr4 ,tesla's earlier machines and disruptive discharge coils and high frequency transformers1 which he used in his investigations and some of which are referred to in his papers printed in this volume4 ,fig4 #big shows a view of part of the exhibits containing the motor apparatus4 ,among these is shown at ,a a large ring intended to exhibit the phenomena of the rotating magnetic field4 ,the field produced was very powerful and exhibited striking effects1 revolving copper balls and eggs and bodies of various shapes at considerable distances and at great speeds4 ,this ring was wound for two-phase circuits1 and the winding was so distributed that a practically uniform field was obtained4 ,this ring was prepared for ,mr4 ,tesla's exhibit by ,mr4 ,c4 ,f4 ,scott1 electrician of the ,westinghouse ,electric and ,manufacturing ,company4 ,illustration3 ,,fig4 #big4 ,a smaller ring1 shown at ,b1 was arranged like the one exhibited at ,a but designed especially to exhibit the rotation of an armature in a rotating field4 ,in connection with these two rings there was an interesting exhibit shown by ,mr4 ,tesla which consisted of a magnet with a coil1 the magnet being arranged to rotate in bearings4 ,with this magnet he first demonstrated the identity between a rotating field and a rotating magnet2 the latter1 when rotating1 exhibited the same phenomena as the rings when they were energized by currents of differing phase4 ,another prominent exhibit was a model illustrated at ,c which is a two-phase motor1 as well as an induction motor and transformer4 ,it consists of a large outer ring of laminated iron wound with two superimposed1 separated windings which can be connected in a variety of ways4 ,this is one of the first models used by ,mr4 ,tesla as an induction motor and rotating transformer4 ,the armature was either a steel or wrought iron disc with a closed coil4 ,when the motor was operated from a two phase generator the windings were connected in two groups1 as usual4 ,when used as an induction motor1 the current induced in one of the windings of the ring was passed through the other winding on the ring and so the motor operated with only two wires4 ,when used as a transformer the outer winding served1 for instance1 as a secondary and the inner as a primary4 ,the model shown at ,d is one of the earliest rotating field motors1 consisting of a thin iron ring wound with two sets of coils and an armature consisting of a series of steel discs partly cut away and arranged on a small arbor4 ,at ,e is shown one of the first rotating field or induction motors used for the regulation of an arc lamp and for other purposes4 ,it comprises a ring of discs with two sets of coils having different self-inductions1 one set being of ,german silver and the other of copper wire4 ,the armature is wound with two closed-circuited coils at right angles to each other4 ,to the armature shaft are fastened levers and other devices to effect the regulation4 ,at ,f is shown a model of a magnetic lag motor2 this embodies a casting with pole projections protruding from two coils between which is arranged to rotate a smooth iron body4 ,when an alternating current is sent through the two coils the pole projections of the field and armature within it are similarly magnetized1 and upon the cessation or reversal of the current the armature and field repel each other and rotation is produced in this way4 ,another interesting exhibit1 shown at ,g1 is an early model of a two field motor energized by currents of different phase4 ,there are two independent fields of laminated iron joined by brass bolts2 in each field is mounted an armature1 both armatures being on the same shaft4 ,the armatures were originally so arranged as to be placed in any position relatively to each other1 and the fields also were arranged to be connected in a number of ways4 ,the motor has served for the exhibition of a number of features2 among other things1 it has been used as a dynamo for the production of currents of any frequency between wide limits4 ,in this case the field1 instead of being energized by direct current1 was energized by currents differing in phase1 which produced a rotation of the field2 the armature was then rotated in the same or in opposite direction to the movement of the field2 and so any number of alternations of the currents induced in the armature1 from a small to a high number1 determined by the frequency of the energizing field coils and the speed of the armature1 was obtained4 ,illustration3 ,,fig4 #bih4 ,the models ,h1 ,i1 ,j1 represent a variety of rotating field1 synchronous motors which are of special value in long distance transmission work4 ,the principle embodied in these motors was enunciated by ,mr4 ,tesla in his lecture before the ,american ,institute of ,electrical ,engineers1 in ,may1 #ahhhag4 ,it involves the production of the rotating field in one of the elements of the motor by currents differing in phase and energizing the other element by direct currents4 ,the armatures are of the two and three phase type4 ,k is a model of a motor shown in an enlarged view in ,fig4 #bih4 ,this machine1 together with that shown in ,fig4 #bii1 was exhibited at the same lecture1 in ,may1 #ahhh4 ,they were the first rotating field motors which were independently tested1 having for that purpose been placed in the hands of ,prof4 ,anthony in the winter of #ahhg-hh4 ,from these tests it was shown that the efficiency and output of these motors was quite satisfactory in every respect4 #ag ,see ,part ,i1 ,chap4 ,,iii1 page #i4 ,illustration3 ,,fig4 #bii4 ,it was intended to exhibit the model shown in ,fig4 #bii1 but it was unavailable for that purpose owing to the fact that it was some time ago handed over to the care of ,prof4 ,ayrton in ,england4 ,this model was originally provided with twelve independent coils2 this number1 as ,mr4 ,tesla pointed out in his first lecture1 being divisible by two and three1 was selected in order to make various connections for two and three-phase operations1 and during ,mr4 ,tesla's experiments was used in many ways with from two to six phases4 ,the model1 ,fig4 #bih1 consists of a magnetic frame of laminated iron with four polar projections between which an armature is supported on brass bolts passing through the frame4 ,a great variety of armatures was used in connection with these two and other fields4 ,some of the armatures are shown in front on the table1 ,fig4 #big1 and several are also shown enlarged in ,figs4 #cjj to #caj4 ,an interesting exhibit is that shown at ,l1 ,fig4 #big4 ,this is an armature of hardened steel which was used in a demonstration before the ,society of ,arts in ,boston1 by ,prof4 ,anthony4 ,another curious exhibit is shown enlarged in ,fig4 #cja4 ,this consists of thick discs of wrought iron placed lengthwise1 with a mass of copper cast around them4 ,the discs were arranged longitudinally to afford an easier starting by reason of the induced current formed in the iron discs1 which differed in phase from those in the copper4 ,this armature would start with a single circuit and run in synchronism1 and represents one of the earliest types of such an armature4 ,fig4 #cje is another striking exhibit4 ,this is one of the earliest types of an armature with holes beneath the periphery1 in which copper conductors are imbedded4 ,the armature has eight closed circuits and was used in many different ways4 ,fig4 #cjd is a type of synchronous armature consisting of a block of soft steel wound with a coil closed upon itself4 ,this armature was used in connection with the field shown in ,fig4 #bih and gave excellent results4 ,illustration3 ,,fig4 #cjj4 ,illustration3 ,,fig4 #cja4 ,illustration3 ,,fig4 #cjb4 ,illustration3 ,,fig4 #cjc4 ,illustration3 ,,fig4 #cjd4 ,illustration3 ,,fig4 #cje4 ,illustration3 ,,fig4 #cjf4 ,illustration3 ,,fig4 #cjg4 ,illustration3 ,,fig4 #cjh4 ,illustration3 ,,fig4 #cji4 ,illustration3 ,,fig4 #caj4 ,fig4 #cjb represents a synchronous armature with a large coil around a body of iron4 ,there is another very small coil at right angles to the first4 ,this small coil was used for the purpose of increasing the starting torque and was found very effective in this connection4 ,figs4 #cjf and #cjh show a favorite construction of armature2 the iron body is made up of two sets of discs cut away and placed at right angles to each other1 the interstices being wound with coils4 ,the one shown in ,fig4 #cjh is provided with an additional groove on each of the projections formed by the discs1 for the purpose of increasing the starting torque by a wire wound in these projections4 ,fig4 #cjg is a form of armature similarly constructed1 but with four independent coils wound upon the four projections4 ,this armature was used to reduce the speed of the motor with reference to that of the generator4 ,fig4 #cjj is still another armature with a great number of independent circuits closed upon themselves1 so that all the dead points on the armature are done away with1 and the armature has a large starting torque4 ,fig4 #cjc is another type of armature for a four-pole motor but with coils wound upon a smooth surface4 ,a number of these armatures have hollow shafts1 as they have been used in many ways4 ,figs4 #cji and #caj represent armatures to which either alternating or direct current was conveyed by means of sliding rings4 ,fig4 #cji consists of a soft iron body with a single coil wound around it1 the ends of the coil being connected to two sliding rings to which1 usually1 direct current was conveyed4 ,the armature shown in ,fig4 #caj has three insulated rings on a shaft and was used in connection with two or three phase circuits4 ,all these models shown represent early work1 and the enlarged engravings are made from photographs taken early in #ahhh4 ,there is a great number of other models which were exhibited1 but which are not brought out sharply in the engraving1 ,fig4 #big4 ,for example at ,m is a model of a motor comprising an armature with a hollow shaft wound with two or three coils for two or three-phase circuits2 the armature was arranged to be stationary and the generating circuits were connected directly to the generator4 ,around the armature is arranged to rotate on its shaft a casting forming six closed circuits4 ,on the outside this casting was turned smooth and the belt was placed on it for driving with any desired appliance4 ,this also is a very early model4 ,on the left side of the table there are seen a large variety of models1 ,n1 ,o1 ,p1 etc41 with fields of various shapes4 ,each of these models involves some distinct idea and they all represent gradual development chiefly interesting as showing ,mr4 ,tesla's efforts to adapt his system to the existing high frequencies4 ,on the right side of the table1 at ,s1 ,t1 are shown1 on separate supports1 larger and more perfected armatures of commercial motors1 and in the space around the table a variety of motors and generators supplying currents to them was exhibited4 ,the high frequency exhibit embraced ,mr4 ,tesla's first original apparatus used in his investigations4 ,there was exhibited a glass tube with one layer of silk-covered wire wound at the top and a copper ribbon on the inside4 ,this was the first disruptive discharge coil constructed by him4 ,at ,u is shown the disruptive discharge coil exhibited by him in his lecture before the ,american ,institute of ,electrical ,engineers1 in ,may1 #ahia4ah ,at ,v and ,w are shown some of the first high frequency transformers4 ,a number of various fields and armatures of small models of high frequency apparatus as shown at ,x and ,y1 and others not visible in the picture1 were exhibited4 ,in the annexed space the dynamo then used by ,mr4 ,tesla at ,columbia ,college was exhibited2 also another form of high frequency dynamo used4 #ah ,see ,part ,,ii1 ,chap4 ,,xxvi41 page #ade4 ,illustration3 ,,fig4 #caa4 ,in this space also was arranged a battery of ,leyden jars and his large disruptive discharge coil which was used for exhibiting the light phenomena in the adjoining dark room4 ,the coil was operated at only a small fraction of its capacity1 as the necessary condensers and transformers could not be had and as ,mr4 ,tesla's stay was limited to one week2 notwithstanding1 the phenomena were of a striking character4 ,in the room were arranged two large plates placed at a distance of about eighteen feet from each other4 ,between them were placed two long tables with all sorts of phosphorescent bulbs and tubes2 many of these were prepared with great care and marked legibly with the names which would shine with phosphorescent glow4 ,among them were some with the names of ,helmholtz1 ,faraday1 ,maxwell1 ,henry1 ,franklin1 etc4 ,mr4 ,tesla had also not forgotten the greatest living poet of his own country1 ,zmaj ,jovan2 two or three were prepared with inscriptions1 like ,welcome1 ,electricians1 and produced a beautiful effect4 ,each represented some phase of this work and stood for some individual experiment of importance4 ,outside the room was the small battery seen in ,fig4 #caa1 for the exhibition of some of the impedance and other phenomena of interest4 ,thus1 for instance1 a thick copper bar bent in arched form was provided with clamps for the attachment of lamps1 and a number of lamps were kept at incandescence on the bar2 there was also a little motor shown on the table operated by the disruptive discharge4 ,as will be remembered by those who visited the ,exposition1 the ,westinghouse ,company made a line exhibit of the various commercial motors of the ,tesla system1 while the twelve generators in ,machinery ,hall were of the two-phase type constructed for distributing light and power4 ,mr4 ,tesla1 also exhibited some models of his oscillators4 ,,chapter ,,xliii4 ,,the ,,tesla ,,mechanical ,,and ,,electrical ,,oscillators4 ,on the evening of ,friday1 ,august #be1 #ahic1 ,mr4 ,tesla delivered a lecture on his mechanical and electrical oscillators1 before the members of the ,electrical ,congress1 in the hall adjoining the ,agricultural ,building1 at the ,world's ,fair1 ,chicago4 ,besides the apparatus in the room1 he employed an air compressor1 which was driven by an electric motor4 ,mr4 ,tesla was introduced by ,dr4 ,elisha ,gray1 and began by stating that the problem he had set out to solve was to construct1 first1 a mechanism which would produce oscillations of a perfectly constant period independent of the pressure of steam or air applied1 within the widest limits1 and also independent of frictional losses and load4 ,secondly1 to produce electric currents of a perfectly constant period independently of the working conditions1 and to produce these currents with mechanism which should be reliable and positive in its action without resorting to spark gaps and breaks4 ,this he successfully accomplished in his apparatus1 and with this apparatus1 now1 scientific men will be provided with the necessaries for carrying on investigations with alternating currents with great precision4 ,these two inventions ,mr4 ,tesla called1 quite appropriately1 a mechanical and an electrical oscillator1 respectively4 ,the former is substantially constructed in the following way4 ,there is a piston in a cylinder made to reciprocate automatically by proper dispositions of parts1 similar to a reciprocating tool4 ,mr4 ,tesla pointed out that he had done a great deal of work in perfecting his apparatus so that it would work efficiently at such high frequency of reciprocation as he contemplated1 but he did not dwell on the many difficulties encountered4 ,he exhibited1 however1 the pieces of a steel arbor which had been actually torn apart while vibrating against a minute air cushion4 ,with the piston above referred to there is associated in one of his models in an independent chamber an air spring1 or dash pot1 or else he obtains the spring within the chambers of the oscillator itself4 ,to appreciate the beauty of this it is only necessary to say that in that disposition1 as he showed it1 no matter what the rigidity of the spring and no matter what the weight of the moving parts1 in other words1 no matter what the period of vibrations1 the vibrations of the spring are always isochronous with the applied pressure4 ,owing to this1 the results obtained with these vibrations are truly wonderful4 ,mr4 ,tesla provides for an air spring of tremendous rigidity1 and he is enabled to vibrate big weights at an enormous rate1 considering the inertia1 owing to the recoil of the spring4 ,thus1 for instance1 in one of these experiments1 he vibrates a weight of approximately #bj pounds at the rate of about #hj per second and with a stroke of about #g_/h inch1 but by shortening the stroke the weight could be vibrated many hundred times1 and has been1 in other experiments4 ,to start the vibrations1 a powerful blow is struck1 but the adjustment can be so made that only a minute effort is required to start1 and1 even without any special provision it will start by merely turning on the pressure suddenly4 ,the vibration being1 of course1 isochronous1 any change of pressure merely produces a shortening or lengthening of the stroke4 ,mr4 ,tesla showed a number of very clear drawings1 illustrating the construction of the apparatus from which its working was plainly discernible4 ,special provisions are made so as to equalize the pressure within the dash pot and the outer atmosphere4 ,for this purpose the inside chambers of the dash pot are arranged to communicate with the outer atmosphere so that no matter how the temperature of the enclosed air might vary1 it still retains the same mean density as the outer atmosphere1 and by this means a spring of constant rigidity is obtained4 ,now1 of course1 the pressure of the atmosphere may vary1 and this would vary the rigidity of the spring1 and consequently the period of vibration1 and this feature constitutes one of the great beauties of the apparatus2 for1 as ,mr4 ,tesla pointed out1 this mechanical system acts exactly like a string tightly stretched between two points1 and with fixed nodes1 so that slight changes of the tension do not in the least alter the period of oscillation4 ,the applications of such an apparatus are1 of course1 numerous and obvious4 ,the first is1 of course1 to produce electric currents1 and by a number of models and apparatus on the lecture platform1 ,mr4 ,tesla showed how this could be carried out in practice by combining an electric generator with his oscillator4 ,he pointed out what conditions must be observed in order that the period of vibration of the electrical system might not disturb the mechanical oscillation in such a way as to alter the periodicity1 but merely to shorten the stroke4 ,he combines a condenser with a self-induction1 and gives to the electrical system the same period as that at which the machine itself oscillates1 so that both together then fall in step and electrical and mechanical resonance is obtained1 and maintained absolutely unvaried4 ,next he showed a model of a motor with delicate wheelwork1 which was driven by these currents at a constant speed1 no matter what the air pressure applied was1 so that this motor could be employed as a clock4 ,he also showed a clock so constructed that it could be attached to one of the oscillators1 and would keep absolutely correct time4 ,another curious and interesting feature which ,mr4 ,tesla pointed out was that1 instead of controlling the motion of the reciprocating piston by means of a spring1 so as to obtain isochronous vibration1 he was actually able to control the mechanical motion by the natural vibration of the electro-magnetic system1 and he said that the case was a very simple one1 and was quite analogous to that of a pendulum4 ,thus1 supposing we had a pendulum of great weight1 preferably1 which would be maintained in vibration by force1 periodically applied2 now that force1 no matter how it might vary1 although it would oscillate the pendulum1 would have no control over its period4 ,mr4 ,tesla also described a very interesting phenomenon which he illustrated by an experiment4 ,by means of this new apparatus1 he is able to produce an alternating current in which the ,e4 ,m4 ,f4 of the impulses in one direction preponderates over that of those in the other1 so that there is produced the effect of a direct current4 ,in fact he expressed the hope that these currents would be capable of application in many instances1 serving as direct currents4 ,the principle involved in this preponderating ,e4 ,m4 ,f4 he explains in this way3 ,suppose a conductor is moved into the magnetic field and then suddenly withdrawn4 ,if the current is not retarded1 then the work performed will be a mere fractional one2 but if the current is retarded1 then the magnetic field acts as a spring4 ,imagine that the motion of the conductor is arrested by the current generated1 and that at the instant when it stops to move into the field1 there is still the maximum current flowing in the conductor2 then this current will1 according to ,lenz's law1 drive the conductor out of the field again1 and if the conductor has no resistance1 then it would leave the field with the velocity it entered it4 ,now it is clear that if1 instead of simply depending on the current to drive the conductor out of the field1 the mechanically applied force is so timed that it helps the conductor to get out of the field1 then it might leave the field with higher velocity than it entered it1 and thus one impulse is made to preponderate in ,e4 ,m4 ,f4 over the other4 ,with a current of this nature1 ,mr4 ,tesla energized magnets strongly1 and performed many interesting experiments bearing out the fact that one of the current impulses preponderates4 ,among them was one in which he attached to his oscillator a ring magnet with a small air gap between the poles4 ,this magnet was oscillated up and down #hj times a second4 ,a copper disc1 when inserted within the air gap of the ring magnet1 was brought into rapid rotation4 ,mr4 ,tesla remarked that this experiment also seemed to demonstrate that the lines of flow of current through a metallic mass are disturbed by the presence of a magnet in a manner quite independently of the so-called ,hall effect4 ,he showed also a very interesting method of making a connection with the oscillating magnet4 ,this was accomplished by attaching to the magnet small insulated steel rods1 and connecting to these rods the ends of the energizing coil4 ,as the magnet was vibrated1 stationary nodes were produced in the steel rods1 and at these points the terminals of a direct current source were attached4 ,mr4 ,tesla also pointed out that one of the uses of currents1 such as those produced in his apparatus1 would be to select any given one of a number of devices connected to the same circuit by picking out the vibration by resonance4 ,there is indeed little doubt that with ,mr4 ,tesla's devices1 harmonic and synchronous telegraphy will receive a fresh impetus1 and vast possibilities are again opened up4 ,mr4 ,tesla was very much elated over his latest achievements1 and said that he hoped that in the hands of practical1 as well as scientific men1 the devices described by him would yield important results4 ,he laid special stress on the facility now afforded for investigating the effect of mechanical vibration in all directions1 and also showed that he had observed a number of facts in connection with iron cores4 ,illustration3 ,,fig4 #cab4 ,the engraving1 ,fig4 #cab1 shows1 in perspective1 one of the forms of apparatus used by ,mr4 ,tesla in his earlier investigations in this field of work1 and its interior construction is made plain by the sectional view shown in ,fig4 #cac4 ,it will be noted that the piston ,p is fitted into the hollow of a cylinder ,c which is provided with channel ports ,o ,o1 and ,i1 extending all around the inside surface4 ,in this particular apparatus there are two channels ,o ,o for the outlet of the working fluid and one1 ,i1 for the inlet4 ,the piston ,p is provided with two slots ,s ,s' at a carefully determined distance1 one from the other4 ,the tubes ,t ,t which are screwed into the holes drilled into the piston1 establish communication between the slots ,s ,s' and chambers on each side of the piston1 each of these chambers connecting with the slot which is remote from it4 ,the piston ,p is screwed tightly on a shaft ,a which passes through fitting boxes at the end of the cylinder ,c4 ,the boxes project to a carefully determined distance into the hollow of the cylinder ,c1 thus determining the length of the stroke4 ,surrounding the whole is a jacket ,j4 ,this jacket acts chiefly to diminish the sound produced by the oscillator and as a jacket when the oscillator is driven by steam1 in which case a somewhat different arrangement of the magnets is employed4 ,the apparatus here illustrated was intended for demonstration purposes1 air being used as most convenient for this purpose4 ,a magnetic frame ,m ,m is fastened so as to closely surround the oscillator and is provided with energizing coils which establish two strong magnetic fields on opposite sides4 ,the magnetic frame is made up of thin sheet iron4 ,in the intensely concentrated field thus produced1 there are arranged two pairs of coils ,h ,h supported in metallic frames which are screwed on the shaft ,a of the piston and have additional bearings in the boxes ,b ,b on each side4 ,the whole is mounted on a metallic base resting on two wooden blocks4 ,illustration3 ,,fig4 #cac4 ,the operation of the device is as follows3 ,the working fluid being admitted through an inlet pipe to the slot ,i and the piston being supposed to be in the position indicated1 it is sufficient1 though not necessary1 to give a gentle tap on one of the shaft ends protruding from the boxes ,b4 ,assume that the motion imparted be such as to move the piston to the left 7when looking at the diagram7 then the air rushes through the slot ,s' and tube ,t into the chamber to the left4 ,the pressure now drives the piston towards the right and1 owing to its inertia1 it overshoots the position of equilibrium and allows the air to rush through the slot ,s and tube ,t into the chamber to the right1 while the communication to the left hand chamber is cut off1 the air of the latter chamber escaping through the outlet ,o on the left4 ,on the return stroke a similar operation takes place on the right hand side4 ,this oscillation is maintained continuously and the apparatus performs vibrations from a scarcely perceptible quiver amounting to no more than #a of an inch1 up to vibrations of a little over #c_/h of an inch1 according to the air pressure and load4 ,it is indeed interesting to see how an incandescent lamp is kept burning with the apparatus showing a scarcely perceptible quiver4 ,to perfect the mechanical part of the apparatus so that oscillations are maintained economically was one thing1 and ,mr4 ,tesla hinted in his lecture at the great difficulties he had first encountered to accomplish this4 ,but to produce oscillations which would be of constant period was another task of no mean proportions4 ,as already pointed out1 ,mr4 ,tesla obtains the constancy of period in three distinct ways4 ,thus1 he provides properly calculated chambers1 as in the case illustrated1 in the oscillator itself2 or he associates with the oscillator an air spring of constant resilience4 ,but the most interesting of all1 perhaps1 is the maintenance of the constancy of oscillation by the reaction of the electromagnetic part of the combination4 ,mr4 ,tesla winds his coils1 by preference1 for high tension and associates with them a condenser1 making the natural period of the combination fairly approximating to the average period at which the piston would oscillate without any particular provision being made for the constancy of period under varying pressure and load4 ,as the piston with the coils is perfectly free to move1 it is extremely susceptible to the influence of the natural vibration set up in the circuits of the coils ,h ,h4 ,the mechanical efficiency of the apparatus is very high owing to the fact that friction is reduced to a minimum and the weights which are moved are small2 the output of the oscillator is therefore a very large one4 ,theoretically considered1 when the various advantages which ,mr4 ,tesla holds out are examined1 it is surprising1 considering the simplicity of the arrangement1 that nothing was done in this direction before4 ,no doubt many inventors1 at one time or other1 have entertained the idea of generating currents by attaching a coil or a magnetic core to the piston of a steam engine1 or generating currents by the vibrations of a tuning fork1 or similar devices1 but the disadvantages of such arrangements from an engineering standpoint must be obvious4 ,mr4 ,tesla1 however1 in the introductory remarks of his lecture1 pointed out how by a series of conclusions he was driven to take up this new line of work by the necessity of producing currents of constant period and as a result of his endeavors to maintain electrical oscillation in the most simple and economical manner4 ,,index4 ,alternate ,current ,electrostatic ,apparatus #cib ,alternating ,current ,generators for ,high ,frequency #aeb1 #cgd1 #bbd ,alternating ,motors and ,transformers #g ,american ,institute ,electrical ,engineers ,lecture #ade ,anthony1 ,w4 ,a41 ,tests of ,tesla ,motors #h ,apparatus for ,producing ,high ,vacua #bgf ,arc ,lighting1 ,tesla ,direct1 ,system #dea ,auxiliary ,brush ,regulation #dch ,biography1 ,tesla #d ,brush1 ,anti-,sparking #dcb ,brush1 ,third1 ,regulation #dch ,brush1 ,phenomena in ,high ,vacuum #bbf ,carborundum ,button for ,tesla ,lamps #adj1 #bec ,commutator1 ,anti-,sparking #dcb ,combination of ,synchronizing and ,torque ,motor #ie ,condensers with ,plates in ,oil #dah ,conversion with ,disruptive ,discharge #aic1 #bjd1 #cjc ,current or ,dynamic ,electricity ,phenomena #cbg ,direct ,current ,arc ,lighting #dea ,dischargers1 ,forms of #cje ,disruptive ,discharge ,coil #bjg1 #bba ,disruptive ,discharge ,phenomena #bab ,dynamos1 ,improved ,direct ,current #ddh ,early ,phase ,motors #dgg ,effects with ,high ,frequency and ,high ,potential ,currents #aai ,electrical ,congress ,lecture1 ,chicago4 #dhf ,electric ,resonance #cdj ,electric ,discharges in ,vacuum ,tubes #cif ,electrolytic ,registering ,meter #dbj ,eye1 ,observations on the #bid ,flames1 ,electrostatic1 ,non-,consuming #aff1 #bgb ,forbes ,unipolar ,generator #dfh1 #dgd ,franklin ,institute ,lecture #bid ,generators1 ,pyromagnetic #dbi ,high ,potential1 ,high ,frequency3 ,brush ,phenomena in ,high ,vacuum #bbf ,carborundum ,buttons #adj1 #bec ,disruptive ,discharge ,phenomena #bab ,flames1 ,electrostatic1 ,non-,consuming #aff1 #bgb ,impedance1 ,novel ,phenomena #aid1 #cch ,lighting ,lamps ,through ,body #cei ,luminous ,effects with ,gases #cfh ,massage with ,currents #cid ,motor with ,single ,wire #bcd1 #ccj ,no ,wire ,motors #bce ,oil ,insulation of ,induction ,coils #agc1 #bba ,ozone1 ,production of #aga ,phosphorescence #cfg ,physiological ,effects #afb1 #cid ,resonance #cdj ,spinning ,filament #afh ,streaming ,discharges of ,high ,tension ,coil #aee1 #afc ,telegraphy without ,wires #cdf ,impedance1 ,novel ,phenomena #aid1 #cch ,improvements in ,unipolar ,generators #dfe ,improved ,direct ,current ,dynamos and ,motors #ddh ,induction ,motors #ib ,institution ,electrical ,engineers ,lecture #aih ,lamps and ,motor operated on a ,single ,wire #ccj ,lamps with ,single ,straight ,fiber #ahc ,lamps containing only a ,gas #ahh ,lamps with ,refractory ,button #agg1 #bci1 #cfj ,lamps for ,simple ,phosphorescence #ahg1 #bhb1 #cfd ,lecture1 ,tesla before3 ,american ,institute ,electrical ,engineers #ade ,royal ,institution #abd ,institution ,electrical ,engineers #aih ,franklin ,institute and ,national ,electric ,light ,association #bid ,electrical ,congress1 ,chicago #dhf ,lighting ,lamps ,through the ,body #cei ,light ,phenomena with ,high ,frequencies #cdi ,luminous ,effects with ,gases at ,low-,pressure #cfh ,magnetic ,lag ,motor #fg ,massage with ,currents of ,high ,frequency #cid ,mechanical and ,electrical ,oscillators #dhf ,method of obtaining ,direct from ,alternating currents #dji ,method of obtaining ,difference of ,phase by ,magnetic ,shielding #ga ,motors3 ,with ,circuits of ,different ,resistance #gi ,with ,closed ,conductors #i ,combination of ,synchronizing and ,torque #ie ,with ,condenser in ,armature ,circuit #aja ,with ,condenser in one of the ,field ,circuits #ajf ,with ,coinciding ,maxima of ,magnetic ,effect in ,armature and ,field #hc ,with ,current ,lag ,artificially ,secured #eh ,early ,phase #dgg ,with ,equal ,magnetic ,energies in ,field and ,armature #ha ,or ,generator1 obtaining ,desired ,speed of #cf ,improved ,direct ,current #ddh ,induction #ib ,magnetic ,lag #fg ,no ,wire #bce ,with ,phase ,difference in ,magnetization of ,inner and ,outer ,parts of ,core #hh ,regulator for ,rotary ,current #de ,single ,circuit1 ,self-starting ,synchronizing #ej ,single ,phase #gf ,with ,single ,wire to ,generator #bcd1 #ccj ,synchronizing #i ,thermo-,magnetic #dbd ,utilizing ,continuous ,current ,generators #ca ,national ,electric ,light ,association ,lecture #bid ,no ,wire ,motor #bce ,observations on the ,eye #bid ,oil1 ,condensers with ,plates in #dah ,oil ,insulation of ,induction ,coils #agc1 #bba ,oscillators1 ,mechanical and ,electrical #dhf ,ozone1 ,production of #aga ,phenomena ,produced by ,electrostatic ,force #cah ,phosphorescence and ,sulphide of ,zinc #cfg ,physiological ,effects of ,high ,frequency #afb1 #cid ,polyphase ,systems #bf ,polyphase ,transformer #aji ,pyromagnetic ,generators #dbi ,regulator for ,rotary ,current ,motors #de ,resonance1 ,electric1 ,phenomena of #cdj ,resultant ,attraction #g ,rotating ,field ,transformers #i ,rotating ,magnetic ,field #i ,royal ,institution ,lecture #abd ,scope of ,lectures #aai ,single ,phase ,motor #gf ,single ,circuit1 ,self-,starting ,synchronizing ,motors #ej ,spinning ,filament ,effects #afh ,streaming ,discharges of ,high ,tension ,coil #aee1 #afc ,synchronizing ,motors #i ,telegraphy without ,wires #bdf ,transformer with ,shield between ,primary and ,secondary #aac ,thermo-,magnetic ,motors #dbd ,thomson1 ,j4 ,j41 on ,vacuum ,tubes #cig1 #djb1 #djf ,thomson1 ,sir ,w41 ,current ,accumulator #dga ,transformers3 ,alternating #g ,magnetic ,shield #aac ,polyphase #aji ,rotating ,field #i ,tubes3 ,coated with ,yttria1 etc4 #ahg ,coated with ,sulphide of ,zinc1 etc4 #bij1 #cfg ,unipolar ,generators #dfe ,unipolar ,generator1 ,forbes #dfh1 #dgd ,yttria1 ,coated ,tubes #ahg ,zinc1 ,tubes ,coated with ,sulphide of #cfg