,transcriber's ,notes3 ,underscores 80 before and after a word or phrase indicate italics in the original text4 ,equal signs 80 before and after a word or phrase indicate bold in the original text4 ,small capitals have been converted to ,,solid capitals4 ,illustrations have been moved so they do not break up paragraphs4 ,typographical and punctuation errors have been silently corrected4 ,,signalling ,,across ,,space ,,without ,,wires4 ,,being ,a ,,description ,,of ,,the ,,work ,,of ,,hertz ,,his ,,successors4 ,,by ,,prof4 ,,oliver ,j4 ,,lodge1 ,f4,r4,s4 ,,third ,,edition1 ,with ,additional ,remarks concerning the ,application to ,telegraphy1 and ,later ,developments4 ,,london3 8,,the ,,electrician0 ,,printing ,,and ,,publishing ,,company1 ,,limited1 ,,salisbury ,,court1 ,,fleet ,,street4 ,copyright4 ,,works ,,by ,,dr4 ,o4 ,j4 ,,lodge4 ,lightning ,conductors and ,lightning ,guards4 ,a ,complete ,treatise on the subject of ,electric ,discharges in general4 ,pioneers of ,science4 ,a popular ,illustrated ,history of the ,early ,astronomers and their ,work up to ,recent ,times4 ,modern ,views of ,electricity4 ,elementary ,mechanics4 ,protection of ,buildings from ,lightning4 ,mann ,lectures to the ,society of ,arts1 #ahhh4 ,secondary ,batteries and the ,electrical ,storage of ,energy4 ,cantor ,lectures to the ,society of ,arts1 #ahhc4 ,,table ,,of ,,contents4 7,the lines in italics which look like headings of paragraphs are really statements about experiments which were at that place shown47 #a4 ,,royal ,,institution ,,lecture ,,on ,,the ,,work ,,of ,,hertz ,,and ,,some ,,of ,,his ,,successors3-- ,,pages ,biographical ,introduction #a ,elementary ,explanation about ,electrical ,radiation and ,absorption and the ,effect of ,syntony #c-h ,syntonic ,leyden ,jar ,experiment #f1 #ba ,side ,observations on the ,effect of ,light on ,electric ,discharge #i-ab ,various ,detectors of ,radiation #ac-bc ,physiological ,non-,effect of ,sufficiently ,rapid ,alternations #ag ,boltzmann ,gap ,detector--the ,precursor of the ,coherer #ah ,branly's ,observations 7see also ,appendix1 page #ie7 #bj ,early ,form of ,coherer and of ,branly ,filings ,tube #ba-bc ,early ,signalling over #dj or #fj yards #bd-be ,use of ,telephone as ,receiver #bf ,experiments showing ,syntony #bg-bh ,hypothesis concerning the ,nature of ,vision #bi-ca ,summary of ,various ,detectors of ,radiation #cj ,radiation ,detected from extremely ,weak ,sparks1 and by very compact ,receiver with ,collecting ,wire #cb-cd ,vacuum ,filings ,tube #cd ,effect of ,metallic ,enclosure #ce-ch ,experiments on ,reflection1 ,refraction1 and ,polarisation of ,radiation #ci-db ,note about ,electric ,waves on ,wires #dc #b4 ,,application ,,of ,,hertz ,,waves ,,and ,,coherer ,,signalling ,,to ,,telegraphy #de-dh ,coherer ,behaviour and ,tommasina's ,experiment #di ,single-,point ,coherer #ee ,general ,remarks about ,patent ,law #ej ,attempts at ,syntonic ,telegraphy #eb-fj ,syntonic ,radiators and ,receivers #ea-ef #c4 ,,details ,,of ,,other ,,telegraphic ,,developments3-- ,popoff's #ahie ,demonstration #fj-fb ,slaby's ,overland ,experiments #fc-ff ,marconi's ,recent ,demonstration #ff-gb #d4 ,a ,,history ,,of ,,the ,,coherer ,,principle #gc-hg ,professor ,hughes' ,early ,observations before ,hertz or ,branly #hh-id ,work of ,monsieur ,branly #ie-ajh #e4 ,,communications ,,with ,,respect ,,to ,,coherer ,,phenomena ,,on ,a ,,large ,,scale3-- ,professor ,elihu ,thomson #aji ,dr4 ,morton #aaa #f4 ,,photo-,,electric ,,researches ,,of ,,drs4 ,,elster ,,and ,,geitel #aae-abf #g4 ,,photo-,,electric ,,researches ,,of ,,professor ,,righi #abg ,,signalling ,,through ,,space ,,without ,,wires4 ,,the ,,work ,,of ,,hertz ,,and ,,some ,,of ,,his ,,successors4 ,the following pages 7up to page #db7 are the ,notes of a ,lecture delivered by ,dr4 ,o4 ,j4 ,lodge before the ,royal ,institution of ,great ,britain on ,friday evening1 ,june #a1 #ahid4 ,these notes have been revised by ,dr4 ,lodge1 and prepared for publication in the form here presented4 ,after page #db an account is given of the later applications of ,hertzian wave experiments to wireless telegraphy1 and a series of ,appendices are also given4 ,introductory4--#ahid4 ,the untimely end of a young and brilliant career cannot fail to strike a note of sadness and awaken a chord of sympathy in the hearts of his friends and fellow-workers4 ,of men thus cut down in the early prime of their powers there will occur to us here the names of ,fresnel1 of ,carnot1 of ,clifford1 and now of ,hertz4 ,his was a strenuous and favoured youth2 he was surrounded from his birth with all the influences that go to make an accomplished man of science--accomplished both on the experimental and on the mathematical side4 ,the front rank of scientific workers is weaker by his death1 which occurred on ,january #a1 #ahid1 the thirty-seventh year of his life4 ,yet did he not go till he had effected an achievement which will hand his name down to posterity as the founder of an epoch in experimental physics4 ,in mathematical and speculative physics others had sown the seed4 ,it was sown by ,faraday1 it was sown by ,thomson and by ,stokes1 by ,weber also doubtless1 and by ,helmholtz2 but in this particular department it was sown by none more fruitfully and plentifully than by ,clerk ,maxwell4 ,of the seed thus sown ,hertz reaped the fruits4 ,through his experimental discovery1 ,germany awoke to the truth of ,clerk ,maxwell's theory of light1 of light and electricity combined1 and the able army of workers in that country 7not forgetting some in ,switzerland1 ,france1 and ,ireland7 have done most of the gleaning after ,hertz4 ,this is the work of ,hertz which is best known1 the work which brought him immediate fame4 ,it is not always that public notice is so well justified4 ,the popular instinct is generous and trustful1 and it is apt to be misled4 ,the scientific eminence accorded to a few energetic persons by popular estimate is more or less amusing to those working on the same lines4 ,in the case of ,hertz no such mistake has been made4 ,his name is not over well-known1 and his work is immensely greater in every way than that of several who have made more noise4 ,his best known discovery is by no means his only one1 and no less than eighteen ,papers were contributed to ,german periodicals by him1 in addition to the papers incorporated in his now well-known book on electric waves4 ,in closing these introductory and personal remarks1 ,i should like to say that the enthusiastic admiration for ,hertz's spirit and character felt and expressed by students and workers who came into contact with him is not easily to be exaggerated4 ,never was a man more painfully anxious to avoid wounding the susceptibilities of others2 and he was accustomed to deprecate the prominence given to him by speakers and writers in this country1 lest it might seem to exalt him unduly above other and older workers among his own sensitive countrymen4 ,speaking of the other great workers in physics in ,germany1 it is not out of place to record the sorrow with which we have heard of the recent death of ,dr4 ,august ,kundt1 ,professor in the ,university of ,berlin1 successor to ,von ,helmholtz in that capacity4 ,when ,i consented to discourse on the work of ,hertz1 my intention was to repeat some of his actual experiments1 and especially to demonstrate his less-known discoveries and observations4 ,but the fascination exerted upon me by electric oscillation experiments1 when ,i1 too1 was independently working at them in the spring of #ahhh1a resumed its hold1 and my lecture will accordingly consist of experimental demonstrations of the outcome of ,hertz's work rather than any precise repetition of portions of that work itself4 #a ,phil4 ,mag41 ,,xxvi41 pp4 #bbi1 #bcj1 ,august1 #ahhh2 or 8,lightning ,conductors and ,lightning ,guards10 pp4 #ajd1 #aje2 also ,proc4 ,roy4 ,soc41 ,vol4 #ej1 p4 #bg4 ,in case a minority of my audience are in the predicament of not knowing anything about the subject1 a five minutes' explanatory prelude may be permitted2 and the simplest way will be for me hastily to summarise our knowledge of the subject before the era of ,hertz4 ,illustration3 ,,fig4 #a4--,oscillations of ,dumb-bell ,hertz ,vibrator 7after ,bjerknes74 ,just as a pebble thrown into a pond excites surface ripples1 which can heave up and down floating straws under which they pass1 so a struck bell or tuning fork emits energy into the air in the form of what are called sound waves1 and this radiant energy is able to set up vibrations in other suitable elastic bodies4 ,if the body receiving them has its natural or free vibrations violently damped1 so that when left to itself it speedily returns to rest 7,fig4 #a71 then it can respond fully to notes of almost any pitch4 ,this is the case with your ears and the tones of my voice4 ,tones must be exceedingly shrill before they cease to excite the ear at all4 ,if1 on the other hand1 the receiving body has a persistent period of vibration1 continuing in motion long after it is left to itself 7,fig4 #b7 like another tuning fork or bell1 for instance1 then far more facility of response exists1 but great accuracy of tuning is necessary if it is to be fully called out2 for if the receiver is not thus accurately syntonised with the source1 it fails more or less completely to resound4 ,illustration3 ,,fig4 #b4--,oscillation of ,ring-shaped ,hertz ,resonator excited by ,syntonic ,vibrator 7after ,bjerknes74 ,illustration3 ,,fig4 #c4--,oscillation of ,ring ,resonator not quite syntonic with ,radiator4 7,for method of obtaining these curves see ,fig4 #ad47 ,conversely1 if the source is a persistent vibrator1 correct tuning is essential1 or it will destroy at one moment 7,fig4 #c7 motion which it originated the previous moment4 ,whereas1 if it is a dead-beat or strongly-damped exciter1 almost anything will respond equally well or equally ill to it4 ,what ,i have said of sounding bodies is true of all vibrators in a medium competent to transmit waves4 ,now a sending telephone or a microphone1 when spoken to1 emits waves into the ether1 and this radiant energy is likewise able to set up vibration in suitable bodies4 ,but we have no delicate means of directly detecting these electrical or etherial waves2 and if they are to produce a perceptible effect at a distance1 they must be confined1 as by a speaking-tube1 prevented from spreading1 and concentrated on the distant receiver4 ,this is the function of the telegraph wire2 it is to the ether what a speaking-tube is to air4 ,a metal wire in air 7in function1 not in details of analogy7 is like a long hollow cavity surrounded by nearly rigid but slightly elastic walls4 ,sphere charged from ,electrophorus4 ,furthermore1 any conductor electrically charged or discharged with sufficient suddenness must emit electrical waves into the ether1 because the charge given to it will not settle down instantly1 but will surge to and fro several times first2 and these surgings or electric oscillations must1 according to ,maxwell1 start waves in the ether1 because at the end of each half-swing they cause electrostatic1 and at the middle of each half-swing they cause electromagnetic effects1 and the rapid alternation from one of these modes of energy to the other constitutes etherial waves4#b ,if a wire is handy they will run along it1 and may be felt a long way off4 ,if no wire exists they will spread out like sound from a bell1 or light from a spark1 and their intensity will decrease according to the inverse square of the distance4 #b ,strictly speaking1 in the waves themselves there is no lag or difference of phase between the electric and the magnetic vibrations2 the difference exists in emitter or absorber1 but not in the transmitting medium4 ,true radiation of energy does not begin till about a quarter wave length from the source1 and within that distance the initial quarter period difference of phase is obliterated4 ,maxwell and his followers well knew that there would be such waves2 they knew the rate at which they would go1 they knew that they would go slower in glass and water than in air1 they knew that they would curl round sharp edges1 that they would be partly absorbed but mainly reflected by conductors1 that if turned back upon themselves they would produce the phenomena of stationary waves1 or interference1 or nodes and loops2 it was known how to calculate the length of such waves1 and even how to produce them of any required or predetermined wave length from #a1jjj miles to a foot4 ,other things were known about them which would take too long to enumerate2 any homogeneous insulator would transmit them1 would refract or concentrate them if it were of suitable shape1 would reflect none of a particular mode of vibration at a certain angle1 and so on1 and so on4 ,all this was known1 ,i say1 known with varying degrees of confidence2 but by some known with as great confidence as1 perhaps even more confidence than1 is legitimate before the actuality of experimental verification4 ,hertz supplied the verification4 ,he inserted suitable conductors in the path of such waves1 conductors adapted for the occurrence in them of induced electric oscillations1 and to the surprise of everyone1 himself doubtless included1 he found that the secondary electric surgings thus excited were strong enough to display themselves by minute electric sparks4 ,illustration3 ,,fig4 #d4--;,experiment with ,syntonic ,leyden ,jars 7cf4 page #ba74 ,syntonic ,leyden ,jars4 ,i shall show this in a form which requires great precision of tuning or syntony1 both emitter and receiver being persistently vibrating things giving some #cj or #dj swings before damping has a serious effect4 ,i take two ,leyden jars with circuits about a yard in diameter1 and situated about two yards apart 7,fig4 #d74 ,i charge and discharge one jar1 and observe that the surgings set up in the other can cause it to overflow if it is syntonised with the first4#c #c ,see ,nature1 ,vol4 ,,xli41 p4 #cfh1 where ,i first described this experiment2 or quotation in ,j4 ,j4 ,thomson's 8,recent ,researches10 p4 #cie4 ,a closed circuit such as this is a feeble radiator and a feeble absorber1 so it is not adapted for action at a distance4 ,in fact1 ,i doubt whether it will visibly act at a range beyond the at which true radiation of broken-off energy occurs4 ,if the coatings of the jar are separated to a greater distance1 so that the dielectric is more exposed1 it radiates better2 because in true radiation the electrostatic and the magnetic energies must be equal1 whereas in a ring circuit the magnetic energy predominates4 ,by separating the coats of the jar as far as possible we get a typical ,hertz vibrator 7,fig4 #e71 whose dielectric extends out into the room1 and thus radiates very powerfully4 ,illustration3 ,,fig4 #e4--,standard ,hertz ,radiator4 ,ordinary ,size ,hertz ,vibrator4 ,in consequence of its radiation of energy1 its vibrations are rapidly damped1 and it only gives some three or four good strong swings 7,fig4 #a74 ,hence it follows that it has a wide range of excitation2 i4e41 it can excite sparks in conductors barely at all in tune with it4 ,the two conditions1 conspicuous energy of radiation and persistent vibration electrically produced1 are at present incompatible4 ,whenever these two conditions coexist1 considerable power or activity will1 of course1 be necessary in the source of energy4 ,at present they only coexist in the sun and other stars1 in the electric arc1 and in furnaces4 ,two ,circular ,vibrators ,sparking in sympathy4 ,the receiver ,hertz used was chiefly a circular resonator 7,fig4 #f71 not a good absorber but a persistent vibrator1 well adapted for picking up disturbances of precise and measurable wave length4 ,its mode of vibration when excited by emitter in tune with it is depicted in ,fig4 #b4 ,i find that the circular resonators can act as senders too2 here is one exciting quite long sparks in a second one4 ,electric ,syntony4--,that was his discovery1 but he did not stop there4 ,he at once proceeded to apply his discovery to the verification of what had already been predicted about the waves1 and by laborious and difficult interference experiments he ascertained that the previously calculated length of the waves was thoroughly borne out by fact4 ,these interference experiments in free space are his greatest achievement4 ,illustration3 ,,fig4 #f4--;,circular ,resonator4 7,the knobs ought to nearly touch each other47 ,illustration3 ,,fig4 #f;,a4--,any circular ,resonator can be used as a sender by bringing its knobs near the sparking knobs of a coil2 but a simple arrangement is to take two semi-circles1 as in above figure1 and make them the coil terminals4 ,the capacity of the cut ends can be varied1 and the period thereby lengthened1 by expanding them into plates4 ,he worked out every detail of the theory splendidly1 separately analysing the electric and the magnetic oscillation1 using language not always such as we should use now1 but himself growing in theoretic insight through the medium of what would have been to most physicists a confusing maze of troublesome facts1 and disentangling all their main relations most harmoniously4 ,holtz ,machine1 ,a and ,b ,sparks2 ,glass and ,quartz ,panes in ,screen4 ,while ,hertz was observing sparks such as these1 the primary or exciting spark and the secondary or excited one1 he observed as a bye issue that the secondary spark occurred more easily if the light from the primary fell upon its knobs4 ,he examined this new influence of light in many ways1 and showed that although spark light and electric brush light were peculiarly effective1 any source of light that gave very ultra-violet rays produced the same result4 ,illustration3 ,,fig4 #g4--;,experiment arranged to show effect on one spark of light from another4 ,the ,b spark occurs more easily when it can see the ,a spark through the window1 unless the window is glazed with glass4 ,a quartz pane transmits the effect3 glass cuts it off4 ,the above figure represents my way of showing the experiment4 ,it will be observed that with this arrangement the ,b knobs are at the same potential up to the instant of the flash1 and in that case the ultra-violet portion of the light of the ,a spark assists the occurrence of the ,b spark4 ,but it is interesting to note what ,elster and ,geitel have found 7see ,appendix ,,iv41 ,fig4 #ei71 that if the ,b knobs were subjected to steady strain instead of to impulsive rush--e4g41 if they were connected to the inner coats of the jars instead of the outer coatings--that then the effect of ultra-violet light on either spark gap would exert a deterrent influence1 so that the spark would probably occur at the other1 or non-illuminated gap4 ,with the altered connections it is1 of course1 not feasible to illuminate one spark by the light of the other2 the sparks are then alternative1 not successive4 ,wiedemann and ,ebert1 and a number of experimenters1 have repeated and extended this discovery1 proving that it is the cathode knob on which illumination takes effect2 and ,hallwachs and ,righi made the important observation1 which ,elster and ,geitel1 ,stoletow1 ,branly1 and others have extended1 that a freshly-polished zinc or other oxidisable surface1 if charged negatively1 is gradually discharged by ultra-violet light4 ,illustration3 ,,fig4 #h4--,zinc ,rod in ,arc ,light1 protected by ,glass ,screen4 ,the lenses are of quartz1 but there is no need for any lenses in this experiment2 leakage of electricity begins directly the glass plate is withdrawn4 ,it is easy to fail in reproducing this experimental result if the right conditions are not satisfied2 but if they are it is absurdly easy1 and the thing might have been observed nearly a century ago4 ,zinc discharging ,negative ,electricity in ,light2 ,gold ,leaf ,electroscope2 ,glass and ,quartz ,panes2 ,quartz ,prism4 ,take a piece of zinc1 clean it with emery paper1 connect it to a gold leaf electroscope1 and expose it to an arc lamp4 7,fig4 #h74 ,if charged positively nothing appears to happen1 the action is very slow2 but a negative charge leaks away in a few seconds if the light is bright4 ,any source of light rich in ultra-violet rays will do2 the light from a spark is perhaps most powerful of all4 ,a pane of glass cuts off all the action2 so does atmospheric air in sufficient thickness 7at any rate1 town air71 hence sunlight is not powerful4 ,a pane of quartz transmits the action almost undiminished1 but fluorspar may be more transparent still4 ,condensing the arc rays with a quartz lens and analysing them with a quartz prism or reflection grating1 we find that the most effective part of the light is high up in the ultra-violet1 surprisingly far beyond the limits of the visible spectrum#d 7,fig4 #i1 next page74 #d ,while preparing for the lecture it occurred to me to try1 if possible during the lecture itself1 some new experiments on the effect of light on negatively charged bits of rock and ice1 because if the effect is not limited to metals it must be important in connection with atmospheric electricity4 ,when ,mr4 ,branly coated an aluminium plate with an insulating varnish1 he found that its charge was able to soak in and out of the varnish during illumination 7,comptes ,rendus1 ,vol4 ,,cx41 p4 #hih1 #ahij74 ,now the mountain tops of a negatively charged earth are exposed to very ultra-violet rays1 and the air is a dielectric in which quiet up-carrying and sudden downpour of electricity could go on in a manner not very unlike the well-known behaviour of water vapour2 and this perhaps may be the reason1 or one of the reasons1 why it is not unusual to experience a thunderstorm after a few fine days4 ,i have now tried these experiments on such geological fragments as were handy1 and find that many of them discharge negative electricity under the action of a naked arc1 especially from the side of the specimens which was somewhat dusty1 but that when wet they discharge much less rapidly1 and when positively charged hardly at all4 ,ice and garden soil discharge negative electrification1 too1 under ultra-violet illumination1 but not so quickly as limestone1 mica schist1 ferruginous quartz1 clay1 and some other specimens4 ,granite barely acts2 it seems to insulate too well4 ,the ice and soil were tried in their usual moist condition1 but1 when thoroughly dry1 soil discharges quite rapidly4 ,no rock tested was found to discharge as quickly as does a surface of perfectly bright metal1 such as iron1 but many discharged much more quickly than ordinary dull iron1 and rather more quickly than when the bright iron surface was thinly oiled or wetted with water4 ,to-day 7,june #e1 #ahid7 ,i find that the leaves of ,geranium discharge positive electrification five times as quickly as negative1 under the action of an arc light1 and that glass cuts the effect off while quartz transmits it4 7,for ,elster and ,geitel's experiments1 and those of ,righi1 see ,appendices1 p4 #aae et seq47 ,this is rather a digression1 but ,i have taken some pains to show it properly because of the interest betrayed by ,lord ,kelvin on this matter1 and the caution which he felt about accepting the results of the ,continental experimenters too hastily4 ,it is probably a chemical phenomenon1 and ,i am disposed to express it as a modification of the ,volta contact effect#e with illumination4 #e ,see ,b4 ,a4 ,report1 #ahhd1 pp4 #ejb-eai2 or ,phil4 ,mag41 ,vol4 ,,xix41 pp4 #bfg-ceb4 ,illustration3 ,,fig4 #i4--,zinc ,rod discharging ,negative ,electricity in the very ,ultra-violet ,light of a ,spectrum formed by a ,quartz ,train4 ,the best discharging light is found far beyond the limits of the visible spectrum4 ,return now to the ,hertz vibrator1 or ,leyden jar with its coatings well separated1 so that we can get into its electric as well as its magnetic field4 ,here is a great one giving waves #cj metres long1 radiating while it lasts with an activity of #ajj ,h4,p41 and making ten million complete electric vibrations per second4 ,it is made of four large copper sheets soldered together two and two1 strung up by thin rope to a gallery1 and each pair connected with the other by several yards of ,no4 #j pure copper rod1 interrupted by a pair of sparking knobs 7,fig4 #aj74 ,large ,hertz ,vibrator in action2 ,abel's ,fuse ,detector2 ,vacuum ,tube ,detector2 ,striking of an ,arc4 ,its great radiating power damps it down very rapidly1 so that it does not make above two or three swings2 but nevertheless1 each time it is excited1 sparks can be drawn from most of the reasonably elongated conductors in the theatre of this ,institution1 and indeed from wire fencing and iron roofs outside this building4 ,a suitably situated gas leak can be ignited by these induced sparks4 ,an ,abel's fuse connecting the water pipes with the gas pipes will blow off2 vacuum tubes connected to nothing will glow 7this fact has been familiar to all who have worked with ,hertz waves since #ahhi71 electric leads1 if anywhere near each other1 as they are in some incandescent lamp-holders1 may spark across to each other1 thus striking an arc and blowing their fuses4 ,this blowing of fuses by electric radiation frequently happened at ,liverpool till the suspensions of the theatre lamps were altered4 ,they had at first been held in position by wire guides1 which served as collectors of the ,hertz waves or impulses4 ,illustration3 ,,fig4 #aj4--;,hertz ,oscillator on reduced scale1 th inch to a foot4 ,the striking of an arc by the little reverberating sparks between two lamp-carbons connected with the #ajj-volt mains ,i incidentally now demonstrate4 ,an arc is started directly the large ,hertz vibrator is excited at a distance4 ,there are some who think that lightning flashes can do none of these secondary things4 ,they are mistaken4 ,specimens of ,emitters and ,receivers4 ,on the table are specimens of various emitters and receivers such as have been used by different people2 the orthodox ,hertz radiator 7,fig4 #e71 and the orthodox ,hertz receivers3--,a circular ring 7,fig4 #f7 for interference experiments1 because it is but little damped1 and a straight wire for receiving at a distance1 because it is a much better absorber4 ,beside these are the spheres and ellipsoids 7or elliptical plates71 which ,i have myself introduced and mainly used 7,fig4 #ai71 because they are powerful radiators and absorbers1 and because their theory has been worked out by ,horace ,lamb and ,j4 ,j4 ,thomson4 ,also dumb-bells 7,fig4 #aa7 without air gap1 which must be excited by a positive spark at one end and a negative spark at the other1 and many other shapes1 the most recent of mine being the inside of a hollow cylinder with sparks at ends of a diameter 7,fig4 #ab72 this being a feeble radiator1 but a very persistent vibrator1#f and1 therefore1 well adapted for interference and diffraction experiments4 ,but1 indeed1 spheres can be made to vibrate longer than usual by putting them into copper hats or enclosures1 in which an aperture of varying size can be made to let the waves out 7,figs4 #bj and #ba74 #f ,j4 ,j4 ,thomson1 8,recent ,researches10 #cdd4 ,illustration3 ,,fig4 #aa4--;,a ,small ,dumb-bell ,form of ,radiator for ,impulsive ,rush4 ,illustration3 ,,fig4 #ab4--;,dr4 ,lodge's ,hollow ,cylindrical ,radiator1 arranged horizontally against the outside of a ,metal-lined ,box containing the ,spark-producing ,apparatus4 ,half natural size4 ,emitting #c in4 waves4 ,many of these senders will do for receivers too1 giving off sparks to other insulated bodies or to earth2 but besides the ,hertz type of receiver1 many other detectors of radiation have been employed4 ,vacuum tubes can be used1 either directly or on the trigger principle1 as by ,zehnder 7,fig4 #ac71g the resonator spark precipitating a discharge from some auxiliary battery or source of energy1 and so making a feeble disturbance very visible4 ,explosives may be used for the same purpose1 either in the form of mixed water-gases or in the form of an ,abel's fuse4 ,fitz,gerald found that a tremendously sensitive galvanometer could indicate that a feeble spark had passed1 by reason of the consequent disturbance of electrical equilibrium which settled down again through the galvanometer4#h ,this was the method he used in this theatre four years ago4 ,blyth used a one sided electrometer1 and ,v4 ,bjerknes has greatly developed this method 7,fig4 #ad71 abolishing the need for a spark1 and making the electrometer metrical1 integrating and satisfactory4#i ,with this detector many measurements have been made at ,bonn by ,bjerknes1 ,yule1 ,barton and others on waves concentrated and kept from space dissipation by guiding wires4 #g ,wied4 ,ann41 ,,xlvii41 p4 #gg4 #h ,fitz,gerald1 ,nature1 ,vol4 ,,xli41 p4 #bie1 and ,vol4 ,,xlii41 p4 #agb4 #i ,wied4 ,ann41 #dd1 p4 #gd4 ,illustration3 ,,fig4 #ac4--,zehnder's ,trigger ,tube4 ,half ,natural ,size4 ,the two right-hand terminals1 close together1 are attached to the ,hertz receiver2 another pair of terminals are connected to some source just not able to make the tube glow until the scintilla occurs and makes the gas more conducting--as observed by ,schuster and others4 ,mr4 ,boys has experimented on the mechanical force exerted by electrical surgings1 and ,hertz also made observations of the same kind4 ,various ,detectors4 ,going back to older methods of detecting electrical radiation1 we have1 most important of all1 a discovery made long before man existed1 by a creature that developed a sensitive cavity on its skin2 a creature which never so much as had a name to be remembered by 7though perhaps we now call it trilobite74 ,then1 in recent times we recall the photographic plate and the thermopile1 with its modification1 the radiomicrometer2 also the so-called bolometer1 or otherwise-known ,siemens' pyrometer1 applied to astronomy by ,langley1 and applied to the detection of electric waves in wires by ,rubens and ,ritter and ,paalzow and ,arons4 ,the thermal junction was applied to the same purpose by ,kolacek1 ,d4 ,e4 ,jones and others4 ,and1 before all these1 the late ,mr4 ,gregory1 of ,cooper's ,hill1 made his singularly sensitive expansion meter1 whereby waves in free space could be detected by the minute rise of temperature they caused in a platinum wire1 a kind of early and sensitive form of ,cardew voltmeter4 ,illustration3 ,,fig4 #ad4--;,bjerknes' ,apparatus1 showing 7#a7 a ,hertz vibrator connected to an induction coil2 7#b7 a nearly closed circuit receiver properly tuned with the vibrator2 and 7#c7 a one sided electrometer for inserting in the air gap of #b4 ,the receiver is not provided with knobs1 as shown1 but its open circuit is terminated by the quadrants of the electrometer1 which is shown on an enlarged scale alongside4 ,the needle is at zero potential and is attracted by both quadrants4 ,by calculation from the indications of this electrometer ,bjerknes plotted the curves #a1 #b and #c on pages #d and #e4 ,fig4 #a represents the oscillations of the primary vibrator1 rapidly damped by radiation of energy4 ,fig4 #b represents the vibrations thereby set up in the resonating circuit when the two are accurately in tune2 and which persist for many swings4 ,fig4 #c shows the vibrations excited in the same circuit when slightly out of tune with the exciter4 ,a receiver of this kind makes many swings before it is seriously damped1 though the open plate radiator does not4 ,going back to the physiological method of detecting surgings1 ,hertz tried the frog's leg nerve-muscle preparation1 which to the steadier types of electrical stimulus is so surpassingly sensitive1 and to which we owe the discovery of current electricity4 ,but he failed to get any result4 ,ritter has succeeded2 but1 in my experience1 failure is the normal and proper result4 ,working with my colleague1 ,prof4 ,gotch1 at ,liverpool1 ,i too have tried the nerve and muscle preparation of the frog 7,fig4 #ae71 and we find that an excessively violent stimulus of a rapidly alternating character1 if pure and unaccompanied by secondary actions1 produces no effect--no stimulating effect1 that is--even though the voltage is so high that sparks are ready to jump between the needles in direct contact with the nerve4 ,all that such oscillations do1 if continued1 is to produce a temporary paralysis or fatigue of the nerve1 so that it is unable to transmit the nerve impulses evoked by other stimuli1 from which paralysis it recovers readily enough in course of time4 ,illustration3 ,,fig4 #ae4--;,experiment of ,gotch and ,lodge on the physiological effect of rapid pure electric alternations4 ,nerve-muscle preparation1 with four needles1 or else non-polarisable electrodes applied to the nerve4 ,c and ,d are the terminals of a rapidly-alternating electric current from a conductor at zero potential 7namely1 the terminals of a derived circuit from a wire connecting the outer coats of a pair of discharging ,leyden jars71 while ,a and ,b are the terminals of an ordinary very weak galvanic or induction coil stimulus only just sufficient to make the muscle twitch4 ,the ,c ,d terminals do not stimulate the nerve1 though at very high alternative potentials1 but they gradually and temporarily paralyse it1 so that the test terminals ,a ,b produce no effect for a time4 ,this has been expected from experiments on human beings1 such experiments as ,tesla's and those of d',arsonval4 ,but an entire animal is not at all a satisfactory instrument wherewith to attack the question2 its nerves are so embedded in conducting tissues that it may easily be doubted whether the alternating type of stimulus ever reaches them at all4 ,by dissecting out a nerve and muscle from a deceased frog after the historic manner of physiologists1 and applying the stimulus direct to the nerve1 at the same time as some other well known _/th a volt stimulus is applied to another part of the same nerve further from the muscle1 it can be shown that rapid electric alternations1 if entirely unaccompanied by static charge or by resultant algebraic electric transmission1 evoke no excitatory response until they are so violent as to give rise to secondary effects such as heat or mechanical shock4 ,yet1 notwithstanding this inaction1 they gradually and slowly exert a paralysing or obstructive action on the portion of the nerve to which they are applied1 so that the nerve impulse excited by the feeble just perceptible _/th-volts stimulus above is gradually throttled on its way down to the muscle1 and remains so throttled for a time varying from a few minutes to an hour after the cessation of the violence4 ,i did not show this experiment at the lecture4 ,air ,gap and ,electroscope charged by ,glass ,rod and discharged by the ,wave ,impulse from a moderately distant ,sphere excited by ,coil4 ,illustration3 ,,fig4 #af4--;,air gap for ,electroscope4 ,natural size4 ,the bottom plate is connected to1 and represents1 the cap of an electroscope2 the 8knob0 above it1 mentioned in text1 is the polished end of the screw1 whose terminal is connected with the case of the instrument or 8earth40 ,the electroscope being charged to the verge of overflow1 the impact of weak electric waves collected by a bit of wire sticking up from the left-hand binding screw precipitates the collapse of the leaves4 ,among trigger methods of detecting electric radiation1 ,i have spoken of the ,zehnder vacuum tubes2 another method is one used by ,boltzmann4#aj ,a pile of several hundred volts is on the verge of charging an electroscope through an air gap just too wide to break down4 ,very slight electric surgings precipitate the discharge across the gap1 and the leaves diverge4 ,i show this in a modified and simple form4 ,on the cap of an electroscope is placed a highly polished knob or rounded end connected to the sole1 and just not touching the cap1 or1 rather1 just not touching a plate connected with the cap 7,fig4 #af71 the distance between knob and plate being almost infinitesimal1 such a distance as is appreciated in spherometry4 ,such an electroscope overflows suddenly and completely with any gentle rise of potential4 ,bring excited glass near it1 the leaves diverge gradually and then suddenly collapse1 because the air space snaps3 remove the glass1 and they rediverge with negative electricity2 the knob above the cap being then charged positively1 and to the verge of sparking4 ,in this condition any electrical waves1 collected if weak by a foot or so of wire projecting from the cap1 will discharge the electroscope by exciting surgings in the wire1 and so breaking down the air gap4 ,the chief interest about this experiment seems to me the extremely definite dielectric strength of so infinitesimal an air space4 ,moreover1 it is a detector for ,hertz waves that might have been used last century2 it might have been used by ,benjamin ,franklin4 #aj ,weid4 ,ann41 #dj1 p4 #cii4 ,for to excite them no coil or anything complicated is necessary2 it is sufficient to flick a metal sphere or cylinder with a silk handkerchief and then discharge it with a well-polished knob4 ,if it is not well polished the discharge is comparatively gradual1 and the vibrations are weak2 the more polished are the sides of an air gap1 the more sudden is the collapse and the more vigorous the consequent radiation1 especially the radiation of high frequency1 the higher harmonics of the disturbance4 ,for delicate experiments it is sometimes well to repolish the knobs every hour or so4 ,for metrical experiments it is often better to let the knobs get into a less efficient but more permanent state4 ,this is true of all senders or radiators4 ,for the generation of the1 so to speak1 8infra-red0 long-period ,hertz waves any knobs will do1 but to generate the 8ultra-violet0 short-period waves high polish is essential4 ,microphonic ,detectors4 ,receivers or detectors1 which for the present ,i temporarily call microphonic1 are liable to respond best to the more rapid vibrations4 ,their sensitiveness is to me surprising1 though of course it does not approach the sensitiveness of the eye2 at the same time ,i am by no means sure that the eye differs from them in kind4 ,it is these detectors that ,i wish specially to bring to your notice4 ,prof4 ,minchin1 whose long and patient work in connection with photo-electricity is now becoming known1 and who has devised an instrument more sensitive to radiation than even ,boys' radiomicrometer1 in that it responds to the radiation of a star while the radiomicrometer does not1 found some years ago that some of his light-excitable cells lost their sensitiveness capriciously on tapping1 and later he found that they frequently regained it again while ,mr4 ,gregory's ,hertz-wave experiments were going on in the same room4 ,these 8impulsion cells10 as he terms them1 are troublesome things for ordinary persons to make and work with--at least ,i have never presumed to try--but in ,mr4 ,minchin's hands they are surprisingly sensitive to electric waves4#aa ,the sensitiveness of selenium to light is known to everyone1 and ,mr4 ,shelford ,bidwell has made experiments on the variations of conductivity exhibited by a mixture of sulphur and carbon4 ,nearly four years ago ,m4 ,edouard ,branly found that a burnished coat of porphyrised copper spread on glass or ebonite1 diminished its resistance enormously1 from some millions to some hundreds of ohms1 when it was exposed to the neighbourhood1 even the distant neighbourhood1 of ,leyden jar or coil sparks4 ,he likewise found that a tube of metallic filings behaved similarly1 and that both recovered their original resistance on shaking or tapping4 ,mr4 ,croft exhibited this fact recently at the ,physical ,society4 ,m4 ,branly also made pastes and solid rods of filings1 in ,canada balsam and in sulphur1 and found them likewise sensitive4#ab #aa ,phil4 ,mag41 ,vol4 ,,xxxi41 p4 #bbc4 #ab ,e4 ,branly1 ,comptes ,rendus1 ,vol4 ,,cxi41 p4 #ghe2 and ,vol4 ,,cxii41 p4 #ij4 ,with me the matter arose somewhat differently1 as an outcome of the air gap detector employed with an electroscope by ,boltzmann 7,fig4 #af74 ,for ,i had observed in #ahhi that two knobs sufficiently close together1 far too close to stand any voltage such as an electroscope can show1 could1 when a spark passed between them1 actually cohere2 conducting an ordinary bell-ringing current if a single voltaic cell was in circuit2 and1 if there were no such cell1 exhibiting an electromotive force of their own sufficient to disturb a low resistance galvanometer vigorously1 and sometimes requiring a faintly perceptible amount of force to detach them4 ,the experiment was described to the ,institution of ,electrical ,engineers in #ahij1ac and ,prof4 ,hughes said he had observed the same thing4 #ac ,journal ,institution of ,electrical ,engineers1 #ahij1 ,vol4 ,,xix41 pp4 #ceb-d2 or 8,lightning ,conductors and ,lightning ,guards10 pp4 #chb-d4 ,illustration3 ,,fig4 #af;,a4--,receiver in ,syntonic ,jar ,experiment1 with ,knob ,coherer and ,tapper-back 7cf4 ,fig4 #d74 ,the experiment of the syntonic ,leyden jars can be conveniently shown with the double-knob or #ahhi coherer4 ,the pair of knobs are arranged to connect the coatings of the receiving jar 7a large condenser being interposed to prevent their completing a purely metallic circuit71 and in circuit with them is a battery and a bell4 ,every time the receiving jar responds syntonically to the electric vibration of the other jar1 the knobs cohere 7if properly adjusted7 and the bell rings4 ,if the bell is free in air it continues ringing until the knobs are gently tapped asunder2 but if the bell stands on the same table as the knobs1 especially if it rests one foot on the actual stand1 then its first stroke taps them back instantly and automatically1 and so every discharge of the sending jar is signalled by a single stroke of the bell4 ,here we have in essence a system of very distinctly syntonic telegraphy1 for the jars and their circuits must be accurately tuned together1 if there is to be any response4 ,a very little error in tuning1 easily made by altering the position of the slider 7,fig4 #d71 will make them quite unresponsive1 unless the distance between them is reduced4 ,illustration3 ,,fig4 #ag4--;,early ,form of ,coherer1 consisting of a spiral of thin iron wire mounted on an adjustable spindle and an aluminium plate4 ,when the lever is moved clockwise the tip of the iron wire presses gently against the aluminium plate1 whose end is bent at right angles and passed through into the hollow circular wooden box1 of which the upper figure shows the top and general appearance1 and the lower figure shows the inside4 ,at the maximum distance of response the tuning required is excessively sharp4 ,but1 certainly1 for these closed and durably-vibrating circuits1 the distance of response is small1 as has been said before4 ,fig4 #af;,a shows the syntonic ,leyden jar experiment arranged with the double knob coherer1 instead of with the spark gap of ,fig4 #d4 ,coherer in open1 responding to ,feeble ,stimuli3--,small ,sphere1 ,gas-lighter1 ,distant ,sphere1 ,electrophorus4 ,well1 this arrangement1 which ,i call a coherer1 is the most astonishingly sensitive detector of ,hertz waves4 ,it differs from an actual air gap in that the insulating film is not really insulating2 the film breaks down not only much more easily1 but also in a less discontinuous and more permanent manner1 than an air gap4 ,branly's tube of filings1 a series of bad contacts1 clearly works on the same plan2 and though a tube of filings is by no means so sensitive1 yet it is in many respects easier to work with1 and except for very feeble stimuli1 is more metrical4 ,if the filings used are coarse1 say turnings or borings1 the tube approximates to a single coherer2 if they are fine1 it has a larger range of sensibility4 ,in every case what these receivers feel are sudden jerks of current2 smooth sinuous vibrations are ineffective4 ,they seem to me to respond best to waves a few inches long1 but doubtless that is determined chiefly by the dimensions of some conductor with which they happen to be associated4 7,figs4 #ag and #ah47 ,illustration3 ,,fig4 #ah4--;,early ,form of ,iron ,borings ,tube4 ,one-half natural size1 with solid brass cylinder terminals in each end of the tube1 making contact with the borings4 ,experiment showing ,filings ,tube responding to ,sphere1 to ,electrophorus1 and to a ,quasi-8,spark0 from the ,discharge of an ordinary ,gold-leaf ,electroscope4 ,i picture the action as follows3 ,suppose two fairly clean pieces of metal in light contact--say two pieces of brass or of iron--connected to a single voltaic cell2 a film of what may be called oxide intervenes between the surfaces so that only an insignificant current is allowed to pass1 because a volt or two is insufficient to break down the insulating film1 except perhaps at one or two atoms4#ad ,if the film is not permitted to conduct at all1 it is not very sensitive2 the most sensitive condition is attained when an infinitesimal current passes1 strong enough just to show on a moderate galvanometer4 #ad ,see ,phil4 ,mag41 ,jan41 #ahid1 p4 #id1 where this explanation 7whether true or not7 was first given1 and where the author first published his fuller experience of coherer behaviour4 ,now let the slightest surging occur1 say by reason of a sphere being charged and discharged at a distance of forty yards2 the film at once breaks down1 perhaps not completely--that is a question of intensity--but permanently4 ,as ,i imagine1 more molecules get within each other's range1 incipient cohesion sets in and the momentary electric quiver acts somewhat like a flux4 ,it is a singular variety of electric welding4 ,a stronger stimulus enables more molecules to hold on1 the process is surprisingly metrical2 and as far as ,i roughly know at present1 the change of resistance is proportional to the energy of the electric radiation1 from a source of given frequency4 ,it is to be specially noted that a battery current is not needed to effect the cohesion1 only to demonstrate it4 ,the battery can be applied after the spark has occurred1 and the resistance will be found changed as much as if the battery had been on all the time4 ,the incipient cohesion electrically caused can be mechanically destroyed4 ,sound vibrations1 or any other feeble mechanical disturbances1 such as scratches or taps1 are well adapted to restore the contact to its original high resistance sensitive condition4 ,the more feeble the electrical disturbance the slighter is the corresponding mechanical stimulus needed for restoration4 ,when working with the radiating sphere 7,fig4 #ai7 at a distance of forty yards out of window1 ,i could not for this reason shout to my assistant to cause him to press the key of the coil and make a spark1 but ,i showed him a duster instead1 this being a silent signal which had no disturbing effect on the coherer or tube of filings4 ,i mention #dj yards1 because that was one of the first outdoor experiments2 but ,i should think that something more like half-a-mile was nearer the limit of sensitiveness for this particular apparatus as then arranged4 ,however1 this is a rash statement not at present verified4#ae ,at #dj or #fj yards the exciting spark could be distinctly heard1 and it was interesting to watch the spot of light begin its long excursion and actually travel a distance of #b in4 or #c in4 before the sound arrived4 ,this experiment proved definitely enough that the efficient cause travelled quicker than sound1 and disposed completely of any sceptical doubts as to sound waves being1 perhaps1 the real cause of the phenomenon4 ,signals were obtained across the full width of the college quadrangle1 and later1 with larger apparatus1 between the college tower and another high building half-a-mile away4 #ae ,this statement has been absurdly misunderstood1 as if it was a prediction of what would always be the limit of sensitiveness for any apparatus and any sized sender4 ,nothing of the kind was in my mind4 ,such predictions are always preposterous1 and ,i am not obliged to those who imagined that ,i had been guilty of one of them4--,o4 ,j4 ,l41 #ahii4 ,illustration3 ,,fig4 #ai4--,radiator used in the library of the ,royal ,institution1 exciting the ,coherer 7,fig4 #ag7 on the lecture table in the ,theatre4 ,i also used a radiator with two or with three large spheres between two knobs1 and described it in ,nature1 ,vol4 #da1 p4 #dfb1 #ahij4 ,this is the radiator which ,prof4 ,righi has improved and made in a compact form with oil between the two middle spheres4 ,invariably1 when the receiver is in good condition1 sound or other mechanical disturbance acts one way1 viz41 in the direction of increasing resistance1 while electrical radiation or jerks act the other way1 decreasing it4 ,while getting the receiver into condition1 or when it is getting out of order1 vibrations and sometimes electric discharges act irregularly2 and an occasional good shaking does the filings good4 ,i have taken rough measurements of the resistance by the simple process of restoring the original galvanometer deflection by adding or removing resistance coils4 ,a half-inch tube1 #h in4 long1 of selected iron turnings 7,fig4 #ah7 had a resistance of #b1ejj ohms in the sensitive state4 ,a feeble stimulus1 caused by a distant electrophorus spark1 brought it down #djj ohms4 ,a rather stronger one reduced it by #ejj and #fjj1 while a trace of spark given to a point of the circuit itself ran it down #a1djj ohms4 ,this is only to give an idea of the quantities4 ,i have not yet done any seriously metrical experiments4 ,added later4--,my assistant1 ,mr4 ,e4 ,e4 ,robinson1 early noticed that when a telephone was used as receiver1 say with a single-point coherer 7see illustration on opposite page71 which is a very sensitive arrangement1 every disturbance of the coherer due to received waves is accompanied by a crackle or tick in the telephone1 without any tapping back being necessary4 ,this is1 indeed1 the easiest mode of receiving signals1 and we often practised it4 ,if a suitable1 well-damped galvanometer1 such as a ,thomson marine speaking-galvanometer1 is included also in the circuit 7a more sensitive one is sometimes necessary--and we frequently used a ,d',arsonval--but it must be well damped71 the meaning of these ticks is recognised2 each represents a minute change in the resistance of the coherer--not at all the full change usually employed1 but little subsidiary changes1 sometimes up and sometimes down1 barely sufficient to affect a galvanometer1 but quite adequate 7being so sudden7 to disturb a telephone4 ,this method of receiving1 which at first is very sensitive1 after a time becomes less so2 the point shows signs of fatigue1 probably due to too perfect cohesion having been gradually established1 and a mechanical tap back is desirable to restore it to its original condition4 ,if all the signals received were precisely of the same strength1 ,i doubt if these superposed crimples of resistance would occur2 but signals depending on quality of sending spark never are of the same strength1 and accordingly the sudden slight variations of resistance do occur4 ,usually an ordinary high resistance telephone was employed1 and it was joined to the coherer circuit through one of the usual small transformers--a plan which has many obvious advantages4 ,illustration3 ,simplest ,receiving ,arrangement3 a ,telephone in ,circuit with ,single-point ,coherer without ,tapper-back4 ,b a needle resting against a watch-spring ,a adjusted by screw ,c4 ,illustration3 ,syntonic ,sender and ,receiver used in the experiments plotted on page #bh4 ,the switch enables the coherer ,k to be connected either to the tuned resonator ,m ,l ,n or to the detecting circuit ,e ,f4 ,weak impulses are felt when the switch is ,c ,e1 ,d ,f2 strong impulses when the switch is ,c ,a1 ,d ,b2 provided the coil ,l is similar to the coil of the radiator above4 ,the impulses are plotted in the diagram ,fig4 #ai;,a4 ,illustration3 ,october #bg1 #ahig4 ,,fig4 #ai;,a4--,current through ,coherer after successive ,electrical ,stimuli1 without any mechanical tapping back4 ,the sudden rises are obtained when the circuits are syntonised4 ,weaker stimuli cause the descents4 ,the fluctuations of resistance of a coherer dependent on various strengths of stimulus are instructively shown in some metrical experiments made by ,mr4 ,robinson1 and a plotting of which ,i showed to the ,physical ,society of ,london in #ahig4 ,this plotting is here reproduced1 and it shows the singular fact that1 whereas a stronger electrical stimulus usually decreases the resistance1 as is natural1 a weaker subsequent stimulus usually increases it again3 so that alternately strong and weak stimuli send the curve zigzagging up and down1 until it gets into a condition demanding rejuvenation by a mechanical tap back4 ,sometimes a decidedly strong electrical stimulus knocks down the conductivity of the coherer as if it had been tapped back4 ,this is almost certainly due to a burning of the delicate contacts--a blowing of a fuse as it were1--and the effect of this electrical burn back is quite different from the effect of a mechanical tap back1 inasmuch as it leaves the coherer insensitive4 ,a shaking up is necessary to restore it4 ,i now call your attention to the ,table on next page of various kinds of detector for electric radiation distributed in groups4 ,selenium is inserted in this table in the microphone column1 because it is a substance which in certain states is well known to behave to visible light as these other microphonic detectors behave to ,hertz waves4 ,it is inserted with a query1 to indicate that its position in the table is not certainly known4 ,it may possibly belong to some other column4 ,electrical ,theory of ,vision4 ,and ,i want to suggest that quite possibly the sensitiveness of the eye is of the coherer kind4 ,as ,i am not a physiologist1 ,i cannot be seriously blamed for making wild and hazardous speculations in that region4 ,i therefore wish to guess that some part of the retina is an electrical organ1 say like that of some fishes1 maintaining an electromotive force which is prevented from stimulating the nerves solely by an intervening layer of badly conducting material1 or of conducting powder with gaps in it2 but that when light falls upon the retina these gaps become more or less conducting1 and the nerves are stimulated4 ,i do not feel clear which part is taken by the rods and cones1 and which part by the pigment cells2 ,i must not try to make the hypothesis too definite at present1 though ,i hope it is obvious what ,i intend to suggest4 ,if ,i had to make a demonstration model of the eye on these lines1 ,i should arrange a little battery to excite a frog's nerve-muscle preparation through a circuit completed all except a layer of filings or a single bad contact4 ,such an arrangement would respond to ,hertz waves4 ,or1 if ,i wanted actual light to act1 instead of grosser waves1 ,i would use a layer of selenium4 ,but the bad contact and the ,hertz waves are the most instructive1 because we do not at present really know what the selenium is doing1 any more than what the retina is doing4 ,and observe that 7to my surprise1 ,i confess7 the rough outline of a theory of vision thus suggested is in accordance with some of the principal views of the physiologist ,hering4 ,the sensation of light is due to the electrical stimulus2 the sensation of black is due to the mechanical or tapping back stimulus4 ,darkness is physiologically not the mere cessation of light4 ,both are positive sensations1 and both stimuli are necessary2 for until the filings are tapped back vision is persistent4 ,in the eye model the period of mechanical tremor should be1 say1 th second1 so as to give the right amount of persistence of impression4 ---------------------------------------- ------------------------------ ,,detectors ,,of ,,radiation4 ---------------------------------------- ------------------------- ,physio- ,chemical4 ,thermal4 ,electrical4 ,mechanical4,microphonic4 logical4 ---------------------------------------- ------------------------- ,selenium4787 ,eye4 ,photo- ,thermopile4 ,spark4 ,electro- ,impulsion graphic 7,hertz47 meter4 ,cell4 ,plate4 7,blyth and 7,minchin47 ,bjerknes47 ,frog's ,explosive ,bolometer4 ,telephone2 ,suspended ,filings4 ,leg ,gases4 7,rubens and ,air-gap ,wires4 7,branly47 7,hertz ,ritter47 and ,arc4 7,hertz and and 7,lodge47 ,boys47 ,ritter47 ,photo- ,expanding ,vacuum ,tube4 ,coherer4 electric ,wire4 7,dragoumis47 ,hughes and ,cell4 7,gregory47 ,galvanometer4 ,lodge4 ,thermal 7,fitzgerald47 ,junction4 ,air-gap and 7,klemencic47,electroscope4 7,boltzmann47 ,trigger ,tube4 7,warburg and ,zehnder47 ---------------------------------------- ------------------------- ,the cross against the frog's leg indicates that it does not appear really to respond to radiation1 unless stimulated in some secondary manner4 ,the names against the other things are unimportant1 but suggest the persons who applied the detector to electric radiation4 ,the interrogation mark against ,selenium indicates that its position in the microphonic column may be doubtful4 ,no doubt in the eye the tapping back is done automatically by the tissues1 so that it is always ready for a new impression1 until fatigued4 ,and by mounting an electric bell or other vibrator on the same board as a tube of filings1 it is possible to arrange so that a feeble electric stimulus shall produce a feeble steady effect1 a stronger stimulus a stronger effect1 and so on2 the tremor asserting its predominance1 and bringing the spot back1 whenever the electric stimulus ceases4 ,an electric bell thus close to the tube is1 indeed1 not the best vibrator2 clockwork might do better1 because the bell contains in itself a jerky current1 which produces one effect1 and a mechanical vibration1 which produces an opposite effect1 hence the spot of light can hardly keep still4 ,by lessening the vibration--say1 by detaching the bell from actual contact with the board1 the electric jerks of the intermittent current drive the spot violently up the scale2 mechanical tremor brings it down again4 ,it must be clearly understood that electric jerks1 due to the make-and-break of an ordinary current1 are quite adequate to electrically stimulate a coherer in their neighbourhood4 ,it is constantly to be noticed that a coherer responds best to excessively short sparks of a certain sharp quality4 ,you observe that the eye on this hypothesis is1 in electrometer language1 heterostatic4 ,the energy of vision is supplied by the organism2 the light only pulls a trigger4 ,whereas the organ of hearing is idiostatic4 ,i might draw further analogies between this arrangement and the eye1 e4g41 about the effect of blows or disorder causing irregular conduction and stimulation1 of the galvanometer in the one instrument1 of the brain cells in the other4 ,a handy portable exciter of electric waves is one of the ordinary hand electric gas-lighters1 containing a small revolving doubler--i4e41 an inductive or replenishing machine4 ,a coherer can feel a gas-lighter across a lecture theatre4 ,minchin often used them for stimulating his impulsion cells4 ,i find that when held near they act a little even when no ordinary spark occurs1 plainly because of the little incipient sparks at the brushes or tinfoil contacts inside4 ,a ,voss machine acts similarly1 giving a small deflection while working up before it sparks3 indeed1 these small sparks are often more effective than bigger ones4 ,demonstration of ,ordinary ,holtz ,machine ,sparks not exciting ,tube3 except by help of a polished knob4 ,and notice here that our model eye has a well-defined range of vision4 ,it cannot see waves too long for it4 ,the powerful disturbance caused by the violent flashes of a ,holtz or ,wimshurst or ,voss machine it is blind to4 ,the loud sparks have no effect on it4 ,they are like infra-red radiation to the eye4 ,if the knobs of the machine are well polished the coherer begins to respond again1 evidently by reason of some high harmonics1 due to vibrations in the terminal rods2 and these are the vibrations to which it responds when excited simply by an induction coil4 ,the coil should have knobs instead of points4 ,sparks from points or dirty knobs hardly excite the coherer at all4 ,but hold a well-polished sphere or third knob between even the dirty knobs of a ,voss machine1 and the coherer responds at once to the surgings got up in that clean sphere4 ,feeble short sparks again are often more powerful exciters than are strong long ones4 ,i suppose because they are more sudden4 ,this is instructively shown with an electrophorous lid4 ,spark it to a knuckle1 and it does very little4 ,spark it to a clean knob held in the hand and it works well4 ,but now spark it to an insulated sphere1 there is some effect4 ,discharge the sphere1 and take a second spark1 without recharging the lid2 do this several times2 and at last1 when the spark is inaudible1 invisible1 and otherwise imperceptible1 the coherer some yards away responds more violently than ever1 and the spot of light rushes from the scale4 ,if a coherer be attached by a side wire to the gas pipes1 and an electrophorous spark be given to either the gas pipes or the water pipes or even to the hot-water system in any other room of the building1 the coherer responds4 ,it is surprising how far these impulses can be felt along an ordinary uninsulated wire or other conductor4 ,in fact1 when thus connected to gas pipes one day when ,i tried it1 the spot of light could hardly keep still five seconds4 ,whether there was a distant thunderstorm1 or whether it was only picking up telegraphic jerks1 ,i do not know4 ,the jerk of turning on or off an extra ,swan lamp can affect it when sensitive4 ,i hope to try for long-wave radiation from the sun1 filtering out the ordinary well-known waves by a blackboard or other sufficiently opaque substance4 ,i did not succeed in this1 for a sensitive coherer in an outside shed unprotected by the thick walls of a substantial building cannot be kept quiet for long4 ,i found its spot of light liable to frequent weak and occasionally violent excursions1 and ,i could not trace any of these to the influence of the sun4 ,there were evidently too many terrestrial sources of disturbance in a city like ,liverpool to make the experiment feasible4 ,i don't know that it might not possibly be successful in some isolated country place2 but clearly the arrangement must be highly sensitive in order to succeed4 ,we can easily see the detector respond to a distant source of radiation now1 viz41 to a #e in4 sphere placed in the library between secondary coil knobs2 separated from the receiver1 therefore1 by several walls and some heavily gilded paper1 as well as by #bj or #cj yards of space 7,fig4 #ai47 ,illustration3 ,,fig4 #ai;,b4--,a ,portable ,detector1 ,b the ,collecting ,wire4 ,also ,i exhibit 7,fig4 #ai;,b7 a small complete detector made by my assistant1 ,mr4 ,davies1 which is quite portable and easily set up4 ,the essentials 7battery1 galvanometer1 and coherer7 are all in a copper cylinder1 ,a1 three inches by two4 ,a bit of wire1 ,b1 a few inches long1 pegged into it1 helps it to collect waves4 ,it is just conceivable that at some distant date1 say by dint of inserting gold wires or powder in the retina1 we may be enabled to see waves which at present we are blind to4 ,observe how simple the production and detection of ,hertz waves are now4 ,an electrophorus or a frictional machine serves to excite them2 a voltaic cell1 a rough galvanometer1 and a bad contact serves to detect them4 ,indeed1 they might have been observed at the beginning of the century1 before galvanometers were known3 a frog's leg or an iodide of starch paper would do almost as well4 ,a bad contact was at one time regarded as a simple nuisance1 because of the singularly uncertain and capricious character of the current transmitted by it4 ,hughes observed its sensitiveness to sound waves1 and it became the microphone4 ,now it turns out to be sensitive to electric waves1 if it be made of any oxidisable medal 7not of carbon71#af and we have an instrument which might be called a micro-something1 but which1 as it appears to act by cohesion1 ,i at present call a coherer4 ,perhaps some of the capriciousness of an anathematised bad contact was sometimes due to the fact that it was responding to stray electric radiation4 7,see ,appendix ,,iii41 pp4 #aji and #aaa47 #af ,fitz,gerald tells me that he has succeeded with carbon also4 ,my experience is that the less oxidisable the metal1 the more sensitive and also the more troublesome is the detector4 ,mr4 ,robinson has now made me a hydrogen vacuum tube of brass filings1 which beats the coherer for sensitiveness4 ,july1 #ahid4 ,the breaking down of cohesion by mechanical tremor is an ancient process1 observed on a large scale by engineers in railway axles and girders2 indeed1 the cutting of small girders by persistent blows of hammer and chisel reminded me the other day of the tapping back of our cohering surfaces after they have been exposed to the uniting effect of an electric jerk4 ,receiver in ,metallic ,enclosure4 ,if a coherer is shut up in a complete metallic enclosure1 waves cannot get at it1 but if wires are led from it to an outside ordinary galvanometer1 it remains nearly as sensitive as it was before 7nearly1 not quite71 for the circuit picks up the waves and they run along the insulated wires into the closed box4 ,to screen it effectively1 it is necessary to enclose battery and galvanometer and every bit of wire connection2 the only thing that may be left outside is the needle of the galvanometer4 ,accordingly1 here we have a compact arrangement of battery and galvanometer coil and coherer1 all shut up in a copper box 7,fig4 #ai;,c74 ,the galvanometer coil is fixed against the side of the box at such height that it can act conveniently on an outside suspended compass needle4 ,the slow magnetic action of the current in the coil has no difficulty in getting through copper1 as everyone knows3 only a perfect conductor could screen off that2 but the ,hertz waves are effectively kept out by the sheet copper4 ,illustration3 ,,fig4 #ai;,c4--,protected ,detector4 ,a is an occasional wire passing through shuttered aperture4 ,e is a lead tube enclosing leading wires1 as in ,fig4 #ba4 ,it must be said1 however1 that the box must be exceedingly well closed for the screening to be perfect4 ,the very narrowest chink permits their entrance1 and at one time ,i thought ,i should have to solder a lid on before they could be kept entirely out4 ,clamping a copper lid on to a flange in six places was not enough4 ,but by the use of pads of tinfoil and tight clamping1 chinks can be avoided1 and the inside of the box becomes then electrically dark4 ,if even an inch of the circuit protrudes1 it at once becomes slightly sensitive again2 and if a mere single wire protrudes through the box1 not connected to anything at either end1 provided it is insulated where it passes through1 the waves will utilise it as a speaking-tube1 and run blithely in4 ,and this happens whether the wire be connected to anything inside or not1 though it acts more strongly when connected4 ,in careful experiments1 where the galvanometer is protected in one copper box and the coherer in another1 the wires connecting the two must be encased in a metal tube 7,figs4 #ai;,c and #ba71 and this tube must be well connected with the metal of both enclosures1 if nothing is to get in but what is wanted4 ,illustration3 ,,fig4 #bj4--,spherical ,radiator for emitting a ,horizontal ,beam1 arranged inside a ,copper ,hat1 fixed against the outside of a metal-lined ,box1 which contains induction coil and battery and key4 ,one-eighth natural size4 ,the wires pass into the box through glass tubes not shown4 ,similarly when definite radiation is desired1 it is well to put the radiator in a copper hat open in only one direction 7,fig4 #bj71 and in order to guard against reflected and collateral surgings running along the wires which pass outside to the exciting coil and battery1 as they are liable to do1 ,i am accustomed to put all the sending apparatus in a packing case lined with tinfoil1 to the outside of which the sending hat 7,fig4 #bj7 is fixed1 and to pull the key of the primary exciting circuit by a string from outside1 so that not even key connections shall protrude1 else exact optical experiments are impossible4 ,illustration3 ,,fig4 #ba4--;,general arrangement of experiments with the ,copper 8,hat10 showing ,metal ,box on a ,stool1 standing outside the ,theatre4 ,the ,box is not exactly represented1 but inside it the ,radiators were fixed with a graduated series of apertures2 the ,copper ,hat containing the ,coherer is seen on the ,table with the ,metal ,box on the left of the ,table containing ,battery and ,galvanometer ,coil connected to it by a compo pipe conveying the wires1 as in ,fig4 #ai;,c2 the ,lamp and ,scale barely indicated at one side of the ,table2 a ,paraffin ,prism2 and a ,polarising ,grid of copper wires stretched on a frame4 7,this figure is from a thumbnail sketch by ,mr4 ,a4 ,p4 ,trotter1 taken at the ,lecture in #ahid47 ,even then1 with the lid of the hat well clamped on1 something gets out1 but it is not enough to cause serious disturbance of qualitative results4 ,the sender must evidently be thought of as emitting a momentary blaze of light which escapes through every chink4 ,or1 indeed1 since the waves are some inches long1 the difficulty of keeping them out of an enclosure may be likened to the difficulty of excluding sound2 though the difficulty is not quite so great as that1 since a reasonable thickness of metal is really opaque4 ,i fancied once or twice ,i detected a trace of transparency in such metal sheets as ordinary tinplate1 but unnoticed chinks elsewhere may have deceived me4 ,it is a thing easy to make sure of as soon as ,i have more time4 7,tinplate is quite opaque4 ,lead paper lets a little through47 ,one thing in this connection is noticeable1 and that is how little radiation gets either in or out of a small round hole4 ,a narrow long chink in the receiver box lets in a lot2 a round hole the size of a shilling lets in hardly any1 unless indeed a bit of insulated wire protrudes through it like a collecting ear trumpet1 as at ,a1 ,fig4 #ai;,c4 ,it may be asked how the waves get out of the metal tube of an electric gas-lighter4 ,but they do not2 they get out through the handle1 which being of ebonite is transparent4 ,wrap up the handle in tinfoil1 and a gas-lighter is powerless4 ,,optical ,,experiments4 ,and now1 in conclusion1 ,i will show some of the ordinary optical experiments with ,hertz waves1 using as source either one of two devices3 either a #e in4 sphere with sparks to ends of a diameter 7,fig4 #ai71 an arrangement which emits #g in4 waves but of so dead-beat a character that it is wise to enclose it in a copper hat to prolong them and send them out in the desired direction1 or else a #b in4 hollow cylinder with spark knobs at ends of an internal diameter 7,fig4 #ab74 ,this last emits #c in4 waves of a very fairly persistent character1 but with nothing like the intensity of one of the outside radiators4 ,as receiver there is no need to use anything sensitive1 so ,i employ a glass tube full of coarse iron filings1 put at the back of a copper hat with its mouth turned well askew to the source1 which is put outside the door at a distance of some yards1 so that only a little direct radiation can reach the tube4 ,sometimes the tube is put lengthways in the hat instead of crossways1 which makes it less sensitive1 and has also the advantage of doing away with the polarising1 or rather analysing1 power of a crossway tube4 ,the radiation from the sphere is still too strong1 but it can be stopped down by a diaphragm plate with holes in it of varying size clamped on the sending box 7right-hand side of ,fig4 #ba74 ,reflection4 ,having thus reduced the excursion of the spot of light to a foot or so1 a metal plate is held as reflector1 and at once the spot travels a couple of yards4 ,a wet cloth reflects something1 but a thin glass plate1 if dry1 reflects next to nothing1 being1 as is well known1 too thin to give anything but 8the black spot40 ,i have fancied that it reflects something of the #c in4 waves4 ,with reference to the reflecting power of different substances1 it may be interesting to give the following numbers showing the motion of the spot of light when #h in4 waves were reflected into the copper hat1 the angle of incidence being about #de deg41 by the following mirrors3-- ,sheet of window glass #j or at most #a division4 ,human body #g divisions4 ,drawing board #ab 0 ,towel soaked with tap-water #ab 0 ,tea-paper 7lead87 #dj 0 ,dutch metal paper #gj 0 ,tinfoil #hj 0 ,sheet copper #ajj and up against stops4 ,refracting ,prism and ,lens4 ,a block of paraffin about a cubic foot in volume is cast into the shape of a prism with angles #ge deg41 #fj deg41 and #de deg4 ,using the large angle1 the rays are refracted into the receiving hat 7,fig4 #ba71 and produce an effect much larger than when the prism is removed4 ,an ordinary #i in4 glass lens is next placed near the source1 and by means of the light of a taper it is focussed between source and receiver4 ,the lens is seen to increase the effect by concentrating the electric radiation4 ,arago ,disc2 ,grating2 and ,zone-plate4 ,the lens helps us to set correctly an #ah in4 circular copper disc in position for showing the bright diffraction spot4 ,removing the disc1 the effect is much the same as when it was present1 in accordance with the theory of ,poisson4 ,add the lens and the effect is greater4 ,with a diffraction grating of copper strips #b in4 broad and #b in4 apart1 ,i have not yet succeeded in getting good results4 ,it is difficult to get sharp nodes and interference effects with these sensitive detectors in a room4 ,i expect to do better when ,i can try out of doors1 away from so many reflecting surfaces2 indoors it is like trying delicate optical experiments in a small whitewashed chamber well supplied with looking-glasses2 nor have ,i ever succeeded in getting clear concentration with this zone-plate having ,newton's rings fixed to it in tinfoil4 ,the coherer1 at any rate in a room1 does not seem well adapted to interference experiments2 it is probably too sensitive1 and responds even at the nodes1 unless they are made more perfect than is easily practicable4 ,but really there is nothing of much interest now in diffraction effects1 except the demonstration of the waves and the measure of their length4 ,there was immense interest in ,hertz's time1 because then the wave character of the radiation had to be proved2 but every possible kind of wave must give interference and diffraction effects1 and their theory is1 so to say1 worked out4 ,more interest attaches to polarisation1 double refraction1 and dispersion experiments4 ,illustration3 ,,fig4 #bb4--,zone-plate of ,tinfoil on ,glass4 ,every circular strip is of area equal to central space4 ,polarising and ,analysing ,grids4 ,polarisation experiments are easy enough4 ,radiation from a sphere1 or cylinder1 or dumb-bell is already strongly polarised1 and the tube acts as a partial analyser1 responding much more vigorously when its length is parallel to the line of sparks than when they are crossed2 but a convenient extra polariser is a grid of wires something like what was used by ,hertz1 only on a much smaller scale2 say an #ah in4 octagonal frame of copper strip with a harp of parallel copper wires 7see ,fig4 #ba1 on floor74 ,the spark-line of the radiator 7,fig4 #bj7 being set at #de deg41 a vertical grid placed over the receiver reduces the reflection to about one-half1 and a crossed grid over the source reduces it to nearly nothing4 ,rotating either grid a little rapidly increases the effect1 which becomes a maximum when they are parallel4 ,the interposition of a third grid1 with its wires at #de deg41 between two crossed grids1 restores some of the obliterated effect4 ,radiation reflected from a grid is strongly polarised1 of course1 in a plane normal to that of the radiation which gets through it4 ,they are thus analogous in their effect to ,nicols1 or to a pile of plates4 ,the electric vibrations which get through these grids are at right angles to the wires4 ,vibrations parallel to the wires are reflected or absorbed4 ,reflecting ,paraffin ,surface2 ,direction of ,vibrations in ,polarised ,light4 ,to demonstrate that the so-called plane of polarisation of the radiation transmitted by a grid is at right angles to the electric vibration1#ag i4e41 that when light is reflected from the boundary of a transparent substance at the polarising angle the electric vibrations of the reflected beam are perpendicular to the plane of reflection1 ,i use the same paraffin prism as before2 but this time ,i use its largest face as a reflector1 and set it at something near the polarising angle4 ,when the line of wires of the grid over the mouth of the emitter is parallel to the plane of incidence1 in which case the electric vibrations are perpendicular to the plane of incidence1 plenty of radiation is reflected by the paraffin face4 ,turning the grid so that the electric vibrations are in the plane of incidence1 we find that the paraffin surface set at the proper angle is able to reflect hardly anything4 ,in other words1 the vibrations contemplated by ,fresnel are the electric vibrations2 those dealt with by ,mc,cullagh are the magnetic ones4 ,thus are some of the surmises of genius verified and made obvious to the wayfaring man4 ,,end ,,of ,,lecture4 #ag ,cf4 ,trouton1 in ,nature1 ,vol4 #ci1 p4 #cic2 and many optical experiments by ,mr4 ,trouton1 ,vol4 #dj1 p4 #cih4 ,since then the above described and depicted apparatus for electro-optic experiments has been imitated in a neat1 compact form by ,prof4 ,j4 ,chunder ,bose1 of ,calcutta1 and with it he has obtained many admirable and interesting optical results4 ,see ,proc4 ,roy4 ,soc4 ,,note ,,with ,,reference ,,to ,,electric ,,waves ,,on ,,wires4 ,it may be well to explain that in my ,royal ,institution lecture ,i made no reference to the transmission of waves along wires4 ,i regard the transmission of waves in free space as the special discovery of ,hertz2 though undoubtedly he got them on wires too4 ,their transmission along wires is1 however1 a much older thing4 ,von ,bezold saw them in #ahgj1 and ,i myself got quantitative evidence of nodes and loops in wires when working with ,mr4 ,chattock in the session #ahhg-h 7see1 for instance1 contemporary reports of the ,bath ,meeting of the ,british ,association1 #ahhh1 in ,the ,electrician71 and ,i exhibited them some time afterwards to the ,physical ,society1 the wires themselves becoming momentarily luminous at every discharge except at the nodes1 thus enabling the waves to be actually seen1 having been made stationary by reflexion as in the corresponding acoustic experiment of ,melde4 ,this experiment does not appear to have been properly known 7p4 #gh74 ,illustration3 ,,fig4 #bc4 ,it may be worth mentioning that the arrangement frequently referred to in ,germany by the name of ,lecher 7viz41 that shown in ,fig4 #bc71 and on which a great number of experiments have been made1 is nothing but a pair of ,leyden jars with long wires leading from their outer coats1 such as ,i constantly employed in these experiments4 ,the wires from the outer coat in my experiment were very long1 sometimes going five or six times round a large hall1 like telegraph wires4 ,and many measurements of wave length were thus made by me at the same period as that in which ,hertz was working at ,carlsruhe4 ,the use of air dielectric instead of glass permits the capacity to be adjusted1 and also readily enables the capacity to be small1 and the frequency1 therefore1 high2 but otherwise the arrangement is the same in principle as had frequently been used by myself in the series of experiments called 8the recoil kick0 7,proc4 ,roy4 ,soc41 ,june #ahia1 ,vol4 #ej1 pp4 #bc-ci74 ,for these and other reasons no reference has been made in my lecture to the work done on wires by ,sarasin and ,de la ,rive2 nor to other excellent work done by ,lecher1 ,rubens1 ,arons1 ,paalzow1 ,ritter1 ,blondlot1 ,curie1 ,d4 ,e4 ,jones1 ,yule1 ,barton1 and other experimenters4 ,,application ,,of ,,this ,,method ,,of ,,signalling ,,at ,a ,,distance ,,to ,,actual ,,telegraphy4 ,although the method of signalling to a moderate distance through walls or other non-conducting obstructions by means of ,hertz waves emitted from one station and detected by ,branly filing tubes at another station was practised by the author and by several other persons in this country1 it was not applied by them to actual telegraphy4 ,the idea of replacing a galvanometer1 which was preferably a well-damped or speaking galvanometer1 by a relay working an ordinary sounder or ,morse was an obvious one1 but so far as the present author was concerned he did not realise that there would be any particular practical advantage in thus with difficulty telegraphing across space instead of with ease by the highly developed and simple telegraphic and telephonic methods rendered possible by the use of a connecting wire4 ,in this non-perception of the practical uses of wireless telegraphy he undoubtedly erred4 ,but others were not so blind1 though equally busy2 and notably ,dr4 ,alexander ,muirhead foresaw the telegraphic importance of this method of signalling immediately after hearing the author's lecture on ,june #ast1 #ahid1 and arranged a siphon recorder for the purpose4 ,captain ,jackson also1 at ,devonport1 made experiments for the ,admiralty1 and succeeded in telegraphing between ships in #ahie 7or #ahif74 ,prof4 ,popoff's telegraphic application in #ahie is mentioned on page #fb4 ,by some chance a knowledge of the coherer method of detecting electric waves did not spread fast in ,germany1 the many ,german workers in ,hertz waves continuing1 for some time after #ahid1 the older and less efficient1 though for metrical purposes often more convenient1 mode of detecting them4 ,but1 in ,italy1 the work described in the preceding lecture became well known1 and the subject was developed largely1 especially by ,prof4 ,righi1 of ,bologna1 in the optical direction4 ,it was also developed in the same direction with many most interesting results by ,prof4 ,bose1 of ,calcutta1 as mentioned in the text4 ,prof4 ,righi made a large number of experiments1 which he has since described in an ,italian treatise1 8,optic ,elettrica10 and it appears that it was from him that ,signor ,marconi learned about the subject1 and immediately conceived the idea of applying it to commercial telegraphy4 ,he appears to have worked at the subject for a short time in ,italy1 aiming at getting the receiver to be more satisfactory and dependable1 and improving the early form of ,branly filings tube depicted on page #bc by greatly diminishing its size1 bringing the terminals closer together1 and replacing the coarse borings by fine filings4 ,he also sealed them up in a vacuum1 just as the author did1 as related on page #cd4 ,the only differences1 indeed1 between his procedure and the author's during this time were that ,signor ,marconi preferred nickel filings with a little mercury and a low vacuum1 whereas the author adhered chiefly to iron and brass filings and to high vacua4 ,at last he brought it over to ,dublin1 where he was advised to take it to the ,chief of the ,government ,telegraphs1 ,mr4 ,preece1 and accordingly he took his1 at that time1 crude apparatus to the ,post ,office in a sealed box4 ,there was no point of novelty in it at this stage4 ,with the powerful aid of the ,post ,office ,signor ,marconi proceeded to develop his system of telegraphy on a large scale2 and1 sometimes failing1 sometimes succeeding1 gradually increased the distance over which signalling was possible1 and especially began to develop from unpromising beginnings his special method for long-distance1 viz41 the employment of a sending and receiving conducting plate or other small surface1 at the top of a lofty pole1 connected through what was at that time supposed apparently to be the real radiator1 with the earth4 ,this elevated plate1 connected as it now is through a simple spark gap with the earth1 is an obvious modification of a ,hertz vibrator2 for it may be regarded simply as a ,hertz vibrator with its axis vertical1 as ,hertz often used it1 and with its lower plate replaced by the earth1 so as to double the available capacity2 but the action of a pair of such elevated plates1 connected through the earth conductively and through the air inductively1 as now used by ,marconi for sender and receiver respectively1 is not quite like that of a ,hertz vibrator and a ,hertz receiver acting on one another by emitted radiation in the ordinary way4 ,if it were not the same earth to which the plates were connected1 they would have to act ordinarily by radiation1 but since it is the same earth1 and that earth conducting 7possibly1 indeed1 with a submerged cable sheath connecting favourably-chosen stations71 then the two elevated plates are partially like the greatly separated terminals of a single ,hertz vibrator4 ,only one of the plates is charged during a sending operation1 the other is at zero potential1 but some trace of the electrostatic lines from one plate may extend in curved lines to the other1 just as they extend to every elevated conductor within hail of the sender in any direction4 ,then comes the snap of the spark gap and the sudden discharge1 equivalent to the rush of an opposite charge of electricity suddenly into the sending plate1 disturbing the electric equilibrium at a distance--at any distance to which any trace of electrostatic field had been able to reach--and giving a kind of what is called in lightning a 8return stroke40 ,the effect of this on the distant plate and conductor must be almost infinitesimal2 nevertheless1 separating it from the earth is the most sensitive detector to a minute sudden rush or jerk of electricity that can be imagined1 or that has hitherto been invented1--the coherer4 ,accordingly1 absurdly minute though the disturbance is1 the coherer feels it1 instantly increases in conductivity1 works the relay1 and gives the signal4 ,every spark at the distant spark gap causes a similar rush in or out of the distant elevated plate1 and the receiving plate collects such a fraction of this disturbance as to stimulate the coherer and give a signal every time4 ,not that it is to be supposed never to miss fire4 ,at the present time a coherer is not a rough instrument that can be left free from expert attention with safety for a long time4 ,there are times when it goes on working for days or even weeks1 but there are other times when it gives trouble and needs some form of attention4 ,let us hope that these latter times will become less frequent1 and that the whole thing will become quite dependable before long4 ,the pertinacious way in which ,mr4 ,marconi and his able co-operators have1 at great expense1 gradually worked the method up from its early difficult and capricious stage to its present great distances and comparative dependableness is worthy of all praise4 ,telegraphy by means of ,hertz waves1 though perhaps chiefly developed in this country1 has also been pursued successfully by ,prof4 ,slaby in ,germany1 who has attained considerable distance over land1 with its numerous obstacles1 and has published an account of his researches in a book called 8,funkentelegraphie02 while like success over land has been attained by ,m4 ,e4 ,ducretet1 ,m4 ,blondel and others in ,france4 ,m4 ,ducretet has1 indeed1 put on the market a compact apparatus whereby beginners can readily try their hands at this mode of signalling2 as well as a large-scale apparatus like that employed by ,lieutenant ,tissot for lighthouse signalling on the coast of ,brittany4 ,the filings tube now chiefly employed by the author is of the following form3--,it is a sealed glass tube containing carefully selected iron filings1 and exhausted to the highest vacuum4 ,close together are two little silver globes melted each on its own platinum wire terminal1 which are connected with convenient screws on an ebonite stand4 ,the filings are adjusted so as just to cover the two silver globes1 and no more2 a pocket1 or reservoir1 however1 is sometimes provided whereby more or fewer filings can be easily introduced into the working compartment for experimental purposes4 ,this pocket serves to fix the whole tube to its ebonite body1 which is provided with a clamp to attach it to the stiff spring1 or movable lever1 or other form of support1 through which it is to receive the mechanical shocks necessary to restore or decohere it after an electrical stimulus4 ,the usual plan is to employ an electrical hammer to rap strongly on a stiff brass spring to which the ebonite is clamped1 but another plan is to attach the coherer to a lever tilted strongly by an electromagnet after the fashion of a sounder4 ,a rapid succession of gentle taps is often better than one violent one1 but experience is the best test of the kind of restoration wanted1 for it depends a good deal on the strength of the electrical stimulus4 ,there are methods of dispensing with this decohering operation altogether4 ,after a fairly strong electric stimulus all the filings are stuck together into a sort of mat1 and nothing but a thorough shaking up will pull them asunder again4 ,a still more violent electric shock may indeed have a decohering effect1 but it is not a plan to be recommended1 for it seems to be a heat effect1 akin to the blowing of a fuse4 ,for protecting a coherer from undesired stimuli1 e4g41 from the radiator at its own station1 the general method is described on page #ce1 c41 and the details of it1 with the necessary switch for changing over from sending to receiving1 are mentioned further on 7page #fj74 ,but by referring to page #ajf it will be seen that ,m4 ,branly had already employed such a protecting case1 and had worked details out admirably4 ,recently ,signor ,tommasina has shown that1 if one end of a short rod or wire be dipped into filings while sparks are occurring in the neighbourhood1 the filings adhere to it and to each other1 and with care a long string of them can be picked up4 ,the author has examined the behaviour of filings under electrical influence on a glass plate in a microscope1 and their movements towards the formation of a complete conducting bridge between the tinfoil terminals together with their disjunctive behaviour when the electrical stimulus is too strong1 the thorough cohesion set up by a succession of electrical stimuli1 and the partial or complete disruption by an appropriate mechanical stimulus is instructive4 ,an earlier and most important telegraphic application1 based upon information given in the preceding lecture1 was made in #ahie by ,prof4 ,popoff1 of ,russia1 and will be mentioned shortly 7see page #fb74 ,i now proceed to developments of syntonic or attuned telegraphy on the true ,hertz-wave principle1 the preliminary experiments on which are mentioned above in connection with the figures on page #bg4 ,,further ,,developments ,,in ,,the ,,telegraphic ,,direction4 ,,syntonic ,,telegraphy4 ,in the present state of the law in this country it appears to be necessary for a scientific man whose investigations may have any practical bearing to refrain from communicating his work to any scientific society1 or publishing it in any journal until he has registered it and paid a fee to the ,government under the so-called ,patent ,law4 ,this unfortunate system is well calculated to prevent scientific men in general from giving any attention to practical applications1 and to deter them from an attempt to make their researches useful to the community4 ,if a scientific worker publishes in the natural way1 no one has any rights in the thing published2 it is given away and lies useless1 for no one will care to expend capital upon a thing over which he has no effective control4 ,in this case practical developments generally wait until some outsider steps in and either patents some slight addition or modification1 or else1 as sometimes happens1 patents the whole thing1 with some slight addition4 ,if a scientific worker refrains from publishing and himself takes out a patent1 there are innumerable troubles and possible litigation ahead of him1 at least if the thing turns out at all remunerative2 but the probability is that1 in his otherwise occupied hands1 it will not so turn out until the period of his patent right has expired4 ,pending a much-to-be-desired emendation of the law1 whereby the courts can take cognisance of discoveries or fundamental steps in an invention communicated to and officially dated by a responsible scientific society1 and can thereafter award to the discoverer such due and moderate recompense as shall seem appropriate when a great industry has risen on the basis of that same discovery or fundamental invention--pending this much-to-be-desired modification of the law1 it appears to be necessary to go through the inappropriate and repulsive form of registering a claim to an attempt at a monopoly4 ,the instinct of the scientific worker is to publish everything1 to hope that any useful aspect of it may be as quickly as possible utilised1 and to trust to the instinct for fair play that he shall not be the loser when the thing becomes commercially profitable4 ,to grant him a monopoly is to grant him a more than doubtful boon2 to grant him the privilege of fighting for his monopoly is to grant him a pernicious privilege1 which will sap his energy1 waste his time1 and destroy his power of future production4 ,illustration3 ,,fig4 #bd 7,fig4 #e of ,specification #aa1ege_/ig74--,syntonic ,radiator1 adapted for sending and for receiving4 ,however1 the author1 in consultation with friends1 decided that registration was1 under present conditions1 necessary1 and1 accordingly1 for his attempt at syntony and other improvements in the ,hertz wave method of signalling1 he can refer here to certain patents taken out1 in conjunction chiefly with ,dr4 ,alexander ,muirhead1 his co-worker1 which are numbered respectively as follows3-- ,illustration3 ,,fig4 #be 7,fig4 #ac of ,specification #aa1ege_/ig74--;,diagram of connections for ,syntonic ,receiver2 e being coherer and w a non-inductive conducting or capacity shunt1 to eliminate the self-induction of the receiving instrument4 7#a7 #aa1ege of #ahig1 wherein is described the general syntonic principle and the mode of prolonging the duration of the vibrations emitted by a radiator or by a receiver4 ,this is done by adding to it electromagnetic inertia 7that is1 a self-induction coil7 in such a way as to lessen its radiating power1 converting its type of emission from something like a whip-crack into something more like that of a struck string4 7,not pushing it so far as to make it like a fork1 though that could be done if desired3 see ,journal ,inst4,e4,e41 ,december1 #ahih47 ,but too prolonged a duration of vibration is not desirable1 for it can only be obtained at the expense of radiating power4 ,for the most distant signalling the single pulse or whip-crack is the best1 and this is what in practice has hitherto always been employed2 but1 with it1 tuning is of course impossible4 ,a radiator with several swings is less violent at its first impulse than is a momentary emitter2 but then the lessened emitting power of a radiator is to be compensated by a correspondingly prolonged duration of vibration on the part of the receiver or absorber1 thus rendering the radiator susceptible of tuning to a special similarly-tuned receiver or resonator4 ,the tuned resonator is then to respond1 not to the first impulse of the radiator1 but to a rapidly worked up succession of properly timed impulses2 so that at length1 after an accumulation of two or three1 or perhaps four1 swings1 the electrostatic charges in its terminal plates become sufficient to overflow and spit off into the coherer1 thereby effecting its stimulation and giving the signal4 ,a resonator not properly tuned--i4e41 one tuned to some different frequency of vibration--would not be able to accumulate impulses1 and hence would not respond1 unless of course it were so much too near the radiator that the very first swing stimulated it sufficiently to disturb the coherer2 in which case1 again1 there is no room for tuning4 ,the two points to attend to for syntonic discrimination are3 7a7 that the receiver shall not be so near the emitter as to feel its impulses too easily1 i4e41 without accumulation2 7b7 that the properly tuned receiver shall be so arranged that it can work up and accumulate the impulses of the radiator1 and before attaining its maximum swing can overflow into the coherer associated with it and thus give the signal4 ,illustration3 ,,fig4 #bf 7,fig4 #aj of ,specification #aa1ege_/ig74--;,interchangeable ,self-,induction ,coils for signalling to different stations4 ,illustration3 ,,fig4 #bg 7,fig4 #c of ,specification #aa1ege_/ig74--;,diagrammatic representation of ,syntonic ,radiator and ,receiver4 ,the middle spark gap h h is unnecessary1 though sometimes helpful4 ,the main charging is done by impulsive rush at the outside knobs4 ,illustration3 ,,fig4 #bh 7,fig4 #g of ,specification #aa1ege_/ig74--,syntonic ,radiator with earth connection arranged for sending4 ,the general appearance of a pair of signalling stations on this plan is shown in ,fig4 #bd1 where the huts contain the sending and receiving instruments4 ,the self-induction coil joining the two capacity-areas is better depicted in ,fig4 #be1 which also shows one mode of joining up the coherer to a syntonic receiver4 7,the galvanometer and shunt are1 of course1 merely typical of any kind of telegraphic instrument whatever47 ,fig4 #bf indicates one form of sender with three alternative syntonising coils for speaking to three distant attuned stations4 ,fig4 #bg shows a radiator arranged for receiving1 but illustrates another method of charging1 and one frequently employed by the author1 viz41 the method by impulsive rush 7compare ,figs4 #aa1 #ab and #ai1 on pp4 #ad and #be of this book74 ,the terminals of the ,ruhmkorff coil are here connected1 not to the capacity-areas direct1 but to a pair of knobs near the centre of gravity of each area1 so that when the discharge occurs each area is suddenly charged oppositely1 and the two opposite charges are left to surge into one another and set up the oscillations4 ,this impulsive method of charging is essentially that adopted in the spherical whip-crack emitter depicted in ,fig4 #ai 7p4 #be1 ante71 the two poles of the sphere having but small capacity and being joined by as thick a conductor as the equator of the sphere4 ,but for such a radiator as is indicated in ,fig4 #bd or ,fig4 #bg the author commonly found that a third short spark gap in the middle was an improvement1 and so1 as is well known1 did ,prof4 ,righi find it1 and embodied it in his well-known double-sphere double-knob emitter4 ,illustration3 ,,fig4 #bi 7,fig4 #ab of ,specification #aa1ege_/ig74--,single-point ,coherer1 with clockwork ,tapper-back operating on the projecting end of the spring clamped at ,p and lightly touching a needle point n4 ,the specification also contains figures of earth-connected forms of radiators1 with or without self-induction coils1 of which ,fig4 #bh may be here reproduced2 and likewise a modification of the point coherer depicted in ,fig4 #ag1 on page #bb 7see ,fig4 #bi1 and also fig4 on page #bg71 where the spiral wire spring is replaced by a piece of straight watch-spring1 clamped at one end1 adjusted by a screw at the other1 and lightly touched by a needle point at its middle2 a very gentle tapping back stimulus being provided in the form of a clockwork or other mechanically-driven motor grazing lightly against one end of the spring protruding beyond the clamp for the purpose4 ,illustration3 ,,fig4 #cj 7,fig4 #ad of ,specification #aa1ege_/ig74--;,another diagram of connections for ,syntonic ,receiver1 with ,coherer in a secondary or transformer circuit2 a conducting or a capacity shunt for the telegraphic instrument being applicable as before4 ,illustration3 ,,figs4 #ca and #cb 7,figs4 #e and #f of ,specification #ah1fdd_/ig74--,modes of connecting a ,coherer to one or to a pair of ,syntonic ,radiators so that it may feel their electrostatic disturbance4 ,illustration3 ,,fig4 #cc 7,fig4 #aa of ,specification #ah1fdd_/ig74--;,actual connections for a ,sending and ,receiving ,station on the plan shown in ,fig4 #cg4 ,left-hand side shows spark sending1 right-hand side shows ,coherer receiving4 ,fig4 #cj shows a coherer inserted in a secondary or transformer circuit1 and operated inductively by the oscillations of the receiver1 which are thus transformed up and raised in potential4 7#b7 ,no4 #af1dje1 #ahig1 wherein are described chiefly various practical methods of decohering1 by means of cams and otherwise1 which are appropriate when working rapidly with automatic transmitter and siphon recorder4 7#c7 ,no4 #ah1fdd1 #ahig1 represents different ways of connecting up a coherer to a syntonic resonator1 so as to get the benefit of its overflow without interfering with the working up of the electric oscillations1 e4g41 ,figs4 #ca1 #cb and #cc4 ,it also shows a plan for constantly decohering by a rapidly revolving cam a number of coherers in parallel1 so that one at least is always ready to receive an impulse 7,fig4 #cd74 ,further1 it arranges to utilise the earth or a cable sheath1 or other uninsulated conductor1 for the purpose of conveying electric impulses to a distance 7,figs4 #ce1 #cf1 #cg and #ch74 ,and next it is arranged to assist the coherer to feel the full effect of any electric jerk by shunting out the battery and galvanometer1 which are necessarily in series with it1 by means of a condenser of moderate capacity 7,fig4 #ce71 which also shows a self-induction mode of sending a stimulus along an uninsulated line4 ,this condenser obstructs all steady currents1 such as give the signal1 but it transmits freely any momentary electric impulses1 such as stimulate a coherer4 ,illustration3 ,,fig4 #cd 7,fig4 #a of ,specification #ah1fdd_/ig74--,single-point ,coherers in parallel1 with successive decoherence4 ,illustration3 ,,fig4 #ce 7,fig4 #c of ,specification #ah1fdd_/ig74--;,a self-induction method of sending jerks into a badly insulated line1 and arrangement for detecting such jerks by a single-point ,coherer4 ,illustration3 ,,fig4 #cf 7,fig4 #d of ,specification #ah1fdd_/ig74--;,another arrangement for sending jerks into a bare or badly insulated line1 and connections for ,coherer detection4 ,illustration3 ,,fig4 #cg 7,fig4 #aj of ,specification #ah1fdd_/ig74--;,another mode of sending a jerk from a spark gap at j into a badly insulated cable or other conductor1 which is connected at the other end to a ,coherer1 the circuit being completed inductively through the air by means of the areas p1 p4 ,the dotted lines s represent the switch connection of ,fig4 #cc4 ,illustration3 ,,fig4 #ch 7,fig4 #ac of ,specification #ah1fdd_/ig74--;,another method of signalling through a pair of imperfect conductors1 such as gas and water pipes i1 without the above elevated inductive connection4 ,illustration3 ,,fig4 #ci 7,fig4 #c of ,specification #bi1jfi_/ig74--;,diagram of ,coherer connection to ,syntonic ,collector1 with capacity shunt for telegraphic instrument4 7#d7 ,no4 #bi1jfi1 #ahig4 ,in this patent various methods of connecting up the shunting condenser1 whose object it is to transmit all jerks undiluted to the coherer1 are shown1 all adapted to work with a syntonic resonator 7,fig4 #ci74 ,there is also shown a complete switch 7,fig4 #dj7 for effecting the transition from 8sending0 to 8receiving10 exposing the coherer to the full effect of the distant radiator1 and completely protecting and isolating it from its home radiator2 the switch being so arranged that signalling is impossible unless the home coherer is protected4 ,a rotating commutator is also shown1 whose object is to expose the coherer to the full influence of a receiver1 especially of a non-syntonic receiver or simple collector1 without its being shunted or otherwise interfered with by the telegraphic apparatus2 to which1 however1 immediately afterwards the rotating commutator connects it1 and then effects the tapping back4 ,connections are shown 7,fig4 #da7 for a complete sending and receiving station on this plan with a syntonic radiator and resonator indicated 7though not to scale74 ,but with syntonic resonators the revolving commutator method is not found to be necessary2 the sending and receiving switch1 together with the closed box for protecting the coherer in an instantly accessible manner is therefore the chief feature of this diagram4 ,illustration3 ,,fig4 #dj 7,fig4 #f of ,specification #bi1jfi_/ig74--,switch at a ,sending and ,receiving ,station1 to change all the connections with a protected ,coherer from receiving to sending by depressing the knob l4 ,illustration3 ,,fig4 #da 7,fig4 #g of ,specification #bi1jfi_/ig74--;,diagram of connections at a protected ,coherer ,station with ,syntonic ,radiator and ,collector4 ,,earlier ,,telegraphic ,,advances4 ,in ,april1 #ahie1 a communication was made to the ,russian ,physical ,society by ,prof4 ,a4 ,popoff1 of the ,torpedo ,school1 ,cronstadt1 ,russia1 and appears in the ,journal of that ,society for ,january1 #ahif4 ,in this communication the use of an elevated wire and of a tapper-back worked through a relay by the coherer current are clearly described1 and signalling was effected for a distance of #e kilometres 7#c miles74 ,an extract from this communication is given in ,the ,electrician for ,december1 #ahig1 ,vol4 ,,xl41 page #bce1 and from it we reproduce ,fig4 #db1 illustrating the tapping back arrangement4 ,the following extracts from this paper may also be quoted3-- 8,on using a sensitive relay in the circuit with the coherer tube1 and an ordinary electric bell in the other circuit of the relay1 for sound signals and as an automatic tapper for the coherer1 ,i obtain an apparatus which exactly answers every electric wave by a short ring1 and by rhythmical strokes if electric vibrations be excited continuously40 8,on connecting an electromagnetic recorder in parallel with the bell1 tracing a straight line along the paper band which is moved by a #ab-;hour clockwork cylinder1 ,i obtain an instrument registering by a cross line on the moving band every electric wave that reaches the coherer from across the atmosphere4 ,such an apparatus was placed at the ,meteorological ,observatory at ,st4 ,petersburg in ,july1 #ahie1 one of the electrodes of the coherer being connected by an insulated wire with an ordinary lightning conductor1 the other electrode of the tube-coherer being connected with the ground40 ,illustration3 ,,fig4 #db 7,fig4 #b on p4 #bce of ,the ,electrician1 ,vol4 ,,xl474--,method of automatic tapping back by relay current employed for telegraphy by ,prof4 ,popoff in #ahie4 ,prof4 ,popoff then goes on to say that his apparatus works well as a lightning recorder1 and that he hopes it can be used for signalling to great distances4 ,he says3-- 8,i can detect waves at the distance of one kilometre if ,i employ as sender a ,hertz vibrator with #cj centimetre spheres1 and if ,i use the ordinary ,siemens relay2 but with a ,bjerknes vibrator #ij centimetres diameter1 and a more sensitive relay1 ,i reach five kilometres of good working40 ,thus it is plain that ,prof4 ,popoff employed the elevated wire as receiver in #ahie1 but did not employ it as sender4 ,in #ahig ,prof4 ,slaby1 of ,berlin1 published 7in ,german7 a book called 8,spark ,telegraphy10 in which he described his success in signalling from #c to #ac miles across land4 ,from this book we take the following illustrations of the coherer and its connections3-- ,fig4 #dc shows the coherer tied on to a glass tube1 by which it is supported4 ,illustration3 ,,fig4 #dc 7,fig4 #g of ,slaby's book74 ,fig4 #dd shows the simplest form of its connection to a one-cell battery ,a and a polarised relay ,b1 which switches on another battery of several cells a operating the ,morse instrument or electric bell or sounder b and also the tapper-back c1 the hammer of which raps gently on the coherer tube at every signal4 ,illustration3 ,,fig4 #dd 7,fig4 #h of ,slaby's book74--,slaby's arrangement of ,coherer and of tapper-back and relay connections4 ,the actual apparatus is depicted in two views1 ,figs4 #de and #df1 where will be recognised on the left-hand side the coherer and tapper-back2 in the middle the batteries1 both for relay and for coherer circuits2 and on the right-hand side a relay and the signalling or calling instrument1 in this case shown as an ordinary electric bell4 ,illustration3 ,,fig4 #de 7,fig4 #af of ,slaby's book74--,view of ,slaby's ,receiving ,apparatus1 with call-bell rung by relay1 or with ,morse instrument joined on to terminals ,m1 and switch to change from ,calling to ,signalling4 ,k ,k are the terminals of elevated wire and earth1 and the ,coherer and ,tapper-back are close to them4 ,illustration3 ,,fig4 #df 7,fig4 #ag of ,prof4 ,slaby's book74--,an elevation view of ,prof4 ,slaby's same ,apparatus1 showing the electromagnet and hammer of the tapper-back worked by relay current from local battery1 as in ,popoff's plan of #ahie4 ,a ,morse instrument is to be connected to the terminals ,m1 and either it or the bell can be switched into the circuit at pleasure4 ,the form of relay depicted is special to ,slaby1 but the rest of the arrangements are practically identical with those shown by ,marconi at ,dover4 ,fig4 #dg gives a diagram of the actual connections4 ,fig4 #dh is a picture of one of ,slaby's signalling stations1 showing the way the elevated wire enters the building4 ,illustration3 ,,fig4 #dg 7,fig4 #ai of 8,spark ,telegraphy074--,diagram of ,slaby's connections in the above apparatus4 ,f is the coherer and ,k the tapper-back4 ,during ,september1 #ahii1 the ,marconi method of signalling to long distances was demonstrated before the ,british ,association at ,dover4 ,the chief feature of the installation was the elevated wire supported by a mast1 and terminating at the top in a small conductor1 which is usually made of wire netting1 and is suspended from an insulating rod4 ,the lower end of this elevated wire passed into the building through an aperture1 and was connected to one terminal of the usual ,ruhmkorff coil1 the other terminal of which was earthed4 ,the signalling key was of the simplest description1 being nothing more than a well-insulated ,morse key worked by hand and causing a make-and-break in the primary circuit of the coil4 ,the ordinary trembling break of the induction coil was at work in the usual way1 so that while the signalling key was depressed continuously there was a torrent of sparks between the knobs of the secondary4 ,this method of signalling was identical with that employed by everyone since the time of ,hertz1 except that1 instead of connecting the secondary terminals to two insulated plates1 one was now connected to earth and the other to a small insulated conductor at considerable elevation4 ,illustration3 ,,fig4 #dh 7,fig4 #aa of ,prof4 ,slaby's book on 8,spark ,telegraphy074 ,illustration3 ,,fig4 #di 7p4 #gfb1 ,the ,electrician1 ,vol4 ,,xliii474--,marconi ,signalling ,mast at ,dover ,town ,hall4 ,illustration3 ,,fig4 #ej 7,fig4 #a1 p4 #g1 ,the ,electrician1 ,vol4 ,,xliii474--,mast at ,south ,foreland2 from which ,signals went to a similar ,mast at ,wimereux1 near ,boulogne4 ,from this mast in the town of ,dover 7,fig4 #di7 signals could be sent to another loftier mast at the ,south ,foreland 7,fig4 #ej71 where it is itself elevated by chalk cliffs far above the sea4 ,from this ,south ,foreland station1 which was similar in all essential respects to the ,dover station1 except that its elevation was greater1 messages could be sent and received to and from a station near ,boulogne1 on the coast of ,france1 and to and from the ,east ,goodwins lightship4 ,the signalling was slow1 but appeared dependable1 and the simplicity of all the arrangements was remarkable 7,fig4 #ea74 ,concerning the receiving apparatus there is little to be said1 since it is in essence the same as that which has already been described4 ,it consists of a coherer of the plug tube pattern1 something like that depicted on page #bc1 but excessively reduced in size1 the glass tube being the size of a quill1 the two silver plugs close together separated only by a very few nickel filings4 ,this tube is mounted so that it can be struck after each signal by a light electric hammer worked by a current from a local battery switched on by a ,siemens' polarised relay1 which is itself actuated by the coherer current4 ,whenever the coherer receives a signal the same current that works the tapper works also the ,morse instrument standing on the table alongside1 and records a short or a long signal on the tape4 ,the coherer with its tapper1 the polarised relay1 and the battery 7a few dry cells7 are all enclosed in one oblong iron box1 through an aperture in which the lower end of the elevated wire can be inserted and brought into direct connection with the coherer4 ,to change from transmitting to receiving nothing is needed but the detachment of this wire from the ,ruhmkorff coil terminal and its insertion through the aperture of the enclosing box so as to touch the coherer circuit4 ,the object of the box is1 of course1 the protection of the coherer from undesired disturbances1 exactly as described on page #cd1 and the collecting wire has the function there described likewise4 ,the electric tapper-back is also mentioned on page #ca1 but not as being operated through a relay by the coherer circuit's own current4 ,this last improvement seems to have been devised and employed by ,prof4 ,popoff at ,cronstadt in #ahie 7see ,fig4 #db74 ,no doubt it was arrived at independently again by ,mr4 ,marconi and the telegraph officials who assisted him in his early experiments in this country4 ,the other box shown in ,fig4 #ea is probably a stand-by in case of accident4 ,it is difficult to imagine a simpler contrivance1 and it appeared to work at ,dover dependably1 the messages coming out slowly in ordinary dots and dashes1 the torrent of sparks being sufficiently rapid not to necessitate the breaking up of the dash into a series of dots4 ,the sluggishness of the ,morse instrument or the relay1 or the circuit as a whole1 enabled this excellent result to be attained with apparent ease4 ,illustration3 ,,fig4 #ea 7p4 #gfa1 ,the ,electrician1 ,vol4 ,,xliii474--,apparatus for ,sending and ,receiving1 shown by ,prof4 ,fleming to the ,british ,association at ,dover4 ,a diagram of ,marconi's connection of sensitive tube to the relay and tapper-back and ,morse instrument1 where ,w represents the elevated wire1 is given in ,fig4 #eb4 ,illustration3 ,,fig4 #eb 7,fig4 #b1 of p4 #fia1 ,the ,electrician1 ,vol4 ,,xlii474--,diagram of the connection of ,relay and ,tapper-back and ,morse ,instrument1 as given in ,mr4 ,marconi's ,paper in the ,journal of the ,inst4 ,elec4 ,engineers for ,april1 #ahii2 the relay being an ordinary ,siemens polarised relay4 ,the mast at the ,south ,foreland was stated to be #aej ft4 high1 but the cliff on which it stands must be at a still greater elevation above the sea4 ,it was from this station that the real distant signalling was performed1 and probably not from the lower mast at ,dover4 ,,the ,,history ,,of ,,the ,,coherer ,,principle4 ,the following1 written by ,dr4 ,oliver ,lodge1 appeared in 8,,the ,,electrician0 for ,november #abth1 #ahig3-- ,probably the earliest discovery of cohesion under electric influence was contained in that old1 forgotten observation of ,guitard in #ahej1 that when dusty air was electrified from a point the dust particles tended to cohere into strings or flakes4 ,the same thing no doubt occurs in the formation of snowflakes under the influence of atmospheric electrification2 and the cohesion of small drops into large ones in the proximity of a charged cloud is exceedingly familiar1 since it results in the ordinary thunder-shower4 ,great light was thrown on these meteorological phenomena by the discovery of ,lord ,rayleigh in #ahgi of the curious behaviour of a small fountain or vertical water-jet when exposed to the neighbourhood of a stick of excited sealing-wax4 ,a smooth orifice being arranged to throw a jet of water about three or four feet nearly vertically1 the jet breaks into drops1 and the drops scatter in all directions1 rebounding from one another and giving a shower of fine spray2 but if a stick of sealing-wax be rubbed on the sleeve of a coat and brought within one or two yards of the place where the jet breaks into drops1 it will be found that the scattering ceases1 the fine spray is no longer formed1 and the broken jet rises and descends in great blobs of water4 ,the rain-shower has1 in fact1 been converted into a thunder-shower4 ,further experiments1 conducted chiefly with two jets1 elucidated the phenomenon4#ah ,arranging two nearly parallel jets from neighbouring orifices so as to impinge against each other1 they were found ordinarily to rebound after colliding1 a sort of film or superficial layer appearing to prevent amalgamation of the jets into one2 but if a slight difference of electric potential were maintained between the two jets1 say by connecting them to the terminals of a ,leclanch cell1 then the boundary layer broke down1--the two colliding jets no longer separated with a rebound1 but amalgamated and became one4 #ah ,proc4 ,roy4 ,soc41 #ahgi and #ahhb4 ,lord ,rayleigh developed a similar explanation for the single jet4 ,the scattering of the jet in its ordinary state was due to the rebound of colliding drops1 as could be seen by examining it with a sufficiently instantaneous or intermittent mode of illumination2 but if an electric charge were in the neighbourhood it must be supposed that a trace of potential difference existed between the drops1 which caused them to amalgamate into one whenever they collided1 and thus speedily to become united into a comparatively few large drops1 which then continued on their parabolic way4 ,at first sight it would seem as if the neighbourhood of a negative charge should charge all the drops positively at the place whence they break off from the earth-connected parent jet1 and should thus cause them all to repel each other4 ,and if the electrified sealing-wax is held too close1 this is exactly what happens4 ,all the drops are then similarly electrified1 and scatter more violently than ever1 never in that case coming into any rebounding or other contact with each other4 ,but under a gentler electric influence the similar charging has a less marked result1 and a polarisation difference of potential of one or two volts may without difficulty be supposed to exist in the air between drops1 partly because they are not all equally charged and partly because each is a conductor acted on inductively by a neighbouring electrified body4 ,in this connection it must be remembered that rubbed sealing wax is at a potential of several thousand volts1 and therefore can readily cause a potential gradient of two or three volts per millimetre throughout a yard or two of space4 ,the next stage was the re-discovery1 in #ahhc1 of ,guitard's old dust phenomenon by the present writer and the late ,j4 ,w4 ,clark 7,nature1 ,july1 #ahhc2 ,phil4 ,mag41 ,march1 #ahhd71 when they were working together at the dust-free region seen over hot bodies when strongly illuminated in dusty air4 ,the fact of such dust-free spaces was discovered by ,tyndall1 and they can readily be seen by placing a lighted spirit lamp or a hot poker in the beam of an electric lamp4 ,tyndall thought the dust was calcined or burnt up1 and that thus the air was freed from it2 but this is an utterly erroneous explanation1 and the true explanation is of a more recondite character1 being connected with the bombarding effect of gas molecules as illustrated in the ,crookes radiometer4 ,the dust particles are beaten away from the hot body by a molecular bombardment1 which manifests itself even at ordinary pressures on bodies of sufficiently small size1 as indeed was also otherwise shown by ,tait and ,dewar and ,osborne ,reynolds in the course of remarkable theoretical and practical investigations4#ai ,before arriving at this explanation1 however1 we experimented to see if the phenomenon was caused by the air having become slightly electrified1 perhaps by reason of its having streamed as an upward convection current over the surface of the warm solid1 at which we were looking1 in a thick smoky atmosphere1 in the concentrated light of an electric arc4 ,we therefore purposely electrified the rod1 to see what that would do1 and we found to our surprise1 directly the electric machine was turned1 that the smoky atmosphere almost instantaneously disappeared1 and the box became quite clear4 ,this experiment1 after development1 though described in ,july1 #ahhc1 was shown in public for the first time at the ,dublin ,royal ,society 7,nature1 ,april #bd1 #ahhd71 and subsequently at the ,british ,association meeting in ,montreal#bj in #ahhd1 and was applied to the experimental clearing of rooms from dense smoke or fume4 ,it has often been shown since1 by ,mr4 ,swan and others1 and has become fairly well known4#ba #ai 8,dimensional ,properties of ,matter10 ,phil4 ,trans41 #ahgi4 #bj ,evening ,lecture on 8,dust10 by the writer1 see ,nature1 ,vol4 #ca1 p4 #bfe2 also ,journal of the ,royal ,institution1 ,may1 #ahhf4 #ba ,apparatus for the purpose is now in the catalogue of ,messrs4 ,ducretet1 of ,paris1 but they supply a pair of combs of points4 ,it makes a more interesting experiment if only one point is used1 in a moderate space1 and the electric supply regulated so as not to hurry the disappearance of the smoke too quickly1 but to exhibit the stages of aggregation which precede the final disappearance by deposition4 ,any kind of smoke serves1 but a bit of magnesium ribbon burnt under a bell jar is cleanly and effective4 ,it should be looked at in a window or other good light1 of course4 ,the next observation of cohesion under electrical influence was made by the writer in #ahhi1 while working at the protection of telegraphic instruments and cables from lightning1--a research which resulted in the use of choke coils as supplementary to the air gaps of the ordinary lightning guard1 and thus to the forms of instrument constructed by ,dr4 ,alex4 ,muirhead for telegraphic work in this country1 and to the supplementary additions adopted by the ,westinghouse ,company for their non-arcing guards adapted to electric light and power installations in ,america4 ,the observation of cohesion was a bye-issue1 noticed when the knobs of the lightning guard were brought too close together4#bb #bb ,journal of the ,institution of ,electrical ,engineers for #ahij1 pp4 #ceb-d4 ,when lightning itself strikes a guard1 it has indeed often been found that the opposite sides of the protective air gap are fused together4 ,this1 no doubt1 may be partly due to a straightforward melting or welding by heat1 but it is probably not solely that4 ,molten metals without a flux do not so readily weld4 ,it is almost certainly due to a cohesive action also1 the difference of potential between the molten terminals resulting in adhesion and amalgamation1 a phenomenon also observed in the frequent locking of an electric arc formed between two metallic electrodes4 ,however this may be1 certainly the phenomenon occurs on a small scale1 for if the pair of knobs or points placed as a shunt to protect a galvanometer or other telegraphic instrument from lightning 7or what is easier experimentally and essentially the same thing1 from a ,leyden jar discharge7 be set too close together1 the galvanometer will be found to be short-circuited after a spark1 and the knobs will be found1 both by mechanical and electrical tests1 to be feebly united at a single point4#bc ,not only1 however1 is the galvanometer short-circuited by the metallic junction so formed1 but at the instant of the formation of the joint it experiences a very perceptible kick1 indicating a momentary current1 coincident no doubt with the electric discharge1 but one from which it would have been protected had not the junction occurred4 ,the galvanometer kick is clearly an effect due to the uniting metals1 but it has not yet been fully elucidated2 it seems to have been first observed by ,mr4 ,stroh in his excellent researches on microphonic action1 related in the ,journal of the ,society of ,telegraph ,engineers1 #ahhc and #ahhg1 and it may possibly be thermo-electric1 as ,prof4 ,hughes1 who also observed it1 thinks likely2 but it may be electro-chemical1 or it may be connected with an effect observed later by ,fitz,gerald in his galvanometer mode of detecting ,hertzian waves1 which he published at the ,royal ,institution in #ahij4 ,the point of present interest is the cohesion which sets in between the knobs when the spark occurs3 an extremely feeble spark was found sufficient to produce the effect1 provided the surfaces were already almost infinitely close together1 i4e41 provided they were already in what would be called contact1 with the merest imperceptible film of 7probably7 oxide separating them1 just the kind of film which a chemical flux is useful in removing4 ,the electrical stimulus appears to act as such a flux1 and the adhesion of the two surfaces was demonstrated by an electric bell and single cell in circuit4 ,every time the spark occurred the bell rang1 and continued ringing1 until the table1 or some part of the support of the knobs1 was tapped so as to shake or jar them asunder again4#bd ,the arrangement constitutes a convenient detector in the syntonic ,leyden jar experiment1 depicted in ,fig4 #d1 p4 #f 7see also p4 #ba74 #bc 8,modern ,views10 second edition1 p4 #cei4 #bd ,journal of the ,institution of ,electrical ,engineers1 #ahij1 p4 #ceb4 ,see also remarks by ,mr4 ,stroh in two microphone discussions1 ,journal of the ,institution of ,electrical ,engineers1 #ahhc and #ahhg4 ,if the electric bell stands on the same table as the support of the sparking knobs1 or1 still better1 if it be put into mechanical contact with them1 its tremor is quite sufficient to break the contact asunder again2 unless the spark1 and therefore the adhesion1 has been too strong4 ,raising the bell into the air1 it ceases to interrupt the spark-induced continuity1 and in that case continues to ring2 but directly it is replaced so that its vibration can reach the cohered surfaces through their solid supports it usually happens that a few strokes--often1 indeed1 the first stroke--of the bell1 sometimes even the incipient movement of the hammer preparatory to a stroke1 is sufficient to break the circuit and suspend instantly the action1 restoring the gap to its original condition and leaving the circuit ready to be completed again by another spark4 ,the spark in these early experiments was usually supplied from the outer coats of a pair of oppositely-charged small ,leyden jars1 whose knobs sparked into each other2 the idea being to ascertain all the conditions pertaining to the feeble residue of a lighting discharge which is liable to be conducted by telegraph wires to a distance1 and there cause some damage to sensitive instruments not suitably protected from sudden electric jerks1 whose laws of flow are quite different from those proper to steady currents4 ,meanwhile1 in #ahhg and #ahhh1 had been performed the great experiments of ,hertz on electric waves in free space4 ,the writer1 assisted by ,prof4 ,chattock1 had also made some experiments concerning the production and detection of waves on a system of long parallel wires stretched on insulators across and around a large room1 and excited by the discharge of a pair of condensers1 an arrangement very similar to that now known under the name of ,lecher2 and clear experimental evidence of the existence of nodes and loops on such wires1 as well as a method of approximately measuring the wave length1 was given4#be ,the brush luminosity of the wires1 afterwards observed more strikingly by ,tesla1 was also seen and shown to the ,physical ,society4 ,the interest of these experiments was1 however1 altogether eclipsed by the brilliant and masterly investigation at ,carlsruhe by ,hertz1 who1 as everyone except the ,british public is aware1 put into practice ,fitz,gerald's #ahhc suggestion that ,leyden jar discharges should emit ,maxwellian radiation1 and conclusively demonstrated the existence and some of the properties of such waves by this very means2 using1 however1 ,leydens of small capacity1 and with the coatings well separated1 so that the electrostatic energy of the charge should have an intensity comparable with the magnetic energy of the discharge1 even at some distance from the circuit4 #be ,verbally to ,section ,a at ,bath1 #ahhh4 ,see also ,phil4 ,mag41 ,august1 #ahhh1 p4 #bbi2 and ,the ,electrician1 ,vol4 #ba1 pp4 #fjg-h4 ,the whole subject of electric waves was thus laid open to physicists1 and many have been the workers in the field4 ,trouton1 of ,dublin1 worked long and successfully at their optical analogies1 with the very inadequate means of detection then known2#bf and since better means have been known perhaps the most complete set of experiments published1 after ,hertz himself1 is that contained in the book 8,optice ,elettrica10 by ,prof4 ,righi1 of ,bologna2 but some account of several previous researches is contained in the second edition of 8,modern ,views of ,electricity10 in the chapter called 8,recent ,progress10 of date #ahib4 ,the means used by ,hertz and his immediate followers to detect the waves was simply the little spark which they excited in conductors upon which they fell2 electric currents being set up in such conductors by the act of reflection4 ,the effect was often at that time attributed to electric resonance or syntony1 but there was very little true resonance in these experiments2 the first swing was usually much more powerful than any of the succeeding ones1 and was competent to cause the little spark2 if it failed the remainder of the swings had but a poor chance of success4 ,consequently precision of tuning was not really important1 though no doubt it would help a little4 #bf ,nature1 ,vols4 #ci and #dj4 ,it is interesting to note that a magnetic needle detector not unlike ,rutherford's had been used long ago by ,joseph ,henry at ,washington1 and that minute induced sparks1 identical in all respects with those discovered by ,hertz1 had been seen in recent times both by ,edison and by ,silvanus ,thompson1 being styled 8etheric force0 by the former2 but their theoretic significance had not been perceived1 and they were somewhat sceptically regarded4 ,yet ,henry1 even in those pre-,maxwellian days1 was led to an intuition concerning the spread of electrical disturbance surprisingly near the truth4 ,the truth indeed it was in some sort1 but it was not worked out or grasped in detail1 and so cannot be considered as more than a brilliant guess2 but the fact that an observation of the widespread surgings induced in the neighbourhood of a primary discharge had been made by ,henry1 and had been seen by others to be capable of giving actual sparks1 before the time of ,hertz1 although it has no real bearing on ,hertz's fresh discovery1 and did not lead those who1 like the writer1 had long been trying to think of a detector for ,maxwellian waves to discover one1 nevertheless is instructive as showing how frequently it happens that a fact is lying ready to hand but is not taken up and appreciated until some special or extra stimulus has been supplied4 ,after ,hertz's results had become well-known1 the writer devised a plan whereby real electric resonance could be demonstrated with a pair of actual glass ,leyden jars of ordinary pattern1 by connecting each to a discharge circuit1 the one complete1 the other with an air gap1 and providing the first or receiving jar with an overflow path or bye-circuit provided with an air gap across which a visible spark could occur whenever the induced oscillations or surgings accumulated in its main circuit were sufficiently intense to make the jar overflow4#bg ,the air gap was most easily provided by a strip of tinfoil pasted over the lip of the jar1 but it served equally well if wires led from the two coatings to a pair of adjustable knobs near together1 like a lightning guard1 between which the overflow spark could pass4 ,the same knobs indeed were used as had already served for the lightning experiments2 and1 as in that case1 if the knobs are arranged very close together and are put in circuit with a battery and a bell1 cohesion sets in and the bell rings whenever the overflow occurs4 ,the bell continues to ring until the stand is tapped1 but if the bell itself touches the stand or the table1 it rapidly breaks contact by its vibration1 exactly as described1 p4 #gg 7see also ,fig4 #af;,a1 p4 #ba74 ,closed ,leyden jar circuits are not strong radiators1 nor was this resonance then observed excited by true waves4 ,no attempt was at this time made to apply the cohesion principle to the detection of true ,hertz waves such as could be felt at a considerable distance from a strongly radiating source4 ,before this time1 ,fitz,gerald and ,trouton had hit upon their galvanometer method of demonstrating to an audience the occurrence of the minute scarcely-visible spark in the gap of a ,hertz receiver4#bh #bg ,nature1 ,vol4 #da1 p4 #cfh2 or1 8,modern ,views of ,electricity10 second edition1 p4 #cch4 ,see also ,fig4 #d1 p4 #f4 #bh ,nature1 ,vol4 #da1 p4 #bie2 and ,vol4 #db1 p4 #agb4 ,prof4 ,minchin also1 working at ,cooper's ,hill with his sensitive photo-electric cells1 especially with some which he called 8impulsion cells10 that behaved abnormally when subjected to taps or other mechanical vibrations1 found that when ,mr4 ,gregory was working a ,hertz radiator in another part of the same laboratory the electrometer connected to his cells responded4#bi ,many other detectors have been devised and used1 but this of ,minchin's almost certainly depends on the cohesion principle1 though its action seemed paradoxical then4 ,moreover he was able1 by its aid1 to signal without wires over a considerable number of yards1 at that early date 7#ahij and #ahia74 ,about the same time1 ,prof4 ,boltzmann used a charged gold-leaf electroscope for the same purpose1 having it so arranged that the electroscope was on the point of discharging across a minute air gap1 so that its leaves were dilated by a definite amount4 ,the slightest excess of charge would make it discharge and the leaves instantly collapse4 ,in this charged condition it was sensitive to very minute electric surgings1 and if ,hertz waves were excited in another part of the room1 the wave disturbances caused the gap to break down and the electroscope leaves to collapse4#cj ,this method is not a cohesion method1 but it led the writer1 when subsequently repeating ,boltzmann's results with modifications1 to realise that1 if the gap were almost closed1 cohesion could be made to set in by the surgings induced by regular ,hertz waves 7,fig4 #af1 p4 #ah74 #bi ,phil4 ,mag41 ,march1 #ahia2 also ,january1 #ahid4 #cj ,wied4 ,ann41 ,vol4 #dj4 ,the ,boltzmann gap method was accordingly modified in several ways2 one way was to make it of carbon and to connect it1 with its wave collector1 to the terminals of #aaj-volt electric light leads1 so that whenever a ,hertz vibrator was discharged and induced a minute spark across the gap1 that same spark might close the circuit and establish an arc4 ,this plan forced itself on my attention by the behaviour of sundry ,swan lamps suspended with shades so as to illuminate my lecture table1 which became short-circuited whenever a large ,hertz vibrator was at work2 for the lamps were at that time kept from rotation1 and thereby from glaring into the eyes of the audience instead of being screened from them1 by a couple of copper wires stretched across the theatre4 ,so long as those wires were there1 the fuses used to blow whenever a ,hertz oscillator was started2 an experiment which was interesting enough1 and was shown to several people1 including1 ,i think1 ,prof4 ,fitz,gerald1 but which was sufficiently a nuisance to necessitate the wires1 which were acting as collecting wires1 being taken down and replaced by stretched silk threads1 which are there to this day4 ,another modification was to connect the gap to an ,abel's fuse or to a gas leak1 which exploded or ignited under the influence of a feeble spark4 ,yet another was to connect it to a single cell and electric bell or galvanometer1 as already explained4 ,meanwhile1 however1 and well before these later experiments on the detection of ,hertz waves were in progress1 certain discoveries had been made by ,m4 ,branly1 ,professor of ,physics in the ,catholic ,institute of ,paris1 which were of the greatest interest and importance4 ,prof4 ,branly had found that a coat or varnish of fine copper dust1 porphyrised copper or other such substance1 though it could only conduct a current very feebly1 and much as a blacklead pencil trace conducts1 under ordinary conditions1 yet fell in resistance enormously whenever an electric spark occurred in its neighbourhood2 somewhat in the fashion that the resistance of selenium falls on exposure to light4 ,it is not clear that ,m4 ,branly recognised that he was dealing with ,hertz waves or true electrical radiation1 but his observations were most satisfactory and conclusive1 and he measured the reduction of resistance caused in a number of different substances1 including an assemblage of metallic filings1 and conglomerates or paste of filings in various viscous liquids and in dry powders4 ,moreover1 he found that the spark was still operative in reducing resistance even when it was several yards distant4 ,the account of ,prof4 ,branly's experiments is to be found in a couple of short communications to the ,french ,academy of ,science 7,comptes ,rendus1 ,vols4 #aaa and #aab71 and the writer had intended to reproduce in abstract the gist of these memoirs2 but to readers of ,the ,electrician this is unnecessary1 as a descriptive article from ,la ,lumire ,electrique has already been translated in full1 in ,july and ,august1 #ahia 7see ,the ,electrician1 ,vol4 ,,xxvii41 pp4 #bba and #ddh1 now reproduced as ,appendix74 ,unfortunately the writer1 in common perhaps with others1 must confess to having overlooked these articles at the time1 probably by reason of their coincidence with the holiday season4 ,in his second edition of 8,modern ,views of ,electricity10 published in #ahib1 though he refers on page #cei to the cohesion principle in this connection1 the writer is clearly ignorant of ,branly's experiments4 ,the matter seems to have been ignored in this country till #ahib1 when ,dr4 ,dawson ,turner described the experiments to the ,british ,association in ,edinburgh1 and even till #ahic1 when ,mr4 ,croft brought them to the notice of the ,london ,physical ,society4 ,prof4 ,minchin at once realised that here was a phenomenon analogous to what he had been observing with his impulsion cells1 and after a few trials wrote a ,paper to the ,physical ,society recounting his repetitions and modifications of ,branly's experiments4#ca ,this ,paper1 before it was read1 was circulated by the ,society to its country members1 and so came to the eye of the writer1 who at once wrote a short note summarising some of his work in the same direction1 and pointing out that this discovery of ,branly's1 thus made known to him1 was another case of the electrical cohesion phenomenon already observed by several experimenters4 ,this is published along with ,prof4 ,minchin's ,paper in the ,phil4 ,mag4 for ,january1 #ahid1 and to it the friendly reader is referred4 ,the writer at once proceeded to try the ,branly tube of filings1 and found it far superior in manageability to either the ,boltzmann gap or his own delicately adjusted cohering knobs2 though immediately afterwards he and ,fitz,gerald together arranged a single-point coherer1 of iron and aluminium 7point of sewing needle resting on aluminium foil71 of what was at that time extraordinary sensitiveness and of reasonable manageability4 ,a whole series of quasi-optical experiments were then undertaken with the new detector1 and were shown to students and to the ,liverpool ,physical ,society2 moreover1 before long1 various improved methods of arranging the filings were gradually adopted1 especially by sealing them up in vacuum or in an atmosphere of hydrogen 7see page #cd7 so as to protect them from continued oxidation by the air1 and to prevent the film which hypothetically separates the surfaces from growing too thick4 ,indeed1 brass filings in hydrogen speedily got too clean1 and became so sensitive that it was almost impossible to restore the original high resistance by tapping4 ,consequently1 a perfect or ,sprengel vacuum was preferred to hydrogen4 ,almost any filings tube could detect signals from a distance of #fj yards1 with a mere six-inch sphere as emitter and without the slightest trouble1 but the single-point coherer was usually much more sensitive than any filings tube4 ,mr4 ,shelford ,bidwell has also worked with varieties of powder4 #ca ,phil4 ,mag41 ,january1 #ahid4 ,the tapping back was at first performed by hand1 and for optical experiments this is still1 perhaps1 the most convenient plan2 but automatic tappers were very soon arranged1 just as with the old knobs2 an electric bell mounted on the base of a filings tube 7see page #ca7 was not found very satisfactory1 however1 because of the disturbances caused by the little sparks at its contact-breaker1 to which the previous coarser knob-arrangements had failed to respond2 so a clockwork tapper1 consisting of a rotating spoke wheel driven by the clockwork of a ,morse instrument1 and giving to the filings tube or to a coherer a series of jerks occurring at regular intervals1 to imitate what the writer supposed must occur in the eye1 viz41 a restoration to sensitiveness after an interval corresponding to the persistence of impression1 was also employed4 ,many of these things were shown at a ,friday evening lecture at the ,royal ,institution on ,june #a1 #ahid1 while others were shown the same autumn at the ,b4,a4 meeting at ,oxford4 ,in both cases signalling was easily carried on from a distance through walls and other obstacles1 an emitter being outside and a galvanometer detector inside the room4 ,distance without obstacle was no difficulty in these experiments1 only free distance is not very easy to get in a town1 and stupidly enough no attempt was made to apply any but the feeblest power so as to test how far the disturbance could really be detected4 ,mr4 ,rutherford1 however1 with a magnetic detector of his own invention1 constructed on a totally different principle1 and probably much less sensitive than a coherer1 did make the attempt and succeeded in signalling across half-a-mile1 full of intervening streets and houses at ,cambridge4#cb #cb ,phil4 ,trans41 #ahig1 ,a41 communicated to the ,royal ,soc41 ,june1 #ahif4 ,numbers of people have worked at the detection of ,hertz waves with filing tube receivers1 and every one of them must have known that the transmission of telegraphic messages in this way over moderate distances was but a matter of demand and supply2 ,sir ,w4 ,crookes1 indeed1 had already clearly stated this telegraphic application of ,hertz waves in the ,fortnightly ,review for ,february1 #ahib1 and refers to certain experiments already conducted in that direction1#cc the details of which are unknown to the writer 7but see ,appendix ,i474 ,there remained no doubt a number of points of detail1 and considerable improvements in construction1 if the method was ever to become practically useful2 but these details could safely be left to those who had charge of the ,government monopoly of telegraphs1 especially as their eminent ,head was known to be interested in this kind of subject4 #cc ,quoted in ,the ,electrician 8,notes10 ,october #a1 #ahig4 ,meanwhile the optical developments of the matter excited most interest among physicists1 both here and on the continent2 the writer performed some experiments of the kind1 ,prof4 ,righi at ,bologna performed many more1 and ,prof4 ,chunder ,bose1 of ,calcutta1 repeated several of them with additions and improvements1 using as detector a sort of half-way house between a point coherer and a filings tube by squeezing a few rolls or spirals of wire between a point and a micrometer screw4 ,restoration to sensitiveness was in this case achieved by relaxing the pressure of the screw1 and the writer has not found ,bose's form of coherer specially convenient2 but ,prof4 ,bose's whole apparatus1 constructed as it was precisely on lines published by the writer1 was well designed in detail and exceedingly compact1 being on the scale of an ordinary goniometer2 and with it many experiments familiar in ordinary optics could readily be shown with electric radiation4 ,in all the optical experiments made by any of these observers it was customary to place the axis of the emitter either horizontally1 or vertically1 or inclined1 in other words to emit radiation polarised in any azimuth 7or rather altitude71 and to arrange the collecting part of the receiver to correspond or otherwise1 according as response or no response was desired4 ,in fact1 observations on polarisation were the easiest and the most instructive that could be made with the definite kind of radiation now for the first time at command4 ,the rotation of the plane of polarisation1 the conversion of plane into elliptical polarisation1 the amount of radiation reflected by substances at different angles and different aspects with regard to the direction of vibration1 were readily observed4 ,furthermore1 ever since ,hertz's first discovery1 whenever waves had to travel through a metal grid or alongside a plane conductor1 it was natural to arrange the electric oscillations so as to be normal to the conducting lines or plane1 for if they were tangential they excited electric currents therein1 and their energy became wasted in the production of heat4 ,so1 in so far as earth and water are conductors1 it is desirable to use radiation polarised in a horizontal plane1 i4e41 with the electric oscillations vertical1 if considerable distances are to be traversed by it4 ,with respect to an explanation why metallic cohesion is caused under electrical influence1 the following considerations are offered3-- ,mr4 ,rollo ,appleyard made a liquid coherer of two globules or pools of mercury1 side by side and touching1 but kept apart by a thin film of grease1 such as is easily given by a coat of paraffin oil4 ,connecting up a battery cell to these mercury pools through a key1 he found that every time the key is depressed the pools move together and become one2 he points out moreover that mercury globules shoot out a tentacle towards the positive terminal 7on the principle of the capillary electrometer1 of course71 and this must be taken into account in any coherer theory4#cd ,lord ,rayleigh also devised and exhibited a liquid form of coherer4 ,it is interesting to observe1 as he points out1 that in a mercury form of coherer an appreciable time interval occurs between the depression of the key and the amalgamation of the mercury1 the lag looking as if a film had to be mechanically squeezed out between the oppositely-charged mercury surfaces1 and as if this took a perceptible fraction of a second to accomplish4 ,this experiment conveys the useful suggestion that cohesion may in all cases be the result of electrostatic attraction1 and that the molecular films separating solids in contact may thus also have to be squeezed out1 though as they only touch at single points such extrusion is almost instantaneously achieved4 ,this may very likely be the chief cause1 for although a true electro-chemical extension of the range of cohesion between polarised molecules had seemed to the writer to be a possible explanation also1 he now perceives that the electrostatic force alone may be sufficient4 ,for it is easy to calculate the force of attraction between two surfaces differing in potential by a volt1 and separated from one another by the smallest known thickness of thin film 7which is #aj centimetre1 or #a millimicron1 called by microscopists72 such force per unit area would be given by the square of the potential gradient divided by #h1 that is1 it would amount to #b #a #aj -------- dynes per square centimetre1 #be #cjj which equals #dd atmospheres1 and is a very considerable pressure4 ,a hundred times this attractive pressure would exist if the surfaces were within really molecular distance of each other2 in addition to the force of true cohesion which would then1 still more powerfully1 operate2 but the film thickness assumed above is such as would just prevent the force of cohesion from effectively acting across the gap1 and would leave the electrical attraction due to the one volt alone4 ,three and a half volts could therefore squeeze metals together with a force equal to a ton load per square inch1 and might thus be sufficient to cause them to weld or unite1 especially if the electric stimulus simultaneously acted in any way as a flux1 by reducing the infinitesimal tarnish of oxide or other compound which must be supposed normally to cover them4 #cd ,phil4 ,mag41 ,may and ,july1 #ahig4 ,he also shows electrical cohesion by an emulsion of oil and water1 the two liquids1 thoroughly shaken up1 at once separating when exposed to strong electrical influence4 ,in so far as the approximate contact is not between surfaces1 but between points consisting of relatively few molecules1 the attractive pressure is greater rather than less4 ,thus to take an extreme case1 the attraction between two oppositely-charged molecules differing only by a volt from each other1 and separated by a thin film like the black spot of a soap-film whose thickness was so admirably measured by ,profs4 ,reinold and ,rcker1 is over #a1jjj atmospheres in intensity4 ,these differences of potential across thin films cannot continue for any time1 unless a battery is used1 for the films do not really insulate2 they are able however to act as dielectrics for an instant1 and to be burst with what we must be allowed to call a spark1 though an infinitesimally small one1 if the momentary strain caused by the impulsive rush of electricity is too great4 ,,appendix ,i4 ,,prof4 ,,hughes',s ,,observations4 ,an account of the history of the coherer principle would not be complete without a reference to an interesting reminiscence of early observations recently put on record by the discoverer of the microphone4 ,at each stage of his observations of electrical cohesion between metals the author was confronted by a reference to some earlier observations of ,prof4 ,hughes1 and he felt sure that during the work on the microphone many or all of the phenomena he was then observing must have been previously encountered by ,prof4 ,hughes4 ,no full account was at that time available1 however1 but now it is clear that the observations were made 7like some of ,edison's on what he called etheric force1 and like the very remarkable still earlier ones of ,joseph ,henry7 before the time of ,hertz1 when the existence of electric waves able to excite sparks or perform other energetic acts was unlooked for and not clearly understood4 ,nevertheless1 at this early period it is clear that ,prof4 ,hughes observed1 though he did not follow up the observation1 not only the occurrence of electric waves or impulses in space1 but also the coherer method of detecting them2 in fact1 that he unwittingly made the earliest experiments on wireless telegraphy by this plan4 ,the simplest way is to quote ,prof4 ,hughes's letter to ,mr4 ,j4 ,j4 ,fahie from ,the ,electrician1 ,may #e1 #ahii1 p4 #dj1 beginning with ,mr4 ,fahie's letter as an introduction3-- ,extract from recent letter from ,mr4 ,j4 ,j4 ,fahie to ,prof4 ,hughes4 8,,dear ,,prof4 ,,hughes3 ,i have now in the press a history of ,wireless ,telegraphy from #ahch to #ahii1 and in writing to ,sir ,william ,crookes for information he tells me that many years ago he saw some experiments of yours with the microphone1 in which you signalled from one part of a house to another without connecting wires1 and he desires me to refer to you for particulars4 ,i think1 with ,sir ,william1 that it is a pity you have not hitherto published your results1 and ,i sincerely hope you will now do so4 ,if also you would kindly favour me with a short account1 ,i could find room for it in my book1 which is now in the printer's hands4--,sincerely yours1 ,j4 ,j4 ,,fahie4 ,claremont ,hill1 ,st4 ,helier's1 ,jersey1 ,april #bf1 #ahii40 ,reply from ,prof4 ,d4 ,e4 ,hughes3-- #dj1 ,langham-street1 ,w41 ,april #bi1 #ahii4 ,,dear ,,sir3 ,in reply to yours of the #bfth inst41 in which you say that ,sir ,william ,crookes has told you 8that he saw some experiments of mine on arial telegraphy1 in about ,december1 #ahgi1 of which he thinks ,i ought to have published an account10 and of which you ask for some information1 ,i beg to reply with a few leading experiments that ,i made on this subject from #ahgi up to #ahhf3-- 8,in #ahgi1 being engaged upon experiments with my microphone1 together with my induction balance1 ,i remarked that at some time ,i could not get a perfect balance in the induction balance1 through apparent want of insulation in the coils1 but investigation showed me that the real cause was some loose contact or microphonic joint excited in some portion of the circuit4 ,i then applied the microphone in the circuit1 and found that it gave a current or sound in the telephone receiver1 no matter if the microphone was placed direct in the circuit1 or placed independently at several feet distance from the coils1 through which an intermittent current was passing4 ,after numerous experiments1 ,i found that the effect was entirely caused by the extra current produced in the primary coil of the induction balance4 8,further researches proved that an interrupted current1 in any coil1 through which an electric current was sent1 gave out at each interruption of the primary current1 such intense extra currents1 that the whole atmosphere in the room 7or in several rooms distant7 would have a momentary invisible charge1 which became evident if a microphonic joint was used as a receiver to a telephone4 ,this led me to experiment upon the best form of a receiver for these invisible electric waves1 which evidently permeated great distances1 and through all apparent obstacles1 such as walls1 c4 ,i found that all microphonic contacts or joints were extremely sensitive4 ,those formed of a hard carbon such as coke1 or a combination of a piece of coke resting upon a bright steel contact1 were very sensitive and self-restoring2 whilst a loose contact between metals was equally sensitive1 but would cohere1 or remain in full contact1 after the passage of an electric wave4 8,the sensitiveness of these microphonic contacts in metals has since been rediscovered by ,mons4 ,ed4 ,branly1 of ,paris1 and by ,prof4 ,oliver ,lodge1 in ,england1 by whom the name of #8coherer' has been given to this organ of reception2 but1 as we wish this organ to make a momentary contact and not cohere permanently1 the name seems to me ill-suited for the instrument4 ,the most sensitive and perfect receiver that ,i have yet made does not cohere permanently1 but recovers its original state instantly1 and1 therefore1 requires no tapping or mechanical aid to the separation of the contacts after momentarily being brought into close union4 8,i soon found that1 whilst an invisible spark would produce a thermo-electric current in the microphonic contacts 7sufficient to be heard in the telephone in its circuit71 it was far better and more powerful to use a feeble voltaic cell in the receiving circuit1 the microphonic joint then acting as a relay1 by increasing and diminishing the resistance at the contact1 by the influence of the electric wave received through the atmosphere4 8,i will not describe the numerous forms of the transmitter1 and receiver1 that ,i made in #ahgi1 all of which ,i wrote down in several volumes of manuscripts in #ahgi 7but these have never been published71 most of which can be seen here at my residence at any time2 but ,i will confine myself now to a few salient points4 ,i found that very sudden electric impulses1 whether given out to the atmosphere through the extra current from a coil1 or from a frictional electric machine1 equally affected the microphonic joint1 the effect depending more on the sudden high potential effect than any prolonged action4 ,thus1 a spark obtained by rubbing a piece of sealing-wax was equally as effective as a discharge from a ,leyden jar battery of the same potential4 ,the rubbed sealing-wax1 or charged ,leyden jar1 had no effect1 until they were discharged by a spark1--and it was evident that this spark1 however feeble1 acted upon the whole surrounding atmosphere in the form of waves1 or invisible rays1 of which ,i could not at the time determine4 ,hertz1 however1 by a series of original and masterly experiments1 proved in #ahhg-i1 that they were real waves similar to light1 but of a lower frequency1 though of the same velocity4 ,in #ahgi1 whilst making these experiments on arial transmission1 ,i had two different problems to solve3 #ast1 ,what was the true nature of these electric arial waves1 which seemed1 whilst not visible1 to spurn all idea of insulation1 and to permeate all space to a distance undetermined4 #bnd1 ,to discover the best receiver that could act upon a telephone or telegraph instrument1 so as to be able to utilise 7when required7 these waves for the transmission of messages4 ,the second problem came easy to me1 when ,i found that the microphone1 which ,i had previously discovered in #ahgg-h1 had alone the power of rendering these invisible waves evident1 either in a telephone or galvanometer1 and up to the present time ,i do not know of anything approaching the sensitiveness of a microphonic joint as a receiver4 ,branly's tube1 now used by ,marconi1 was described in my first ,paper to the ,royal ,society 7,may #h1 #ahgh71 as the microphone tube1 filled with loose filings of zinc and silver1 and ,prof4 ,lodge's coherer is an ordinary steel microphone1 used for a different purpose from that in which ,i first described it4 8,during the long-continued experiments on this subject1 between #ahgi and #ahhf1 many curious phenomena came out which would be too long to describe4 ,i found that the effect of the extra current in a coil was not increased by having an iron core as an electromagnet--the extra current was less rapid and1 therefore1 less effective4 ,a similar effect of a delay was produced by ,leyden jar discharges4 ,the material of the contact-breaker of the primary current had also a great effect4 ,thus1 if the current was broken between two1 or one1 piece of carbon1 no effect could be perceived of arial waves1 even at short distances of a few feet4 ,the extra current from a small coil1 without iron1 was as powerful as an intense spark from a secondary coil1 and at that time my experiments seemed to be confined to the use of a single coil of my induction balance1 charged by six ,daniell cells4 ,with higher battery power1 the extra current invariably destroyed the insulation of the coils4 8,in ,december1 #ahgi1 ,i invited several persons to see the results then obtained4 ,amongst others who called on me and saw my results were3-- 8,december1 #ahgi4--,mr4 ,w4 ,h4 ,preece1 ,f4,r4,s42 ,sir ,william ,crookes1 ,f4,r4,s42 ,sir ,w4 ,robert ,austen1 ,f4,r4,s42 ,prof4 ,w4 ,gryll ,adams1 ,f4,r4,s42 ,mr4 ,w4 ,groves4 8,february #bj1 #ahhj4--,mr4 ,spottiswoode1 ,pres4,r4,s42 ,prof4 ,huxley1 ,f4,r4,s42 ,sir ,george ,gabriel ,stokes1 ,f4,r4,s4 8,november #g1 #ahhh4--,prof4 ,dewar1 ,f4,r4,s42 ,mr4 ,lennox1 ,royal ,institution4 8,they all saw experiments upon arial transmission1 as already described1 by means of the extra current produced from a small coil and received upon a semi-metallic microphone1 the results being heard upon a telephone in connection with the receiving microphone4 ,the transmitter and receiver were in different rooms1 about #fj ft4 apart4 ,after trying successfully all distances allowed in my residence in ,portland-street1 my usual method was to put the transmitter in operation and walk up and down ,great ,portland-street with the receiver in my hand1 with the telephone to the ear4 8,the sounds seemed to slightly increase for a distance of #fj yards1 then gradually diminish1 until at #ejj yards ,i could no longer with certainty hear the transmitted signals4 ,what struck me as remarkable was that1 opposite certain houses1 ,i could hear better1 whilst at others the signals could hardly be perceived4 ,hertz's discovery of nodal points in reflected waves 7in #ahhg-i7 has explained to me what was then considered a mystery4 8,at ,mr4 ,a4 ,stroh's telegraph instrument manufactory1 ,mr4 ,stroh and myself could hear perfectly the currents transmitted from the third story to the basement1 but ,i could not detect clear signals at my residence about a mile distant4 ,the innumerable gas and water pipes intervening seemed to absorb or weaken too much the feeble transmitted extra currents from a small coil4 8,the ,president of the ,royal ,society1 ,mr4 ,spottiswoode1 together with the two hon4 secretaries1 ,prof4 ,huxley and ,prof4 ,g4 ,stokes1 called upon me on ,february #bj1 #ahhj1 to see my experiments upon arial transmission of signals4 ,the experiments shown were most successful1 and at first they seemed astonished at the results1 but towards the close of three hours' experiments ,prof4 ,stokes said1 #8that all the results could be explained by known electromagnetic induction effects1 and therefore he could not accept my view of actual arial electric waves unknown up to that time1 but thought ,i had quite enough original matter to form a ,paper on the subject to be read at the ,royal ,society4' 8,i was so discouraged at being unable to convince them of the truth of these arial electric waves1 that ,i actually refused to write a ,paper on the subject1 until ,i was better prepared to demonstrate the existence of these waves2 and ,i continued my experiments for some years1 in hopes of arriving at a perfect scientific demonstration of the existence of arial electric waves1 produced by a spark from the extra currents in coils1 or from frictional electricity or secondary coils4 ,the triumphant demonstration of these waves was reserved to ,prof4 ,hertz1 who by his masterly researches upon the subject in #ahhg-i completely demonstrating not only their existence but their identity with ordinary light1 in having the power of being reflected and refracted1 c41 with nodal points1 by means of which the length of the waves could be measured1 ,hertz's experiments were far more conclusive than mine1 although he used a much less effective receiver than the microphone or coherer4 8,i then felt it was now too late to bring forward my previous experiments1 and through not publishing my results1 and means employed1 ,i have been forced to see others remake the discoveries ,i had previously made as to the sensitiveness of the microphonic contact1 and its useful employment as a receiver for electric arial waves4 ,amongst the earliest workers in the field of arial transmission ,i would draw attention to the experiments of ,prof4 ,henry1 who describes in his work1 published by the ,smithsonian ,institute1 ,washington1 ,d4,c41 ,u4,s4,a41 ,vol4 ,i41 p4 #bjc 7date unknown1 probably about #ahej71 that he magnetised a needle in a coil at #cj ft4 distance1 and magnetised a needle by a discharge of lightning at eight miles distance4 8,marconi has lately demonstrated that by the use of the ,hertzian waves and ,branly's coherer he has been enabled to transmit and receive arial electric waves to a greater distance than previously ever dreamed of by the numerous discoverers and inventors who have worked silently in this field4 ,his efforts at demonstration merit the success he has received2 and if 7as ,i have lately read7 he has discovered the means of concentrating these waves on a single point desired without diminishing its power1 then the world will be right in placing his name on the highest pinnacle in relation to arial electric telegraphy4--,yours1 c41 ,d4 ,e4 ,,hughes40 ,,appendix ,,ii4 ,,variations ,,of ,,conductivity ,,under ,,electrical ,,influence4 ,the following is abstracted from an article by ,m4 ,e4 ,branly in ,la ,lumire ,electrique of ,may #af1 #ahia1 and is taken from ,the ,electrician of ,june #bf1 #ahia3-- ,the object of this article is to describe the first results obtained in an investigation of the variation of resistance of a large number of conductors under various electrical influences4 ,the substances which up to the present have presented the greatest variations in conductivity are the powders or filings of metals4 ,the enormous resistance offered by metal in a state of powder is well known2 indeed1 if we take a somewhat long column of very fine metallic powder the passage of the current is completely stopped4 ,the increase in the electrical conductivity by pressure of powdered conducting substances is well known1 and has had various practical applications4 ,the variations of conductivity1 however1 which occur on subjecting conducting bodies to various electrical influences have not been previously investigated4 ,the ,effect of ,electric ,sparks4--,let us take a circuit comprising a single cell1 a galvanometer1 and some powdered metal enclosed in an ebonite tube of #a square centimetre cross-section and a few centimetres long4 ,close the extremities of the tube with two cylindrical copper tubes pressing against the powdered metal and connected to the rest of the circuit4 ,if the powder is sufficiently fine1 even a very sensitive galvanometer does not show any evidence of a current passing4 ,the resistance is of the order of millions of ohms1 although the same metal melted or under pressure would only offer 7the dimensions being the same7 a resistance equal to a fraction of an ohm4 ,there being1 therefore1 no current in the circuit1 a ,leyden jar is discharged at some little distance off1 and the abrupt and permanent deflection of the galvanometer needle shows that an immediate and a permanent reduction of the resistance has been caused4 ,the resistance of the metal is no longer to be measured in millions of ohms1 but in hundreds4 ,its conductivity increases with the number and intensity of the sparks4 ,some #bj or #cj centimetres from a circuit comprising some metallic filings contained in an ebonite cup1 let us place a hollow brass sphere1 #ae to #bj centimetres in diameter1 insulated by a vertical glass support4 ,the filings offer an enormous resistance and the galvanometer needle remains at zero4 ,but if we bring an electrified stick of resin near the sphere1 a little spark will pass between the stick and the sphere1 and immediately the needle of the galvanometer is violently jerked and then remains permanently deflected4 ,on some fresh filings being placed in the ebonite cup1 the resistance of the circuit will again keep the needle at zero4 ,if now the charged brass sphere is touched with the finger1 there is a minute discharge and the galvanometer needle is again deflected4 ,with a few accumulators the experiment can easily be made without a galvanometer4 ,the circuit consists of the battery1 some metallic powder1 a platinum wire1 and a mercury cup4 ,the resistance of the powder is so high that the interruption of the circuit takes place without any sparking at the mercury cup4 ,if now a ,leyden jar is discharged in the neighbourhood of the circuit the powder is rendered conducting1 the platinum wire immediately becomes red hot1 and a violent spark occurs on breaking the circuit4 ,the influence of the spark decreases as the distance increases1 but its influence is observable several metres away from the powder1 even with a small ,wimshurst machine4 ,repeating the spark increases the conductivity2 in fact1 with certain substances successive sparks produce successive jerks1 and a gradually increasing and persistent deflection of the galvanometer4 ,influence of a ,conductor traversed by ,condenser ,discharges4--,while using a ,wimshurst machine it was noticed that the reduction in the resistance of the filings frequently took place before discharge4 ,this led me to the following experiment3 ,take a long brass tube1 one end of which is close to the circuit containing the metallic powder2 its other end1 several metres distant from the circuit1 is fairly close to a charged ,leyden jar4 ,a spark takes place and the conductor is charged4 ,at the same instant1 the conductivity of the metallic powder is greatly increased4 ,the following arrangement1 owing to its efficacy1 convenience1 and regularity of action was used by me in most of my researches1 and ,i shall briefly call it the ,a arrangement 7see ,fig4 #ec74 ,illustration3 ,,fig4 #ec4 ,illustration3 ,,fig4 #ed4 ,the source of electricity is a two-plate ,holtz machine driven at from #ajj to #djj revolutions4 ,a sensitive substance is introduced into one of the arms of a ,wheatstone bridge1 or into the circuit of a single ,daniell cell at a distance of some #aj metres 7#cd;ft47 from the ,holtz machine4 ,between the discharge knobs of the machine and the ,wheatstone bridge1 and connected to the former1 there are two insulated brass tubes1 ,a ,a1 running parallel to one another #dj centimetres apart4 ,the ,leyden jars usually attached to a ,holtz machine may be dispensed with1 the capacity of the long brass tubes being in some measure equivalent to them4 ,the knobs ,s were #a mm41 #e mm41 or #a mm4 apart4 ,when the plates were rotated sparks rapidly succeeded each other4 ,experiments showed that these sparks had no direct effect at a distance of #aj metres4 ,the two tubes ,a ,a are not absolutely necessary1 the diminution of resistance is easily produced if only one is employed1 and in some cases1 indeed1 a single conductor is more efficacious4 ,an increase in the speed of the machine increases its action to a marked extent4 ,the sparks at ,s may be suppressed by drawing the knobs apart1 but the conductor ,a will still continue to exert its influence1 especially if there is a spark gap anywhere about4 ,effects of ,induced ,currents4--,the passage of induced currents through a sensitive substance produces similar effects to those described above4 ,in one instance an induction coil was taken1 having two similar wires4 ,the circuit of the secondary wire was closed through a tube containing filings1 the galvanometer being also in circuit4 ,care was taken to ascertain before introducing the filings into the circuit that the currents on make-and-break gave equal and opposite deflections4 ,filings were then introduced into the circuit1 the primary being made and broken at regular intervals4 ,the following table gives the results obtained in the case of zinc filings3-- ,,zinc ,,filings4 ,galvanometer throws4 ,galvanometer throws4 #ast closing #a #ast opening #ah #bnd 0 #fd #bnd 0 #ajj #crd 0 #adf #crd 0 #adj ,effects of ,passing ,continuous ,currents of ,high ,e4,m4,f4--,if a continuous current of high ,e4,m4,f4 is employed1 it renders a sensitive substance conducting4 ,the phenomenon may be shown in the following manner4 ,a circuit is made up consisting of a battery1 a sensitive substance1 and a galvanometer4 ,the ,e4,m4,f4 of the battery is first one volt1 then #ajj volts1 then one volt4 ,below ,i give the galvanometer deflections obtained with an ,e4,m4,f4 of one volt for three different substances before and after the application of the ,e4,m4,f4 of #ajj volts3-- ,before application of current4 ,after application of current4 #af #ajj #j #ae #a #ejj ,in the case of some measurements taken on a ,wheatstone bridge a prism of aluminium filings interposed between two copper electrodes offered a resistance of several million ohms before a high ,e4,m4,f4 was applied1 but only offered a resistance of #cej ohms after the application of this pressure for one minute4 ,the time during which the powder should be interposed in the battery circuit should not be too short4 ,thus1 in one instance1 the application for #aj sec4 of #ge mercury sulphate cells produced no effect1 but their application for #fj sec4 resulted in the resistance being reduced from several megohms to #b1ejj ohms4 ,it should be observed that the phenomenon of suddenly increased conductivity occurs1 even if the sensitive substance is not in circuit with a battery at the time it is influenced4 ,thus1 the metallic filings1 after having been placed in circuit with a ,daniell cell1 and its high resistance observed1 may then be completely insulated and submitted in this condition to the action of a distant spark1 or of a charged rod1 or of induced currents4 ,if1 after this1 the filings are replaced in their original circuit1 the enormous increase in their conductivity is immediately apparent4 ,the conductivity produced by these various methods takes place throughout the whole mass of the metallic filings1 and in every direction1 as the following experiment will show4 ,a vertical ebonite cup containing aluminium powder 7see ,fig4 #ed7 is placed between two metal plates1 ,a1 ,b2 laterally the powder is in contact with two short rods1 ,c1 ,d1 which pass through the sides of the ebonite cylinder4 ,a and ,b can be connected to two terminals of one of the arms of the ,wheatstone bridge1 ,c and ,d being free1 and vice vers4 ,whatever arrangement is adopted1 if a battery of #ajj cells is joined up for a few seconds with one or the other of the pairs of terminals1 the increase in the conductivity is immediately visible in that direction1 and is found to exist also in the direction at right angles4 ,substances in which ,diminution of ,resistance has been ,observed4--,the substances in which the phenomenon of the sudden increase of conductivity is most easily observed are filings of iron1 aluminium1 copper1 brass1 antimony1 tellurium1 cadmium1 zinc1 bismuth1 c4 ,the size of the grains and their nature are not the only elements to be considered1 for grains of lead of the same size1 but coming from different quarters1 offer at the same temperature great differences in resistance 7#bj1jjj to #ejj1jjj ohms74 ,extremely fine metallic powder1 as a rule1 offers almost perfect resistance to the passage of a current4 ,but if we take a sufficiently short column and exert a sufficiently great pressure a point is soon reached when the electrical influence will effect a sudden increase in the conductivity4 ,thus1 a layer of copper reduced by hydrogen1 which does not become conducting under the influence of the electric spark or otherwise1 will become so on being submitted to a pressure of #ejj grammes to the square centimetre 7#g lb4 per square inch74 ,instead of using pressure1 ,i employed as a conductor in some experiments a very fine coating of powdered copper spread on a sheet of unpolished glass or ebonite ,e 7,fig4 #ee71 seven centimetres long and two centimetres broad4 ,a layer of this kind1 polished with a burnisher1 has a very variable resistance4 ,with a little care one can prepare sheets which are more or less sensitive to electrical action4 ,illustration3 ,,fig4 #ee4 ,metal powder or metal filings are not the only sensitive substances1 as powdered galena1 which is slightly conducting under pressure1 conducts much better after having been submitted to electrical influence4 ,powdered binoxide of maganese is not very sensitive unless mixed with powdered antimony and compressed4 ,making use of the ,a arrangement1 with very short sparks at ,s 7,fig4 #ce71 the phenomenon of increased conductivity can be observed with platinised and silvered glass1 also with glass covered with gold1 silver and aluminium foil4 ,some of the mixtures employed had the consistency of paste4 ,these were mixtures of colza oil and iron1 or antimony filings1 and of ether or petroleum and aluminium1 and plumbago1 c4 ,other mixtures were solid4 ,if we make a mixture of iron filings and ,canada balsam1 melted in a water bath1 and pour the paste into a little ebonite cup1 the ends of which are closed by metallic rods1 a substance is obtained which solidifies on cooling4 ,the resistance of such a mixture is lowered from several megohms to a few hundred ohms by an electric spark4 ,similar results are obtained with a solid rod composed of fused flowers of sulphur and iron or aluminium filings1 also by a mixture of melted resin and aluminium filings4 ,in the preparation of these solid sensitive mixtures care must be taken that the insulating substance should only form a small percentage of the whole4 ,some interesting results are also obtained with mixtures of sulphur and aluminium1 and with resin and aluminium1 when in a state of powder4 ,when cold1 these mixtures as a rule do not conduct either directly or after they have been exposed to electrical influences1 but they become conducting on combining pressure with electrical influences4 ,thus1 a mixture of flowers of sulphur and aluminium filings in equal volumes was placed in a glass tube #bd mm4 in diameter4 ,the weight of the mixture was #bj grammes1 and the height of the column #bb mm42 with a pressure of #ahf grammes per square centimetre 7#b lb4 per square inch74 ,the mixture is not conducting1 but after exposure to electrical influence1 obtained by the ,a arrangement1 the resistance falls to #ij ohms4 ,in a similar manner a mixture of selenium and aluminium1 placed in a tube #ii mm4 long1 was not conducting until after it was exposed to the combined influence of pressure and electricity4 ,the following is one of the group of numerous experiments of a slightly different character4 ,a mixture of flowers of sulphur and fine aluminium filings1 containing two of sulphur to one of aluminium1 is placed in a cylindrical glass tube #ce mm4 long4 ,by means of a piston1 a pressure of #bj kilogrammes per square centimetre 7#bhd lb4 per square inch7 was applied4 ,it was only necessary to connect the column for #aj sec4 to the poles of a #be cell battery1 for the resistance originally infinite to be reduced to #d1jjj ohms4 ,the arrangement shown in ,fig4 #ef illustrates another order of experiment4 ,two rods of copper were oxidised in the flame of a ,bunsen burner1 and were then arranged to lie across each other1 as shown1 and were connected to the terminals of the arm of a ,wheatstone bridge1 the high resistance of the circuit being due to the layers of oxide4 ,amongst the many measurements made1 ,i found1 in one case1 a resistance of #hj1jjj ohms1 which1 after exposure to the influence of the electric spark1 was reduced to #g ohms4 ,analogous effects are obtained with oxidised steel rods4 ,another pretty experiment is to place a cylinder of copper1 with an oxidised hemispherical head1 on a sheet of oxidised copper4 ,before exposure to the influence of the electric spark1 the oxide offers considerable resistance4 ,the experiment can be repeated several times by merely moving the cylinder from one place to another on the oxidised sheet of copper1 thus showing that the phenomenon only takes place at the point of contact of the two layers of oxide4 ,illustration3 ,,fig4 #ef4 ,in conclusion1 it may be worth noting that1 for most of the substances enumerated1 an elevation of temperature diminishes the resistance1 but the effect of a rise of temperature is transient1 and is incomparably less than the effect due to currents of high potential4 ,for a few substances the two effects are opposed4 99 99 99 99 99 ,a second article by ,mr4 ,branly in ,la ,lumire ,electrique was abstracted in ,the ,electrician for ,august #ba1 #ahia1 as follows3-- ,in a preceding article ,i showed that certain substances undergo an increase in conductivity under various electrical influences1 and that these substances are numerous4 ,the increase in conductivity varies with the energy of the exciting source4 ,if the electric influence is due to the passage of a continuous current1 the increase in conductivity is greater the greater the electromotive force of the battery employed4 ,there is1 however1 no proportionality1 the increased conductivity growing more rapidly than the number of cells1 and tending quickly to a maximum4 ,if the electric action consists in the passage of discharge currents in metallic rods1 as in arrangement ,a 7,fig4 #ec1 p4 #ig71 the conductivity increases with the length of spark at ,s1 and it also increases when the rods are brought nearer the sensitive substance4 ,successive sparks are additive in their effects1 although1 if the action of the first one has been very powerful1 the resistance is sometimes almost immediately reduced to a minimum4 ,restoration of ,original ,resistance4--,the conductivity causes by the various electrical influences lasts sometimes for a long period 7#bd hours or more71 but it is always possible to make it rapidly disappear1 particularly by a shock4 ,the majority of substances tested showed an increase of resistance on being shaken previous to being submitted to any special electrical influence1 but after having been influenced the effect of shock is much more marked4 ,the phenomenon is best seen with the metallic filings1 but it can also be observed with metalised ebonite sheets with mixtures of liquid insulators and metallic powders1 mixtures of metallic filings and insulating substances 7compressed or not compressed71 and finally with solid bodies4 ,i observed the return to original resistance in the following manner3--,the sensitive substance was placed at ,k 7,fig4 #ec71 and formed part of a circuit which included a ,daniell cell and galvanometer4 ,at first no current passes4 ,sparks are then caused at ,s1 and the needle of the galvanometer is permanently deflected4 ,on smartly tapping the table supporting the ebonite cap in which the sensitive substance is contained1 the original condition is completely restored4 ,when the electric action has been of a powerful character1 violent blows are necessary4 ,i employed for the purpose of these shocks a hammer fixed on the table1 the blows of which could be regulated4 ,with some substances1 when feebly electrified1 the return seemed to be spontaneous1 although it was slower than the return of the galvanometer needle to equilibrium4 ,this restoration of the original resistance is attributable to surrounding trepidations1 as it was only necessary to walk about the room at a distance of a few metres1 or to shake a distant wall4 ,this spontaneous return to original resistance after weak electrical action was visible with a mixture of equal parts of fine selenium and tellurium powders4 ,the restoration of resistance by shock was not observable so long as the electrical influence was at work4 ,after having been submitted to powerful electric action1 shock does not seem to entirely restore substances to their original state1 in fact1 the substances generally show greater sensitiveness to electric action4 ,thus1 a mixture of colza oil and antimony powder being exposed to the influence of arrangement ,a1 a spark of #e mm4 was at first necessary to break down the resistance1 but after the conductivity had been made to disappear by means of blows1 a spark of only #a mm4 was sufficient to again render the substance conducting4 ,finely powdered aluminium has an extremely high resistance4 ,a vertical column of powdered aluminium #e mm4 long of #d sq4 cms4 cross-section1 submitted to considerable pressure1 completely stopped the current from a ,daniell cell4 ,the influence of arrangement ,a produced no effect1 but1 by direct contact with a ,leyden jar1 the resistance was reduced to #ej ohms4 ,the effect of shock was then tried1 and after this the sparks produced by arrangement ,a were able to reduce the resistance4 ,the following experiment is also of the same kind4 ,aluminium filings placed in a parallelipidic trough completely stopped the current from a ,daniell cell1 and the resistance offered to a single cell remained infinite after the trough had been placed in the circuit of #be sulphate of mercury cells for #ajsec4 ,the aluminium was next placed in circuit with a battery of #ge cells2 a single ,daniell cell was then able to send a current through the substance4 ,the original resistance was restored by shock1 but not the original condition of things1 since a single cell was able to send a current after the aluminium had been circuited for #aj sec4 with a battery of only #be cells4 ,i may add that if the restoration of resistance was brought about by a violent shock1 it was necessary to place the aluminium in circuit with #ge cells for one minute before the resistance was again broken down4 ,it must be observed that electrical influence is not always necessary to restore conductivity after an apparent return to the original resistance1 repeated feeble blows being sometimes successful in bringing this about4 ,both in the case of slow return by time and sudden return by shock1 the original value of the resistance is often increased4 ,rods of ,carr carbon1 #a metre long and #a mm4 in diameter1 were particularly noticeable for this phenomenon4 ,return to ,original ,resistance by ,temperature ,elevation4--,a plate of coppered ebonite rendered conducting by electricity1 and placed close to a gas jet1 quickly regained its original resistance4 ,a solid rod of resin and aluminium1 or of sulphur and aluminium1 rendered conducting by connection to the poles of a small battery will regain its original resistance by shock2 but if the conducting state has been caused by powerful means1 such1 for instance1 as direct contact with a ,leyden jar1 shock no longer has any effect1 at least such a shock as the fragile nature of the material can stand4 ,a slight rise of temperature1 however1 has the desired result4 ,by suitably regulating the electric action it is possible to get a substance into such a condition that the warmth of the fingers suffices to annul conductivity4 ,influence of ,surroundings4--,electric action gives rise to no alteration of resistance when the substance is entirely within a closed metal box4 ,the sensitive substance1 in circuit with a ,daniell cell and a galvanometer1 is placed inside a brass box 7,fig4 #ed1 p4 #ig74 ,the absence of current is ascertained1 the circuit broken1 and the box closed4 ,a ,wimshurst machine is then worked a little way off1 and will be found to have had no effect4 ,the same result will be obtained if the circuit is kept closed during the time the ,wimshurst machine is in operation4 ,if a wire connected at some point to the circuit is passed out through a hole in the box to a distance of #bj cm4 to #ej cm41 the influence of the ,wimshurst machine makes itself felt4 ,on tapping the lid to restore resistance the galvanometer needle remains deflected so long as the sparks continue to pass4 ,if1 however1 the wires are pushed in so that they only project a few millimetres1 the sparks still passing1 a few taps suffice to bring back the needle to zero4 ,on touching the end of the wire with the fingers or a piece of metal conductivity is immediately restored4 ,the movements of the galvanometer needle were rendered visible in these experiments by looking through a piece of wide mesh wire-gauze with a telescope4 ,the respective position of the things was also reversed2 that is to say1 a ,ruhmkorff coil and a periodically discharged ,leyden jar were placed inside1 and the sensitive substance outside1 the box1 with the same results4 ,in some later experiments with a larger metallic case 7,fig4 #eg71 and with the ,daniel cell1 sensitive substance1 delicate galvanometer1 and ,wheatstone ,bridge placed inside1 ,i found that a double casing was necessary in order to absolutely suppress all effects4 ,a glass covering afforded no protection4 ,illustration3 ,,fig4 #eg4 ,considerations on the ,mechanism of the ,effects ,produced4--,what conclusions are we to draw from the experiments described8 ,the substances employed in these investigations were not conductors1 since the metallic particles composing them were separated from each other in the midst of an insulating medium4 ,it was not surprising that currents of high potential1 and especially currents induced by discharges1 should spark across the insulating intervals4 ,but as the conductivity persisted afterwards1 even for the weakest thermo-electric currents1 there is some ground for supposing that the insulating medium is transformed by the passage of the current1 and that certain actions1 such as shock and rise of temperature1 bring about a modification of this new state of the insulating body4 ,actual movement of the metallic particles cannot be imagined in experiments where the particles1 in a layer a few millimetres thick1 were fixed in an invariable relative position by extreme pressures1 reaching at times to more than #ajj kilogrammes per sq4 cm4 7#a1dbj lb4 to the square inch74 ,moreover1 in the case of solid mixtures1 in which the same variations of resistance were produced1 displacement seems out of the question4 ,to explain the persistence of the conductivity after the cessation of the electrical influence1 are we to suppose in the case of metallic filings a partial volatilisation of the particles creating a conducting medium between the grains of metal8 ,in the case of mixtures of metallic powders1 and insulating substances agglomerated by fusion1 are we to suppose that the thin insulating layers are pierced by the passage of very small sparks1 and that the holes left behind are coated with conducting material8 ,if this explication is admissible for induced currents1 it must hold good for continuous currents4 ,if so1 we must conclude that these mechanical actions may be produced by batteries of only #aj to #bj volts electromotive force1 and which only cause an insignificant current to pass4 ,the following experiment is worth quoting in this connection3-- ,a circuit was formed by a ,daniell cell1 a sensitive galvanometer1 and some aluminium filings in an ebonite cup4 ,the galvanometer needle remained at zero4 ,the filings were cut out of this circuit1 and switched for one minute into circuit with a battery of #dc sulphate of mercury cells4 ,on being replaced in the first circuit1 the filings exhibited high conductivity4 ,the result was the same when #aj or #bj cells were employed1 or when the current was diminished by interposing in the circuit a column of distilled water1 #dj cm4 long and #bj mm4 in diameter4 ,the cells used 7platinum1 sulphate of mercury1 sulphate of zinc1 zinc7 had a high internal resistance4 ,thus1 #dc cells 7#fj volts71 when short-circuited1 only gave a current of #e milliamperes4 ,the same battery1 with the column of distilled water in circuit only1 caused a deflection of #ajj mm4 on a scale one metre off1 with an astatic galvanometer wound with #ej1jjj turns4 ,we can1 therefore1 see how infinitesimally small the initial current must have been when the filings were added to the circuit4 ,the battery acted1 therefore1 essentially by virtue of its electromotive force4 ,if mechanical displacement of particles or transportation of conducting bodies seem inadmissible1 it is probable that there is a modification of the insulator itself1 the modification persisting for some time by virtue of a sort of 8coercive force40 ,an electric current of high potential1 which would be completely stopped by a thick insulating sheet1 may be supposed to gradually traverse the very thin dielectric layers between the conducting particles1 the passage being effected very rapidly if the electric pressure is great1 and more slowly if the pressure is less4 ,increase of ,resistance4--,an increase of resistance was observed in these investigations less often than a diminution2 nevertheless1 a number of frequently repeated experiments enable me to say that increase of resistance is not exceptional1 and that the conditions under which it takes place are well defined4 ,short columns of antimony or aluminium powder when subjected to a pressure of about #a kilogramme per square centimetre 7#adb lb4 per square inch71 and offering but a low resistance1 exhibited an increase of resistance under the influence of a powerful electrification4 ,peroxide of lead1 a fairly good conductor1 always exhibited an increase2 so also did some kinds of platinised glass1 while others showed alternate effects4 ,for instance1 a sheet of platinised glass1 which offered a resistance of #gjj ohms1 became highly conducting after #aej sulphate of mercury cells had been applied to it for #ajsec4 ,this condition of conductivity was annulled by contact with a charged ,leyden jar1 and reappeared after again applying #aej cells for #ajsec41 and so on4 ,similar effects were obtained with a thin layer of a mixture of selenium and tellurium poured1 when fused1 into a groove in a sheet of mica placed between two copper plates4 ,these alternations were always observed several times in succession1 and at intervals of several days4 ,these augmentations and alternations are in no way incompatible with the hypothesis of a physical modification of the insulator by electrical influence4 ,,appendix ,,iii4 ,in connection with the branch of the subject dealt with on page #cd1 the following communications from ,prof4 ,elihu ,thomson and ,dr4 ,william ,j4 ,morton1 ,m4,d41 which appeared respectively in the ,electrical ,engineer1 of ,new ,york1 ,july #d and ,october #bd1 #ahid1 will be read with interest4 ,prof4 ,thomson writes3-- ,,curious ,,effects ,,of ,,hertzian ,,waves4 ,in the issue of the ,london ,electrician of ,june #h1 #ahid1 under the heading1 8,hertzian ,waves at the ,royal ,institution10 the following remark occurs3 8,it is wholly probable1 as ,dr4 ,lodge suggests1 that ,hertzian waves may often have manifested themselves in physical laboratories to the annoyance of the workers1 c40 ,i may mention in this connection that in #ahgg1 if ,i remember the year correctly1 while working a ,ruhmkorff induction coil1 one terminal of which was grounded and the other terminal of which was attached to an insulated metallic body1 ,prof4 ,houston and ,i noticed that when the sparks were passing between the terminals of the coil1 it was possible not only to obtain minute sparks from all metallic bodies in the immediate neighbourhood1 that is1 in the same room1 but that delicate sparks could be taken by holding in the hand a small piece of metal near metallic objects in many other rooms and on different floors in the building1 although the pieces were not connected to ground4 ,these could only have been ,hertzian effects1 but there was no recognition of their true character at the time1 though the effects were seen to be connected with the very quick charging and discharging of the insulated body4 ,an account of these experiments was1 ,i think1 published in the ,journal of the ,franklin ,institute at the time4 ,i desire also to mention1 as coming under my notice within the past year1 a curious and rather amusing illustration of the principle upon which the beautiful instrument for detecting the presence of electric oscillations1 devised by ,dr4 ,lodge and called by him the 8coherer10 is based4 ,it was reported to me when in ,philadelphia that a certain electro-plater had found that he could not pursue his silver plating operations during thunderstorms1 and that if he left his plating over night and a thunderstorm came up the work was invariably ruined4 ,i was disposed to be thoroughly sceptical1 and expressed my disbelief in any such effect4 ,being urged1 however1 ,i went to the silver-plater's shop1 which was a small one1 and questioned the silver-plater himself concerning the circumstance which had been reported4 ,while it was evident that he was not a man who had informed himself electrically1 ,i could not doubt that1 after conversing with him1 he had indeed been stating what was perfectly true1 namely1 that when his operations of plating were going on and a thunderstorm arose1 his batteries1 which were ,smee cells1 acted as though they were short-circuited1 and the deposit of metal was made at too rapid a rate4 ,the secret came out on an inspection of his connections4 ,the connections of his batteries to his baths were made through a number of bad contacts which could not fail to be of high resistance under ordinary conditions4 ,i could readily see that virtually he was working through a considerable resistance and that he had an excess of battery power for the work4 ,under these circumstances a flash of lightning would cause coherence of his badly contacting surfaces1 and would improve the conductivity so as to cause an excessive flow of current1 give a too rapid deposit1 and--as he put it--8make the batteries boil40 ,the incident suggests the use of ,dr4 ,lodge's ingenious instrument in the study of the waves which are propagated during thunderstorms1 of which waves we have practically little or no information4 ,dr4 ,morton's communication is as follows3-- ,,hertzian ,,waves1 ,,carbon ,,microphones ,,and 8,,coherers40 ,about #ah months ago ,i put into use in my office the ,vetter method of controlling the strength of the current derived from the ,edison #aaj volt system of electrical distribution4 ,the controlling devices were a #af c4p4 lamp and a pulverised carbon rheostat4 ,by these means a milliampere1 or fraction thereof1 up to #ajj or more1 if desirable1 can be administered to a patient 7see diagram1 ,fig4 #eh1 on next page74 ,on several occasions when the electrodes of the system above described were permanently attached to some part of a patient's person and a spark was being administered to another patient seated upon a platform charged by an influence machine1 some #ae ft4 distant in the same room1 the first patient would exclaim and protest against receiving a considerable shock4 ,on one occasion1 when the continuous current electrode was in the neighbourhood of a patient's temple1 the patient experienced the sensation of a flash of light2 on other occasions muscular contractions were produced1 always simultaneously with the spark4 ,also upon the occurrence of the spark and shock the needle of the milliamperemeter1 a vertical one and calibrated to a wide range of movement over #e milliamperes1 flew across the scale from1 for instance1 #b to #e milliamperes and remained at the higher reading4 ,that a spark occurring #ae ft4 away should cause a shock to a person in an independent circuit excited my wonder2 it was inexplicable and yet so certain to occur that ,i was obliged to abandon the use of the two pieces of apparatus at the same time4 ,at last1 when time permitted1 ,i set out to investigate4 ,i sought for an ordinary induction circuit of parallel wiring and found none4 ,i then suspected the microphonic rheostat of pulverised carbon and having cut it out of circuit ,i substituted for it a water rheostat4 ,the phenomena now failed to occur4 ,replacing the carbon rheostat and putting a telephone in circuit ,i adjusted the milliammeter to read #b milliamperes1 causing an assistant to evoke the distant spark4 ,all was now clear4 ,at each spark the needle jumped forward and a distinct telephone click was heard from the telephone receiver4 ,i observed that the first jump of the needle was the longest as well as the first click in the receiver the loudest1 both needle jump and click1 dying away gradually at each successive spark until they ceased at from the twentieth to thirtieth4 ,to turn the rheostat off and then on again rendered the experiment repeatable4 ,the reading of the meter1 best adapted to success1 was about #e milliamperes though #bj to #ej yielded good results4 ,illustration3 ,,fig4 #eh4 ,unable to furnish any reason why the electric radiation of a distant spark should reduce the resistance of pulverised carbon ,i refrained from publishing the bare observation in the hopes of finding an explanation by further experimentation1 merely noting to friends the delicacy of the pulverised carbon rheostat as a detector of ,hertzian waves and making some further experiments with it and a telephone receiver in circuit in this direction4 ,the recent publication of the brilliant researches of ,dr4 ,oliver ,j4 ,lodge now makes the entire matter clear4 ,dr4 ,lodge describes a new form of microphonic detector of ,hertzian waves1 consisting of two or more pieces of fairly clean metal in light contact and connected to a voltaic cell1 a film of oxide of the metal intervening between the surfaces1 8so that only an insignificant current is allowed to pass40 ,he writes3 8,now let the slightest surging occur1 say1 by reason of a sphere being charged and discharged at a distance of #dj yards2 the film at once breaks down--perhaps not completely1 that is a question of intensity--but permanently40 ,this detector1 ,dr4 ,lodge terms a 8coherer0 because of the partial metallic cohesion above described4 ,upon this point he says3 8,a bad contact was at one time regarded as a simple nuisance40 444 8,hughes observed its sensitiveness to sound waves1 and it became the microphone4 ,now it turns out to be sensitive to electric waves1 if it be made of any oxidisable metal 7not of carbon7 and we have an instrument which might be called a micro-something but which1 as it appears to act by cohesion1 ,i call at present a coherer40 ,the cohesive result between the metallic surfaces is also referred to as a 8welding effect of an electric jerk40 ,in the volume just published1 entitled 8,the ,work of ,hertz and ,some of ,his ,successors10 reprinted from ,the ,electrician1 ,london1 this foot note is added on p4 #cj3 8,fitz,gerald tells me that he has succeeded with carbon also40 ,my experiments would seem to fully demonstrate that carbon as well as metals may act as coherers4 ,at some recent trials the editors of the ,electrical ,engineer were present and were fully satisfied as to the swinging up of the needle of the milliamperemeter and the click in the telephone receiver1 by repeated tests4 ,the experimental side of the subject has been so exhaustively and admirably presented by ,dr4 ,lodge 7detailed in the publications referred to7 that what is here said has no more than a secondary interest4 ,but it may not prove amiss to gather together all the evidence which tends to demonstrate the influence of disruptive discharges upon neighbouring bad contacts conveying currents4 ,as ,lodge points out1 fuses may easily be 8blown out0 in this manner4 ,this has occurred to me on a number of occasions with #aj ampere fuses4 ,under proper conditions of sparking surfaces and circuit a short spark might suffice4 ,may it not also be the fact that the fuses melted during thunderstorms in their neighbourhood are melted by reason of the effect of the electric radiations or surgings of the lightning stroke throwing a rush of the current already in the circuit through the fuse rather than by the addition of any new current to the circuit by the atmospheric electricity itself4 ,in this connection ,lodge writes3 8,there are some who think that lightning flashes can do none of these secondary things4 ,they are mistaken40 ,in this as in other directions the new facts have a practical bearing and a pursuit of further experiments may lead1 as often happens1 to unexpected developments4 ,so far as carbon contacts are concerned and the fact that ,hertzian waves1 like mechanical motion1 reduce their resistance1 a curious problem is suggested as concerns the principle upon which some carbon transmitters act4 ,an exclusive monopoly of all carbon transmitters is based upon the claim that the variations in resistance are produced by variations in pressure due to a mechanical force1 viz41 sound waves4 ,if my experiments1 above detailed1 are exact1 two facts appear3 #a4 ,that another form of motion1 ether vibration1 causes a variation of resistance of carbon contacts4 #b4 ,that it remains to be proved that variation of pressure is the only means of varying the current strength1 for variation of molecular contact occurs in the present instance without any evidence that it is due to variation of pressure4 ,,appendix ,,iv4 ,,on ,,the ,,diselectrification ,,of ,,metals ,,and ,,other ,,bodies ,,by ,,light4 ,referring to a footnote to my ,royal ,institution lecture1 on page #aa1 ,messrs4 ,elster and ,geitel have been good enough to call my attention to a great deal of work done by them in the same direction4 ,to make amends for my ignorance of this work at the time of my ,royal ,institution lecture1 and to make it better known in this country1 ,i make abstract of their ,papers as follows3-- ,wiedemann's ,annalen1 #ch1 p4 #dj4--8,on the ,dissipation of ,negative ,electricity by ,sun- and ,daylight40 ,with a view to ,arrhenius' theory concerning atmospheric electricity1 we arranged experiments on the photo-electric power of sunlight and diffuse daylight at ,wolfenbttel from the middle of ,may to the middle of ,june1 #ahhi4 ,hoor alone had observed the effect of sunlight2 other experimenters had failed to find it1 but we find a discharging effect even in diffuse daylight4 ,we take an insulated zinc dish1 #bj cm4 diameter1 connect it to a quadrant electrometer or an ,exner's electroscope1 and expose it in the open so that it can be darkened or illuminated at pleasure4 ,sunlight makes it lose a negative charge of #cjj volts in about #fj seconds4 ,a positive charge of #cjj volts is retained4 ,the dissipation of negative electricity ceases in the dark1 and is much weakened by the interposition of glass4 ,but light from the blue sky has a distinct effect4 ,fill the dish with water1 or stretch a damp cloth over it1 and the action stops4 ,a freshly-scrubbed plate acquires a positive charge of #b volts1 which can be increased by blowing4 ,with freshly-cleansed wires of zinc1 aluminium1 or magnesium attached to the knob of the electroscope1 a permanent negative charge is impossible in open sunlight4 ,indeed1 magnesium shows a dissipating action in diffuse evening light4 ,such wires act like glowing bodies4 ,exposing an electroscope so provided in an open space it acquires a positive charge from the atmosphere4 ,no abnormal dissipation of positive electricity has been observed4 ,wied4 ,ann41 #ch1 p4 #dig4--;,continuation of ,same ,subject4 ,our success last time was largely due to the great clearness of the sky in ,june1 and we wished to see if we could get the same effect at the beginning of the winter4 ,the following is our summary of results3 ,bright fresh surfaces of the metals zinc1 aluminium1 magnesium were discharged by both sun- and daylight when they were negatively charged2 and they spontaneously acquired a positive charge1 whose amount could be increased by blowing4#ce ,a still more notable sensitiveness to light is shown by the amalgams of certain metals1 viz41 in the order of their sensitiveness1 ,k1 ,na1 ,zn1 ,sn4 ,since pure mercury shows no effect1 the hypothesis is permissible that the active agent is the metal dissolved in the mercury4 ,if so1 the following are the most active metals3-- #ce ,a fact noticed by ,bichat and ,blondlot4 ,k1 ,na 7,mg1 ,al71 ,zn1 ,sn4 ,all other metals tried1 such as ,sn1 ,cd1 ,pb1 ,cu1 ,fe1 ,hg1 ,pt1 and gas carbon1 show no action4 ,the same is true of nearly all non-metallic bodies2 but one of them--namely1 the powder of ,balmain's luminous paint--acted remarkably well in sunlight4 ,of liquids1 hot and cold water1 and hot and cold salt solution were completely inactive2 consequently wetting the surface of metals destroys their sensibility to light4 ,the illumination experiments can be arranged in either of two ways4 ,for experiments in free space we use zinc1 aluminium1 or magnesium wires1 or small amalgamated spheres of zinc provided with an iron rod4 ,with these it can be easily shown that the illuminated surface of certain metals act in the same way as a flame collector4 ,for demonstration experiments the apparatus described#cf is better1 and with this we show the following3-- ,amalgamated zinc1 negatively charged1 discharges almost instantly in sunlight2 and if near a positively-electrified body charges itself positively4 ,the same thing happens1 though more slowly1 in diffuse daylight4 ,red glass stops the action1 but the following let some through3--,selenite1 mica1 window glass1 blue 7cobalt7 glass4 #cf ,in this apparatus the mercury amalgams of ,k and ,na are run through a fine funnel1 so that the freshly-formed surface of the drops may be illuminated4 ,under these circumstances1 while pure mercury fell from -#ahe to -#age volts in #cjsec41 amalgam of zinc fell from -#aie to -#aaf in #aesec41 amalgam of sodium fell from -#aie to #j in #ajsec41 and an amalgam of potassium fell from -#aie to #j in #esec4 ,illustration3 ,,fig4 #ei4 ,explanation of ,fig4 #ei4--;,b is a brightly polished amalgamated zinc plate attached to the negative pole of a ,holtz machine1 with the positive knob from #f to #aj centimetres distant4 ,the source of a light is a strip of burning magnesium ribbon #cj to #ej centimetres away4 ,whenever the spark is able just to choose the path ,b ,b1 light shining on the zinc plate checks it and transfers the spark to ,a ,a4 ,wied4 ,ann41 #ci1 p4 #ccb4--,on a ,checking ,action of ,illumination on ,electric ,spark and ,brush ,discharge4 ,if sparks are just able to occur between a brass knob and a clean amalgamated zinc cathode1 illumination of the latter by ultra-violet light tends to check them4 7,this is a curious inversion of ,hertz's fundamental experiment on the subject4 ,it is an effect ,i have not yet observed2 but ,elster and ,geitel's arrangement differs from mine#cg in that the surfaces are at a steady high potential before the spark1 so that light can exert its discharging influence1 whereas in mine the surfaces were at zero potential until the spark-rush occurred4 ,hertz's arrangement was more like mine1 inasmuch as he illuminated the knobs of an induction coil on the verge of sparking4 ,it appears1 then1 that whereas the action of light in discharging negative electricity from clean oxidisable metallic surfaces is definite enough1 its influence on a spark discharge differs according to the conditions of that discharge--in cases of 8steady strain0 it tends to hinder the spark2 in cases of 8sudden rush0 it tends to assist it4--,o4 ,j4 ,l47 #cg ,see ,fig4 #g1 page #i4 ,wied4 ,ann41 #da1 p4 #afa4--,on the use of ,sodium-,amalgam in ,photo-electric ,experiments4 ,elster and ,geitel have repeated some of ,righi's experiments on the discharge of negative electricity from metals in rarefied air1 and find1 in agreement with him1 that a reduction of pressure to about one millimetre increases the discharge velocity about six or seven times4 ,they proceed to try sodium-amalgam exposed to daylight in exhausted tubes1 and describe apparatus for the purpose4 ,such an arrangement simply cannot hold a negative charge in bright daylight1 even although it be unprovided with quartz windows4 ,even paraffin lamps and sodium flames exert some action4 ,they observe that under the action of light the boundary surface of the metal and glass changes1 and the metal begins to cling to the glass4 ,they suppose that ,warburg's vacuum tubes of pure sodium may behave similarly1 and show photo-electric sensibility4 ,the ,same1 p4 #aff4--,on a ,checking ,action of ,magnetism on ,photo-,electric ,discharge in ,rarefied ,gases4 ,the authors point out analogies between the above effects and those they had observed in the action of glowing bodies in air1 and they mention ,lenard and ,wolf's experiments 7,wied4 ,ann4 ,,xxxvii41 p4 #ddc71 tending to show that the effect is due to a disintegrating or evaporative effect of light on surfaces4 ,elster and ,geitel had observed that the discharging power of glowing bodies was diminished by application of a magnetic field1 the effect being the same as if the temperature was lowered2 and they proceed to try if the discharge of negative electricity from illuminated surfaces in highly-rarefied gas could also be checked or hindered by a magnetic field4 ,they find that it can4 ,illustration3 ,,fig4 #fj4 ,explanation of ,fig4 #fj4--,the sodium and mercury are introduced through the tube ,s into the globe ,k4 ,the tube ,s is then closed1 a pump applied to ,x1 and exhaustion carried on for some days4 ,t is an open funnel sealed into the tube 7as is done in some vacuum tubes made by ,holtz7 to show a curious unilateral conductivity of rarefied gas4 ,the object of this funnel is to permit metal from the interior1 free from scum1 to be introduced from ,k to ,d when the whole is tilted4 ,thus a bright surface is exposed to the earth ring ,r4 ,it can be charged negatively1 and its leak under illumination be measured1 through the terminal ,d4 ,sometimes the tube is inverted1 so that the active surface may be at ,d1 further from the earth wire4 ,using the light from sparks admitted through a quartz window into the vacuum tube when a negatively charged amalgamated zinc surface was exposed near an earth-connected platinum ring1 and between the poles of a small electromagnet1 they found that when the tube was full of air at #aj mm4 pressure the magnet had but little effect1 but that at #jae mm41 whereas without the magnet the charge of -#bgj volts disappeared completely in five seconds1 when the magnet was excited it only fell about half that amount in the same time4 ,with hydrogen at #jbd mm4 the result was much the same1 and at either greater or less pressure in both cases the magnet had less effect4 ,in oxygen the loss of charge was not quite so rapid2 and1 again1 at a pressure of ,o#amm41 the magnet more than halved the rate4 ,but in ,,co the rapidity of loss was extreme4#ch ,either at #aa mm4 or at #jjje mm4 the charge of #bgj volts leaked away completely in two seconds when the magnet was not excited2 but in the latter case 7low pressure7 exciting the magnet reduced the speed by about one-half4 ,at the pressure of #aa mm4 the magnet did not seem to produce an effect4 ,with daylight the results are similar4 #ch ,corresponding to the activity of this gas as found by ,wiedemann and ,ebert 7,wied4 ,ann41 ,,xxxiii41 p4 #beh71 in their researches on the influence of light on ease of sparking4 ,illustration3 ,,fig4 #fa4 ,explanation of ,fig4 #fa4--,p is the plate of amalgamated zinc1 and ,r is the earth ring1 as before4 ,ultra-violet light is introduced through a quartz window ,q from a spark gap r4 ,the vessel has a joint at the middle1 so that the sensitive plate can be got at and changed4 ,magnet poles are applied outside this vessel in various positions4 ,the authors then discuss the meaning of the result1 and its bearing on the opposition hypotheses of ,lenard and ,wolf and of ,righi4 ,lenard and ,wolf's view is that the loss of negative electricity is due to dust disintegrated from the surface by the action of light1 but whose existence they consider is established by an observed effect on steam jets4 ,righi1 on the other hand1 believes that gas molecules themselves act the part of electric carriers4 ,elster and ,geitel consider that the magnetic effect observed by them supports this latter view1 it being known that a magnet acts on currents through gases2 and they surmise that the impact of light vibrations may directly assist electric interchange between a gas molecule and the surface1 by setting up in them syntonic stationary vibrations1 something like resonant ,leyden jars4 ,it is to be remembered that phosphorescent substances1 such as ,balmain's paint powder1 exhibit marked photo-electric effect in daylight4 ,illustration3 ,,fig4 #fb4 ,explanation of ,fig4 #fb4--;,a simpler arrangement1 like the one above 7,fig4 #fa71 whereby clean liquid alkali metals can be introduced into the experimental chamber ,b1 from the preliminary chamber ,a1 through a cleansing funnel1 ,f1 which dips its beak into the interior4 ,the unilateral character of the electric motion1 and the charging of neutral surfaces by light1 require special hypotheses1 concerning an ,e4,m4,f4 at the boundary of gases and conductors1 such as ,schuster and ,lehmann have made4 ,weid4 ,ann4 #db1 p4 #efd4--,note on a ,new ,form of ,apparatus for ,demonstrating the ,photo-electric ,discharging ,action of ,daylight4 ,a vacuum tube suitable for experiments with sodium-amalgam or pure sodium1 or the liquid sodium-potassium alloy1 is described1 with the aid of which a current 7shown by the charge of an electroscope7 can be maintained by a dry pile through the rarefied gas above the metal when it is illuminated from ordinary windows4 ,wied4 ,ann4 #dc1 p4 #bbe4--,on the ,dependence of the ,discharging ,action of ,light on the ,nature of the ,illuminated ,surface4 ,experiments also on differently-coloured lights4 ,summary of results4 ,the photo-electrically active metals arrange themselves in the following order--,pure ,k1 alloys of ,k and ,na1 pure ,na4 ,amalgams of ,rb1 ,k1 ,na1 ,li1 ,mg 7,tl1 ,zn72 the same as their voltaic order4 ,with the most sensitive term of the series a candle six metres off can be detected1 and the region of spectral red is not inactive4 ,the later terms of the series demand smaller waves1 and even for potassium blue light gives a much greater effect than red4 ,no discharge of positive electricity is observable with these substances4 ,wied4 ,ann4 #dd1 p4 #gbb4--,on the ,dissipation of ,electric ,charge from ,mineral ,surfaces by ,sunlight4 ,hitherto only ,balmain's paint powder has been observed to be active among non-metallic substances4 ,now they try other phosphorescent bodies1 and arrive at the following results3-- ,fluorspar is conspicuously photo-electric1 both in sunlight and daylight1 especially the variety of fluorite called stinkfluss4 ,freshly-broken surfaces discharge much more rapidly than old surfaces4 ,blue waves1 and not alone the ultra-violet1 have a perceptible effect on fluorspar4 ,in a vacuum the mineral loses its photo-electric sensibility and its conductivity too4 ,contact with damp air restores its sensibility4 ,moistening with water weakens but does not destroy the sensitiveness4 ,on the other hand1 igniting the mineral destroys both its photo-electric power and its exceptional phosphorescent property4 ,distinct traces of photo-electric power are shown by the following minerals also3 ,cryolite1 heavy spar1 celestine1 arragonite1 strontianite1 calcspar1 felspar and granite4 ,the hypothesis that the power of phosphorescing when illuminated is approximately a measure of the discharging power of light has been verified in many cases2 the exceptions can probably be explained by the influence which the electrical conductivity of the illuminated substance exerts on the rate of discharge of electricity from its surface4 ,this agreement confirms the view expressed by us on the occasion of experiments with ,balmain's paint1 that1 during electrical discharge by light1 actions take place which are analogous to those of resonance4 ,messrs4 ,wiedemann and ,ebert had previously been led by other considerations to the same conclusion4 ,we are compelled by the results of the present experiments to conclude that a more rapid discharge of electricity into the atmosphere takes place in sunlight than in darkness from the surfaces of the earth1 which is composed of mineral particles charged1 as the positive sign of the slope of atmospheric potential indicates1 with negative electricity4 ,illustration3 ,,fig4 #fc4 ,explanation of ,fig4 #fc4--;,arrangement used by ,elster and ,geitel for exposing various phosphorescent minerals to daylight1 while under inductive charge4 ,they were put in powder in the tray ,p1 and the transparent wire-gauze ,n above them was charged positively from a battery4 ,the metal cover ,m ,m could be removed and replaced at pleasure1 and the effect on a delicate quadrant electrometer connected to ,p observed4 ,by this method considerable tension can be got up on the mineral surface1 notwithstanding that it is close upon zero potential4 ,the light effect depends on tension1 not potential4 ,it seems to us evident that there exists a direct electric action of sunlight upon the earth1 and that we have given experimental evidence in favour of the theory put forward by von ,bezold and ,arrhenius1 according to which the sun acts on the earth1 not by electrostatic or electro-dynamic action-at-a-distance1 which would involve difficulties of a theoretical character1 but through the medium of the electrical forces of light waves4 ,we hope soon to establish the consequences of this theory in meteorology in another ,paper1 giving the results of two years' observations on the intensity of the most refrangible rays of sunlight and of the slope of atmospheric potential4 ,wied4 ,ann41 #dh1 p4 #cch4--;,experiments on the ,gradient of ,atmospheric ,potential and on ,ultra-,violet ,solar ,radiation4 ,elster and ,geitel describe the observations they have made for two years on solar radiation1 at observing stations of low and high altitude1 as tested by its electrical discharging power2 and they plot curves of such effective radiation for days and months along with the curves of atmospheric potential observed at the same places4 ,these curves are of much interest1 and need study4 ,incidentally they find that1 of the whole effective solar radiation1 #fj per cent4 was absorbed at altitudes above #c1ajj metres2 #bc per cent4 of the remainder was absorbed in the layer between this and a station at #a1fjj metres2 and #dg per cent4 was absorbed between this and #hj metres above sea level4 ,or1 in other words1 of #bcf parts which enter the atmosphere #id reach the highest observing station 7,sonnblickgipfel71 #gb the middle one 7,kolm-,saigurn71 and #ch the lowest 7,wolfenbttel74 ,they discuss the question as to how far the daily variation of terrestrial magnetism is due to electrical currents in the atmosphere excited by sunshine and other meteorological matters4 7,the ,paper and plates are worthy of reproduction in full in the ,philosophical ,magazine47 ,weid4 ,ann41 #df1 p4 #bha4--,on the ,behaviour of ,alkali ,metal ,cathodes in ,geissler ,tubes2 ,on ,photo-,electric ,discharge in a ,magnetic ,field2 and ,on the ,measure of ,photo-,electric ,currents in ,potassium ,cells by means of a ,galvanometer4 ,results3--,the resistance of a ,geissler tube provided with a cathode surface of pure alkali metal is diminished by the light from the sparks of an induction coil2 especially when the pressure is #a to #ja mm4 of mercury4 ,the resistance which rarefied gas opposes to an electric current in a magnetic field is greatest in the direction normal to the magnetic lines4 ,the changes of resistance effected by any kind of light in a vacuum tube with alkali metal cathode can be measured galvanometrically4 7,a ,daniell cell gives #ajj divisions on a ,rosenthal galvanometer when coupled up through such an illuminated tube1 each division meaning about #aj ampere47 ,illustration3 ,,fig4 #fd4 ,explanation of ,fig4 #fd4--;,a vacuum tube of rarefied hydrogen containing alkali metal as cathode1 say the liquid ,k-,na alloy1 or solid ,k or ,na4 ,a spark gap at ,s serves as alternative path1 and a stream of sparks can occur to the plate ,p in the dark4 ,but when light falls on the surface ,a this stream of sparks can cease1 showing that the resistance of the vacuum tube is diminished4 ,illustration3 ,,fig4 #fe4 ,explanation of ,fig4 #fe4--,showing position of magnetic poles with respect to the vacuum tube discharge4 ,with the poles across the line of discharge1 as in ,fig4 on left1 excitation of the magnet opposes the leak from the surface4 ,with the poles as in ,fig4 on right1 the discharge is not much affected1 it is even sometimes slightly increased4 ,illustration3 ,,fig4 #ff4 ,explanation of ,fig4 #ff4--,potassium vacuum bulbs containing millimetre of hydrogen mounted and connected to battery and galvanometer1 and arranged as a photo-electric photometer4 ,wied4 ,ann41 #dh1 p4 #fbe4 ,on the ,photo-,electric ,comparison of ,sources of ,light4 ,attempts to make such a potassium cell into a photometer4 ,wied4 ,ann4 #eb1 p4 #dcc4 ,further ,photo-,electric ,experiments4 ,plates of platinum1 silver1 copper need exceedingly ultra-violet light before they show any photo-electric power2 zinc1 aluminium1 magnesium show it for visible violet and blue light2 the alkali metals1 in an atmosphere of rarefied hydrogen1 advance their range of sensibility into the spectral red2 while under the most favourable conditions they show a sensibility only inferior to that of the eye itself4 ,the authors now use galvanometric methods of measuring the effect1 instead of only electrometers1 and they arrive at the following results3-- 7#a7 ,the three alkali metals ,na1 ,k1 ,rb1 have different sensibility for differently-coloured lights4 ,for long waves their order of sensibility is ,rb1 ,na1 ,k2 though rhubidium is far exceeded by the other two metals in white light4 7#b7 ,illumination of a plane alkali metal cathode surface with polarised light causes greatest discharge if the plane of polarisation is normal to plane of incidence2 and least1 if the two coincide4 7,this is a most remarkable observation4 ,its probable meaning is that the electric oscillations of light are photo-electrically effective in so far as they are normal to the surface on which they act2 while electric oscillations tangential to the surface are scarcely operative4 ,different angles of incidence must be tried before the proof is complete4--,o4 ,j4 ,l47 7#c7 ,electric oscillations of very short period1 such as are given by a ,hertz oscillator1 are commutated by illumination in the presence of alkali metals in rarefied gas1 so as to be able to set up a constant electric tension in the gas4 7,a ,zehnder tube#ci was used1 and the momentary phases of the oscillation during which the metal is negatively charged are apparently taken advantage of by the illumination47 7#d7 ,the photo-electric dissipation showed by powdered fluorspar is dependent on the colour of the mineral1 in such a way that the deepest blue1 violet or green specimens are the most sensitive4 #ci ,see ,fig4 #ac1 p4 #ae4 ,,appendix ,v4 ,,photo-,,electric ,,researches ,,of ,m4 ,,auguste ,,righi4#dj ,m4 ,righi has observed the following facts3 7#a7 ,that ultra-violet rays reduce to sensibly the same potential two metals placed near each other 7plate and gauze parallel and close72 7#b7 ,that several photo-electric couples of this kind can form a battery2 7#c7 ,that a simple metallic plate charges itself positively under the influence of radiation2 7#d7 ,that a voltaic arc formed with a zinc rod gives the strongest effect1 while the sun gives none4 #dj ,comptes ,rendus1 vol4 #ajg1 p4 #eei4 ,besides these facts he finds3--7a7 ,that certain gases and vapours1 such as coal-gas and ,,cs1 absorb the active rays strongly4 7b7 ,that if the discharging body is easily movable it recedes like an electric windmill4 7c7 ,a film of gypsum interposed between gauze and plate charges itself negatively on the side facing the negatively charged plate4 7d7 ,radiation produces its discharging effect even on non-conductors 7ebonite and sulphur74 ,with glass1 resin and varnishes the action is feeble1 or nearly nothing4 7e7 ,if the experiment is made with a copper gauze and a zinc plate1 the phenomenon nearly disappears on varnishing the gauze4 ,his hypothesis is that radiation produces convection of negative electricity1 the carriers being molecules of air4 7f7 ,the carrying molecules move along the lines of force1 and throw electric shadows4 ,to show this he varnishes a zinc cylinder1 all except a generating line1 charges it negatively to #a1jjj volts with a dry pile1 and places it parallel to a large earth-connected plane1 which has a narrow rectangular portion insulated from the rest and communicating with an electrometer4 ,light only acts on the uncovered line of the cylinder1 and on turning the cylinder round the electrometer is only deflected when it is exposed to some of the 7circular7 lines of force emanating from the active line of the cylinder4 7g7 ,radiation charges positively an insulated metal1 even when it is an enclosure with walls of the same metal2 the metal being certainly uncharged at the beginning of the experiment4 ,the same occurs with sulphur and ebonite4 ,if there is a feeble initial plus charge1 radiation increases it4 7h7 ,while the discharging power of radiation for negative electricity is strongest with zinc and aluminium1 and slower with copper and gold1 following the ,volta series2 the ,e4,m4,f4 set up by radiation1 when it charges things positively1 is greatest with gold and carbon1 and less with zinc and aluminium2 again following the ,volta series1 but inversely4 7i7 ,if radiation falls on an insulated metal plate connected with an electrometer1 in an enclosure of the same metal1 the positive electrification shown by the deflection of the electrometer is greater as the plate is further from the walls of the enclosure4 ,the action stops when the metal has attained a certain electric density1 constant for a given metal2 so the potential of a plate is naturally higher as its capacity is less4 ,it is thus established that radiation acts on the particles of gas in contact with a conductor2 they go away with a negative charge1 leaving plus on the conductor1 until an electric density sufficient to balance this action is attained4 7j7 ,it is probable that if the solar rays do not produce an effect it is because of the absorbing action of the atmosphere4 ,in fact1 if one places a tube whose ends are glazed with selenite between the source of light and the metals being experimented on1 the effects become sensibly stronger when the tube is exhausted4 ,,appendix ,,vi4 ,,elliptically ,,polarised ,,electric ,,radiation4 ,since the delivery of my lecture to the ,royal ,institution1 on ,june #ast1 ,herr ,zehnder has published#da a mode of getting elliptically and circularly polarised electric radiation4 ,he takes a couple of plane polarising grids1 such as are depicted in ,fig4 #ba1 page #cg1 and places them parallel to each other at a little distance apart with their wires crossed4 ,if the two grids are close together they will act like wire-gauze1 reflecting any kind of polarised radiation equally2 but if the warp and woof are an eighth-wave length apart1 and the plane of the incident radiation is at #de to the wires1 the reflected radiation will be circularly polarised4 ,a change in the circumstances will1 of course1 make it elliptical4 ,such a pair of grids acts1 in fact1 like a ,babinet's ,compensator4 #da ,berichte der ,naturforschenden ,gesellschaft zu ,freiburg i4 ,b41 ,bd4 ,,ix4 ,heft #b1 ,june #ba1 #ahid4 ,,appendix ,,vii4 ,,on ,,magnetisation ,,produced ,,by ,,hertzian ,,currents2 ,a ,,magnetic ,,dielectric3#db ,,by ,m4 ,,birkeland4 8,two years ago#dc it was proved by conclusive experiments that ,hertzian waves travelling along an iron wire magnetise transversely the very thin layer into which the alternating current penetrates1 and whose thickness does not exceed some thousandths of a millimetre4 ,once proved that alternate magnetisation can be produced with such rapidity1 other questions present themselves4 ,one asks1 for instance1 if it is not possible to demonstrate in magnetic cylinders stationary magnetic waves analogous to the electric stationary waves along metallic wires40 #db ,abstracted from ,comptes ,rendus1 ,june #aa1 #ahid1 and communicated by ,dr4 ,oliver ,lodge4 #dc ,why two years ago8 ,it was practically proved by ,savart early in the century1 and has been observed over and over again since4 ,however1 it is true that experiments have been more numerous and conclusive of late1 and have been pushed to very high frequencies4--,o4 ,j4 ,l4 ,the author finds that the conductivity of massive iron makes it an unsuitable substance1 and uses instead a mixture of iron filings1 or of chemically-obtained iron powder1 with paraffin1 to which he sometimes adds powdered quartz4 ,this he moulds into cylinders1 and inserts as the core of a spiral in an otherwise ordinary ,hertz resonator4 ,fig4 #fg shows emitter and receiver drawn to scale2 the magnetic cores are introduced into the spiral ,a1 and their effect on the length of the resonator spark is observed4 ,with this arrangement of exciter the electric effect of the spiral is negligible1 since it is well removed from electrostatic disturbance1 and subject only to magnetic4 ,the spiral is of #ab well-insulated turns1 the spark gap is a micrometer with point and knob1 and a pair of adjustable plates to vary the capacity for purposes of tuning4 ,he employed #ab different types of cylinder1 all about #bj centimetres long1 and #d centimetres diameter4 #a4 ,a massive cylinder of soft iron4 #b4 ,a bundle of fine iron wires embedded in paraffin4 #c-i4 ,six cylinders of the agglomerate of chemically-reduced iron in powder and paraffin1 containing respectively #e1 #aj1 #ae1 #bj1 #be and #ej per cent4 of iron4 ,then for control experiments3-- #aj4 ,a cylinder of agglomerate of zinc powder in paraffin1 with #dj per cent4 of zinc4 #aa4 ,a cylinder of brass filings in paraffin1 #bj per cent4 of metal4 #ab4 ,a tube of glass1 #de centimetres diameter1 filled with various electrolytes4 ,illustration3 ,,fig4 #fg4 ,the manner of observing was as follows 7the experiments were done in the laboratory of ,hertz73-- ,the resonator1 with its spiral empty1 was syntonised with the exciter1 and the maximum spark measured4 ,it was between #d and #i millimetres long in these experiments4 ,then one or other of the above cylinders was introduced and the spark length measured afresh4 ,cylinder #a did not affect the maximum spark length4 ,cylinders #b-d reduced the maximum spark to th of its former value2 #g and #h to _/th1 and ,no4 #i to _/th of its former value 7viz41 from #i millimetres to #je millimetre74 ,nos4 #aj and #aa had but a feeble action1 and reduced the spark from #h to #g millimetres4 ,tube ,no4 #ab1 filled with distilled water1 scarcely affected the spark length2 the period of the secondary increases a little1 but the maximum spark is the same as before1 once syntony is re-established4 ,filled1 however1 with dilute sulphuric acid1 containing #aj1 #bj1 or #cj per cent41 the tube reduced the spark considerably1 in each case about the same1 viz41 from #i to #ac about4 7,currents induced by ,maxwellian radiation in electrolytes had been already observed by ,j4 ,j4 ,thomson47 ,while trying to re-establish syntony between primary and secondary1 ,i found that the period of the resonator was considerably increased by the cylinders #b-d1 but that the maximum spark length was much diminished4 ,with the cylinders ,nos4 #e-i in the spiral1 it was no longer possible to establish syntony1 8a fact which is certainly due to their considerable absorption of energy4 ,take1 for example1 cylinder #i3 electromagnetic energy must converge rapidly towards it in order to be transformed1 and the space finds itself empty of energy as air is exhausted of vapour in presence of an absorbing substance40 8,this absorption is probably due to hysteresis in the ferruginous cylinders2 the development of ,joulian heat1 so typically shown by cylinder #ab1 being undoubtedly of the same order in cylinders #c-i as in ,nos4 #aj1 #aa4 8,it is probably by reason of this absorption that ,i have not succeeded in establishing stationary magnetic waves in a circuit of ferro-paraffin40 ,if one of the cylinders #b-i1 is wrapped in tinned paper before introducing it into the spiral ,a1 its action is completely stopped4 7,these conducting cores diminish the period of the resonator2 it is much as if the spiral ,a were partially shunted out2 but the maximum spark returns as soon as syntony is re-established47 ,to examine this further he enclosed the cylinder in drums of cardboard having fine wires either along generating lines1 or along circular parallels4 ,the latter suspended the action of an interior ferruginous cylinder1 the former did not4 ,to find to what depths the magnetism penetrated1 ,birkeland inserted hollow ferruginous drums into ,a1 measured their effect1 and then plunged solid cylinders into them to see whether the effect increased4 ,he thus found that the magnetisation easily traversed #g millimetres thickness of the #aj per cent4 ferro-paraffin1 and #e millimetres of the #be per cent4 ,the substance is comparable to a dieletric on the theory of ,poisson-,mossotti4 8,the results obtained with our magnetic dielectric invite to new researches0--such as the mechanical force excited by electric waves on a delicately-suspended ferro-paraffin needle1 and the rate of propagation of ,maxwellian waves through such a substance4