,transcriber's ,notes ,text printed in italics has been transcribed between underscores1 bold face text has been transcribed between equal signs4 ,small capitals have been replaced with all capitals4 ,single letters in square brackets1 such as ,t and ,v1 represent shapes rather than letters4 ,more ,transcriber's ,notes may be found at the end of this text4 ,harper's ,practical ,books for ,boys ,a ,,series ,,of ,,new ,,handy-,,books ,,for ,,american ,,boys ,each ,crown #hvo1 with many ,illustrations4 ,i ,,harper',s ,,outdoor ,,book ,,for ,,boys ,by ,joseph ,h4 ,adams4 ,with ,additional ,contributions by ,kirk ,munroe1 ,tappan ,adney1 ,capt4 ,howard ,patterson1 ,l4 ,m4 ,yale1 and others4 ,cloth1 #a4ge4 ,,ii ,,harper',s ,,electricity ,,book ,,for ,,boys ,written and ,illustrated by ,joseph ,h4 ,adams4 ,with a ,dictionary of ,electrical ,terms4 ,cloth1 #a4ge4 ,,in ,,press ,,iii ,,harper',s ,,how ,,to ,,understand ,,electrical ,,work ,a ,simple ,explanation of ,electric ,light1 ,heat1 ,power1 and ,traction in ,daily ,life4 ,by ,joseph ,b4 ,baker1 ,technical ,editor1 ,u4 ,s4 ,geological ,survey1 formerly of the ,general ,electric ,company4 ,,iv ,,harper',s ,,indoor ,,book ,,for ,,boys ,by ,joseph ,h4 ,adams and others4 ,cloth1 #a4ge4 ,v ,,harper',s ,,machinery ,,book ,,for ,,boys ,the ,boy's ,own ,book of ,engines and ,machinery4 ,cloth1 #a4ge4 ,,harper ,,brothers1 ,,publishers1 ,,new ,,york ,illustration3 ,copyright1 #aijg1 by ,joseph ,h4 ,adams1 ,n4 ,y4 ,,thomas ,a4 ,,edison ,,dictating ,,to ,,his ,,graphophone ,,harper',s ,,electricity ,,book ,,for ,,boys ,,written ,,and ,,illustrated ,,by ,,joseph ,h4 ,,adams ,,author ,,of 8,,harper',s ,,outdoor ,,book ,,for ,,boys0 ,,with ,,an ,,explanation ,,of ,,electric ,,light1 ,,heat ,,power1 ,,and ,,traction ,,by ,,joseph ,b4 ,,baker ,,technical ,,editor1 ,u4 ,s4 ,,geological ,,survey ,,and ,a ,,dictionary ,,of ,,electrical ,,terms ,illustration ,,harper ,,brothers ,,publishers ,,new ,,york ,,and ,,london ,,mcmvii ,copyright1 #aijg1 by ,,harper ,,brothers4 ,all rights reserved4 ,published ,november1 #aijg4 ,,contents ,,page ,,introduction xi ,part ,i ,,chapter ,i4--,,some ,,general ,,explanations #c ,,an ,,invisible ,,world-,,power -- ,,generating ,,electricity -- ,,what ,a ,,boy ,,can ,,do -- ,,inexpensive ,,tools -- ,,some ,,practical ,,advice ,,chapter ,,ii4--,,cells ,,and ,,batteries #ab ,,simple ,,and ,,inexpensive ,,cells -- ,,how ,,to ,,make ,,cells ,,and ,,batteries -- ,a ,,plunge-,,battery -- ,a ,,storage-,,battery -- ,,dry-,,cells ,,and ,,batteries ,,chapter ,,iii4--,,push-,,buttons ,,and ,,switches #cc ,,how ,,to ,,make ,,push-,,buttons -- ,,switches ,,and ,,cut-,,outs -- ,,table-,,jack ,,switches -- ,,binding-,,posts ,,and ,,connectors -- ,,lightning-,,arresters ,,and ,,fuse-,,blocks -- ,,some ,,practical ,,precautions ,,chapter ,,iv4--,,magnets ,,and ,,induction-,,coils #ed ,,simple ,,and ,,horseshoe ,,magnets -- ,,induction-,,coils -- ,,an ,,electric ,,buzzer -- ,,electric ,,bells -- ,a ,,large ,,induction-,,coil -- ,,circuit-,,interrupters ,,chapter ,v4--,,annunciators ,,and ,,bells #gh ,a ,,drum-,,sounder -- ,a ,,simple ,,annunciator -- ,a ,,double ,,electric ,,bell -- ,,an ,,electric ,,horn -- ,,how ,,to ,,make ,a ,,burglar-,,alarm -- ,,electric ,,call-,,signals -- ,,clock-,,alarms -- ,a ,,dining-,,table ,,call ,,chapter ,,vi4--,,current-,,detectors ,,and ,,galvanometers #ajb ,,how ,,to ,,make ,,detectors -- ,,an ,,astatic ,,current-,,detector -- ,,an ,,astatic ,,galvanometer -- ,a ,,tangent ,,galvanometer ,part ,,ii ,,chapter ,,vii4--,,electrical ,,resistance #abe ,,governing ,,the ,,electric ,,current -- ,,ohm',s ,,law -- ,,resistance-,,coils ,,and ,,rheostats -- ,,how ,,to ,,make ,,simple ,,apparatus -- ,,liquid ,,resistance -- ,,importance ,,of ,,switches -- ,,uses ,,of ,a ,,house-,,current -- ,,running ,a ,,sewing-,,machine1 ,,fan1 ,,or ,,toys -- ,,an ,,easy ,,method ,,for ,a ,,boy',s ,,use ,,chapter ,,viii4--,,the ,,telephone #aef ,,vibratory ,,waves -- ,a ,,bladder ,,telephone -- ,a ,,single 7,,receiver7 ,,line -- ,,plan ,,of ,,installation -- ,a ,,double-,,pole ,,receiver -- ,,the ,,transmitter -- ,,another ,,form ,,of ,,transmitter -- ,,the ,,wiring ,,system -- ,a ,,telephone ,,induction-,,coil -- ,,an ,,installation ,,plan -- ,a ,,portable ,,apparatus ,,chapter ,,ix4--,,line ,,and ,,wireless ,,telegraphs #aij ,a ,,ground ,,telegraph -- ,,how ,,to ,,talk ,,from ,,house ,,to ,,house -- ,,the ,,morse ,,telegraph ,,code -- ,a ,,story ,,of ,,edison -- ,,how ,,detectives ,,used ,,the ,,code -- ,,wireless ,,telegraphy -- ,,its ,,true ,,character -- ,,how ,a ,,boy ,,can ,,make ,a ,,practical ,,apparatus -- ,,receiving ,,and ,,sending ,,poles -- ,,induction-,,coils1 ,,batteries1 ,,coherers ,,and ,,de-,,coherers1 ,,etc4 -- ,,working ,,plans ,,in ,,detail -- ,a,,rograms ,,across ,,the ,,atlantic ,,and1 ,,perhaps1 ,,around ,,the ,,world ,,chapter ,x4--,,dynamos ,,and ,,motors #bbi ,,dependence ,,of ,,modern ,,electricity ,,upon ,,the ,,dynamo -- ,a ,,field ,,of ,,force ,,cutting ,,another ,,field ,,of ,,force -- ,,varieties ,,of ,,dynamos -- ,,simpler ,,forms ,,of ,,generators ,,and ,,motors -- ,,how ,,to ,,make ,a ,,uni-,,direction ,,current ,,machine -- ,,permanent ,,magnet1 ,,armature1 ,,shafts1 ,,wheels1 ,,etc4 -- ,a ,,small ,,dynamo -- ,,machines ,,to ,,light ,,lamps1 ,,run ,,motors1 ,,etc4 -- ,a ,,split-,,ring ,,dynamo -- ,a ,,small ,,motor -- ,,the ,,flat-,,bed ,,motor -- ,,motors ,,of ,,other ,,types ,,chapter ,,xi4--,,galvanism ,,and ,,electro-,,plating #bff ,a ,,fascinating ,,use ,,of ,,electricity -- ,a ,,simple ,,electro-,,plating ,,outfit -- ,,the ,,sulphate ,,of ,,copper ,,bath -- ,,how ,,to ,,make ,,the ,,tank ,,and ,,other ,,apparatus -- ,a ,,variety ,,of ,,beautiful ,,and ,,useful ,,results -- ,,explanations ,,of ,,various ,,batteries -- ,,the ,,cleansing ,,process -- ,,the ,,plating-,,bath -- ,,silver-,,plating -- ,,gold-,,plating -- ,,nickel-,,plating -- ,,finishing -- ,,electrotyping -- ,,practical ,,details ,,of ,,interesting ,,work ,,chapter ,,xii4--,,miscellaneous ,,apparatus #bid ,,making ,a ,,rotary ,,glass-,,cutter -- ,,to ,,smooth ,,glass ,,edges -- ,,cutting ,,holes ,,in ,,glass -- ,,anti-,,hum ,,device ,,for ,,metallic ,,lines -- ,a ,,reel-,,car ,,for ,,wire -- ,,insulators -- ,,joints ,,and ,,splices -- 8,,grounds0 -- ,,the ,,edison ,,roach-,,killer -- ,,an ,,electric ,,mouse-,,killer ,,chapter ,,xiii4--,,frictional ,,electricity #cab ,,its ,,nature -- ,,limited ,,uses -- ,,simplicity ,,of ,,apparatus -- ,a 8,,wimshurst ,,influence ,,machine0 -- ,,materials ,,required -- ,,glass1 ,,tin-,,foil1 ,,spindles1 ,,uprights1 ,,wheels1 ,,etc4 -- ,a ,,large ,,leyden-,,jar -- ,,apparatus ,,for ,,interesting ,,experiments -- ,,necessity ,,of ,,caution ,,chapter ,,xiv4--,,formul #cbg ,,acid-,,proof ,,cements -- ,,hard ,,cement -- ,,soft ,,cement -- ,,very ,,hard ,,cement -- ,,clark',s ,,compound -- ,,battery ,,fluid -- ,,glass ,,rubbing -- ,,acetic ,,glue -- ,,insulators -- ,,non-,,conductors -- ,,insulating ,,varnish -- ,,battery ,,wax ,,chapter ,,xv4--,,electric ,,light1 ,,heat ,,and ,,power #ccd 7,by ,joseph ,b4 ,baker7 ,,the ,,work ,,of ,,the ,,dynamo -- ,,the ,,electric ,,light -- ,,uses ,,of ,,the ,,arc-,,light -- ,,incandescent ,,and ,,other ,,lamps -- ,,electric ,,heat -- ,,electric ,,furnaces -- ,,welding ,,metals -- ,,electric ,,car-,,heaters -- ,,household ,,uses -- ,,electric ,,power -- ,,power ,,from ,,water-,,wheels -- ,,transformers -- ,,rotary ,,converters -- ,,oil-,,switches -- ,,electric ,,traction -- ,,the ,,trolley-,,car -- ,,the ,,continuous-,,current ,,motor -- ,,the ,,controller -- ,,electric ,,locomotives -- ,,other ,,forms ,,of ,,electric ,,traction ,a ,,dictionary ,,of ,,electrical ,,terms #cei ,,introduction ,if a handy-book of electricity like this had fallen into the hands of ,thomas ,a4 ,edison when he was a newsboy on the ,grand ,trunk ,railway1 or when he was a telegraph operator1 he would have devoured it with the utmost eagerness4 ,to be sure1 at that time1 in the early sixties1 all that we knew of electricity and its applications could have been told in a very brief compass4 ,it was an almost unknown field1 and the crude form of the telegraph then in use represented its most important application4 ,there were no electric lights2 there was no telephone or phonograph2 there were no electric motors4 ,telegraphing1 itself1 was a slow and difficult process4 ,all the conditions were as far removed as possible from the broad field of applied electricity indicated in this book4 ,but this does not mean that we have now accomplished all that there is to be done4 ,on the contrary1 the next half-century will be full of wonderful advances4 ,this makes it more than ever essential that we should become acquainted with the principles and present conditions of a science which is being applied more and more closely to the work of every-day life4 ,it is necessary to know this from the inside1 not simply from general descriptions4 ,theory is all very well1 but there is nothing like mastering principles1 and then applying them and working out results for one's self4 ,any active and intelligent boy with an inquiring mind will find a new world opened to him in the satisfaction of making electrical devices for himself according to the suggestions given in this book4 ,this will show him the reasons for things in concrete form1 will familiarize him with principles1 and will develop his mechanical ingenuity4 ,he may be laying the foundation for inventions of his own or for professional success in some of the many fields which electricity now offers4 ,work of this kind brings out what is in one1 and there is no satisfaction greater than that of winning success by one's own efforts4 ,the boy who makes a push-button for his own home1 or builds his own telephone line or wireless telegraph plant1 or by his own ingenuity makes electricity run his mother's sewing-machine and do other home work1 has learned applications of theory which he will never forget4 ,the new world which he will enter is a modern fairyland of science1 for in the use of electricity he has added to himself the control of a powerful genie1 a willing and most useful servant1 who will do his errands or provide new playthings1 who will give him manual training and a vast increase in general knowledge4 ,the contents of this book1 ranging from the preparation of simple cells to the making of dynamos and motors1 and the delightful possibilities of electro-plating1 shows the richness of the field which is made accessible by ,mr4 ,adams' practical explanations1 his carefully tested working plans1 and his numerous and admirable drawings--all of which have been made for this book4 ,it is in keeping with the practical character of the ,electricity ,book that pains are taken throughout to show the simplest and most inexpensive way of choosing materials and securing results4 ,the actual working out of these directions can be done at very small expense4 ,furthermore1 there need be no concern whatever as to possible danger if the book is read with reasonable intelligence4 ,mr4 ,adams has taken pains to place danger-signals wherever special precautions are advisable1 and1 as a father of boys who are constantly working with electricity in his laboratory1 he may be relied upon as a safe and sure counsellor and guide4 ,while this book shows boys what they can do themselves1 its scope has been enlarged by ,mr4 ,baker's chapter explaining briefly the working of electricity all about us1 in light and heat1 in the trolley-car1 and other daily applications4 ,in addition1 ,mr4 ,adams has prepared a ,dictionary of ,electrical ,terms1 and these brief definitions will be found peculiarly helpful in the first reading of the book4 ,it is believed that there is no book in this particular field comparable to ,harper's ,electricity ,book in its comprehensiveness1 practical character1 and the number and usefulness of its illustrations4 ,it follows the successful ,out-door ,book for ,boys in ,harper's series of ,practical ,books for ,boys1 and it will be followed by ,how to ,understand ,electrical ,work1 a book1 not of instructions in making electrical apparatus1 but of explanations of the commercial uses of electricity all about us4 ,part ,i ,,electricity ,,book ,,for ,,boys ,chapter ,i ,,some ,,general ,,explanations ,we are living in the age of electricity1 just as our fathers lived in the age of steam4 ,electricity is the world-power1 the most powerful and terrible of nature's hidden forces4 ,yet1 when man has learned how to harness its fiery energies1 electricity becomes the most docile and useful of his servants4 ,unquestionably1 electricity is to-day the most fascinating and the most profitable field for the investigator and the inventor4 ,the best brains of the country are at work upon its problems4 ,new discoveries are constantly being recorded1 and no labor is thought too great if it but add its mite to the sum total of our knowledge4 ,and yet1 ridiculous as the statement may seem1 we do not know what electricity is4 ,we only know certain of its manifestations--what it can do4 ,all we can say is that it does our bidding2 it propels our trains1 lights our houses and streets1 warms us1 cooks for us1 and performs a thousand and one other tasks at the turn of a button or at the thrust of a switch4 ,but what it is1 we do not know4 ,electricity has no weight1 no bulk1 no color4 ,no one has seen it2 it cannot be classified1 nor analyzed1 nor resolved into its ultimate elements by any known process of science4 ,we must content ourselves with describing it as one manifestation of the energy which fills the universe and appears in a variety of forms--such as heat1 light1 magnetism1 chemical affinity1 and mechanical motion4 ,in all probability it is one of those phenomena of nature that are destined to remain forever secret4 ,thus it stands in line with gravitation1 magnetism1 the active principle of radium1 and the perpetual motion of the solar system4 ,electricity was known to the early ,greeks2 indeed1 it derives its name from the ,greek word for amber 7electron74 ,for many centuries amber was credited with certain special or magical powers4 ,when it was rubbed with a flannel cloth1 8the hidden spirit0 came out and laid hold of small detached objects1 such as bits of paper1 thread1 chips1 or pith-balls4 ,no one could explain this phenomenon4 ,it was looked upon with superstitious awe and the amber itself was regarded as possessing the special attributes of divinity4 ,but as time went on1 it was discovered that in various other substances this mysterious attractive power could be excited1 at will1 through the agency of friction4 ,rubbing a piece of glass rod with silk or leather generated an 8electricity0 identical with that of the amber2 or the same result could be obtained by exciting hard rubber with catskin4 ,the conclusion followed that electricity was not a property of the special materials employed to generate it1 but that it came from without1 from that great reservoir of energy1 the atmosphere4 ,then came ,franklin with his experiment of the kite1 and the invention of the ,leyden-jar and the chemical production of the electric fluid by means of batteries4 ,it was shown that the properties of the new and strange force were the same1 whether it was produced by the static 7frictional7 process or by the galvanic 7chemical7 method4 ,electrical science as a science1 had begun4 ,and yet1 for many years1 electricity was hardly more than a scientific toy4 ,it was not supposed to possess any practical usefulness4 ,the entertaining experiments with the static machine and the ,leyden-jar 7chapter xiii47 were confined to the laboratory and the lecture hall4 ,electricity was an amusing display of unknown energy1 but no one ever dreamed that it could ever be made to serve the practical ends of life4 ,it was not until about #ahej that electrical science became anything more than a name4 ,the galvanic and voltaic batteries 7chapter ii47 opened the way for 8current0 electricity1 which flowed continuously1 instead of jumping and disappearing like the spark from a ,leyden-jar4 ,when the continuous current became an established fact1 the telegraph and telephone headed the line of a long series of developments4 ,finally1 the generation of electricity in greater volume1 and cheaply1 made possible the application of its power for heating1 light1 traction1 and the other forms of activity in which it now does so large a share of the world's work4 ,how electricity works is a question often asked1 but not easily answered4 ,there are certain so-called laws1 but we shall best arrive at a conclusion by simply stating a few of the facts that have been established through the observation and investigation of scientists and electrical engineers4#a #a ,explanations of any technical names or phrases used in the text will be found in the simple dictionary of electrical terms which appears as an appendix4 ,for example1 electricity is always alert1 ready to move1 and continually on the lookout for a chance to obtain its freedom4 ,it will never go the longest way round if there is a short cut2 and it will heat1 light1 or fuse anything in its path that is too weak to carry or resist it4 ,for this reason1 it must be generated in small volume--that is1 just sufficient to do the work required of it4 ,if produced in larger volume1 it must be held in check by resistance1 and only so much allowed to escape as may be needed for the specified work4 ,again1 when electricity is generated this must be done in one of two ways--by friction or chemically4 ,but in both processes there must be air surrounding the generators1 and the fluid must be of a nature through which oxygen and hydrogen can circulate freely4 ,water fluids are suitable for this purpose1 but oils cannot be used1 as they contain hydro-carbon in large quantities and are non-conductors4 ,batteries are chemical generators1 dynamos are magneto-electric1 and static machines are frictional4 ,now the theory is that electricity is drawn from the ether and1 in its normal state1 is quiet4 ,if it be disturbed and collected by mechanical or chemical means1 it is always on the alert to escape and again take its place in the atmosphere4 ,as its volume is increased1 so its energy to get away is multiplied1 and this energy may be transformed1 at will1 into power1 heat1 or light4 ,to express the idea in the simplest language1 it wants to go home1 and in its effort to do so it expresses itself in the form of stored-up power1 precisely like water behind a dam4 ,it is for man's cunning brain to devise all sorts of tasks that this power must perform before it can gain its release4 ,it can't go home until its work is done4 ,nearly every boy has experimented1 at one time or another1 with electricity and electrical apparatus1 and whether it was with some of the simple frictional or galvanic toys1 or with the more complicated induction-coils and motors1 he has undoubtedly found it a most interesting amusement and an ever new and widening field for study4 ,then again1 many boys would like to know something about simple electrical apparatus and how to make and use it4 ,but his school-books relating to the general subject of electricity are hardly definite enough to serve as a practical manual4 ,and yet there are many things in the way of electrical machinery and equipment that a boy can easily construct and use4 ,in this book it is my purpose to show him just what can be done with the aid of the tools that are usually in his possession4 ,while some things may have to be purchased from an electrical supply-house or other sources1 there is still much material to be found about the house that may be put to good use by the amateur electrician4 ,it is not possible or desirable to describe every variety of electrical equipment4 ,we must confine ourselves to apparatus which can be readily understood and operated4 ,the 8practical0 idea is the one to be borne in mind4 ,this book shows a boy how to use his brains and the simple tools and material that may be at his command4 ,care and thought in the construction of the apparatus are the important qualifications for success4 ,the instructions are given in the clearest possible language2 the diagrams and drawings are intelligible to any one who will take the trouble to study them4 ,if your finished apparatus does not work properly1 read the description again and see if you have not made some error4 ,a misplaced or broken wire1 a wrong connection1 or a short circuit will mean all the difference between success and failure4 ,save in one short chapter1 static or frictional electricity 7see ,appendix7 is not considered2 for outside of laboratory experimenting and electro-medical apparatus1 frictional electricity is but a toy--interesting and useful when generated in small volume1 but very dangerous and difficult of control when in great volume4 ,for example1 the bolt of lightning is but the many times multiplied spark stored in the ,leyden-jar by the static machine4 ,for all practical purposes1 galvanic electricity1 in its various phases of direct and alternating current1 meets the requirements of man4 ,with the improved apparatus and the rapid advancement along the line of invention1 electricity is as easily controlled to-day as steam--in fact1 its economical use is even more fully under control and its adaptability more practical4 ,in the following pages there are probably illustrations and descriptions of many things that will seem strange to the boy who has not heard of them2 but if a book were written each year on the subject of electricity1 every new one would include principles and facts not known before4 ,the field of electrical research is so broad and so many are working in it that new discoveries are being made continually4 ,to those familiar with the application of electricity1 it is clearly evident that1 as yet1 we are only beginning to deal with this unknown force4 ,for generations to come1 developments will take place and invention follow invention until electricity assumes its rightful place as the motive force of the world4 ,to the boy interested in this subject a wide field is open1 and the youth of to-day1 who are taking up this study1 are destined to become the successful electrical engineers and inventors of the future4 ,there is no better education for any boy1 in the application and principles of electricity1 than to begin at the very bottom of the ladder and climb up1 constructing and studying as he progresses4 ,when he attempts to design more technical and difficult apparatus the lessons learned in a practical way will be of inestimable value1 greater by far than any theoretical principles deduced from books2 he knows his subject from the ground up2 he understands his machine because he has constructed it with his own hands4 ,as ,i have said already1 the necessary tools are few in number and not expensive4 ,they may include a hammer1 a plane1 awls1 pliers1 wire-cutters1 and tin-shears4 ,the raw material is also cheap--lead1 tin1 wire1 wood1 and simple chemicals4 ,the laboratory may be a corner in the attic1 or even in a boy's bedroom1 so far as the finer work is concerned1 while the hammering and sawing may be done in the cellar4 ,the other best plan1 of course1 is to get the use of a spare room which may be fitted with shelves1 drawers1 and appliances for serious work4 ,to enthusiastic beginners1 as well as to those who have had some experience in electricity1 a needed warning may be given in three words3 8,take no chances40 ,electricity1 the subtle1 stealthy1 and ever-alert force1 will often deal a blow when least expected4 ,for that reason1 a boy should never meddle with a high-tension current or with the mains from dynamos4 ,the current in the house1 used for lighting1 cooking1 or heating purposes1 is always an attractive point for the young electrician1 but the wires should never be touched in any way4 ,too many accidents have happened1 and the conductors1 lamp-sockets1 and plugs should be carefully avoided4 ,the boy should keep strictly to his batteries1 or small dynamos run by water-power from a faucet2 in no case should the wire from power-houses be tampered with4 ,one little knows what a current it may be carrying and what a death-dealing force it possesses4 ,always bear in mind that a naked wire falling from a trolley equipment carries enough force to kill anything it strikes4 ,special attention is called to the dictionary of electrical terms given in the ,appendix4 ,the young student should never pass over a word or a term that he does not thoroughly understand4 ,always look it up at once and every time it occurs1 until you are sure that its meaning is fixed in your mind4 ,this is an education in itself1 at least so far as the theoretical knowledge of our subject is concerned4 ,as a final word1 ,i should like every boy interested in electricity to hear what ,thomas ,a4 ,edison once said to me when ,i was a boy working in his laboratories4 ,i often recall it when things do not go just right at first4 ,i asked the great inventor one day if invention was not made up largely of inspiration4 ,he looked at me quizzically for a moment1 and then replied3 8,my boy1 ,i have little use for a man who works on inspiration4 ,invention is two parts inspiration and ninety-eight per cent4 perspiration40 ,you will never get what you are after unless you work hard for it4 ,you must stick to it until you produce results4 ,if the history of the world's most valuable inventions could be fully known1 the fact would be clearly established that the vital spark of inspiration is but the starting-point4 ,then follow the days1 weeks1 and sometimes years of industrious toil1 failures1 and disappointments1 until finally the desired end is attained4 ,one must work for success2 there is no other means of winning it4 ,as the table of contents shows1 ,part ,i4 of this book explains principles and the simpler forms of electrical appliances4 ,from this we advance to ,part ,,ii41 which deals with more complex forms of electrical work1 most of which1 however1 are within the reach of intelligent boys who have followed the chapters carefully from the first4 ,in a final chapter we have simple explanations of the great commercial uses of electricity1 which we see all about us1 although very few of us have a clear idea as to their operation4 ,chapter ,,ii ,,cells ,,and ,,batteries ,simple ,cells ,in order to generate electricity it is necessary to employ cells1 batteries1 or dynamos4 ,since the construction and operation of a dynamo is somewhat intricate1 it will be better to start with the simpler methods of electric generation1 and so work up to the more complicated forms4 ,for small apparatus1 such as electric bells and light magnets and motors1 the zinc-carbon-sal-ammoniac cell will answer very well2 but for larger machinery1 where more current is required1 the bluestone and the bi-chromate batteries will be found necessary4 ,illustration3 ,,fig4 #a ,,fig4 #b ,,fig4 #c ,,fig4 #e ,,simple ,,battery ,,elements ,a simple and inexpensive cell may be made from electric-light carbons1 with the copper coating removed1 and pencils of zinc1 such as are used for electric-bell batteries and which can be purchased for five cents each4 ,copper wire is to be bound around the top of each pencil of carbon and zinc1 and firmly fastened with the pliers1 so that it will not pull off or become detached4 ,it will be well to cut a groove with a file around the top of both the carbon and zinc1 into which the wire will fit4 ,the elements should then be clamped between two pieces of wood and held with screws1 as shown in ,fig4 #a4 ,a more efficient carbon pole is made by strapping six or more short carbon pencils around one long one1 as shown in ,fig4 #c4 ,the short pieces of electric-light carbons are bound to the longest carbon with heavy elastic bands1 or cotton string dipped in paraffine or wax1 to make the cotton impervious to water and the sal-ammoniac solution4 ,another arrangement of elements is shown in ,fig4 #b1 where a zinc rod is suspended between two carbons1 the carbons being connected by a wire that must not touch the zinc4 ,a fruit-jar1 or a wide-necked pickle-bottle1 may be employed for a cell1 but before the solution is poured in1 the upper edge of the glass should be coated with paraffine4 ,this should be melted and applied with a brush1 or the edge of the glass dipped in the paraffine4 ,the solution is made by dissolving four ounces of sal-ammoniac in a pint of water1 and the jar should be filled three-fourths full4 ,in this solution the carbons and zinc may be suspended1 as shown in the illustration 7,fig4 #d7 of the sal-ammoniac cell4 ,the wood clamps keep the carbon and zinc together1 and the extending ends rest on the top of the jar and hold the poles in suspension4 ,plates of zinc and carbon may be clamped on either side of a square stick and suspended in the sal-ammoniac solution1 as shown in ,fig4 #e1 taking care1 however1 that the screws used for clamping do not touch each other4 ,if one cell is not sufficiently powerful1 several of them may be made and coupled up in series--that is1 by carrying the wire from the zinc of one to the carbon of the next cell1 and so on to the end1 taking care that the wire from the carbon in the first cell and that from the zinc of the last cell will be the ones in hand1 as shown in ,fig4 #f4 ,this constitutes a battery4 ,be sure and keep the ends of the wire apart1 to prevent galvanic action and to save the power of the batteries4 ,this battery is an excellent one for bells and small experimental work1 and when inactive the zincs are not eaten away 7as they would be if suspended in a bi-chromate solution71 for corrosion takes place only as the electricity is required1 or when the circuit is closed4 ,a series of batteries of this description will last about twelve months1 if used for a bell1 and at the end of that time will only require a new zinc and fresh solution4 ,the cell in which the plates shown in ,fig4 #e are used may contain a bi-chromate solution2 and for experimental work1 where electricity is required for a short time only1 this will produce a stronger current4 ,but remember that the solution eats the zinc rapidly1 and the plates must be removed as soon as you have finished using them4 ,the bi-chromate solution is made by slowly pouring four ounces of commercial sulphuric acid into a quart of cold water4 ,this should be done in an earthen jar1 since the heat generated by adding acid to water is enough to crack a glass bottle4 ,never pour the water into the acid4 ,when the solution is about cold1 add four ounces of bi-chromate of potash1 and shake or mix it occasionally until dissolved2 then place it in a bottle and label it3 ,,bi-,,chromate ,,battery ,,fluid ,,poison ,before the zincs are immersed in the bi-chromate solution they should be well amalgamated to prevent the acid from eating them too rapidly4 ,the amalgamating is done by immersing the zincs in a diluted solution of sulphuric acid for a few seconds1 and then rubbing mercury 7quicksilver7 on the surfaces4 ,the mercury will adhere to the chemically cleaned surfaces of any metal except iron and steel1 and so prevent the corroding action of the acid4 ,do not get on too much mercury1 but only enough to give the zinc a thin coat1 so that it will present a silvery or shiny surface4 ,a two-fluid cell is made with an outer glass or porcelain jar and an inner porous cup through which the current can pass when the cup is wet4 ,fig4 #g4 ,illustration3 ,,fig4 #d ,illustration3 ,,fig4 #g ,illustration3 ,,fig4 #h ,illustration3 ,,fig4 #f ,a porous cup is an unglazed earthen receptacle1 similar to a flower-pot1 through which moisture will pass slowly4 ,the porous cup contains an amalgamated plate of zinc immersed in a solution of diluted sulphuric acid--one ounce to one pint of water4 ,the outer cell contains a saturated solution of sulphate of copper in which a cylindrical piece of thin sheet-copper is held by a thin copper strap1 bent over the edge of the outer cell4 ,a few lumps or crystals of the copper sulphate1 or bluestone1 should be dropped to the bottom of the jar to keep the copper solution saturated at all times4 ,when not in use1 the zinc should be removed from the inner cell and washed off2 and if the battery is not to be employed for several days1 it would be well to pour the solutions back into bottles and wash the several parts of the battery1 so that it may be fresh and strong when next required4 ,when in action1 the solutions in both cups should be at the same level1 and be careful never to allow the solutions to get mixed or the copper solution to touch the zinc4 ,coat the top of the porous cell with paraffine to prevent crystallization1 and also to keep it clean4 ,take great care1 in handling the acid solutions1 to wear old clothes1 and do not let the liquids spatter1 for they are strong enough to eat holes in almost anything1 and even to char wood4 ,the two-fluid cells are much stronger than the one-solution cells1 and connected up in series they will develop considerable power4 ,for telegraph-sounders1 large electric bells1 and as accumulators for charging storage-batteries1 the gravity-cell will give the most satisfactory results4 ,the one shown in ,fig4 #h consists of a deep glass jar1 three strips of thin copper riveted together1 and a zinc crow-foot that is caught on the upper edge of the glass jar4 ,these parts will have to be purchased at a supply-house1 together with a pound or two of sulphate of copper 7bluestone74 ,to set up the cell1 place the copper at the bottom and drop in enough of the crystals to generously cover the bottom1 but do not try to imbed the metallic copper in the crystals2 then fill the jar half full of clear water4 ,in another jar dissolve two ounces of sulphate of zinc in enough water to complete the filling of the jar to within two inches of the top2 then hang the zinc crow-foot on the edge of the jar so that it is immersed in the liquid and is suspended about three inches above the top of the copper strip4 ,the wire that leads up from the copper should be insulated with a water-proof coating and well covered with paraffine4 ,a number of these cells may be connected in series to increase the power of the current1 and for a working-battery this will show a high efficiency4 ,note that at first the solutions will mingle4 ,to separate them1 join the two wires and start the action2 then1 in a few hours1 a dividing line will be seen between the white1 or clear1 and the blue solutions1 and the action of the cell will be stronger4 ,after long-continued use it may be necessary to draw off some of the clear zinc sulphate1 or top solution1 and replace it with pure water4 ,the action of the acids reduces the metallic zinc to zinc sulphate and deposits metallic copper on the thin copper strips1 and in this process an electrical current is generated4 ,a ,plunge-battery ,when two or more cells 7in which sulphuric acid1 bi-chromate of potash1 or other strong electropoions are employed7 are coupled in series1 it would be well to arrange the copper and zinc1 or the zinc and carbon1 poles on a board1 so that all of them may be lowered together into the solutions contained in the several jars4 ,a simple arrangement of this kind is shown in ,fig4 #i1 where a rack is built for the jars and at the top of the end boards a projecting piece of wood1 supported by a bracket1 is made fast4 ,a narrow piece of board nearly the length of the jar-rack is fitted with the battery-poles1 as shown at ,fig4 #i ,a4 ,the carbon and zinc1 or copper and zinc1 poles are attached to small blocks of wood 7as described for ,fig4 #e71 and this block in turn is fastened to the under side of the board with brass screws4 ,the poles of the cells are to be connected 7as explained in ,fig4 #f71 and when the battery is in use the poles are immersed in the solution contained in the jars4 ,when the battery is at rest the narrow board should be lifted up and placed on the projecting arms of the rack1 so that the liquid on the poles may drain into the jars directly underneath4 ,one or more of these battery-racks may be constructed1 but they cannot be made to hold conveniently more than four or six cells each2 if more cells are required1 those contained in each rack must be coupled up in series4 ,illustration3 ,,fig4 #i ,illustration3 ,,fig4 #aj ,a simpler plunge-battery is shown in ,fig4 #aj4 ,a cell-rack is made of wood and given two or three coats of shellac4 ,the narrow board 7to the under side of which the battery-poles are attached1 as explained in ,fig4 #i7 is hung on chains or flexible wires1 which in turn are made fast to an iron shaft running the entire length of the cell-rack4 ,this shaft is of half-inch round iron1 and is held in place1 at one end1 by a pin and washer2 while at the other the end is filed with a square shoulder1 and a handle and crank is fitted to it1 so that the shaft may be turned4 ,a small hole1 made at the side of the crank when it is hanging down1 will receive a hard-wood peg1 or a steel nail1 and this will prevent the crank from slipping when the board holding the poles is raised4 ,if a gear-wheel and tongue can be had to fit on the shaft1 it will then be possible to check the shaft securely at any part of a turn of the crank4 ,the battery-poles are to be connected in series along the top of the portable board1 as explained for ,fig4 #f4 ,when two or more of these plunge-batteries are used at one time1 the wire from the carbon of one is to be connected with the zinc pole of the next1 and so on4 ,the wire from the zinc of the first battery1 and the wire from the carbon of the last battery1 will be the ones available for use4 ,a ,storage-battery ,when more current is desired than the simple batteries will give1 a storage-battery should be employed as an accumulator4 ,this result can be secured by coupling primary cells in series1 so that they will be constantly generating and feeding the battery4 ,storage-batteries are too heavy to be shifted about1 like single cells or small plunge-batteries2 they should be placed in a cellar1 where the charging or primary cells can be located close by1 and1 unless positively necessary1 the battery of cells and the accumulator should not be moved4 ,with sufficiently large insulated wires 7,nos4 #ab1 #ad1 or #af copper71 the current may be carried to any part of the house for use in various ways--such as running a light motor or a fan1 lighting a lamp-circuit1 or fusing metals and chemicals for experimental purposes4 ,while the battery to be described is not a light one in weight1 nor as economical as the improved new ,edison storage-battery1 it is a good and constant one1 and1 if not overcharged or abused1 will last for several years4 ,the component parts of a storage-battery are lead in metallic and chemical form1 the electrolyte1 or fluid1 in which the plates are immersed1 and the water-tight and chemical-proof cell or container4 ,from a plumber1 a supply-house1 or a lead-works1 obtain a quantity of three-eighth by one-quarter-inch strip-lead of the kind called chemical1 or desilverized2 also a larger quantity of lead-tape1 one-sixty-fourth of an inch thick and three-eighths of an inch wide4 ,this last is also known as torpedo-lead1 and is kept by electrical supply-houses4 ,if the three-eighths by quarter-inch strip-lead cannot be had1 then purchase eight or ten pounds of heavy sheet-lead1 and1 with a tin-shears1 divide it into strips three-eighths of an inch wide and twenty-nine inches long1 taking care to cut it of uniform width and with true edges4 ,from hard-wood three-eighths or half an inch thick1 cut a block six by seven inches and make four countersunk holes in it1 so that it may be screwed fast to a table or bench1 as shown in ,fig4 #aa ,a4 ,around this the lead strips should be shaped and beaten at the corners to make the angles sharp4 ,from the three-eighths by quarter-inch1 or sheet-lead strips1 make seven frames as shown in ,fig4 #ab4 ,this is done by binding a strip of the lead around the block1 as shown at ,fig4 #aa ,b4 ,where the ends come together insert a short piece of lead1 three-eighths or half-inch1 as shown at ,fig4 #ab ,a1 and solder it fast4 ,a soldering-iron may be heated with a ,bunsen-burner gas-flame or in a charcoal fire4 ,however1 if gas is available1 it would be better to use the blue flame from a ,bunsen burner and direct the hot blast directly on the work with a blow-pipe1 and so fuse the lead points together4 ,after a little practice with the blow-pipe it will be used for many pieces of work in preference to the soldering-iron4 ,if the sheet-lead is used for the frames in place of the three-eighths by quarter-inch strips1 two or three strips will have to be taken1 so as to build up the band of the frame to about a quarter of an inch in thickness4 ,when soldered together1 or fused at the edges1 these built-up frames will be as rigid as the solid metal4 ,illustration3 ,,fig4 #aa ,illustration3 ,,fig4 #ab ,illustration3 ,,fig4 #ac ,now cut a number of strips of the thin lead-tape six inches and a half long1 and others that will necessarily be somewhat longer1 for each frame is to be filled with straight and crimped pieces1 as shown in ,fig4 #ac4 ,if there is a fluting-iron in the house1 the crimping may be done in the brass gears at one end of the machine4 ,or two wheels may be cut from hard-wood with a fret-saw1 and made fast to a block with screws1 as shown in ,fig4 #ad4 ,a handle1 attached to one wheel1 will make it possible to turn the gears2 and they should be placed just far enough apart to allow the tape to pass through without tearing or squeezing4 ,put a washer between the wheel and the block to prevent friction4 ,when a frame is in the position shown in ,fig4 #ac1 and lying on a piece of slate or flat stone1 you will first put in a crimped piece of tape1 as shown at ,fig4 #ac ,a1 and under this arrange a straight piece 7,fig4 #ac ,b72 then1 with the blow-pipe and flame1 fuse fast to the frame and catch the flutes of the crimped piece to the straight one every inch or two4 ,add alternate crimped and straight strips until the frame is filled and presents the appearance of ,fig4 #ac4 ,when the seven frames are ready1 lay three of them aside for the positives and four for the negatives4 ,note that the positives are red and the negatives a dark yellow when they are filled with the active material4 ,there are several methods of depositing the active material in the mesh or net-work of the plates1 but some of them are too technical1 others too complicated1 and still others require charging machinery4 ,the following plan will be the simplest and easiest for the amateur3 ,at a paint-store1 or from a wholesale druggist1 obtain several pounds of oxide of lead 7red-lead7 and a similar quantity of litharge 7yellow-lead74 ,in an earthen vessel1 or large jar1 make a solution composed of water1 twenty ounces1 and commercial sulphuric acid1 two ounces4 ,this is the mixture commonly known as 8one to ten40 ,place some red-lead 7dry7 in an old saucepan or soup-plate1 and add a little of the acid solution3 then1 with an old table-knife or small trowel1 mix the lead into a stiff paste1 like soft putty4 ,do not get it too thin or it will run2 nor too thick1 as then it will not properly adhere to the lead-mesh of the frames4 ,with the frame lying on its side1 plaster in the red composition between the flutes and fill up the frame solid with it4 ,treat all three of the positive frames in the same manner1 taking care that the exposed surfaces of the composition-filling is smooth and flush with the edges of the lead frame and mesh4 ,do not disturb these plates for a while1 but let them remain in position1 so as to set and partially dry4 ,add acid solution to the yellow-lead in a similar manner1 and fill the four negative plates4 ,when partially dry1 the plates will be ready to combine in a pile4 ,illustration3 ,,fig4 #ad ,illustration3 ,,fig4 #ae ,illustration3 ,,fig4 #af ,illustration3 ,,fig4 #ag ,at a supply-house obtain some sheets of cellulous fibre1 three-sixteenths of an inch thick1 or some asbestos cloth4 ,if neither can be had1 then soak some pieces of ordinary brown card-board in a solution of silicate of soda and let them dry4 ,lay a negative 7yellow7 plate on the table with the lug at the left 7,fig4 #ac ,c74 ,on this place a square of the fibre1 asbestos1 or card-board2 and on top of it lay a positive 7red7 plate with the lug at the right side4 ,continue in this manner until the seven plates are stacked1 the four negative lugs being at the left and the three positives at the right4 ,tie the plates securely together with cotton string bound about them in both directions2 then stand the pile up so that the lugs are at the top1 as shown at ,fig4 #ae1 with every alternate lug in an opposite direction4 ,obtain two lead bars three-eighths of an inch square1 or cut strips from the sheet-lead and solder them together1 turning the ends as shown at ,fig4 #ac ,d4 ,drop one of these bars into the lugs of the positive plates1 as shown in ,fig4 #ae ,h1 and solder it fast at the three unions4 ,repeat this with the other bar in the lugs of the negative plates1 and the pile will then be ready for immersion in the electrolyte4 ,to both ends of each plate-bar solder binding-posts1 so that the conductor-wires can be attached at one end and the feed-wires at the other4 ,if a hard rubber or glass cell can be had for the battery so much the better2 if not1 a stout box may be made from pine1 white-wood1 or cypress1 and thoroughly coated with asphaltum varnish or asphaltick4 ,at an electrical supply-house you can purchase some 8,p and ,b0 compound1 which is acid and water proof4 ,this is excellent for the inside coating as well as for the outside of the box4 ,the box should be made of wood not less than three-quarters of an inch thick1 and the sides1 ends1 and bottom should be in one piece1 free from knots1 sappy places1 or cracks4 ,brass screws should be used to hold the boards together1 and before the joints are made the butt-ends of wood and the sides1 against which they impinge1 must be thoroughly coated with the asphaltum or compound4 ,put together the four sides first and then make the bottom fast1 placing the screws two inches apart and countersinking the wood1 so that the screw-heads will lie flush1 as shown in ,fig4 #af4 ,the box should be large enough to allow about one inch of space all around the pile1 and deep enough for the solution to cover the plates and two inches of space above it to the top edge of the cell4 ,the complete storage-battery will then appear as shown in ,fig4 #ag4 ,the electrolyte is composed of sulphuric acid and water in the proportion of one ounce of acid to four of water1 making a five-part solution4 ,this should be mixed in an earthen or glass jar1 and the acid poured slowly into the water1 the latter being stirred while the acid is added4 ,when the solution cools 7for adding acid to water creates heat71 add about two ounces of bicarbonate of soda1 and mix the solution thoroughly4 ,when the pile is in place within the box 7having first removed the string which bound the plates together7 pour the electrolyte slowly into the cell1 taking care that none of it spatters1 for it will eat clothing or anything else that it touches4 ,before placing the pile1 or electrolyte1 in the box1 it should be thoroughly tested for leaks by allowing water to stand in it for several days4 ,indeed1 you should be very generous with the asphaltum1 or compound1 when coating the angles and points inside the box2 for if the acid solution gets at the screws it will corrode them and the box will soon leak and fall apart4 ,as a precaution against the acid working over the top of the box1 the upper edge1 for an inch or two1 should be coated with paraffine over the asphaltum or acid-proof coating4 ,a cell constructed in this way should accumulate about two volts and one hundred ampere-hours1 and will run a one-sixteenth horse-power motor4 ,the expense of making these plates is about twenty-five cents each1 and1 including the cell and coating materials1 each storage-battery will cost approximately two dollars4 ,the lasting qualities of the battery depend on the use or abuse it is put to2 but with ordinary care it should last from three to five years4 ,when the battery ceases to accumulate properly the pile should be removed1 and1 after washing it thoroughly1 the bars should be cut away and new positive plates made and installed4 ,the positive plates are the ones that deteriorate and need replacing2 the negatives are almost everlasting1 and with proper usage will live for fifteen or twenty years4 ,directly the electrolyte is in the cell1 connect the poles of your primary cells so as to begin the accumulation of current4 ,never exhaust the charge of electricity from your storage-cell1 and never leave it uncharged when the electrolyte is in1 or the plates will be ruined4 ,a battery consisting of from five to twenty bluestone cells will be the best with which to charge this accumulator2 and if more than one cell is desired1 any number of them can be made and coupled up in series4 ,take care1 when connecting the wires from the primary cells1 to see that the positive wire is connected with the positive plates and the negative with the lead bar joining the yellow plates4 ,if by accident you should make a misconnection1 bubbles will rise from the electrolyte4 ,this is not right1 so reverse the wires and the accumulation of current will then take place without agitation in the cell4 ,dry-cells and ,batteries ,dry-cells are extensively used nowadays1 since their cleanliness1 high efficiency1 and low internal resistance make them preferable to the ,leclanch and other open-circuit batteries for bells1 annunciators1 and other light work4 ,in the dry-cell1 the electrolyte1 instead of being a liquid1 is a gelatinous or semi-solid mass1 which will not run nor slop over4 ,when the capping of pitch or tar is in place1 the cell may be placed in any position1 with full assurance that the electrolyte will not become displaced nor run out4 ,dry-cells may be made of almost any size for convenience of handling1 but those commonly used vary from one to four inches in diameter1 and from four to fifteen inches high4 ,for bells and general electric work1 a cell two inches and a half in diameter and seven inches high will be found a convenient size to make and handle4 ,the component parts of a dry-cell are the cell itself 7which is made of zinc and acts as the positive pole71 the carbon1 the electrolyte or active excitant element1 and the pitch or tar cap to hold the electrolyte and carbon in place4 ,from a tinsmith obtain some pieces of sheet zinc1 and roll them into cylindrical form as shown in ,fig4 #ah ,a4 ,the sheets should measure seven by eight inches1 and when formed the edges are to be lapped and soldered4 ,illustration3 ,,fig4 #ah ,from a smaller piece of zinc cut round bottoms1 fit them in the cylinders and solder securely in place1 taking care to close up all seams or joints to prevent the escape of the electrolyte4 ,from a supply-house obtain battery-carbons1 one inch and a half wide by half or three-eighths of an inch thick and eight inches long4 ,these should be provided with a thumb-screw or small bolt and nut at the top so as to make wire connections with the carbon4 ,a strip of zinc should be soldered to the outside upper edge of the zinc cup to which wire attachments may be made with thumb-screws or small bolts and nuts4 ,when the parts are ready to assemble1 make a wooden mould or form a trifle larger than the carbon4 ,this is intended to act as a temporary plunger1 and is inserted1 at first1 in place of the carbon plate4 ,this wooden plunger should be smooth1 and given a coat of shellac to prevent it from absorbing any moisture4 ,insert the plunger in the zinc cup and support it so that it will be at least half an inch above the bottom and centred at the middle of the cup4 ,the electrolyte is then placed in the cup1 and1 when it has set a little1 the wooden plunger is removed and the carbon inserted in its place4 ,the electrolyte is composed as follows3 ,ammonium chloride #a part ,zinc chloride #a part ,plaster of ,paris #c parts ,flour part ,water #b parts ,mix these together and place the compound within the zinc cups1 so that the mass settles down and packs closely about the plunger4 ,the space left unfilled about the carbon should be filled with a mixture composed as follows3 ,ammonium chloride #a part ,zinc chloride #a part ,manganese binoxide #a part ,granulated carbon #a part ,flour #a part ,plaster of ,paris #c parts ,water #b parts ,these proportions may be measured in a tin cup1 a table-spoon1 or any other small receptacle4 ,note that the measurement by parts is always by bulk and not by weight4 ,do not fill the zinc cup to the top1 but leave an inch of space1 so that half an inch of sealing material may be added4 ,see that the inside top edge of the zinc cup is clean2 then melt some tar or pitch and pour it over the top of the electrolyte1 so that it binds the zinc cup and carbon into a solid form4 ,drive an awl down through the capping material when it is nearly dry1 and leave the holes open for the escapement of gases4 ,give the outer surface of the zinc cells a coat of asphaltum varnish1 and wrap several thicknesses of heavy paper about them to prevent contact and short-circuiting4 ,protect the bottoms in a similar manner1 and as a result you will have a cell that will appear as shown in ,fig4 #ah ,b4 ,a battery of cells powerful enough for any light work can be made by connecting the cells in series1 each having an electro-motive force of one and a half volts1 with an internal resistance of less than one-third of an ohm4 ,chapter ,,iii ,,push-,,buttons ,,and ,,switches ,push-buttons ,push-buttons and switches are a necessity in every home where electric bells1 lights1 or fans are used1 for with them connections are made or broken4 ,the telegraph-key and the commutators on a motor and dynamo are only improved forms of the push-button1 and this simple little device is really an indispensable part of any electrical equipment4 ,the simplest form of push-button is a bent piece of tin or thin sheet-metal screwed fast to a small block of wood1 as shown in ,fig4 #a4 ,under the screw-head one end of a wire is caught1 and the other wire end is secured by a washer and a screw driven into the block directly under the projecting end of the strip of metal4 ,by pressing a finger on the tin it is brought into contact with the screw-head under it1 and the circuit is closed2 on releasing it1 the tin flies up and the circuit is opened again4 ,an enclosed push-button is shown in ,fig4 #b4 ,it is made of the cover or body of a wooden box1 a spool-end1 and several other small parts4 ,a round piece of thin wood is cut to fit inside the box and so form the base for the button4 ,on this the spring strip is attached with screws1 and the wire ends are made fast1 as shown in ,fig4 #c4 ,the wires are carried through the bottom of the base and along grooves to the edge1 and thence to their final destination4 ,the end of a spool is cut off and glued to the top of the box1 as shown in ,fig4 #b1 and a hole is made in the box to correspond in size with that in the spool4 ,through this aperture the button 7cut from a wooden dowel or shaped out with a knife7 passes1 so that the end projects about a quarter of an inch beyond the spool4 ,to prevent the button from falling out1 a small steel nail should be driven across the inner end1 or a washer may be tacked to the end of the stick1 as shown in ,fig4 #d4 ,illustration3 ,,fig4 #a ,illustration3 ,,fig4 #b ,illustration3 ,,fig4 #c ,illustration3 ,,fig4 #d ,the button is mounted by screwing the base fast to the door or window casing1 it being understood that the wires have been first arranged in place4 ,the button is then set in the hole and the cap is placed over the base1 covering it completely4 ,by means of small screws1 passed through the rim of the box and into the edge of the base1 the cap is held in place4 ,a coat of paint or varnish will finish the wood-work nicely1 and this home-made button should then answer every requirement4 ,switches and ,cut-outs ,in electrical equipment and experimental work1 switches and cut-outs will be found necessary1 particularly so for telegraph and telephone lines4 ,care should be taken to construct them in a strong and durable fashion1 for they will probably be subjected to considerable wear and tear4 ,a simple switch 7,fig4 #e7 is made from a base-block of wood three inches long1 two wide1 and half an inch in thickness1 together with some small metal parts4 ,it has but one contact-point1 and that is the brass-headed tack 7,t in ,fig4 #e7 driven through the binding-post1 the latter being a small plate of brass1 copper1 or even tin screwed to the base-block4 ,the end of a wire is caught under the screw-head before it is driven down4 ,a similar binding-post is arranged at the lower side of the block1 and the movable arm is attached to it with a screw4 ,between the arm and the post-plate there should be a small copper washer1 to make it work more easily4 ,the arm is cut from a thin piece of hard sheet brass or copper 7tin or zinc will also answer very well71 and at the loose end the half of a small spool is attached1 with a brass screw and washer1 to serve as a handle4 ,the end of the screw that passes through a hole in the arm is riveted to the under side to hold it securely in place4 ,this arrangement is shown in ,fig4 #f4 ,illustration3 ,,fig4 #e ,illustration3 ,,fig4 #f ,illustration3 ,,fig4 #g ,illustration3 ,,fig4 #h ,illustration3 ,,fig4 #i ,the under edges of the arm may be slightly bevelled with a file1 so that it will slip up easily on the oval head of the brass tack4 ,the drawing shows an open switch2 when the circuit is closed the arm rests on the tack-head4 ,by means of small screws this switch-board may be fastened to a table or to any part of the wood-work in a house4 ,in ,fig4 #g a complex switch is shown4 ,this is the principle of the shunt-box switch1 of the resistance-coil1 and also of the commutators of a motor4 ,a motorman's controller on a trolley-car is a good example of the shunt1 and1 with it and the resistance-coils1 the car can be started1 stopped1 or run at any speed1 according to the current that is admitted to the motor4 ,the complex switch is made in the same manner as described for the single switch1 except that any number of binding-posts may be employed1 arranged on a radial plan1 so that the end of the arm will rest on any tack-head at will4 ,bells in various parts of the house may be rung by this switch1 or it may be coupled with a series of resistance-coils to control any amount of current4 ,the simple cut-out 7,fig4 #h7 is constructed in the same manner as the simple switch1 except that there are two points of contact instead of one4 ,this is the principle of the telephone and telegraph instrument wiring1 so that a bell or sounder may be rung from a distance4 ,the arm is then thrown over and the bell cut out1 allowing the 8phone0 or key to be brought into use4 ,in lifting the transmitter from the hook on a telephone1 a cut-out is operated and the bell circuit is thrown out of action4 ,it is in operation again directly the transmitter is returned to the hook4 ,the switch cut-out 7,fig4 #i7 is inactive when the arm is in the position shown in the illustration2 but when it is thrown over 7as shown by the dotted line7 it connects the poles at opposite ends of the board4 ,it may be thrown over in both directions1 and is a useful switch for many purposes4 ,for strong currents the lever-switch1 that rests on a brass tack-head1 will not be suitable1 as the switch-bar must be held firmly in place to make a perfect connection4 ,strong currents throw weak switches open1 causing an open or broken circuit4 ,a single pole-switch1 to carry a current up to one hundred and twenty-five volts and twenty-five amperes1 is shown in ,fig4 #aj4 ,this consists of a base-block1 a bar which is attached to the vertical ears of a binding-post1 and a clutch that will hold the bar when it is pressed down between the ears4 ,the base-block should be made from some non-conducting material1 such as soapstone1 marble1 or slate4 ,if a piece of soapstone can be procured1 that will be just the thing1 since it is easily worked into the proper shape and size4 ,soapstone may be sawed and smoothed with a file2 it is easily bored into with a gimlet-bit1 and it is one of the best non-conducting substances4 ,the base for this switch is six inches long1 two inches wide1 and as thick as the soapstone happens to be--say three-quarters of an inch4 ,the top edge may be bevelled for the sake of appearance or left square4 ,two pieces of heavy sheet copper or brass are to be cut as shown at ,a in ,fig4 #aa4 ,the ears are half an inch wide1 and the total height of the strip is two inches and a half1 while the part with two holes in it side by side is one inch and a quarter long1 including the half-inch width of the vertical strip4 ,with round and flat-nosed pliers bend the long ears into shape1 so as to form a keeper for the bar which is then to be riveted in place4 ,omit the holes at the ends of the long ears in the other plate2 then bend it into shape to form a clutch that will hold the bar when it is pressed down between the ears4 ,these binding-posts should be made fast to the base-block with brass machine-screws and nuts1 which will fit in countersunk holes in the bottom of the soapstone4 ,if hard-wood is used for the base1 ordinary brass wood-screws will answer very well4 ,the connection-bar is cut from metal the same thickness as that employed for the binding-posts and clutches2 it should be shaped so as to appear as shown at ,b in ,fig4 #aa4 ,a handle should be driven on the slim end1 and where the lower edge enters between the ears of the clutch1 the corners of the bar should be rounded with a file4 ,countersunk screw-holes are bored in the base1 so that it can be made fast to the wood-work4 ,illustration3 ,,fig4 #aj ,illustration3 ,,fig4 #aa ,illustration3 ,,fig4 #ab ,a double pole-switch is shown in ,fig4 #ab1 and in general construction it is similar to the single pole-switch described above4 ,the binding posts and bars are cut and bent from the patterns ,a and ,b in ,fig4 #aa2 but in this case the long1 slim ends of the bars are omitted4 ,a short turn is made at the handle end of each bar and a hard-wood block is placed between the bar-ends and held in position with screws driven through holes made in the bars and into the ends of the block4 ,a handle is made fast to the middle of the block with a long and slim wood-screw2 or a steel-wire nail may be passed through the handle and block1 a burr slipped over the end opposite the head1 and the small end riveted fast4 ,when the binding-posts 7to which the ends of the bars are attached7 are screwed onto the base1 be sure and see that the bars are parallel and the same distance apart at both ends4 ,in like manner1 when the cleat binding-posts are made fast1 see that they are directly in line with the bars1 so that the yoke will drop into the spaces between the ears without having to be pulled to one side or the other4 ,this is a very useful switch for strong currents1 and may be placed close to a dynamo1 so that the current in both wires may be cut out at once4 ,table-jack ,switches ,a table-jack switch is a most convenient piece of apparatus where several lines of bells1 alarms1 or telephone circuits are to be switched on and off4 ,the single table-jack switch1 shown in ,fig4 #ac1 is made of a hard-wood block three-quarters of an inch thick1 five inches wide1 and seven inches long4 ,it is to be smoothed and varnished1 or given several coats of shellac4 ,at the four corners small holes are made to receive slim screws1 and at one end of the block five short metal plates are screwed fast1 with the heads of the screws countersunk1 so that they will be flush with the top of the plates4 ,these small plates should be half an inch wide and one inch long1 and may be of brass1 copper1 or tin4 ,but if they are of tin the plates are made of a longer strip tacked to the board and then bent over1 as shown at ,a in ,fig4 #ad4 ,they will therefore form short springs1 the upper parts of which will rest against the long spring-arms4 ,from spring brass or copper five arms are to be cut and shaped1 as shown in ,fig4 #ac4 ,holes are made at one end of each1 and others again two inches from these1 through which to pass screws4 ,screw-eyes are passed through copper washers and the end holes in the strips1 and then screwed into the wood plate4 ,these will act as binding-posts1 while the second line of screws will hold the plates down to the base4 ,the arms should be bent1 so that when the screws are driven down the lower edge will press on the small plates under them4 ,the outlet wires are attached to the binding-posts at the head of the block1 and the plug 7,a in ,fig4 #ac7 is inserted between the arm and plate at the foot1 so that contact and connection are made4 ,this plug is a small plate of metal to which the end of a flexible wire is made fast4 ,it should be of copper or brass1 but for light work a strip of tin may be bent over with the wire caught between the plates and a copper tack passed through the sides and riveted1 as shown at ,b in ,fig4 #ad4 ,a double jack-switch 7,fig4 #ae7 is made on the same general plan as the single1 but it has no binding-posts4 ,a block of the same size is used1 and two rows of short plates are made fast at each end4 ,the arms are made with two screw-holes near the middle1 as shown in ,fig4 #ae1 and through these holes screws are driven to hold the arms down to the base4 ,several plugs are used for each end1 so that the in and out lines can be shifted1 and from one to four lines used at a time4 ,illustration3 ,,fig4 #ac ,,fig4 #ad ,,fig4 #ae ,,fig4 #af ,,table-,,jack ,,switches ,a convenient slip-switch for single or double line work is shown in ,fig4 #af4 ,this consists of a small wooden base1 on which a brass arm and handle are screwed fast and connected with a binding-post 7,a in ,fig4 #af74 ,a slip-plate is made from a piece of sheet-brass and bent so as to form a pocket into which the arm will fit4 ,this pocket piece is connected with the binding-post ,b4 ,when the switch is thrown out the circuit is broken1 unless a contact-point1 ,c1 is provided1 from the under side of which a wire leads out to a second circuit4 ,when the switch is in place1 as shown in ,fig4 #af1 the circuit is closed through ,a and ,b2 but when the arm is thrown out the circuit through ,a and ,b is broken and that through ,a and ,c is closed4 ,binding-posts and ,connectors ,to make quick connections between wires and other parts of electrical apparatus1 binding-posts are the most convenient device1 since the turn of a screw binds or releases a wire instantly4 ,binding-posts may be made in many forms1 but the simple ones that a boy will need can be made from screw-eyes1 burrs1 stove-bolts1 and nuts1 together with thin strips of metal and nails4 ,five simple posts are shown in ,fig4 #ag4 ,a is made from a screw and two burrs1 ,b from a screw-eye and two burrs1 and ,c from a thin plate of metal and two screws1 with oval or round heads4 ,this last1 however is more of a connector than a binding-post4 ,the ends of the wires to be connected should be caught under the screw-heads or between the burrs before the screws are driven down4 ,in ,d a simple arrangement of a stove-bolt and two nuts is shown4 ,the under bolt is screwed down tightly against the wood1 and under the head a wire is made fast1 so that another wire may be caught under the upper nut4 ,if a small thumb-nut can be had in place of the plain nut1 it will be easier to bind the upper wire4 ,in ,fig4 #ag ,e a thin strip of metal may be folded over1 and at the loose ends a hole should be punched through which a screw-eye will pass4 ,the metal is held to a wood base with a screw1 under the head of which a wire is caught4 ,the second wire end is slipped between the metal plates1 and a turn of the screw-eye will bind and hold it securely4 ,illustration3 ,,fig4 #ag ,illustration3 ,,fig4 #ah ,connectors are employed to unite the ends of wires temporarily1 and are made in many forms4 ,a simple and useful one is made from a piece of spiral spring fastened to a block of wood by two staples1 as shown at ,fig4 #ah ,a4 ,the ends of the wires are pressed down into the coils of the spring and are held with sufficient security for temporary use4 ,another connector is made from a block of wood1 a strip of thin metal1 and two screw-eyes 7,fig4 #ah ,b74 ,the metal is bent around the ends of the block1 and through holes made in the ends of the strip screw-eyes are driven into the block4 ,when the ends of wires are slipped under the metal1 a turn of the eyes will hold them fast1 as shown at ,fig4 #ah ,b4 ,a short bolt threaded at each end and provided with four nuts will also act as a connector4 ,the inner nuts are screwed on tightly and the outer ones are loose1 so that when wires are placed between them they may be tightened with the fingers1 as shown at ,c in ,fig4 #ah4 ,these are a few simple forms of connectors2 the ingenious boy can devise many others to suit his needs and ideas4 ,lightning-arresters and ,fuse-blocks ,all lines of exposed wire that run from out-doors into the house should be provided at both ends with lightning-arresters1 particularly if they are telephone or telegraph lines1 burglar alarms1 or messenger call-boxes4 ,in many instances where unprotected telephone lines have been the plaything of lightning1 painful accidents have happened1 and it is only the part of prudence to provide against them4 ,it is better to have an arrester at both ends of a line1 and as the cost is insignificant it is hardly worth considering as against its feature of safety4 ,lightning-arresters may be constructed in many ways and of different materials2 the ones here shown and described are easily made and efficient4 ,the principle of all arresters is simply a fuse which burns out whenever the wire is carrying a greater amount of current than is required for the proper working of the apparatus1 thereby arresting the current and protecting the instruments from destruction4 ,induction-coils1 relays1 fine windings on armatures1 or a magnet helix are quickly destroyed if a too powerful current is permitted to pass through them1 and it is therefore advisable to protect them4 ,when a fuse burns out under a trolley-car1 or in the shunt-box of a motor-car or engine1 it is because a greater amount of current is trying to pass in than the motor will safely stand4 ,when a fuse 8blows out10 the apparatus or motor is put out of commission until the fuse is replaced1 but the delicate mechanism and the fine wiring on the field-magnets or armatures are saved4 ,the simplest form of single pole-fuse is a fine piece of lead wire held between two binding-posts1 as shown at ,a in ,fig4 #ai4 ,the lead wire may be of any length2 but for small instruments1 where a moderate current is employed and where there is a possibility of lightning travelling on the wire1 the fuse should be from two to three inches long4 ,for inside work1 however1 where it is to be used simply as a safety1 the wire may be shorter and finer4 ,to make the lightning-arrester shown in ,fig4 #ai1 cut out a hard-wood block five inches long1 an inch wide1 and half an inch thick4 ,give this several coats of shellac2 then place a piece of mica1 or asbestos paper1 over the top of the block1 and make it fast with thick shellac to act as a glue4 ,from small pieces of copper or brass cut two plates one-half by one inch1 and drill holes in them to take screws and screw-eyes4 ,place copper burrs under the screw-eyes for connectors1 and drive two brass screws half-way down in the block through the holes at the inner ends of the binding-post plates4 ,see that these screws fit snugly in the holes in the plates so that contact is perfect4 ,if the holes are too large and the screws fit loosely1 two copper burrs will have to be used and the screws driven in1 so that the heads bind the burrs on the ends of the fuse-wire4 ,from an electrician1 or supply-house1 purchase a few inches of fine lead fuse-wire--say ,nos4 #bj1 #bb1 or #bd--;and twist the ends of a length around the screws1 as shown in the drawing4 ,perfect contact should be had between the lead wire and the screws2 by way of precaution1 a bit of solder will dispel all doubt4 ,just touch the point with a little soldering solution2 then apply a soldering-iron having a drop or two of solder on the end4 ,perfect connection is absolutely necessary for telephone1 telegraph1 or annunciator work1 and where there is a lightning-arrester and the line is not working well1 the trouble may often lie in the poor contact of lead and brass or copper1 or possibly in using wire that is too fine4 ,lead is a very poor conductor1 and a fine wire would act as a check4 ,for a test1 first insert a piece of copper wire to see that the line is working properly2 then use lead wire of sufficient size to carry the current as well as the copper did4 ,the action of metals and wire1 as current retarders1 will be explained in the chapter on resistance and resistance-coils4 ,for general commercial use the base-blocks of all lightning-arresters should be made of porcelain1 slate1 or some of the composition non-conductors1 such as moulded mica1 silex and shellac1 or fibre4 ,as these are not always available1 wood1 with a covering of mica1 will answer every purpose and can be readily adapted for use4 ,the apparatus pictured in ,fig4 #ai is known as a single-pole lightning-arrester1 and is the simplest form of this kind of electrical paraphernalia4 ,in ,fig4 #bj a double-pole arrester is shown4 ,this is constructed in the same manner as described for the single one4 ,the block is five inches long1 two inches wide1 and half or five-eighths of an inch thick4 ,a countersunk hole is made in the middle of all the lightning-arrester blocks through which a screw can be passed to hold the apparatus fast in any desired location4 ,in ,fig4 #ba another form of fuse is shown4 ,it is made from a piece of mica three-quarters of an inch wide and four inches long1 two pieces of thin sheet-copper1 and a piece of lead fuse-wire4 ,the copper is three-quarters of an inch wide1 and one piece of it is bent in the form of a ,v1 as shown at ,a in ,fig4 #ba4 ,one end of the mica strip is dropped in the ,v1 and with a pair of pliers the ,v is closed up by pinching it at the bottom4 ,to further insure its staying in place1 the top and end1 or open edges1 should be soldered4 ,punch a small hole through the copper ends1 at the inside edge1 slip the ends of the fuse-wire in them1 and touch the union with a drop of solder to insure perfect contact4 ,with shears and file cut a ,u from the side of one copper band and from the end of the other2 these will allow the copper ends to pass under the heads of screws1 thus avoiding the necessity of removing the entire screw from the block in order to set the fuse in place4 ,illustration3 ,,fig4 #ai ,,fig4 #bj ,,fig4 #ba ,,fig4 #bb ,,fig4 #bc ,,fig4 #bd ,,fig4 #be ,,fig4 #bf ,,lightning-,,arresters ,,and ,,fuse-,,blocks ,the block on which this fuse is held is shown in ,fig4 #bb1 and is made in a similar manner to the one shown in ,fig4 #ai1 except that the metal plates are a trifle longer and are bent up1 as shown in the drawing4 ,thus the mica fuse-plate will be elevated above the block4 ,if the brass or copper used for the binding-post plates is too thin to stand the pressure of the screws when the fuse ends are screwed fast1 put a few burrs on the screws below the plates2 then the pressure of the screws cannot bend down the extending ears of the plates and make an imperfect contact4 ,another form of fuse-block is shown in ,fig4 #bc4 ,the same sort of a fuse is employed as shown in ,fig4 #ba1 but without the ,u cuts at the ends4 ,the clutches are made by binding brass or copper plates1 as shown in the drawing2 they should then be screwed fast to a base-block five inches long1 one inch and a half wide1 and five-eighths of an inch thick4 ,the opening between them should just admit the copper ends of the fuse1 and pressure should be used to force the fuse in place so that the contact will be perfect4 ,still another form of fuse is shown in ,fig4 #bd4 ,this last may more properly be called a non-sparking fuse1 for the lead wire is encased in a glass tube1 and when it fuses no sparks fly and no small pieces of melted metal can get away from the inside of the tube4 ,the plug is made from a piece of glass tube half an inch in diameter1 two metal caps1 and a short piece of lead wire4 ,the metal caps are of thin sheet-copper1 and are caught at the edges with solder4 ,one end of the lead fuse-wire is passed through a hole in the end of a cap and soldered1 as shown at ,a in ,fig4 #bd4 ,the wire is then passed through the tube and the cap placed over one end of it4 ,this is repeated at the other end and the wire soldered fast4 ,as a result1 you will have a glass tube with metal caps held on the ends of the tube1 by means of the thin lead wire which runs through the middle of the tube4 ,the base-block to which this fuse-plug is attached is of wood one inch and a half wide1 five or six inches long1 and five-eighths of an inch thick4 ,two metal straps are made and screwed fast to the block1 and the circuit wires are attached under the copper burrs and held down by the screw-eyes4 ,to place or replace a fuse-plug1 unscrew the eyes and raise each strap slightly1 so that the copper cap ends will pass under them4 ,a turn or two of the eyes will clamp the plug in position and at the same time bind the circuit wires4 ,a spring lightning-arrester is shown in ,fig4 #be2 it is simply a modified form of that shown and described in ,fig4 #ai4 ,the base-block is five by one-and-a-quarter by five-eighths of an inch1 and is properly protected by a sheet of mica or asbestos4 ,the two metal plates are cut for the binding-posts and screwed in place with screws1 burrs1 and screw-eyes4 ,from spring-brass wire bend a hook and slip one end of it under the screw-head at the left side of the block4 ,from a longer piece of wire make two or three turns around a piece of wood half an inch in diameter2 then form a hook at one end and a turn at the other1 so that it can be made fast under the screw-head of the binding-post4 ,when at rest1 the spring-hook should stand in an upright position1 but when sprung and tied it occupies the position shown in the drawing4 ,the spring-hook is to be bent down so that the two hooks are brought within an inch of each other4 ,they are held in this position with a piece of lead fuse-wire4 ,this last is given a turn about the hooks and one or two turns about itself1 close to each hook1 to prevent the spring from tearing itself away4 ,when the wire is fused by a current the spring-hook flies up and away from possible contact with the short hook attached to the opposite binding-post4 ,this is the construction for a single-pole-spring lightning-arrester2 a double one is made in a similar manner1 and the parts mounted on a wider block1 as shown in ,fig4 #bj4 ,for doubtful currents1 where there is no means of knowing how strong they are1 a combined fuse and single-pole switch is shown in ,fig4 #bf4 ,this is nothing more than a combination of the apparatus shown in ,fig4 #ba1 and the single-pole switch 7,fig4 #aj74 ,the base block is seven inches long and two inches wide4 ,or it may be made half an inch wider if it is to be bevelled at the top1 as shown in the drawing4 ,it should be three-quarters of an inch thick and provided with two countersunk holes for screws that will hold it in place on a ledge or against a casement4 ,the little angles to hold the copper-ended mica fuse-plate are described for the apparatus pictured in ,fig4 #ba4 ,if it is desired that one of the ends should be provided with burrs and a screw-eye1 the little plate of brass should be an inch long and an inch wide1 with a half-inch-square piece snipped from one corner1 as shown at ,a in ,fig4 #bf4 ,it is provided with two holes1 and then bent on the dotted line1 so that the part with the holes will lie on the block and the ear will stand in a vertical position4 ,a reverse-plate made on this pattern will act as one side of the switch-bar clutch at the opposite end of the block4 ,for the metal clutch and keeper at the middle of the block the metal plate 7before it is bent7 will appear as shown at ,b in ,fig4 #bf4 ,the long plate with two holes lies on the base1 while the first ear 7or the one without the hole7 forms part of the clutch for the fuse end1 the ear with the hole acting as one side of the bar-lever strap4 ,an opposite plate to this forms the other side of the clutch and strap1 and the two plates are screwed side by side1 so that the fuse-plate will be held securely when pushed into place4 ,for the switch-bar use a piece of hard copper or brass four inches long1 half an inch wide1 and about one-eighth of an inch thick1 or the same thickness as the copper straps at the ends of the mica fuse-plate4 ,bore a hole at one end of this bar1 and with a copper rivet attach it between the two upright ears at the middle of the block4 ,with a file cut away the two edges at the other end of the bar for a distance of an inch1 so that the bar will have an end as shown at ,c in ,fig4 #bf4 ,drive a small file-handle on this end and give it a coat or two of shellac2 then bevel the lower edges of the bar with a file where it enters between the blades of the clutch4 ,the circuit wires are made fast at both ends of the block1 and the current travels through the binding-posts1 the lead fuse-wire on the mica plate ,d1 and the switch-bar4 ,if the current is too strong1 then when the switch-bar is pushed into the clutch the safety-fuse will burn out and save the apparatus2 or it will arrest a flash of lightning4 ,chapter ,,iv ,,magnets ,,and ,,induction-,,coils ,simple and ,horseshoe ,magnets ,every boy has a horseshoe magnet among his collection of useful odds and ends1 and whether it is a large or small one its working principle is the same4 ,if large enough it will lift a jack-knife1 nails1 or solid weights1 such as a small flat-iron or an iron padlock4 ,a horseshoe magnet is made of highly tempered steel and magnetized so that one end is a north pole and the other a south pole4 ,in more scientific language these poles are known as1 respectively1 positive and negative4 ,once magnetized the instrument retains that property indefinitely1 unless the power is drawn from it by exposure to intense heat1 and even then1 by successive heating and cooling1 the magnetism may be partially restored4 ,an electro-magnet may be made of any scrap of soft iron1 from a piece of ordinary telegraph-wire to a gigantic iron shaft4 ,when a current of electricity passes through a wire a magnetic 8field0 is produced around the wire1 and if the latter is insulated with a covering and coiled about a soft iron object1 such as a nail1 a bolt1 or a rod1 that object becomes a magnet so long as a current of electricity is passing through the coils of wire or helix4 ,a coil of wire in the form of a spiral spring has a stronger field than a straight wire carrying the same current1 for each turn or convolution adds its magnetic field to that of the other turns4 ,a simple form of electro-magnet is made by winding several layers of ,no4 #bj insulated copper wire around a stout nail or a carriage-bolt2 by connecting the ends to a battery of sufficient power1 some very heavy objects may be lifted4 ,a single magnet1 like the one shown in ,fig4 #a1 is made with a piece of soft iron rod six inches long and half an inch in diameter1 the ends of a large spool sawed off and worked on the rod1 and half a pound of ,no4 #bj insulated copper wire4 ,the spool-ends are arranged as shown in ,fig4 #b4 ,an end of the wire is passed through a hole in one flange when you begin to wind the coils1 and when finished1 the other end is passed through a hole at the outer rim of the same flange4 ,this magnet may be held in the hands when in use2 or a hand-magnet may be constructed of a longer piece of iron on one end of which a handle is driven and held in place with a nut and washer1 as shown in ,fig4 #c4 ,the wires from the coil pass through holes made in the handle and come out at the butt end1 where they may be attached by connectors to the pole-wires of a battery4 ,to protect the outer insulated coil of wire from chafing and a possible short-circuit1 it would be well to wrap several thicknesses of stout paper around the coil and glue it fast2 or a leather cover will answer as well4 ,illustration3 ,,fig4 #a ,,fig4 #b ,,fig4 #c ,,fig4 #d ,,fig4 #e ,,fig4 #f ,,fig4 #g ,,simple ,,and ,,horseshoe ,,magnets ,a more powerful magnet may be made from a stout bolt1 two nuts1 and a wooden base1 with about three-quarters of a pound of ,no4 #ah insulated copper wire to wind about the body of the bolt4 ,a block of wood an inch thick1 four inches wide1 and six inches long is provided with a hole at the middle for the bolt to pass through4 ,a larger hole is made at the under side of the block so that a nut can be easily turned in it4 ,a three-quarter-inch machine-bolt1 with a square head1 and seven inches long1 is set in the block1 head up1 as shown in ,fig4 #d2 and composition or thin wooden disks or washers are placed on the bolt to hold the coils of wire in place4 ,the ends of the wire pass out through the bottom washer and are made fast to binding-posts on the block1 and to these latter the battery-poles are made fast when the magnet is in use4 ,coils of wire may be wound on an ordinary spool1 and the hole in the middle may be filled with lengths of soft iron wire4 ,when a current is passing around the spool the wires become highly magnetic1 but lose the magnetism directly the current ceases4 ,horseshoe electro-magnets are made by winding coils on the ends of ,u-shaped pieces of soft iron1 but the winding must be done so that the current will pass around them in opposite directions1 otherwise you would have two negatives instead of a negative and positive4 ,for a small horseshoe magnet a stout iron staple may be used1 but for the larger magnets it would be best to have a blacksmith bend a piece of round iron in the desired shape4 ,a powerful horseshoe magnet may be made from a piece of tire-iron bent as shown in ,fig4 #e ,a2 when wound with ,no4 #ah wire it will appear like ,fig4 #e ,b4 ,a volt or two of current passing through the coils will render this magnet powerful enough to lift several pounds4 ,for bells1 telegraph-sounders1 and other electrical equipment requiring the horseshoe or double magnet1 several kinds may be used1 but the simplest is constructed from two carriage or machine bolts and a yoke of soft iron1 as shown in ,fig4 #f4 ,the yoke is five-eighths of an inch in width1 two inches and a half long1 and provided with two three-eighths-inch holes1 one inch and a half apart from centre to centre4 ,two-inch carriage or machine bolts are used1 and they should be three-eighths of an inch in diameter4 ,the nuts are turned on the thread far enough to admit the yoke1 and then another nut is applied to hold it in place and bind the three pieces into one compact mass4 ,wooden spool-ends or composition washers are placed on the bolts to hold the ends of the wire coils in place1 and the winding may be done on each bolt separately and locked to the yoke after the winding is completed4 ,double cotton-insulated ,no4 #bj or #bb copper wire should be used for the coils4 ,it is a tedious and bothersome job to wind a coil by hand1 and if possible a winder should be employed for this purpose4 ,several varieties of winders are on the market1 but a simple one for ordinary spools may be made from a stick held in an upright piece of wood with staples4 ,this idea is pictured in ,fig4 #g1 where the round stick is shown cut with two grooves into which the staples fit4 ,one end of the stick is made with a square shoulder1 so that a handle and crank can be fitted to it4 ,a few wraps of wire are taken around the crank to prevent it from splitting1 and it is held to the round stick with a slim steel nail4 ,the opposite end of the round stick is shaved off so that it will fit snugly in the hole of a spool2 if it should be too small for some spools1 a few turns of cord around the small end will make it bind4 ,the block to which the shaft and crank is attached may be held in a vise or screwed to the edge of a table4 ,induction-coils ,a simple induction or shocking coil may be made of a two-and-one-half by five-sixteenths-inch bolt1 a thin wooden spool1 and two sizes of insulated copper wire4 ,an induction-coil is a peculiar and wonderful apparatus2 it figures largely in electrical experimenting and is a part of every complete equipment4 ,a piece of curtain-pole may be used for the spool4 ,first bore a five-sixteenths-inch hole through the wood to receive the bolt2 then in a lathe turn it down into a spool with less than one-eighth of an inch of wood about the hole and with flanges about one-eighth of an inch in thickness4 ,smooth the spool with sand-paper1 while it is still in the lathe1 and give it a thin coat or two of shellac4 ,slip the spool on the winder 7,fig4 #g7 and wind on three layers of ,no4 #bd cotton-insulated copper wire1 taking care to wrap the coils evenly and close4 ,bring six inches of the ends out at either end of the spool through small holes pierced in the flanges2 then wrap several thicknesses of brown paper around the coil4 ,a current passing around this three-layer coil will magnetize the bolt4 ,this is the primary coil and the one through which the battery current will pass4 ,a secondary coil is now made over the primary one with eleven or thirteen layers of ,no4 #cj insulated copper wire4 ,it will take some time to carefully put on these layers1 and when doing so mark down each layer so as to keep an accurate count1 for there must be the right number of layers to make the coil act properly4 ,no4 #cj wire is quite fine1 and if the layers are not inclined to lie smooth1 make a wrap or two of brown paper between each three layers4 ,bring six inches of each end of the wire out from the flanges of the spool1 and to protect the outer coil wrap paper about the coils and attach it fast with thread or paraffine4 ,slip the bolt through the hole and screw the nut on the threaded end4 ,cut out a wooden block four inches long1 three inches wide1 and three-quarters of an inch thick1 and with two thin metal straps and screws attach the coil to the middle of the block1 as shown in ,fig4 #h4 ,make four binding-posts and screw them fast at the corners1 and to ,a and ,b of ,fig4 #h attach the ends of the heavy wire from the primary coil1 and to ,c and ,d of ,fig4 #h the ends of the fine wire from the secondary coils4 ,the induction-coil is now ready for any use to which it may be put1 and by mounting it on the block with the delicate wire ends attached to the binding-posts1 it is in less danger of damage than if the wire ends were left loose for rough-and-ready connections4 ,in order to get a shock from this coil it will be necessary to have a pair of handles and a current interrupter4 ,the handles may be made from two pieces of tin rolled into the form of cylinders to which wires are soldered4 ,or1 better yet1 use pieces of thin brass tubing an inch in diameter4 ,the buzzer shown in ,fig4 #i may be employed for a current interrupter1 and a bichromate battery will furnish the current4 ,in order to make the connections1 the wires from the handles are attached to the binding-posts ,c and ,d in ,fig4 #h--that is1 to the wires of the secondary coil4 ,one spool of the battery is connected with ,a of ,fig4 #h and the other with ,a of ,fig4 #i4 ,a wire connects ,c of ,fig4 #i with ,b of ,fig4 #h1 and the circuit is closed4 ,the buzzer now begins to vibrate1 and any one holding the handles will receive a shock the intensity of which depends on the strength of the batteries4 ,a switch should be introduced somewhere in the circuit1 so that it may be opened or closed at will2 a good place for it is between a battery-pole and the binding-post ,a in ,fig4 #h4 ,if the shock is too intense it may be weakened by drawing the carbon and zinc poles partly out of the bichromate solution2 or a regulator may be made of a large glass tube and a glass preserving-jar filled with water4 ,if the tube cannot be had1 an ,argand gas-burner chimney will answer as well4 ,solder a wire to the edge of a small tin or copper disk1 as shown in ,fig4 #aj1 on which the chimney rests at the bottom of the jar1 and another wire to a tin box-cover with some small holes punched in its top1 this latter being suspended within the chimney4 ,this second wire is passed out through a cork at the top of the chimney made of a disk of cardboard and a piece of wood4 ,one wire is connected with ,a of ,fig4 #h and the other with a battery-pole4 ,this apparatus acts the same as a resistance-coil1 and by raising or lowering the box-cover the current is increased or diminished4 ,the closer the cover comes to the disk the stronger the current1 as there is less water for the electricity to pass through and therefore less resistance2 while if the cover touches the disk the current flows as freely as if there were no regulator and the wires ran directly to the cell4 ,an apparatus comprising a coil1 an interrupter1 or armature1 and a switch may be set on one block1 and the arrangement of the several parts is clearly shown in the drawing of the complete galvano-faradic apparatus 7,fig4 #aa74 ,the block should be six inches long1 four inches wide1 and seven-eighths of an inch in thickness4 ,illustration3 ,,fig4 #h ,illustration3 ,,fig4 #i ,illustration3 ,,fig4 #aj ,illustration3 ,,fig4 #aa ,illustration3 ,,fig4 #ab ,the coil is made as described for ,fig4 #h1 the spool being three inches long and one inch and a quarter in diameter4 ,a carriage-bolt three inches and a half long and five-sixteenths of an inch in diameter1 with a bevelled head1 is made fast in the spool1 and this coil is strapped to the block with two metal bands and screws4 ,two binding-posts 7,a and ,b of ,fig4 #aa7 are arranged at the upper corners1 and to these the ends of the secondary coil wires are attached4 ,two more binding-posts 7,c and ,d of ,fig4 #aa7 are arranged at the lower side and provided with a switch to open and close the circuit4 ,one of the primary coil wires is made fast to ,c1 and the other one to a block which contains the set-screw that bears against the vibrating armature4 ,its arrangement and the wire connection is explained in ,fig4 #i ,b4 ,an armature of thin brass or tin is made and attached to a block 7,e in ,fig4 #aa74 ,at the loose end that is opposite the bolt-head several wraps of tin are made and soldered fast1 or a small block of soft iron may be riveted to the armature4 ,it must be of iron or tin1 however1 so as to be attracted by the electro-magnetized bolt-head4 ,this arrangement may be seen in ,fig4 #ab4 ,attach a thick piece of paper over the bolt-head1 so that the lug at the end of the armature will not adhere to it through residual magnetism4 ,in regular galvano-faradic machines the current regulator is formed of a hollow cylinder which is drawn from the core of the coil2 but in this simple machine the water-jar regulator may be connected between a pole of the battery and the binding-posts 7,d or ,e of ,fig4 #aa74 ,the wires of the handles are attached to posts 7,a and ,b of ,fig4 #aa71 and when all the wires are in place and the current turned on by means of the switch1 the vibrator begins to work and the shocking-current is felt through the handles4 ,by means of the regulating-screw that bears on the armature1 the number of vibrations may be increased or diminished1 but for faradic purposes the vibrations should be as quick as possible4 ,much amusement may be had with this apparatus1 and a large number of people may be given a shock by getting them to join hands when standing or sitting in a circle4 ,an ,electric ,buzzer ,this piece of apparatus is1 in theory1 nothing more than the electric bell1 and might properly be included in ,chapter ,v41 on ,annunciators and ,bells4 ,but since it is the logical development of principles just laid down1 it has been thought best to give it its present position4 ,the electric buzzer is constructed on the principle of the telegraph-sounder1 but instead of making a single click or stroke the current is made to act on the armature and keep up a continuous motion so long as the electricity passes through the helix of the cores1 the armature1 and the contact-points of the apparatus4 ,a buzzer has the same movement as an electric bell with the ringing apparatus removed4 ,for offices1 houses1 and quiet calls it is often preferred to the loud ringing of a bell4 ,the electric buzzer shown in ,fig4 #ac is easy to make2 it is operated by the aid of a cell and a push-button4 ,cut a base-block three inches and a half wide1 five inches long1 and three-quarters of an inch thick1 and mount a horseshoe magnet made of bolts and a yoke and coils about at the middle of it1 as shown in ,fig4 #i4 ,the magnet is held to the base by a flat wooden cleat and a screw passed down through a hole in the cleat and into the base1 between the coils4 ,an armature of soft iron1 two inches long and half an inch wide1 is riveted to a piece of spring-brass1 as shown in ,fig4 #ad ,a1 and the end is bent so that it will fit around the corner of a block to which it is held fast with two screws4 ,this armature is mounted so that there is a space one-sixteenth of an inch wide between it and the bolt-heads1 as you can see in ,fig4 #i4 ,the brass is bent out slightly and runs parallel with the armature for one inch and a quarter4 ,against this the end of the screw mounted in block ,b ,fig4 #i rests4 ,illustration3 ,,fig4 #ac ,illustration3 ,,fig4 #ad ,the block ,b is a small piece of hard-wood screwed fast to the side of the base to hold the set-screw and also the wire that comes from the outside of the upper coil4 ,a small hole is made in the edge of the block and the wire passed in1 so that the end rests in the screw-hole as shown by the dotted line4 ,when the screw is placed in the hole and turned1 it comes into contact with the wire and makes a connection4 ,this block and its attachment is shown in ,fig4 #ad ,b4 ,on the base1 near the armature-block1 a binding-post is made fast1 and the current1 passing in through the wire ,a in ,fig4 #i1 goes through the coils and around to the screw ,b1 then through the armature to the block1 and out through the wire ,c4 ,in its circuit the bolts are magnetized1 and they draw the armature1 but the instant they do so the loose spring-brass end is pulled away from the screw-point ,b and the circuit is broken1 the bolts cease to be magnetized1 and the armature flies back under the influence of the spring-brass neck at ,d4 ,the loose brass end1 on touching the screw-point1 conducts the current through the coils again1 with a continual vibrating action1 so long as the electric current is passing in at ,a and out at ,c4 ,the greater the volume of current the greater the number of vibrations1 and to properly regulate the contact the set-screw ,b must be adjusted at the right point4 ,paste pieces of heavy paper over the heads of the bolts to overcome residual magnetism4 ,a single electric bell is made the same as a buzzer1 but continuing on from the end of the armature a wire or rod is mounted with a ball at the end which strikes the bell as the current causes the armature to vibrate4 ,the bell-block may be made longer1 and a bell from an old clock or a bicycle should be mounted at the proper place on a wooden dowel driven into the base4 ,a screw passes through the hole at the middle of the bell and into the top of the dowel4 ,the ball at the end of the rod may be made of brass with a hole in it1 and a drop of solder will hold it in place4 ,or it may be made of wire wound round the end and soldered into a compact mass4 ,a ,large ,induction-coil ,as has been said1 the induction-coil is one of the mysterious phenomena of electrical science4 ,while its practical value is known and recognized in all branches of voltaic electricity for use in transforming currents1 its actual workings have never been clearly explained4 ,the construction of a small induction-coil was explained in the description of a shocker or medical battery4 ,for bigger equipments1 wireless telegraphy and other uses1 a large induction-coil will be necessary1 and the following illustrations and descriptions should enable the young electrician to construct an apparatus that will be both simple and efficient in its working4 ,for the tube 7in which to wind the primary coils7 obtain a piece of red fibre-tubing1 one inch inside diameter and not more than one-eighth of an inch in thickness4 ,the length should be ten inches4 ,if fibre cannot be had use a paste-board tube4 ,from white-wood1 half an inch in thickness1 saw two blocks four inches square and in the centre of each cut a hole so that the tube will pass through it and fit snugly4 ,some shellac and a few slim brass escutcheon pins will hold the blocks in place1 as shown at ,fig4 #ae4 ,the wood blocks and fibre or paper tube should be treated to several successive coats of shellac to give them a good finish and prevent the absorption of moisture4 ,four binding-posts1 with wood screw-ends1 are to be made fast at the top edges of the end-blocks1 as shown at ,fig4 #ae4 ,holes bored in the blocks near the foot of the binding-posts will admit the ends of the coil-wires so that contact can be made4 ,the ends of the conductor-wires should then be placed in the holes in the binding-posts and held in place with the thumb-screws4 ,illustration3 ,,fig4 #ae ,illustration3 ,,fig4 #af ,the primary coil is made by winding four layers of ,no4 #bj insulated copper wire on the tube and between the end-blocks1 as shown at ,fig4 #af4 ,each layer must be wound evenly1 and the strands should lie close to each other4 ,when the first layer is on give it a coat of shellac2 then wrap a piece of thin paper about it and give that also a coat of shellac4 ,when the second layer is on repeat the operation of shellacking and paper-coating1 and continue with the third layer4 ,when the fourth layer is on give the coil a double wrap of paper and two or three coats of shellac to thoroughly insulate it and keep out all moisture4 ,the winding may be done by hand1 but it is much easier to do it on a winder or reel1 which can be operated to revolve the core1 the wire unwinding from its original spool as it is wound on the tube4 ,a convenient winder may be made on a base-board which can be clamped to a table or bench4 ,the board is twelve inches long1 eight or ten inches wide1 and seven-eighths of an inch thick4 ,two uprights1 three inches wide1 ten inches long1 and three-quarters of an inch thick1 are screwed and glued to the ends of the base-board4 ,a notch is cut in the top of the end-boards1 into which the spindle or shaft can rest2 and at the top of the end-pieces two small plates of wood or metal are screwed down to hold the spindle in place when the tube and ends are being revolved4 ,a small hole1 bored in each upright end two inches above the top of the base-board1 will admit a rod on which a spool of wire can revolve1 as shown at ,fig4 #ag4 ,two plugs of wood1 shaped like corks1 are made to fit in the ends of the fibre-tube4 ,a hole is bored through each one so that a wire or rod spindle will pass through them and fit tightly4 ,one end of the rod is bent and provided with a small wooden handle1 by means of which the core may be revolved4 ,this winding-rack makes it easy to handle the core-tube while putting on the layers of wire1 and it holds the tube securely while the wraps of paper and shellac are applied4 ,the secondary coil is laid over the primary1 and should be of ,nos4 #cj to #cf insulated copper wire4 ,the finer the wire the higher the resistance and the longer the spark1 but nothing heavier than ,no4 #cj should be used4 ,begin by making one end of the wire fast to a binding-post2 then turn the core-tube with one hand1 holding the wire in the other4 ,take care not to bind the wire nor stretch it1 but wind it on smoothly and evenly1 like the coils of thread on a new spool of cotton or silk4 ,be very careful to avoid kinks1 breaks1 or uninsulated places in the wire4 ,should the wire become broken1 give the coil a coat of shellac to bind the wound strands2 then make a fine twisted point and cover it with the silk or cotton covering1 with a coat of shellac to hold it in place1 and proceed with the winding4 ,between each layer of wire place a thin sheet of paper and coat it with paraffine1 or shellac1 to make a perfect insulation2 then proceed with the next layer4 ,with a battery and small bell test the wire layers occasionally to see that everything is all right1 and that there are no breaks or short circuits4 ,this is very necessary to avoid making mistakes1 and1 considering the time and care spent in winding the coils1 it would be a great disappointment if the coil were defective4 ,illustration3 ,,fig4 #ag ,illustration3 ,,fig4 #ah ,about one pound and a half of wire should constitute the secondary coil1 and1 if possible1 it is best to have it in one continuous strand1 without splices4 ,over the last coil1 after the winding is completed1 several thicknesses of paper should be laid and well coated with shellac between each wrap4 ,this is a protector to insure the fine wire strands from damage4 ,to improve the appearance of the coil a wrap of thin black or colored leather may be glued fast1 with the seam or point at the under side4 ,the ends of the wires forming the primary coil should be made fast to the binding-posts at one end1 while those of the secondary coil should be attached to the posts at the other end4 ,for the core1 obtain some soft iron wire1 about ,no4 #ah1 and cut a number of lengths4 ,straighten these short wires and fill the tube with them1 packing it closely1 so that the wires will remain in place under a mutual pressure4 ,it is better to make a core of a number of rods or wires rather than to have it of one solid piece of soft iron4 ,now1 from hard-wood1 cut a base three-quarters of an inch thick1 five or six inches wide1 and twelve inches long4 ,attach the coil to the base by means of screws passed up through the board and into the lower edges of the end-blocks4 ,the wood is to be stained and given several successive coats of shellac4 ,now connect the wires of a battery to the binding-posts in contact with the primary coil1 and attach two separate wires to the secondary coil binding-posts4 ,bring these ends near to each other1 and a spark will leap across from one end to the other1 its size or 8fatness0 depending on the strength of the battery4 ,the completed apparatus is shown at ,fig4 #ah4 ,in producing a long spark a condenser is an important factor2 it is used in series with an induction-coil4 ,there are several forms of condensers1 but perhaps the simplest and most efficient is the ,fizeau condenser1 which is made up of layers of tin-foil with paraffined paper as separators4 ,from a florist's supply-house purchase one hundred and fifty sheets of tin-foil seven by nine inches1 or sheets that will cut to that size without waste2 also ten or twelve extra sheets for strips4 ,at a paper supply-house obtain some clear1 thin1 tough paper about the thickness of good writing-paper4 ,be careful to reject any sheets that are perforated or have any fine holes in them4 ,the sheets should be eight by ten inches1 or half an inch larger all around than those of the tin-foil4 ,the paper must be thoroughly soaked in hot paraffine to make it moisture-proof and a perfect non-conductor4 ,this is done by placing about two hundred sheets on the bottom of a clean tin tray1 or photographic developing-dish of porcelain4 ,don't use glass or rubber4 ,after placing some lumps of paraffine on the paper1 put the tray in an oven so as to dissolve the paraffine and thoroughly soak the paper4 ,open the oven door and1 with a pin1 raise up the sheets one at a time1 and draw them out of the liquid paraffine4 ,as soon as it comes in contact with cool air the paraffine solidifies and the sheet of paper becomes stiffened4 ,select each sheet with care1 so that those employed for the condenser are free from holes or imperfect places4 ,from pine or white-wood1 a quarter of an inch in thickness1 cut two boards1 eight by ten inches1 and give them several good coats of shellac4 ,to build up the condenser1 lay one board on a table and on it place two sheets of paraffined paper4 ,on this lay a sheet of tin-foil1 arranging it so that half an inch of paper will be visible around the margin4 ,from the odd sheets of tin-foil cut some strips1 one inch in width and three inches long4 ,place one of these strips at the left end of the first sheet of foil1 as shown at ,fig4 #ai4 ,over this lay a sheet of the paraffined paper1 then another sheet of the foil4 ,now on this second sheet of foil lay the short strip to the right end1 and so proceed until all the foil and paper is in place1 arranging each alternate short strip at the opposite end4 ,care must be taken to observe this order if the condenser is to be of any use4 ,illustration3 ,,fig4 #ai ,illustration3 ,,fig4 #bj ,when the last piece of foil is laid on1 with its short strip above it1 add two or three thicknesses of paper1 and then the other board4 ,with four screw-clamps1 one at each corner1 press together the mass of foil1 paper1 and boards as closely as possible1 then bind the boards about with adhesive tape1 or stout twine1 and release the clamps4 ,attach all the projecting ends of foil at one side by means of a binding-post1 and those at the other end with another binding-post4 ,the complete condenser will then appear as shown in ,fig4 #bj4 ,when in operation one wire leading from the secondary coil should be connected with a binding-post of the condenser1 so that it is in series4 ,the object of the condenser is to increase the efficiency of induction1 and it should be made in proportion to the size of the induction-coil with which it is to be employed4 ,circuit-,interrupters ,when an induction-coil is to be employed as a shocker 7and there is no vibrating armature arranged in connection with the core71 a circuit-interrupter must be employed to get the effect of the pulsations1 as given out by the secondary coil when a current is passing through the primary4 ,there are various forms of circuit-breakers that may be made for this purpose1 but for really efficient service the type shown in ,fig4 #ba is perhaps the best that can be devised4 ,this interrupter consists of a metal cog-wheel with saw-teeth1 a pinion or axle1 and a handle4 ,also a base-block1 with uprights to support it1 and a piece of spring-brass wire1 arranged so as to bear against the wheel4 ,when the wheel is revolved the spring-wire will be driven out by each tooth2 and when released it flies back to the wheel1 striking the bevelled edge of a tooth at each trip4 ,two binding-posts1 arranged on the block1 will provide means of connecting in-and-out wires4 ,with a coat or two of shellac on the wood-work and black asphaltum varnish on all surfaces of the metal that are not used for contact1 this circuit-interrupter will be ready for any use in connection with an induction-coil4 ,the base-block is of pine1 white-wood1 or cypress1 seven-eighths of an inch thick1 three inches wide1 and five inches long4 ,the uprights1 which support the wheel1 are half an inch thick and one inch wide4 ,the wheel is three inches in diameter and is made of brass one-sixteenth of an inch thick4 ,the design of the wheel should be laid out with a compass and marked with lead-pencil or a sharp-pointed awl1 which will leave a mark clear enough to be seen when sawing and filing the teeth and open places4 ,illustration3 ,,fig4 #ba ,illustration3 ,,fig4 #bb ,a true plan is shown at ,fig4 #ba ,a4 ,through the middle of the wheel a small hole is bored to receive the axle of brass which is to be soldered in place4 ,when the wheel is set up1 a metal crank and wooden handle should be soldered fast to one end of the axle4 ,a piece of spring-brass wire is fastened to the block1 with a staple1 and the lower end bent so that the screw in one binding-post will hold it in place4 ,the upper end of the wire is bent in the form of an ,l4 ,from the other binding-post1 through the block and up one support1 a wire is passed1 the end of which comes into contact with the axle4 ,the current1 passing in through one binding-post1 is carried through this wire to the axle1 then to the wheel1 and so on out through the spring-wire and remaining binding-post4 ,when in action the circuit is constantly being broken1 as the spring-wire jumps from the end of one tooth back to the face of the next tooth4 ,the pulsations are increased or diminished by the fast or slow speed of the wheel1 as regulated by the hand motion4 ,the strength of the current is regulated by the force of the battery and should be controlled by a water resistance1 as described for the medical battery1 or shocking-coil4 ,the interrupter1 shown in ,fig4 #bb1 is built up on a block six inches square and seven-eighths of an inch thick4 ,a circle is cut from sheet-lead and laid on the face of the block1 through which pins1 or steel-wire nails1 are driven4 ,the lead circle is five inches in diameter and half an inch in width1 making the inside diameter four inches4 ,the pins or nails are driven a quarter of an inch apart1 and should be properly and accurately separated1 so that an even make-and-break will be the result4 ,it is not necessary to bore holes in the lead1 but the pins or nails should be driven clear through it1 so that perfect contact can be had by the metal parts coming together4 ,otherwise the apparatus would be useless4 ,over the circle of pins a brass bridge is erected1 so that the cross-strips will clear the heads of the pins4 ,a hole is bored at the middle of the bridge so that the revolving axle will pass through it4 ,the axle is made from a piece of stout wire1 or light rod1 and near the foot of it1 and about half an inch above the base-board1 a disk of metal is soldered fast4 ,a piece of spring-brass wire is attached to this disk1 so that when the axle is turned the end of the wire trips from pin to pin1 thus making and breaking the circuit4 ,the upper part of the axle is bent and provided with a small wooden or porcelain knob4 ,one wire from the secondary coil is caught under a screw that holds one end of the brass bridge to the base2 and the other to a screw1 which may be placed at one corner of the block1 and from which a short wire leads to the lead ring4 ,binding-posts may be arranged to serve the same purpose1 and1 of course1 they are much better than the screws1 because they can be easily operated by the fingers and do not require a screw-driver every time the interrupter is placed in series with an induction-coil4 ,an interrupter on this same order may be made from a straight strip of lead with the pins driven through the middle of it4 ,one wire from the secondary coil is made fast to the lead plate1 and the end of the other wire is passed along the pins1 thus making and breaking the circuit in a primitive manner4 ,chapter ,v ,,annunciators ,,and ,,bells ,a ,drum ,sounder ,a unique electric sounder that is sure to attract attention is in the shape of an electric-bell apparatus1 with a drum sounder in place of a bell1 or knockerless buzzer4 ,fig4 #a4 ,the outfit is mounted on a block four inches and a half wide and seven inches long4 ,the cores and yoke are made as described for the electric buzzer 7chapter iv47 and are wound with ,no4 #bb cotton-insulated wire4 ,the magnet is then strapped fast to the block by means of a hard-wood plate having a screw passed down through it2 and between the coils and into the block an armature is made and mounted on a metal plate1 which in turn is screwed to the block4 ,another block1 with a contact-point1 is arranged to interrupt the armature1 and the series is connected as shown in the drawing ,fig4 #a4 ,the end of the wire projecting above the armature is provided with a hard-wood knocker which operates upon the head of the drum4 ,the drum is made from a small tin can1 having one or two small holes punched in the bottom4 ,over the top a thin membrane1 such as a bladder or a piece of sheep-skin or cat-skin1 is drawn and lashed fast with several wraps of wire1 having the ends twisted together securely4 ,the membrane must be wet when drawn over the can end1 and great care should be taken to get it tight and even4 ,then1 when it dries1 it will stretch and draw1 like a drumhead1 and hold its elastic1 resonant surface so long as it does not become moistened or wet4 ,this drum is arranged in the proper position and lashed fast with wires passed over the box and down through holes in the block2 where1 after several turns1 the ends may be securely twisted together4 ,in place of the drum a small wooden box may be lashed fast with its open end against the block1 so as to form a hollow enclosure4 ,the raps of the knocker against its sides will give forth a resonant xylophone tone4 ,an ,annunciator ,a simple annunciator may be made from a core1 a helix1 and some brass strips4 ,a soft iron core1 made of a piece of three-eighth-inch round iron and threaded at one end1 is converted into a magnet by having a spool and wire coil arranged to enclose it4 ,this in turn is screwed into a strip of brass bored and threaded to receive it4 ,fig4 #b4 ,this brass strip is shaped as shown at ,fig4 #c ,a1 and the ears are bent to serve their several purposes4 ,the lowest ears are turned out and the lower part of the plate is bent forward so as to form the hinge on which the drop-bar turns4 ,the drop-bar is only a strip of metal turned up at one end1 on which a numeral or letter can be attached2 while at the other the metal should be bent over so as to form a core into which a pin or wire may be passed and the extending ends bent down1 after being caught through the holes in the ears4 ,above the magnet the strip is bent forward and the top or end ears bent up1 so as to form the hinge on which the armature swings4 ,holes are made in the long ears1 through which screws pass to hold the annunciator fast to the box or wood-work4 ,the armature is made from a strip of brass and is shaped like ,b in ,fig4 #c4 ,the two ears at the top are bent down and fit within those at the top of the first strip4 ,a screw or wire passed through the holes in the ears will complete the hinge4 ,the strip is bent down so as to fall in front of the magnet1 and to its inner side a button or disk of sheet-iron is riveted fast1 so as to form an attraction-plate to be drawn against the magnet when the current is passing around it4 ,the lower part of the armature is bent in hook fashion so as to hold up the drop-bar4 ,a slot is cut in the drop-bar through which the hooked end will project4 ,a short spring is arranged at the top of the annunciator so as to keep the bar and the hook in place when not in action4 ,the current passing around the soft iron core magnetizes it and draws the iron button on the armature towards it4 ,this action immediately releases the hook from under the edge of the metal at the forward end of the slot1 and the bar drops1 bringing the figure down and into plain sight4 ,it is necessary1 of course1 to mount this annunciator so that the bar will not drop down too far4 ,this may be done by having a platform or wire run along under a series of the drops1 so that they will rest on it4 ,illustration3 ,,fig4 #a ,,fig4 #b ,,fig4 #c ,,fig4 #d ,,fig4 #e ,,fig4 #f ,,annunciators ,,and ,,bells ,a ,double ,electric ,bell ,for loud ringing1 and to get the benefit of both the forward and backward stroke of the knocker1 a double bell1 similar to the one shown in ,fig4 #d1 may be constructed upon the general principle of the single-stroke buzzer already described 7chapter iv474 ,two soft iron cores are made1 as described for the other bells1 but instead of being yoked together with iron1 so that the three parts will form a horseshoe magnet1 the yoke is of brass or copper4 ,each core will then be an independent magnet4 ,the spools are wound with ,no4 #bb insulated wire and the ends left free1 so that the coils are not connected together4 ,if the drawing is examined closely you will see that the armature swings on a pivot at the base of the knocker-bar4 ,when the bell is not in action the knocker might rest naturally against one bell or the other2 or it might stand in the centre and not touch a contact-point1 were it not for the small spring which draws it to the left4 ,directly the current is run through the coils it alternately magnetizes first one and then the other4 ,this action is due to the making and breaking of the circuit by the spring on the armature4 ,it first comes into contact with one point1 and then is drawn away from it to come into contact with the other4 ,fig4 #d shows the knocker-bar at rest between both bells and the armature unattracted by either magnet4 ,this position is purposely given so as to indicate the balance of the armature and the spaces between it and the cores and also the contact-points above it4 ,the small1 light wire spring shown in the drawing draws the knocker to one side2 therefore1 when at rest1 one circuit is closed4 ,otherwise the bell would not act when the current is run through the parts--in fact1 the current could not run through at all1 if one or the other contact were not made4 ,the magnets are held fast to a base with a long screw and a small plate of wood laid across them as shown in ,fig4 #d4 ,the armature is a piece of soft iron one-eighth of an inch thick1 half an inch wide1 and three inches long4 ,this has a spring-brass piece attached to it as shown at ,a ,a in ,fig4 #e4 ,small holes are bored through the strip and the iron1 and escutcheon pins are passed through and riveted4 ,a small hole is made down through the middle of the iron plate and a pin is driven into it1 so that a quarter of an inch projects at both sides4 ,another hole is made through the side of the plate for the knocker-bar4 ,then the armature is set in place so that there is a space of one-eighth of an inch between it and the magnet ends4 ,the armature is held in place at the top by a bent metal strip 7,b ,b in ,fig4 #e74 ,this is screwed fast to the base and the bottom is countersunk into the wood4 ,two contact-points 7,c ,c in ,fig4 #e7 are arranged so that when a magnet draws the armature down it brings the opposite end of the armature spring into contact with a point4 ,the wiring is at the under side of the base and is shown in ,fig4 #f4 ,the current enters binding-post ,a1 and passes around coil and magnet ,no4 #a by entering at ,b and leaving at ,c2 from thence to ,d1 entering the armature spring at ,e1 when the small spring has drawn the knocker-bar over to the left4 ,the current passes along the armature and out at ,f2 then along to binding-post ,g1 and so on around through battery ,k and push-button ,l1 thus completing the circuit4 ,directly that this is done the magnet draws the spring end of the armature away from contact-point ,d and up against contact-point ,j1 so that the circuit is broken through coil ,no4 #a and is sent through coil ,no4 #b4 ,this immediately magnetizes core ,no4 #b and draws the armature down to it1 breaking its contact with ,j and re-establishing it with ,d4 ,the rapid alternate making and breaking of the circuit1 and the rapid and strong motion of the armature in its seesaw action1 causes the knocker to rap the bells soundly each time it travels from right to left and back again4 ,two bells of similar size1 or two drums or wooden boxes1 may be employed for this double striker1 and the more current that is run through the coils the more power and a corresponding increase of noise4 ,an ,electric ,horn ,one of the most useful pieces of apparatus where a loud noise is required 7such as in a motor-boat or an automobile7 is the electric horn4 ,it is a rearranged principle of the telephone1 for instead of sound entering or striking against the membrane or tympanum to be transmitted elsewhere1 the disturbance takes place within the horn and the sound is emitted4 ,everybody has been close to a telephone when others have been using it1 and has heard noises1 rasping sounds1 and even the voice of the speaker at the other end of the line4 ,if a cornet were played at the other end of the line it could be distinctly heard through the receiver by many persons in the room1 since its vibrations are loud enough to set up a forcible succession of sound-waves4 ,the same principle operates in the electric horn1 but instead of being agitated at a long distance it is done within the enclosure1 and a very much louder vibration is consequently produced4 ,it is quite as easy to make an electric horn as to construct a bell1 but care must be exercised to have the parts fit accurately and the wiring properly done4 ,if the drawings are studied and the description closely followed1 there is no reason why a horn cannot be made that will demand any one's attention from some distance away4 ,the complete horn is shown in the illustration ,fig4 #g1 and as it is made of wood it is easily attached with screws to a boat or a motor-car4 ,from white-wood1 half an inch thick1 cut two blocks three inches and a quarter square4 ,in one of them 7the rear one7 bore a hole at the centre1 of such size that a piece of three-eighth-inch gas-pipe can be screwed into it4 ,in the other one make a hole two inches in diameter1 so that the cover of a small tin can will fit into it4 ,outside this hole1 and on one side of the block1 cut the wood away and down for one-eighth of an inch1 forming a rabbet1 as shown at ,a in ,fig4 #g4 ,this will be the back of the front block4 ,illustration3 ,,fig4 #g ,,an ,,electric ,,horn ,have a gas or steam fitter cut a piece of two-inch iron pipe one inch and three-quarters long4 ,this will measure a trifle over two inches and a quarter1 outside diameter1 and will form the cylinder or cover for the mechanism4 ,the piece of pipe should fit snugly in the front board1 and at the rear one the wood should be cut away so as to let it in an eighth of an inch1 as shown in the sectional plan of ,fig4 #g4 ,obtain a piece of three-eighth-inch gas-pipe1 threaded at one end4 ,cut it with a hack-saw1 and file the blunt end so that it will measure one inch and seven-eighths long1 as shown at ,c in ,fig4 #g4 ,this is to be screwed into the front of the rear block so that it will project one inch and a half4 ,make a spool to fit the pipe1 as shown at ,b in ,fig4 #g1 or use two wooden button-moulds attached to the pipe with shellac or glue4 ,between them wind on the coils of ,no4 #bb wire to form the helix4 ,cut a hole in the tin-can cover1 as shown at ,d in ,fig4 #g1 and have a tinsmith solder a small funnel to it 7for the horn1 or bell1 as it is called71 cutting away the lower part of the funnel so that the hole in it will correspond in size with that in the can cover4 ,this joint can be made at home by fitting the funnel in the hole and then turning back the edge1 as shown in the sectional drawing at ,e in ,fig4 #g4 ,then1 with a spirit-lamp1 some soldering solution1 and solder1 make a good joint4 ,small holes are to be made at the corners of the blocks1 through which stove-bolts two inches and a half long will fit to bind the front1 back1 and cylinder together4 ,select a good1 clean1 and flat piece of tin and cut a disk two inches and a quarter in diameter1 and through the middle make a small hole4 ,cut two pieces of iron about the size and thickness of a cent1 and bore a small hole through the centre of each4 ,obtain a piece of stout brass wire1 or thin rod1 and file one end of it as shown at ,g in ,fig4 #g1 so that the small end will fit in the holes made in the iron buttons4 ,place one button on either side of the tin disk1 and pass the wire through2 then clamp it in a vise and rivet the top of the rod so that you will have a disk with a button at each side of the centre and all attached firmly to a brass rod1 as shown at ,f in ,fig4 #g4 ,the total length of this rod should be two inches and a half1 and the lower end is to be threaded and provided with two small brass nuts4 ,a piece of spring-brass three-eighths or half an inch wide is made fast to a small block at the back of the horn1 as shown at ,h in ,fig4 #g1 and at its opposite end a contact-piece of metal1 bent at an angle1 is screwed fast4 ,around the back of the back block a wooden frame is attached to protect the rear mechanism of the horn4 ,the parts are now ready to assemble4 ,first see that the metal angle contact-point is in place with the long brass strip resting on it1 and that this in turn is properly fastened to the block on the side opposite the contact-point1 as shown at ,h in ,fig4 #g4 ,there should be a small hole through the middle of the brass strip directly in line with the middle of the hole in the gas-pipe4 ,place this back-board down on the table so that it will lie in a position as indicated in the sectional plan of ,fig4 #g4 ,the gas-pipe is then to be screwed onto the plate4 ,over this the spool with its layers of wire is to be slipped and made fast1 and the cylinder of iron is then placed in position4 ,over this the disk ,f is laid1 so that the brass rod extends down through the pipe and brass strip2 then the nut is screwed on to hold it in place4 ,next comes the front block1 with its horn or bell1 and the entire mass is locked together by means of the four bolts at the corners4 ,the wiring is simple4 ,one inlet being through block ,i1 the current passes through strip ,j to contact-point ,k2 then through the coil and out at wire ,l4 ,the inlet and outlet wires are connected to a battery and to a push-button or switch1 so that the horn can be operated4 ,the proper adjustment of this horn depends on the nuts at the foot of the brass rod4 ,they must be screwed on tight enough to draw the strip ,j so that it rests on the contact-point ,k4 ,the current1 passing in at ,i1 through ,j1 ,k1 the coil1 and out at ,l1 magnetizes the piece of pipe and draws the iron buttons or disks attached to the tin disk4 ,but so soon as it does so it breaks the contact between ,j and ,k1 and the buttons fly back into place1 having been drawn there by the rigidity of the tin disk to which they are attached4 ,again the current is closed and the magnet draws the iron buttons4 ,the brass rod moves but a very slight distance up and down--enough1 however1 to make and break the contact between ,j and ,k4 ,as a result of this rapid movement and the consequent snapping of the tin disk1 a loud noise is emitted through the bell1 which can be heard a long distance and closely resembles a long blast blown on a fish-horn4 ,burglar-alarms ,a unique burglar-alarm trap may be made from a plate of wood1 five by six inches and half an inch thick1 a movable lever1 and a brass strip having the ends turned out4 ,these are arranged as shown in ,fig4 #h4 ,the brass strip is fastened to the plate with screws1 and the ends extend out for half an inch from the board4 ,the lever is made from a strip of brass1 and the upper part is bent out so as to clear the strip and screws that are under it4 ,a hole is made at the lower end of the lever1 through which a brass ring and the end of a spring may be fastened4 ,the opposite end of the spring is attached to a screw1 and a wire carried from it to a binding-post1 ,a4 ,another wire connects the back plate with binding-post ,b4 ,a string or piece of fine picture-wire is made fast to the ring and carried to any part of a room4 ,to set the trap1 make the block fast in any convenient place1 such as the door-casing or the surbase1 and carry the string out from the trap and fasten the end of it4 ,any one running against it in the dark will draw the lever over to the right side and connect the circuit4 ,illustration3 ,,fig4 #h ,illustration3 ,,fig4 #i ,illustration3 ,,fig4 #aj ,when setting the trap1 have the string adjusted so that the lever is in a vertical position1 as shown in the drawing of ,fig4 #h4 ,when the string is disturbed it will pull the top of the lever over to the right side2 but if the string is broken by the person running against it1 the spring attached to the bottom of the lever draws it over to the right side with a snap1 and the top of the lever goes to the left side1 when the circuit is closed and the alarm given4 ,this trap is connected the same as a push-button1 one wire leading to the bell1 the other to the battery2 then the battery and bell are connected together so that when the circuit is closed the bell will ring until some one throws a switch open to break it4 ,another form of circuit-closer is shown in the door-trap 7,fig4 #i74 ,this is a wooden block that rests on the floor close to the bottom of a door1 and is held in place by means of four sharp-pointed nails driven down through the corners of the block4 ,the points should project a quarter of an inch or more1 according to whether the block is on a hard floor or on a carpet4 ,the front edge of the block is bevelled so that the bottom of a door that fits closely to the floor will pass over it4 ,the block is five by seven inches1 and three-quarters of an inch thick4 ,at the left side a strip of metal 7,a7 is held close to the block with straps or wide staples driven over it1 but not so close but that it can move freely back and forth4 ,to the front end a round piece of wood is made fast4 ,this is the bumper against which the door will strike when opened4 ,at the middle of the strip a screw is riveted fast2 or it may be a machine-screw let into a threaded hole in the metal4 ,at the right side of the block another strip of metal 7,b7 is attached1 but this is held fast with a screw at the middle and a screw-eye and washer at the rear end to act as a binding-post4 ,the front end of this strip is turned up so as to form a stop2 then a movable lever 7,c7 mounted over both strips1 with one end bent up1 is attached to the block with a screw4 ,a slot is cut at one end so that the screw in the movable strip 7,a7 will move freely in it1 and near the other end a small hole is made to receive the end of a spiral spring 7,d74 ,to set the trap1 the block is placed on the floor and the wires from battery and bell are made fast to the binding-posts4 ,the spring ,d keeps the lever ,c away from the strip-end ,b1 while at the same time it throws the strip ,a forward4 ,when the door is opened it shoves the bumper and strip ,a back through the staples1 while the screw operates lever ,c and causes its loose end to come into contact with the end ,b1 thereby closing the circuit and ringing the bell or buzzer4 ,when the door is closed again the spring draws lever ,c away from ,b1 and the circuit is opened4 ,the block acts as an obstruction as well as an alarm1 for the pins will hold in the floor and the little block will stand its ground4 ,a simple form of contact for doors is shown at ,fig4 #aj4 ,this is simply two strips of spring-brass bent as shown1 and screwed fast on either side the crack of a door1 at the hinge side1 so that when the door is opened one piece of metal bears on the other and the circuit is closed4 ,this is to be operated in connection with a switch1 so that the circuit may be opened in the daytime when the door is in use4 ,signals and ,alarms ,there are many different kinds of electric call-signals used in and about the house2 among these are some that a boy can readily make--for example1 the ordinary call-buttons and the signals between house and stable or other out-buildings4 ,a portable call-bell1 or alarm1 is one of the most convenient things in any home4 ,it may be temporarily rigged up from one room to another1 or from one floor to the next1 the small1 flexible wire being run over the tops of door-casings1 where it is held by slim nails or pins driven into the wood-work4 ,the main terminal of this portable outfit consists of a wooden box that will hold a large dry-cell1 and to the side of which an electric bell or buzzer may be attached4 ,binding-posts are arranged at another side1 to which the ends of the flexible wire-cord can be made fast1 and a cover fitted to the box to hide the battery and wiring4 ,the complete outfit1 except the flexible wire-cord and push-button1 will appear as shown in ,fig4 #aa4 ,no definite size can be laid down for the construction of this box1 as dry-cells vary in size and shape1 some being long and thin1 while others are short and fat4 ,by removing the cover and looking into the box1 it will appear as shown in ,fig4 #ab4 ,the carbon is connected with one binding-post and the zinc to one of the poles of the bell4 ,the other bell-pole is connected with the remaining binding-post1 and it requires but a switch or push-button to close the circuit between the two binding-posts4 ,this is done by the long line of flexible wire-cord1 which may be of the silk or cotton covered kind1 having the two strands twisted together as is customary with flexible electric-light wire4 ,a pear-shaped push-button may be connected at the end of the line1 and this may be arranged at the head of a bed or on a chair placed conveniently near an invalid's couch4 ,this same apparatus is a very convenient thing for a lecturer where a stereopticon is used4 ,a buzzer takes the place of the bell1 which would be too loud in a hall or lecture-room1 and the cord1 passing from the apparatus close to the operator1 is hung over the lecturer's stand1 or the button held by him in the hand1 to be pressed whenever he desires the pictures changed4 ,illustration3 ,,fig4 #aa ,illustration3 ,,fig4 #ab ,illustration3 ,,fig4 #ac ,this apparatus can be used also in connection with an alarm-clock1 where the winding-key is exposed at the back1 as it is in most of the nickel-cased clocks that are operated by a spring and which have to be wound each day4 ,for this purpose obtain a piece of hard rubber or fibre1 one-sixteenth of an inch thick1 an inch long1 and half an inch wide4 ,a piece of stout card-board or a thin piece of hard-wood soaked in hot paraffine will answer just as well1 if the fibre or rubber cannot be had4 ,bore a small hole at the two upper corners and one at the middle near the lower edge4 ,obtain three garter-clips1 with springs1 and rivet one of them fast to the little plate of non-conducting material4 ,cut two lengths of old brass watch-chain1 four inches long1 or obtain eight inches of chain at a hardware-store1 and divide it in half4 ,attach a garter-clip to one end of each piece1 and make the other end fast in the holes at the corners of the small plate as shown in ,fig4 #ac4 ,this will be the connector and will close the circuit when the alarm goes off4 ,when the clock is wound and the alarm-spring is tight1 catch one binding-post with a clip at the end of a chain and the other post with the remaining clip4 ,place the clock near the box and grasp the alarm-key with the clip on the plate4 ,when the alarm goes off the bell on the clock will begin to ring1 and when the key has made one revolution it twists the two pieces of chain together1 closes the circuit1 and the electric bell rings until some one unfastens one of the clips on the binding-posts and breaks the circuit4 ,the great advantage in this double-alarm outfit is that it keeps the bell ringing until the attention of the sleeper is attracted4 ,the bell on the clock will stop ringing directly the spring is unwound or run down2 but in so doing it twists the chain and sets the electric mechanism in motion1 to run until it is stopped1 or until the battery polarizes or is exhausted4 ,a ,dining-table ,call ,one of the most convenient of house electric-calls is that between the dining-room and the butler's pantry or the kitchen1 its purpose being to summon the waitress without the necessity of ringing a bell at the table1 or calling4 ,there are various forms of push-buttons for this purpose--some embedded in the floor1 others hanging from the centre light1 and others again where the wire runs up from under the table1 and the pear-shaped push rests on the cloth within easy reach4 ,these last are good enough in their way1 but are inconvenient1 unsightly1 and quite liable to get out of order4 ,in order to use the floor-push the table must stand in exactly the right place2 with the drop-string from a chandelier the cord is continually getting in the way2 and as for the portable push that comes from under the table1 one must be forever hunting for the button every time the table is set4 ,and yet it is quite possible to avoid all these troubles and construct an apparatus that is always in order and always available1 wherever the table may be placed4 ,a visitor at a certain house noticed that the number of the family present at a meal was apt to vary largely1 necessitating frequent lengthenings and shortenings of the table4 ,and yet the waitress invariably appeared just at the right time1 and whether one end or the other of the table was to be served1 she was always on the spot where she was needed4 ,the visitor tried to study it out1 but was finally obliged to ask for an explanation of the mystery4 ,the boy of the house smiled and intimated that he was responsible for this domestic miracle2 later on1 when dinner was over1 he removed the centre leaves from the table and displayed the simple apparatus that he had constructed and which had worked for several years without adjustment or repairs4 ,the illustration 7,fig4 #ad7 represents the frame of a dining-table with the middle cross-bar made fast to the side-rails1 so as to support the mechanism4 ,at both ends1 and inside the rail1 push-buttons are arranged and wires carried from them to binding-posts close at hand1 as may be seen at the left side4 ,the cross-bar at the middle of the table supports a large spool on which the flexible cord is wound1 and kept taut by means of a clock-spring4 ,this spool takes up the slack between the ends of the table when it is lengthened or shortened1 while the smaller one opposite it keeps taut the feed-wires that come up through the floor4 ,a short distance from the floor the wire is provided with a connector1 so that when the rug is removed the feed-wires may be disconnected and slipped down4 ,the large spool can be had at any dry-goods store where braids or fancy cords are kept4 ,it should be about four inches long1 three inches in diameter1 and with sides thick enough to enable screws to be driven into it without fear of splitting the wood4 ,an old clock-spring is attached at one side of the spool1 while at the other two circular bands of brass are made fast1 one within the other4 ,an axle of stout wire should be driven through the spool2 but if the hole is too large1 wooden plugs may be glued in at each end so that a front view of the spool will appear as shown at ,a4 ,the metal bands are cut with shears from sheet-brass1 and are attached with fine steel nails1 the heads of which are driven in flush with the wood4 ,a hole is made in the side of the spool1 close beside each band1 so that the ends of wires may be brought through them and attached to the bands4 ,this arrangement is illustrated at ,b1 and at ,c the opposite end is shown1 with its clock-spring1 one end of which is made fast to the side of the spool and the other to the cross-rail4 ,a small round piece of wood is slipped over the axle1 at the spring side1 and projects a quarter of an inch beyond the spring4 ,this is to keep the spring away from the arm that stands out on that side to hold the spool in place4 ,illustration3 ,,fig4 #ad ,a ,,dining-,,table ,,call ,about half an inch of space is left between the spool and the arm at the opposite side1 so that the spring contact-strips may be made fast to the arm and still have room to act4 ,a view looking down on the spool and springs is shown at ,d1 and ,e illustrates the arrangement of the circular strips and the spring contact-strips4 ,if the table is to remain permanently in the same position1 only one spool will be required1 for the floor wires can come up and connect directly with the contact-strips4 ,but if the table is to be moved about1 a tension-spool1 independent of the push-button wires1 is necessary so that the position of the table may be changed without unwinding the large spool and dropping the cords down to the floor4 ,the smaller spool is made and mounted in the same manner1 and should be placed close to the large one4 ,but a lighter spring will operate it4 ,one end of a double wire-cord is made fast to binding-posts1 mounted on a yoke of hard rubber or fibre1 so that the terminals will be kept apart1 as shown at ,f4 ,the other ends are passed through the holes at one side of the small spool and soldered fast to the circular strips1 or a small screw may be passed down through the hole1 binding the wire and touching the edge of one strip4 ,take care that it does not touch the other strip4 ,the cord is then wound on the spool1 and it is slipped in place so that the loose end of the spring is caught and held over a nail or screw-head4 ,turn the spool over several times to partially wind the spring2 then attach the terminals to the wires that come up from the floor and the tension of the spring will draw the wires taut4 ,the two contact-strips of brass1 that rest against the brass circles1 have insulated wires leading out from them in order to connect them with the corresponding wires leading from the strips of the larger spool4 ,a simple way to mount the spools is shown at ,a in ,fig4 #ae4 ,a notch is cut in the face of the blocks large enough to admit the axle2 then a face-plate is screwed over the end of the block to hold the axle in place4 ,this arrangement makes it easy to remove the spool1 in case of necessity1 without detaching the arms from the cross-rail4 ,illustration3 ,,fig4 #ae ,two sets of wires are wound on the large spool1 one leading to the right-hand and the other to the left-hand push-button on the table-rails4 ,the ends of the wires are arranged so that one leading from both directions is made fast to one circular strip on the spool1 the other two being attached to the remaining band4 ,this is more clearly shown at ,b in ,fig4 #ae1 where the ends are visible as they are twisted together and pass through their respective holes4 ,the spool is then turned over1 and six or eight feet of wire wound on from each side4 ,the spring is coiled up and caught on the nail or screw1 and the ends of the wires are made fast to the binding-posts near the push-buttons4 ,the wires from both push-buttons are then in connection with the circular bands1 which in turn are connected to the bands on the smaller spool1 and lead the current down through the floor wires4 ,by pushing the button at either end the circuit is closed and the buzzer or bell is rung in the kitchen or pantry4 ,arranged in this manner1 the wires are kept off the floor1 no matter where the table is moved1 and it can be drawn open as wide as may be found necessary to put in leaves4 ,when closed again1 the spring causes the large spool to revolve and wind up the wire4 ,chapter ,,vi ,,current-,,detectors ,,and ,,galvanometers ,a current-detector is a necessary part of the amateur electrician's equipment2 technically1 this piece of apparatus is called a galvanoscope4 ,when a wire or a number of them are brought near a magnetic needle or a small compass1 the needle will be deflected from its north and south line and will point east and west1 or west and east1 according to the direction in which the current is passing through the wires4 ,all wires that are conducting electricity have a magnetic field1 and when brought near the magnetized needle of a compass they have the power to act on it the same as another and stronger magnet would4 ,the action of detectors depends upon two things--first1 the magnetized needle that1 when properly balanced1 will point north and south2 and1 secondly1 a current of electricity passing through a wire or wires held above the needle1 or both above and below it4 ,this is more clearly shown in ,fig4 #a1 where a compass is resting on a wire connected to a battery4 ,the wire also passes over the top of the compass1 which doubles the electro-magnetic field4 ,when the compass 7with the needle pointing north7 is resting on the wire that is attached to the zinc pole of a battery1 and when the end of the wire that passes back over the top of the compass is attached to the carbon pole1 the needle will fly around and point to the east4 ,when the wires are reversed1 the needle will point to the west4 ,thus the combination of a battery or other source of electric current1 a magnetic needle1 and a coil of wire properly arranged1 make an instrument that will detect electric currents and may be correctly called a current-detector4 ,the pressure of more or less current is determined by instruments wound with wire of different sizes2 the finer the wire the more sensitive the instrument1 and consequently the more delicate4 ,a very weak current can only be detected with a delicate and sensitive instrument4 ,the coarser the wire and the larger the instrument1 the better it will be for testing strong currents that would perhaps burn out the fine wire of the more delicate apparatus4 ,this instrument1 when placed between a source of electricity and a piece of apparatus1 such as a bell1 a motor1 or lamp1 does not weaken the current1 for it requires no waste of electricity to operate the magnetic needle4 ,consequently1 when a very weak current is being used for any tests1 it is well to place a detector between the battery and the apparatus to show that the current is actually passing through the wire4 ,a simple detector is made by winding fifteen or twenty feet of cotton-insulated copper wire ,no4 #bf or #bh around the lower end of a drinking-glass4 ,leave six inches of each end loose2 then after slipping the coil from the glass1 tie the wires with thread at least four times around the circle1 so as to bind the wires together4 ,press two sides of the hoop together so as to flatten it2 then with paraffine attach the coil to a square block of wood1 as shown in ,fig4 #b4 ,illustration3 ,,fig4 #a ,illustration3 ,,fig4 #b ,illustration3 ,,fig4 #c ,illustration3 ,,fig4 #d ,illustration3 ,,fig4 #e ,from a thin clock-spring1 not more than three-eighths of an inch wide1 cut a piece two inches and a half long1 and with a stout pair of tin-shears cut the ends so as to point them1 as shown in ,fig4 #c ,a4 ,with two pair of pliers bend a hump at the middle of the strip on the dotted lines shown in ,a1 so that a side-view will appear like ,b in ,fig4 #c4 ,turn this strip over on a hard-wood block or a piece of lead1 and with a stout steel-wire nail and a hammer dent the inverted ,v at the middle so that it will rest on the top of a needle-point without falling off4 ,with three little pieces of wood make a bridge and attach it to the wooden base over the paraffine that holds the wire-coil1 and drive a needle down in the middle of it1 taking care that it does not go through the back and touch the wires underneath4 ,on this needle hang the strip of steel spring1 and1 if it does not properly balance1 trim it with the shears or a hard file until it is adjusted properly4 ,rub this piece of steel over the pole ends of a large horseshoe magnet1 or place it within the helix of a large coil and turn a powerful current through the coil4 ,this will magnetize the strip of steel1 which will then become a magnetic needle and hold the magnetism4 ,attach two binding-posts to corners of the block1 and make the loose ends of the coil-wires fast to them4 ,you now have a current-detector1 or galvanoscope1 as shown in ,fig4 #d4 ,turn the block so that the needle points to north and south and parallel to the strands of wire4 ,when the conductors from the poles of a battery or dynamo are made fast to the binding-posts1 the needle will fly around to a position at right angles to that which it first occupied1 as shown by the dotted line ,a ,a in ,fig4 #d4 ,when the connection is broken the needle will turn around again and point to north and south1 since the magnetic field about the wire ceases and disappears the instant the circuit is broken4 ,this is one of the strange and unknown phenomena of electricity1 for while the current exerts a force that deflects the needle1 it does not destroy its magnetism4 ,on the breaking of the contact1 no matter how long it may have held the needle away from its true course1 it again points to north1 and its magnetism is not affected4 ,another simple current-detector is shown in ,fig4 #e4 ,a piece of broomstick is sawed in half and both pieces are made fast to a block which is mounted on a base of wood three-quarters of an inch in thickness4 ,the vertical block should measure five inches long1 three inches high1 and five-eighths of an inch thick4 ,the half-circular pieces of wood are mounted so that the flat surfaces are three inches apart and the lower edges are one inch above the base-block4 ,these may be held in place with glue and screws driven through the back of the vertical block and into the ends of the projecting half-circular pieces4 ,the base-block is six inches long and four inches wide1 and the vertical block is mounted on it one inch from an edge4 ,the pieces of broomstick are two inches long1 and at the front ends a thin bar of brass or copper is screwed fast to hold them apart and in proper position1 as shown at ,a in ,fig4 #e4 ,to improve the appearance of this mounting1 all the wood-work may be stained and shellacked before the metal parts are attached4 ,with ,no4 #bf1 #bh1 or #cj cotton-insulated wire make from fifteen to twenty wraps about the middle of the half-circular pieces of wood and carry the ends down through small holes in the base-block and thence through grooves cut at the under side of the block to the front corners1 where they are to be made fast to binding-posts4 ,a needle is to be set in the base-block midway between the two pieces of half-circular wood and through the strands of wire4 ,great care must be taken that the needle does not touch any bare wires1 and as a precautionary measure it would be well to wrap the needle with a piece of insulating-tape where it passes through the strands of wire4 ,now place on the top of it a magnetized piece of steel1 as described for the detector shown in ,fig4 #d4 ,as it may not always be convenient to turn the instrument so that the needle points north1 a small bar of magnetized steel or a stout needle that has been magnetized with a horseshoe magnet or a helix1 may be laid across the half-circular wood pieces1 so that it is parallel with the top layer of wires--in fact1 it should rest on top of them4 ,by means of this needle1 or bar1 the magnetic piece of steel balanced on the vertical needle between the upper and lower strands of insulated wire may be held in one position no matter which way the block is turned4 ,when the current passes in through one binding-post and out through the other 7having thus travelled through the coil on the half-circular blocks7 the needle is deflected and points out at the brass bar and back at the upright block4 ,when making any of these pieces of apparatus1 where delicately balanced magnetic needles are employed1 all parts of the mounting blocks or other sections must be put together with glue and brass nails or screws4 ,it will not do to use steel or iron nails1 screw-eyes1 or washers1 nor pieces of sheet-iron1 tin1 or steel1 for they will exert their influence on the vital parts of the apparatus and so destroy their usefulness4 ,this is not so important when making buzzers1 bells1 motor-induction coils1 or similar things1 but in delicate instruments1 where magnetic needles or electro-magnets are used for recording1 measuring1 or detecting1 iron and steel parts should be carefully avoided1 except where their use is expressly indicated4 ,an ,astatic ,current-detector ,astatic current-detectors and galvanometers are those having two magnetic needles arranged with the poles in opposed directions4 ,the ordinary magnetic or compass needle points to the ,north1 and in order to deflect it a strong magnetic field must be created near it4 ,for strong electric currents the ordinary single-needle current-detector meets all requirements1 but for weak currents it will be necessary to arrange a pair of needles1 one above the other1 with their poles in opposite directions1 and placed within or near one or two coils of fine wire4 ,this apparatus will be affected by the weakest of currents1 and will indicate their presence unerringly4 ,the word 8astatic0 means having no magnetic directive tendency4 ,if the needles of this astatic pair are separated and pivoted each will point to ,north and ,south1 after the ordinary fashion4 ,for all astatic instruments we must employ two magnetic needles in parallel1 either side by side or one above another1 as shown in ,fig4 #f1 with the ,n and ,s poles arranged as indicated4 ,this combination is usually called ,nobili's pair4 ,if both needles are of equal length and magnetic strength1 they will be astatic1 for the power of one counterbalances that of the other4 ,as a consequent neither points to ,north4 ,a compound needle of this form requires but a very feeble current to turn it one way or the other1 and this is the theory upon which all astatic instruments are constructed4 ,a simple astatic current-detector may be made from a single coil of fine insulated wire1 a pair of magnetic needles1 and a support from which to suspend them1 together with a base-block4 ,for the base-block obtain a piece of white-wood1 pine1 or cypress1 four inches square and three-quarters of an inch thick4 ,sand-paper it smooth1 and then give it two or three coats of shellac4 ,from a strip of copper or brass 7do not use tin or iron7 make a bridge1 in the form of an inverted ,v1 seven inches high1 using metal one-sixteenth of an inch thick and half an inch wide4 ,this bridge is to be screwed to the outside of the block1 as shown at ,fig4 #g1 so that it will be rigid and firm4 ,a small hole is drilled through the top of the bridge to admit a screw-eye for the tension4 ,make a coil of ,no4 #cj insulated wire1 using ten or fifteen feet1 and wind it about the base of a drinking-glass to shape it2 then remove it and tie the coil1 in several places1 with cotton or silk thread1 so as to hold the strands together4 ,shape it in the form of an ellipse and make it fast to the middle of the base-board with small brass or copper straps1 and copper tacks or brass screws4 ,be very careful not to use iron1 steel1 or tin about this instrument1 as the presence of these metals would deflect the needles and make them useless4 ,separate the strands at the top of the coil so that one of the needles may be slipped through to occupy a position in the middle of the coil4 ,ordinary large compass needles may be employed for this apparatus1 or magnetized pieces of highly tempered steel piano-wire will answer just as well4 ,illustration3 ,,fig4 #f ,illustration3 ,,fig4 #g ,illustration3 ,,fig4 #h ,a short piece of brass1 copper1 or wood will act as the carrier-bar for the needles4 ,these should be pushed through holes made in the bar1 and held in place with a drop of shellac or melted paraffine4 ,a small hole is drilled at the top of the bar1 or a small eye can be attached1 through which to pass the end of a thread4 ,the upper end of the thread is tied in a screw-eye1 the screw part of which passes up through the hole in the bridge and into a wooden button or knob1 which can be turned to shorten or lengthen the thread1 and so raise or lower the needles4 ,the lower needle must be pivoted at an equal distance between the upper and lower parts of the coil4 ,two binding-posts are arranged at the corners of the base1 and the ends of the coil wires are attached under the screw-heads4 ,the in-and-out wires are to be made fast under the copper washers on the screw-eyes4 ,owing to the astatic qualities of the needles1 the base-block does not have to be turned so that the coil may face ,north and ,south1 as in the current-detector4 ,when the slightest current of electricity passes through the coil it instantly affects the needles1 turning them to the right or left according to the way in which the current is running through the coil4 ,an ,astatic ,galvanometer ,the sensitiveness of an astatic detector may be increased by the added strength of the coil-field for a given current4 ,there are two ways of accomplishing this result4 ,the number of turns of wire may be increased in the coil1 or two coils may be used1 placed side by side4 ,the latter method is the more satisfactory1 since then the coil does not have to be opened at the top to admit the lower needle1 the latter being dropped down between the coils4 ,this apparatus is shown in the illustration of an astatic galvanometer1 ,fig4 #h4 ,the general arrangement of needles1 bridge1 and coils1 is the same as described for the astatic current-detector4 ,each coil is made separately of ten feet of ,no4 #cj insulated copper wire1 wound about the base of a drinking-glass to shape it2 then pressed into elliptical shape1 and fastened to a base-block with a brass or copper strip1 and held down with small brass screws4 ,the base-block should be four inches square1 with the corners sawed off4 ,smooth the block with sand-paper1 and then give it several good coats of shellac4 ,the bridge is made from brass one-sixteenth of an inch thick and half an inch wide4 ,the coils of wire are arranged about half an inch apart1 and at both ends a small separator-block is placed between the coils1 and then bound with silk or cotton thread4 ,a circular indicator disk of bristol-board should be cut out and marked and attached to the top of the coils with a few drops of sealing-wax or paraffine2 then the needles are suspended so as to hang properly1 one above the card1 the other between the coils4 ,three binding-posts are placed at one end of the block1 and to them the end wires of the coils are led and attached4 ,to the first binding-post 7at the left7 the strand of wire leading to the first coil is attached4 ,it leads in and is coiled as the hands move on a clock1 from left to right4 ,the leading-out wire from the coil is made fast to the middle post4 ,the leading-in wire to the second coil is also made fast to the middle post4 ,the coil wires should have the turns in the same direction as the first coil2 then the last wire is attached to the right-hand post4 ,when making connections for a strong current1 use an end and middle post4 ,this arrangement will operate but one coil4 ,for very weak currents make the leading in and out wires fast to the end-posts4 ,this latter plan is more clearly shown in the diagram1 ,fig4 #i4 ,a and ,b represent the coils1 ,c1 ,d1 and ,e the binding-posts4 ,the current1 entering at ,c1 passes through the coil ,a 7as the hands move about the dial of a clock7 and out at ,d1 where connection is made with the wire leading in to coil ,b4 ,the current passes through this coil in the same direction as the clock hands move1 and out to post ,e4 ,be careful to arrange the wiring and connections after this exact manner1 otherwise the instrument will not be of any use4 ,the adjustment at the top of the bridge may be made with an inverted screw-eye and a small cork into which the eye can be screwed1 thus raising or lowering the needles to the proper position4 ,be sure to have the needles in parallel when at rest4 ,as the needles and coils are very sensitive it would be well to cover the instrument with an inverted glass jar4 ,a bluestone or gravity battery jar will answer very well1 and after the wires are connected to the binding-posts the glass may be placed over the entire apparatus4 ,a ,tangent ,galvanometer ,for testing the various degrees of intensity of a current a tangent galvanometer is usually employed4 ,in this apparatus the increased strength is indicated by the index-pointer as it plays over a scale or graduated circle4 ,a simple tangent galvanometer may be made from a flat hoop of wood-fibre or brass1 mounted on a base by means of two uprights1 together with the necessary compass needle1 an index-card1 insulated wire1 and binding-posts for the electrical connections4 ,this piece of apparatus is shown in ,fig4 #aj4 ,it is built on a base-block six by seven inches and three-quarters of an inch thick4 ,the block should be of selected wood1 and after it is made smooth it should be given several coats of shellac4 ,two upright pieces of wood1 five inches long1 half an inch thick1 and one inch in width1 are screwed fast to the rear edges of the base-block to support the hoop on which the insulated wire is wound4 ,be careful not to use any iron or steel in the construction of this or any other recording instrument1 except where it is expressly stated4 ,screws1 nails1 staples1 or any bits of anchoring wire should be of copper or brass4 ,string1 thread1 or silk may be used1 especially where coils of wire are to be bound or fastened to hoops or base-blocks4 ,the balance of the indicating needle is so delicate1 and the sensitiveness of the coils is so easily affected1 that nothing about or near the instruments should be of iron or steel4 ,the hoop may be made of very thin hickory wood1 steamed and bent so as to form a ring six inches outside diameter and one inch wide4 ,it is even possible to construct a satisfactory hoop from a ribbon of brown paper1 rolled and lapped1 the several thicknesses being glued as the turns are made4 ,if a metal hoop is to be used1 solder the ends of a thin1 hard ribbon of brass1 copper1 or zinc4 ,this strip should be provided with holes1 set in pairs about four inches apart1 all around the hoop1 and where the hoop is to be attached to the uprights two holes should be made close to the margins through which brass screws may pass4 ,across the middle of the hoop a strip of wood six inches long1 an inch wide1 and a quarter of an inch thick is made fast4 ,on this the graduated card is placed1 and at the centre the balanced magnetic needle is arranged on a pivot4 ,after the cross-stick is in place1 wind five turns of ,no4 #bd insulated copper wire about the hoop1 keeping it as nearly in the centre as possible4 ,one end of the wire 7the beginning7 is to be attached to the first binding-post on the front of the base1 and the other end to the second post4 ,the wire should be wound round the hoop in the same direction as the clock hands travel about a dial4 ,another coil1 composed of ten turns of wire1 is made over the first one1 the beginning end being attached to the middle binding-post and the last end to the third post4 ,this arrangement is shown in ,fig4 #aa1 ,d and ,e representing the coils1 while ,a1 ,b1 and ,c are the binding-posts4 ,the current enters at ,a1 passes through coil ,d1 and out at post ,b4 ,the next passage is in at ,b1 through ,e1 and out at ,c4 ,a current passing in at ,a will travel to ,b1 thence through ,e1 and out at ,c4 ,if the leading-in wire is made fast to ,a1 and the out wire to ,c1 the current will travel through the entire coil4 ,under this plan one or both coils may be used 7the short or long one as desired7 by making connections with the first and second binding-posts1 the second and third1 or the first and third1 as the strength of the current will warrant4 ,strong currents will deflect the needle when travelling through a short coil1 but the weaker the current the more coils it will have to pass through to properly deflect the needle and indicating pointer4 ,illustration3 ,,fig4 #aj ,,fig4 #aa ,,fig4 #ab ,,fig4 #ac ,,fig4 #ad ,,fig4 #ae ,,tangent ,,galvanometers ,when the coils are all on1 the hoop should be attached to the uprights with small brass screws driven through holes in the hoop and into the wood4 ,the wire is bound to the hoop by means of threads or silk passed through each pair of holes in the hoop1 and then tied fast4 ,fine insulated wire may be used in place of the thread1 but care should be taken that the insulation is in perfect shape on both the binding and coil wires2 otherwise a short-circuit will quickly destroy the value of the coils4 ,the hoop should not touch the base-block1 but should clear it by a quarter or half an inch4 ,make the coil ends fast 7as described for the astatic galvanometer and illustrated at ,fig4 #i7 by means of binding-posts4 ,the wires need not be carried over the top of the block1 but may run through holes under the hoop and along grooves cut in the under side of the block and leading to the foot of the binding-posts4 ,the graduated card should be made from a piece of stout bristol-board or heavy card-board having a smooth1 hard surface4 ,it is laid out with a pencil or pen compass1 as shown at ,fig4 #ab1 and should be three inches in diameter4 ,the card is placed on the wood strip or ledge1 so that the zero marks will be at the front and rear1 or at right angles to the hoop and coils of wire4 ,the compass needle1 when at rest1 should lie parallel with the coils1 so that the current will deflect the needle and send the indicator around to one side or the other of zero1 according to the direction in which the current is passing through the coils4 ,this is more clearly shown at ,fig4 #ac4 ,the circle represents the outside diameter of the card2 the dark cross-piece1 the magnetic needle2 and the pointed indicator1 a stiff paper1 or very thin brass or copper strip1 cut and attached to the needle with shellac or paraffine4 ,when at rest the magnetic needle should be parallel to the coils4 ,to insure this the instrument must be moved so that the lines of wire forming the coil will run ,north and ,south4 ,otherwise the ,n-seeking end of the magnetic shaft will point to ,north1 irrespective of the position occupied by the wire coil4 ,the magnetic needle may be made as described for the compass 7see chapter iv41 ,magnets and ,induction ,coils74 ,it should be arranged to rest on a brass pivot pressed down into the cross-piece of wood4 ,the indicator-needle may be cut from stiff paper1 thin sheet-fibre1 or very thin cold-rolled brass or copper1 the latter being commonly known as hard or spring-brass4 ,only one pointer is really necessary--that pointing to the front4 ,but the weight of the material would have a tendency to upset the magnetic needle1 and therefore it is better to carry an equally long tail or end1 on the opposite side1 to properly balance the needle4 ,a very weak current1 passing in through the first post and out at the third1 will cause the indicator to be deflected considerably1 or so that it will point from #dj to #fj on either side of the zero point1 according to the direction in which the current is running through the coils4 ,when not in use the magnetic needle should be removed from the pivot1 and placed in a box or other safe place1 where it will not become damaged4 ,a differently arranged tangent galvanometer is shown at ,fig4 #ad4 ,as the line of binding-posts would indicate1 there are several coils of wire about the circle or hoop4 ,this galvanometer can be used for either strong or weak currents1 since it is wound with both coarse and fine insulated wire4 ,an upright plate of wood1 seven inches wide and eight inches high1 supports the hoop and compass4 ,the top corners are sawed off1 and four inches above the bottom a straight cut is made across the plate1 five inches wide and arched in a half-circle five inches in diameter4 ,a shelf of wood a quarter of an inch thick1 three inches wide1 and five inches long is made1 and attached as a ledge in this arched opening1 so that a compass three inches in diameter may rest upon it4 ,the shelf should be arranged so that it will hold the compass in the middle of the circle instead of at one side4 ,the turns of wire will then be in line with the magnetic needle when the latter is at rest4 ,a base-block seven inches long1 three inches wide1 and seven-eighths of an inch thick is cut and attached to the upright plate by driving screws through the bottom of the plate and into the rear edge of the base4 ,the corners are to be cut from the front of the base1 and ten small holes are to be bored half an inch out from the upright and about a quarter of an inch apart4 ,these are for the end wires that will extend down from the coils1 and from thence to the binding-post holes4 ,grooves may be cut in the under side of the base-block for the wires to rest1 in1 as shown at ,fig4 #ae1 which is a view of the inverted base4 ,a hoop is made of brass1 six inches in diameter and an inch wide4 ,it is held to the upright plate with copper wire passed through a small hole1 bored at the inner edge of the band1 and back through two small holes bored in the plate1 the ends being twisted together at the back of the plate4 ,a wire at the top1 bottom1 and both sides will be sufficient to hold it securely in place4 ,the first coil of wire is made of ,no4 #ah insulated1 and the beginning end is made fast to the binding-post at the left4 ,the wire is carried up through the first hole under the hoop1 and after three turns have been made the end is carried down through the second hole and made fast to the foot of the second binding-post4 ,the second coil is of ,no4 #bd insulated copper wire4 ,the beginning end is made fast to the second binding-post1 carried up through the third hole1 given five turns about the hoop1 drawn down through the fourth hole1 and attached to the third binding-post4 ,the third coil is of the same size wire but has ten turns4 ,the fourth coil has twenty turns1 and the fifth1 of ,no4 #cj insulated wire1 has thirty turns1 the last end being attached to the post at the right4 ,in all the coils there should be a total of sixty-eight turns1 or about one hundred and five feet of wire4 ,for strong currents the in-and-out wires may be attached to posts ,nos4 #a and #b at the left1 and for weaker currents to ,nos4 #b and #c4 ,for still weaker currents1 use ,nos4 #c and #d1 and so on4 ,to detect the very weakest currents1 attach the in-and-out wires to the first and last post1 and let the current travel through all the coils or the entire length of the wire wound about the hoop4 ,the magnetic needle is made in the same manner as described for ,fig4 #aj1 and the pointer is attached in a similar fashion4 ,but instead of being mounted on a pivot over a card1 and so exposed to the open air and possible draughts1 the delicate mechanism is arranged within a brass hoop1 which is made fast to the ledge4 ,the graduated card is at the bottom of the hoop1 or box formed by it1 and to protect the needle and prevent it from being displaced it should be covered with glass4 ,this can be done by making a split ring of spring-brass wire and pressing it down inside the hoop4 ,over this a round piece of glass is placed1 and another hoop is pressed in above it to hold the glass in position4 ,if the rings are carefully made and of stout wire they will stay in place2 otherwise a drop of melted sealing-wax or paraffine will be necessary to keep them where they are wanted4 ,the glass should be arranged close enough to the needle to prevent it from jumping or being shaken off the supporting pin1 but not so close as to prevent its moving easily4 ,part ,,ii ,chapter ,,vii ,,electrical ,,resistance ,the science of controlling forces is so well understood and figured out that it becomes a simple mechanical proposition to adapt the various types of controllers to any form of power that may be employed4 ,the tremendous force stored within the mechanism of a great transatlantic liner is governed by the twist of a man's wrist4 ,the locomotive that will pull a hundred cars loaded with coal1 representing a weight of thousands of tons1 is started and stopped by a short lever that is drawn in one direction or the other by a man's hand4 ,great forces of all kinds are quite as easily controlled as the supply of gas through a jet--by simply turning the key that lets out so much as may be required1 no matter what the pressure is back of the flow4 ,this same principle applies to electricity1 but the means of governing it is vastly different from the methods employed for other forces4 ,electricity is an unknown and unseen force1 coming from apparently nowhere and returning to its undiscovered country immediately upon the completion of its work4 ,the flow of steam1 water1 liquid air1 gas1 and compressed air through pipes is governed by a throttle or cock1 which allows as much or as little to pass as may be required2 and if the joints1 unions1 and couplings in the pipes are not absolutely tight there will be a leakage4 ,electricity is controlled by resistance in its passage through solid wires1 rods1 or bars1 and cannot be confined within a given space like water1 nor held in tanks or pipes as a vapor or gas4 ,it is invisible1 colorless1 odorless1 and occupies no apparent space that can be measured2 it is the most powerful and terrible and yet docile force known to man1 doing his bidding at all times when properly governed and regulated4 ,in some respects1 electricity can be compared to water stored in a tank--for instance1 if you have a tank of water containing fifty gallons at an elevation of twenty-five feet1 and a pipe leading down from it1 the pressure of the water at the outlet of the pipe will be a given number of pounds4 ,now if the tank were double the size the pressure at the outlet of the pipe would be proportionately greater4 ,now if you have a battery made up of a number of cells they will develop a given number of volts1 and if the number of the cells be doubled the voltage will be correspondingly increased4 ,or if you have a dynamo giving a certain number of volts1 that number may be increased by doubling the size4 ,the water contained within the tank represents its pressure at the outlet of the pipe4 ,the current in volts1 generated in a battery or dynamo1 represents its pressure on an outlet or conductor wire2 and both represent the force behind their respective conductors4 ,the valve1 or faucet1 at the end of the pipe plus the friction in the pipe would represent the resistance to the flow of water1 while the resistance-coils or other mediums plus the size of the wire1 or conductor and switch1 would regulate the flow of electric current4 ,the flow of water in a pipe under certain pressure would represent its gallons per minute or hour1 while with electricity its flow in a wire or other conductor would represent its amperage4 ,it is to govern the flow of current that resisting mediums are employed4 ,the resistance of electric current is measured in ohms1 and it is with this phase that we are interested in this chapter4 ,if there is only a small resistance put in the path of a current1 then it requires but a small pressure or voltage to send it through the wires or circuit4 ,this is easily understood by the boy who has experimented with small incandescent lamps in which short pieces of carbon-filament are contained4 ,it requires the pressure of a few volts only to send the current through the carbon2 but for the large carbon-filaments1 measuring ten or twelve inches in length1 from one hundred to five hundred volts may be necessary4 ,the ordinary house lamps require one hundred and ten volts and half an ampere to give sixteen candle-power4 ,it is easily understood1 then1 that it requires a high pressure or voltage to force the current through the resisting carbon-filament1 or across the space from one carbon to the other in the arc-lamps used for street lighting4 ,the shorter and larger the conducting wires the less the resistance1 and consequently the lower the voltage or pressure necessary to force it4 ,contrariwise the longer and finer the conducting wares1 the greater the resistance4 ,as copper is the best commercial conductor of electric currents1 it is in universal use1 and in it the minimum of resistance is offered to the current4 ,iron wire is a poorer conductor1 and is not used for high voltage 7such as trolleys or transmission of power71 but is confined to telegraph and telephone lines and low-pressure work4 ,german-silver wire1 one of the poorest conductors1 is not used for lines at all1 but is employed solely as a resisting medium for controlling current4 ,ohm's ,law ,this is the fundamental formula expressing the relations between current1 electro-motive force1 and resistance in an active electric circuit4 ,it may be expressed in several ways with the same result1 as follows3 #a4 ,the current strength is equal to the ,e4 ,m4 ,f4 7electro-motive force7 divided by the resistance4 #b4 ,the ,e4 ,m4 ,f4 7electro-motive force7 is equal to the current strength multiplied by the resistance4 #c4 ,the resistance is equal to the ,e4 ,m4 ,f4 7electro-motive force7 divided by the current strength4 ,all these are different forms of the same statement2 and when figuring electrical data1 ,c stands for current1 ,e for electro-motive force1 and ,r for resistance4 ,resistance-coils and ,rheostats ,the method by which electricity is controlled is resistance4 ,no matter how great the voltage of a current1 nor its volume in amperes1 it can be brought down from the deadly force of the electric trolley-current to the mild degree needed to run a small fan-motor1 an electric bell1 or a miniature lamp4 ,this is accomplished by means of resisting mediums1 such as fluids or wires1 which hold back the current1 and allow only the small quantity to pass that may be required to operate the apparatus4 ,the jump from the high voltage of the trolley-current to the low one required for the electric bell1 a lamp1 or a small motor1 is frequently made in traction-work1 but in this case regular transformers are used4 ,for the small apparatus1 that may have its current supplied from a battery1 or a small dynamo driven by a water-motor1 the forms of resistance-coils and rheostats described on the following pages should meet every requirement4 ,the standard unit of resistance is called an ohm1 so named after ,dr4 ,g4 ,s4 ,ohm1 a ,german electrician1 whose theory on the subject is accepted as the basis on which to calculate all electrical resistance4 ,the legal ohm is the resistance of a mercury column one square millimetre in cross-sectional area and one hundred and six centimetres in length1 and at a temperature of #j ,centigrade or #cb ,fahrenheit1 or the freezing-point for water4 ,the conductivity of metals is dependent greatly on their temperature1 a hot wire being a much better conductor than a cold one4 ,since counter-electro-motive force sometimes gives a spurious resistance1 the ohmic resistance is the true standard by which all current is gauged4 ,in technical mechanism and close readings the ohmic resistance counts for a great deal1 but in the simple apparatus that a boy can make the ,german-silver resistance coils and the liquid resistance will answer every purpose4 ,to give a clearer idea of the principle of the rheostats1 a short description of the mercurial column will first be presented4 ,during the early part of the last century wires were not used as a resisting medium for electric currents4 ,in their place1 glass tubes1 filled with mercury sealed at one end and corked at the other1 were arranged in rows and supported in a wooden rack4 ,illustration3 ,fig4 #a ,wires led out from the top and bottom of each tube1 and were brought down to metal buttons arranged in a row along the front edge of the base-plate1 as shown in the illustration of a mercurial rheostat 7,fig4 #a74 ,each tube represented a certain resistance--one or more ohms1 as required4 ,the outlet wire was attached to the button at one end of the row1 and the inlet could be moved along from button to button1 until the required amount of current was obtained4 ,the mercurial rheostat was an expensive1 cumbersome1 and treacherous thing to handle2 it was liable to break1 and its weight often prohibited its use in places where the more convenient and easily handled ,german-silver rheostats are now in universal employment4 ,overheating the mercury in the columns caused it to expand1 and sometimes1 before the switch could be thrown open1 an end would be forced out and the mercury would climb over the edge of the glass columns4 ,all metals have a certain amount of resistance for electric currents1 and some have more than others4 ,german-silver1 for instance--a metal made of a mixture of other metals with about eighteen per cent4 of nickel 7see ,appendix7--is considered to be the best commercial resistance medium1 while pure copper is regarded as the best commercial conductor4 ,unalloyed copper is universally employed for electric conductors of high voltage2 but for telegraph and telephone work1 galvanized iron wire is still used extensively4 ,the finer the wire1 the higher is its resistance1 and the more resistant the metal1 the greater are the number of ohms to a given length4 ,to nine feet and nine inches of ,no4 #cj copper wire there is one ohm resistance1 while to ,no4 #bd--which is six sizes coarser--there is one ohm to thirty-nine feet and one inch4 ,in many cases it is necessary to use the coarser wire and greater length1 as the current would superheat or burn the fine wire1 while the coarser would conduct it safely4 ,for very high voltage and amperage--such as used in traction cars1 in power stations1 and in manufacturing plants--castings of ,german-silver are employed and linked in series4 ,they are more easily handled than the coils of wire1 and a greater number of them can be accommodated in a small space4 ,illustration3 ,fig4 #b ,for light currents in experimental work1 where batteries are employed1 obtain a pound or two of bare ,german-silver wire1 from ,nos4 #bd to #cj1 and wind the strands on a round piece of stick attached to a winder 7see ,magnets and ,induction-,coils1 chapter iv474 ,make several of these coils1 two or three inches long1 with the wire wound closely and evenly4 ,when pulled apart the coils will appear as shown in ,fig4 #b ,a1 and will resemble a spiral spring4 ,this can be made fast over a porcelain knob and the ends caught down1 as shown at ,b in ,fig4 #b1 or it may be drawn over a round stick1 a porcelain tube1 or a lug made of plaster of ,paris and dextrine 7three parts of the former to one of the latter71 as shown at ,c in ,fig4 #b1 and the ends securely bound with a strand or two of wire1 twisted tight to keep the ends from slipping4 ,the lugs may be made in a mold1 using as a pattern a piece of broom-handle--shellacked and oiled to prevent the plaster from adhering to it4 ,obtain a small square and deep box1 and drop some of the wet mixture down in the bottom2 on this place the broomstick1 small end down 7it should be slightly tapered71 and around it pour in the wet plaster mixture4 ,while it is setting1 turn the stick with the thumb and fingers1 so as to shape the hole perfectly then draw it out1 and a true mold will be the result4 ,when dry enough1 pour some shellac down into the mold and revolve it1 so that the shellac will be evenly distributed1 and let it harden for a day4 ,then saw off the end of the mold1 so that it will be open at both ends4 ,in order to make the lugs1 pour in the plaster mixture1 taking care to oil the mold before each pouring1 so that the lug can be drawn out when the mixture has set4 ,if it sticks1 tap the small end gently to start it4 ,for coils where there is little or no heat1 ordinary pieces of broom-handle1 or round sticks having a coat or two of shellac1 will answer very well2 but where the current heats the core1 it must be of some material that will not char4 ,another method of making resistance-coils is to measure off a length of wire2 then double it1 and with a small staple attach the loop end at one end of the 7wooden7 core4 ,pay out the two strands of wire an equal distance apart with the thumb and fingers1 and with the other hand twist the core4 ,at the other end of the spool catch the loose ends of the wire under small staples1 taking great care not to let the staples touch or even be driven close together4 ,this arrangement is shown at ,d in ,fig4 #b1 and for a field resistance-board any number of these coils may be made4 ,illustration3 ,fig4 #c ,in ,fig4 #c the mode of connecting coils is shown4 ,the dots represent contact-points to which the movable arm can be shifted4 ,the wires at the bottom of coil1 ,nos4 #a and #b1 are connected together1 while those at the top of ,no4 #b and #c are joined1 and so on to the end4 ,the leading-in current is connected at pole ,h and so on to ,j1 while the leading-out wire is made fast to pole ,i4 ,the switch-arm is moved on the first dot1 or contact-point1 and the current passes up wire ,a1 down coil ,no4 #a1 up coil ,no4 #b1 down ,no4 #c1 up ,no4 #d1 and so on to ,no4 #f1 and down wire ,g and out at ,i4 ,supposing that this offers too much resistance1 the switch-arm is moved up one point4 ,this cuts out coil ,no4 #a1 as the current passes up wire ,b1 through coil ,no4 #b1 down ,no4 #c1 and so on1 and out through ,g and pole ,i4 ,another move of the switch and coil ,no4 #b is cut out1 the current passing up wire ,c1 down coil ,no4 #c1 up ,no4 #d1 and so on1 and out at ,i4 ,each move of the switch cuts out one coil1 lessening the resistance2 but when moved to the last contact-point the current flows without resistance--in at ,h1 through the switch-arm1 and out at ,i4 ,the plan of arranging the coils suggested at ,fig4 #b ,b is shown in ,fig4 #d1 where four of the coils are arranged in series over porcelain knobs1 and the lower ends made fast to the base-board with small staples4 ,small pieces of brass are used for the switch contact-plates2 those are provided with one plain and one countersunk hole for a flat and round headed screw4 ,the screw-heads are arranged in a semicircular fashion1 so that the switch-arm1 attached at one end to the screw ,j1 will touch each plate as it is moved forward or backward4 ,illustration3 ,fig4 #d ,fig4 #e ,,two ,,simple ,,forms ,,of ,,rheostats ,the current passing in at binding-post ,a travels to ,j and ,b1 the latter being the resting-plate for the switch-arm4 ,a move of the arm to ,c sends the current up over the first coil and down2 then over the second1 third1 and fourth coils1 and out at ,g2 through plate ,h 7which is the rest at the right side71 and out at ,i4 ,a move of the switch-arm to ,d cuts out the first coil2 a move to ,e1 the first and second coils2 and so on until the last plate is reached1 when the current will pass without resistance in at ,a1 through ,j1 and out at ,i4 ,a simple arrangement for a resistance-coil is shown in ,fig4 #e4 ,this consists of a set of small metal plates in which two holes are made1 one for a screw1 the other for a screw-eye 7see ,binding-posts1 chapter iii474 ,two lines of steel-wire nails are driven along a board1 and ,german-silver wire is drawn around them in zig-zag fashion1 beginning at the left and going towards the right side of the board4 ,one end of wire is made fast under the screw-head on plate ,a4 ,the strand is carried out around the first nail on the lower row and over the first one on the upper row1 then down1 up1 down until six nails have been turned4 ,the wire is then carried down to the screw in plate ,b1 given two turns1 and carried up again and over the nail on the top row1 repeating the direction of zigzag ,no4 #a1 until six of them are made4 ,the end of the wire is then made fast to plate ,g1 and all the screws are driven in to hold the plates and wire securely4 ,the inlet wire is attached to ,a1 the outlet to ,g1 and any degree of resistance can be had by moving the inlet wire to the various plates along the line1 cutting out sections ,nos4 #a to #f as desired4 ,for heavier wire the arrangement as shown in ,fig4 #f should be satisfactory4 ,illustration3 ,fig4 #f ,illustration3 ,fig4 #g ,a frame twelve by fifteen inches is constructed of wood three-quarters of an inch thick and one inch and a quarter wide1 having the ends securely fastened with glue and screws4 ,spirals are wound of ,german-silver wire 7any size from ,no4 #af to #bb71 and drawn apart4 ,the ends are caught to the frame with small staples1 and each alternate coil-end is joined1 as shown in ,fig4 #f4 ,the leading-out wires to the contact-points on the switch should be of insulated copper1 and are to run down the sides of the frame1 and so to the switch-board4 ,to clearly illustrate1 however1 the plan of wiring1 the drawing is made so as to show the leads from the coil-ends to the switch4 ,care should be taken to study this drawing well1 so as not to make an error in connecting a wrong end to a contact-point1 thereby causing a short circuit4 ,when properly connected the current passes in at ,a and out at ,i2 but if wires are improperly connected1 the current will jump when the switch-arm reaches the misconnected contact4 ,the switch is an important part of every rheostat1 and should be carefully and accurately made4 ,one of the simplest and most practical switches is constructed from a short1 flat bar of brass or copper having a knob attached at one end and a hole provided at the other through which a screw may pass 7see ,switches1 chapter iii474 ,the contact-points are made from one or two copper washers1 with the holes countersunk so that a machine screw of brass1 with a flat head1 will fit the hole snugly4 ,the top of the head will then be flush with the top of the washer1 as shown at ,fig4 #g ,a4 ,the bolt is passed down through a piece of board1 then slate or soapstone1 and caught with a washer and nut1 as shown at ,fig4 #g ,b4 ,a loop of wire is passed about the bolt end1 then another nut is screwed tightly over it to hold it in place1 as well as to lock the first nut4 ,the binding-posts that hold the inlet and outlet wires may be made of bolts and nuts also1 as shown at ,fig4 #g ,b2 but the bolt must be passed through the switchboard so that the head is at the rear and the ends project out to receive the nuts4 ,a very compact and simple rheostat and switch is shown in ,fig4 #h4 ,it is composed of a base-board1 eight blocks of hard-wood1 and a top strip used as a binder to lock the upper ends of the blocks together4 ,the hard-wood blocks are three-quarters of an inch thick1 one inch and a half wide1 and four inches long4 ,a small hole is made near each end of the block and through one of them an end of the wire is passed4 ,the wire is then wound round the block1 taking care to lay it on evenly1 and with about one-eighth of an inch of space between each strand4 ,when the opposite hole is reached1 pass the end of the wire through it and clip it4 ,the block will then resemble ,fig4 #g ,c4 ,there should be three or four inches of wire at each end for convenience in connection1 and when the eight blocks are wound they are to be mounted on end at the rear side of a base-board measuring ten inches long1 three inches wide at the ends1 and nine at the middle 7or across the face of the switchboard to the rear edge behind the blocks74 ,use slim steel-wire nails and glue to attach the blocks to the base2 or slender screws may be employed4 ,across the top lay a piece of wood a quarter of an inch in thickness1 and drive small nails or screws down through it and into the blocks4 ,illustration3 ,fig4 #h ,fig4 #aj ,fig4 #i ,,compact ,,forms ,,of ,,rheostats ,connect the ends of the coils together in series1 as already described1 and carry the wires under the base-plate in grooves cut with a ,v-shaped chisel4 ,if the sunken wires are bothersome1 the work may be avoided by running the wires direct to the foot of the contact-points and elevating the rheostat on four small blocks that may be screwed1 or nailed and glued1 under the corners1 as shown in ,fig4 #h4 ,these will raise the base half an inch or more above the table on which the rheostat will rest so as to allow room for the under wires4 ,a rheostat of round blocks standing on end is shown at ,fig4 #i ,a4 ,these are pieces of curtain-pole1 four inches long and wound with loops of ,no4 #af or #ah wire1 as shown at ,fig4 #i ,b4 ,the loop and loose ends are caught with staples1 and when arranged on a base-board they are to be connected in series as before described4 ,one long1 slim screw passed up through the base-board and into the lower end of the block will hold each block securely in place4 ,to keep it from twisting1 a little glue may be placed under the blocks so that when the screw draws the block down to the base it will stay there permanently upon the hardening of the glue4 ,the leading wires should be slipped under the washers forming the contact-points of the switch2 or they may be carried under the board to the nuts that hold the lower ends of the bolts4 ,another form of rheostat 7,fig4 #aj ,a7 is made by sawing a one-inch curtain-pole into four-inch lengths and cross-cutting each piece with eight or ten notches1 as shown at ,fig4 #aj ,b4 ,these pieces are screwed and glued fast along each side of a base-board eight inches wide and fourteen inches long1 so that the notches face the outer edges of the board4 ,the strand of wire passes round these upright blocks and fits into the notches so as to prevent them from falling down4 ,the top end of wire at each pair of blocks is made fast by a turn or two of another piece of wire and a twist to hold it securely2 then the loose end is carried down through a hole and along under the board to the foot of a contact-point4 ,any number of these upright coils may be made1 and on a long board the switch may be arranged at one side instead of at the end1 as shown in ,fig4 #aj ,a4 ,when making ten or more coils it is best to use three or four sizes of wire1 beginning with fine and ending with coarse4 ,for instance1 in a twelve-coil rheostat make three coils of ,no4 #bf1 three of ,no4 #bb1 and three of ,no4 #ah2 or if coarser wire is required use ,nos4 #bj1 #af1 and #ab4 ,german-silver comes bare and insulated4 ,it is preferable to have the fine wire insulated1 but the heavier sizes may be bare1 as it is cheaper2 moreover1 if heated too much the insulation will burn or char off4 ,when cutting out the coils always begin at the end where the finer wire is wound2 then as the current is admitted more freely the heavier wires will conduct it without becoming overheated4 ,for running a sewing-machine1 fan1 or other small direct-current motor wound for low voltage1 the house current 7if electric lights are used in the house7 may be brought down to the required voltage with ,german-silver rheostats similar to these already described4 ,another and very simple method is to arrange sixteen-candle-power lamps in series1 as shown in ,fig4 #aa4 ,six porcelain lamp-sockets are screwed fast to a wood base and the leading in and out wires brought to binding-posts or the contact-points of a switch4 ,the leading-in wire to the series is made fast at binding-post ,a1 which in turn is connected with screw ,b1 under the head of which the switch-arm is held4 ,when the switch is thrown over to contact-point ,c the current passes through lamp ,no4 #a back to point ,d2 through lamp ,no4 #b back to ,e2 then through lamps ,nos4 #c1 #d1 #e1 and #f1 and out through point ,i to post ,j4 ,a turn of the switch to ,d cuts out lamp ,no4 #a1 to ,e cuts out ,no4 #b1 and so on4 ,the filaments of incandescent lamps in their vacuum are among the very best mediums of resistance1 and with a short series of lamps a current of #bbj volts can quickly be cut down to a few volts for light experimental work or to run some small piece of apparatus4 ,illustration3 ,fig4 #aa ,illustration3 ,fig4 #ab ,illustration3 ,fig4 #ad ,lamps in series are often used to cut down the current for operating electric toys and trains4 ,the adjustment of the current should never be left to children1 however1 but should be attended to by some one qualified to look after the apparatus4 ,otherwise an unpleasant or even dangerous shock may be received4 ,another simple form of resistance apparatus is made from the carbon pencils used for arc lights4 ,short pieces will answer very well1 but if the long bare ones can be had they will be found preferable4 ,do not use the copper-plated ones as they would conduct the current too freely2 they should be bare and black4 ,now around the ends of each piece take several turns of copper wire for the terminals and cut-out wires4 ,fasten those pencils down on a board 7as shown at ,fig4 #ab7 by boring small holes through the board1 passing a loop of copper wire down through the holes1 and giving the ends a twist underneath4 ,the leading wires to and from the contact-points should be insulated and may be above or below the board4 ,from the descriptions already given1 the connections of this rheostat can readily be understood4 ,the rheostat shown in ,fig4 #ac is perhaps the most complete and practical apparatus that a boy could make or would need4 ,it is composed of a frame1 six porcelain tubes1 a switchboard1 and the necessary ,german-silver and copper wire4 ,from an electrical supply-house obtain six porcelain tubes fourteen by three-quarter inch4 ,porcelain tubes and rods warp in the firing and are seldom straight2 in purchasing these select them as nearly perfect as possible in shape1 size1 and length4 ,illustration3 ,fig4 #ac ,a ,,panel ,,rheostat ,buy1 also1 twelve small porcelain knobs that are the right size to fit inside the large tubes4 ,these should have holes bored through them to admit screws4 ,construct a frame of hard-wood to accommodate the tubes1 as shown in the drawing1 and leave one end loose4 ,with slim screws make the porcelain knobs fast to the top and bottom strips of the frame1 as shown in ,fig4 #ad4 ,the porcelain rods will fit over these and will thus be held securely in the frame1 one small knob entering the tube at each end1 as indicated by the dotted lines in ,fig4 #ad4 ,the first porcelain tube to the left is wound with ,no4 #bb ,german-silver wire1 the next with ,no4 #bj1 the third with ,no4 #ah1 then ,nos4 #af1 #ad1 and #ab2 so that in this field a broad range can be had for a current of #aaj volts4 ,the coils are connected in series1 as explained for the other rheostats1 and the leading wires brought down to the back of a switchboard of which ,fig4 #ac ,a is the front and ,fig4 #ac ,b the rear view4 ,the switchboard is made of thin slate or soapstone2 or a fibre-board may be employed4 ,fibre-board is especially made for electrical work1 and can be had from a large supply-house in pieces of various thickness1 three-eighths of an inch being about right for this board4 ,brass bolts and nuts and copper washers are used for the contact-poles1 and when the ends of the leading wires are looped around the bolts the nuts are to be screwed down tightly so as to make good contacts4 ,this rheostat may be used when lying on a table1 or it can be hung up by means of two screw-eyes driven in the top of the frame1 as shown in ,fig4 #ac ,a4 ,a convenient form of rheostat for fine wire and high resistance is shown in ,fig4 #ae4 ,this is on the plan of the well-known ,wheatstone rheostat and does not require a switchboard nor a series of coils4 ,two rollers1 one of wood the other of metal or brass-covered wood1 are set in a frame1 and by means of a handle and projecting ends with square shoulders1 one or the other of the rollers may be turned so that the wire on one winds up while on the other it unwinds4 ,the wooden roller may be made from a piece of curtain-rod one inch in diameter1 and it should have a thread cut on it4 ,this will have to be done on a screw-cutting lathe1 and any machinist will do it for a few cents4 ,there should be from twelve to sixteen threads to the inch--no more--although there may be as few as eight4 ,twelve will be found a good number1 as that does not crowd the coils and the risk of their touching is minimized4 ,the ends of the roller should have bearings that will fit in holes made in the end-pieces of the frame1 and at one end of each roller a square shoulder is to be cut1 as shown at ,a in ,fig4 #af4 ,a short handle may be made from two small pieces of wood1 as shown at ,b in ,fig4 #af4 ,it must be provided with a square hole so that it will fit on the roller ends4 ,the metal roller may be made from a piece of light brass tubing one inch in diameter through which a wooden core is slipped2 or it can be a piece of brass-covered curtain-pole with the ends shaped the same as the wooden one4 ,the wood roller should have a collar of thin brass or copper 7or other soft metal except lead7 attached to the front end2 or several turns of wire may be made about the roller so as to form a contact-point4 ,a piece of spring brass1 copper1 or tin rests on this collar and is held fast under a binding-post1 which in turn is screwed to the wooden frame4 ,a similar strip of spring metal is held under another post on the opposite side of the frame and bears on the metal roller4 ,illustration3 ,fig4 #ae ,illustration3 ,fig4 #af ,german-silver wire is wound on the wooden roller1 one end having been made fast to the metal collar2 and when all the thread grooves on the wood roller are filled the opposite end of the wire is attached to the rear end of the metal roller4 ,the current entering at binding-post ,no4 #a crosses on the strip of spring metal to the collar1 travels along the coil of wire1 and crosses to the metal roller and is conducted out at binding-post ,no4 #b 7see ,fig4 #ae74 ,if the resistance is too great slip the handle over the end of the metal roller and give it several turns4 ,the current will then pass with greater freedom as the wire on the wooden roller becomes shorter4 ,this may be readily seen by connecting a small lamp in series with a battery and this rheostat4 ,as the metal cylinder is turned the current flows more freely and the filament becomes red1 then white1 and finally burns to its full capacity4 ,take care1 however1 not to admit too much current as it will burn out the lamp4 ,some sort of adjustment should be made to prevent the rollers turning of themselves and thus allowing the wire coils to slacken4 ,this may be done by boring the two holes for the rollers to fit in and then1 with a key-hole saw1 cutting the stick as shown at ,c in ,fig4 #af1 taking care not to split it at the ends4 ,the result will be a long slot which1 however1 has nothing to do with the bearings4 ,down through the middle of the stick make a hole with an awl1 so that the screw-eye will move easily in the upper half but will hold in the lower half4 ,under the head of the eye place a small copper washer2 then with the thumb and finger drive the screw-eye down until the head rests on the washer4 ,a slight turn of the eye when it is in the right place will draw the upper and lower parts of the stick together and bind the wood about the bearing ends of the rollers4 ,the rollers should not be held too tightly as that would strain the wire when winding it from one to the other4 ,it should be just tight enough to keep the wire taut4 ,two or more of these roller resistance-frames may be made and connected in series so that a close adjustment can be had when using battery currents for experimenting4 ,liquid ,resistance ,apart from metallic1 mercurial1 or carbon resistance a form of liquid apparatus is frequently used in laboratory and light experimental work4 ,illustration3 ,fig4 #ag ,illustration3 ,fig4 #ai ,this style of resistance equipment is the least expensive to make1 and will give excellent satisfaction to the boy who is using light currents for induction-coils1 lamps1 galvanometers1 and testing in general4 ,the simplest form of liquid resistance is made by using a glass bottle with the upper part cut away4 ,the cutting may be done with a steel-wheel glass-cutter4 ,the bottle should then be tapped on the cut line until the top part falls away4 ,go over the sharp edges with an old file to chafe the edge and round it2 then solder a tin1 copper1 or brass disk to a piece of well-insulated wire and drop it down in the bottom of the receptacle1 as shown at ,fig4 #ag4 ,cut a smaller disk of metal1 or use a brass button1 and suspend it on a copper wire which passes through a small hole in a piece of wood at the top of the jar4 ,notches should be cut at the under side of this wood cross-piece so that it will fit on top of the jar and stay in place4 ,the jar is to be nearly filled with water1 having a teaspoonful of sulphate of copper dissolved in it4 ,this will turn the water a bluish color and make it a slightly better conductor1 particularly when the button is lowered close to the round disk4 ,if a high resistance is desired the copper may be omitted leaving the water in its pure state4 ,the wires leading in and out of the jar should be connected between the apparatus and the battery so that the proper amperage can be had by raising or lowering the button4 ,a series of these liquid resistance-jars may be made of glass tubes an inch in diameter and twelve inches long4 ,one end of them may be stopped with a cement made of plaster of ,paris six parts1 ground silex or fine white sand two parts1 and dextrine two parts4 ,mix the ingredients together when dry1 taking care to break all small lumps in the dextrine2 then add water until it is of a thick consistency like soft putty4 ,solder the ends of some copper wires to disks of copper or brass and set them on the middle of bone-buttons2 these in turn are to be imbedded in the mixture after the wire has been passed through a hole in the bottom4 ,their location can be seen in the bottom of the tubes ,fig4 #ah1 and ,fig4 #ai ,a is an enlarged figure drawing of the plate1 button1 and wire4 ,the wires are brought out under the lower edge of the tubes1 and enough of the composition is floated about the bottom and outer edge of the tube to form a base1 as shown in the drawing4 ,a base-board is made six inches wide and long enough to accommodate the desired number of tubes4 ,two pieces of wood one inch wide and three-quarters of an inch thick have hollow notches cut from them at one side1 as shown at ,fig4 #ai ,b4 ,in these notches the tubes are gripped4 ,screws are passed through one stick and into the other so as to clamp the wood and tubes securely together4 ,the rear stick is supported on two uprights which are made fast to the rear edge of the base-plate with screws and glue4 ,along the front of the base-board small metal contact plates1 or binding-posts1 are arranged 7see ,binding-posts1 chapter iii47 and the wires led to them from the tubes1 as shown in the drawing4 ,the top or drop wires in the tubes are provided with metal buttons at the ends2 or the end of the wire may be rolled up so as to form a little knob4 ,the manner of connecting the wires was freely explained in the resistance-coil descriptions and may be studied out by examining the drawing closely4 ,in this resistance-apparatus there are two ways of cutting out a medium--first1 by lowering the wire in the tube so that both contact-points meet2 and second1 by cutting out the first tube altogether by connecting the incoming wire with the second binding-post4 ,then again the resistance may be regulated quite accurately by raising or lowering the wires in the liquid4 ,for example1 there is too much resistance if the current has to travel through all the tubes4 ,if it is too strong when one tube is cut out1 the wire in tube ,no4 #a is lowered so that the contacts are an inch apart4 ,then the more accurate adjustment is made by dropping the wire in the second tube1 as shown in ,fig4 #ah4 ,the wires leading out at the top of the tubes are pinched over the edge to hold them in place4 ,they should be cotton insulated and the part that is in the liquid should be coated with hot paraffine4 ,the water may be made a slightly better conductor if a small portion of sulphate of zinc1 or sulphate of copper1 is added to each tubeful4 ,illustration3 ,fig4 #ah ,hittorf's resistance-tube is one of the oldest on these lines1 and two or more of them are coupled in series1 as described for this water-tube resistance2 glass tubes are employed that have one end sealed with a permanent composition1 as described for ,fig4 #ah4 ,a metallic cadmium electrode is placed at the bottom of the tube1 and the tube is then filled with a solution of cadmium iodide one part and amylic alcohol nine parts1 and then corked4 ,a wire passing down through or at the side of the cork is attached to another small piece of metallic cadmium1 which touches the top of or is suspended a short distance in the liquid4 ,as the alcohol is volatile the cork cannot be left out of the tube1 and the wire must be drawn through the cork with a needle so that no opening is left for evaporation4 ,a number of these tubes may be made and coupled in series and the wires led down to the contact-points of a switch4 ,chapter ,,viii ,,the ,,telephone ,for direct communication over short or moderately long distances1 nothing has been invented as yet that will take the place of the telephone4 ,a few years ago1 when this instrument was first brought out1 it was the wonder of the times1 just as wireless telegraphy is to-day4 ,starting with the simple form of the two cups with membranes across the ends1 and a string or a wire connecting them1 we have to-day the complex and wonderful electric telephone1 giving perfect service up to a distance of two thousand miles4 ,some day inventors in the science of telephony will make it possible to communicate across or under the oceans1 and when the boys of to-day grow to manhood they should be able to transact business by 'phone from ,san ,francisco to the ,far ,east1 or from the cities near the ,atlantic coast to ,london1 ,paris1 or ,berlin4 ,it is hardly necessary to enter into the history of telephones1 as this information may be readily found in any modern encyclopdia or reference work4 ,but the boy who is interested in electricity wants to know how to make a telephone1 and how to do it in the up-to-date way1 with the wire and ground lines1 switches1 cut-outs1 bell connections1 and other vital parts1 properly constructed and assembled4 ,in this laudable ambition we will endeavor to help him4 ,the general principle of the telephone may be explained in the statement that it is an apparatus for the conveyance of the human voice1 or indeed any sounds which are the direct result of vibration4 ,sound is due to the vibrations of matter4 ,a piano string produces sound because of its vibration when struck1 or pulled to one side and then released4 ,this vibration sets the air in rapid motion1 and the result is the recording of the sound on our ear-drums1 the latter corresponding to the film of sheepskin or bladder drawn over the hollow cup or cylinder of a toy telephone4 ,when the head of a drum is struck with a small stick it vibrates4 ,in this case the vibrations are set in motion by the blow1 while in the telephone a similar phenomenon is the result of vibratory waves falling from the voice on the thin membrane1 or disk of metal1 in the transmitter4 ,when these vibrations reach the ear-drum the nervous system1 corresponding to electricity in the mechanical telephone1 carries this sound to our brains1 where it is recorded and understood4 ,in the telephone the wire1 charged with electricity1 carries the sound from one place to another1 through the agencies of magnetism and vibration4 ,over short distances1 however1 magnetism and electricity need not be employed for the transmission of sound4 ,a short-line telephone may be built on purely vibratory principles4 ,almost every boy has made a 8phone0 with two tomato-cans over which a membrane is drawn at one end and tied4 ,the middle of the membrane is punctured1 and a button1 or other small1 flat object1 is arranged in connection with the wires that lead from can to can4 ,a ,bladder ,telephone ,a really practical talking apparatus of this simple nature may be made from two fresh beef bladders obtained from a slaughter-house or from the butcher4 ,you will also need two boards with holes cut in them1 two buttons1 some tacks1 and a length of fine1 hard1 brass1 copper1 or tinned iron wire4 ,the size should be ,no4 #bb or ,no4 #bd4 ,the boards should be ten by fourteen inches and half an inch in thickness4 ,cut holes in them eight inches in diameter1 having first struck a circle with a compass4 ,this may be done with a keyhole saw and the edges sand-papered to remove rough places4 ,prepare the bladders by blowing them up and tieing them4 ,leave them inflated for a day or two until they have stretched1 but do not let them get hard or dry4 ,when the bladders are ready1 cut off the necks1 and also remove about one-third of the material1 measuring from end to end4 ,soak the bladders in warm water until they become soft and white4 ,stretch them1 loosely but evenly1 over the opening in the boards1 letting the inside of the bladder be on top1 and tack them temporarily all around1 one inch from the edge of the opening4 ,test for evenness by pushing down the bladder at the middle4 ,if it stretches smoothly and without wrinkles it will do2 otherwise the position and tacks must be changed until it sets perfectly smooth4 ,illustration3 ,fig4 #a ,illustration3 ,fig4 #b ,illustration3 ,fig4 #c ,illustration3 ,fig4 #d ,the bladder must now be permanently fastened to the board by means of a leather band half an inch wide and tacks driven closely1 as shown in ,fig4 #a4 ,with a sharp knife trim away the rough edges of the bladder that extend beyond the circle of leather4 ,attach a piece of the fine wire to a button1 as shown in ,fig4 #b1 and pass the free end through the centre of the bladder until the button rests on its surface4 ,then fasten an eight-pound weight to the end of the wire and set in the sun for a few hours1 until thoroughly dry1 as shown at ,fig4 #c4 ,when both drums are complete1 place one at each end of a line1 and connect the short wires with the long wire1 drawing the latter quite taut4 ,the course of the main wire should be as straight as possible1 and should it be too long it may be supported by string loops fastened to the limbs of trees1 or suspended from the cross-piece of supports made in the form of a gallows-tree or letter ,f4 ,to communicate it will be necessary to tap on the button with a lead-pencil or small hard-wood stick4 ,the vibration will be heard at the other end of the line and will attract attention4 ,by speaking close to the bladder in a clear1 distinct tone1 the sound will carry for at least a quarter of a mile1 and the return vibrations of the voice at the other end of the line can be clearly recognized4 ,a ,single 7,receiver7 ,line ,the principal parts of the modern telephone apparatus are the transmitter1 receiver1 induction-coil1 signal-bell1 push-button1 batteries1 and switch4 ,the boxes1 wall-plates1 etc41 etc41 are but accessories to which the active parts are attached4 ,the first telephone that came into general use was the invention of ,graham ,bell1 and the principle of his receiver has not been materially changed from that day to this1 except that now a double-pole magnet and two fine wire coils are employed in place of the single magnet and one coil4 ,a practical form of single magnet receiver that any boy can easily construct is shown in ,fig4 #d1 and ,fig4 #e is a sectional drawing of the receiver drawn as though it had been sliced or sawed in two1 from front to rear4 ,it is made from a piece of curtain-pole one inch and an eighth in diameter and three inches and a half long4 ,a hole three-eighths of an inch in diameter is bored its entire length at the middle1 and through this the magnet passes4 ,at one end of this tube a wooden pill-box 7,e7 is made fast with glue1 or a wooden cup may be turned out on a lathe and attached to the magnet tube4 ,if the pill-box is employed it should be two inches and a half in diameter1 and at four equidistant places inside the box small lugs of wood are to be glued fast4 ,into these lugs the screws employed to hold the cap are driven4 ,the walls of pill-boxes are so thin that without these lugs the cap could not be fastened over the thin disk of metal 7,d7 unless it were tied or wired on1 and that would not look well4 ,if the cup is turned the walls should be left thick enough to pass the screws into1 and the inside diameter should then be one inch and three-quarters4 ,illustration3 ,fig4 #e ,illustration3 ,fig4 #f ,the cap 7,b7 is made from thin wood1 fibre1 or hard rubber4 ,it is provided with a thin rim or collar to separate its inner side from the face of the disk 7,d74 ,four small holes are bored near the edge of this cap1 so that the screws which hold it fast to the cup 7,e7 may pass through them4 ,the magnet 7,m7 is a piece of hard steel three-eighths of an inch in diameter and four inches and a quarter long4 ,this may be purchased at a supply-house1 and if it is not hard enough a blacksmith can make it so by heating and plunging it in cold water several times4 ,it may be magnetized by rubbing it over the surface of a large horseshoe magnet1 or if you live near a power station you can get one of the workmen to magnetize it for you at a trifling cost4 ,should you happen to possess a bar magnet of soft iron with a number of coils of wire1 and also a storage-battery1 the steel bar may be substituted for the soft iron core and the current turned on4 ,after five minutes the steel can be withdrawn4 ,it is now a magnet1 and will hold its magnetism indefinitely4 ,now have a thin1 flat spool turned from maple or boxwood to fit over one end of the rod1 and wind it with a number of layers of ,no4 #cf copper wire insulated with silk4 ,this is known in the electrical supply-houses as 8phone0-receiver insulated wire1 and will cost about fifty cents an ounce4 ,one ounce will be enough for two receivers4 ,it should be wound evenly and smoothly1 like the strands of thread on a spool1 and this may be done with the aid of the winder described on page #eh4 ,when the wire is in place a drop of hot paraffine will hold the end so that the wire will not unwind4 ,the ends of this spool-winding should be made fast to heavier wires1 which are run through small holes in the tube 7,a7 and project out at the end1 as shown at ,f ,f4 ,the magnet1 with its wire-wound spool on the end1 is then pushed through the hole in ,a until the top end of the rod is slightly below the edges of the cup 7,e71 so that when the metal disk 7,d7 is laid over the cup 7,e7 the space between the magnet and disk1 or diaphragm 7,d71 is one-sixteenth of an inch 7see ,fig4 #e74 ,put some shellac on the magnet1 so that when it is in the right place the shellac will dry and hold it fast4 ,the cap 7,b7 holds the disk 7,d7 in place1 and protects the spool and its fine wire from being damaged and from collecting dust4 ,after giving the exterior a coat of black paint and a finishing coat or two of shellac1 the receiver will be ready for use4 ,the original telephone apparatus was made up of these receivers only--one at each of a line in connection with a battery1 bell1 push-button1 and switch4 ,on a window-casing1 or the wall through which the wires passed1 a lightning-arrester was arranged and made fast4 ,using receivers only1 it was necessary to speak through the same instrument that one heard through1 and for a few years this unhandy method of communication was the only one possible4 ,then the transmitter was invented4 ,plan of ,installation ,many of these single-receiver lines are still in use1 and as they require but a small amount of constructive skill a diagram of the wiring and the plan of arrangement is shown in ,fig4 #f4 ,at the left side1 ,r is the receiver at one end of the line and ,r #b that at the other1 line ,no4 #a being a continuous wire between the two receivers4 ,when the boy at ,r wishes to call his friend at ,r #b he uses his push-button 7,p ,b71 and the battery 7,b ,b7 operates the electric bell 7,e ,b #b7 at the other end4 ,in order to have the bell connections operative1 the switch 7,s #b7 must be thrown over to the left when the line is 8quiet10 while the switch 7,s7 should be thrown to the right4 ,with the switches in this position the boy at either end may call his friend at the opposite end4 ,with the switch 7,s #b7 thrown to the left 7the position it should be in1 except when talking over the line71 the boy at the other end pushes his button 7,p ,b71 first throwing switch ,s to the left4 ,this makes connection for the battery 7,b ,b71 and the circuit is closed through wires that join line ,no4 #a and line ,no4 #b at #a and #b4 ,the branch lines to the bell 7,e ,b #b7 join the main lines at #c and #d1 through switch ,s #b1 when the bar is thrown to the left4 ,the circuit being complete1 the batteries 7,b ,b7 at one end of the line ring the bell 7,e ,b #b7 at the other end of the line4 ,in the reverse manner1 when the switch 7,s7 is thrown to the right1 the boy at the opposite end rings the bell 7,e ,b7 by pressing on the button 7,p ,b #b71 first throwing switch ,s #b over to the right4 ,if the boy at the left is calling up the boy at the right1 the switch 7,s7 should be thrown to the left1 and he keeps ringing until the other operator throws switch ,s #b over to the right4 ,if now he has the receiver 7,r7 up to his ear he can hear the vibration of the bell 7,e ,b #b7 ringing through the receiver 7,r7 at his end of the line4 ,but when the boy summoned to ,r #b takes up the receiver and places it to his ear1 he throws switch ,s #b over to the right side1 and the boy at ,r leaves switch ,s over on the left side4 ,this brings the lines into direct connection with the receivers in series4 ,be careful1 when setting up this line1 to have the batteries 7,b ,b7 in series with ,b #b ,b #b2 otherwise there would be counter-action4 ,the carbon of one cell should be connected with the zinc of the next cell1 and so on4 ,another receiver is shown at ,fig4 #g4 ,the tube 7,a7 and the cup are turned from one piece of wood1 and the cap 7,b7 from another piece4 ,the length of the receiver is five inches1 and the cap is two inches and a half across4 ,the shank1 or handle1 through which the magnet is passed measures one inch and a quarter in diameter4 ,these wood parts will have to be made by a wood-turner2 and before the long piece is put in a lathe the hole1 three-eighths of an inch in diameter1 should be bored4 ,it must be done carefully1 so that the wood shell will be of even thickness all around the hole4 ,also two small holes should be made the entire length of the handle1 through which the wires leading from the coil to the binding-posts may pass4 ,illustration3 ,fig4 #g ,the spool for the fine insulated wire coil is turned from box-wood or maple1 and wound as described in chapter iv41 on ,magnets and ,induction-coils4 ,small binding-posts 7,f ,f7 with screw ends should be driven down into the holes at the end of the handle and over the bare ends of the wires that project out of the holes4 ,the magnet 7,m7 is three-eighths of an inch in diameter1 and is provided with the spool and coil 7,c7 at the large end of the receiver4 ,the disk 7,d7 is of very thin iron1 and is held in place by the cap 7,b7 and four small brass screws driven through the edge of ,b and into the cup end of ,a4 ,a screw-eye should be driven into the small end of the receiver from which it may hang from a hook4 ,if a double hook and bar is employed the receiver will hang in the fork1 being held there by the rim of wood turned at the small end of ,a4 ,a ,double-pole ,receiver ,illustration3 ,fig4 #h ,another form of receiver is shown at ,fig4 #h4 ,this is a double-pole receiver1 with the coils of fine wire arranged on the ends of a bent band of steel and located in the cup 7,a71 so that the ends of the magnet are close to the diaphragm 7,d74 ,fig4 #h is a sectional view of an assembled receiver1 but a good idea can be had from the drawings of the separate parts4 ,the magnet 7,m7 is of steel one-eighth of an inch thick and five-eighths of an inch wide4 ,a blacksmith will make this at a small cost4 ,it should measure two and one-half inches wide1 two and one-half inches long1 the ends being five-eighths of an inch apart4 ,thin wooden spools are made from wood or fibre to fit over the steel ends1 and are wound with ,no4 #cf silk-insulated wire4 ,a wooden cup1 or shell 7,a71 is turned from cherry1 maple1 or other close-grained wood1 and at the back a hole is cut just large enough for the magnet ends to slip through exclusive of the coils wound on them4 ,a plug of wood 7,a ,a7 is driven between the ends of the magnet to hold them in place4 ,some shellac on the edges of the hole and the plug will harden and keep the parts in place4 ,the coils 7,c ,c7 are placed on the magnet ends1 and the fine wires are made fast to the binding-posts 7,e ,e71 the latter being screwed fast to the shell 7,a74 ,the diaphragm 7,d7 is then arranged in place and held with the cap 7,b7 and the small screws which pass through it and into the shell 7,a74 ,the ,transmitter ,with any one of these receivers a more complete and convenient telephone can be made by the addition of a transmitter and an induction-coil4 ,following the invention of the receiver1 several transmitters were designed and patented1 among them being the ,edison1 ,blake1 ,clamond1 ,western ,union1 and ,hunning4 ,the ,edison and ,hunning are the ones in general use1 and as either of them can easily be made by a boy a simplified type of both is shown in ,figs4 #i and #aa4 ,illustration3 ,,fig4 #i ,,fig4 #aj ,,fig4 #aa ,,fig4 #ab ,,simplified ,,type ,,of ,,transmitter ,some small blocks of wood1 tin funnels1 small screws1 granulated or powdered carbon1 some thin pieces of flat carbon1 and a piece of very thin ferrotype plate will be the principal things needed in making a transmitter similar to the one shown in ,fig4 #i4 ,all that is visible from the outside is a plate of wood screwed to a block of wood1 and a mouth-piece made fast to the thin board4 ,in ,fig4 #aj an interior section is shown1 which when once understood will be found extremely simple4 ,the block 7,a7 is of pine1 white-wood1 birch1 or cherry1 and is two inches and three-quarters square and five-eighths or three-quarters of an inch thick4 ,a hole seven-eighths of an inch in diameter is bored in the centre of this block1 half an inch deep1 and a path is cut at the face of the block one inch and a half in diameter and one-eighth of an inch deep4 ,be careful to cut these holes accurately and smoothly1 and if it is not possible to do so1 it would be well to have them put in a lathe and turned out4 ,the face-plate 7,b7 is two inches square1 with a three-quarter-inch hole in it1 and the under-side is cut away for one-eighth of an inch in depth and one inch and a half in diameter4 ,the object of these depressions in block ,a and face-plate ,b is to give space for the diaphragm 7,d7 to vibrate when the voice falls on it through the mouth-piece 7,c74 ,from carbon one-eighth of an inch in thickness two round buttons are cut measuring three-quarters of an inch across4 ,a small hole is bored in the centre of each button1 and one of them is provided with a very small brass screw and nut1 as shown at ,f ,f4 ,one side of the button-hole is countersunk1 so that the head of the screw will fit down into it and be flush with the face of the carbon4 ,with a small three-cornered or square file cut the surface of the buttons with criss-cross lines1 as shown at ,f ,f4 ,when the buttons are mounted in the receiver these surfaces will face each other4 ,cut a small washer from felt or flannel1 and place it in the bottom of the hole in block ,a4 ,line the side of the hole with a narrow strip of the same goods2 then place the button 7,f ,f7 in the hole1 pass the screw through the hole and through the block 7,a71 and make it fast with the nut1 as shown at ,f4 ,place a thin1 flat washer under the nut1 and twist a fine piece of insulated copper wire between washer and nut for terminal connections1 taking care that the end of the wire under the nut is bare and bright1 so that perfect contact is assured4 ,since the practice of telephony involves such delicate and sensitive vibratory and electrical phenomena1 it is best to solder all joints and unions wherever practicable1 and so avoid the possibility of loose connections or corrosion of united wires4 ,from very thin ferrotype plate cut a piece two inches square1 and at the middle of it attach the other carbon button by means of a small rivet which you can make from a piece of copper wire4 ,or a very small brass machine screw may be passed through the button and plate2 then gently tapped at the face of the plate to rivet it fast1 as shown at ,e4 ,lay the block down flat and partly fill the cavity with carbon granules until the button is covered4 ,do not fill up to the top of the hole4 ,over this lay the disk 7,d71 so that the carbon button at the under side of it will fit in the top part of the hole between the sides of felt or flannel4 ,make the disk fast to the block 7,a7 with small pins made by clipping ordinary pins in half and filing the ends4 ,a slim bolt 7,g7 is passed through the block 7,a71 and a wire terminal is caught under a nut and between a washer at the back of the block1 as described for ,f4 ,the japan or lacquer must be scraped away from the disk 7,d7 where the bolt-head touches it1 so that perfect electrical contact will be the result4 ,a small tin funnel is cut and made fast to the face-plate 7,b71 or if an electrical supply-house is at hand a mouth-piece of hard rubber or composition may be had for a few cents4 ,the block 7,b7 is then screwed fast to ,a1 forming the transmitter shown at ,fig4 #i4 ,when this transmitter stands in a vertical position the granules1 or small particles of carbon1 drop down between the buttons of carbon1 packing closely at the bottom of the cavity4 ,at the middle they are loosely placed1 and at the top there are none4 ,as the high or low vibrations of the voice fall on the disk 7,d7 they act accordingly on the carbon granules1 which in turn conduct the vibrations to the rear carbon button1 and1 by the aid of electricity reproduce the same sound1 in high or low tone1 through the receiver at the other end of a line4 ,this improved transmitter makes it possible to talk in a moderate tone of voice over distances up to one thousand miles1 while with the old form of the instrument it was necessary to talk very loud in order to be heard only a few miles away4 ,where a portable apparatus is desired1 this block may be attached to a box or an upright staff4 ,this transmitter will not work when on its back or so that the funnel is on top1 because the particles of carbon would settle on the rear button and not touch the front one4 ,it is essential that the carbon grains should touch both buttons at the same time1 and at the lower part of the cavity they should lie quite solid4 ,it is not necessary1 however1 to pack it in1 for the vibratory action of the voice1 or other sounds1 will cause the particles to adjust themselves and settle in a compact mass4 ,another ,form of ,transmitter ,in ,fig4 #aa another style of transmitter is shown4 ,it is assembled on the front of a box4 ,this front or cover swings on hinges1 and can be opened so that the mechanism in the interior of the box may be gotten at easily4 ,a sectional view of this transmitter is shown in ,fig4 #ab4 ,a hole one inch and a half in diameter is cut in the cover 7,a74 ,a round or square block 7,b7 two inches and a quarter across and half an inch thick is made fast to the rear of the cover1 and in this a hole is bored seven-eighths of an inch in diameter and one-quarter of an inch deep4 ,the sides and bottom of this hole are lined with flannel or felt1 and a carbon button with roughened surface1 as shown at ,f ,f1 is made fast in it by a small machine screw and nut 7,f74 ,a diaphragm 7,d7 is cut from thin ferrotype plate1 and a carbon button is made fast to the middle of it by a small machine screw or a rivet made from soft copper or brass4 ,when the block 7,b7 has been screwed fast to ,a1 place some granules of carbon in the space 7,h72 then lay the diaphragm over the opening1 and make it fast with small screws or pins driven around the edge4 ,from a small tin funnel and a tin-can cap make a mouth-piece 7,c7 by cutting a hole in the cap and slipping the funnel through it1 then cutting the end of the funnel that projects through the hole and bending back the ears so that they lap on the inner side of the cap4 ,these small ears may be soldered to the cap so as to hold the mouth-piece securely in place4 ,from felt or flannel cut a washer the size of the can top and about three-eighths of an inch in width4 ,lay this over the diaphragm2 then place the mouth-piece on it and fasten it to the door 7,a7 with small screws4 ,the use of this washer is to prevent any false vibrations in the mouth-piece affecting the sensitive diaphragm4 ,make a small hole through ,a and ,b and pass a bolt 7,e7 through this hole1 taking care to lap a thin piece of sheet-brass on the diaphragm 7,d71 bending it over so that it will lie under the head of the bolt 7,e74 ,the diaphragm must be scraped where the metal touches it1 so as to make perfect electrical connection between ,d and ,e4 ,at the rear end of ,e arrange a washer and nut 7,g71 so that the current passing in at ,g travels through ,e and ,d1 then through the carbon buttons and granules1 and out at ,f4 ,from pine or white-wood one-quarter or three-eighths of an inch thick make a box four inches wide1 six inches high1 and two inches and a half deep4 ,to the front of this attach a cover1 which should measure a quarter of an inch larger all around than the width and height of the box4 ,use brass hinges for this work so that the cover may be opened4 ,fasten a transmitter to the front of the cover1 or make one on the cover1 as shown in ,fig4 #aa1 and attach the box to a back-board or wall-plate five inches wide and seven inches high made of pine or white-wood half an inch in thickness 7see ,fig4 #ac74 ,illustration3 ,,fig4 #ac ,illustration3 ,,fig4 #ad ,illustration3 ,,fig4 #ae ,illustration3 ,,fig4 #af ,at the left side of the box cut a slot through the wood1 so that a lever and hook may project and work up and down4 ,the end of this lever is provided with a hook on which a receiver may be hung1 as shown in ,fig4 #ac1 and the inside mechanism is arranged as shown at ,fig4 #ad4 ,a is an angle-piece of brass or copper1 which acts as a bracket and which is screwed fast to the inside of the box4 ,b is the lever and hook1 which is cut from a strip of brass4 ,the attached end is made wider1 and an ear 7,c71 to which a wire is soldered1 projects down beyond the screw4 ,a view looking down on this lever and bracket is shown at ,fig4 #ae4 ,a is the bracket1 ,b the lever1 and ,e the screw or bolt holding the two parts together1 with a thin copper washer between them to prevent friction4 ,when the lever and bracket are made fast to the box1 a spring 7,d7 should be arranged1 so that when the receiver is removed from the hook the lever will be drawn up to the top of the slot4 ,a small contact-plate 7,f7 is made of brass1 and fastened at the lower end of the slot4 ,on this the lever should rest when the receiver is on the hook4 ,a contact-wire is soldered to this plate1 which in turn is screwed fast to the inside of the box4 ,this mechanism is part of a make-and-break switch to cut out and cut in the bells or telephone1 and will be more clearly understood by referring to the diagram in ,fig4 #ag4 ,at the right side of the box a small push-button is made fast1 and this1 with two binding-posts at the top and four at the underside of the box1 will complete the exterior equipment of one end of a line4 ,the construction of the push-button is shown in ,fig4 #af1 ,a being the box and ,b the button which passes through a small hole made in the side of the box4 ,c is a strip of spring-brass screwed fast to the box4 ,it must be strong enough to press the small bone or hard rubber button towards the outside of the box4 ,a wire is caught under one screw-head1 and another one is passed under the screw-head which holds the other spring 7,d7 to the box4 ,when the button 7,b7 is pushed in1 it brings spring ,c into contact with ,d1 and the circuit is closed4 ,directly the finger is removed from ,b the spring 7,c7 pushes it out and breaks the circuit4 ,this button is used only in connection with the call-bells1 and has nothing to do with the telephone4 ,the wires leading from the interior of the box pass through the wall-plate and along in grooves to the foot of the binding-posts1 which are arranged below the box on the back-board1 as shown in ,fig4 #ac4 ,a buzzer or bell is made fast to the inside of the box1 unless it is too large to fit conveniently1 in which case it may be attached to the wall above or below the box4 ,the ,wiring ,system ,fig4 #ag shows the wiring system for this outfit1 which1 when properly set up and connected1 should operate on a circuit or line several miles in length1 provided that the batteries are strong enough4 ,this system may be installed in the box shown in ,fig4 #ac1 the flexible cord containing two wires being attached to the binding-posts at the top of the box and to the posts at the end of the receiver4 ,this system differs from the one shown in ,fig4 #f only in the addition of receivers ,t and ,t #b1 and in the substitution of the automatic lever-switches 7,l ,s and ,l ,s #b7 for the plain switches 7,s and ,s #b7 in ,fig4 #f4 ,when the line is 8quiet0 the receiver 7,r7 should be hanging on the lever-switch 7,l ,s71 which rests on the contact-plate 7,a74 ,at the opposite side of the line the receiver 7,r #b7 hangs on the lever-switch 7,l ,s #b71 which in turn rests on the contact-plate 7,a ,a74 ,this puts the bell circuit in service4 ,illustration3 ,,fig4 #ag ,,plan ,,of ,,telephone ,,circuit1 ,,comprising ,,receivers1 ,,transmitter1 ,,electric ,,buzzers ,,or ,,bells1 ,,lever-,,switches1 ,,push-,,buttons ,,and ,,batteries ,,for ,,stations ,,not ,,over ,,five ,,miles ,,apart4 ,if the boy at the left wishes to call up the boy at the right he removes the receiver 7,r7 from the hook 7,l ,s7 and presses on the button 7,p ,b74 ,this closes the circuit through the battery 7,c ,c ,c71 and operates the electric buzzer or bell 7,e ,b #b7 at the other end of the system1 through line ,no4 #a and line ,no4 #b4 ,the operation may be clearly understood by following the lines in the drawing with a pointer4 ,the boy at the left may keep on calling the boy at the right so long as the receiver 7,r #b7 hangs on the lever 7,l ,s #b7 and holds it down against the plate 7,a ,a74 ,but directly the receiver 7,r #b7 is removed1 the lever 7,l ,s #b7 flies up--being drawn upward by the spring 7,d7 shown in ,fig4 #ad--;and closes the telephone circuit through the spring-contact 7,b ,b71 at the same time cutting out the bell circuit4 ,the boy at the left having already removed his receiver1 the telephone circuit is then complete through lines ,nos4 #a and #b and batteries ,c ,c ,c and ,c #b ,c #b ,c #b1 the boys at both ends speaking into the transmitters and hearing through the receivers4 ,the contacts ,b and ,b ,b are made from spring-brass or copper1 and are attached inside the boxes at the back1 so that when the levers are up contact is made1 but when down the circuit is broken or opened4 ,in ,fig4 #ah an interior view of a box is shown1 the door being thrown open and the receiver left hanging on the hook4 ,illustration3 ,,fig4 #ah ,,fig4 #ai ,,fig4 #bj ,,telephone ,,installation4 ,,interior ,,view ,,of ,,box ,the arrangement of the several parts will be found convenient and easy of access4 ,e ,b is the electric buzzer1 ,l ,s the lever-switch1 ,p ,b the push-button1 ,t the transmitter1 and ,r the receiver4 ,nos4 #a1 #b1 #c1 #d1 #e1 #f1 #g1 #h are binding-posts or terminals1 and ,b is the spring-contact against which the lever-switch 7,l ,s7 strikes when drawn up by the spring 7,d74 ,the wires that pass from #f to #g and from #d to #h should be soldered fast to one side of the hinge1 and those running from the terminals or nuts at the back of the transmitter 7,t7 to #g and #h should be similarly secured4 ,small brass hinges are not liable to become corroded at the joints1 but to insure against any such possibility the ends of several fine wires may be soldered to each leaf of the hinge1 so that when the door is closed the wires will be compressed between the hinge-plates4 ,for long-distance communication it will be necessary to install an induction-coil1 so that the direct current furnished by the batteries1 in series with the transmitter1 can by induction be transformed into alternating current over the lines connecting the two sets of apparatus4 ,this system is somewhat more complicated and requires more care in making the connections1 but once in operation it will be found far superior to either of the systems hitherto described4 ,a ,telephone ,induction-coil ,it will be necessary to make two induction-coils1 as described in chapter iv41 page #fb1 ,fig4 #h4 ,a telephone coil for moderately long-distance circuits is made on a wooden spool turned from a piece of wood three inches and a half long and one inch square1 as shown at ,fig4 #ai4 ,the core-sheath is turned down so that it is about one-sixteenth of an inch thick4 ,this spool is given a coat or two of shellac1 and two holes are made at each end1 as shown in the drawing4 ,the first winding or primary coil is made up of two layers of ,no4 #bj double-insulated copper wire1 one end projecting from a hole at one end of the spool1 the other from a hole at the other end4 ,this coil is given two or three thin coats of shellac to bind the strands of wire and thoroughly insulate them1 and over the layer a piece of paper is to be wrapped and shellacked4 ,the secondary coil is made up of twelve layers of ,no4 #cd silk-insulated copper wire1 and between each layer a sheet of paper should be wound so that it will make two complete wraps4 ,each paper separator should be given a coat of shellac or hot paraffine2 then the turns of wire should be continued just as thread is wound upon a spool1 smoothly1 closely1 and evenly1 until the last wrap is on4 ,three or four wraps of paper should be fastened on the coil to protect it1 and it may then be screwed fast inside a box4 ,the core-hole within the coil should be packed with lengths of ,no4 #bd soft ,swedes iron wire three inches and a half long4 ,in ,fig4 #ai the wires are shown projecting from the end of a spool1 and ,fig4 #bj depicts a completed telephone induction-coil4 ,the installation of the induction-coils is shown in ,fig4 #ba4 ,illustration3 ,,fig4 #ba ,,plan ,,of ,,telephone ,,circuit1 ,,comprising ,,receivers1 ,,transmitters1 ,,electric ,,buzzers ,,or ,,bells1 ,,lever-,,switches1 ,,induction-,,coils1 ,,push-,,buttons1 ,,and ,,batteries ,,for ,,stations ,,up ,,to ,,five ,,hundred ,,miles ,,apart4 ,the wiring is comparatively simple1 and may be easily followed if the description and plan are constantly consulted when setting up the line4 ,r and ,r #b are the receivers1 ,t and ,t #b the transmitters1 ,c #a and ,c #b the batteries1 ,e ,b and ,e ,b #b the buzzers or bells1 ,p ,b and ,p ,b #b the push-buttons1 and ,l ,s and ,l ,s #b the lever-switches4 ,for convenience of illustration the induction-coils are separated4 ,the primary coil 7,p ,c7 is indicated by the heavy spring line and the secondary coil 7,s ,c7 by the fine spring line4 ,when the line is 8dead0 both receivers are hanging from the hooks of the lever-switches4 ,if the boy at the left wishes to call the boy at the right he lifts the receiver 7,r7 from the hook 7,l ,s7 and presses the button 7,p ,b74 ,this throws the battery 7,c #a ,c #a ,c #a7 in circuit with lines ,nos4 #a and #b1 and operates the buzzer 7,e ,b #b74 ,when the boy at the right lifts his receiver 7,r #b7 from the hook 7,l ,s #b71 the bell circuit is cut out and the 'phone circuit is cut in4 ,when the lever-switches are drawn up against the contact-springs 7,a1 ,b1 and ,c and ,a ,a1 ,b ,b1 and ,c ,c71 both batteries are thrown into circuit with the transmitters at their respective ends through the primary coils 7,p ,c and ,p ,c #b74 ,by inductance through the secondary coils 7,s ,c and ,s ,c #b71 lines ,nos4 #a and #b are electrified1 and when the voice strikes the disks in the transmitters the same tone and vibration is heard through the receivers at the other end of the line4 ,while conversation is going on the batteries at either end are being drawn upon or depleted2 but as soon as the receivers are hung on the hooks and the lever-switches are drawn away from the contact-springs1 the flow of current is stopped4 ,the buzzers or bells consume but a small amount of current when operated1 and in dry cells the active parts recuperate quickly and depolarize4 ,the greatest drain on a battery1 therefore1 is when the line is closed for conversation4 ,an ,installation ,plan ,a simple manner in which to install this apparatus in boxes is shown in ,fig4 #bb4 ,the box is depicted with the front opened and with the receiver hanging on the hook4 ,when the lever-switch 7,l ,s7 is down it rests on the contact-spring 7,a71 thus throwing in the bell circuit4 ,when the boy at the other end of the line pushes the button on his box it operates the buzzer 7,e ,b74 ,this can be understood by following with a pointer the wires from the buzzer to the outlet-posts 7,nos4 #a and #c7 at the bottom of the wall-plate4 ,illustration3 ,fig4 #bb ,when the receiver 7,r7 is lifted from the hook 7,l ,s71 it cuts out the bell circuit and cuts in the telephone circuit1 through the spring-contacts 7,b and ,c74 ,this circuit may easily be followed through the wires connecting transmitter1 receiver1 induction-coil1 and batteries4 ,the heavy lines leading out from the induction-coil are the primary coil wires1 and the fine hair lines are those forming the secondary coil4 ,the medium lines are those that connect the binding-posts1 batteries1 and lines4 ,when the bell circuit is connected the impulse coming from the other end of the line enters through wire ,no4 #aj to post ,no4 #c1 thence to strip ,e and plate ,g1 and so on to ,e ,b1 which it operates4 ,the current then passes from ,e ,b to contact ,a1 through ,l ,s to post ,no4 #a1 and out on wire ,no4 #aa4 ,to operate the buzzer at other end of the line the button 7,p ,b7 is pushed in4 ,this moves the spring 7,e7 away from the plate 7,g71 and brings it into contact with ,f4 ,this connects the circuit through the battery wire 7,no4 #h7 to post ,no4 #a to line ,no4 #aa without going into the box1 and from wire ,no4 #i to post ,no4 #b2 thence to hinge ,no4 #g to plate ,f1 through ,e1 down to post ,no4 #c1 and out through wire ,no4 #aj4 ,in this manner the current is taken from the batteries at the foot of wires ,nos4 #h and #i1 and used to ring the buzzer at the other end of the line4 ,when the hook 7,l ,s7 is up the circuit is closed through ,t1 ,i ,c1 and battery4 ,the current runs from the battery through wire ,no4 #h to post ,no4 #a1 to ,l ,s1 through ,c and primary coil out to hinge ,no4 #f1 through transmitter to hinge ,no4 #g1 to post ,no4 #b1 and back to battery through wire ,no4 #i4 ,by inductance the sound is carried over the line1 in at wire ,no4 #aj1 to post ,no4 #c1 through secondary coil to post ,no4 #d1 through receiver ,r to post ,no4 #e1 through ,b and ,l ,s to post ,no4 #a1 and out through wire ,no4 #aa4 ,at the other end of the line it goes through the same parts of the apparatus4 ,a ,portable ,apparatus ,for convenience it is often desirable to have a portable transmitter1 and so avoid the inconvenience of having to stand while speaking4 ,a neat portable apparatus that will stand on a ledge or table1 and which may be moved about within the radius of the connecting lines1 is shown in ,fig4 #bc4 ,the wooden base is four inches square and the upright one inch and a half square4 ,the stand is twelve inches high over all1 and on the bottom a plate of iron or lead must be screwed fast to make it bottom-heavy1 so that it will not topple over4 ,the lever-switch may be arranged at the back of the upright and the push-button at the front near the base1 as shown at ,a4 ,the wall-box contains the buzzer and induction-coil1 and within it the wiring is arranged from the portable stand to the batteries and line as shown at ,c4 ,this illustration is too small1 however1 to show the complete wiring1 and the young electrician is therefore referred to ,fig4 #bb4 ,the battery 7,b7 is composed of as many dry or wet cells as may be required to operate the line4 ,these must be connected in series at both ends4 ,at ,d a rear view of the upright and transmitter is shown to illustrate the manner in which the wiring can be done4 ,if a hollow upright is made of four thin pieces of wood a much neater appearance may be secured by enclosing the wires4 ,illustration3 ,,fig4 #bc ,a ,,portable ,,apparatus ,in all of these telephone systems one wire must lead to the ground1 or be connected with a water-pipe1 taking care1 however1 to solder the wire to a galvanized pipe so that perfect contact will be the result4 ,if the wire is carried directly to the ground it must be attached to a plate1 which in turn is buried deep enough to reach moist earth1 as described in the chapter on ,line and ,wireless ,telegraphs1 page #bae4 ,care and accuracy will lead to success in telephony1 but one slip or error will throw the best system out of order and render it useless4 ,this1 indeed1 applies to all electrical apparatus2 there can be no half-way2 it will either work or it won't4 ,chapter ,,ix ,,line ,,and ,,wireless ,,telegraphs ,a ,ground ,telegraph ,nearly every boy is interested in telegraphy1 and it is a fascinating field for study and experimental work1 to say nothing of the amusement to be gotten out of it4 ,the instruments are not difficult to make1 and two boys can easily have a line between their houses4 ,the key is a modified form of the push-button1 and is simply a contact maker and breaker for opening and closing an electrical circuit4 ,a practical telegraph-key is shown in ,fig4 #a1 and in ,fig4 #b is given the side elevation4 ,the base-board is four inches wide1 six inches long1 and half an inch in thickness4 ,at the front end a small metal connector-plate is screwed fast1 and through a hole in the middle of it a brass-headed upholsterer's tack is driven for the underside of the key to strike against4 ,two ,l pieces of metal are bent and attached to the middle of the board to support the key-bar1 and at the rear of the board another upholsterer's tack is driven in the wood for the end of the bar to strike on and make a click4 ,the bar is of brass or iron1 measuring three-eighths by half an inch1 and is provided with a hole bored at an equal distance from each end for a small bolt to pass through1 in order to pivot it between the ,l plates4 ,a hole made at the forward end will admit a brass screw that in turn will hold a spool-end to act as a finger-piece4 ,the screw should be cut off and riveted at the underside4 ,a short1 strong spring is to be attached to the back of the base-block and to the end of the key-bar by means of a hook1 which may be made from a steel-wire nail flattened4 ,it is bound to the top of the bar with wire1 as shown in ,figs4 #b and #c4 ,illustration3 ,,fig4 #a ,illustration3 ,,fig4 #d ,the incoming and outgoing wires are made fast to one end of the connector-plate and to one of the ,l pieces that support the key4 ,when the key is at rest the circuit is open1 but when pressed down against the brass tack it is closed1 and whether pressed down or released it clicks at both movements4 ,a simple switch may be connected with the ,l-plate and the connection-post at the opposite side of the key-base1 so that1 if necessary1 the circuit may be closed4 ,or an arm may be caught under the screw at the ,l-plate1 and brought forward so that it can be thrown in against a screw-head on the connector-plate1 as shown in ,fig4 #c4 ,the screw-head may be flattened with a file1 and the underside of the switch bevelled at the edges1 so that it will mount easily on the screw4 ,in ,fig4 #d 7page #aia7 a simple telegraph-sounder is shown4 ,a base-board1 four inches wide1 six inches long1 and seven-eighths of an inch in thickness1 is made of hard-wood1 and two holes are bored1 with the centres two inches from one end1 so that the lower nuts of the horseshoe magnet will fit in them1 as shown in ,fig4 #e4 ,this allows the yoke to rest flat on the top of the base1 and with a stout screw passed down through a hole in the middle of the yoke and into the wood the magnets are held in an upright position4 ,from the base-block to the top of the bolt the magnets are two inches and a quarter high4 ,the bar of brass or iron to which the armature 7,a in ,fig4 #e7 is attached is four inches and a half in length and three-eighths by half an inch thick4 ,at the middle of the bar and through the side a hole is bored1 through which a small bolt may be passed to hold it between the upright blocks of wood4 ,at the front end two small holes are to be bored1 so that its armature may be riveted to it with brass escutcheon-pins or slim round-headed screws4 ,the heads are at the top and the riveting is underneath4 ,a small block of wood is cut1 as shown in ,fig4 #f1 against which the two upright pieces of wood are made fast4 ,this block is two inches and a half long1 one inch and a quarter high1 and seven-eighths of an inch wide4 ,the laps cut from each side are an inch wide and a quarter of an inch deep1 to receive the uprights of the same dimensions4 ,at the top of this block a brass-headed nail is driven for the underside of the bar to strike on4 ,a hook and spring are to be attached to the rear of the sounder-bar1 as described for the key1 and at the front of the base two binding-posts are arranged1 to which the loose ends of the coil-wires are attached4 ,just behind the yoke1 and directly under the armature-bar1 a long screw is driven into the base-block1 as shown at ,b in ,fig4 #e4 ,it must not touch the yoke1 and the head should be less than one-eighth of an inch below the bar when at rest4 ,on this the armature-bar strikes and clicks when drawn to the magnets4 ,the armature must not touch the magnets2 otherwise the residual magnetism would hold it down4 ,the screw must be nicely adjusted1 so that a loud1 clear click will result4 ,illustration3 ,,fig4 #b ,,fig4 #c ,,fig4 #e ,,fig4 #f ,,fig4 #h ,,telegraph ,,key ,,and ,,sounder ,when the sounder is at rest the rear end lies on the brass tack in the block1 and the armature is about a quarter of an inch above the top of the magnets4 ,the armature is of soft iron1 two inches and a half long1 seven-eighths of an inch wide1 and an eighth of an inch thick4 ,these small scraps of metal may be procured at a blacksmith's shop1 and1 for a few cents1 he will bore the holes in the required places2 or if you have a breast or hand drill the metal may be held in a vise and properly perforated4 ,by connecting one wire from the key directly with one of the binding-posts of the sounder1 and the other with the poles of a battery1 and so on to the sounder1 the apparatus is ready for use4 ,by pressing on the key the circuit is closed1 and the magnetism of the sounder-cores draws the armature down with a click4 ,on releasing the key the bar flies back to rest1 having been pulled down by the spring1 and it clicks on the brass tack-head4 ,these two instruments may be placed any distance apart1 miles if necessary1 so long as sufficient current is employed to work the sounder4 ,two sets of instruments must be made if boys in separate houses are to have a line4 ,each one must have a key1 sounder1 and cell1 or several cells connected in series to form a battery1 according to the current required4 ,in the plan of the telegraph-line connections 7,fig4 #g1 page #aif7 a clear idea is given for the wiring2 and if the line and return wires are to be very long1 it would be best to have them of ,no4 #ad galvanized telegraph-wire1 copper being too expensive1 although much better4 ,these wires must not touch each other1 and when attached to a house1 barn1 or trees1 porcelain or glass insulators should be used4 ,if nothing better can be had1 the necks of some stout glass bottles may be held with wooden pins or large nails1 and the wire twisted to them1 as shown in ,fig4 #h4 ,when the line is not in use the switches on both keys should be closed2 otherwise it would be impossible for the boy having the closed switch to call up the boy with the open one4 ,take great care in wiring your apparatus to study the plan1 for a misconnected wire will throw the whole system out of order4 ,illustration3 ,,fig4 #g ,to operate the line see that all switches are closed and that the connections are in good condition4 ,when the boy in house ,no4 #b wants to call up his friend in house ,no4 #a he throws open the switchon key1 as shown in the plan1 and by pressing down on the finger-key his sounder and that in house ,no4 #a click simultaneously4 ,as soon as he raises or releases the key the armatures rise1 making the up-click4 ,if he presses his key and releases it quickly the two clicks on the sounder in house ,no4 #a are close together2 this makes what is called a dot4 ,if the key is held down longer it makes a long time between clicks1 and this is called a dash4 ,the dot and dash are the two elements of the telegraphic code4 ,you will understand that the boy in house ,no4 #b hears just what the one in ,no4 #a is hearing1 since the electric current passing through both coils causes the magnets to act in unison4 ,so soon as the operator in house ,no4 #b has finished he closes his switch1 and the other in house ,no4 #a opens his switch on the key and begins his reply4 ,this is the simple principle of the telegraph1 and all the improved apparatus is based on it1 no matter how complicated4 ,the complete ,morse alphabet is appended3 ,illustration3 ,the ,morse ,telegraph ,code ,any persevering boy can soon learn the dot-and-dash letters of the ,morse code1 and very quickly become a fairly good operator4 ,telegraphic messages are sent and received in this way1 and are read by the sound of the clicks4 ,various kinds of recording instruments are also employed1 so that when an operator is away from his table the automatic recorder takes down the message on a paper tape4 ,in the stock-ticker1 employed in brokerage offices1 the recording is done by letters and numerals1 and the paper tape drops into a basket beside the machine1 so that any one picking up the strip of paper can see the quotations from the opening of business up to the time of reading them4 ,these quotations are sent out directly from the floor of the exchanges1 and by the action of one man's hand thousands of machines are set in operation all over the city4 ,perhaps the most unique and wonderful telegraphic signal-apparatus is that located on the floor of the ,new ,york ,produce ,exchange and the ,chicago ,exchange4 ,the dials1 side by side1 are operated by direct wire from ,chicago4 ,when the ,new ,york operator flashes a quotation it appears simultaneously on the ,new ,york dial and simultaneously on the ,chicago dial1 and vice versa4 ,electrical instruments are not the only means by which the ,morse alphabet may be transmitted1 for in some instances instruments would be in the way1 while in others the wires might be down and communication cut off4 ,this is interestingly illustrated by an event in ,thomas ,a4 ,edison's life4 ,when he was a boy and an apprentice telegraph operator on the ,grand ,trunk ,line1 an ice-jam had broken the cable between ,port ,huron1 in ,michigan1 and ,sarnia1 in ,canada1 so that communication by electricity was cut off4 ,the river at that point is a mile and a half wide1 the ice made the passage impossible1 and there was no way of repairing the cable4 ,edison impulsively jumped on a locomotive standing near the river-bank and seized the whistle-cord4 ,he had an idea that blasts of the whistle might be broken into long and short sounds corresponding to the dots and dashes of the ,morse code4 ,in a moment the whistle sounded over the river3 8,toot1 toot1 toot1 toot1--toot1 tooooot1--tooooot--tooooot--toot1 toot--toot1 toot40 8,halloo1 ,sarnia6 ,do you get me8 ,do you hear what ,i say80 ,no answer4 8,do you hear what ,i say1 ,sarnia80 ,a third1 fourth1 and fifth time the message went across1 to receive no response4 ,then suddenly the operator at ,sarnia heard familiar sounds1 and1 opening the station door1 he clearly caught the toot1 toot of the far-away whistle4 ,he found a locomotive1 and1 mounting to the cab1 responded to ,edison1 and soon messages were tooted back and forth as freely as though the parted cable were again in operation4 ,some years ago the police of ,new ,york were mystified over a murder case4 ,the man they suspected had not fled1 but was still in his usual place1 and attending to his business quite as though nothing had happened to connect him with the tragedy4 ,detectives in plain clothes had been following him and watching closely his every move in and out of restaurants and shops and at social affairs2 but not the slightest proof could be secured against him4 ,one noon-time they followed him into a caf1 where he had gone with a friend4 ,the detectives took seats near him1 but each of them sat at different tables in the room full of people4 ,when in the caf the suspect sat next the wall1 a habit the detectives had noticed4 ,consequently1 only those persons who sat at one side of him or directly in front could see his face4 ,during the time they were in the restaurant the detectives communicated with each other by tapping on the table tops with a lead-pencil2 and something the man said1 which the nearest detective heard1 led to the climax4 ,one detective rose1 paid his check1 and loitered near the door2 another got up a little later and sauntered out1 but returned with a cardboard sign4 ,going over to the table where the suspected criminal and his friend sat1 he deliberately tacked it on the wall above them1 then went out again1 leaving the third detective to watch the face of the man as he read3 #ajjj ,,reward for information leading to the arrest of the murderer of ------------ on ,march --------1 #ahgf ,the man cast a glance about the restaurant1 then said to his companion3 8,did ,i show any signs of agitation80 ,the third detective rose1 stepped over to the man1 tapped him on the shoulder1 and said1 8,i want you40 ,there would have been a scene of violence had not the other two detectives closed in on the man1 and within six months he paid the penalty of his crime4 ,if it had not been for the dot-and-dash alphabet1 tapped out with lead-pencils1 the detectives could not have communicated2 but like ,edison1 they used the means at hand to open up and carry on a silent conversation4 ,wireless ,telegraphy ,everybody nowadays understands that wireless telegraphy means the transmission of electrical vibrations through the ether and earth without the aid of wires or any visible means of conductivity4 ,the feat of sending an electrical communication over thousands of miles of wire1 or through submarine cables1 is wonderful enough1 for all that custom has made it an every-day miracle4 ,to accomplish this same end by sending our messages through the apparently empty air is indeed awe-inspiring and almost beyond belief4 ,and yet we know that wireless telegraphy is to-day a real scientific fact4 ,at first sight it would seem that the instruments must be complicated and necessarily beyond the ability of the average boy to make1 and far too expensive as well4 ,as a matter of fact1 the young electrician may construct his wireless apparatus at a very moderate cost1 it being understood that the sending and receiving poles may be mounted on a housetop or barn4 ,but first let us consider the theory upon which we are to work4 ,there is no doubt but that electricity is the highest known form of vibration--so high1 indeed1 that as yet man has been unable to invent any instrument to record the number of pulsations per second4 ,this vibration will occur in1 and can be sent through1 the ordinary form of conductor1 such as metals1 water1 fluids and liquids1 wet earth1 air and ice4 ,also through what we call the ether4 ,now the ether of the atmosphere1 estimated to be fifteen trillion times lighter than air1 is the medium through which the electrical vibrations pass in travelling in their radial direction from a central point1 corresponding to the ripples or wavelets formed when a pond or surface of still water is disturbed4 ,ether is so fine a substance that the organs of sense are not delicate enough to detect it1 and it is of such a volatile and uneasy nature that it is continually in motion4 ,it vibrates under certain conditions1 and when disturbed 7as by a dynamo7 it undoubtedly forms the active principle of electricity and magnetism4 ,james ,clark ,maxwell believed that magnetism1 electricity1 and light are all transmitted by vibrations in one common ether1 and he finally demonstrated his theory by proving that pulsations of light1 electricity1 and magnetism differed only in their wave lengths4 ,in #ahhg ,professor ,hertz succeeded in establishing proof positive that ,maxwell's theories were correct1 and1 after elaborate experiments1 he proved that all these forces used ether as a common medium4 ,therefore1 if it were not for the ether1 wireless telegraphy1 with all its wonders1 would not be possible4 ,we understand1 then1 that the waves of ether are set in motion from a central disturbing point1 and this can be accomplished only by means of electrical impulse4 ,suppose that we strike a bell held high in the air4 ,the sound is the result of the vibrations of its mass sending its pulsating energy through the air4 ,the length of the sound-waves is measured in the direction in which the waves are travelling1 and if the air is quiet and not disturbed by wind the sound will travel equally in all directions4 ,the sound of a bell will not travel so well against a wind as it will with it1 just as the ripples on a pond would be checked by an adverse set of wavelets4 ,now the ether can be made to vibrate in a similar manner to the air by a charge of electricity oscillating or surging to and fro on a wire several hundred thousand times in a second4 ,these oscillations strike out and affect the surrounding ether1 so that1 according to the intensity of the disruptive charge at the starting-point1 the ether waves may be made to reach near or distant points4 ,this is1 perhaps1 more clearly shown by the action of a pendulum4 ,in ,fig4 #i the rod and ball are at rest1 but if drawn to one side and released it swings over to the other side nearly as far away from its central position of rest as from the starting-point4 ,if allowed to swing to and fro it will oscillate until at last it will come to rest in a vertical position4 ,this same oscillation 7oscillation being a form of vibration7 takes place in the water when a stone has been flung into it1 and in the ether when affected by the electrical discharge4 ,in ,fig4 #aj are shown the principal varieties of vibration--the oscillating1 pulsating1 and alternating4 ,it is known that if these oscillations are damped1 so that the over-intense agitation of the central disturbance is lessened1 a new series of vibrations1 such as the pulsating or alternating1 is set up1 and these secondary vibrations possess the power to travel around the world--yes1 and perhaps to other worlds in the planetary cosmos4 ,illustration3 ,,fig4 #i ,,fig4 #aj ,,fig4 #aa ,,oscillation ,,and ,,vibration ,the study of ether disturbances1 wave currents1 oscillating currents1 and the other phenomena dependant upon this invisible force is most interesting and fascinating1 and were it possible to devote more space to this topic several chapters could be written on the scientific theory of wireless telegraphy4#b #b ,for further information on this subject the student is referred to such well-known books as ,signalling ,across ,space ,without ,wires1 by ,prof4 ,oliver ,j4 ,lodge1 and ,wireless ,telegraphy1 by ,c4 ,h4 ,sewall4 ,the principle difference between wire1 or line1 and wireless telegraphy is that the overhead wire1 or underground or submarine cable1 is omitted4 ,in its stead the ether of the air is set in vibratory motion by properly constructed instruments1 and the communication is recorded at a distance by instruments especially designed to receive the transmitted waves4 ,it seems to be the popular impression that a wireless message sent from one point to another travels in a straight line1 as indicated by ,fig4 #aa1 ,b representing ,boston1 which receives the message from ,n4 ,y41 or ,new ,york4 ,as a matter of fact1 if several sets of wireless receiving instruments were located on the circumference of a circle the same distance from ,new ,york in all directions1 or even at nearer or farther points1 they would all receive the same message4 ,instead of travelling in one direction1 the ether waves are set in motion by the electrical disturbance1 just as water is agitated by the stone thrown into it4 ,the ripples1 or wavelets1 are started from the central point of disturbance and radiate out1 so that instead of reaching ,boston only the waves travel over every inch of ground1 or air space1 in all directions1 and would be recorded in every town and village within the sphere of energy set up by the original force that put the ether waves in motion4 ,the stronger this initial force the wider its field of action4 ,this is shown at ,fig4 #ab1 which is an area comprising ,philadelphia1 ,pittsburg1 ,buffalo1 ,washington1 and other cities4 ,moreover1 the waves of electrical disturbance would carry far beyond in all directions1 taking in the cities of the north1 south1 and west1 and at the east1 going far out to sea1 beyond ,boston harbor and below ,cape ,hatteras1 where ships carrying receiving instruments could pick up the messages4 ,like the ripples on the water1 the radiating waves1 or rings1 become larger as they reach out farther and farther from the centre of disturbance1 until at last they are imperceptible1 and lose their shape and force4 ,illustration3 ,,fig4 #ab ,at great distances1 therefore1 the ether disturbance becomes so slight that it is impossible to record the vibration or message sent out2 and until some improved forms of apparatus and coherer are invented1 or the original disturbing force is enormously increased1 it will be impossible to send messages at longer distances than four or five thousand miles from a central point4 ,both ,marconi and ,de ,forrest assert that they are perfecting coherers which will make it possible to girdle the earth with a message1 and that within the next few years an aerogram may be sent out from a station1 and1 after instantly encircling the earth and being recorded during its passage at all intermediate stations1 it will return and be received at the original sending-point4 ,this1 of course1 is a matter of future achievement2 but now that messages across the ,atlantic are a commercial fact1 it seems quite possible that the greater feat of overriding space and reaching any point on the earth's surface will soon be a reality4 ,and now to proceed from theory to the construction of a practical wireless apparatus having a radial area of action over some ten or fifteen miles4 ,the principal parts of a wireless apparatus include the antennas 7or receiving and sending poles with their terminal connections71 the induction-coil1 strong primary batteries or dynamo1 the coherer and de-coherer1 the telegraph key and sounder 7or a telephone receiver71 and the necessary connection wires1 binding-posts1 and ground-plates4 ,a large induction-coil with many layers of fine insulated wire will be necessary for the perfect operative outfit4 ,the most practical coil for the amateur is a ,ruhmkorff induction-coil4 7,see the directions and illustrations for constructing this coil1 beginning on page #ei of chapter iv47 ,the sending apparatus is practically the same in all outfits1 and consists of a source of electrical energy1 such as a battery1 or dynamo1 the essential induction-coil and adjustable spark-gap between the brass balls on terminal rods1 and the make-and-break switch1 or telegraph-key4 ,it is in the various forms of coherers and receiving apparatus that the different inventors claim superiority and originality4 ,the systems also differ in their theory of harmonic tuning or vibratory sympathy4 ,this is accomplished by means of coils and condensers1 so that the messages sent out on one set of instruments will not be picked up or recorded by the receiving apparatus of competitors4 ,having made or purchased an induction-coil of proper and adequate size1 it will now be necessary to construct the parts so that an adjustable spark-gap may be secured4 ,make a hollow wooden base for the induction-coil to rest on4 ,it should be a trifle longer than the length of the coil and about seven inches wide4 ,this may be made from wood half an inch thick4 ,the base should be two inches high1 so that it will be easy and convenient to make wire connections under it4 ,mount the induction-coil on the base and make it fast with screws1 arranging it so that the binding-posts are on the side rather than at the top of the coil1 as shown in ,fig4 #ac4 ,cut a thin board and mount it across the top of the induction-coil on two short blocks1 and to this attach two double-pole binding-posts 7,p ,p74 ,the fine wires from the induction-coil are made fast to the foot of each post1 and from the posts the aerial wire 7,a ,w7 and ground wire 7,g ,w7 lead out4 ,fasten two binding-posts at the forward corners of the base1 and to them make connection-wires fast to the heavy or primary wires of the coil4 ,wires ,b and ,c lead out from these posts to the battery and key1 and to complete this part of the sending1 or transmitting apparatus it will be necessary to have two terminal rods and balls attached to the top of the binding-posts 7,p ,p74 ,this part of the apparatus is generally called the oscillator1 and the rods are balanced on the posts1 so that they can be moved in order to increase or diminish the space 7,s ,g71 or spark-gap1 between the brass balls4 ,when1 after experiment1 the proper space has been determined1 the set screw at the top of the posts will hold the terminal rods securely in place4 ,obtain a piece of brass1 copper1 or ,german-silver rod three-sixteenths of an inch in diameter4 ,now cut two short rods1 each six inches long1 and two inches from one end flatten the rods with a hammer1 as shown at ,a in ,fig4 #ad4 ,flatten the rod in two places at the other end1 as shown at ,b ,b in ,fig4 #ad2 then bore holes through the flattened parts 7,a71 so that the binding-screws at the top of the posts 7,p ,p7 will pass through them4 ,obtain two brass balls from one to one inch and a half in diameter4 ,if they are solid or cast brass they may be attached to the ends of the terminal rods by threading1 so that it will be easy to remove them4 ,if the balls are of spun sheet-metal it will be necessary to solder them fast to the ends of the rods1 and1 when polishing the balls1 the rods will have to be removed from the binding-posts4 ,it is imperative that the balls should be kept polished and in bright condition at all times1 to facilitate the action of the impulsive sparks4 ,illustration3 ,,fig4 #ac ,illustration3 ,,fig4 #ad ,to counterbalance these balls there should be handles at the long ends of the rods4 ,these handles may be of wood1 or made of composition molded directly on the rods4 ,a good composition that can be easily made and molded is composed of eight parts plaster of ,paris and two parts of dextrin made into a thick paste with water4 ,the dextrin may be purchased at a paint-store1 and is the color of light-brown sugar4 ,mix the dry plaster and dextrin together1 so that they are homogeneous2 then add water to make the pasty mass4 ,use an old table-knife to apply the wet composition to the bars4 ,the flattened parts will help to hold the mass in place until it sets4 ,it is best to make two mixtures of the paste and put one on first1 leaving it rough on the surface1 so that the last coat will stick to it4 ,when the last coat is nearly dry it may be rubbed smooth with the fingers and a little water1 or allowed to dry hard1 and then smoothed down with an old file and sand-paper4 ,if solid brass balls are used for the terminals the composition handles may be made heavier2 but in any event the proper amount of composition should be used1 so that when the rod is balanced on a nail or piece of wire passed through the hole it will not tip down at one end or the other1 but will remain in a horizontal position4 ,the overhead part of the apparatus employed to collect the electric waves is called the antenn1 and in the various commercial forms of wireless apparatus this feature differs4 ,the general principle1 however1 is the same1 and in ,figs4 #ae1 #af1 #ag1 and #ah some simple forms of construction are shown4 ,great care must be taken to properly insulate the rod1 wire1 or fingers of these antenn1 so that the full force of the vibration is carried directly down to the coherer and sounder or receiver4 ,for this purpose1 porcelain1 glass1 or gutta-percha knobs must be employed4 ,in ,fig4 #ae the apparatus consists of an upright stick1 a cross-stick1 and a brace1 or bracket1 to hold them in proper place4 ,porcelain knobs are made fast to the sticks with linen string or stout cotton line4 ,then an insulated copper wire is run through the holes in the knobs1 and from the outer knob a rod of brass1 copper1 or ,german-silver1 or even a piece of galvanized-iron lightning-rod1 is suspended4 ,care should be taken to see that the joint between rod and wire is soldered so as to make perfect contact4 ,otherwise rust or corrosion will cause imperfect contact of metals1 and interrupted vibrations would be the result4 ,the upright stick should be ten or fifteen feet high1 and may be attached to a house-top1 a chimney1 or on the corner of a barn roof4 ,another form of single antenna is shown in ,fig4 #af4 ,this is a rod held fast in a porcelain insulator with cement4 ,the insulator1 in turn1 is slipped over the end of a staff1 or pole1 which is erected on a building top or out in the open1 the same as a flag-pole4 ,near the foot of the rod1 and just above the insulator1 a conducting-wire is made fast and soldered4 ,this is run down through porcelain insulators to the apparatus4 ,if the pole is erected on a house-top it may be braced with wires1 to stay it1 but care must be taken not to have these wires come into contact with the rod1 or conducting-wire4 ,illustration3 ,,fig4 #ae ,,fig4 #af ,,fig4 #ag ,,fig4 #ah ,,types ,,of ,,antenn ,another form of antennas is shown in ,fig4 #ag1 where rods are suspended from a wire which1 in turn1 is drawn taut between two insulators4 ,the insulators are held in a framework composed of two uprights and a cross-piece of wood4 ,this frame may be nailed fast to a chimney and to the gable of a roof1 as shown in the drawing2 and to steady the rods1 so that they will not swing in a high wind1 the lower ends should be tied together with cotton string1 the ends of which should be fastened to the uprights4 ,the leading-in wire is made fast to the top wire1 from which the rods are suspended1 and all the exposed joints should be soldered to insure perfect contact and conductivity4 ,a modified form of the ,marconi antenn is shown in ,fig4 #ah4 ,this is made of a metal hoop three of four feet in diameter held in shape by cross-sticks of wood1 which can be lashed fast to the ring4 ,leading down from it are numerous copper wires which terminate in a single wire1 the whole apparatus resembling a funnel4 ,the upper unions where the wires join the ring need not be soldered1 but at the bottom1 where they all come together and join the leading-in wire1 it is quite necessary that a good soldered joint be made4 ,this funnel may be hung between two upright poles on a house-top1 or suspended from the towers or chimneys4 ,almost any metal plate will do for the ground1 or the ground-wire 7,g ,w in ,fig4 #ac7 may be bound to a gas or water pipe which goes down deep in the ground1 where it is moist4 ,rust or white lead in the joints of gas-mains sometimes prevent perfect contact1 but in water-pipes the current will flow readily through either the metal or the water4 ,to insure the most perfect results1 it is best to have an independent ground composed of metal1 and connected directly with the oscillator1 or coherer1 by an insulated copper wire4 ,a simple and easily constructed ground is a sheet of metal1 preferably copper1 brass1 or zinc1 to the upper edge of which two wires are soldered1 as shown in ,fig4 #ai4 ,this is embedded in the ground three or four feet below the surface4 ,another ground-plate is a sheet of metal bent in ,v shape and then inverted4 ,two wires are soldered to the angle1 and the ends brought together and soldered4 ,this ground is buried three or four feet deep1 and stands in a vertical position1 as shown at ,fig4 #bj4 ,at ,fig4 #ba a flat ground is shown4 ,this is a sheet of metal cut with pointed ends4 ,the ground-wire is soldered to the middle of it1 and it is then buried deep enough to be embedded in moist earth4 ,one of the best grounds is an old broiler with a copper wire soldered to the ends of the handles1 as shown at ,fig4 #bb4 ,this is buried deep in the ground in a vertical position1 and the insulated copper wire is carried up to the instruments4 ,the most important part of the wireless telegraphic apparatus is now to be constructed1 and this requires some care and patience4 ,the coherer is the delicate1 sensitive part of the apparatus on which hinges success or failure4 ,there are various kinds of coherers designed and used by different inventors1 but while the materials differ and the construction takes various forms1 the same basic principle applies to all4 ,illustration3 ,,fig4 #ai ,,fig4 #bj ,,fig4 #ba ,,fig4 #bb ,,types ,,of ,,grounds ,the coherer can best be explained as a short glass tube in which iron or other metallic filings are enclosed4 ,corks are placed in both ends of the tube1 and through these corks the ends of wire are passed1 so that they occupy the position shown in ,fig4 #bc1 the ends being separated a quarter of an inch4 ,metal filings will not conduct an electric current the same as a solid rod or bar of the same metal1 but resist the passage of current4 ,after long periods of experimenting with various devices to detect the presence of feeble currents1 or oscillations1 in the ether1 the coherer of metal filings was adopted4 ,when the oscillations surge through the resonator1 the pressure1 or potential1 finally breaks down the air film separating the little particles of metal1 and then gently welds their sharp edges and corners together so as to form a conductor for the current4 ,before this process of cohesion takes place these fine particles offer a very high resistance to the electrical energy generated by a dry cell or battery--so much so that no current is permitted to pass4 ,but once the oscillations in the ether cause them to cohere--presto6 the resistance drops from thousands of ohms to hundreds1 and the current from the dry cell now flows easily through the coherer and deflects the needle of a galvanometer4 ,this is the common principle of all coherers of the granulated metal type1 although there are many modifications of the idea4 ,the action of the electric and oscillatory currents on particles of metal can best be understood by placing some fine iron filings on a board1 as shown at ,fig4 #bd1 and then inserting the aerial and ground wires in the filings1 but separated by an eighth or a quarter of an inch4 ,a temporary connection may be made as shown in ,fig4 #be4 ,illustration3 ,,fig4 #bc ,illustration3 ,,fig4 #bf ,illustration3 ,,fig4 #bg ,illustration3 ,,fig4 #bd ,illustration3 ,,fig4 #be ,a ,a are aerials on both instruments2 ,c is the open coherer1 or board with iron filings1 in which the ends of the aerial and ground wires are embedded2 ,d ,c is a dry cell2 and ,r is a telegraphic relay1 or sounder4 ,if the wire across ,c was not parted and covered with filings1 the dry cell would operate ,r1 but the high resistance of the particles of metal holds back the current4 ,on the opposite side1 ,i ,c is the induction-coil2 ,k is the telegraphic key1 or switch1 which makes and breaks the current2 ,s ,b is the storage-batteries1 or source of electric energy2 and ,s ,g the spark-gap between the brass balls on the terminal rods4 ,by closing the circuit at ,k the current flows through the primary of the induction-coil1 affects the secondary coil1 and causes a spark to leap across the gap between the brass balls4 ,this instantly sets the ether in motion from ,a on the right1 and the impulse is picked up by ,a on the left4 ,this oscillation breaks down the resistance of the filings at ,c1 and the current from battery1 or dry cell 7,d ,c71 flows through the filings and operates the sounder1 or relay 7,r74 ,this operation takes place instantly1 and the particles of metal are seen to cohere1 or shift1 so that better contact is established4 ,but as soon as the spark has jumped across the gap the action of cohesion ceases until the key 7,k7 is again operated to close the circuit and cause another spark to leap across the gap4 ,the shifting of the metal particles on the board 7,c7 is what takes place in the glass tube of the coherer1 ,fig4 #bc1 but in this confined space the particles will not drop apart again as on the flat surface1 but will continue to cohere4 ,a de-coherer is necessary1 therefore1 to knock the particles apart1 so that the next oscillatory impulse will have a strong and individual effect4 ,there are several forms of de-coherers in use1 but for the amateur telegrapher an electric-bell movement without the bell1 or1 in other words1 a buzzer with a knocker on the armature1 will answer every purpose4 7,see description of buzzer on page #fd47 ,it must be properly mounted1 so that on its back stroke1 or rebound1 the knocker will strike the glass tube and shake the particles of metal apart4 ,for this purpose the vibrations of the armature should be so regulated as to obtain the greatest possible speed1 in order that the dots and dashes 7or short and long periods7 will be accurately recorded through the coherer and made audible by the sounder or telephone receiver4 ,another form of coherer is shown in ,fig4 #bf4 ,this is made of a small piece of glass tube1 two rods that will accurately fit in the tube1 some nickel filings1 two binding-posts1 and a base-block three inches and a half long4 ,the two binding-posts are mounted on the block1 and through the holes in the body of the posts the rods are slipped4 ,they pass into the tube1 and the blunt ends press the small mass of filings together1 as shown in the drawing4 ,by means of the binding-posts these coherer-rods may be held in place and the proper pressure against the filings adjusted2 then maintained by the set-screws4 ,the nickel filings may be procured by filing the edge of a five-cent piece4 ,obtain a few filings from the edge of a dime and add them to the nickel1 so that the mixture will be in the proportion of one part silver to nine parts nickel4 ,this mixture will be found to work better than the iron filings alone4 ,the aerial and ground wires are made fast to the foot-screws of the binding-posts1 and the base on which the coherer is mounted may be attached to a table or ledge on which the other parts of the receiving and recording apparatus are also installed4 ,another form of coherer is shown at ,fig4 #bg4 ,this is constructed in a somewhat similar manner to the one just described4 ,a glass tube is provided with two corks having holes in them to receive the coherer-rods4 ,two plugs of silver are arranged to accurately fit within the tube1 and into these the ends of the coherer-rods are screwed or soldered4 ,between these silver plugs1 or terminals1 the filings of nickel and silver are placed1 and the rods are pushed together and caught in the binding-posts4 ,the aerial and ground wires are made fast to the foot-screws of the posts4 ,for long-distance communication it is necessary to have a condenser placed in series with the sparking or sending-out apparatus4 7,see the type of condenser described and illustrated in chapter iv41 page #gb47 ,an astatic galvanometer is also a valuable part of the receiving apparatus1 and the one described on page #aaa will show clearly the presence of oscillatory currents by the rapid and sensitive deflections of the needle4 ,for local service1 where a moderately powerful battery is employed1 a telegraph-key1 such as described on page #aij1 will answer very well1 but for high-tension work1 where a powerful storage-battery or small dynamo is employed1 it will be necessary to have a non-sparking key1 so that the direct current will not form an arc between the terminals of a key4 ,most of the keys used for wireless telegraphy have high insulated pressure-knobs1 or the make and break is done in oil1 so that the spark or arc cannot jump or be formed between the points4 ,the plan of a simple non-sparking dry switch is shown at ,fig4 #bh4 ,this is built up on a block three inches wide and five inches long4 ,it consists of a bar 7,a71 two spring interrupters 7,b and ,c71 a spring 7,d71 and the binding-posts 7,e ,e74 ,they are arranged as shown in ,fig4 #bh1 and a front elevation is given in ,fig4 #bi4 ,the strip 7,b7 lies flat on the block1 and is connected with one binding-post by a wire attached under one screw-head and run along the under side of the base in a groove to the foot of the post4 ,strip ,c is of spring-brass1 and is made fast to the base with screws4 ,this is 8dead10 as no current passes through it1 and its only use is to interrupt4 ,the bar 7,a7 is arranged as explained for the line telegraph-key1 and the remaining binding-post is connected to it by a wire run under the base and brought up to one of the angle-pieces forming the hinge4 ,a high wood or porcelain knob is made fast at the forward end of the bar1 so that when high-tension current is employed the spark will not jump from the bar to the operator's hand4 ,the complete key ready for operation is shown at ,fig4 #cj1 and to make it permanent it should be screwed fast to the table1 or cabinet1 on which the coil and condenser rest4 ,the plan of a 8wet0 key is shown in ,fig4 #ca1 and the complete key in ,fig4 #cb4 ,illustration3 ,,fig4 #bh ,,fig4 #bi ,,fig4 #cj ,,fig4 #ca ,,fig4 #cb ,,dry ,,and ,,wet ,,non-,,sparking ,,switches ,a base of wood three by five inches is made and given several coats of shellac4 ,obtain a small rubber or composition pill or salve box1 and make it fast to the front end of the base with an oval-headed brass screw driven down through the centre of the box4 ,a wire leading to one binding-post is arranged to come into contact with the screw1 and the other post is connected by wire to one hinge-plate supporting the bar4 ,the long machine screw1 or rivet1 passed down through the knob and into the bar1 extends down below the bar for half an inch or more1 so that when the knob is pressed down the end of the screw1 or rivet1 will strike the top of the screw at the bottom of the box without the bar coming in contact with the edge of the box4 ,when in operation the composition box is filled with olive oil or thin machinery oil1 so that when contact is made by pressing the knob down the circuit will be instantly broken1 the spring at the rear end of the bar drawing it back to rest4 ,the oil prevents any sparks jumping across2 and also breaks an arc1 should one form between the contact-points4 ,with the addition of a good storage-battery 7the strength of which must be governed by the size of the induction-coil and the distance the messages are sent7 and a dry-cell or two for the receiving apparatus1 the parts of the wireless apparatus are now ready for assembling4 ,full directions for making storage-cells is given in chapter ii41 page #ba1 and for dry-cells in chapter ii41 page #bi4 ,for short-distance work the plan shown in ,figs4 #cc and #cd will be found a very satisfactory form of apparatus4 ,one of each kind of instrument should be at every point where communication is to be established4 ,in the sending apparatus 7,fig4 #cc7 ,s ,c are the storage-cells1 ,k the key1 and ,i ,c the induction-coil4 ,t ,t are the terminals and balls1 ,s ,g the spark-gap1 and ,p ,p the posts that hold the terminal rods4 ,a ,w is the aerial wire running up from one post1 and ,g ,w the ground-wire connecting the other terminal post with the ground-plates4 ,in the receiving apparatus 7,fig4 #cd7 ,c is the coherer1 ,d ,c the de-coherer1 ,t ,s the telegraphic sounder1 or relay1 and ,a ,g the astatic galvanometer4 ,b is the dry-cell1 or battery1 and ,d ,c ,s the de-coherer switch1 so that when the apparatus is not in use the dry-cell will not operate the buzzer or de-coherer4 ,a ,w is the aerial wire and ,g ,w the ground-wire4 ,two or more storage-cells may be connected in series 7that is1 the negative of one with the positive pole of the other7 until a sufficiently powerful source of current is secured for the transmission of messages4 ,illustration3 ,,fig4 #cc ,illustration3 ,,fig4 #cd ,to operate the apparatus1 the circuit is closed with ,k1 and the current from ,s ,c flows around the primary coil in ,i ,c and affects the secondary coil1 causing the spark to leap across the gap 7,s ,g74 ,this causes a disturbance through the wires ,a ,w and ,g ,w1 and the ether waves are set in oscillatory motion from the antenn on the house-top4 ,this affects the antenn at the receiving-point1 and the impression is recorded through the coherer 7,c7 on the telegraphic sounder or relay 7,t ,s71 which is operated by the current from dry-cell or battery 7,b71 since the oscillations have broken the resistance of the filings in the coherer 7,c74 ,the instant that the current passes through the coherer and operates ,t ,s1 the astatic galvanometer indicates the presence of current by the deflected needle4 ,illustration3 ,,fig4 #ce ,when the apparatus is in operation ,d ,c ,s is closed1 so that the current from ,b operates the coherer 7,d ,c74 ,directly communication is broken off1 the switch 7,d ,c ,s7 should be opened2 otherwise the buzzer would keep up a continuous tapping4 ,for long-distance work a more efficient sending apparatus is shown in ,fig4 #ce4 ,this is composed of an induction-coil1 with the terminal rods and brass balls forming the spark-gap1 an oil key 7,k71 and three or more large storage-cells1 or a dynamo 7if power can be had to run it74 ,a condenser is placed in connection with the aerial and ground wires1 so that added intensity or higher voltage is given the spark as it leaps across the gap4 ,in operation this apparatus is similar to the one already described4 ,where contact is made with ,k the primary coil is charged1 and by induction the current affects the secondary coil1 the current or high voltage from which is stored in the condenser4 ,when a sufficient quantity is accumulated the spark leaps across ,s ,g and affects wires ,a ,w and ,g ,w4 ,this action is almost instantaneous1 and directly the impulse sets the ether in motion the same impulse is recorded on the distant coherers and sounders4 ,there are a great many modifications of this apparatus1 but the principles are practically the same1 and while the construction of this apparatus is within the ability of the average boy1 many of the more complicated forms of coherers and other parts would be beyond his knowledge and skill4 ,marconi has realized his ambition to send messages across the ocean without wires1 and is now doing so on a commercial basis1 and at the rate of twenty-five words a minute4 ,it is but the next step to establish communication half-way around the world1 and finally to girdle the earth4 ,chapter ,x ,,dynamos ,,and ,,motors ,to adequately treat of dynamos and motors1 a good-sized book rather than this single chapter would be necessary1 and only a general survey of the subject is possible4 ,its importance is unquestionable2 indeed1 the whole science of applied electricity dates from the invention of the dynamo4 ,without mechanical production of electricity there could be no such thing as electric traction1 heat1 light1 power1 and electro-metallurgy1 since the chemical generation of electricity is far too expensive for commercial use4 ,surely it is a part of ordinary education nowadays to have a clear and definite idea of the principles of electrical science1 and in no department of human knowledge has there been more constant and rapid advance4 ,it is only a truism to assert that the school-boy of to-day knows a hundredfold more about electricity and its varied phenomena than did the scientists and philosophers of old--,volta and ,galvani and ,benjamin ,franklin4 ,yet it was for these forerunners to open and blaze the way for others to follow4 ,a beginning must always be made1 and the ,marconis and ,edisons of to-day are glad to acknowledge their indebtedness to the experimenters and inventors of the past4 ,and now to our subject4 ,all dynamos are constructed on practically the same principle--a field of force rapidly and continuously cutting another field of force1 and so generating electric current4 ,the common practice in all dynamos and motors is to have the armature fields revolve within1 or cut the forces of the main fields of the apparatus4 ,there are many different kinds of dynamos generating as many varieties of current--currents with high voltage and low amperage2 currents with low voltage and high amperage2 currents direct for lighting1 heating1 and power2 currents alternating1 for high-tension power or transmission1 electro-metallurgy1 and other uses4 ,it is not the intention in this chapter to review all of these forms1 nor to explain the complicated and intricate systems of winding fields and armatures for special purposes4 ,consequently1 only a few of the simpler forms of generators and motors will be here described1 leaving the more complex problems for the consideration of the advanced student4 ,for his use a list of practical text-books is appended in a foot-note4#c #c ,first ,principles of ,electricity and ,magnetism1 by ,c4 ,h4 ,w4 ,biggs2 ,the ,dynamo3 ,how ,made and ,used1 by ,s4 ,r4 ,bottone2 ,dynamo ,electric ,machinery1 by ,professor ,s4 ,p4 ,thompson2 ,practical ,dynamo ,building for ,amateurs1 by ,frederick ,walker4 ,the ,uni-direction ,dynamo ,the uni-direction current machine is about the simplest practicable dynamo that a boy can make4 ,it may be operated by hand1 or can be run by motive power4 ,the field is a permanent magnet similar to a horseshoe magnet4 ,this must be made by a blacksmith1 but if a large parallel magnet can be purchased at a reasonable price so much the better1 as time and trouble will be saved4 ,this magnet should measure ten inches long and four inches and a half across1 with a clear space seven inches long and one inch and three-quarters wide1 inside measure4 ,the metal should be half an inch thick and one inch and a quarter wide4 ,a blacksmith will make and temper this magnet form2 then1 if there is a power-station near at hand where electricity is generated for traction or lighting purposes1 one of the workmen will magnetize it for you at a small cost2 or it can be wound with several coils of wire1 one over the other1 and a current run through it4 ,when properly magnetized it should be powerful enough to raise ten pounds of iron4 ,this may be tested by shutting off the current and trying its lifting power4 ,if the magnet is too weak to attract the weight the current should be turned on and another test made a few minutes later4 ,before the steel is tempered there should be four holes bored in the magnet and countersunk1 so that screws may be passed through it and into the wooden base below1 as shown at ,fig4 #a4 ,this wooden base is fourteen inches long1 eight inches wide1 and one inch in thickness4 ,it may be made of pine1 white-wood1 birch1 or any good dry wood that may be at hand4 ,the blocks on which the magnet rests are an inch and a quarter square and seven inches long4 ,the magnet is mounted directly in the middle of the base1 an equal distance from both edges and ends1 as shown in the plan drawing 7,fig4 #aj74 ,the blocks are attached with glue and brass screws driven up from the underside of the base4 ,from a brass strip three-eighths of an inch wide and one-eighth of an inch thick cut a piece six inches long1 and bore holes at either end through which long1 slim1 oval-headed brass screws may pass4 ,use brass1 copper1 or ,german-silver for this bar1 and not iron or steel4 ,to the underside1 and at the middle1 solder or screw fast a small block of brass1 through which a hole is to be bored for the spindle or shaft4 ,this finished bar is shown in ,fig4 #b4 ,when mounted over the magnet and held down with brass screws driven into the wood base1 its end view will appear as shown in ,fig4 #c1 ,a being the bar1 ,b ,b the screws which hold it down1 ,d the base into which they are driven1 and ,c ,c the blocks under the magnet 7,n ,s74 ,the object of this bar is to support one end of the armature shaft4 ,from brass one-eighth of an inch thick bend and form two angles1 as shown at ,fig4 #d4 ,two holes for screws are to be drilled in the part that rests on the base1 and one hole1 for the shaft to pass through1 is bored near the top of the upright plate4 ,the centre of this last hole must be the same height from the base as is the hole in the bar 7,fig4 #b7 when mounted over the magnet1 as shown at ,fig4 #c4 ,the location of these plates is shown in the plan 7,fig4 #aj74 ,there is one plate at each end of the base1 as indicated at ,b and ,b ,b1 the shaft passing through the hole in the brass block at the underside of the bar 7,c74 ,these angles are the end-bearings for the armature shaft1 and should be accurately centred so that the armature will be properly centred between the ,n and ,s bars of the magnet4 ,illustration3 ,,fig4 #a ,,fig4 #b ,,fig4 #c ,,fig4 #d ,,fig4 #e ,,fig4 #f ,,fig4 #g ,,fig4 #h ,,fig4 #i ,,details ,,of ,,uni-,,direction ,,dynamo ,the armature is made from soft1 round iron rod one inch and a half in diameter and five inches long4 ,a channel is cut all around it1 lengthwise1 five-eighths of an inch wide and half an inch deep1 as shown in ,fig4 #e4 ,this will have to be done at a machine-shop in a short bed-planer1 since it would be a long and tedious job to cut it out with a hack-saw4 ,the sharp corners should be rounded off from the central lug1 so that they will not cut the strands of fine wire that are to be wound round it4 ,two brass disks1 or washers1 are to be cut1 one inch and a half in diameter and from one-eighth to one-quarter of an inch thick1 for the armature ends4 ,a quarter-inch hole is to be made in the centre of each for the shaft to fit in1 and two smaller holes must be drilled near the edge1 and opposite each other1 so that machine-screws may pass through them and into holes bored and threaded in the ends of the armature1 as shown at ,fig4 #e4 ,these ends will appear as shown at ,fig4 #f1 and the middle hole should be threaded so as to receive the end of a shaft4 ,when the shaft is screwed in tight the end that passes through the brass disk must be tapped with a light hammer to rivet the end1 and so insure that the shaft will not unscrew4 ,the shafts should be of hard brass or of steel4 ,the one at the front should be one inch and a half in length1 and that at the rear six inches long1 measuring from the outer face of the brass end to the end of the shaft4 ,from boxwood or maple turn a cylinder three-quarters of an inch in diameter and an inch long1 with a quarter-inch hole through it4 ,over this slip a piece of three-quarter-inch brass or copper tubing that fits snugly1 and at opposite sides drill holes and drive in short screws that will hold the tube fast to the hub4 ,they must not be so long as to reach the hole through the centre4 ,place this hub in a vise1 and with a hack-saw cut the tube across in two opposite places1 so that you will have the cylinder with two half-circular shells or commutators screwed fast to it1 as shown at ,fig4 #g4 ,this hub will fit over the shaft at the front end of the armature1 and will occupy the position shown at ,f in ,fig4 #aj4 ,cut two small blocks of wood for the brushes and binding-posts1 and bore a hole through them1 so that the foot-screw of a binding-post may pass through the block and into the post1 as shown at ,fig4 #h4 ,from thin spring copper cut a narrow strip and bend it over the block1 catching it at the top with a screw and lapping it under the binding-post at the outside4 ,from boxwood or maple have a small wooden pulley turned1 with a groove in it and a quarter-inch hole through the centre4 ,this pulley should be half an inch wide and one inch and a half in diameter1 as shown at ,fig4 #i4 ,this is to be attached at the end of the long shaft1 where it will occupy the position shown at ,e in ,fig4 #aj4 ,all the parts are now ready for assembling except the armature1 which must be wound4 ,before laying on the turns of wire the channel in the iron must be lined with silk1 held in place with glue or shellac4 ,a band of silk ribbon is given two turns about the centre of the iron1 and the sides are so completely covered with silk that not a single strand of wire will come into direct contact with the iron4 ,great care must be taken1 when winding on the wire1 not to kink1 chafe1 or part the strands4 ,the channel should be filled but not overcrowded1 and when full several wraps of insulating tape should be made fast about the armature to hold the wire firmly in place and prevent it from working out at the centre when the armature is driven at high speed4 ,the armature1 when properly wound and wrapped1 will appear as shown at ,a in ,fig4 #aa1 and it is then ready to have the ends screwed on4 ,several sizes of wire may be used to wind the armature1 according to the current desired1 but for general use it would be well to use ,no4 #cj silk-insulated copper wire4 ,illustration3 ,,fig4 #aj ,,fig4 #aa ,,plan ,,of ,,the ,,uni-,,direction ,,dynamo ,about four ounces should be enough for this armature1 and the ends are to be passed through small holes in the brass end 7,b72 see ,fig4 #aa4 ,one end must be soldered to one commutator1 the other end to the other commutator4 ,the end-piece 7,b7 is attached to the iron armature 7,a7 with machine-screws2 then ,c is to be made fast in a similar manner4 ,when putting the parts together1 it would be well to use some shellac on the wooden cylinder and driving-wheel to make them hold to the shaft4 ,by following the plan in ,fig4 #aj1 it will be an easy matter to put the parts together2 when they are assembled the complete machine will appear as shown in the drawing 7,fig4 #ab74 ,the driving-wheel should be of wood five-eighths of an inch thick and six inches in diameter1 and held in the frame of wood and metal brackets by a bolt4 ,a short handle can be arranged with which to turn the wheel1 and a small leather belt will transmit the power to the small wheel on the armature shaft4 ,as the armature is revolved the lines of force are cut and the current is carried out through the wire attached to the binding-posts on the blocks 7,g ,g74 ,illustration3 ,,fig4 #ab ,considerable current may be generated if the armature is driven at higher speed than the hand-wheel will cause it to revolve4 ,this can be accomplished by running the belt over a larger wheel1 such as the fly-wheel of a sewing-machine1 or connecting it to a large pulley on a water-motor4 ,the latter may be attached to a faucet in the wash-tub if there is pressure enough to do the work4 ,a ,small ,dynamo ,all dynamos are constructed on the same general principle as that of the uni-direction machine just described2 but they differ in their windings1 the quantities of metal electrified1 the sizes and lengths of wire wound on both armature and field1 and in their shape and speeds4 ,in large dynamos it is impossible to employ steel magnets of the required size4 ,in place of them soft iron cores are used and magnetized by external electric current2 or the wiring is done in 8series0 or 8shunt10 so that the fields will be self-exciting once the machine has been properly started4 ,the principal difference in dynamos is1 perhaps1 more clearly illustrated by the diagrams shown in ,figs4 #ac1 #ad1 #ae1 and #af4 ,in ,fig4 #ac the arrangement of armature and field-magnet is the same as in the uni-direction machine1 the field 7,f7 being of magnetized steel1 while the armature 7,a7 is of soft iron wound with coils of fine wire1 the ends of which are brought out at the commutators 7,c71 through which the current is carried to the brushes 7,b and ,b ,b74 ,if1 however1 the soft iron cores are used1 a separate magnetizing electric current must be passed through the coils of wire wound about the field-pieces1 so that they will become temporary magnets--the same as the cores of an electric bell movement1 a telegraph-sounder1 or the induction-coil core when a current is passed through the primary coil4 ,the armature 7,a7 is then driven at high speed by power1 and the current is taken off for use through wires that lead from ,b and ,b ,b4 ,in all of these figures the armatures rotate1 in the space between the large pole-pieces of the field-magnets1 in the same direction as the hands of a clock move4 ,in these figure drawings the field-magnets1 commutators1 and brushes only are shown1 the armature being indicated by the circle 7,a74 ,figure #ac represents a dynamo1 the field-magnets of which are excited by a separate battery or generator4 ,this is known as a 8separately excited0 machine1 and is employed for various uses4 ,the brushes 7,b and ,b ,b7 are connected to the external circuit--that is1 with the motor or other apparatus for which current is to be generated4 ,the magnetic field in which the armature rotates will be constant if the exciting current is constant1 like the magnetism in the magnet of the uni-direction current machine4 ,the induced electro-motive force 7which depends upon the rate at which the lines of force are cut7 will be constant for the given speed at which the armature rotates4 ,this action is the same as that described for the uni-direction current machine4 ,figure #ad is the diagram of a 8series0-wound dynamo4 ,the field and armature are soft gray iron1 and are wound in series--that is1 one end of the magnet-winding is made fast to the brush ,b1 the other to the brush ,b ,b1 and the apparatus to be operated by the current is let in between ,b ,b and the magnet1 as shown by the indicated electric arc-light in the illustration4 ,the field-magnet coils1 the armature1 and the external conductors are in series with each other1 forming a simple circuit4 ,when the armature is driven at high speed the field-magnets become self-exciting1 with the result that current is generated4 ,its simple course is through ,b ,b to commutators on the hub1 thence through one winding on the iron armature ,a1 to ,b1 through field ,f1 and back to ,b ,b again1 operating in its course any pieces of equipment designed for electric impulse1 such as motors1 or lamps1 trolley-cars1 trains1 or electric machinery4 ,illustration3 ,,fig4 #ac ,illustration3 ,,fig4 #ad ,illustration3 ,,fig4 #ae ,illustration3 ,,fig4 #af ,the third type1 shown in ,fig4 #ae1 is known as 8shunt0-winding4 ,the field-magnet coils and the external resistance are in parallel1 or shunt with each other1 instead of in series4 ,the brushes are connected with the external circuit1 and also with the ends of the field-magnet coils4 ,this is clearly shown in the drawing4 ,the ends of the field-coils are connected with brushes ,b and ,b ,b1 and the external circuit wires are connected also with the same brushes1 and pass down to such an apparatus as a plating bath1 in which the current runs through the electrode1 the electrolyte1 and the cathode1 most of the current generated passing through the external circuit4 ,the field-coils are of fine wire1 and when the armature is rotated there will always be a current through the field-magnets1 whether the external circuit is complete or not4 ,if a break occurs in the external circuit1 a more powerful current will consequently pass through the field-magnets4 ,in ,fig4 #af a 8compound0-wound dynamo is shown4 ,it is a combination of the series and the shunt machine4 ,the field-magnet coils are composed of two sizes of wire4 ,there are comparatively four turns of stout wire and many turns of fine wire1 the ends of both being connected1 as shown in the drawing4 ,the stout wire leads out to lamps which are arranged in series1 as shown at the foot of the drawing4 ,the current developed by this dynamo is one of 8constant potential10 and is used almost exclusively for incandescent lamps1 the 8constant0 current from the series-wound machine being used for arc-lamps1 power1 and other commercial purposes4 ,it will not be necessary to use the first or last systems1 nor to experiment with the alternating current1 with its phases and cycles4 ,all that a boy wants is a good direct-current machine that will light lamps1 run sewing-machines or motors1 and furnish the power for long-distance wireless telegraphy and other apparatus requiring considerable current4 ,to begin with1 it would be better to make a small dynamo and study its principles as you progress2 then it will be a great deal easier to construct a larger one4 ,it will be necessary to have the iron parts made at a blacksmith-shop1 since the various cutting1 threading1 and tapping operations call for the use of special iron-working tools4 ,soft iron should be used1 and if a piece of cast-iron can be procured for the lugs or magnet ends it will give better service than wrought-iron4 ,from three-quarter-inch round iron cut two cores1 each three inches and a half long1 and thread them at both ends1 as shown at ,b ,b in ,fig4 #ag4 ,from band-iron five-eighths of an inch thick and one inch and a half wide cut a yoke 7,a71 and bore the indicated holes two inches and three-quarters apart1 centre to centre4 ,these should be threaded so that the cores 7,b ,b7 will screw into them4 ,from a bar of iron cut off two blocks one inch and a half by one inch and a half by two inches for the lugs4 ,now1 with a hack-saw and a half-round file1 cut out one side of each lug1 as shown at ,c4 ,these lugs are to be bored and threaded at one end1 so that they can be screwed on the lower ends of the cores 7,c ,c74 ,for a larger dynamo the yoke should be made six inches long1 one inch thick1 and two inches and a half wide4 ,the cores should be of one-inch iron pipe4 ,these will be hollow1 as shown at ,b ,b in ,fig4 #ah4 ,for the ends cast-iron blocks must be made or cast from a pattern two inches and three-quarters square and four inches high1 as shown at ,c4 ,the yoke 7,a7 and the lugs 7,c7 are bored and threaded to receive the one-inch pipe1 and when set up this will constitute an iron field-magnet six inches wide1 two inches thick1 and nine inches high4 ,this1 if properly wound1 should develop a quarter of a horse-power4 ,illustration3 ,,fig4 #ag ,illustration3 ,,fig4 #ah ,illustration3 ,,fig4 #ai ,illustration3 ,,fig4 #bj ,illustration3 ,,fig4 #ba ,the parts shown in ,fig4 #ag1 when screwed together1 will give you a field-magnet two by one and a half by five and three-quarter inches high1 and will appear as shown in ,fig4 #ai1 ,a being the yoke at the top1 ,b ,b the cores1 ,c ,c the lugs1 and ,d a strip of brass screwed fast across the back of the lugs 7,c ,c71 and in which a hole is bored to act as a bearing for one end of the armature shaft4 ,between the lugs and the strip 7,d7 fibre washers three-eighths of an inch in thickness are placed to keep the strip away from the lugs4 ,a hole is bored directly through the middle of each lug1 from front to rear1 and it is threaded at each end so that a machine-screw will fit in it4 ,the brass strip 7,d7 is five-eighths of an inch wide1 three-sixteenths of an inch thick1 and four inches long4 ,copper or ,german-silver may be used in place of brass1 but iron or steel must not be employed1 since these metals are susceptible to magnetism4 ,two holes should be made in the bottom of each lug1 and threaded1 so that machine-screws may be passed through a wooden base and into them in order to hold the dynamo on the base4 ,figure #bj is an end view of the field-magnets showing the yoke at ,a1 the core at ,b1 the lug at ,c1 and the bearing and binding-strip of yellow metal at ,d4 ,two blocks of hard-wood1 an inch square and one inch and a half long1 are cut and provided with holes1 so that they can be fastened to the lugs ,c ,c with long1 slim machine-screws1 as shown at ,e ,e in ,fig4 #ba4 ,this is a view looking down on the magnets1 blocks1 and straps4 ,these blocks are to support the brushes and terminals1 and should be linked across the face with a brass strap ,g1 so that the other end of the armature shaft may be supported4 ,care must be taken1 when setting straps ,d and ,g1 to have them line4 ,the holes1 too1 must be centred1 since the armature must revolve accurately within the field-lugs 7,c ,c7 without touching them1 and there is but one-sixteenth of an inch space between them4 ,from hard-wood half an inch in thickness cut a base1 six by seven inches1 and two strips an inch wide and five inches long4 ,with glue and screws driven up from the underside of the strips fasten them to the base1 as shown at ,fig4 #bb4 ,then make the field-magnets fast to the base with long machine-screws1 using washers under the heads at the underside of the base-board4 ,the mounting should then appear as shown in ,fig4 #bh4 ,illustration3 ,,fig4 #bh ,from steel1 half an inch in diameter1 cut a shaft five inches long4 ,have it turned down smaller at one end for three-eighths of an inch1 and at the other end for a distance of one inch and a half1 as shown at ,fig4 #bc4 ,this is for the armature1 and it should fit between ,d and ,g in ,fig4 #ba1 and should revolve easily in the holes cut to receive it in both straps1 with not more than one-eighth of an inch play forward or backward4 ,the long1 projecting end should be at the rear1 and should extend beyond strip ,d for three-quarters of an inch1 so that the driving-pulley can be made fast to it4 ,the armature is made up of segments or laminations of soft iron and insulated copper wire4 ,the laminated armature works much better than does the solid metal ring or lug1 and a pattern may be made from a piece of tin from which all the sections can be cut4 ,with a compass1 strike a two-inch circle on a clear piece of tin2 then mark it off1 as shown at ,fig4 #bd1 and cut it out with shears4 ,the hole at the centre of the pattern need not be bored1 but a small pinhole should be made so that a centre-punch can be used to indicate the middle of each plate for subsequent perforation4 ,ordinary soft band iron may be employed for this purpose1 and the sections should not be more than one-sixteenth of an inch in thickness4 ,it will take some time to cut out the required number of pieces for this small armature4 ,when they are all ready they should be slipped over the shaft1 and if they have been properly matched and cut1 they should appear as a solid body1 one inch and a half long4 ,arrange these laminations on the armature shaft so that when the shaft is in position the mass of iron will be within the lugs of the field-magnets4 ,the holes through the iron plate should be so snug as to call for some driving to put them in place4 ,each disk of iron should be given a coat of shellac to insulate it1 and between each piece there should be a thin cardboard or stout paper separator to keep the disks apart4 ,these paper washers should be dipped in hot paraffine1 or thick shellac may be used to obtain a good sticking effect and so solidify the laminations into a compact mass4 ,when this operation is completed the armature core should appear as shown in ,fig4 #be4 ,illustration3 ,,fig4 #bb ,illustration3 ,,fig4 #bc ,illustration3 ,,fig4 #bd ,illustration3 ,,fig4 #be ,illustration3 ,,fig4 #bf ,illustration3 ,,fig4 #bg ,illustration3 ,,fig4 #bi ,illustration3 ,,fig4 #cj ,from maple1 or other hard-wood with a close grain1 make a cylinder three-quarters of an inch long and one inch in diameter to fit the shaft4 ,over this drive a piece of copper or brass tubing1 and at four equal distances1 near the rear or inner edge1 make holes and drive small1 round-headed screws into the wood4 ,then1 with a hack-saw1 cut the tube into four equal parts between the screws4 ,this is the commutator4 ,in order to hold the quarter circular plates fast to the cylinder1 remove one screw at a time1 and place thick shellac on the cylinder4 ,then press the plate firmly into place and reset the screw4 ,repeat this with the other three1 and the armature will be ready for the winding4 ,the voltage and amperage of a dynamo is reckoned by its windings1 the size of wire1 the number of turns1 and the direction4 ,this is a matter of figuring1 and need not now concern the young electrician1 since it is a technical and theoretical subject that may be studied later on in more advanced text-books4 ,for this dynamo use ,no4 #bb cotton-insulated copper wire for the armature1 and ,no4 #af double cotton-insulated copper wire for the field4 ,the armature1 when properly wound and ready for assembling with the brushes and wiring1 will appear as shown in ,fig4 #bf4 ,a small driving-wheel two inches in diameter and half an inch thick must now be turned from brass and provided with a ,v-shaped groove on its face4 ,the hub1 at one side1 is fitted with a set-screw1 so that it can be bound tightly on the shaft4 ,this pulley is made fast to the shaft at the rear of the dynamo1 and on the opposite end to where the commutator hub is attached4 ,a diagram of the wiring is shown in ,fig4 #bi1 and in ,fig4 #cj the mode of attaching the ends of the coil wires to the commutators is indicated4 ,two complete coils of wire must be made about each channel of the armature1 as illustrated on the drum of ,fig4 #cj4 ,these are separated by a strip of cardboard dipped in paraffine and placed at the centre of a channel while the winding is going on4 ,in some armatures the coils are laid one over the other2 but with this construction1 and in the case of a short-circuit1 a broken wire1 or a burn-out1 it is impossible to reach the under coil without removing the good one4 ,begin by attaching one end of the fine insulated wire to commutator ,no4 #a2 then half fill the channel1 winding the wire about the armature1 as indicated in ,fig4 #cj4 ,when the required number of turns has been made1 carry the end around the screw in commutator ,no4 #b1 baring the wire to insure perfect contact when caught under the screw-head4 ,from ,no4 #b carry the wire around through the channel at right angles to the first one1 and after half filling it bring the end out to commutator ,no4 #c4 ,carry the wire in again and fill up the other half of the first channel1 and bring the end out to commutator ,no4 #d4 ,fill up the remaining half of the second channel2 then attach the final end to commutator ,no4 #a1 and the armature winding will be complete without having once broken the strand of wire4 ,to keep the coils of wire in place1 and to prevent them from flying out1 under the centrifugal force of high speed1 it would be well to bind the middle of the armature with wires or adhesive tape4 ,after driving down the small screws over the leading-in and leading-out wires the armature will be ready to mount in the bearings4 ,as the blocks that support the brushes and binding-posts partly close the opening to the cavity at the front1 the armature will have to be inserted from the back into the strip 7,g7 in ,fig4 #ba4 ,then the back strip 7,d7 is screwed in place4 ,the armature1 when properly mounted1 should revolve freely and easily within the field-lugs without friction1 and the lugs must by no means touch the armature4 ,from thin spring-copper brushes may be cut and mounted on the block under the binding-posts1 so that one will rest on top of the commutators while the other presses up against the underside4 ,the wiring is then to be placed on the field-magnets4 ,this is carried out as described for the electric magnets on pages #ed-eh of chapter iv41 each core receiving five or seven layers1 or as much as it will hold without overlapping the lug or yoke4 ,the ends of the wires are connected as shown at ,fig4 #ad or ,fig4 #ae1 the ends being carried down through the base and up again in the right location to meet the foot of a binding-post4 ,the complete dynamo will appear as shown in ,fig4 #bh4 ,before the dynamo is started for the first time it would be well to run a strong current through the field coils4 ,the residual magnetism retained by the cores and iron parts will then be ready for the next impulse when the dynamo is started again4 ,larger dynamos may be made of this type4 ,with an armature1 the core of which is four inches in diameter and six inches long1 having eight instead of four channels1 and placed within a field of proportionate size1 the dynamo will develop one horse-power4 ,a ,split-ring ,dynamo ,another type of dynamo is shown in ,fig4 #ca4 ,this is composed of a wrought or cast iron split-ring wound for the field1 an armature made up of laminations1 and the necessary brushes1 posts1 commutators1 and wire4 ,illustration3 ,,fig4 #ca ,have a blacksmith shape an open ring of iron1 in the form of a ,c1 three-eighths of an inch thick and four inches wide4 ,the opening should be three inches wide1 as shown in ,fig4 #cb4 ,this ring should measure five inches on its outside diameter1 and the ends are to be bored and threaded to receive machine-screws4 ,two lugs are to be made from wrought-iron to fit on these ends4 ,these should be four inches long1 an inch and a half high1 and three-quarters of an inch thick at top and bottom4 ,they should be hollowed out at the middle1 so that an armature two inches in diameter will have one-eighth of an inch play all around when arranged to revolve within them4 ,holes are made through the lugs to receive machine-screws1 which are driven into the holes in the ends of the iron 7,c74 ,wrought-iron ,l pieces are made one inch and a half high and an inch across the bottom1 and with machine-screws they are made fast to the backs of the lugs to act as feet on which the field-magnet may rest1 as shown in ,fig4 #cc4 ,across the back of the lugs1 and set away from them by fibre washers1 a strap of brass is made fast4 ,this measures three-quarters of an inch wide and a quarter of an inch thick1 and at the middle of it a three-eighth-inch hole is bored to receive the rear end of the armature shaft4 ,this is shown in ,fig4 #cd1 which is a front view of the field1 or ,c1 iron1 the lugs 7,l ,l7 and feet 7,f ,f71 the armature bearing 7,s71 and the base 7,b71 of three-quarter-inch hard-wood4 ,the field-magnet is bolted to the base with lag-screws1 so that it will be held securely in place4 ,the laminations for the armature core are two inches in diameter1 and are cut from soft iron one-sixteenth of an inch thick4 ,they have eight channels1 as shown in ,fig4 #ce1 and the tubing on the commutator hub is divided into four parts so that the terminals from each coil can be brought to a commutator1 as described for ,fig4 #cj4 ,in the eight-channel armature1 however1 there is but one coil of wire in each channel4 ,illustration3 ,,fig4 #cb ,,fig4 #cc ,,fig4 #cd ,,fig4 #ce ,,fig4 #cf ,,fig4 #cg ,,fig4 #ch ,,details ,,of ,,split-,,ring ,,dynamo ,in ,fig4 #cf a plan of the armature is shown1 ,s representing the shaft1 ,b ,b the bearings1 ,l the laminations1 ,c the commutators and hub1 ,p the driving-pulley1 and ,n ,n the nuts that hold the laminations together and lock them to the shaft4 ,the shaft is half an inch in diameter1 the laminations four inches thick1 and the commutator barrel one inch in diameter and three-quarters of an inch long4 ,the shaft is turned down from the middle to where ,p and ,c are attached2 then at the front end it is made smaller1 where it passes through the front bearing4 ,with the detailed description already given for the construction of the small dynamo1 it should be an easy matter to carry out the work on this one1 and a quarter horse-power generator should be the result4 ,the field-magnet is wound with five or seven layers of ,no4 #af double cotton-insulated wire1 and the armature with ,no4 #bb silk or cotton-covered wire4 ,the connections may be made for either the series or the shunt windings shown in ,figs4 #ad and #ae4 ,another type of field is shown in ,fig4 #cg1 where two plates of iron are screwed to one core1 and the lugs are1 in turn1 made fast to the inner sides of the plates within which the armature revolves4 ,the 8,manchester0 type is shown in ,fig4 #ch1 where two cores1 constructed by a top and bottom yoke1 are excited by the coils1 and the lugs are arranged between the cores1 so that the armature revolves within them4 ,a ,small ,motor ,the shapes1 types1 powers1 and forms of motors are as varied and different as those of dynamos1 each inventor designing a different type and claiming superiority4 ,the one common principle1 however1 is the same--that of an armature revolving within a field1 and lines of force cutting lines of force4 ,a motor is the reverse of a dynamo4 ,instead of generating current to develop power or light1 a current must be run through a motor to obtain power4 ,motors are divided into two classes3 the ,d ,c1 or direct current1 and the ,a ,c1 or alternating current4 ,for the amateur the direct-current motor will meet every requirement1 and since the battery1 or dynamo current1 that may be available to run a motor1 is in all probability a direct one1 it will be necessary to construct a motor that is adapted to this source of power and for the present avoid the complications of the alternating current both in generation and in use4 ,the direct-current motor is an electrical machine driven by direct current1 the latter being generated in any desired way4 ,this current is forced through the machine by electro-motive force1 or voltage2 the higher the pressure1 or voltage1 the more efficient the machine4 ,be careful lest too much current 7amperage7 is allowed to flow1 for the heat developed thereby will burn out the wiring4 ,motors are so constructed that when a current is passed through the field and armature coils the armature is rotated4 ,the speed of the armature is regulated by the amount of amperage and voltage that passes through the series of magnets1 and this rotating power is called the torque4 ,torque is a twisting or turning force1 and when a pulley is made fast to the armature shaft1 and belted to connect with machinery1 this torque1 or force1 is employed for work4 ,the speed of an armature when at full work is usually from twelve hundred to two thousand revolutions a minute4 ,as few machines are designed to work at that velocity1 a system of speeding down with back gears1 or counter-shafts and pulleys1 is employed4 ,the motor itself cannot be slowed down without losing power4 ,the efficiency of motors is due to the centrifugal motion of the mass of iron and wire in the armature and the momentum it develops when spurred on by the magnetism of the field-magnets acting upon certain electrified sections of the armature4 ,the armature of a working motor is usually of such high resistance that the current employed to run it would heat and burn out the wires if the full force of the current was permitted to flow through it for any length of time4 ,as the armature rotates it has counter electro-motive force impressed upon it4 ,this acts like resistance1 and reduces the current passing through4 ,the higher the speed the less current it takes1 so that after a motor has attained its highest1 or normal speed1 it is using less than half the current required to start it4 ,reduction of current in the armature reduces torque1 so that the turning force of the armature is reduced as its speed of rotation increases4 ,on the other hand1 the momentum1 or 8throw10 produces power at high speed1 together with an actual saving of current4 ,an armature revolving at sixteen hundred revolutions1 and giving half a horse-power on a current of five amperes1 is more economical than one making three to five hundred revolutions1 and giving half a horse-power on a current of fifteen to twenty amperes4 ,thus1 a slowly turning armature takes more current and exerts higher torque than a rapidly rotating one4 ,to protect the fine wire on the armature from burning1 in high-voltage machines a starting-box1 or rheostat1 is employed4 ,the motor begins working on a reduced current1 and as it picks up speed more current is let in1 and so on until the full force of the current is flowing through the motor4 ,it is then turning fast enough to protect itself through the counter electro-motive force4 ,this can be understood better after some practical experience has been had in the construction and running of motors4 ,of the various forms of motors but three will be illustrated and described2 but the boy with ideas can readily design and construct other types as he comes to need them4 ,the ,flat-bed ,motor ,the simplest of all motors is the flat-bed type1 illustrated in ,fig4 #ci4 ,this is composed of a magnet on a shaft revolving before a fixed magnet attached to the upright board of the base4 ,where space is no object1 this motor will develop considerable power from a number of dry-cells or a storage-battery4 ,now1 in the section relating to dynamos1 four different systems of wiring were shown4 ,in motors of the direct-current type but one system will be described--that of the series-winding1 illustrated in ,fig4 #dj4 ,the current1 entering at ,a1 passes to the brush 7,b71 thence through the commutator 7,c7 and the armature coils4 ,it runs on through the brush 7,b ,b71 the field-coils 7,f71 and out at ,d4 ,this is the same course the current takes in the series-wound dynamo illustrated in ,fig4 #ad1 page #bda1 and with such a dynamo current could be generated to run any series-wound1 direct-current motor4 ,illustration3 ,,fig4 #ci ,,fig4 #dj ,,fig4 #da ,,fig4 #db ,,fig4 #dc ,a ,,flat-,,bed ,,motor ,,and ,,parts ,from hard-wood half an inch thick cut a base-piece six inches and a half long by three inches and a half wide4 ,arrange this base on cross-strips three-quarters of an inch wide and half an inch thick1 making the union with glue and screws driven up from the underside4 ,to one end of this base attach an upright or back two inches and three-quarters high1 and allow the lower edge to extend down to the bottom of the cross-strip1 as shown at the left of ,fig4 #ci4 ,make this fast to the end of the base and side of the cross-strip with glue and screws2 then give the wood a coat of stain and shellac to properly finish it4 ,now have a blacksmith make two ,u pieces of soft iron for the field and armature cores1 as shown in ,fig4 #da4 ,these are of quarter-inch iron one inch and a half in width4 ,they are one inch and three-quarters across and the same in length4 ,one of them should have a half-inch hole bored in the end 7at the middle71 and above and below it smaller holes for round-headed screws to pass through4 ,by means of these screws the ,u is held to the wooden back4 ,the other ,u is to have a three-eighth-inch hole bored in it so that it will fit on the armature shaft4 ,wind the ,u irons with six layers of ,no4 #bj cotton-insulated wire1 having first covered the bare iron with several wraps of paper4 ,use thick shellac freely after each layer is on1 so that the turns of wire will be well insulated and bound to each other4 ,follow the wiring diagram shown in ,fig4 #dj when winding these cores1 and when the field is ready1 make it fast to the back with three-quarter-inch round-headed brass screws4 ,directly in the middle of the hole through the field iron bore a quarter-inch hole for the armature shaft to pass through2 then make an ,l piece1 of brass1 two inches high1 three-quarters of an inch wide1 and with the foot an inch long1 as shown at ,fig4 #db4 ,two holes are made in the foot through which screws will pass into the base1 and near the top a quarter-inch hole is to be bored1 the centre of which is to line with that through the back1 at the middle of the field core4 ,the shaft is made from steel three-eighths of an inch in diameter and six inches and a half long4 ,one inch from one end the shaft should be turned down to a quarter of an inch in diameter1 and one inch and a quarter from the other end it must be reduced to a similar size4 ,the short end mounts in the back and the long one receives the pulley1 after the latter passes through the ,l bearing4 ,a piece of three-eighth-inch brass tubing an inch long is slipped over the shaft two inches from the pulley end and secured with a flush set-screw4 ,this tubing is then threaded and provided with two nuts1 one at either end1 so that when the armature ,u is slipped on the collar the nuts can be tightened and made to hold the magnet securely on the shaft4 ,this shaft is clearly shown in the sectional drawings ,fig4 #dc4 ,at the left side the shaft 7,s7 passes into the wood back through the quarter-inch hole4 ,at the outside a brass plate with a quarter-inch hole is screwed fast and acts as a bearing4 ,the shaft does not touch the field-magnet 7,f ,m71 because the hole is large enough for the quarter-inch shaft to clear it4 ,a fibre washer 7,f ,w7 is placed on the shaft before it is slipped through the back4 ,this prevents the shaft from playing too much1 and deadens any sound of 8jumping0 while rotating4 ,at the middle the shaft 7,s7 passes through the brass collar on which the threads are cut4 ,a ,m represents the armature magnet1 and ,w ,w the washers and nuts employed to bind it in place4 ,at the right1 ,s again represents the shaft1 ,b the bearing1 ,c the commutator hub1 and ,p the pulley1 while ,r is the small block under the hub to which the brushes and binding-posts are attached4 ,from the descriptions already given of dynamos1 and with these figure drawings as a guide1 it should be an easy matter to assemble this motor4 ,the ends of the field and armature magnets should be separated an eighth of an inch4 ,the hub for the commutators is three-quarters of an inch long and three-quarters of an inch in diameter4 ,the commutators are made as described for the uni-direction current machine1 care being taken to keep the holding screws from touching the shaft4 ,a three-quarter-inch cube of wood is mounted on the base1 under the commutator hub1 and to this the brushes and binding-posts are made fast1 as shown in ,fig4 #ci4 ,unless the armature happens to be in a certain position this motor is not self-starting1 but a twist on the pulley1 as the current is turned on1 will give it the necessary start4 ,its speed will then depend on the amount of current forced through the coils4 ,another ,simple ,motor ,another type of motor is shown in ,fig4 #dd1 where one field-winding magnetizes both the core and the lugs4 ,the frame of this motor is made up of two plates of soft iron a quarter of an inch thick1 six inches long1 and two inches and a half wide4 ,each plate is bent at one end so as to form a foot three-quarters of an inch long1 and a half-inch hole is drilled one inch and a quarter up from the bottom1 at the middle of each plate4 ,through this hole pass the machine-screws which hold the iron core in place between the side-plates4 ,the core is made of three-quarter-inch round iron two inches and three-quarters long1 and drilled and threaded at each end to receive the binding machine-screws4 ,two lugs are cut from iron1 and hollowed at one side so that an armature two inches in diameter will rotate within them when made fast to the side-plates4 ,the lugs are two inches and a half long1 an inch wide1 and two inches and a half high4 ,from iron five-eighths of an inch wide and one-eighth of an inch thick make two side-strips with ,l ends4 ,these are four inches long1 and are provided with two holes so that the machine-screws which hold the lugs to the inside plates will also hold these strips in place1 at the outside1 as shown in ,fig4 #de4 ,at the rear these strips extend half an inch beyond the frame4 ,across the back a brass strip of the same size as the iron strips is arranged4 ,it is held at the ends by screws1 or small bolts1 made fast to the ,l ends of the side-strips4 ,directly in the middle of the back-strip a hole is made for the armature shaft1 and beyond it the pulley is keyed or screwed fast to the shaft4 ,at the front a similar strip is made and attached4 ,this latter has a small hole in the middle of it to serve as a bearing for the forward end of the shaft4 ,across the top of the motor a brass strip or band is made fast with machine-screws2 and at the angles formed by the front ends of the side-strips and the front cross-strips hard-wood blocks are attached4 ,to these the brushes and binding-posts are made fast1 so that one brush at the top of the left-hand block rests on the top of the commutator4 ,the one at the underside of the opposite block must rest on the underside of the commutator4 ,illustration3 ,,fig4 #dd ,illustration3 ,,fig4 #de ,the armature core is made up of laminations as described for the dynamo armatures4 ,in a really efficient motor the armature should have eight or more channels4 ,the other parts of the motor may be assembled and wired as described on the preceding pages4 ,the armature should be wound with ,no4 #bj or #bb insulated copper wire1 and the field with ,no4 #af or #ah4 ,for high voltage1 however1 the armature should be wound with finer wire and a rheostat used to start it4 ,a ,third ,type of ,motor ,the third type is but a duplicate of the series-wound dynamo1 the general plan of which is shown in ,fig4 #dj4 ,this motor can be made any size1 but as its dimensions are increased the weight of the field-magnets and armature must be proportionately enlarged4 ,for an efficient and powerful motor1 the field should stand ten inches high and six inches broad4 ,the iron cores are five inches long and one inch and a half in diameter4 ,these should be made by a blacksmith and bolted together4 ,the armature is three inches in diameter and four inches long1 and should develop two-thirds of a horse-power when sufficient current is running through the coils to drive it at sixteen hundred revolutions4 ,the wiring is carried out as shown in ,fig4 #dj1 and the armature hung and wound as suggested for the dynamo shown in ,fig4 #bh1 page #bdf4 ,chapter ,,xi ,,galvanism ,,and ,,electro-,,plating ,simple ,electro-plating ,to the average boy experimenter1 electro-plating is one of the most fascinating of the uses to which electricity may be put4 ,in scientific language the process is known as electrolysis1 and involves the separation of a chemical compound into its constituent parts or elements by the action of an electric current and the proper apparatus4 ,electrolysis cannot take place1 however1 unless the liquid in the tank1 commonly called the electrolyte 7no relation to electric light71 is a conductor4 ,water1 or water with mixtures of chemicals1 such as sulphate of copper1 sulphate of zinc1 chloride of nickel1 cyanide and nitrate of silver1 or uranium and other metallic salts1 are good conductors4 ,oil is a non-conductor1 and a current will not pass through it1 no matter what the pressure may be4 ,the simplest electro-plating outfit1 and the one that a boy should start with1 is the sulphate of copper bath1 such as is commonly employed by makers of electrotypes1 and which is in extensive use by refiners of copper for high-grade electrical use4 ,more than half of the total output of copper in the world is used for electrical work--conductors1 switches1 and all sorts of parts--and since any impurity in the copper interferes with its conducting powers1 it is most important that it should be free from any traces of carbon or arsenic4 ,the electrolytic refining of copper is now a very important process in connection with electric work1 and about half a million tons of copper are treated annually to free it from all impurities4 ,moreover1 the gold1 silver1 and other valuable metals which may be found in copper-ore are thus recovered4 ,the electro-plating1 electrotyping1 and refining operations are one and the same thing2 but in the first instance the object to be plated is left in the solution only a short time or until a blush of copper has been applied4 ,in the second process the wax mold is left in long enough for a thin shell of copper to be deposited2 and in the third1 the kathodes are immersed until they are heavily coated with copper4 ,to carry on any of these operations it will be necessary to have a small tank or glass jar to hold the plating-bath or electrolyte4 ,preferably it should be of a square or oblong shape4 ,but a serviceable tank may be constructed from white-wood1 pine1 or cypress1 if proper care is taken in making and water-proofing 7,fig4 #a74 ,for experimental purposes a tank eighteen inches long1 ten inches wide1 and twelve inches deep will be quite large enough to use as a copper bath4 ,for silver1 nickel1 or gold1 smaller tanks should be employed1 as they contain less liquid1 or electrolyte1 which in the more valuable metals is expensive4 ,obtain a clear plank twelve inches wide1 well seasoned1 and free from knots or sappy places4 ,cut two sides twenty inches long and two ends eight inches long4 ,with chisel1 saw1 and plane shape the ends of the side planks as shown at ,fig4 #b2 or if there is a mill at hand it would be well to have the ends cut with a buzz-saw1 thus insuring that they will be accurate and fit snugly4 ,screw-holes are bored with a gimlet-bit1 and countersunk1 so that screws will pass freely through them and take hold in the edges of the boards4 ,screws and plenty of white-lead1 or asphaltum varnish1 should be used on these points to make them water-tight2 then the lower edge of the frame is prepared for the bottom board4 ,turn the tank bottom up1 and1 with a fat steel-wire nail and a hammer1 dent a groove at the middle of the edge of the planks all around1 as shown in ,fig4 #c4 ,it will not do to cut this out with a gouge-chisel1 because it is intended that the wood should swell out again if necessary4 ,the object of driving the wood down is to form a valley into which a line of cotton string-wicking1 soaked in asphaltum varnish or imbedded in white-lead1 may be laid4 ,this should be done 7as shown in ,fig4 #d7 before the bottom is screwed on1 so that afterwards 7in the event of the joint leaking7 the wood will swell and force the wicking out1 and thus properly close the fissure4 ,the bottom board should be provided with holes all around the edge1 not more than two inches apart1 through which screws can be driven into the lower edge of the tank4 ,treat the wood1 both in and outside1 to several successive coats of asphaltum varnish1 and as a result you will have a tank resembling ,fig4 #a4 ,two shallow grooves are to be cut in the top of each end board of the tank1 for the cross-bars to fit in immovably4 ,these bars should be about three inches apart2 and the ones holding the anodes1 or flat copper plates1 should be close to one side1 leaving plenty of room for objects of various sizes to be properly immersed4 ,another manner in which the bottom of the tank can be attached is shown in ,fig4 #e1 which is a view of the tank sides turned bottom up4 ,a rabbet is cut from the lower edges of the sides and ends1 before they are screwed together1 and a bottom is fashioned of such shape as to accurately fit in the lap formed by the rabbet4 ,this rabbet and the outer edge of the bottom plank should be well smeared with white-lead1 and all put together at the same time1 driving the screws into the edge of the bottom plank1 through the lower edges of the sides and bottom1 and also through the bottom board into the lower edges of the sides and ends 7,fig4 #f74 ,still another and stronger way in which to make a tank for a large bath is to cut the planks as shown at ,fig4 #g4 ,the sides are then bolted together1 locking the ends and bottom1 so that they cannot warp or get away4 ,the bolts are of three-eighth-inch round iron-rod1 threaded at both ends and provided with nuts4 ,large washers are placed against the wood and under the nuts1 so that when the nuts are screwed on tightly they will not tear the wood1 but will bear on the washers4 ,the points are all to be well smeared with white-lead or acid-proof cement 7see ,formul7 before the parts are put together and bolted1 so as to avoid any possibility of leakage4 7,fig4 #h shows the completed tank47 ,illustration3 ,,fig4 #a ,,fig4 #b ,,fig4 #c ,,fig4 #d ,,fig4 #e ,,fig4 #f ,,fig4 #g ,,fig4 #h ,,tank ,,for ,,electro-,,plating ,now obtain two copper rods long enough to span the tank1 with an inch or two projecting beyond the tank at either side4 ,at one end of these attach binding-posts1 to which the wires from a battery can be connected1 leaving the opposite ends free1 as shown at ,fig4 #i 7see page #bge74 ,anodes1 or pure soft copper plates1 are hung on the positive rod1 while on the negative one the objects to be plated1 or kathodes1 are suspended on fine copper wires just heavy enough to properly conduct the current4 ,the positive wire leads from the carbon1 or copper pole1 of the battery1 while the negative one is connected with the zinc4 ,the anodes are plates of soft sheet or cast copper1 and should be as nearly pure as possible for electrolytic work2 but if they are to be re-deposited1 to free them from impurities1 they may be in thin ingot form1 just as the copper comes from the mines4 ,the general principle of electro-refining of copper is very simple4 ,a cast plate of the crude copper is hung from the positive pole in a bath of sulphate of copper1 made by dissolving all the sulphate of copper1 or bluestone1 that the water will take up4 ,drop a few lumps on the bottom of the tank to supply any deficiency1 then add an ounce of sulphuric acid to each gallon of liquid1 to make it more active and a better conductor4 ,the crude copper plate is to be the leading-in pole for the current1 while a thin sheet of pure copper1 no thicker than tissue-paper1 is suspended from the opposite rod for the leading-out pole2 or in place of the thin sheet1 some copper wires may be suspended from the rod4 ,the electrodes--that is1 the copper plate and the thin sheet or wires--are placed close together1 so that the current may pass freely and not cause internal resistance in the battery4 ,the electric current1 in its passage from the crude copper plate to the pure copper sheet or wires1 decomposes the sulphate of copper solution and causes it to deposit its metallic copper on the sheet or wires2 and at the same time it takes from the crude copper a like portion of metallic copper and converts it into chemical copper4 ,the electric current really takes the copper from the solution and adds it to the pure copper sheet1 while the remaining constituents of the decomposed solution help themselves to some copper from the crude plate4 ,in this way the crude copper diminishes and the pure copper sheet increases in size1 the impurities as well as the salts of other metals being precipitated to the bottom of the tank1 or mingled with the solution1 which must be purified or replaced from time to time by fresh solution4 ,this is the process of copper-plating1 and any metal object may be properly cleansed and coated with copper by suspending it in the bath and running the current through it4 ,when the refining process is employed1 any metal will answer as a depository for the copper1 but as the intention is to produce a pure copper plate which can be melted and cast into ingots1 it is of course necessary to have the original kathode of the same metal2 otherwise an impure mixture will be the result4 ,if1 for example1 a piece of cast-iron be used upon which to deposit the copper1 then the iron will be enclosed in a deposit of pure copper2 in other words1 the result will be a heavily copper-plated piece of iron1 and the smelting process will bring about a fusion of the two metals4 ,it is not necessary to have absolutely pure copper for the anodes when copper-plating or electrotyping2 but the purer the copper the less the solution is fouled1 and it will not require replenishing so often4 ,an object intended to receive a plating of copper need not be of metal at all2 it may be of any material1 so long as it possesses a conducting surface4 ,a mold or a cast made of any plastic material1 such as wax or cement1 may have its surface made conductive by the application of graphite1 finely pulverized carbon1 or metal dusts held on by some medium not soluble in water4 ,the wax molds1 or impressions of type and cuts1 are dusted with plumbago1 and then suspended in the copper solution4 ,a wire from the negative pole is connected so as to come in contact with the plumbago1 and the copper deposit immediately begins to form on the face of the wax4 ,when the film of copper has become heavy enough1 the mold is drawn out of the solution1 and the thin shell of metal removed from the wax and cut apart1 so that each shell is separated from its neighbor and freed from marginal scraps4 ,flowers1 leaves1 laces1 and various other objects can be given a coat of copper by thus preparing their surfaces1 and some most beautiful effects may be secured by copper-coating roses2 then placing them for a short time in a gold bath1 and afterwards chemically treating the surface plating so as to imitate ,roman1 ,tuscan1 or ormolu gold1 in bright or antique finish4 ,coins1 medallions1 bas-reliefs1 medals1 and various other things are reproduced by the electro-plating process1 and their surfaces finished in gold1 silver1 bronze1 or other effects4 ,years ago this was not possible1 because the old method was to make a fac-simile cast in metal of the object desired1 and then chase or refinish the surface4 ,this was a costly and tedious task4 ,when ,brugnalelli1 an ,italian electrician1 electro-gilded two silver coins in #ahje1 he laid the foundation for the modern process1 but it did not come into general use until about #ahci1 when electro-plating and the electro-depositing of metals was begun on a practical scale4 ,before the invention of the dynamos for generating current1 batteries had to be employed1 and this made the process somewhat more expensive than the present method4 ,our boy amateurs1 however1 will have to be content with the battery system1 since they are not supposed to have access to direct-current power1 such as is used for arc or street lighting4 ,various forms of batteries may be used for this work1 and they will be described in detail4 ,for the copper-plating bath it will be necessary to have the anodes of soft1 cast1 or sheet1 copper sufficiently heavy so as not to waste away too quickly4 ,these should be of the proper size to fit within the bath1 and either one large one or several small ones may be employed4 ,stout copper bands should be riveted to the top of the plates1 by means of which they may be hung on the bar and so suspended in the solution 7,fig4 #aj74 ,the contact-points should be kept clean and bright1 so that the current will not meet with any resistance in passing from the rod to the plates4 ,in ,fig4 #i a complete outfit is shown for any plating process1 the difference being only in the solution and anodes4 ,for silver-plating a silver solution and silver anodes are required1 while for gold the gold solution and gold anodes will be necessary4 ,in this illustration1 ,a represents the tank1 ,b the battery1 ,c ,c the anodes1 ,d ,d ,d the kathodes1 or articles to be plated1 ,e the positive rod1 ,f the negative1 and ,g1 ,h the leading-in and leading-out wires4 ,there is often a doubt in a boy's mind as to how the battery is to be connected up to the bath and the articles suspended in it4 ,but there will be no difficulty about it once that the principle of the process is thoroughly understood4 ,illustration3 ,,fig4 #i4 ,it is well to remember that the electro-plating bath is just the reverse of a battery in its action4 ,the process carried on in a battery is the generation of electricity by the action of the acid on the positive metal1 accompanied by the formation of a salt on one of the elements2 while in the plating-bath the current from an external source 7the battery or dynamo7 breaks up the salts in solution and deposits the metal on one of the elements 7the kathode74 ,the remaining element in the solution attacks the salts1 in chemical lumps or granular form1 and dissolves them to take the place of the exhausted salts2 or it attacks the metal anode from which these salts were originally made1 and eats off the portion necessary to replace the loss caused by the action of the current in depositing the fruits of this robbery in metallic form upon the article to be plated 7the kathode74 ,there should be no confusion in the matter of properly connecting the poles if one remembers that the current is flowing through the battery as well as through the wires and the solution in the tank4 ,get clearly in your mind that the current originates in the battery of zinc and carbon or zinc and copper4 ,the zinc is electro-positive to carbon or copper1 and at a higher electric level the current flows from the zinc plate inside the cell to the carbon or copper2 therefore1 the zinc is the positive pole4 ,now the current1 having flowed through the battery from zinc to carbon1 or the negative plate1 is bound to flow out of the battery from the carbon through the apparatus and back again to the zinc in the battery4 ,therefore1 the wire 7,g7 attached to the carbon of the battery leads a positive or current1 although the carbon is negative2 in the battery1 and the wire 7,h7 leading out is negative1 or -1 although it returns the current to the positive pole of the battery4 ,this is the simple explanation of the circulation of current2 but to cut it down still more1 always remember to attach the wire from the anode rod to the carbon1 or copper1 of the battery1 and the kathode rod to the zinc of the battery4 ,in copper-plating this is easy to determine without any regard to wires1 because if the wires are misconnected there will be no deposit1 and the kathode will turn a dark color4 ,if everything is all right a slight rose-colored blush of copper will appear at once on the kathode4 ,too little current will make the process a long and tedious one1 while too much current will deposit a brown mud on the kathode1 which will have to be washed off or removed and the article thoroughly cleansed before a new action is allowed to take place4 ,with a series of cells it is an easy matter to properly govern the current by cutting out some of the cells or by using resistance-coils 7see chapter vii4 on ,electrical ,resistance74 ,cells and batteries for electro-plating may be made or purchased1 and primary batteries should be used4 ,the use of the secondary or storage-battery is not necessary for plating purposes1 since no great volume of current is needed1 and it can be generated in a battery of cells while the work is going on4 ,one of the best primary batteries is the ,benson cell1 shown in connection with the plating-bath1 and also in ,fig4 #aa4 ,it consists of an outer glass jar 7,g ,j71 which contains a cylinder of amalgamated zinc 7,z 1 or positive7 covered with diluted sulphuric acid--one part acid to three parts water4 ,an inner porous cup 7,p ,c7 contains concentrated nitric acid1 into which the carbon 7,c -1 or negative7 is plunged4 ,the liquid in the inner cup and glass cell should be at the same level4 ,illustration3 ,,fig4 #aj ,,fig4 #aa ,,fig4 #ab ,,the ,,benson ,,cell ,,primary ,,battery ,there is no polarizing in this cell1 for the hydrogen liberated at the zinc plate1 in passing through the nitric acid on its way to the carbon-pole1 decomposes the nitric acid and is itself oxidized4 ,a cell with a glass jar six inches in diameter and eight inches high will develop about two volts of electro-motive force2 and as its internal resistance is very low it will furnish a steady current for several hours4 ,any number of these cells may be made and connected in series2 but when not in use it would be well to remove and wash the zincs4 ,any bichromate battery will answer very well for plating1 the ,grenet being an especially good one4 ,a well-amalgamated zinc plate forms one pole1 and a pair of carbon plates1 one on each side of the zinc and joined at the top1 make up the other pole4 ,when not in use the entire plunge part should be removed from the bichromate solution1 rinsed off in water1 and laid across the top of the jar1 ready for its next employment4 ,the zinc and carbons must be joined together so that they are well insulated1 and with no chance of the zinc coming into contact with the carbons4 ,this may be done with four pieces of hard-wood soaked in hot paraffine and then locked together with stove-bolts and nuts1 as shown at ,fig4 #ab4 ,holes must be made in the top corners of the carbons and zinc1 and with small bolts and nuts the connecting wires can be made fast4 ,to charge this battery1 add five fluid ounces of sulphuric acid to three pints of cold water1 pouring the acid slowly into the water and stirring it at the same time with a glass or carbon rod4 ,when this becomes cold1 after standing a few hours1 add six ounces of finely pulverized bichromate of potash4 ,mix this thoroughly1 and pour some of the solution into the glass cell until it is three-fourths full2 then it will be ready to receive the carbons and zinc4 ,when arranging the wood-clamps on the carbon and zinc plates it would be well to make two of the clamps longer than the others so that they will extend out far enough to rest on the top edge of the jar4 ,to keep them in position at the middle of the jar1 notches should be cut at the underside of these clamps1 so that they will fit down over the edge of the jar4 ,any number of these cells may be connected together to obtain the desired amount of current1 or electro-motive force4 ,other batteries suitable for electro-plating are the ,edison primary1 ,taylor1 ,fuller1 ,daniell1 gravity1 ,groves1 and ,merdingers4 ,all of these may be purchased at large electrical equipment or supply houses4 ,the ,cleansing ,process ,one of the most important operations of the plating process is to properly cleanse the articles to be plated before they are placed in the bath4 ,when once cleaned the surfaces of these objects must not be touched with the fingers1 or any dusty or greasy object2 otherwise the electro-deposited metal will not hold on the surface1 but will peel off1 in time1 or blister4 ,a very small trace of foreign matter is sufficient to prevent the deposit from adhering to the surface to be plated2 therefore1 great care must be taken to eliminate all trace of anything that would interfere with the perfect transmission of metallic molecules to the prepared surfaces4 ,acids are chiefly employed to remove foreign matter from new metallic surfaces2 and for copper1 brass1 iron1 zinc1 gold1 and silver a table is given on page #bha which will show the right proportion of acids to water in order to cleanse the various metals4 ,in the following scale the numerals stand for parts4 ,for example3 the first one means #ajj parts water1 #ej parts nitric acid1 #ajj parts sulphuric acid1 and #b parts hydrochloric acid--making in all #beb parts4 ,these can be measured in a glass graduate4 ---------------------------------------- -------- ,nitric,sulphuric,hydrochloric ,water ,acid ,acid ,acid ---------------------------------------- -------- ,copper and brass #ajj #ej #ajj #b ,gold #ajj 444 444 #ae ,silver #ajj #aj 444 444 ,wrought-iron #ajj #b #h #b ,cast-iron #ajj #c #ab #c ,zinc #ajj 444 #aj 444 ---------------------------------------- -------- ,twist a piece of fine copper wire about part of the object to be cleaned and plated2 then dip it in the acid and rinse off in clean warm or hot water1 and rub the surface briskly with a brush dipped in the liquid4 ,dip it again several times1 and rinse in the same manner2 then1 when it is bright and clean1 place it in the bath1 twist the loose end of the wire around the negative rod1 and start the current flowing1 taking care that the object is thoroughly immersed4 ,tarnished gold or silver articles may be cleaned by immersing them in a hot solution of cyanide of potassium2 or a strong warm solution of carbonate of ammonia will loosen the tarnish on silver1 so that it can be brushed off4 ,corroded brass1 copper1 ,german-silver1 and bronze should be cleansed in a solution composed of sulphuric acid1 three ounces2 nitric acid1 one and three-quarters ounces2 and water1 four ounces4 ,this soon loosens and dissolves the corrosion2 then the article should be brushed off1 dipped in hot water1 and rinsed4 ,then replace it in the solution for a minute or two and rinse again1 when it will be ready for the plating-bath4 ,corroded zinc should be immersed in a solution of sulphuric acid1 one ounce2 hydrochloric acid1 two ounces2 and distilled or rain water1 one gallon4 ,it should be well brushed after the acid has bitten off the corrosion4 ,rusty iron or steel should be pickled in a solution of sulphuric acid1 six ounces1 hydrochloric acid1 one ounce1 and water1 one gallon4 ,when the rust has been removed1 immerse the object in a solution composed of sulphuric acid1 one pint1 and distilled water1 one gallon4 ,before the acid is added to the water dissolve one-quarter-pound of sulphate of zinc in the water2 then add the acid1 pouring it slowly and stirring the water4 ,lead1 tin1 pewter1 and their compounds may be cleansed by immersing them in a hot solution of caustic soda or potash1 then rinsing in hot water4 ,take great care if caustic is used1 as it will burn the skin and tissues of the body4 ,do not let the fingers come into contact with any cleansed article1 because the oily secretions of the body will stick to the metal and cause the coat of deposited metal to strip off or present a spotted appearance4 ,the ,plating-bath ,the object to be plated should not touch the bottom or sides of the plating-vat1 and it should be far enough away from the anodes to avoid any possibility of coming into contact with them4 ,it will not do to place the anode and kathode too close together1 as the plate will be deposited unevenly2 the thicker coating will appear on the parts closest to the anode4 ,neither should they be separated too far1 as the resistance of the cell is thereby increased1 and of course this means a waste of energy4 ,the knowledge of how to arrange the anode and kathode is a matter to be learned by experience1 but by carefully watching the deposit it will not be a difficult matter to determine the proper positions4 ,for many reasons the glass tank is preferable for amateur electro-plating work1 since the objects may be watched without disturbing their electric connections and without removing them from the liquid4 ,a very good plan for the copper bath1 when spherical1 cylindrical1 or hollow objects are to be plated1 is to line the inside of the tank with strips or a sheet of copper1 hung on hooks that will catch on the sides2 then connect the positive wire directly to these strips4 ,with this arrangement but one rod1 the negative1 is in use1 and the objects to be plated are suspended from it4 ,it follows that the objects will take up the copper deposit from all sides1 and a more evenly distributed coating will be the result4 ,it is better to start up the current gradually1 rather than to put on at the beginning a large amount of electro-motive force4 ,by watching the character of the deposit you can soon tell if you have the proper strength of current4 ,if everything is working properly the copper deposit will have a beautiful flesh tint2 but if the current is too strong it takes on a dark-red tone and resembles the surface of a brick4 ,this is not right1 and the object must be removed and washed off1 the current reduced1 and the object replaced in the bath4 ,when a sufficiently heavy coating of the copper has been applied1 remove the object and wash thoroughly in running or warm water to free it from any remaining copper fluid4 ,if this is not done the surface1 in drying1 will turn a dull brown1 and will have to be bitten off with the acid solution for cleansing copper4 ,the finer the copper deposit the better and smoother it will be2 the grain will be smaller1 and it will not present a rough surface1 which is always difficult to plate over with silver or gold1 unless a frosted effect is desired4 ,non-conducting objects are usually plated with copper first1 and then replated with the metal desired for the final finish4 ,to make the surface conductive1 finely powdered black-lead1 or plumbago of the best kind1 or finely pulverized gas-carbon is brushed over the surface4 ,this must be thoroughly done2 and if the deposit is slow about appearing at any spot it may be hastened by touching it with the end of an insulated wire attached to the main conductor4 ,this1 of course1 will only answer for objects strong enough to stand the brushing treatment2 it will not do for flowers1 insects1 and other delicate things1 that are to be silver or gold plated4 ,these should be given a film of silver by soaking in a solution of alcohol and nitrate of silver1 made by shaking two parts of the chemical into one hundred parts of grain-alcohol1 with the aid of heat and in a well-corked bottle4 ,when dry1 the object should be subjected to a bath of sulphuretted hydrogen gas under a hood4 ,the sulphuretted hydrogen is made by bringing a bar of wrought-iron to a white-heat in the kitchen range or furnace fire1 and touching it with a stick of sulphur4 ,the iron will melt and drop like wax4 ,these drops should be collected in a bottle4 ,now pour over them diluted sulphuric acid1 one part acid to three parts water1 and the gas will at once rise4 ,it will be quickly recognized by its odor1 which is similar to that of over-ripe eggs4 ,it can be led off through a tube to the place where you wish to use it1 and when through1 the operation of gas-generation may be stopped by pouring off the liquid4 ,all objects prepared in this way should be given a preliminary coating of thin copper before they are plated with any other metal4 ,silver-plating ,plating in silver is done in practically the same way as described for the coppering process4 ,thin strips or sheets of pure silver are used for the anodes1 and the electrolyte is composed of nitrate of silver1 cyanide of potassium1 and water4 ,dissolve three and one-half ounces of nitrate of silver in one gallon of water2 or if more water is needed to fill the tank1 add it in the proportion of three and one-half ounces of the nitrate to each gallon of water4 ,dissolve two ounces of cyanide of potassium in a quart of water1 and slowly add this to the nitrate solution4 ,a precipitate of cyanide of silver will be formed4 ,keep adding and stirring until no more precipitate is formed1 but be careful not to get an excess of the cyanide in the solution4 ,gather this precipitate1 and wash it on filtering-paper by pouring water over it4 ,the filter-paper should be rolled in a funnel shape thus permitting the water to run away and leaving the precipitate in the paper4 ,this precipitate is to be dissolved in more cyanide solution1 and added to the quantity in the tank4 ,there should be about two ounces of the potassium cyanide per gallon over and above what was originally put in4 ,the silver anodes show the condition of the fluid4 ,if the solution is in good order they will have a clear1 creamy appearance1 but will tarnish or turn pink if there is not sufficient free cyanide in the solution4 ,the proper strength of current is indicated by the appearance of the plated objects4 ,a clear white surface shows that everything is all right1 the solution in proper working order1 and the proper current to do the work4 ,too much current will make the color of the kathodes yellow or gray1 while too little current will act slowly and require a long time to deposit the silver4 ,the adhesion of silver-plate is rendered more perfect by amalgamating the objects in a solution of nitrate of mercury1 one ounce to one gallon of water4 ,after the objects have been properly cleansed they are immersed in this solution for a minute1 then placed in the silver-bath and connected with the negative-rod1 so that the electro-depositing action begins at once4 ,gold-plating ,the gold-bath is made in the same manner as the silver one just described1 with the exception that chloride of gold is used in place of the nitrate of silver in the first solution4 ,this solution must be heated to #aej ,fahrenheit when the process is going on2 or a cold bath may be made of water1 #ejjj parts2 potassium cyanide1 one hundred parts2 and pure gold1 fifty parts4 ,the gold must be dissolved in hydrochloric acid1 and added to the water and potassium4 ,very pretty effects may be obtained in gold-plating by changing the tones from yellow to a greenish hue by the addition of a little cyanide of silver to the solution1 or by the use of a silver anode4 ,a reddish tinge may be had by adding a small portion of sulphate of copper to the solution1 or hanging a small copper anode beside the gold one4 ,in the hot gold-bath the articles should be kept in motion1 or the solution stirred about them with a glass rod4 ,when the solution is perfectly balanced and working right the anodes should be a clear dead yellow1 and the articles in process of plating should be of the same hue4 ,a gold-plating outfit is shown in ,fig4 #ac1 and consists of the tank and bath1 a cell1 and a resistance-coil 7,r71 through which the strength of the current is regulated4 ,the current1 passing out of the cell from the carbon 7,c71 is regulated through the resistance-coils 7,r7 by the switch 7,s74 ,from thence it passes to the rod from which the anode 7,a7 is suspended1 across the electrolyte 7,e7 to the kathode 7,k71 on which the metal is deposited1 and then returns through the negative wire to the zinc 7,z7 in the cell4 ,if the hot bath is used the gold solution may be contained in a glazed earthen jar or a porcelain-lined metal jar or kettle4 ,but if the latter is used care must be taken to see that none of the enamel is chipped1 or a short-circuit will be established between the rods4 ,this jar or kettle may then be placed on a gas-stove1 and a thermometer should be suspended so that the mercury bulb is half an inch below the surface of the liquid1 as shown at ,t in ,fig4 #ac4 ,as the liquid simmers or evaporates away a little water should be added from time to time to keep the bulk of the liquid up to its normal or original quantity4 ,illustration3 ,,fig4 #ac ,nickel-plating ,the nickel-plating process is similar1 in a general way1 to the others2 it is carried on in a cold bath--that is1 at the normal temperature1 without being heated or chilled artificially4 ,there are a great many formul for the nickel as well as for the other baths1 but the generally accepted one is composed of double nickel ammonium-sulphate1 three parts2 ammonium carbonate1 three parts2 and water1 one hundred parts4 ,another good one is composed of nickel sulphate1 nitrate1 or chloride1 one part2 sodium bisulphate1 one part2 and water1 twenty parts4 ,nickel anodes are used in bath to maintain the strength1 and great care must be taken to have the bath perfectly balanced--that is1 not too acid nor too alkaline4 ,to test this1 have some blue-and-red litmus paper4 ,if the blue paper is dipped in an acid solution1 it will turn red2 and back to blue again if placed in an alkaline solution4 ,if the nickel solution is too strong with alkali1 a trifle more of the nickel salts must be added1 so that both the red-and-blue litmus paper1 when dipped in the liquid1 will not change color4 ,if the bath is too alkaline1 it will give a disagreeable yellowish color to the deposit of metal on the kathode2 and if too acid1 the metal will not adhere properly to the kathode1 and will strip1 peel1 or blister off4 ,finishing ,when the articles have been plated they will have a somewhat different appearance to what may have been expected4 ,for instance1 copper-plated articles will have a bright fleshy-pink hue2 silver1 an opaque creamy-white2 gold1 a dead lemon-yellow color1 and nickel much the appearance of the silver1 but slightly bluer in its tone4 ,articles removed from the bath should be shaken over the bath so as to remove the solution2 then they should be immediately plunged into hot water1 rinsed thoroughly1 and allowed to dry slowly4 ,when a silvered or gilded object is perfectly dry it should be rubbed rapidly with a brush and some fine silver-polishing powder until the opaque white or yellow gives place to a silver or gold lustre4 ,it will then be ready for burnishing with a steel burnisher1 or the article may be left with a frosted silver or gold surface4 ,steel burnishers can be had at any tool-supply house1 and when used they should be frequently dipped in castile soapy water to lubricate them4 ,they will then glide smoothly over the surface of the deposited metal1 driving the grain down and making it bright at the same time4 ,if the soapy water were not used the action of the hard burnisher over the plate would have a tendency to tear away the film of deposited metal4 ,the burnisher must always be clean and bright1 otherwise it would scratch the plated articles2 and1 when not in use1 keep the bright polishing surfaces wrapped in a piece of oiled flannel4 ,small articles1 such as sleeve-buttons1 rings1 studs1 and other things not larger than a twenty-five-cent piece1 may be polished by being tumbled in a sawdust bag4 ,a cotton bag is made1 three feet long and six inches in diameter1 closed at one end and half-filled with fine sawdust4 ,the articles are then put in the bag and the end closed4 ,grasp the ends of the bag with both hands1 as if to jump rope with it2 then swing it to and fro1 until the articles have had a good tumbling4 ,look at them to see if they are bright enough2 if not1 keep up the tumbling4 ,when old work is to be re-plated1 or gone over1 it will be necessary to remove all of the old plate before a really good job can be done4 ,in some cases it may be removed with a scratch-brush or pumice-stone2 but1 as a rule1 it can be removed much quicker and more satisfactorily with acids4 ,silver may be removed from copper1 brass1 or ,german-silver with a solution of sulphuric acid1 with one ounce of nitrate of potash to each two quarts of acid4 ,stir the potash into the acid1 then immerse the article4 ,if the action becomes weak before the silver is all off1 then heat the solution and add more of the potash 7saltpetre74 ,gold may be removed from silver by heating the article to a cherry-red1 and dropping it into diluted sulphuric acid--one part acid to two parts water4 ,this will cause the gold to peel and fall off easily4 ,electrotyping ,the term electrotyping is interpreted in several ways1 but1 in general1 it means the process of electro-plating an article1 or mold1 with a metal coating1 generally copper1 of sufficient thickness1 so that when it is removed1 or separated from its original1 it forms an independent object which1 to all appearances1 will be a fac-simile of the original4 ,to obtain a positive copy a cast has to be taken from a negative or reverse4 ,this negative is called the mold or matrix1 and can be of plaster1 glue1 wax1 or other compositions4 ,there are a number of processes in use1 but the ,adams process 7no relation to the author7 will give a boy a clear idea of this electro-chemical and mechanical art4 ,this process was patented in #ahgj1 and is said to give a perfect conduction to wax and other molds1 with greater certainty and rapidity than any other1 and will accomplish in a few minutes that which plumbago 7black-lead7 alone would require from two to four hours to effect4 ,as applied to the electrotyping of type1 and cuts for illustration1 the warm wax impression is taken by pressing the chase or form of type into a bed of wax by power or hydraulic pressure4 ,then remove it1 and while the wax is still warm1 powdered tin1 bronze1 or white bronze powder is freely dusted all over it with a soft hair-brush1 until the surface presents a bright1 metallic appearance4 ,the superfluous powder is then dusted off1 and the mold is immersed in alcohol1 and afterwards washed in water to remove the air from the surface4 ,it is then placed in the copper bath and the connection made from the negative pole to the face of the mold1 so that the current will flow over its entire surface4 ,a deposit of copper will quickly appear1 and become heavier as the mold is left in longer4 ,when a mold has received the required deposit it should be taken from the bath and the copper film removed from it4 ,this is done by placing the mold in an inclined position and passing a stream of hot water over the back of the copper film4 ,this softens the wax and enables one to strip the film off1 taking care at the same time not to crack or bend the thin copper positive4 ,the thin coating of wax1 which adheres to the face of the copper1 can be removed by placing it1 face up1 on a wire rack and pouring a solution of caustic potash over it1 which1 in draining through1 will fall into a vessel or tank beneath the rack4 ,the potash dissolves the wax in a short time1 and the electro-deposited shell may then be rinsed in several changes of cold water1 or held under the faucet until thoroughly freed from the caustic4 ,as many1 if not all1 of the chemicals used in the various plating processes1 and also the cleaning fluids1 are highly poisonous1 great care should be taken when handling them4 ,do not let the fingers or hands come in contact with caustic solutions or cyanide baths4 ,never use any of these solutions if you have recently cut your fingers or hands1 and do not allow the cyanides or caustics to get under the finger-nails4 ,never add any acid to liquids containing cyanide or ferro-cyanide while in a closed room4 ,this should always be done in the open air1 where the fumes can pass away1 for the gases which rise from these admixtures are poisonous when inhaled4 ,chapter ,,xii ,,miscellaneous ,,apparatus ,the field of applied electricity is such a wide one as to preclude any exhaustive handling of the subject in a book of this size4 ,the aim has been to acquaint the young student with the basic principles of the science1 and it is his part to develop these principles along the lines indicated in the preceding pages4 ,but there are some practical applications that may be properly grouped under the heading of this chapter4 ,they may serve as a stimulus to the inventive faculties of the youthful experimenter1 and since the pieces of apparatus now to be described are useful in themselves1 the time spent in their construction will not be wasted4 ,a ,rotary ,glass-cutter ,when making a circle of glass it is generally best to let a glazier cut the disk1 otherwise many panes are likely to get broken before the young workman succeeds in getting out a perfect one4 ,but with a rotary glass-cutter the task is a comparatively simple one1 and the tool is really an indispensable piece of apparatus in every electrician's kit4 7,see ,figs4 #a and #b47 ,the wooden form is turned from pine or white-wood1 and is three inches in diameter at the large end1 or bottom1 one inch in diameter at the top1 and two inches high4 ,it is covered with felt held on with glue4 ,directly in the middle of the top a small hole is bored one-eighth of an inch in diameter1 and in this aperture an awl or marker is placed1 handle up1 as shown in ,fig4 #b4 ,notice that the awl is not made fast to the form1 but is removable at pleasure4 ,a hard brass strip twelve inches long1 five-eighths of an inch wide1 and one-eighth of an inch thick is cut at the end to receive a steel-wheel glass-cutter1 as shown at the foot of ,fig4 #a4 ,a number of one-eighth-inch holes are bored along the strip1 and half an inch apart1 measuring from centre to centre4 ,to cut a disk of glass the form is placed at the centre of the pane1 the latter being imposed on a smooth table-top over a piece of cloth4 ,the strip1 or arm1 is laid on the form1 and over a small washer1 so that one of the holes lines with that in the form4 ,the awl is passed down through the strip and into the block1 and the cutter is arranged in the slot at the end of the arm4 ,press down lightly on the handle of the awl1 to keep the form from slipping2 then the cutter is drawn around the glass1 describing the circle1 and cutting the surface of the glass1 as shown by the solid line in ,fig4 #d4 ,the disk must not be removed from the pane until the margin is broken away4 ,with a straight-edge and a cutter score the glass across the corners1 as indicated by the dotted lines in ,fig4 #d2 then tap the glass at the underside along the line and break off the corners4 ,after the corners have been removed tap the glass again1 following the line of the circle2 then break away the remaining fragments and smooth the edge4 ,illustration3 ,,fig4 #a ,,fig4 #b ,,fig4 #c ,,fig4 #d ,,fig4 #e ,,fig4 #f ,,glass-,,cutting ,,appliances ,to ,smooth ,glass ,edges ,to smooth the rough edge of glass there are several methods4 ,the simplest way is to hold the disk or straight-edge against a fine grindstone and use plenty of water4 ,the glass must be held edgewise1 as shown in ,fig4 #e1 and not flatwise1 as shown in ,fig4 #f4 ,to properly grind a disk two workmen are necessary1 one to turn the stone1 and the other to hold the disk by spreading the hands and grasping it at the middle on both sides 7see ,fig4 #e74 ,in this manner the glass may be held securely1 and slowly turned1 so that an even surface will be ground4 ,when the flat edge is smoothed1 tilt the glass first to one side and then the other1 and grind off the sharp edges4 ,another method is to lay the glass on a table1 upon a piece of felt or cloth1 and allow the edge to project over the table for two or three inches4 ,hold the glass down with one hand to prevent its slipping2 then1 with a piece of corundum1 or a rough whetstone and glycerine1 work down the edge until it is smooth1 turning the glass continually so that the edge you are working on hangs over the table4 ,this process of grinding is somewhat tedious1 but perseverance and patience will win out4 ,to ,cut ,holes in ,glass ,holes may be cut in glass in several ways by an expert1 but the boy who is a novice in this line should stick to slow and sure methods and take no chances4 ,fortunately1 glass is little used in voltaic electricity1 but it is indispensable in the construction of the frictional machines1 ,leyden-jars1 and condensers1 where glass is used as the dielectric1 also for the covering-plates to instruments4 ,the simplest method is that of rotating a copper tube forward and backward over the glass1 using fine emery dust for the cutting medium and oil of turpentine as a lubricant4 ,the copper tube must be held in a rack1 so that its location will not shift during the rotating or cutting motion4 ,the rack in which the tube is held may be of any size1 but to take a disk or square of glass1 twenty inches across1 the frame should be twenty-two inches long1 ten inches wide1 and twelve inches high1 as shown in ,fig4 #c4 ,the side-plates are eleven inches high and ten inches wide1 the top is twenty-two inches long and ten inches wide1 while the under ledge is twenty and a quarter inches long by ten inches wide4 ,this frame is put together with glue and screws4 ,across the back1 from the corners down to the middle of the under ledge1 battens or braces are made fast to prevent the frame from racking4 ,a hole is made through the middle of the top and under ledge for the copper tube to pass through4 ,if different-sized tubes are to be used1 blocks to fit the top and under board are to be cut and bored1 so that they may be held in place with screws when in use4 ,to cut a hole in glass1 place the disk or pane on a felt or cloth-covered table1 and over it arrange the frame1 so that the tube will rest on the spot to be drilled4 ,drop the copper tube down through the hole1 having first spread the bottom of the tube slightly1 so that it will not split the glass4 ,now put some emery inside the tube so that it will fall on the glass2 then place a wooden plug in the top of the tube and arrange an awl1 or hand-plate1 so that the tube may be pressed down4 ,take one turn about the tube with a linen line1 or gut-thong1 and make the ends fast to a bow1 so that it will draw the string taut but not too tight4 ,lubricate the foot of the tube with oil of turpentine1 and draw the bow back and forth4 ,at first the motion will cause the copper to scratch the glass1 and then cut it1 until finally a perfectly drilled hole is formed4 ,during the operation both glass and frame must be held securely1 and the bow drawn evenly and without any jerking motion4 ,holes of different sizes may be cut with tubes of various diameters4 ,small holes may be cut with a highly tempered steel-drill and glycerine1 the drill being held in a hand-drilling tool or in a brace4 ,anti-hum ,device for ,metallic ,lines ,in overhead wires1 where galvanized or hard copper wire is used1 the hum due to the tension of the wires1 and the wind blowing through them1 causes a musical vibration which becomes most annoying at times4 ,this can be overcome by a simple device known as an 8anti-hum40 ,it consists of a knob made of wood or rubber1 through which a hole is bored1 and around which a groove is cut4 ,one end of the wire is passed through the hole and a loop formed1 the loose end being wrapped about the incoming wire4 ,the other end of the line is passed around the knob in the groove1 and the end twisted about the line-wire4 ,the knob is then an insulator and a sound-deadener at the same time4 ,to complete the metallic circuit a loop of wire is passed under the knob1 the ends of which are made fast to the line-wires1 as shown at ,fig4 #g4 ,illustration3 ,,fig4 #g ,illustration3 ,,fig4 #h ,a ,reel-car for ,wire ,it is not always convenient nor possible to carry about a heavy roll of wire when hanging a line1 especially if it is ,no4 #ab galvanized wire1 of which there are from fifty to a hundred pounds in one roll4 ,wire should be unwound as it is paid out1 and not slipped off from the coil1 since it is liable to kink2 therefore1 some portable means of transporting it should be provided4 ,line-wires over long distances are paid out from a reel-truck drawn by horses4 ,for the use of the amateur electrician the reel-car shown in ,fig4 #h should meet all requirements4 ,the reel is made from two six-inch boards1 a barrel-head or a round platform of boards1 four trunk-rollers1 and a bolt4 ,from a six-inch board cut two pieces five feet long4 ,eighteen inches from either end cut one edge away so as to form handles1 as shown at ,c ,c ,c ,c in ,fig4 #h1 rounding the upper and under edges to take off the sharp corners4 ,cut four cross-pieces sixteen inches long2 and from two-by-four-inch spruce joist cut four legs twelve inches long1 and plane the four sides4 ,nail two of the cross-pieces to the legs2 then nail on the side-boards and so form the frame of the reel4 ,bore a half-inch hole through a piece of joist2 then nail it between the remaining two cross-boards1 taking care to get it in the centre1 as shown at ,a4 ,arrange these pieces at the middle of the frame1 making them fast with nails driven through the side-boards and into the ends of these cross-pieces4 ,drive some pieces of matched boards together1 and with a string1 a nail1 and a pencil describe a circle twenty inches in diameter4 ,with a compass-saw cut the boards on the line1 and join them with four battens made fast at the underside with nails4 ,do not make the battens so that they will extend out to the edge of the circle1 but keep them in an inch or two1 so that the under edge of the turn-table will rest on four trunk-rollers screwed fast to the top edges of the side-boards and end cross-pieces1 as shown at ,b4 ,a half-inch bolt is passed down through a hole made at the middle of the table1 and through the block4 ,between the block and the underside of the table several large iron washers should be placed on the bolt1 so that they will keep the table slightly above the rollers1 the main weight of the table and its load of wire being held by the middle cross-brace4 ,the object of the trunk-rollers is to relieve the side strain on the bolt1 and also to prevent friction between the edge of the table and the frame1 in case the tension on the wire pulls it to one side4 ,bore six holes in the table1 on a circle of twelve inches1 and drive hard-wood pegs in them1 as shown in ,fig4 #h4 ,when a roll of wire is lying on the table two boys can easily lift and carry the car1 and as they do so the wire will pay out4 ,give all the wood-work a coat of dark-green paint1 and oil the trunk-rollers and the wood where the bolt passes through4 ,a pair of nuts should be placed on the lower end of the bolt and a washer under its head4 ,these lock-nuts must be screwed on with two monkey-wrenches1 forced in opposite directions1 so that one nut will be driven tightly against the other4 ,this is to prevent the turning of the table from unscrewing the nuts4 ,insulators ,for telegraph and telephone lines1 where pole1 tree1 or building attachments are necessary1 insulators must be used to carry the wires without loss of current4 ,the regular glass1 porcelain1 or hard rubber insulators1 made for pole and bracket use1 are of course the best4 ,they can be purchased at any supply-house for a few cents each1 but there are other devices which will answer equally well and which will cost little or nothing4 ,obtain some bottles of stout glass1 the green or dark glass being the toughest2 then carefully break the bottle part away4 ,in doing this hold the bottle by the neck1 with a piece of old cloth wrapped about it1 to prevent the glass chips from flying4 ,save all of the neck and part of the shoulder1 as shown in ,fig4 #i1 so that the wire and its anchoring loop will not slip off and fall down on the peg or cross-tree4 ,hard-wood pegs cut from sticks one inch and a half square should be whittled down so that they will fit in the neck and come up to the top4 ,the pegs should be long enough at the bottom to permit of their being fastened to the supporting poles1 trees1 or building4 ,in ,fig4 #aj three ways of attaching insulators are shown4 ,at ,a the peg is nailed to the top of a pole1 or a hole is bored in the pole and the peg driven down in it4 ,at ,b two sticks with peg ends are nailed to a pole in the form of a ,v1 and across the sticks a cross-brace is made fast to prevent the sticks from spreading or dropping down4 ,this cross-brace is made fast to both the sticks and the pole so as to form a rigid triangle4 ,at ,c the usual form of cross-tree1 or ,t brace1 is shown4 ,the pegs may be nailed to the face of the cross-plate1 or holes may be bored in the top and the pegs driven down into them4 ,if the cross-piece is more than two feet long1 bracket-iron should be screwed fast to the pole and brace at both sides1 as shown at ,c4 ,where a cross-plate is made fast to a pole1 a lap should be cut out so that the plate can lie against a flat surface rather than on a round one 7see ,d in ,fig4 #aj74 ,the shoulder of the bottle-necks must not rest on a cross-piece1 or touch anything that would lead to the ground or to other wires4 ,the shoulder acts as a collar1 and so sheds water that in wet weather the current cannot be grounded through the rain4 ,the underside of the collar should always be dry1 and also that part of the peg protected by the collar1 thereby insuring against the loss of current4 ,the relative position of insulator and peg is shown at ,fig4 #i1 and if the pegs are cut carefully the bottle-necks should fit them accurately4 ,joints and ,splices ,it is essential in electrical work to have joints1 splices1 unions1 and contacts made perfectly tight1 so that the current will flow through them uninterruptedly4 ,a poor contact or weak joint may throw a whole system out of order4 ,for this reason all joints should be soldered wherever practicable4 ,in line work1 however1 this is impossible1 except where trolley-wires are joined1 and these are brazed in the open air by an apparatus especially designed for the purpose4 ,in telegraph and telephone lines perfect contact is absolutely necessary1 and where attachments are made to insulators the main-line should never be turned around the insulator4 ,the wire is brought up against the insulator1 and with a ,u wire the main-line is tightly bound to it1 as shown at ,fig4 #aa4 ,if it is necessary to bind the main-line more securely to the insulator1 one or two turns may be taken around the insulator with the ,u or anchoring wire2 then with a pair of plyers a tight wrap is made4 ,when joining two ends of wire together1 never make loops as shown in ,fig4 #ab ,a4 ,this construction gives poor contact1 for the wire loops will wear and finally break apart4 ,moreover1 the rust that forms between the loops will often cause an open circuit and one difficult to locate4 ,care must be taken to make all splices secure and with perfect contact of wires1 and the only manner in which this can be done is to pass the ends of wires together for three or four inches1 as shown in ,fig4 #ab ,b4 ,illustration3 ,,fig4 #i ,illustration3 ,,fig4 #aj ,illustration3 ,,fig4 #aa ,illustration3 ,,fig4 #ab ,illustration3 ,,fig4 #ac ,grasp one wire with a pair of plyers1 and with the fingers start the coil or twist1 then with another pair of plyers finish the wrapping evenly and snugly4 ,treat the other end in a similar manner1 and as a result you will have the splice pictured in ,fig4 #ab ,b1 the many wraps insuring perfect contact4 ,this same method is to be employed for inside wires1 and after the wrap is made heat the joint and touch it with soldering solution4 ,the solder will run in between the coils and permanently unite the joint4 ,the bare wires should then be covered with adhesive tape4 ,avoid sharp turns and angles in lines1 and where it is not possible to arrange them otherwise it would be well to put in a curved loop1 as shown at ,fig4 #ac4 ,a represents a pole1 ,b ,b the line1 and ,c the quarter-circular loop let in to avoid the sharp turn about the insulator4 ,the current will pass around the angle as well as through the loop1 but a galvanometer test would show that the greater current passed through the loop and avoided the sharp turn4 8,grounds0 ,illustration3 ,,fig4 #ad ,illustration3 ,,fig4 #ae ,illustration3 ,,fig4 #af ,in the chapter on wireless telegraphy several good 8grounds0 were described1 any one of which would be admirably adapted to telegraph or telephone circuits4 ,in ,figs4 #ad1 #ae1 and #af are illustrated three other 8grounds0 that can easily be made from inexpensive material4 ,the first one1 ,fig4 #ad1 is an ordinary tin pan with the wire soldered to the middle of the bottom4 ,the wire must be soldered to be of use1 as the pan would soon rust around a simple hole and make the 8ground0 a high-resistance one4 ,if the pan is buried deep enough in the earth1 and bottom up1 it will last for several years1 or so long as the air does not get at it to induce corrosion4 ,the star-shaped 8ground0 is cut from a piece of sheet zinc1 copper1 or brass1 and is about twelve inches in diameter4 ,the wire is soldered to the middle of it1 and it is buried four feet deep1 lying flat at the bottom of the hole4 ,in ,fig4 #af a pail or large tin can is shown with the wire passing down through the interior and finally reaching the bottom1 where it is soldered fast4 ,the can is filled with small chunks of carbon1 or charcoal1 and some holes are punched around the outer edge and bottom to let the water out4 ,the can is then buried three or four feet in the ground4 ,use nothing but copper wire for 8grounds10 and it should be heavy--nothing smaller than ,no4 #ad4 ,the wire should be well insulated down to and below the surface for a foot or two1 so that perfect action will take place and a complete 8ground0 secured4 ,the ,edison ,roach-killer ,when ,edison was a boy he invented the first electrocution apparatus on record4 ,at a certain station on the ,grand ,trunk ,railroad1 where ,edison was employed as a telegraph operator1 the roaches were so thick that at night they would crawl up the partition between the windows and reach the ceiling1 where they would go to sleep4 ,during the day they were apt to become dizzy1 lose their footing1 and drop down on the heads of the operators4 ,this did not suit young ,edison1 so he devised a scheme for their destruction4 ,while watching a piece of telegraph apparatus one day1 he saw a roach try to step from a bar charged with positive electricity to one through which a negative current flowed4 ,the insect's feet were moist and so made a connection between the two bars4 ,as a consequence a short-circuit of high tension passed through its body and it dropped dead4 ,this put an idea into ,edison's head1 and the electrocution apparatus was soon in working order4 ,the 8killer0 was the most simple device one could imagine1 and was composed of two long1 narrow strips of heavy tin-foil pasted side by side on a smooth board1 with a space of one-eighth of an inch between them1 as shown at ,fig4 #ag4 ,to one strip a positive wire was connected1 while to the other a negative or ground was made fast4 ,high-tension current1 or that from an induction-coil1 was connected with the wires1 and the resulting voltage was strong enough to give one a severe shock if the fingers of one hand were placed on one plate and those of the other hand on the other plate4 ,this device was arranged across the window-casing in the path the roaches were accustomed to travel on their nightly trips up the side wall4 ,it was not long after dark before roach number one sauntered up the wall1 crossed the under strip1 and stepped over on the upper one4 ,but he went no farther1 and he1 with many of his friends and relations1 were gathered up in a dust-pan the next morning and thrown into the stove4 ,illustration3 ,,fig4 #ag ,illustration3 ,,fig4 #ah ,in electricity1 as in many other things1 simplicity is the key-note of success2 and from this little device to employ the alternating current for ridding a house of an insect nuisance sprang the grim apparatus known as the 8death chair10 used in the execution of first-degree criminals in the ,state of ,new ,york4 ,many people think the mechanism for electrocution is a complicated one1 but it is quite as simple as the ,edison roach-killer4 ,one pole is placed at the head of the criminal and the other at the feet1 the latter being bound fast so that perfect contact can be had4 ,then an alternating current of fifteen hundred to two thousand volts is run through the body1 and death is instantaneous and void of pain4 ,an ,electric ,mouse-killer ,a modification of the simple roach-killer was recently used by the author in his laboratory to get rid of some troublesome mice4 ,a piece of board was cut twelve inches square1 the edges being bevelled so that it would be an easy matter for the mice to climb up on it4 ,an inch-wide circle of sheet brass was prepared measuring eleven inches outside diameter and nine inches inside4 ,another circle was cut measuring eight inches and a half outside and six inches inside diameter4 ,both circles were attached to the board with copper tacks and polished as bright as possible1 the finished board appearing as shown in ,fig4 #ah4 ,wires were soldered to each strip1 and these in turn were connected to a high-tension current of several thousand volts4 ,crumbs and small pieces of meat were placed on the board inside the circles1 and the trap was set in a convenient place on the floor of the laboratory4 ,the next morning several mice lay dead on the floor1 but at some distance from the board1 and this seemed a little mysterious4 ,the following night the author worked late in the laboratory4 ,after finishing what he had on hand1 he turned down the lights and sat down and watched the trap4 ,presently ,mr4 ,mouse appeared from somewhere4 ,he sniffed the air1 then approached closer to the board1 sniffed again1 and1 evidently concluding that he was on the right trail1 he climbed up the side of the board and stood on the outer strip4 ,he placed one fore-foot on the inner strip1 and1 bang6 up he went in the air1 and landed on the floor a foot or more away4 ,his jump into space was due to the electric action on his muscles1 for the current literally tore his nervous system into shreds4 ,mr4 ,mouse lost a great many friends and relatives that season in the same manner1 and the apparatus is confidently recommended as a certain and humane agent for the destruction of all small vermin4 ,chapter ,,xiii ,,frictional ,,electricity ,frictional electricity is high potential1 current alternating1 and of high voltage but very low amperage4 ,apart from certain uses in laboratory and medical practice1 it is valueless4 ,in its greater volume it is akin to the lightning-bolt and is dangerous2 but in its smaller volume it is a comparatively harmless toy4 ,from the glass rod1 or the amber1 rubbed on a catskin to the modern static machines is a long jump1 and the period of exploitation covers centuries of interesting experiments1 most of which1 however1 have been practically useless for any commercial purpose4 ,static or frictional electricity is generated by friction only1 without the aid of magnets1 coils of wire1 or armatures rotating at high speed4 ,the simple process of the glass and catskin has been variously modified1 until at last ,wimshurst invented and perfected what is known as the 8,wimshurst ,influence ,machine40 ,it is self-charging1 and does not require 8starting40 ,it will work all the year round in any climate and temperature1 and is the greatest improvement ever made in static electric machines4 ,apart from its efficiency under all conditions1 it is the simplest of all machines to make1 and can easily be constructed by a boy who is handy with tools1 and who can obtain the glass and brass parts necessary in its construction4 ,the principal parts of an influence machine are the glass disks1 wooden bosses1 driving pulleys and crank1 glass standards1 brass arms with the spark-balls at the ends1 and the base with the uprights on which these parts are built up and held in position4 ,a ,wimshurst ,influence ,machine ,obtain a stiff piece of brown paper twenty inches square1 and with a compass describe a circle twenty inches in diameter4 ,inside of this circle make another one fourteen inches in diameter1 and near the centre a third circle six inches in diameter4 ,another circle four inches in diameter should be drawn inside of the six-inch circle1 so that when the bosses are made fast to the glass plates they can be properly centred4 ,also mark sixteen lines radiating from the centre1 equal distances apart1 as shown in ,fig4 #a4 ,from a dealer in glass purchase two clear1 white panes of glass eighteen inches square4 ,be careful not to get the green glass1 as this is not nearly so good as the white for static machine construction4 ,if it is possible to get crystal plate so much the better4 ,the panes should be thin1 or about one-sixteenth of an inch in thickness1 and free from bubbles1 wavy places1 scratches1 or other blemishes4 ,from these panes cut two disks sixteen inches in diameter with a rotary cutter1 as described in the chapter on ,miscellaneous ,apparatus1 page #bid1 and rub the edges with a water-stone 7see chapter on ,formul1 page #ccj47 ,from flat1 thin tin-foil cut thirty-two wedge-shaped pieces four inches long4 ,they should be one inch and a half wide at one end and three-quarters of an inch at the other1 as shown at ,fig4 #b ,a4 ,give each plate of glass two thin coats of shellac on both sides2 then lay one on the paper pattern 7,fig4 #a7 so that the outside edge of the glass will lie on the largest circle4 ,place a weight at the middle of the glass to hold it in place2 then make sixteen of the tin-foil sectors fast to the plate1 using shellac as the sticking medium4 ,but first give one side of each sector a thin coat of shellac1 allowing it to dry2 then give it another coat when applying it to the glass4 ,the sectors are to be symmetrically arranged on the glass1 using a line of the pattern as a centre for each piece 7as shown at ,a in ,fig4 #a71 and the fourteen and six inch circles as the outer and inner boundaries4 ,each piece1 as it is applied1 should be pressed down upon the glass1 so that it will stick smoothly1 without air bubbles or creases4 ,a very good plan is to lay a piece of soft blotting-paper over the sector and drive it down with a small squeegee-roller such as is used in photography1 taking care1 however1 not to shift the sector from its proper position4 ,when all the sectors are on1 the plate should appear as shown in ,fig4 #b4 ,after the shellac1 which holds the sectors to the glass1 is dry1 run a brush full of shellac around the inner and outer extremities of the tin-foil strips for half or three-quarters of an inch in from the ends4 ,the shellac will hold the sectors firmly to the glass1 and will slightly insulate them as well1 thereby preventing the escape of electricity4 ,apply the remaining sectors to the other plate of glass in a similar manner2 and as a result two disks of glass1 with the applied strips1 will be ready to mount in the frame4 ,illustration3 ,,fig4 #a ,,fig4 #b ,,fig4 #c ,,fig4 #d ,,fig4 #e ,,fig4 #f ,,details ,,of ,,wimshurst ,,influence ,,machine ,a hole three-quarters of an inch in diameter should be made in each glass plate1 so that a three-eighths spindle may pass through them and into the bosses1 so as to keep them in proper line4 ,it is preferable1 however1 not to bore these holes if bosses and accurately bushed holes can be made in the uprights of the frame which support these disks4 ,at a wood-working mill have two bosses made that will measure four inches in diameter at the large end1 and one inch and a half at the small one4 ,they should be of such length that when the plates and two bosses are arranged in line 7to appear as shown in ,a ,a at ,fig4 #i7 they will fill the entire space between the uprights ,b ,b4 ,near the small end a groove is turned in each boss1 so that a round leather belt will fit in it1 as shown in ,fig4 #c4 ,the base is made from pine1 white-wood1 cypress1 or any other wood that is soft and easily worked4 ,it is composed of two strips twenty-four inches long1 three inches wide1 and one inch and a quarter in thickness1 and two cross-pieces fourteen inches long1 three inches wide1 and one inch and a half thick4 ,these are put together with glue and screws1 and at both sides of the base notches are cut to accommodate the feet of the uprights4 ,the uprights are seventeen inches high1 three inches wide1 and one inch and a half thick4 ,the notch at the foot of each one is cut so that1 when fitted in place1 the foot of the upright will rest on a table on a line with the bottom of the end cross-pieces under each corner4 ,at the foot of the uprights a piece of sheet rubber should be made fast1 with glue or shellac1 so that when in operation the machine will not move about or slide4 ,a groove is cut at one side of each upright six inches above the bottom1 as shown at ,fig4 #d ,a4 ,in this groove the driving-wheel axles fit1 and near the top holes are made in the uprights through which the spindles pass1 which in turn support the bosses and glass disks4 ,at the middle of each cross-piece forming the ends of the base a one-inch hole1 for the glass standard rods1 is bored through the wood1 as shown at ,fig4 #d ,b ,b4 ,after attaching the uprights to the base with glue and screws1 and giving all the wood-work several successive coats of shellac1 the frame will be ready for its mountings4 ,the driving-wheels are of wood seven-eighths of an inch thick and seven inches in diameter2 they should be turned on a lathe and a groove cut in the edge so that a round leather belt will fit in it4 ,these wheels are mounted on a wooden axle that can be made from a round curtain-pole1 with a half-inch hole bored through its entire length4 ,the axle is as long as the distance between uprights ,b ,b in ,fig4 #i4 ,the wheels are to be arranged and glued fast to the axle1 so that the grooves will line directly under those in the bosses1 as shown in ,fig4 #i4 ,a half-inch axle is driven through the hub1 and at one end it is threaded and provided with two washers and nuts2 or a square shoulder and one washer and nut may be used1 so that a crank and handle may be held fast4 ,shellac should be put on the shaft to make it hold fast in the hub4 ,the complete apparatus of wheels1 axle1 hub1 and handle is shown at ,fig4 #e1 and in the frame this is so hung that the iron axle rests in the grooves cut in the uprights4 ,to hold this in place two metal straps1 as shown in ,fig4 #f1 are made and screwed fast to the wood4 ,when finally adjusted the driving-wheels should rotate freely whenever the crank is turned4 ,the wooden bosses1 ,fig4 #c1 are given two or three coats of shellac2 then they are made fast to the glass disks on the same side to which the tin-foil sectors are attached4 ,the disks should be placed over the paper plan1 ,fig4 #a1 and so adjusted that the outer line tallies with the large circle4 ,acetic glue#d is then applied to the flat surface of the boss1 and the latter is placed at the middle of the disk to line with the small circle4 ,place a weight on the end of the boss to hold it down1 and leave it for ten or twelve hours or until thoroughly dry4 #d ,see ,formul1 ,chapter xiv41 for the recipe of acetic glue4 ,both bosses should be set at the same time so that they may dry together4 ,if the bosses are turned on a lathe a hole should be made in each one about half-way through from the small end4 ,this1 in turn1 should be bushed or lined with a piece of brass tube1 which should fit snugly in the hole4 ,a little shellac painted on each piece of tube will make it stick4 ,pieces of steel rod that will just fit within the tubing are to be cut long enough to enter the full length of the hole1 pass through the holes made in the top of the uprights1 and extend half an inch beyond1 as shown in ,fig4 #i4 ,the bosses and axles will then appear as shown in ,fig4 #g4 ,flat places should be filed on each rod where it passes through the wood upright2 a set-screw will then hold it fast and keep it from revolving4 ,when the hole1 or tubing1 is oiled so that the boss and disk will revolve freely on the axle1 the disks1 bosses1 and axles are ready to be mounted in the frame4 ,a red fibre washer1 such as is used in faucets1 should be made fast to one glass disk at the centre1 so as to separate the disks and prevent them from touching when they are revolving in opposite directions4 ,these fibre washers can be had from a plumber or purchased at a hardware store4 ,shellac or acetic glue will hold the washers in place4 ,illustration3 ,,fig4 #g ,illustration3 ,,fig4 #h ,illustration3 ,,fig4 #i ,illustration3 ,,fig4 #aj ,mount one disk by holding the boss with the small end opposite a hole in one upright1 and slip an axle through from the outside of the upright4 ,hold the other disk in place1 and slip the remaining axle through the other upright and into the boss4 ,when both plates are in place and centred1 turn the set-screws down on the flattened axles to hold them in place4 ,to reduce the friction between the bosses and the uprights it would be well to place a fibre washer between them4 ,a few drops of oil on these washers will lubricate them properly1 and allow the machine to run easier4 ,an end view of the apparatus1 as so far assembled1 will appear as shown in ,fig4 #i1 ,a being the disks1 bosses1 and axles1 ,b ,b the uprights supporting them1 ,c the hub1 and ,d ,d the driving-wheels4 ,the handle and crank 7,e7 extends out far enough from the side to allow a free swinging motion without hitting the upright or base4 ,having arranged these disks and wheels so as to revolve freely1 it will now be necessary to construct and add the other vital parts and the connecting links in the chain of the complete working mechanism4 ,from a supply-house obtain two solid glass rods an inch in diameter and fifteen inches long4 ,these fit in the holes 7,b ,b7 bored in the end-pieces of the base1 ,fig4 #d4 ,procure two brass balls1 two or two and a half inches in diameter1 such as come on brass beds1 and two short pieces of brass tubing1 one inch inside diameter1 that will fit over the ends of the rods4 ,these tubings are to be soldered fast to the balls so that both tubes and balls will remain at the top of the glass rods4 ,from brass rod three-sixteenths or a quarter of an inch in diameter make two forks1 as shown at ,fig4 #h1 and solder small brass balls at the ends of the rods4 ,the prongs of the fork are six inches long and the shank four inches in length4 ,along the inside of the forks small holes are bored1 and brass wires1 or 8points10 are soldered fast4 ,these extend out for half an inch from the rods1 and are known as the 8comb10 or collectors4 ,the forks should be so far apart that when mounted with the glass disks revolving between them the points will not touch or scratch the tin-foil sectors1 and yet be as close to them as possible4 ,a hole should be bored in the brass balls1 and the shank of the fork passed through and soldered in place1 as shown in ,fig4 #aj4 ,a three-eighth-inch hole is bored directly in the top of each brass ball to hold the quadrant rods1 which extend over the top of the disks4 ,in the illustration of the complete machine 7,fig4 #ab7 the arrangement of the glass pillars1 balls1 combs1 and quadrant rods is shown4 ,the rods are three-eighths of an inch in diameter and are loose in the holes at the top of the balls1 so that they can be moved or shifted about1 according as to whether it is a left or a right handed person who may be turning the crank4 ,at the upper end of each rod a brass ball is soldered1 one being three-quarters of an inch in diameter1 the other two inches4 ,the projecting ends of the forks should be provided with metal handles or brass balls1 as shown in ,fig4 #ab2 these may be slipped over the end or soldered fast4 ,obtain two small brass balls with shanks1 such as screw on iron bed-posts1 and have the extending ends of the axles that support the bosses threaded1 so that the balls will screw on them4 ,bore a quarter-inch hole through each ball1 and slip a brass rod through it and solder it fast4 ,each end of these rods should be tipped with a bunch of tinsel or fine copper wires4 ,these are the 8neutralizers10 and the ends are curved so that the brushes of fine wires will just touch the disks when the latter are revolved1 as shown in ,fig4 #ab4 ,the ball holding the rod is to be screwed fast to the axle2 then the axle is pushed back into the boss and made fast in the head of the upright with the set-screw4 ,illustration3 ,,fig4 #ab ,the rod-and-ball at the opposite side of the disks is arranged in a similar manner1 but the rod points in an opposite direction to that on the first side4 ,cord or leather belts connect the driving-pulleys and bosses1 the belt on one side running up straight over the boss and down again around the driving-pulley4 ,the belt at the opposite side is crossed1 so that the direction of the boss is reversed2 and in this manner the disks are made to revolve in opposite directions1 although the driving-pulleys are both going in the same direction4 ,a portion of the sectors are omitted in the illustration 7,fig4 #ab7 so that a better view of the working parts may be had4 ,when the disks are revolving the accumulated electricity discharges from one ball to the other1 above the plates1 in the form of bright blue sparks sufficiently powerful to puncture cardboard if it is held midway between the balls4 ,a ,large ,leyden-jar ,when experimenting with this machine it would be well to have one or more ,leyden-jars to accumulate static charges4 ,a large one of considerable capacity is easily made from a battery jar1 tin-foil1 brass rods and chain1 and some other small parts4 ,obtain a bluestone battery jar1 and after heating it to drive all moisture from the surface1 give it a coat of shellac inside and out4 ,with tin-foil1 set with shellac1 cover the bottom and inside of the jar for two-thirds of its height from the bottom1 as shown in ,fig4 #aa4 ,cover the outside and bottom in a similar manner1 and the same height from the bottom1 and provide a cork1 or wooden cap1 for the top4 ,if a large1 flat cork cannot be had1 then make a stopper by cutting two circular pieces of wood1 each half an inch thick1 the inner one to fit snugly within the jar1 the other to lap over the edges a quarter of an inch all around4 ,fasten these pieces together with glue1 as shown at ,fig4 #ac1 and give them several good coats of shellac4 ,make a small hole at the middle of this cap and pass a quarter-inch rod through it1 leaving six inches above and below the cap4 ,to the top of the rod solder a brass ball4 ,at the foot a piece of brass chain is to be made fast1 so that several links of it rest on the tin-foil at the bottom of the jar4 ,to charge a jar from the ,wimshurst machine1 stand the jar on a glass-legged stool1 and connect a copper wire between one of the overhead balls on the machine and the ball at the top of the rod in the stopper of the jar4 ,make another wire fast to the other ball at the top of the machine1 and place it under the jar so that the tin-foil on the bottom touches it4 ,by operating the machine the jar is charged4 ,to discharge the jar make a ,t-yoke1 as shown at ,fig4 #ad1 by nailing a brass rod fast to a wooden handle and soldering brass knobs1 or hammering a lead bullet1 on the ends of the rod4 ,hold one knob against the top knob of the jar and bring the other near the foil coating at the outside1 when a spark will jump from the foil to the knob with a loud snap4 ,a ,glass-legged ,stool ,one of the most useful accessories in playing with frictional electricity will be a glass-legged stool4 ,a stool with glass feet is perhaps too expensive for a boy to purchase1 but one may be made at little or no cost from a piece of stout plank1 four glass telegraph line-insulators1 and the wooden screw-pins on which they rest when attached to a pole4 ,illustration3 ,,fig4 #aa ,illustration3 ,,fig4 #ac ,illustration3 ,,fig4 #ad ,illustration3 ,,fig4 #ae ,illustration3 ,,fig4 #af ,the general plan of the stool is shown at ,fig4 #ae1 and the top measures twelve by fifteen by two inches4 ,under each corner a screw-pin is made fast by boring a hole in the wood and setting the pin in glue4 ,the pins are cut at the top1 as shown in ,fig4 #af1 and when they are set in place the glass insulators may be screwed on4 ,the wood-work should be given a few coats of shellac to lend it a good appearance and help to insulate it4 ,there are a great many interesting experiments that may be performed with static or frictional electricity1 and these may be looked up in the text-books on electricity used in school4 ,a word of caution will not be misplaced4 ,remember that the current1 in large volume1 is dangerous4 ,for example1 a series of charged ,leyden-jars may contain enough electricity to give a very severe shock to the nervous system of the person who chances to discharge it4 ,its medical use should be under the advice and supervision of a physician4 ,chapter ,,xiv ,,formul ,in the construction of electrical apparatus there are many things1 such as paint1 cement1 non-conducting compounds1 and acid-proof substances1 that are necessary in assembling the parts which make up complete working outfits4 ,accurate formulas and directions for these things will save the amateur trouble and expense1 since they indicate the materials which have been put to the test of time and wear by others who have had abundant experience along these lines4 ,the amateur will not need a large number of compounds1 but such as are necessary should be of the best4 ,those which are described in this chapter can be relied upon to give working results4 ,acid-proof ,cements ,one of the best acid-proof cements is made by adding shellac1 dissolved in grain alcohol1 to red-lead until it is at the right consistency4 ,it can be used in liquid form or in a putty-like paste4 ,the consistency is governed by the amount of shellac added to the red-lead4 ,the lead should be pulverized and free from lumps4 ,this cement can be mixed in a small tin cup or on a piece of glass1 with a knife having a thin blade4 ,it should be used as soon as it is mixed1 since it 8sets0 as quickly as shellac1 and then dries from the outside towards the middle4 ,in a week or two it will become dry and hard like stone4 ,another cement1 which will also dry as hard as a stone and will hold soapstone slabs together as if they were of one solid piece1 is made of litharge 7yellow lead7 and glycerine4 ,the glycerine is added to the pulverized litharge to make a paste1 or it can be mixed and kneaded like thin putty4 ,it should be used very soon after mixing1 as it sets rapidly4 ,hard ,cement ,a medium hard cement is made from plaster of ,paris1 six parts2 silex1 or fine sand1 two parts2 dextrine1 two parts 7by measure74 ,mix with water until soft2 then work with a trowel or knife4 ,soft ,cement ,a good soft cement is made of plaster of ,paris1 five parts2 pulverized asbestos1 five parts 7by weight74 ,add water enough to make a soft paste1 and use with a trowel or knife4 ,this is a heat-proof compound and is commonly known as asbestos cement4 ,very ,hard ,cement ,one of the hardest cements that can be made is composed of hydraulic cement 7,portland or ,edison71 five parts2 silex1 or white sand1 five parts 7by measure74 ,mix with water and use like plaster with a trowel or spatula4 ,care must be taken when the parts are combined to see that the cement is free from lumps4 ,these must be broken before the silex1 or sand1 and water are added4 ,then the two parts should be mixed together at first and moistened afterwards4 ,the proper way is to place some water at the bottom of a pan2 then add the dry mixture by the handfuls1 sprinkling it around so that the water can enter into it without forming lumps4 ,keep adding and mixing until the mass is at the right consistency to work4 ,all these cements are acid-proof4 ,clark's ,compound ,for exterior insulation1 where the parts are exposed to the weather1 a superior compound is made up of mineral pitch1 ten parts2 silica1 six parts2 tar1 one part 7all parts by weight74 ,this is called ,clark's compound1 after the man who invented it and used it successfully4 ,it is heated1 thoroughly mixed1 and used with a brush or spatula4 ,battery ,fluid ,a depolarizing solution for use in zinc-carbon batteries like the ,grenet is composed as follows3 ,dissolve one pound of bichromate potash or soda in ten pounds of water 7by weight74 ,when it is thoroughly dissolved add two and one-half pounds of sulphuric acid1 slowly pouring it into the bichromate solution and stirring it with a glass rod4 ,the addition of the acid will heat the solution4 ,do not use it until it has entirely cooled4 ,glass ,rubbing ,to rub the edges of glass1 such as the disks for ,wimshurst machines1 obtain a piece of hard sandstone1 such as is used for sharpening knives or scythes4 ,the glass is placed on a table so that the edge extends beyond4 ,oil of turpentine is rubbed or dropped on the surface of the stone1 and the edge of the glass is moistened with a rag soaked in the turpentine4 ,hold the glass down securely with one hand1 and with the other grasp the stone and give it a forward and backward motion1 grinding the glass along its edge and not crosswise4 ,with care and patience a rough edge can soon be brought to a smooth one1 and a soft1 rounded corner substituted for the hard1 angular1 cutting edge that makes the glass a difficult thing to handle4 ,use plenty of lubricant in the form of oil of turpentine to make the work easy4 ,acetic ,glue ,one of the best glues for glass and wood or glass and fibre is made by placing some high-grade glue 7either flake or granulated7 in a cup or tin and covering it with cold water4 ,allow it to stand several hours until the glue absorbs all the water it will and becomes soft2 then pour the water off1 and add glacial acetic acid to cover the glue4 ,the proportion should be eighteen parts of glue to two of acid4 ,heat the mass until it is reduced to liquid1 stirring it until it is thoroughly mixed4 ,when ready for use it should be poured into a bottle and well corked to keep the air away from it4 ,insulators ,apart from glass and porcelain1 insulators can be made from non-conducting compounds1 the best of which is molded mica4 ,ground mica or mica dust is mixed with thick shellac until it is in a putty-like state4 ,it may then be forced into oiled molds of any desired shape4 ,hydraulic pressure is employed for almost every form of molded mica that is made for commercial purposes2 but as a boy cannot employ that means to get the best results1 he must use all the pressure that his hands and a flat board will give4 ,another compound is made from pulverized asbestos and shellac1 with a small portion of ground or pulverized mica added1 in the proportion of asbestos1 six parts2 mica1 four parts4 ,shellac is added to make a pasty mass1 which is kneaded into a thick putty and forced into oiled molds until it sets4 ,it is then removed and allowed to dry in the open air1 and the mold used for more insulators4 ,non-conductors ,when working in different materials that seem adapted to electrical apparatus1 it is necessary to know whether they can be used safely or not4 ,often a material seems to be just the thing1 but if it should be a partial conductor1 when a non-conductor is desired1 it would be hazardous to use it4 ,a list of non-conductors is therefore valuable to the amateur4 ,some of the principal non-conductors1 among the many1 are as follows3 glass1 porcelain1 slate1 marble1 hard stone1 soapstone1 concrete 7dry71 hard rubber1 soft rubber1 composition fibre1 mica1 asbestos1 pitch1 tar1 shellac1 cotton1 silk2 cotton1 silk and woollen fabrics1 transite 7dry71 electrobestus 7dry71 duranoid2 celluloid1 dry wood 7well seasoned71 paper1 pith1 leather1 and oil4 ,while this account of formul and material might be extended1 this is not necessary inasmuch as the formul and practical directions which have been given will answer all usual practical requirements4 ,insulating ,varnish ,there are several good insulating varnishes that can be used in electrical work1 the most valuable being shellac dissolved in alcohol and applied with a brush4 ,to make good shellac1 purchase the orange-colored flake shellac by the pound from a paint-store1 place some of it in a wide-necked bottle1 and cover it with alcohol2 then cork the bottle and let it stand for a few hours4 ,shake the bottle occasionally until the shellac is thoroughly dissolved4 ,it can be thinned by adding alcohol4 ,always keep the bottle corked1 taking out only what is necessary from time to time4 ,another varnish can be made by dissolving red sealing-wax in alcohol and adding a small portion of shellac4 ,this can be applied with a soft brush1 and is a good varnish4 ,when colors are to be applied to distinguish the poles1 red is used for the positive current-poles and blue or black for the negative1 if they are colored at all4 ,a very good black varnish is made by adding lampblack to shellac2 another consists of thick asphaltum or asphaltum varnish4 ,this is waterproof1 and dries hard1 yet with an elastic finish4 ,battery ,wax ,for the upper edges of glass cells1 such as the ,leclanch or other open-circuit batteries1 there is nothing superior to hot paraffine brushed about the upper edge to prevent the sal-ammoniac or other fluids from creeping up over the top4 ,the paraffine can be colored with red-lead1 green dust1 or powders of various colors if desired1 but generally the paraffine is used without color1 so that it has a frosted-glass appearance when it is cool and dry4 ,a black wax for use in stopping the tops of dry cells and coating the tops of carbons is composed of paraffine1 eight parts2 pitch1 one part2 lampblack1 one part4 ,heat the mixture and stir it until thoroughly mixed2 then apply with a brush1 or dip the parts into the warm fluid4 ,another good black wax is composed of tar and pitch in equal parts4 ,they are made into a pasty mass with turpentine heated over a stove1 but not over an open flame1 because the ingredients are inflammable4 ,the compound should be like very thick molasses1 and can be worked with an old table-knife4 ,chapter ,,xv ,,electric ,,light1 ,,heat1 ,,and ,,power ,for the use of the cuts in this chapter1 the ,publishers desire to acknowledge the courtesy of the ,general ,electric ,company1 the ,thomson ,electric ,welding ,company1 and the ,cooper ,hewitt ,electric ,company4 ,with the discovery of the reversibility of the dynamo1 the invention of the telephone1 and the improvements in the electric light began the great modern development of electricity which proved that marvellous agent to be a master-workman4 ,many of the things electrical that we ordinarily think of as modern inventions are merely modern applications of phenomena that were discovered many years ago4 ,the pioneers in the science of dynamic electricity performed their experiments with the electric light1 electro-magnets1 etc41 by using galvanic batteries4 ,but for practical purposes the consuming of zinc and chemicals in such batteries was too expensive a way to generate electricity1 and prevented any commercial use of the results of their experiments until cheaper electricity could be had4 ,the ,work of the ,dynamo ,the invention of the dynamo1 with which we obtain electricity from mechanical power1 changed all that4 ,instead of consuming zinc in primary batteries1 men could obtain it by burning coal1 which is much cheaper1 under the boiler of a steam-engine used to drive the dynamo4 ,thus it is that modern electricity comes from mechanical power4 ,it is really the energy of a steam-engine or a water-wheel1 or some other 8prime mover10 working through the medium of electricity1 that is transmitted to a distance and distributed over wires4 ,the electricity may then be transmuted into light1 heat1 or chemical energy as the case may be1 to light our electric lamps1 develop the intense heat of the electric furnace1 and charge storage-batteries4 ,moreover1 some time after the invention of the dynamo it was found that the mechanical power put into one of these machines could be transmitted electrically and reproduced as mechanical power4 ,in other words1 a dynamo could be made to revolve and give out power1 as a motor1 by supplying it with current from another dynamo4 ,this showed the way to transmute electricity back again into mechanical power1 to run our electric cars and trains1 and all kinds of machinery in our factories and elsewhere4 ,nowadays the dynamo is used to generate nearly all the electricity that we need4 ,even in such comparatively old electrical applications as electro-plating and the telegraph and telephone1 primary batteries are being supplanted by motor dynamos1 which we shall learn about later4 ,it is from the invention of the dynamo and the discovery that it was reversible that we date the beginning of what are known as heavy electrical engineering applications1 including electric light1 heat1 and power4 ,in this closing chapter it is purposed to learn a little about these applications1 and in so doing to summarize briefly the things that we have already studied4 ,the ,electric ,light ,in the chapter on ,electrical ,resistance we learned that an electric current always encounters a resistance in passing through a conductor1 and that when the current is strong enough the conductor is heated up4 ,the electric light is produced by the heating of a conductor of one kind or another to incandescence by the electrical friction of the current passing through it4 ,the first electric light was made by ,sir ,humphry ,davy over a hundred years ago4 ,he discovered that when a current from a great many cells of battery was interrupted the spark did not simply appear for an instant and then go out1 as it does when only a few cells are used1 but remained playing between the terminals of the circuit4 ,he found by experiment that if pieces of carbon are used as the terminals--or 8electrodes10 as they are called--the electricity passes between them in an intensely hot flame1 or 8arc40 ,the latter1 which is due to the electrical resistance of the vapor of carbon1 heats up the carbon-points so that they give a brilliant white light4 ,illustration3 ,fig4 #a ,illustration3 ,fig4 #b ,before the dynamo came into use1 the electric light was rarely seen1 except as a philosophical experiment2 but as soon as cheap electricity became available1 commercial electric arc-lamps were made by many inventors and have been continually improved4 ,fig4 #a shows one form of modern arc-lamp1 with its case removed to show the interior mechanism4 ,in most arc-lamps the lamp itself consists of a pair of carbon or other electrodes in the form of long rods arranged vertically1 with their tips normally in contact4 ,when the current is turned on1 the mechanism lifts the upper electrode away from the lower one4 ,the interruption of the circuit thus caused 8strikes the arc0 between the tips1 and the mechanism keeps the arc-distance unchanged as the carbons burn away4 ,some arc-lamps are made to burn on continuous-current1 and others on alternating-current circuits4 ,when continuous current is used1 the upper 7or positive7 carbon burns away about twice as fast as the lower one1 forming a cup1 or 8crater10 from which most of the light comes4 ,uses of the ,arc-,light ,the first commercial use of the arc-light on a large scale was for street-lighting1 to replace the old-fashioned gas-lamps4 ,but another important use is in search-lights1 in which the arc-lamp is fitted with a powerful reflector for throwing a very bright light to a distance4 ,fig4 #b is a view of a search-light arranged to go on top of a ship's pilot-house4 ,in war-time the ships carry search-lights to help them find the enemy's ships and repel attack2 and they are used in the army also1 by having a portable dynamo and engine drawn by horses4 ,the arc is also employed in projectors for lecture-rooms1 and sometimes for the headlights of steam and electric locomotives and interurban electric cars4 ,incandescent and ,other ,lamps ,the arc-lamp came into wide use for lighting large spaces like streets1 stores1 and public halls1 but was found to be too intense for lighting smaller places like private houses4 ,after many experiments1 ,edison succeeded in subdividing the electric light into the small pear-shaped 8incandescent0 lamps that we now see everywhere4 ,in this kind of electric lamp the light comes from a thin 8filament0 of carbon1 contained in a glass globe from which all air has been removed4 ,since there is no oxygen to support combustion1 the filament may be heated white-hot by the current without being consumed4 ,illustration3 ,fig4 #c ,in certain other forms of incandescent lamps that are just coming into use1 the filaments are made of rare metals--osmium1 tantalum1 etc4--that will stand a high temperature without melting4 ,the ,nernst lamp has a filament consisting of a mixture of certain materials that has to be heated before it will conduct electricity4 ,then there are the so-called 8vapor0 lamps1 consisting of a glass tube full of conducting metallic vapor which gives out light when a current is passed through it4 ,the best-known form is the ,cooper ,hewitt mercury vapor-lamp shown in ,fig4 #c1 which gives a peculiar greenish light4 ,from the point of view of efficiency1 the electric light1 wonderful as it is1 leaves much to be desired4 ,the light always comes from a hot resistance2 and whether this resistance is a mass of conducting vapor1 as in the arc and vapor lamps1 or a solid conducting filament1 as in the so-called 8incandescent0 lamps1 much more heat than light is produced4 ,a needed improvement1 therefore1 is in the direction of obtaining a greater percentage of light for a given amount of electrical energy4 ,electric ,heat ,the generation of heat in electrical devices usually means wasted energy--sometimes a very serious waste1 as we have just seen4 ,there are certain kinds of electrical apparatus1 however1 that are designed to transform all of the electrical energy delivered to them into heat1 for various industrial and household purposes4 ,illustration3 ,fig4 #d ,electric ,furnaces ,by far the most important application of electric heat1 as such1 is in electric furnaces1 by means of which we attain the highest temperatures known to man4 ,the electric furnace consists of a chamber of 8refractory0 material1 containing the substances to be acted upon by the heat1 with a pair of big carbon electrodes thrust into the centre1 as shown in ,fig4 #d1 which is a picture of ,moissan's electric furnace for the distillation of metals1 and supplied with heavy continuous or alternating currents4 ,the apparatus is therefore a sort of gigantic electric arc-lamp1 so enclosed that the whole of the intense heat of the arc is confined and concentrated on the smelting or other work4 ,in many places where cheap electric power is to be had--as in the vicinity of the great ,niagara ,falls power-plants--electric furnaces are employed in what are known as electrometallurgical and electrochemical manufacturing processes4 ,by their aid many metals and other substances that were formerly scientific curiosities1 or entirely unknown1 are produced commercially2 such as aluminum1 certain rare metals1 and calcium carbide1 from which that wonderful illuminant1 acetylene-gas1 is obtained4 ,welding ,metals ,another useful application of electric heat is in the welding of metals4 ,instead of heating the pieces to be welded in a forge1 their ends are simply butted together and the electricity--generally from an alternating-current transformer--turned on4 ,the heat developed by the 8contact resistance0 between the pieces quickly softens the metal so that the pieces may be forced together1 forming a perfect weld in a few minutes without any hammering4 ,fig4 #e is a view of one form of electric welding-machine in which this is accomplished4 ,the electric process can weld certain metals that cannot be joined securely by ordinary welding methods1 and is used in several special arts4 ,welding is also performed by the heat of a special electric arc-lamp1 which a workman holds in his hand like a blow-pipe or torch4 ,this process is especially useful in joining the edges of sheet-steel1 in making tanks for electric 8transformers10 etc4 ,the workmen have to wear smoked glasses in order to protect their eyes from the intense glare of the arc4 ,illustration3 ,fig4 #e ,electric ,car-heaters ,perhaps the simplest and best-known application of electric heat is the electric car-heater1 consisting of coils of high-resistance wire--such as iron or ,german-silver wire--mounted on an insulating1 non-combustible frame which is placed under the seats of the car4 ,part of the current from the trolley wire or third rail passes through the resistance-coils1 heating them up and thereby warming the air in the car4 ,household ,uses ,nowadays electric heat is being more and more widely utilized in what are known as household electric heating-appliances4 ,one of the most useful of these is the electric flat-iron1 shown in ,fig4 #f4 ,this flat-iron is designed to do away with the use of a hot stove of any kind1 and is internally heated by means of a resistance-coil of peculiar shape placed in the bottom of the iron close against its working face4 ,the iron is connected to an electric-light socket by means of an attaching plug on the end of a long1 flexible cord4 ,it takes only a few minutes to get hot1 and its use saves much time and labor4 ,the list of special heating-appliances that are now made includes curling-iron heaters2 heating-pads1 for taking the place of hot-water bags in the sick-room2 cigar-lighters1 in which a little grid 8resistance0 is made incandescent by pressing a button2 foot-warmers2 and radiators to dry wet shoes or skirts on rainy days4 ,for industrial use there are glue-pots1 for bookbinders and pattern-makers2 large flat-irons1 for tailor-shops and laundries2 and electric ovens1 for drying certain parts of electrical machines and for cooking various kinds of 8prepared foods40 ,many electric cooking-utensils are made for the household1 such as coffee-percolators1 egg-boilers1 ovens1 disk stoves1 etc4 ,each one is equipped with a resistance-coil like that in the electric flat-iron just described1 so that it contains its own source of heat1 which is under perfect control by means of a switch4 ,an 8electric kitchen0 consists of a number of these utensils1 wired to a convenient table or stand1 as shown in ,fig4 #g4 ,illustration3 ,fig4 #f ,illustration3 ,fig4 #g ,electric ,power ,we have seen that the modern way to generate electricity is from mechanical energy applied through a dynamo1 and that the 8electric power0 thus generated may be transmitted over wires to a distance and there transformed into other forms of energy1 such as light1 heat1 and chemical energy1 or reproduced again as mechanical energy4 ,the last mentioned of these transformations is the most important of them all1 because it is the one that means the most for the advancement of civilization4 ,before the invention of the dynamo and the discovery that it was reversible1 mechanical power could be employed only in the place where it was generated1 so that its use was restricted2 whereas nowadays the field of power is broadened and its cost reduced by electrical transmission and distribution4 ,in the chapter on ,dynamos and ,motors we learned how to make and use those machines4 ,let us review1 very briefly1 just what happens in the double transformation--of mechanical energy into electricity and then back again at the end of a line of wires--that we call electric-power transmission4 ,in the dynamo1 the power of the water-wheel1 or whatever other prime mover is used1 is exerted in generating electricity by forcing the electric conductors of the machine through a magnetic field4 ,the electricity is led away to a distance--a hundred miles1 perhaps--by wires and allowed to enter another machine similar to the dynamo1 but operating as a motor4 ,here the first process is reversed3 the electricity passing through the conductors of the motor reacts upon its magnetic field1 causing the machine to revolve and thus generating mechanical power again4 ,the line-wires carry the power just as positively as though a long shaft ran from the prime mover to the receiving end of the line1 and much more economically4 ,the action that goes on is similar to the operation of the telephone--which is indeed a special case of electric-power transmission--as already explained in a former chapter3 the sound of the voice being transformed1 at the telephone-transmitter1 into electrical energy in the form of alternating currents1 then carried as such over the line and finally reproduced as sound again at the receiver4 ,power from ,water-wheels 8,hydro-electric0 transmissions--i4 e41 electric transmissions of power from a water-wheel as prime mover--are the most important because they bring into use cheap water-power that formerly ran to waste4 ,there are many hydro-electric transmissions in this country1 ,mexico1 and ,canada1 some of them utilizing the power of waterfalls or rapids located in mountainous and inaccessible parts4 ,the alternating current is nearly always used because by it men can much more easily and safely generate1 transmit1 and receive the high voltages that have to be used than by the continuous current4 ,the machinery at the 8main generating station0 consists of big alternating-current dynamos1 which sometimes have vertical shafts instead of horizontal ones1 so that they may be driven directly by turbines4 ,the current is generated at a moderate potential1 which is then 8stepped-up10 by 8static transformers10 to the comparatively high-line voltage that is required in long-distance transmissions4 ,illustration3 ,fig4 #h ,transformers ,fig4 #h is a view of a very large transformer of over #bejj electrical horse-power capacity4 ,in the picture the containing-tank is represented as transparent1 so as to show the transformer proper inside4 ,the latter is really a special kind of induction-coil1 with primary and secondary windings1 and a core1 weighing many tons1 built up of thin sheets of steel4 ,in this kind of transformer1 the tank is filled with oil1 to keep the transformer cool in operation1 and to help insulate it against the high potential to which it is subjected4 ,at the receiving end1 or 8sub-station10 the high-voltage electric power enters a set of 8step-down0 transformers1 from which it is delivered again1 at moderate potential1 to the motors4 ,sometimes power is distributed from a single great generating station to several sub-stations4 ,in the ,necaxa transmission1 in ,mexico1 over #ce1jjj horse-power is taken from a waterfall in the mountains and transmitted at #fj1jjj volts potential to ,mexico ,city1 #ajj miles away1 and to the mining town of ,el ,oro1 seventy-four miles farther on4 ,several kinds of motors are used at the receiving end of electric-power transmission-lines1 according to the work that they are called upon to do4 ,for 8stationary0 work1 like driving the machines in mills and factories1 two principal kinds of alternating-current motors are employed--synchronous and induction motors4 ,the former are built just like alternating-current dynamos1 and when they are running they keep 8in step0 with the dynamo at the other end of the line2 i4 e41 the motion of their field windings relatively to their armatures keeps exact pace with the same motion at the dynamo1 just as though a long shaft ran from one machine to the other instead of the electric wires of the transmission-line4 ,a motor of this type1 at work driving an air-compressor1 is shown in ,fig4 #i4 ,the induction-motor is really a sort of transformer1 the primary winding of which is the fixed part1 or field1 and the secondary winding the rotating armature4 ,it does not keep in step with the dynamo1 like the synchronous motor1 but adapts its speed to the 8load10 or amount of work that it is called upon to do1 like a continuous-current motor4 ,illustration3 ,fig4 #i ,rotary ,converters ,sometimes alternating-current electric power is transformed at the sub-station into continuous-current power4 ,this is done by a special kind of transformer called a 8rotary converter40 ,the static transformers of which we have just been speaking are built1 like ordinary reduction-coils1 with no moving parts1 and operate by taking in alternating currents at a given potential and giving out alternating currents at a different potential1 higher or lower as the case may be4 ,the rotary converter1 however1 is built something like a dynamo1 with a stationary field and a revolving armature1 and ordinarily operates by receiving an alternating current at a given potential and delivering a continuous current of the same or a different potential4 ,this kind of transformation is employed wherever it is desired to obtain any large amount of continuous current from an alternating-current transmission-line2 and especially to obtain 8#ejj-volt continuous current0 for operating street and interurban electric railways1 as we shall see under the next heading4 ,fig4 #aj shows one form of rotary converter built for supplying continuous current for trolley service4 ,illustration3 ,fig4 #aj ,oftentimes the sub-station of a transmission system contains both static transformers and rotary converters1 to supply both alternating current and continuous current from the same high-voltage alternating-current line4 ,when the continuous current has to be transformed from one voltage to another1 a 8motor dynamo0 is used1 consisting of an electric motor driving a dynamo on a common shaft4 ,one of the most interesting features of electric-power transmission is the care that is taken to avoid the terrible danger from the high potentials1 and at the same time prevent loss of power on the way4 ,the electricity in the machinery and in the line-wires that extend across the country is veritable lightning1 and has to be carefully guarded from doing any damage or escaping4 ,to prevent leakage1 the insulation of all of the station machinery and apparatus is made extra good1 with 8high dielectric strength10 so that it will not be punctured by the high voltage2 and the line-insulators are made very large1 and electrically and mechanically strong--quite unlike the ordinary-sized glass or porcelain insulators that are employed for telegraph and telephone lines4 ,each insulator before being put up is tested under a 8breakdown voltage0 much higher than it is to stand in actual service4 ,oil-switches ,the switching of high-voltage electric power is a knotty problem4 ,the circuit cannot be interrupted by 8air-break0 switches1 such as are used in ordinary electric-light stations1 for any attempt to do so would result in a destructive arc many feet long1 that could not be extinguished4 ,therefore 8oil-switches0 are always used to control the line-circuits at the main generating station and the sub-stations4 ,in these oil-switches--which are designed to be operated from a distance1 by hand-levers1 or sometimes by electric motors--the circuit is made and broken under the surface of oil1 which prevents the formation of an arc4 ,moreover1 the switchboard attendant does not have to come anywhere near the deadly high-voltage wires1 but can make the necessary connections at a safe distance4 ,electric ,traction ,the use of the electric motor to propel vehicles of all kinds is called electric traction4 ,it is1 of course1 a branch of electric power1 which we have just been considering2 and it is in many respects the most important branch4 ,the wealth of a country is largely built up and maintained by its facilities for transportation1 such as its canals1 highways1 railroads1 and street and interurban car-lines4 ,in this field electric power is playing a most important part1 although it was not many years ago that the first experimental electric cars were put in to replace horses on the street-railways of our cities4 ,the change was found to be so successful that the field of the trolley-car was widened and extended very rapidly1 until now we have our great suburban and interurban electric railways1 with cars almost or quite as big as those on the steam-railroads and running at even higher speeds4 ,during the last few years1 also1 the sphere of the steam-railroad itself has been invaded by electricity1 by the construction of powerful electric locomotives to draw passenger and freight trains4 ,the ,trolley-car ,let us consider just what it is that makes a trolley-car go4 ,since electric power is only mechanical energy in another form1 we know that the motionless copper trolley-wire1 suspended over the track in our streets1 is the means of propelling the car just as truly--though in a different way--as if it were a moving steel cable to which the car was attached4 ,we must keep in mind the fact that the electricity is not itself the source of power1 but only the medium of transmission4 ,the engine in the power-house1 by turning a dynamo there1 maintains a constant electric pressure1 or 8constant potential10 as it is termed1 in the trolley-wire4 ,this pressure of electricity forces the power through the motors of the car as soon as the motorman makes the connection to them by turning the handle of his 8controller40 ,illustration3 ,fig4 #aa ,the ,continuous-current ,motor ,fig4 #aa is a view of one form of continuous-current motor4 ,there is not much of the motor itself to be seen1 because it is entirely enclosed in a cast-iron case4 ,the shaft of the motor has a small 8spur gear0 fixed on one end1 driving a gear-wheel which is fixed on the car axle4 ,by this arrangement more than one revolution of the motor armature is required to make one revolution of the car-wheel1 which multiplies the force exerted in turning the wheel4 ,illustration3 ,fig4 #ab ,the ,controller ,fig4 #ab is a view of a type of controller that is used on the platform of trolley-cars4 ,the cover is removed to show the contacts1 inside1 by which the electric power is turned on gradually by the controller handle4 ,the trains of electric cars that run on the elevated structures and in the subways of our large cities are supplied with power from a 8third rail0 placed by the side of the track1 on insulating supports1 and the motors on all the cars are controlled from a single 8master-controller0 on the front platform of the forward car4 ,this system of control1 known as the 8multiple-unit0 system1 gives electric trains several advantages over the old kind1 drawn by steam-locomotives2 such as they used to have on the ,new ,york elevated roads1 for example4 ,for one thing1 the train can be started much more quickly1 since all the motors begin to turn the car-wheels at the same instant4 ,then again1 the system enables a long train of cars to be controlled as easily as a single car1 and better 8traction0 between wheels and track is obtained4 ,electric ,locomotives ,several of the great steam-railroads are now adopting the electric locomotive to draw their trains4 ,fig4 #ac is a view of one of the great continuous current electric locomotives that are used by the ,new ,york ,central ,railroad to handle many of its passenger-trains in and out of the ,grand ,central ,station1 in ,new ,york city4 ,the motors of this powerful electric engine1 unlike those of trolley-cars1 are 8gearless02 that is1 their armatures are fixed directly on the locomotive axles so that they revolve at the same speed as the driving-wheels4 ,illustration3 ,fig4 #ac ,all of the railway motors considered thus far have been of the continuous-current type1 although the current to operate them is often obtained from alternating current transmission-systems1 through rotary converters1 as described above4 ,the alternating current is also beginning to be employed to drive cars and trains4 ,one type of alternating current railway motor1 designed for 8single-phase0 operation1 is in use on several interurban systems in this country1 running on high-voltage alternating current most of the time1 but on continuous current when within the city limits4 ,other ,forms of ,electric ,traction ,electric traction also includes electric automobiles1 supplied by storage-batteries2 a slow-speed electric locomotive for drawing canal-boats1 and called 8the electric mule02 and an ingenious gasolene-electric outfit for driving cars by electric motors without any trolley1 third rail1 or storage-battery4 ,the last-mentioned arrangement consists of a set of electric car-motors mounted on the trucks in the usual way1 but supplied with current by a dynamo mounted on the car itself and driven by a gasolene-engine4 ,thus the car carries its own power-station about with it1 and is independent of any outside source of electricity4 99 99 99 99 99 ,the old alchemists sought to transmute matter from one form to another2 and especially lead and other 8base metals0 into gold1 in order that they might grow rich by concentrating the precious metal in their own selfish hands4 ,the modern miracle that electricity works for us1 the transmutation of energy1 is a higher and broader thing1 because it multiplies and distributes the world's good things4 ,,appendix ,a ,,dictionary ,,of ,,electrical ,,terms ,,and ,,phrases ,everybody is interested in electricity1 but the ordinary reader1 and particularly the boy who attempts to use this manual intelligently1 will come across many technical words and terms that require explanation4 ,it would be impossible to incorporate all needful definitions in the text proper1 and the reader is therefore referred to the technical dictionary on the succeeding pages4 ,care has been taken in its compilation to make the definitions complete1 simple1 and concise4 ,some of the more advanced technical terms have been purposely omitted as not necessary in a book dealing with elementary principles4 ,the student in the higher branches of the science will consult1 of course1 the more advanced text-books4 ,but for our practical purposes this elementary dictionary should answer every requirement4 ,to read it over is an education in itself1 and the young experimenter in electrical science should always refer to it when he comes across a word or phrase that he does not fully understand4 ,a ,a4 ,an abbreviation for the word anode4 ,absolute4 ,complete by itself4 ,in quantities it refers to fixed units4 ,a galvanometer gives absolute readings if it is graduated to read direct amperes or volts4 ,an absolute vacuum is one in which all residual gases are exhausted2 an absolute void is the theoretical consequent4 ,the absolute unit of current is measured in one1 two1 three1 or more amperes or volts4 ,a-,c4 ,an abbreviation expressing alternating current4 ,acceleration4 ,the rate of change in velocity4 ,the increase or decrease of motion when acted upon by the electric current4 ,accumulator4 ,a term applied to a secondary battery1 commonly called a storage-battery4 ,accumulator1 ,electrostatic4 7,see ,electrostatic ,accumulator47 ,accumulator1 ,storage4 ,a storage-battery4 ,acid4 ,a compound of hydrogen capable of uniting with a base to form salts4 ,sour1 resembling vinegar4 ,a sharp1 biting fluid4 ,acidometer4 ,a hydrometer used to determine the gravity of acids4 ,it is employed chiefly in running storage-batteries to determine when the charge is complete4 ,adapter4 ,a screw-coupling to engage with different size screws on either end1 and used chiefly to connect incandescent lamps to gas-fixtures4 ,adherence4 ,the attraction between surfaces of iron due to electro-magnetic action4 ,the term is used in connection with electric brakes--electro-magnetic adherence4 ,adjustment4 ,any change in an apparatus rendering it more efficient and correct in its work4 ,aerial ,conductor4 ,a wire or electric conductor carried over housetops or poles1 or otherwise suspended in the air1 as distinguished from underground or submarine conductors4 ,affinity4 ,the attraction of atoms and molecules for each other1 due to chemical or electrical action4 ,air-condenser4 ,a static condenser whose dielectric is air4 ,air-line ,wire4 ,in telegraphy that portion of the line-wire which is strung on poles and carried through the air4 ,alarm1 ,burglar4 ,a system of circuits with an alarm-bell1 the wires of which extend over a house or building1 connecting the windows and doors with the annunciator4 ,alarm1 ,electric4 ,an appliance for calling attention1 generally through the ringing of a bell or the operating of a horn4 ,alarm1 ,fire and ,heat4 ,an expansion apparatus that automatically closes a circuit and rings a bell4 ,alive1 or 8,live40 ,a term applied to a wire or circuit that is charged with electricity4 ,a 8live0 wire4 ,active circuits or wires4 ,alloy4 ,any mixture of two or more metals making a scientific compound4 ,for example3 copper and zinc to form brass2 copper1 tin1 and zinc to form bronze2 copper1 nickel1 and zinc to form ,german-silver4 ,alternating ,current4 7,see ,current1 ,alternating47 ,alternating ,current-power4 ,electrical distribution employing the alternating current from dynamos or converters4 ,alternation4 ,a change in the direction of a current2 to and fro4 ,alternations may take place with a frequency ranging from #ejj to #aj1jjj or more vibrations per second4 ,alternator4 ,an electric generator-dynamo supplying an alternating current4 ,amalgam4 ,a combination of mercury with any other metal4 ,amalgamation4 ,the application of mercury to a metal1 the surface of which has been cleansed with acid4 ,mercury will adhere to all metals1 except iron and steel1 and particularly to zinc1 which is treated with mercury to retard the corrosive action of acid on its surface4 ,amber4 ,a fossil resin1 valuable only in frictional electric experiments4 ,most of it is gathered on the shores of the ,baltic ,sea between ,knigsberg and ,memel4 ,it is also found in small quantities at ,gay ,head1 ,massachusetts1 and in the ,new ,jersey green sand4 ,when rubbed with a cloth it becomes excited with negative electricity4 ,ammeter4 ,the commercial name for an ampere-meter4 ,an instrument designed to show1 by direct reading1 the number of amperes of current which are passing through a circuit4 ,ampere4 ,the practical unit of electric current strength4 ,it is the measure of the current produced by an electro-motive force of one volt through a resistance of one ohm4 ,ampere-currents4 ,the currents theoretically assumed to be the cause of magnetism4 ,ampere-hour4 ,the quantity of electricity passed by a current of one ampere in one hour4 ,it is used by electric light and power companies as the unit of energy supplied by them1 and on which they base their reckoning for measuring the charges for current consumed4 ,ampere-ring4 ,a conductor forming a ring or circle4 ,used in electric balances for measuring current4 ,animal ,electricity4 ,a form of electricity of high tension generated in certain animal systems--the ,torpedo1 ,gymnotus1 and ,clurus4 ,the shocks given by these fish1 and particularly the electric eel1 are often very severe4 ,annealing4 ,the process of softening yellow metals by heating them to a cherry redness1 then allowing them to cool gradually in the air4 ,electric annealing is done by passing a current through the body to be annealed1 and heating it to redness2 then allowing it to cool gradually4 ,annunciator4 ,an apparatus for giving a call from one place to another1 as from a living-room to a hotel office1 or for designating a window or door that may have been opened when protected by a burglar-alarm4 ,annunciator-drop4 ,the little shutter which is dropped by some forms of annunciators1 and whose fall discloses a number or letter1 designating the location from which the call was sent4 ,anode4 ,the positive terminal in a broken1 metallic1 or true conducting circuit4 ,the terminal connected to the carbon-plate of a battery1 or to its equivalent in any other form of electric generator1 such as a dynamo or a voltaic pile4 ,the copper1 nickel1 gold1 or silver plates hung in an electro-plating bath1 and from which the metal is supplied to fill the deficiency made by the electro-deposition of metal on the kathode or negative object in the bath4 ,anti-hum4 ,a shackle inserted directly in a line-wire near a pole4 ,it is provided with a washer or cushion of rubber to take up the vibrations of a wire4 ,to continue the circuit a bridle1 or curved piece of wire1 is connected with the line-wires that are attached to the shackle4 ,arc4 ,a term applied to an electric current flowing from carbon to carbon1 or from metals separated by a short gap1 as in the arc street-lamps4 ,the original arc was produced by two vertical rods1 through which the current passed up and down4 ,when not in action the upper ends touched1 but as the current flowed the ends were separated1 so that the current1 passing up one carbon across the gap and down the other1 formed the segment of a circle in jumping from one tip to the other4 ,an arc of electric flame is of brilliant and dazzling whiteness4 ,the voltaic arc is the source of the most intense heat and light yet produced by man4 ,the light is due principally to the incandescence of the ends of carbon-pencils1 when a current of sufficient strength is passing through them and jumping over the gap4 ,undoubtedly the transferred carbon particles have much to do with its formation4 ,the conductivity of the intervening air and the intense heating to which it is subjected1 together with its coefficient of resistance1 are other factors in the brilliant light produced4 ,arc-lamp4 ,an electric lamp which derives its light from the voltaic arc1 by means of carbon-pencils and a current jumping from one to the other4 ,arc1 ,quiet4 ,an arc free from the hissing sound so common in arc-lights4 ,arc1 ,simple4 ,a voltaic arc produced between only two electrodes4 ,armature4 ,a body of iron or other material susceptible to magnetization1 and which is placed on or near the poles of a magnet4 ,that part of an electric mechanism which by magnetism is drawn to or repelled from a magnet4 ,the core of a dynamo or motor which revolves within the field magnets1 and which is the active principle in the generation of current by mechanical means1 or in the distribution of power through electrical influence4 ,armatures are sometimes made of steel1 and are permanent magnets4 ,these are used in magneto-generators1 telegraph instruments1 and other apparatus4 ,armature-bar4 ,an armature in a dynamo or motor whose winding is made up of conductors in the form of bars4 ,armature-coil4 ,the insulated wire wound around the core of the armature of an electric current-generator or motor4 ,armature-core4 ,the central mass of iron on which the insulated wire is wound2 it is rotated in the field of an electric current-generator or motor4 ,armored4 ,protected by armor2 as cables may be surrounded by a proper sheathing to guard them from injury4 ,astatic4 ,having no magnetic directive tendency1 the latter being a general consequent of the earth's magnetism4 ,astatic ,circuit4 7,see ,circuit1 ,astatic47 ,astatic ,couple4 7,see ,couple1 ,astatic47 ,astatic ,needle4 ,a combination of two magnetic needles so adjusted as to have as slight directive tendency as possible4 ,the combination is generally made up of two needles arranged one above the other with the poles in opposite directions--commonly called 8,nobili's ,pair40 ,these needles require but a slight electro-force to turn them one way or the other1 and are used in astatic galvanometers4 ,atmospheric ,electricity4 7,see ,electricity1 ,atmospheric47 ,atom4 ,the ultimate particle or division of an elementary substance4 ,electricity is largely responsible for the presence of atoms in the atmosphere4 ,atomic ,attraction4 ,the attraction of atoms for each other4 ,principally due to electric disturbance4 ,attraction4 ,the tendency to approach and adhere or cohere which is shown in all forms of matter4 ,it includes gravitation1 cohesion1 adhesion1 chemical affinity1 electro-magnetic and dynamic attraction4 ,aurora4 ,a luminous electric display seen in the northern heavens4 ,it is commonly thought to be the electric discharges of the earth into the atmosphere1 due to revolution of the former and to the heat produced at the equator4 ,as compared to the static machine for generating frictional electricity1 the earth represents the revolving wheel gathering the current and discharging it at the poles4 ,automatic ,cut-out4 ,an electro-magnetic switch introduced into a circuit1 so as to break the circuit of the latter should it become overloaded with current2 it also acts in the event of a mechanical interruption4 ,automatic ,regulation4 ,a speed regulator worked by electricity so that a uniform flow of current may be secured automatically4 ,ayrton's ,condenser4 ,this is a pile of glass plates separated by small pieces of glass at the four comers1 so that the plates cannot touch each other4 ,tin-foil is pasted on both sides of every plate1 and the two coatings are connected4 ,the tin-foil on each second plate is smaller in area than that on the others1 and the plates are connected in two sets1 negative and positive4 ,in this construction it will be seen that the glass is not the dielectric proper1 but acts only as the plane to which the tin-foil is pasted4 ,one set of plates are connected to a binding-post by strips of tin-foil1 and the other set are connected to another binding-post in a similar manner4 ,b ,b4 ,an abbreviation for ,beaum1 the inventor of the hydrometer scale4 ,thus1 in speaking of the gravity of fluids1 #bj ,b4 means twenty degrees ,beaum4 ,back ,induction4 ,a demagnetizing force produced in a dynamo when a lead is given to the brushes4 7,see also ,induction1 ,back47 ,back ,shock4 ,a lightning stroke received after the main discharge4 ,it is caused by a charge induced in neighboring surfaces by the main discharge4 ,bad ,earth4 ,a poor ground connection1 or one having comparatively strong electrical resistance4 ,balance4 ,a proper adjustment between the apparatus and the electro-motive force1 thus securing the best possible results4 ,b4 ,s4 ,w-,g4 ,abbreviations for ,brown ,sharp and wire-gauge1 and referring to the sizes of wire and sheet-metal thicknesses that are considered standards in ,america4 ,bar-armature4 ,an armature in which the conductors are constructed of bars4 ,bar-magnet4 ,one whose core presents the appearance of a straight bar1 or rod1 without curve or bend4 ,bare-carbons4 ,electric light carbons whose surfaces are not electro-plated with copper4 ,barometer4 ,an apparatus for measuring the pressure exerted by the atmosphere4 ,it consists of a glass tube #ca inches long1 closed at one end1 filled with mercury1 and then inverted1 with its open end immersed in a cistern of mercury4 ,the column of mercury falls to a height proportional to the pressure of the atmosphere4 ,at the sea-level it ranges from #cj to #ca inches4 ,bar-windings4 ,the windings of an armature constructed of copper bars4 ,bath4 ,in electro-plating1 the solution or electrolyte used for depositing metal on the object to be plated4 ,it may be a solution of copper1 silver1 nickel1 or other metal4 ,in electro-therapeutics it is a bath of water with suitable electrodes and connections for treating patients with electricity4 ,bath-stripping4 ,a solution used for stripping or removing the metal plating from an object4 ,batten4 ,a strip of wood grooved longitudinally1 in which electric light or power wires are set4 ,the grooved strip is screwed to the wall1 the wires being laid in the grooves1 and then covered with a thin wooden strip fastened on with small nails4 ,battery4 ,a combination of parts1 or elements1 for the production of electrical action4 ,a number of cells connected parallel or in series for the generation of electricity4 ,under this heading there are at least one hundred different kinds4 ,nowadays the dynamo is the cheap and efficient generator of electricity4 ,battery ,cell1 ,elements of4 ,the plates of zinc and carbon1 or of zinc and copper1 in a cell are called elements4 ,the plate unattacked by the solution1 such as the carbon or copper1 is the negative element1 while the one attacked and corroded by the electrolyte is the positive4 ,battery1 ,dry4 ,a form of open circuit cell in which the electrolyte is made practically solid1 so that the cell may be placed in any position4 ,a zinc cup is filled with the electrolyte and a carbon-rod placed in the middle1 care being taken to avoid contact between cup and carbon at the bottom of the cell4 ,the gelatinous chemical mass is then packed in closely about the carbon1 so as to nearly fill the cup4 ,a capping of asphaltum1 wax1 or other non-conducting and sealing material is placed over the electrolyte1 and this hardens about the carbon and around the top inner edge of the zinc cup4 ,the latter becomes the positive pole1 the carbon the negative4 ,binding-posts1 or connections1 may be attached to the zinc and carbon to facilitate connections4 ,battery1 ,galvanic4 ,the old name for a voltaic battery4 ,battery1 ,gravity4 ,a battery in which the separation of fluids is obtained through their difference in specific gravity--for example1 the bluestone cell4 ,the sulphate of copper solution1 being the more dense1 goes to the bottom1 while the zinc solution stays at the top4 ,in its action the acid at the top corrodes the zinc1 while at the bottom the solution is decomposed and deposits metallic copper on the thin copper plates4 ,battery1 ,leclanch4 ,an open circuit battery consisting of a jar1 a porous cup1 and the carbon and zinc elements1 the electrolyte of which is a solution of ammonium chloride 7sal-ammoniac74 ,the carbon plate is placed in the porous cup1 and packed in with a mixture of powdered manganese binoxide and graphite1 to serve as a depolarizer4 ,a half-saturated solution of sal-ammoniac is placed in the outer jar1 and a rod of zinc suspended in it4 ,another form of the battery is to omit the porous cup and use twice the bulk of carbon1 both elements being suspended in the one solution of sal-ammoniac2 this form of battery is used for open-circuit work only1 such as bells1 buzzers1 and annunciators4 ,it is not adapted for lights1 power1 or plating purposes4 ,battery ,mud4 ,a deposit of mud-like character which forms at the bottom of gravity batteries1 and which consists of metallic copper precipitated by the zinc4 ,it only occurs where wasteful action has taken place4 ,battery of ,dynamos4 ,a term used in speaking of a number of dynamos coupled to supply the same circuit4 ,they may be coupled in series or parallel4 ,battery1 ,plunge4 ,a battery in a cabinet or frame1 so arranged that the active plates can be removed or raised out of the solutions4 ,this is usually accomplished by having the plates attached to a movable frame which1 by means of a ratchet-shaft and chains1 can be raised or lowered4 ,its object is to prevent the corrosion of the plates when not in use4 ,battery1 ,primary4 ,a voltaic cell or battery generating electric energy by direct consumption of material4 ,the ordinary voltaic cell1 or galvanic battery1 is a primary battery4 ,battery1 ,secondary4 ,a storage-battery1 an accumulator4 ,battery ,solution4 ,the active excitant liquid1 or electrolyte1 placed within a cell to corrode the positive element4 ,also called ,electropoion4 ,battery1 ,storage4 ,a secondary battery2 an accumulator2 a battery which accumulates electricity generated by primary cells or a dynamo4 ,battery-gauge4 ,a galvanometer used for testing batteries and connections4 ,it is usually small in size1 and may be carried in a pocket4 ,battery-jar4 ,a glass1 earthen1 or lead vessel which contains the fluids and elements of each separate cell of a battery4 ,baum ,hydrometer4 7,see ,hydrometer1 ,baum47 ,becquerel ,ray and ,radiation4 ,an invisible ray discovered by ,becquerel1 which is given out by some compounds and chemicals--notably uranium--and which has the power to penetrate many opaque bodies and objects impenetrable to the actinic rays of ordinary light4 ,these rays are used chiefly in connection with the photographic dry-plate4 ,bell1 ,electric4 ,a bell rung by electricity4 ,the current excites an electro-magnet1 attracting or releasing an armature which is attached to a vibrating or pivoted arm1 on the end of which the knocker is fastened4 ,bichromate of ,potash4 ,a strong1 yellowish-red chemical1 used chiefly in battery fluids and electrolytes4 ,bifilar ,winding4 ,the method followed in winding resistance-coils4 ,to prevent them from creating fields of force1 the wire is doubled and the looped end started in the coil4 ,since the current passes in opposite senses in the two lays of the winding1 no field of force is produced4 ,binding4 ,unattached wire wound round armature-coils to hold them in place4 ,binding-post4 ,an arrangement for receiving the loose ends of wires in an electric circuit and securing them1 by means of screws1 so that perfect contact will be the result4 ,bi-polar4 ,possessing two poles4 ,bi-telephone4 ,a pair of telephones arranged with a curved connecting arm or spring so that they can be simultaneously applied to both ears4 ,blasting1 ,electric4 ,the ignition of a blasting charge of powder1 dynamite1 or other high explosive by an electric spark1 or by the heating1 to red or white heat1 of a thin wire imbedded in the explosive4 ,block ,system4 ,a system of signalling on railroads4 ,signal-posts are arranged at stated spaces1 and on these signals appear automatically1 showing the location of trains to the engineers of trains in the rear4 ,bluestone4 ,a trade name for sulphate of copper in a crystallized state4 ,bobbin4 ,a spool of wood or other non-conducting substance wound with insulated wire4 ,in a tangent galvanometer the bobbin becomes a ring with a channel to receive the wire4 ,boiling4 ,in secondary1 or storage1 batteries the escaping of hydrogen and oxygen gases1 when the battery is fully charged1 resembles water boiling4 ,bonded ,rails4 ,rails used in an electric traction system1 and which are linked or connected together to form a perfect circuit4 ,used principally in the third-rail system4 ,brake1 ,electro-magnetic4 ,a brake to stop the wheels of a moving car4 ,it consists of a shoe1 or ring1 which by magnetic force is drawn against a rotating wheel to stop its revolution4 ,branch4 ,a conductor which leads off from a main line to distribute current locally4 ,brassing4 ,a process of electro-depositing brass in a bath containing both copper and zinc4 ,a plate of brass is used as an anode4 ,brazing1 ,electric4 ,a process in which the spelter is melted by electric current1 so that the two parts are united as one4 ,break4 ,a point where an electric conductor is broken1 as by a switch or a cut-out4 ,bridge4 ,a special bar of copper connecting the dynamos with the bus wire in electric lighting or power stations4 ,bronzing4 ,the deposition of bronze by electro-plating methods4 ,the mixture is of copper and tin1 and a cast bronze plate is used as an anode4 ,brush4 ,a term applied to the pieces of copper1 carbon1 or other conducting medium in dynamos and motors1 that bear against the cylindrical surface of the commutators to collect or feed in the current4 ,bug4 ,any fault or trouble in the connections or workings of an electrical apparatus4 ,the term originated in quadruplex telegraphy1 and probably had some connection with the ,edison bug-killer that he invented when a boy4 ,buoy1 ,electric4 ,a buoy to indicate dangerous channels in harbors and to mark wrecks and reefs4 ,it is provided with an electric light at night1 and with a gong or an electric horn by day4 ,burner1 ,electric4 ,a gas-burner so arranged that the flame may be lighted by electricity operated by a push-button at some distance from the fixture1 or1 close at hand1 by means of a chain or pull-string4 ,burning4 ,in a dynamo1 the improper contact of brushes and commutator1 whereby a spark is produced and an arc formed which generates heat and causes the metal parts to burn4 ,bus-rod4 ,a copper conductor used in power-plants to receive the current from the battery of dynamos4 ,the distributing leads are connected to these rods4 ,butt-joint4 ,a joint made by bringing the ends of wires together so that the ends butt4 ,they are then soldered or brazed4 ,button1 ,electric4 ,a form of switch that is operated by pushing a button mounted on a suitable base4 ,used principally for ringing bells1 operating lights1 etc4 ,buzzer4 ,an electric alarm1 or call1 produced by the rapid vibration of an armature acted upon by electro-magnetism4 ,the sound is magnified by enclosing the mechanism in a resonant box4 ,an apparatus resembling an electric bell minus the bell and clapper4 ,the buzzer is used in places where the loud ring of a bell would be a nuisance4 ,c ,c4 ,an abbreviation for centigrade when speaking of thermal temperature4 ,in chemistry the centigrade scale is used extensively1 but in air temperatures the ,fahrenheit scale is universally employed4 ,cable1 ,aerial4 ,a cable that contains a number of wires separately insulated1 the entire mass being protected by an external insulation4 ,it is suspended in the air from pole to pole1 and sometimes its weight is so great that a supporting wire is carried along with it 7usually overhead71 the large cable being suspended from it by cable-hangers4 ,cable ,box4 ,a box to receive cable ends and protect them2 also1 the box in which cable ends and line-wires are joined4 ,submarine cable boxes are usually near the ground1 while telephone and telegraph cable boxes are mounted on poles1 the cables running from the ground and up the poles to the boxes4 ,cable-core4 ,the conductors of a cable which make up its interior mass4 ,for the convenience of linemen the wires are often insulated with different-colored materials so that testing is not necessary when making connections4 ,cable-hanger4 ,a metallic grip1 usually of sheet metal1 arranged to clasp two or more wires4 ,it is fastened to the supporting wire by a hook and eye1 or by small bolts with thumb-nuts4 ,cable-head4 ,a rectangular board equipped with binding-posts and fuse wires so that the connections may be made between the cable ends and the overhead or line-wires of a system4 ,cables4 ,an insulated electric conductor of large diameter1 often protected by armor or metallic sheathing1 and generally containing1 or made up1 of several separately insulated wires4 ,cables supply current to traction lines2 power1 through subterranean passages2 communication1 by submarine connection2 and light1 by overhead or underground conduits4 ,call-bell4 ,a bell that is rung by pressing a button1 and which is operated by electricity4 ,calling-drop4 ,a drop-shutter which is worked by electricity in a telegraph or telephone exchange2 it denotes the location from which the call was sent in4 ,small red incandescent lamps have taken the place of the drops in most of the large telephone exchanges1 for they are noiseless and do not annoy the operators as the drops and buzzers did4 ,candle-power4 ,the amount of light given by the standard candle4 ,the legal ,english and ,american standard is a sperm candle burning two grains a minute4 ,candle1 ,standard4 ,the standard of illuminating power2 a flame which consumes two grains of sperm wax per minute1 and produces a light of a brightness equal to one candle-power4 ,caoutchouc4 ,india-rubber4 ,so named because originally its chief use was to erase or rub off pencil marks4 ,it is a substance existing1 in a thick fluid state1 in the sap or juices of certain tropical trees and vines2 it possesses a very high value as an insulator for wire and circuits4 ,the unworked1 crude rubber is called virgin gum1 but after it is kneaded it is called masticated or pure gum rubber4 ,capacity4 ,a term used when speaking of the carrying power of a wire or circuit4 ,the capacity of a wire1 rod1 bar1 or other conductor is sufficient so long as the current does not heat it4 ,directly electric heat is generated1 we speak of the conductor as being overloaded or having its capacity overtaxed4 ,capacity of a ,telegraph ,conductor4 ,the electric capacity may be identical in quality with that of any other conductor4 ,in quantity it varies not only in different wires1 but for the same wire under different conditions4 ,a wire reacting through the surrounding air1 or other dielectric1 upon the earth represents one element of a condenser1 the earth in general representing the other4 ,a wire placed near the earth has greater capacity than one strung upon high poles1 although the wires may be of identical length and size and of the same metal4 ,the effect of high capacity is to retard the transmission of current1 the low capacity facilitates transmission4 ,capacity1 ,storage4 ,in secondary batteries1 the quantity of electric current they can supply1 when fully charged1 without exhaustion4 ,this capacity is measured or reckoned in ampere-hours4 ,carbon4 ,one of the elements in graphitic form used as an electric-current conductor4 ,it is the only substance which conducts electricity1 and which cannot be melted with comparative ease by increase of current4 ,it exists in three modifications--charcoal1 graphite1 and the diamond4 ,in its graphitic form it is used as an electro-current conductor1 as in batteries and arc-light electrodes1 and as filaments in incandescent lamps4 ,in arc-lamp use the carbons are usually electro-plated on the outside with a film of copper which acts as a better conductor4 ,carbon1 ,artificial4 ,carbon-dust1 powdered coke1 or gas carbon is mixed with molasses1 coal-tar1 syrup1 or some similar carbonaceous fluid1 so that the mass is plastic4 ,it can then be moulded or pressed into shapes1 and heated to full redness for several hours by artificial or electric heat4 ,for lamp-carbons the mixture is forced through a round die by heavy pressure1 and is cut into suitable lengths1 then fired or baked4 ,after removing and cooling1 the carbons are sometimes dipped again into the fluid used for cementing the original mass and re-ignited4 ,this process is termed 8nourishing40 ,all carbon is a resisting medium1 but at high temperature the resistance is only about one-third as great2 that is1 the current will pass through a red-hot carbon three times better than through the cold carbon2 or a current of thirty amperes will be conducted as easily through a hot carbon as ten amperes through a cold one4 ,carbon-cored4 ,a carbon for arc-lamps1 the core being of softer carbon than the outer surface4 ,it is supposed to give a steadier light1 and fixes the position of the arc4 ,carbon-dioxide4 ,a compound gas1 or carbonic-acid gas4 ,it is a dielectric4 ,carbon-holders4 ,in arc-lamps1 the clamps arranged to hold the carbon-pencils4 ,carbonization4 ,the ignition of an organic substance in a closed vessel1 so as to expel all constituents from it except the carbon4 ,a destructive distillation4 ,carbon ,resistance4 7,see ,resistance1 ,carbon47 ,carbon ,volatilization4 ,in arc-lamps the heat is so intense that it is believed a part of the carbon-pencil is volatilized1 as vapor1 before being burned or oxidized by the oxygen of the air4 ,carbons1 ,bare4 7,see ,bare ,carbons47 ,carrying ,capacity4 ,in a current-conductor1 its carrying capacity up to the heating-point4 ,it is expressed in amperes4 ,cascade4 ,the arrangement of a series of ,leyden-jars in properly insulated stools1 or supports1 for accumulating frictional electricity4 ,they are arranged in a manner somewhat similar to a battery of galvanic cells1 the inner coating of one being connected to the outer coating of the next1 and so on through the series4 ,case-hardening1 ,electric4 ,a process by which the surface of iron is converted into steel by applying a proper carbonaceous material to it while it is being heated by an electric current4 ,cautery1 ,electric4 ,an electro-surgical appliance for removing diseased parts or arresting hemorrhages4 ,it takes the place of the knife or other cutting instrument4 ,it is a loop of platinum wire heated to whiteness by an electric current4 ,c4,c4 ,an abbreviation commonly used for cubic-centimeter4 ,it is usually written in small letters1 as #ej c4c41 meaning #ej cubic-centimeters4 ,cell1 ,electrolytic4 ,a vessel containing the electrolyte used for electro-plating4 ,cell1 ,regenerated4 ,a cell restored to its proper functions by a process of recharging4 ,cell1 ,standard4 ,meaning the same as battery4 ,the vessel1 including its contents1 in which electricity is generated4 ,cell1 ,storage4 ,two plates of metal1 or compounds of metal1 whose chemical relations are changed by the passage of an electric current from one plate to the other through an electrolyte in which they are immersed4 ,cements1 ,electrical4 ,cements of a non-conducting nature1 such as marine glue and sticky compounds1 used in electrical work4 ,centrifugal ,force4 ,a diametric revolving force which throws a body away from its axis of rotation4 ,a merry-go-round is a simple example of this force4 ,the more rapidly the platform revolves the greater the tendency for those on it to be thrown off and out from the centre4 ,the high velocity attained by the armatures in motors and dynamos would throw the wires out of place and cause them to rub against the surfaces of the field-magnets4 ,consequently1 wire bands or binders are necessary to keep the coils of wire from spreading under the influence of the centrifugal force4 ,charge4 ,the quantity of electricity that is present on the surface of a body or conductor4 ,the component chemical parts that are employed to excite the elements of a cell in generating electric current4 ,charge1 ,residual4 ,after a ,leyden-jar1 or other condenser1 has been discharged by the ordinary methods1 a second discharge 7of less amount7 can be had after a few minutes' waiting4 ,this is due to what is known as the residual charge1 and is connected in some way with the molecular distortion of the dielectric4 ,chemical ,change4 ,when bodies unite so as to satisfy affinity1 or to bring about the freeing of thermal or other energy1 the union is usually accompanied by sensible heat or light4 ,sulphuric acid added to water produces heat2 a match in burning produces light4 ,another form of chemical change is decomposition or separation 7the reverse of combination71 such as takes place in the voltaic-battery1 the electro-plating bath1 and other forms of electrolysis4 ,this is not accompanied by heat or light1 but by the evolution of electricity4 ,chemical ,element4 7,see ,element1 ,chemical47 ,chemistry4 ,the science which treats of the atomic and molecular relations of the elements and their chemical compounds4 ,chemistry is divided into many departments1 but electro-chemistry treats only of the science wherein electricity plays an active part1 such as batteries1 electro-plating1 and electro-metallurgy4 ,choking-coil4 7,see ,coil1 ,choking47 ,circle1 ,magic4 ,a form of electro-magnet4 ,it is a thick circle of round iron used in connection with a magnetized coil to illustrate electro-magnetic attraction4 ,circuit4 ,a conducting-path for electric currents4 ,properly speaking1 a complete circuit has the ends joined1 and includes a source of current1 an apparatus1 and other elements introduced in the path4 ,when the circuit is complete it is called active4 ,the term circuit is also applied to portions of a true circuit--as1 an internal or external circuit4 ,circuit1 ,astatic4 ,a circuit so wound1 with reference to the direction of the currents passing through it1 that the terrestrial or other lines of force have no directive effect upon it4 ,circuit-breaker4 ,any apparatus for opening and closing a circuit1 such as switches1 automatic cut-outs1 lightning-arresters1 and the like4 ,a ratchet-wheel engaged with a spring1 or wire1 which rests against the teeth4 ,the current passes through the wire1 the wheel1 and axle4 ,the wheel is revolved by a crank1 and as the ratchets pass the spring1 or wire1 an instantaneous make-and-break occurs4 ,the speed of the wheel regulates the frequency of the interruptions4 ,circuit1 ,external4 ,a portion of the circuit not included within the generator1 such as a secondary telegraph key and sounder4 ,circuit1 ,grounded4 ,a circuit in which the ground is used as a conductor4 ,this is common in telegraph and telephone lines1 particularly for short distances where the conductivity of the earth does not offer too much resistance4 ,circuit1 ,incandescent4 ,a circuit in which incandescent lamps are installed4 ,circuit ,indicator4 ,a pocket-compass1 galvanometer1 or other device for indicating or detecting the condition of a wire1 whether it is active or dead1 and1 if active1 in which direction the current is flowing4 ,it may also give a general idea of its strength4 ,circuit1 ,internal4 ,that portion of an electric circuit which is included within the generator4 ,circuit ,loop4 ,a minor circuit introduced1 in series1 into another circuit by a switch or cut-out1 so that it becomes a part of the main circuit4 ,circuit1 ,main4 a circuit or main line1 includes the apparatus supplying current to it4 ,thus distinguished from a local circuit4 ,circuit1 ,metallic4 ,a circuit in which the current outside the generator passes through metal parts or wire1 but not through the ground4 ,electric light and power lines are always metallic circuits4 ,an electro-plating apparatus may be properly termed a metallic circuit1 although a part of the circuit is formed by the electrolyte in the bath4 ,the essential meaning of the words metallic circuit is that the earth does not form a part of the return circuit4 ,circuit1 ,open4 ,a circuit in which a switch has been opened to prevent the continuous flow of current1 such as an electric-bell circuit1 which normally remains open1 and which is active only when the push-button is pressed1 thereby closing the circuit and operating the bell4 ,an open-circuit battery is one that remains inactive when the circuit is open4 ,circuit1 ,parallel4 ,a term signifying a multiple circuit4 ,circuit1 ,quadruple4 ,a single circuit capable of having four messages transmitted over it simultaneously--two in one direction1 and two in the other4 ,circuit1 ,return4 ,in telegraphy the ground is used as the return circuit4 ,it is also that portion of a circuit which leads from an apparatus back to the terminal of a dynamo or battery1 usually the negative wire4 ,circuit1 ,short4 ,a connection between two parts of a circuit1 causing the current to skip a great part of its appointed path4 ,short-circuits prevent the proper working of any electrical apparatus4 ,circuit1 ,simple4 ,a circuit containing a single generator1 the proper wire for carrying the current1 and a switch to operate it4 ,an electric-bell line1 a single telegraph line1 or a direct telephone line are all simple circuits4 ,clamp4 ,a tool for grasping and holding the ends of wires while joining them4 ,the appliance for holding the carbon-pencils in arc-lamps4 ,cleats4 ,blocks of wood1 porcelain1 or other insulating material used to hold wires against a wall or beam4 ,they have one1 two1 and three notches at one side1 for single1 double1 and three wire systems4 ,clutch1 ,electric4 ,a form of magnetic brake applied to car-wheels1 the armatures of motors1 and other revolving mechanism1 whereby the current1 passing through a coil1 magnetizes a mass of cast-iron1 and brings it to bear frictionally upon the moving parts of the mechanism4 ,code1 ,cipher4 ,a set of disconnected words which1 in accordance with a prearranged key1 stand for whole sentences and phrases4 ,commercially the system is used as a short-cut--ten words perhaps meaning what otherwise it would take forty or fifty words to express4 ,it is used extensively in telegraphy1 both as an abbreviated message and as a means for securing secrecy4 ,coherer4 ,conducting particles constituting a semi-conducting bridge between two electrodes1 and serving to detect electro-magnetic waves4 ,the coherer in wireless telegraphy is understood to mean that form of radio-receiver which1 being normally at high resistance1 is1 under the influence of ,hertzian-waves1 changed to a low resistance1 thus becoming relatively a conductor4 ,tubes of various kinds have been used for this purpose4 ,within them is a filling of carbon granules1 copper filings1 nickel and silver filings1 and other substances4 ,marconi's coherer consists of a tube one and one-half inches long and one-twelfth inch internal diameter4 ,this is filled with filings--#ij per cent4 of nickel1 #aj per cent4 of silver4 ,a globule of mercury coats the outer surface of each grain with a thin film of the quicksilver4 ,into both ends a piece of pure silver wire is plugged4 ,these latter are a quarter of an inch long1 and fit the tube very accurately4 ,the tube is thus sealed1 and it is considered preferable to have a slight vacuum within it4 ,coil4 ,a strand of wire wound in circular form about a spool1 a soft-iron core1 or in layers1 as a coil of rope4 ,an electro-magnetic generator4 ,a helix4 7,see also ,induction1 ,resistance1 ,magnetizing47 ,coil1 ,choking4 ,a form of resistance to regulate the flow of current4 ,any coil of insulated wire wound upon a laminated or divided iron core forms a choking-coil4 ,in alternating-current work special choking-coils are used4 ,they have a movable iron core1 and by thrusting it in or out the power is increased or diminished1 thus raising or lowering the lights1 the same as gas is regulated4 ,coil1 ,faradic4 ,the name given to a medical induction-coil or faradic machine4 ,coil1 ,induction4 ,a coil in which the electro-motive force of a portion of a circuit is1 by induction1 made to produce higher or lower electro-motive forces in an adjacent circuit1 or in a circuit a part of which adjoins the original circuit4 ,there are three principal parts to all induction-coils--the core1 the primary coil1 and the secondary coil4 ,the core is a mass of soft iron1 cast or wrought1 but preferably divided--for example1 a bundle of rods or bars4 ,the primary coil of comparatively larger wire is wound about this core1 each layer being properly insulated and varnished1 or coated with melted paraffine1 to bind the wires4 ,the secondary coil is of fine wire1 and is wound about the primary coil4 ,a great many turns of the fine wire are necessary1 and care must be taken to properly insulate each layer and shellac the wires4 ,the primary must be well insulated from the secondary coil1 so as to prevent sparking1 which would destroy the insulation4 ,a make-and-break is operated by the primary coil1 and is constructed upon the general form of an electric bell or buzzer movement4 ,extra currents which interfere with the action of an induction-coil are avoided by the use of a condenser4 7,see also ,condenser47 ,the induction-coil produces a rapid succession of sparks which may spring across a gap of thirty or forty inches1 according to the size of the coil4 ,induction-coils are used extensively in electric work1 especially in telephone transmitters1 wireless telegraphy1 electric welding1 and in the alternating-current system4 ,coil1 ,magnetizing4 ,a coil of insulated wire so wound that a well or aperture will be formed4 ,within this well a piece of steel is placed1 so that an electric current1 passing through the wires1 will magnetize the steel2 or a steel rod may be passed in and out of the hole several times while a strong current is travelling through the coil1 thus magnetizing the rod4 ,coil1 ,resistance4 ,a coil so constructed that it will offer resistance to a steady current of too great electro-motive force for the safety of the apparatus4 ,generally the coil is made by doubling the wire without breaking it1 then starting at the doubled end to wind it in coil or spring fashion4 ,if the wire is too heavy to wind double1 a single strand is wound on a square or triangular insulator in which notches are made4 ,then1 alternately between the coils1 the second strand is wound4 ,the strands are joined at one end of the coil1 but those at the other are left free for unions with other wires4 7,see also ,resistance47 ,coil1 ,retarding4 ,a choking-coil4 ,a resistance-coil4 ,coil1 ,ribbon4 ,instead of wire1 flat1 thin strips of sheet-metal are sometimes used for resistance-coils1 doubled1 as explained above4 ,the wraps are insulated with sheet-mica1 micanite1 or asbestos1 to prevent short-circuiting4 ,coil1 ,ruhmkorff4 ,a common type of induction-coil with a vibrator or circuit-breaker4 ,used with constant and direct current4 ,a step-up transformer with a circuit-breaker attachment4 ,coils1 ,idle4 ,coils in a dynamo in which no electro-motive force is being generated or developed4 ,coils that1 through broken connections or short circuits1 are inactive4 ,column1 ,electric4 ,an old name for the voltaic pile4 ,the apparatus made up of a pile of disks of copper and zinc1 separated by pieces of flannel wet with acidulated water4 ,comb4 ,a bar from which a number of teeth project like the teeth of a comb4 ,it is used as a collector of electricity from the plate of a frictional electric machine4 ,commutator4 ,an apparatus used on motors and dynamos and induction-coils for changing the direction of currents4 ,it is made in a variety of types1 but usually in the shape of insulated bars closely packed about an armature shaft4 ,commutator-bars4 ,the metallic segments of a dynamo or motor-commutator4 ,commutators1 ,quiet4 ,commutators that do not spark during the revolutions of the armature4 ,compass4 ,an apparatus for indicating the directive force of the earth upon the magnetic needle4 ,it consists of a case covered with glass1 in which a magnetized needle1 normally pointing to the north1 is balanced on a point at the centre4 ,under the needle a card is arranged on which the degrees or points of the compass are inscribed4 ,a valuable instrument in electrical work1 magnetism1 etc4 ,compass1 ,liquid4 ,a form of marine compass4 ,the needle is attached to a card or disk which floats in alcohol or other spirits1 so as to check undue oscillation4 ,compass1 ,mariners'4 ,a compass in which the needle is attached to a card that rotates in pointing to the north4 ,a mark1 called the 8lubber's mark10 is made upon the case1 and this is in line with the ship's keel1 so that a glance at the card will indicate the direction in which the ship is headed4 ,compass1 ,spirit4 ,a form of mariners' compass in which the bowl1 or case1 is sealed and filled with alcohol4 ,the compass-card works as a spindle1 and1 by a series of air compartments1 floats on the alcohol4 ,the friction of the pivot is thereby greatly diminished1 making the compass a very sensitive one4 ,compass1 ,standard4 ,a compass employed as a standard by which to compare other compasses4 ,condenser4 ,an appliance for storing up electro-static charges2 it is also called a static accumulator4 ,the telegraphic condenser consists of a box packed full of sheets of tin-foil having a sheet of paraffined paper or sheet-mica between every two sheets4 ,the alternate sheets of tin-foil are connected together1 and each set has its binding-post4 7,see also ,electrostatic ,accumulator47 ,condenser1 ,air4 7,see ,air-condenser47 ,condenser1 ,ayrton's4 7,see ,ayrton's ,condenser47 ,condenser-plate4 7,see ,plate1 ,condenser47 ,condenser1 ,sliding4 ,an apparatus in the form of a ,leyden-jar whose coatings can be slid past each other to diminish or increase the face area1 and also to diminish or increase the capacity of the condenser4 ,conductance4 ,the conducting power of a mass of material1 varying according to its shape and dimensions4 ,the cylindrical or round conductor is the best type for the conveyance of electric currents4 ,conduction4 ,the transmission of electricity through an immobile medium1 such as a wire1 or rod1 or a bar4 ,conductivity4 ,ability to conduct electric currents4 ,the conductivity of a wire is its power to conduct or transmit a current4 ,glass has no conductivity1 and it is therefore a non-conductor4 ,conductivity1 ,variable4 ,the change in the conducting or transmitting powers of metals and substances under different temperatures4 ,hot metal conducts an electric current better than cold4 ,a hot carbon-pencil in an arc-light conducts the current better than when the light is first started1 for as it warms up under the influence of the arc-flame the current passes more freely4 ,five minutes after the current is turned on the lamps in the circuit give a steady light1 and do not sputter as when they first start up4 ,conductor4 ,anything which permits the passage of electric current4 ,the term conductor is a relative one1 and1 excepting a vacuum1 there is probably no substance that has not some conductive power4 ,metals1 beginning with silver1 are the best conductors1 liquids next1 glass the worst4 ,the ether1 or air1 is a conductor of sound and electric vibratory disturbances1 but not in the same sense as the ground4 ,the air conducts frictional electricity1 while the ground acts as a conductor for the galvanic current1 or 8current electricity40 ,by this last term is meant electricity which flows continually1 instead of discharging all at once1 with an accompanying spark or flash4 ,conductor1 ,overhead4 ,overhead electric lines1 wires or cables1 for conducting current4 ,generally poles are erected for this purpose4 ,conductor1 ,prime4 ,a cylindrical or spherical body with no points or angles1 but rounded everywhere and generally of metal4 ,if made of other material1 such as wood1 glass1 or composition1 its entire surface is rendered conductive by being covered with sheet-metal1 such as tin-foil1 gold-leaf or tinsel1 applied to it with paste1 shellac1 or glue4 ,a prime conductor should be mounted on an insulated stand2 it is employed to collect and retain frictional electricity generated by a static machine4 ,conductor1 ,underground4 ,an insulated conductor which is placed under the surface of the earth1 passing through conduits4 ,connect4 ,the act of bringing two ends of wire together1 either temporarily or permanently4 ,bringing one end of a conductor into contact with another so as to establish an electric connection4 ,connector4 ,a sleeve1 with screws or other clamping device1 into which the ends of wires or rods may be passed and held securely4 ,a binding-post and spring-jack comes under this head4 ,contact4 ,the electrical union of two conductors1 whether temporary or permanent4 ,it may be established by touching the ends or terminals of a circuit through the agency of a push-button1 a telegraph-key1 an electric switch1 etc4 ,contact-breaker4 7,the same as ,circuit-breaker1 which see47 ,contact1 ,loose4 ,a contact formed by two or several surfaces imposed one upon another and held by their weight alone4 ,contact-point4 ,a point1 or stud1 often of silver or platinum1 arranged to come into touch with a contact-spring1 such as the vibrating armature of an electric bell4 ,contact-spring4 ,a spring connected at one end of a lead and arranged to press against another spring or plate1 so that a plug may be inserted between the contact-points4 ,controller4 ,the lever or handle on the switch-board of a resistance-coil1 by means of which electric current is let in or kept out of a circuit4 ,controlling ,force4 ,in galvanometers and similar instruments1 the force used to bring the needle or indicator back to zero4 ,converter4 ,an induction-coil used with the alternating current for changing the potential difference and inverting the available current4 ,high alternating voltage may be converted into lower direct-current voltage1 thereby increasing the amperage or current4 ,a converter consists of a core of thin iron sheets1 wound with a primary coil of fine insulated wire1 with many convolutions or turns4 ,also1 a secondary coil made up of coarse insulated wire with fewer convolutions4 ,the coil may be jacketed with iron to increase the permanence4 ,converter1 ,rotary4 ,a combined motor and dynamo whose function is to transform a current of high or low voltage 7,a-,c41 or ,d-,c47 into any other kind of current desired4 ,convolution4 ,the state of being convolved2 a turn1 wrap1 fold1 or whorl4 ,a clock-spring is a familiar example4 ,copper-bath4 ,a solution of sulphate of copper used in electro-plating1 electrotyping1 and copper-refining by electricity4 ,cord1 ,flexible4 ,a flexible-wire conductor made up of many strands of fine wire and properly insulated so that it may be easily twisted1 bent1 or wrapped4 ,flexible wire is used as the conductors for portable electric lights1 push-buttons1 medical coils1 etc4 ,core4 ,the iron mass 7generally located in the centre of a coil or helix7 which becomes highly magnetic when a current is flowing around it1 but which looses its magnetism immediately that the current ceases to flow4 ,a conductor or the conductors of an electric cable made up of a single strand or many strands laid together and twisted4 ,these may be of bare metal1 or each one insulated from the others4 ,core-disks4 ,disks of thin wire1 for building up armature-cores4 ,the usual form of a core is round or cylindrical4 ,a number of thin disks1 or laminations1 of iron strung upon the central shaft1 and pressed firmly together by the end-nuts or keys4 ,this arrangement gives a cylinder as a base on which to wind the insulated wire that forms a part of the armature4 ,core-disks1 ,pierced4 ,core-disks for an armature of a motor or dynamo1 which have been pierced or bored out around the periphery4 ,tubes of insulating material1 such as fibre1 rubber1 or paraffined paper1 are inserted in the holes and through these the windings of wire are carried4 ,the coils are thus imbedded in the solid mass of iron1 and are protected from eddy currents2 also they act to reduce the reluctance of the air-gaps4 ,this arrangement is very good1 from a mechanical point of view1 but in practice its use is confined to small motors only1 and dynamos generating under one hundred volts4 ,core-disks1 ,toothed4 ,core-disks of an armature or motor where notches are cut from the periphery4 ,when they are locked together1 to form the armature-core1 the coils of wire lie in the grooves formed by a number of the disks bound together4 ,this construction reduces the actual air-gaps and keeps the coils equally spaced4 ,core1 ,laminated4 ,the core of an armature1 an induction-coil1 a converter1 or any similar piece of apparatus1 which is made up of plates or disks1 insulated more or less perfectly from one another by means of mica or paraffined paper4 ,the object of laminations is to prevent the formation of ,foucault currents4 ,a core built up of disks is sometimes called a radially laminated core4 ,core1 ,ring4 ,a dynamo or motor armature-core which forms a complete ring4 ,core1 ,stranded4 ,the core of a cable1 or a conducting core made up of a number of separate wires or strands laid or twisted together4 ,core1 ,tubular4 ,tubes used as cores for electro-magnets1 and also to produce small magnetizing power4 ,tubular cores are nearly as efficient as solid ones in straight magnets1 because the principal reluctance is due to the air-path4 ,on increasing the current1 however1 the tubular core becomes less efficient4 ,coulomb4 ,the practical unit of electrical quantity4 ,it is the quantity passed by a current of one ampere intensity in one second4 ,couple4 ,the combination of two electrodes and a liquid1 the electrodes being immersed in the latter1 and being acted on differentially by the liquid4 ,this combination constitutes a source of electro-motive force1 and1 consequently of current1 and is called the galvanic or voltaic cell or battery4 ,couple1 ,astatic44 ,a term sometimes applied to astatic needles when working in pairs4 ,coupling4 ,the union of cells or generators constituting a battery2 the volume of current1 or electro-motive force1 is thereby increased4 ,c4 ,p4 ,an abbreviation for 8candle power02 also meaning 8chemically pure10 when speaking of chemicals4 ,crater4 ,the depression that forms in the positive carbon of a voltaic-arc4 ,creeping4 ,a phenomena met with in solution batteries4 ,the electrolyte creeps up the sides of the containing jar and evaporates1 leaving a deposit of salts4 ,still more solution creeps up through the salts until it gets clear to the top and runs over4 ,to prevent this the tops of the jars should be brushed with hot paraffine for a distance of two inches from the upper edge4 ,the salts will not form on paraffine4 ,oil is sometimes poured on the top of the battery solution1 but this affects the elements if it touches them1 and makes their surfaces non-conducting4 ,crucible1 ,electric4 ,a crucible for melting refractory substances1 or for reducing ores by means of the electric arc produced within it4 ,probably the result obtained is due more to current incandescence than to the action of the arc4 ,crystallization1 ,electric4 ,under proper conditions many substances and liquids take a crystalline form4 ,when such action is brought about by means of electricity the term electric crystallization may be applied to the phenomenon4 ,a solution of nitrate of silver1 when decomposed by a current1 will give crystals of metallic silver4 ,a solution of common salt or brine1 when electrically decomposed1 will produce sodium and chlorine4 ,the sodium appears at the leading-out electrode and readily unites with carbonic-acid gas1 which is injected into the apparatus4 ,the result of the combination is carbonate of soda1 one of the most important products of the alkali industry4 ,current1 ,alternating4 ,a current flowing alternately in opposite directions4 ,it is a succession of currents1 each of short duration and of direction opposite to that of its predecessor4 ,abbreviation1 ,a-,c4 ,current1 ,amperage4 ,the volume of electricity passing through any circuit per second1 the flow being uniform4 ,current1 ,constant4 ,an unvarying current4 ,a constant-current system is one in which the current is uniformly maintained--for example1 in electric light1 power1 and heat plants4 ,current1 ,continuous4 ,a current of one direction only1 or the reverse of an alternating current4 ,current1 ,direct4 ,a current of unvarying direction1 as distinguished from the alternating4 ,abbreviation1 ,d-,c4 ,current ,distribution1 ,uniform4 ,a steady current2 a current whose density in a conductor is always the same at all points4 ,current1 ,induced4 ,a current caused by electro-dynamic induction4 ,current1 ,low ,potential4 ,a current of low pressure4 ,a term applied to low electro-motive force4 ,current1 ,make-and-break4 ,a current which is continually broken or interrupted and started again4 ,the term is applied only where the interruptions occur in rapid succession1 as in the action of an induction-coil or pole-changer4 ,the alternating current4 ,current-meter4 ,an apparatus for indicating the strength of a current1 such as an ammeter4 ,current1 ,oscillating4 ,a current periodically alternating4 ,current1 ,periodic4 ,a current with periodically varying strength or direction4 ,a current alternating periodically4 ,current1 ,polarizing4 ,a current which causes polarization4 ,current-reverser4 ,a switch or other contrivance for reversing the direction of a current in a conductor4 ,current1 ,undulating4 ,a current whose direction is constant but whose strength is continuously varying4 ,currents1 ,eddy4 ,useless currents in an armature1 in the pole pieces1 and in the magnetic cores of dynamos and motors4 ,they are created by the high speed of the armature in its rotation1 or by other electric currents induced by the armature's motion through magnetic fields4 ,currents1 ,faradic4 ,induced currents4 ,they take their name from ,michael ,faraday1 the original investigator of the phenomena of electro-magnetic induction4 ,the secondary or induced electro-magnetic currents and their accompanying phenomena4 ,a series of alternating electro-static discharges from influence machine1 such as the ,holtz and ,wimshurst4 ,the simple and commonly understood ,faradic currents are those produced in the medical battery1 and used in medical therapeutics4 ,currents1 ,foucault4 ,a form of currents produced in revolving armature-cores2 sometimes called eddy currents4 ,they are useless4 ,currents1 ,harmonic4 ,currents which alternate periodically1 and vary harmonically4 ,currents which vibrate at certain pitches1 as1 for instance1 the currents in wireless telegraphy4 ,two instruments must be tuned to the same pitch in order to be responsive4 ,thus an instrument sending out waves of #gj1jjj vibrations cannot be recorded by one tuned much below or above the same number4 ,sound waves of sympathetic or harmonic vibrations4 ,currents1 ,positive4 7,see ,positive ,currents47 ,cut-in4 ,to electrically connect a piece of mechanism or a conductor with a circuit4 ,cut-out4 ,the reverse of the cut-in4 ,to remove from a circuit any conducting device4 ,the cut-out may be so arranged as to leave the circuit complete in some other way4 ,an appliance for removing a piece of apparatus from a circuit so that no more current shall pass through the former4 ,cut-out1 ,automatic4 ,a safety device for automatically cutting out a circuit to prevent accident or the burning-out of an apparatus1 due to an overload of current4 ,it is worked by an electro-magnet and spring4 ,an overload of current causes a magnet of high resistance to draw an armature towards it1 and this1 in turn1 releases the spring of the cut-out device4 ,sometimes a strip or wire of fusible metal is employed which is in circuit with a switch4 ,the excess of current fuses the metal1 and the broken circuit releases a spring-jack1 which1 in turn1 breaks the circuit4 ,cut-out1 ,safety4 ,a block of non-conducting material1 such as marble1 slate1 or porcelain1 carrying a safety-fuse or plugs4 ,in these is enclosed a piece of fusible wire1 which burns out or melts and breaks the circuit before the apparatus is damaged4 ,cut-out1 ,wedge4 ,a cut-out operated by a wedge1 such as a spring-jack or the plugs at the end of the flexible wires on the switch-boards of telephone exchanges4 ,d ,damper4 ,a frame of copper on which the wire in a galvanometer is sometimes coiled4 ,it acts to check the needle oscillations4 ,a brass or copper sheathing or tube placed between the primary and secondary coils of an induction-coil to cut off induction and diminish the current and potential of the secondary circuit4 ,when the tube is drawn out gradually the induction increases4 ,it is commonly used in medical coils to adjust their strength of action4 ,d-,c4 ,an abbreviation for direct current4 ,dead ,earth4 ,a fault in telegraph and telephone lines which consists in the ground-wire being improperly grounded1 or not fully connected with the earth4 ,dead ,turns4 ,a term applied to the ten to twenty per cent4 of the convolutions or turns of wire on an armature which are considered to be dead4 ,there are supposed to be about eighty per cent4 of the turns on an armature that are active in magnetizing the core2 the balance are outside the magnetic field and are termed dead1 although they are necessary to the production of electro-motive force4 ,dead ,wire4 ,a wire in the electric circuit through which no current is passing4 ,a disused or abandoned electric conductor1 such as a telegraph wire1 or a wire which may be in circuit1 but through which at the time of speaking no electrical action is taking place4 ,death1 ,electrical4 ,death resulting from an electric current passing through the animal body--electrocution2 accidental death by electric shock2 premeditated death through bringing the body in direct contact with conductors carrying high electro-motive force4 ,high electro-motive force is essential1 and the alternating current is most fatal4 ,decomposition1 ,electrolytic4 ,the decomposition or separation of a compound liquid into its constituents by electrolysis4 ,the liquid must be a conductor or electrolyte1 and the decomposition is carried on by means of electricity4 ,the conversion of two or more chemicals into a new compound or substance4 ,deflection4 ,in magnetism1 the movement of the needle out of the plane4 ,it is due to disturbance1 or to the needle's attraction towards a mass of iron or steel or another magnet4 ,demagnetization4 ,the removal of magnetism from a paramagnetic substance4 ,the process is principally in use for watches which have become magnetized by exposure to the magnetic field surrounding dynamos or motors4 ,density1 ,electric4 ,the relative quantity of electricity1 as a charge1 upon a unit area of surface4 ,it may be positive or negative4 ,surface density1 as the charge of a ,leyden-jar4 ,depolarization4 ,a term applied to the removal of permanent magnetism1 such as that from a horseshoe magnet1 a watch1 or a bar-magnet4 ,heat is the common depolarizer1 but counter electro-magnetic forces are employed also in the various forms of apparatus known as demagnetizers4 ,deposit1 ,electrolytic4 ,the metal or other substances precipitated by the action of a battery or other current-generator1 as in the plating processes4 ,detector4 ,a portable galvanometer1 by means of which a current and its approximate strength can be detected and measured4 ,diaphragm4 ,in telephones and microphones1 a disk of iron thrown into motion by sound-waves or by electric impulse4 ,it is usually a thin plate of japanned iron1 such as is used in the ferrotype photographic process for making tin-types4 ,dielectric4 ,any substance through which electrostatic induction is allowed to occur1 such as glass or rubber4 ,it is a non-conductor for all electric currents4 ,dielectric ,resistance4 ,the resistance a body offers to perforation or destruction by an electric discharge4 ,dimmer4 ,an adjustable choke or resistance coil used for regulating the intensity of electric incandescent lamps4 ,it is employed extensively in theatres for raising or lowering the brilliancy of lights4 ,dipping4 ,the process of cleaning articles by dipping them in acids or caustic soda1 preparatory to electro-plating4 ,simple immersion1 with or without current1 to put a blush of metal on a cleaned surface4 ,dipping-needle4 ,a magnetic needle mounted on a horizontal bearing so that it will dip vertically when excited by a current passing horizontally about it4 ,the ordinary compass-needle is mounted on a point1 and swings freely to the right or left only4 ,direct ,current4 7,see ,current1 ,direct47 ,discharge4 ,the eruptive discharge from a ,leyden-jar or accumulator of a volume of electricity stored within it4 ,the abstraction of a charge from a conductor by connecting it to the earth or to another conductor4 ,discharge1 ,disruptive4 ,the discharge of a static charge through a dielectric4 ,it involves the mechanical perforation of the dielectric4 ,disconnect4 ,to break an electric circuit or open it so as to stop the flow of current2 to remove a part of a circuit or a piece of apparatus from a circuit4 ,distillation1 ,electric4 ,the distilling of a liquid by the employment of electricity1 which1 by electrifying the liquid1 assists the effects of heat4 ,it is asserted that the process is accelerated by the electrification of the liquid or fluid1 but it must be a conductor liquid or electrolyte4 ,oil1 being a non-conductor1 is not affected by any electric current1 no matter what its specific gravity may be4 ,distributing ,centre4 ,the centre of distribution in a system having branch circuits1 such as the electric-light or telephone outlets from a main station4 ,door-opener1 ,electric4 ,a magnetic contrivance arranged in connection with a lock1 by means of which the latch is released by pressing a distant push-button4 ,this device is used in flats and apartment-houses for opening a door from any of the apartments in the house4 ,double ,filament ,lamp4 ,an incandescent lamp having two filaments1 one with a high capacity1 the other with a low one4 ,the high capacity may be from sixteen to fifty candle-power1 the other from one to five4 ,a turn of the bulb in its socket1 or the pulling of a string which operates a switch in the socket1 cuts out the current from the long filament and sends it through the shorter and finer one1 thus giving a weaker light4 ,these 8hy-lo0 lamps are useful as night lamps in halls1 bath-rooms1 or in sick-rooms1 where a low or weak light is required all night4 ,double ,pole-switch4 ,a cut-out that is arranged to cut out the circuit of both the negative and positive leads at the same time4 ,double-push4 ,a contact-push having two contacts and arranged so that pressure upon it opens one contact and closes the other4 ,double ,throw-switch4 ,a switch so arranged that it can be thrown into either one of two contacts2 a throw-over switch4 ,driving-pulley4 ,the broad-faced or channelled pulley on an armature shaft by means of which the power from a motor may be transmitted mechanically4 ,dry ,battery4 7,see ,battery1 ,dry47 ,duct4 ,the space in an underground conduit for a single wire or cable4 ,duplex ,wire4 ,an insulated conductor having two distinct wires twisted or laid together1 but properly insulated from each other4 ,dynamic ,electricity4 ,electricity in motion or flowing1 as distinguished from static or frictional electricity4 ,electricity of relatively low potential or electro-motive force in large quantity or amperage4 ,dynamo4 ,an apparatus consisting of a core and field-magnets1 properly wound with insulated wire1 which1 when put into operation by revolving the core or armature at high speed1 develops electric current2 a mechanical generator of electricity4 ,dynamo1 ,motor4 7,see ,motor-dynamo47 ,e ,earth4 ,the accidental grounding of a circuit is termed an 8earth40 ,earth-plate4 ,a plate buried in the ground to receive the ends of telegraph lines and other circuits1 and so give a ground connection4 ,copper plates are often used1 but in houses the ground is usually formed by attaching a wire to the gas or water pipes4 ,earth ,return4 ,the grounding of a wire in a circuit at both ends gives the circuit an earth return4 ,this method is commonly used in telegraph lines1 both in the wire and wireless systems4 ,eddy ,currents4 7,see ,currents1 ,eddy47 ,edison ,distributing-box4 ,a box used in the ,edison 8three-wire0 system1 from which the outlets pass to local circuits4 ,edison ,lalande ,cell4 ,a zinc-copper battery having a depolarizing coating of copper oxide on the copper element1 the couple being immersed in an electrolyte composed of potash or caustic soda4 ,ediswan4 ,a term applied to the incandescent lamps invented by ,edison and ,swan and used extensively in ,great ,britain4 ,also applied to other apparatus designed by the two inventors4 ,efficiency4 ,the relation of work done to the electrical energy absorbed4 ,the efficiency is not equal to the energy absorbed1 because it always takes more power to generate a current than is given back in actual efficiency4 ,this is due to mechanical friction and to the resistance of the air in a mechanism such as a dynamo when revolving at high speed4 ,efficiency1 ,electrical4 ,in a generator it is the total electrical energy produced1 both that wasted and that actually used in driving machinery or apparatus4 ,efflorescence4 ,the dry salts on a jar or vessel containing liquid that collects above the water or evaporation line4 ,this is due to creeping4 ,elasticity4 ,a property in some bodies and forces through which they recover their former figure1 shape1 or dimensions when the external pressure or stress is removed4 ,water has no elasticity4 ,air is very elastic2 steam has a great volume of elasticity2 while electricity is undoubtedly the most elastic of all in its motion through air1 water1 and other conducting mediums4 ,electric4 ,pertaining to electricity2 anything connected with the use of electricity4 ,it has been a much-abused word1 and its meaning has been garbled by the impostor1 the crook1 and the 8business thief0 in foisting on the public wares in which there was no electrical property whatever4 8,electric0 toothbrushes1 combs1 corsets1 belts1 and the like may contain a few bits of magnetized steel1 but they possess no active therapeutic value4 ,electrical ,engineer4 ,the profession of electrical engineer calls for the highest knowledge of electricity1 both theoretical and practical4 ,it embraces the designing and installation of all kinds of electrical apparatus4 ,electrician4 ,one versed in the practices and science of electricity2 a practical lineman or wireman4 ,electricity4 ,one of the hidden and mysterious powers of nature1 which man has brought under control to serve his ends1 and which manifests itself mainly through attraction and repulsion2 the most powerful and yet the most docile force known to man1 coming from nowhere and without form1 weight1 or color1 invisible and inaudible2 an energy which fills the universe and which is the active principle in heat1 light1 magnetism1 chemical affinity1 and mechanical motion4 ,electricity1 ,atmospheric4 ,the electric currents of the atmosphere1 variable but never absent4 ,they include lightning1 frictional electricity1 the ,aurora ,borealis1 the electric waves used in wireless telegraphy1 etc4 ,benjamin ,franklin indicated the method of drawing electricity from the clouds4 ,in ,june1 #ageb1 he flew a kite1 and by its moistened cord drew an electric current from the clouds so that sparks were visible on a brass key at the ground end of the cord4 ,later1 when a fine wire was substituted for the cord1 and a kite was flown in a thunder-storm1 the electric spark was vivid4 ,this experiment confirmed his hypothesis that lightning was identical with the disruptive discharges of electricity4 ,electricity1 ,latent4 ,the bound charge of static electricity4 ,electricity1 ,negative4 7,see ,negative ,electricity47 ,electricity1 ,positive4 7,see ,positive ,electricity47 ,electricity1 ,voltaic4 ,electricity of low potential difference and large current intensity4 ,electricity produced by a voltaic battery or dynamo as opposed to static electricity1 which is frictional and practically uncontrollable for commercial purposes4 ,electrification4 ,the process of imparting an electric charge to a surface4 ,the term is applied chiefly to electro-static phenomena4 ,electrization4 ,in electro-therapeutics1 the subjection of the human system to electric treatment4 ,an electric tonic imparted by electro-medical baths through the nervous system4 ,electro-chemistry4 ,that branch of science which treats of the relations between electric and chemical forces in their different reactions and compounds4 ,it deals with electro-plating1 electro-fusing1 electrolysis1 etc4 ,electro-culture4 ,the application of electricity to the cultivation of plants4 ,the use of electricity has been found very beneficial in some forms of plant growth4 ,electrocution4 ,capital punishment inflicted by electric current from a dynamo of high electro-motive force4 ,the current used is from #aejj to #bjjj volts1 and it acts to break down the tissues of the body4 ,electrode4 ,the terminals of an open electric circuit4 ,the terminals between which an electric arc is formed1 as in the arc-light4 ,the terminals of the conductors of an electric circuit immersed in an electrolytic solution1 such as the carbon and zinc of a battery4 ,electrolier4 ,a fixture for supporting electric lamps1 similar to a chandelier for gas or candles4 ,combination electroliers conduct both gas and electricity4 ,electrolysis4 ,the separation of a chemical compound into its constituted parts by the action of an electric current4 ,electrolyte4 ,a body susceptible of decomposition by the electric current4 ,it must be a fluid body and a conductor capable of diffusion as well as composite in its make-up4 ,an elemental body such as pure water cannot be an electrolyte4 ,electrolytic ,decomposition4 7,see ,decomposition1 ,electrolytic47 ,electrolytic ,deposit4 7,see ,deposit1 ,electrolytic47 ,electrolytic ,resistance4 7,see ,resistance1 ,electrolytic47 ,electro-magnetic ,induction4 7,see ,induction1 ,electro-,magnetic47 ,electro-magnetism4 ,magnetism created by electric current4 ,that branch of electrical science which treats of the magnetic relations of a field of force produced by a current4 ,electro-medical ,bath4 ,a bath provided with connections and electrodes for causing a current of electricity to pass through the body of the patient4 ,electrometer4 ,an instrument used for measuring static electricity4 ,electrometers are different from galvanometers1 since the latter depend on a current flowing through wires to create an action of the magnetic needles4 ,electro-motive ,force4 ,voltage4 ,it may be compared to the pressure of water in hydraulic systems4 ,the unit of electro-motive force is the volt4 ,electro-motor4 ,a term sometimes applied to a current-generator1 such as a small dynamo or voltaic battery4 ,electro-plating4 7,see ,plating1 ,electro47 ,electropoion ,fluid4 ,an acid depolarizing solution for use in zinc-carbon couples1 such as the 8,grenet0 and 8,daniell0 cells4 ,the bi-chromate-of-potash and sulphuric-acid solution for battery charges is a good example4 ,electroscope4 ,an apparatus for indicating the presence of an electric charge and whether the charge is negative or positive4 ,electrostatic ,accumulator4 ,two conducting surfaces1 separated by a dielectric and arranged for the opposite charging of the two surfaces4 ,a faradic or static machine for accumulating frictional electricity is an example4 ,electrostatics4 ,that division of electric science which treats of the phenomena of the electric charge1 or of electricity in repose1 as contrasted with electro-dynamics or electricity in motion4 ,electrotype4 ,the reproduction of a form of type or engraving by the copper electro-plating process4 ,the original is coated with plumbago and a wax impression taken of it4 ,the face of the negative is made conductive with plumbago or tin dust1 then suspended in a copper bath and connected with the current4 ,a film of copper will be deposited on the face of the wax impression4 ,element1 ,chemical4 ,original forms of matter that cannot be separated into simple constituents by any known process4 ,there are about seventy in all1 but as science advances the list is constantly being revised4 ,new elements are discovered and known ones are being resolved into simpler forms4 ,elements of ,battery ,cell4 7,see ,battery ,cell1 ,elements of47 ,emergency ,switch4 ,an auxiliary switch used as a controller on a car to reverse the action of the motor4 ,e-,m-,f4 ,an abbreviation for electro-motive force1 or voltage4 ,equalizer4 ,a term applied to a wire or bar in electro-magnetic mechanism for equalizing the pressure over a system4 ,exciter4 ,a generator used for exciting the field-magnets of a dynamo4 ,extension ,call-bell4 ,a bell connected with a telephone call-bell1 and located in another part of a building so as to give a distant summons4 ,external ,circuit4 7,see ,circuit1 ,external47 ,f ,f4 ,the sign commonly employed to designate ,fahrenheit4 ,thus1 #cj ,f4 means #cj degrees ,fahrenheit1 or #cj degrees above zero4 ,false ,magnetic ,poles4 7,see ,magnetic ,poles1 ,false47 ,faradic4 ,induced current produced from induction-coils and faradic machines4 ,a series of alternating electrostatic discharges1 as from a ,holtz influence machine4 ,faradic ,coil4 7,see ,coil1 ,faradic47 ,faradic ,currents4 7,see ,currents1 ,faradic47 ,faradic ,machine4 ,an apparatus designed to produce faradic current4 ,feed4 ,to furnish an electric current1 also spoken of in connection with the mechanism that moves the carbons in arc-lamps4 ,feeders1 or ,feed ,wires4 ,the conductors which convey electric currents at different points1 as in the trolley system4 ,the current is carried along in large cables strung on poles or laid underground1 and at proper distances lines are run in to feed the trolley wire4 ,field4 ,the space in the neighborhood of a dynamo or motor1 or other generator of electric current1 from which the apparatus takes its electricity1 both electrostatic and magnetic4 ,field-magnet4 7,see ,magnet1 ,field47 ,field of ,force4 ,the space in the neighborhood of an attracting or repelling mass or system4 ,there are two kinds of fields of force--the electro-magnetic and the static--from which the respective pieces of apparatus draw their store of electricity4 ,filament4 ,a long1 thin piece of solid substance4 ,it is generally as thin as a thread and flexible enough to be bent4 ,the hairlike element in an incandescent lamp which1 when heated by a current1 glows and radiates light4 ,filaments1 ,paper4 ,filaments for incandescent lamps made of carbonized paper4 ,they were the ones originally used in electric lamps1 but have been superseded by other substances easier to handle and more durable4 ,flow4 ,the volume of a current or stream escaping through a conductor1 such as a wire1 rod or pipe4 ,fluorescence4 ,the property of converting ether waves of one length into waves of another length4 ,the phenomenon is utilized in the production of ,geissler tubes and ,x-rays4 ,fluoroscope4 ,an apparatus for making examinations by means of the ,x-rays4 ,fluoroscopic ,screen4 ,a screen overspread with fluorescent material and employed for fluoroscopic examinations in connection with the ,x-rays4 ,force4 ,any change in the condition of matter with respect to motion or rest4 ,force is measured by the acceleration or change of motion that it can impart to a body of a unit mass in a unit of time4 ,for instance1 ten pounds pressure of steam will be indicated on a gauge made for measuring steam4 ,that pressure of steam1 with the proper volume behind it1 is capable of instantly producing a given part of a horse-power4 ,in the same way ten volts of electro-motive force is capable of pushing a current so as to exert a certain fraction of horse-power4 ,force1 ,electro-magnetic4 ,the force of attraction or repulsion exerted by the electro-magnet4 ,it is also known as electric force in the electro-magnetic system4 ,foucault ,currents4 7,see ,currents1 ,foucault47 ,fractional ,distillation4 ,the process of evaporating liquids by heat1 the most volatile being the first treated4 ,when that has been evaporated and distilled the heat is raised and the next most volatile liquid is evaporated1 and so on until all are evaporated1 leaving as a residue the solids that were a part of the original mass of liquid4 ,friction4 ,the effect of rubbing1 or the resistance which a moving body encounters when in contact with another body4 ,frictional ,electric ,machine4 ,an apparatus for the development or generation of high-tension frictional electricity4 ,frictional ,electricity4 ,electricity produced by the friction of dissimilar substances4 ,full ,load4 ,a complete load4 ,the greatest load a machine or secondary battery will carry permanently4 ,the full capacity of a motor running at its registered speed for its horse-power4 ,furnace1 ,electric4 ,a furnace in which the heat is produced by the electric arc4 ,it is the hottest furnace known to man1 and temperatures as high as #gejj ,fahrenheit have been developed in it4 ,fuse1 ,electric4 ,a fuse for igniting an explosive charge by electricity4 ,it is made by bringing the terminals or ends of wires close together1 so that they will spark when a current passes through them4 ,or a thin piece of highly resistant wire may be imbedded in an explosive and brought to white heat by current4 ,fuse-block4 ,an insulator having a safety-fuse made fast to it4 ,fuse-box4 ,a box containing a safety-fuse1 generally of porcelain1 enamelled iron1 or some other non-conductor4 ,fuse-links4 ,links composed of strips or plates of fusible metal serving the purpose of safety-fuses4 ,fusing-current4 ,a current of sufficient strength to cause the blowing or fusing of a metal4 ,g ,galvanic4 ,voltaic4 ,relating to current electricity or the electro-chemical relations of metals4 ,galvanic ,taste4 ,a salty taste in the mouth resulting from the passage of a light current from a voltaic battery1 the ends of the wires being held to either side of the tongue4 ,this has been called tasting electricity1 but it is really the decomposition of saliva on the surface of the tongue1 due to electrolysis or the passage of a current through a liquid4 ,galvanism4 ,the science of voltaic1 or current1 electricity4 ,galvanizing4 ,coating iron with a thin layer of zinc by immersing the object in the molten metal4 ,galvano-faradic4 ,in medical electricity the shocking-coil4 ,the application of the voltaic current1 induced by a secondary current 7induction-coil71 to any part of the body4 ,galvanometer4 ,an instrument for measuring current strength4 ,a magnetic needle influenced by the passage of a current through a wire or coil located near it4 ,galvanometer1 ,tangent4 ,a galvanometer provided with two magnetic needles differing in length1 the shorter one serving to measure tangents1 the longer being used for sine measurements of current strength4 ,galvanoscope4 ,an instrument1 generally of the galvanometer type1 used to ascertain whether a current is flowing or not4 ,generator4 ,an apparatus for maintaining an electric current1 such as a dynamo1 a faradic machine1 a battery1 etc4 ,german-silver4 ,an alloy of copper1 nickel1 and zinc4 ,used chiefly in resistance-coils1 either in the form of wire or in strips of the sheet-metal4 ,gold-bath4 ,a solution of gold used for depositing that metal in the electro-plating bath4 ,graphite4 ,a form of carbon4 ,it occurs in nature as a mineral1 and also is made artificially by the agency of electric heat4 ,gravity ,battery4 7,see ,battery1 ,gravity47 ,grounded ,circuit4 7,see ,circuit1 ,grounded47 ,ground-plate4 7,see ,plate1 ,ground47 ,ground-wire4 ,the contact of a conductor1 in an electric circuit1 with the earth4 ,it permits the escape of current if another ground-wire exists4 ,guard ,tube4 ,a tube inserted in a wooden or brick partition to insulate wires that may pass through it4 ,these tubes are made of porcelain1 gutta-percha1 compositions of a non-conducting nature1 and fibre4 ,gutta-percha4 ,caoutchouc treated with sulphur to harden it2 sometimes called vulcanized rubber or vulcanite4 ,it is a product obtained from tropical trees1 and when properly treated it is a valuable insulator in electrical work1 particularly in submarine cables1 since it offers great resistance to the destructive agencies of the ocean's depths4 ,h ,hand ,generator4 ,a magneto-generator driven by hand for the generation of light currents4 ,harmonic ,currents4 7,see ,currents1 ,harmonic47 ,harmonic ,receiver4 ,a receiver containing a vibrating reed acted on by an electro-magnet4 ,such a reed answers only to impulses tuned to its pitch4 ,heat4 ,one of the force agents of nature4 ,it is recognized in its effects through expansion1 fusion1 evaporation1 and generation of energy4 ,heat1 ,electric4 ,caused by a resisting medium1 such as carbon or ,german-silver1 when too much current is forced through it4 ,the principle of the car-warmers1 electric iron1 electric chafing-dish1 etc4 ,helix4 ,a coil of wire4 ,properly a coil of wire so wound as to follow the outlines of a screw without overlaying itself4 ,horse-power1 ,electric4 ,meaning the same as in mechanics4 ,referred to when speaking of the working capacity of a motor or the power required to drive a dynamo4 ,horse-power ,hour4 ,a unit or standard of electrical work theoretically equal to that accomplished by one horse during one hour4 ,horseshoe ,magnet4 7,see ,magnet1 ,horseshoe47 ,h-,p4 ,abbreviation for horse-power4 ,hydrometer4 ,an instrument employed to determine the amount of moisture in the atmosphere4 ,an instrument for determining through flotation the density or specific gravity of liquids and fluids4 ,it consists of a weighted glass bulb or hollow metallic cylinder with a long stem on which the ,baum scale is marked4 ,dropping it into a liquid it floats in a vertical position1 and sinks to a level consistent with the gravity of the fluid4 ,hydrometer1 ,baum4 ,an apparatus for testing the gravity of fluids4 ,the zero point corresponds to the specific gravity of water for liquids heavier than water4 ,a gauge1 valuable in testing acids and other fluids used in electrical work4 ,i ,igniter4 ,a mechanical hand apparatus1 in which a battery1 induction-coil1 and vibrator are located1 and whose spark1 jumping across a gap at the end of a rod1 ignites or lights a gas flame1 blasting-powder1 or dynamite4 ,i-,h-,p4 ,an abbreviation for indicated horse-power4 ,illuminating ,power4 ,any source of light as compared with a standard light--as1 for instance1 the illuminating power of an electric light reckoned in candle-power4 ,illumination4 ,a light given from any source and projected on a surface1 per unit of area1 directly or by reflection4 ,it is stated in terms--as1 for instance1 the candle-power of a lamp4 ,when speaking of an incandescent lamp we say it illuminates equal to four candle-power or it gives a light equal to sixteen candle-power4 ,immersion1 ,simple4 ,plating1 without the aid of a battery1 by simply immersing the metal in a solution of metallic salt4 ,impulse4 ,the motion produced by the sudden or momentary action of a force upon a body4 ,an electro-magnetic impulse is the action produced by the electro-magnetic waves in magnetizing a mass of soft iron and attracting to it another mass of iron or steel4 ,an electro-motive impulse is one where the force rises so high as to produce an impulsive discharge such as that from a ,leyden-jar4 ,incandescence1 ,electric4 ,the heating of a conductor to red or white heat by the passage of an electric current4 ,for example1 an incandescent lamp4 ,incandescent ,circuit4 7,see ,circuit1 ,incandescent47 ,incandescent ,lamp-filament4 7,see ,filament47 ,india-rubber4 7,see ,caoutchouc and ,gutta-percha47 ,indicator-card4 ,the card used in galvanoscopes1 volt and ampere meters1 and other instruments4 ,it is provided with a moving needle and is marked with a graduated scale4 ,induced4 ,caused by induction1 and not directly4 ,induced ,current4 7,see ,current1 ,induced47 ,inductance4 ,that capacity of a circuit which enables it to exercise induction and create lines of force4 ,inductance is the ratio between the total induction through a circuit to the current producing it4 ,induction1 ,back4 ,a demagnetizing force produced in a dynamo armature when a lead is given to the brushes4 ,when the brushes are so set the windings on the armature are virtually divided into two sets3 one a direct magnetizing set1 the other a cross-magnetizing set which exerts a demagnetizing action on the other set4 ,the position of the brushes on a dynamo or motor is indicated by their location1 and if changed back induction will be the result4 ,induction-coil4 7,see ,coil1 ,induction47 ,induction1 ,electro-magnetic4 ,when negative and positive currents are brought towards each other against their material repulsive tendencies the result is work1 or energy1 and the consequent energy increases the intensity of both currents temporarily4 ,the variations thus temporarily produced in the currents are examples of electro-magnetic induction4 ,a current is surrounded by lines of force4 ,the approach of two circuits--one negative1 the other positive--involves a change in the lines of force about the secondary circuit4 ,lines of force and current are so intimately connected that a change in one compels a change in the other4 ,therefore1 the induced current in the secondary may be attributed to the change in the field of force in which it lies4 ,the inner and outer coils of wire about the soft iron wire composing an induction-coil are the best and simplest examples of electro-magnetic induction4 ,induction1 ,magnetic4 ,the magnetization of iron or other paramagnetic substances by a magnetic field4 ,the magnetic influence of a bar excited under these conditions is shown by throwing iron filings upon it4 ,they will adhere to both ends 7that is at the negative and positive poles7 but not at the middle4 ,inductor4 ,a mass of iron in a current generator which is moved past a magnet-pole to increase the number of lines of force issuing therefrom4 ,it is generally laminated1 and is used in inductor dynamos and motors of the alternating-current type4 ,influence1 ,electric4 ,electric induction or influence which may be electro-static1 current1 or electro-magnetic4 ,influence ,machine4 ,a static electric machine worked by induction1 and used to build up charges of opposite nature on two separate prime-conductors4 ,installation4 ,the entire apparatus1 building1 and appurtenances of a technical or manufacturing plant or power-house4 ,an electric-light installation would mean the machinery1 street-lines1 lamps1 etc4 ,insulating ,joint4 ,used for the purpose of insulating a gas-pipe from an electric circuit4 ,insulating ,varnish4 ,a varnish composed of insulating material1 such as gums1 shellac1 or diluted rubber4 ,shellac dissolved in alcohol is perhaps the best4 ,it is easy to make and dries quickly1 making an insulating surface practical for almost every ordinary use4 ,insulation4 ,the dielectric or non-conducting materials which are used to prevent the leakage of electricity4 ,the covering for magnet wires1 and overhead conduits for power lines and electric lighting4 ,insulation1 ,oil4 ,any non-combustible oil may be employed as an insulator to prevent electrical leakage in induction-coils1 transformers1 and the like4 ,its principal advantage lies in its being in liquid form1 permitting of easy handling4 ,moreover1 if pierced by a spark from a coil1 it at once closes again without becoming ignited4 ,a solid insulator1 if pierced1 is permanently injured4 ,insulator4 ,any insulating substance or material to prevent the escape of current4 ,the knobs of porcelain or glass to which wires are made fast4 ,insulator1 ,porcelain4 ,an insulator made of porcelain and used to support a wire4 ,intensity4 ,the intensity or strength of a current is its amperage4 ,the strength of a magnetic field1 its power to attract or magnetize4 ,internal ,circuit4 7,see ,circuit1 ,internal47 ,internal ,resistance4 7,see ,resistance1 ,internal47 ,interrupter4 ,a circuit-breaker4 ,any device which breaks or interrupts a circuit4 ,it may be operated by hand or automatically4 ,the vibrator of an induction-coil4 ,the commutators of an armature4 ,isolated ,plant4 ,the system of supplying electric energy by independent generating dynamos for each house1 factory1 or traction line4 ,isolation1 ,electric4 ,a term applied to 8electric sunstroke40 ,exposure to powerful arc-light produces effects resembling those of sunstroke4 ,j ,joint4 ,the point where two or more electric conductors join4 ,joint ,resistance4 ,the united resistance offered by a number of resistances connected in parallel4 ,jumper4 ,a short circuit-shunt employed temporarily around an apparatus1 lamp1 or motor to cut out the current4 ,jump-spark4 ,a disruptive spark excited between two conducting surfaces in distinction from a spark excited by a rubbing contact4 ,k ,kaolin4 ,a form of earth or product of decomposed feldspar composed of silica and alumina4 ,it is serviceable in insulating compounds4 ,kathode4 ,the terminal of an electric circuit whence an electrolyzing current passes from a solution4 ,it is the terminal connected to the zinc pole of a battery or the article on which the electro-deposit is made4 ,key4 ,the arm of a telegraphic sounder by which the circuit is made and broken4 ,a pivoted lever with a finger-piece which1 when depressed1 makes contact between a point and a stationary contact on the base4 ,keyboard4 ,a board1 or table1 on which keys or switches are mounted4 ,a switchboard4 ,kilowatt4 ,a compound unit2 one thousand watts2 an electric-current measure4 ,abbreviation1 ,k-,w4 ,kilowatt ,hour4 ,the result in work equal to the expenditure or exertion of one kilowatt in one hour4 ,kinetoscope4 ,a photographic instrument invented by ,edison for obtaining the effect of a panorama or moving objects by the display of pictures in rapid succession--in familiar parlance1 8moving pictures40 ,knife ,switch4 ,a switch with a narrow and deep1 movable blade1 or bar of copper or brass1 which resembles the blade of a knife4 ,it is forced between two spring-clamps attached to one terminal so as to make perfect contact4 ,l ,laminated4 ,made up of thin plates1 as an armature-core4 ,laminated ,core4 7,see ,core1 ,laminated47 ,lamp-,arc4 ,a lamp in which the light is produced by a voltaic arc4 ,carbon electrodes are used1 and a special mechanism operates and regulates the space between the carbons so that a perfect arc may be maintained4 ,lamp1 ,incandescent4 ,a lamp in which the light is produced through heating a filament to whiteness by the electric current4 ,it consists of a glass bulb from which the air is exhausted and sealed1 after the filament is enclosed4 ,the ends of the filament are attached to platinum wires1 which in turn are made fast to the contact-plates at the head of the lamp1 so as to connect with the current4 ,lamp-socket4 ,a receptacle for an incandescent lamp4 ,it is generally made of brass and provided with a key-switch to turn the current on and off4 ,latent ,electricity4 7,see ,electricity1 ,latent47 ,lead4 7,not the metal47 ,an insulated conductor which leads to and from a source of power2 an insulated conductor to and from a telegraph or telephone instrument2 a circuit1 a battery1 or a station4 ,not a part of the line circuit4 ,that part of an electric light or power circuit which leads from the main to the lamps or motors4 ,leading-in ,wires4 ,the wires which lead into a building from an aerial circuit4 ,the wires which lead in and out from a lamp1 battery1 or instrument4 ,leak4 ,an escape of electrical energy through leakage4 ,this is more liable to occur in bare than in insulated wires4 ,the escape of current from bare trolley wires is much greater than that from the insulated conductors1 particularly in damp or rainy weather4 ,leclanch ,battery4 7,see ,battery1 ,leclanch47 ,leyden-jar4 ,a type of static condenser4 ,its usual form is a glass jar4 ,tin-foil is pasted about its inner and outer surfaces covering about half the wall4 ,the balance of the glass is painted with shellac or insulating varnish4 ,the mouth is closed with a cork stopper1 and through its centre a brass rod is passed which1 by a short chain1 is connected with the interior coating of the jar4 ,the top of the rod is provided with a brass knob or ball1 and from this last the spark is drawn4 ,lightning4 ,the electro-static discharge of clouds floating in the atmosphere4 ,it is the highest form of frictional electricity1 uncontrollable and very dangerous1 since the strength of a single flash may run into hundreds of thousands of volts4 ,lightning-arrester4 ,an apparatus for use with electric lines to carry off to earth any lightning discharges that such lines may pick up2 or it may be a form of fuse which burns out before the current can do any harm to the electrical mechanism4 ,line-insulator4 ,an insulator serving to support an aerial line4 ,lineman4 ,a workman whose business is the practical part of electrical construction in lines and conducting circuits4 ,link-fuse4 ,a plate of fusible metal in the shape of a link4 ,it is used as a safety-fuse in connection with copper terminals4 ,liquefaction1 ,electric4 ,the conversion of a solid into a liquid by the sole agency of electricity in its heat action upon the solid4 ,liquid ,resistance4 7,see ,resistance1 ,liquid47 ,lithanode4 ,a block of compressed lead binoxide1 with platinum connections1 for use in a storage battery4 ,litharge4 ,yellow-lead4 ,a chemical form of metallic lead4 ,load4 ,in a dynamo1 the amperes of current delivered by it under given conditions of speed1 etc4 ,local ,action4 ,in a battery1 the loss of current due to impurities in the zinc4 ,the currents may circulate in exceedingly minute circles1 but they waste zinc and chemicals and contribute nothing to the efficiency of the battery4 ,in a dynamo1 the loss of energy through the formation of eddy currents in its core or armature1 in the pole pieces1 or in other conducting bodies4 ,lodestone4 ,the scientific name is magnetite4 ,some samples possess polarity and attract iron2 these are called lodestones4 ,loop4 ,a portion of a circuit introduced in series into another circuit4 ,low ,frequency4 ,a frequency 7in current vibrations7 of comparatively few alternations per second4 ,low ,potential ,current4 7,see ,current1 ,low ,potential47 ,luminescence4 ,the power or properties some bodies have of giving out light when their molecular mass is excited4 ,for example1 phosphorus and radium4 ,luminous ,heat4 ,the radiation of heat by electric current1 which at the same time produces light4 ,for example1 the filament in an incandescent lamp4 ,luminous ,jar4 ,a ,leyden-jar whose coatings are of lozenge-shaped pieces of tin-foil between which are very short spaces4 ,when discharged1 sparks appear all over the surface where the small plates of metal nearly join4 ,m ,magnet4 ,a substance or metal having the power to attract iron and steel4 ,magnet-bar4 ,a magnet in the shape of a straight bar4 7,see ,bar-magnet47 ,magnet-coil4 ,a coil of insulated wire enclosing a core of soft iron through which a current of electricity is passed to magnetize the iron4 ,magnet-core4 ,an iron bar or mass of iron around which insulated wire is wound in order to create an electro-magnet4 ,magnet1 ,electric4 ,a magnet consisting of a bar of iron1 a bundle of iron wires1 or an iron tube1 around which a coil of insulated wire is wound4 ,when a current is passing through the coil its influence magnetizes the iron core1 but directly the current ceases the magnetism disappears4 ,magnet1 ,field4 ,the electro or permanent magnet in a dynamo or motor1 used to produce the area of electric energy4 ,magnet1 ,horseshoe4 ,a magnet of ,u shape with the poles or ends brought closer together than the other parts of the limbs4 ,a soft iron bar is placed across the poles when not in use1 as this serves to conserve the magnetism4 ,magnet1 ,permanent4 ,a term applied to a hard steel magnet possessing high retentivity1 or the power to hold its magnetism indefinitely4 ,magnet1 ,regulator4 ,an electro-magnet whose armature moves in such a manner as to automatically shift the commutator-brushes1 on a motor or dynamo1 to a position which insures the preservation of both brushes and commutator-bars1 and also produces a constant current4 ,magnet1 ,simple4 ,a magnet made of one piece of metal4 ,magnet ,wire4 ,insulated wire used for coils4 ,cotton or silk covered wire is the most serviceable for winding magnets4 ,magnetic ,adherence4 ,the tendency of a mass of iron to adhere to the poles of a magnet4 ,magnetic ,attraction and ,repulsion4 ,the attraction of a magnet for iron1 steel1 nickel1 and cobalt2 also of unlike poles of magnets for each other4 ,the like poles repel4 ,magnetic ,circuit-breakers4 ,an automatic switch1 or breaker1 whose action is excited and controlled by an electro-magnet4 ,magnetic ,concentration of ,ores4 ,the separation of iron and steel from their gangue by magnetic attraction4 ,it is applicable only when either the ore or the gangue is susceptible to the magnet4 ,magnetic ,control4 ,the control of a magnetic needle1 magnet1 index1 armature1 or other iron indicator in a galvanometer1 ammeter1 or voltmeter by a magnetic field4 ,magnetic ,dip4 ,the inclination from the horizontal position of a magnetic needle that is free to move in a vertical plane4 ,magnetic ,field1 ,rotary4 ,a magnetic field resulting from a rotary current4 ,magnetic ,field1 ,shifting4 ,a magnetic field which rotates4 ,its lines of magnetic force vary1 therefore1 in position4 ,magnetic ,field1 ,uniform4 ,a field of uniform strength in all portions1 such as the magnetic field of the earth4 ,magnetic ,force4 ,the power of attraction and repulsion exercised by a magnet2 the force of attraction and repulsion which a magnet exercises1 and which1 in its ultimate essence1 is unknown to science4 ,magnetic ,induction4 7,see ,induction1 ,magnetic47 ,magnetic ,needle4 ,a magnet having a cup or small depression at its centre1 and poised on a sharp pin of brass1 so as to be free to rotate4 ,its ,n pole points to the north1 and its ,s pole to the south4 ,a compass needle4 ,magnetic ,poles4 ,the terrestrial points towards which the north or south poles of the magnetic needle are attracted4 ,there are two poles3 the arctic1 or negative1 which attracts the positive or ,n pole of the magnetic needle2 and the antarctic1 or positive1 which attracts the ,s pole of the needle4 ,magnetic ,poles1 ,false4 ,it has been established that there are other poles on the earth that attract the magnetic needle when the latter is brought into their vicinity4 ,these are called false poles1 and are probably caused by large deposits of iron lying close to the surface of the earth4 ,magnetic ,separator4 ,an apparatus for separating magnetic substances from mixtures4 ,it is used chiefly in separating iron ore from earth and rock4 ,the mineral falls on an iron cylinder1 or drum1 magnetized by coils1 and adheres there1 while the earth or crushed rock drops below4 ,the particles of iron are afterwards removed by a scraper4 ,the machine is also used in separating iron filings and chips from brass1 copper1 or other metals1 the iron adhering to the magnet1 while the brass and other chips drop underneath4 ,magnetism4 ,the phenomena of attraction exerted by one body for another4 ,it has been commonly understood that magnetism and electricity are very closely related1 for without electricity magnetism could not exist1 although it has not been shown clearly that magnetism plays any part in the generation of electricity4 ,magnetism is the phenomenal force exerted by one body having two poles 7negative and positive7 for like bodies4 ,the horseshoe magnet or a bar of magnetized steel are the simplest examples of this4 ,if both ends of the horseshoe were positive they would not attract1 but would repel4 ,if both ends of a bar were positive they would repel2 but as one is negative1 or north-seeking1 and the other positive1 they exert lines of force which attract like bodies1 such as bits of iron1 nails1 and needles4 ,no energy is required to maintain magnetism in a tempered steel object1 such as the wiring about a soft iron core when it has been magnetized1 but electric current must flow about the soft iron core in order to render it a magnet4 ,so soon as the current ceases to flow the magnetism ceases and the soft iron fails to attract4 ,magnetism1 ,uniform4 ,magnetism that is uniform throughout a mass of magnetic steel1 or a core that is electro-magnetic4 ,magnetize4 ,to impart magnetic property to a substance capable of receiving it4 ,magnetizing-coil4 7,see ,coil1 ,magnetizing47 ,magneto ,call-bell4 ,a call-bell used principally in telephone systems1 and operated by a current from a magneto-electric generator4 ,the current is excited by turning the handle at the side of the telephone-box before removing the receiver from the hook4 ,magneto-generator4 ,a current-generator composed of a permanent magnet and a revolving armature which is rotated between the poles of the permanent magnet4 ,main ,circuit4 7,see ,circuit1 ,main47 ,main ,feeder4 ,the main wire in a district to which all the feeder wires are attached4 ,main ,switch4 ,the switch connected to the main wire of a line1 or the main-switch controlling a number of auxiliary switches4 ,mains1 ,electric4 ,the large conductors in a system of electric light or power distribution4 ,make and ,break1 ,automatic4 ,an apparatus which enables the armature of a magnet to make and break its circuit automatically4 ,make-and-break ,current4 7,see ,current1 ,make-and-break47 ,mercurial ,air-pump4 ,an air-pump operated by mercury to obtain a high vacuum1 and used extensively for exhausting incandescent-lamp bulbs4 ,mercury ,tube4 ,a glass tube sealed and containing mercury4 ,it is so arranged as to give out fluorescent light when shaken or agitated by an electric current4 ,for example1 the ,geissler tubes1 the ,cooper-,hewitt light1 ,crook's tubes1 etc4 ,metallic ,arc4 ,an arc which forms between metallic electrodes4 ,metallic ,circuit4 7,see ,circuit1 ,metallic47 ,metallic ,conductor4 ,a conductor composed of a metal4 ,metallic ,filament4 ,a metal wire used in an incandescent lamp--the filament4 ,metallic ,resistance4 7,see ,resistance1 ,metallic47 ,metallurgy4 ,the art of working metals4 ,electro-metallurgy applies to the processes wherein electricity plays the most important part4 ,mica4 ,a natural mineral of sheet form and translucent1 used extensively as an insulator in electrical equipment and mechanism4 ,mica1 ,moulded4 ,a composition composed of ground mica and shellac as a binder4 ,when heated and pressed into various shapes and forms1 it is a valuable insulator1 and is employed for hooks1 locks1 tubes1 sockets1 and the like4 ,micanite4 ,an insulating material made by cementing laminations of pure mica together and cementing them with shellac or other suitable non-conducting adhesives4 ,molecular ,adhesion4 ,the attraction of similar molecules for each other4 ,molecular ,attraction4 ,the attraction of molecules1 or physical affinity4 ,molecular ,resistance4 ,the resistance which a mass or electrolyte offers when contained in an insulated vessel and a current of electricity is passed through it4 ,molecule4 ,one of the invisible particles supposed to constitute matter of every kind2 the smallest particle of matter that can exist independently4 ,it is made up of atoms1 but an atom cannot exist alone4 ,morse ,receiver4 ,the receiving instrument once universally used in the ,morse system of telegraphy1 but now superseded by the sounder4 ,morse ,recorder4 ,an apparatus which automatically records on a ribbon of paper the dots and dashes of the ,morse telegraph alphabet4 ,morse ,sounder4 ,an electro-magnetic instrument designed to make a sharp1 clicking sound when its armature lever is drawn down by the attraction of the magnets4 ,morse ,system4 ,a telegraphic system invented by ,prof4 ,s4 ,f4 ,b4 ,morse1 in which1 by means of alternating makes and breaks of varying duration1 the dots and dashes of the ,morse alphabet are reproduced and received at a distance through the agency of wires and the electro-magnetic sounder4 ,motor1 ,electric4 ,a machine or apparatus for converting electric energy into mechanical kinetic energy or power4 ,the electrical energy is usually generated by a dynamo1 and distributed on conductors to motors located at various points4 ,electric motors are of two types--the ,a-,c41 or alternating current1 and the ,d-,c41 or direct current4 ,motor-car1 ,electric4 ,a self-propelling car driven by stored electricity4 ,motor-dynamo4 ,a motor driven by a dynamo whose armature is firmly attached or connected to that of the dynamo4 ,it is used for modifying a current4 ,if the dynamo generates an alternating current of high potential1 the motor converts it into a direct current of lower voltage but increased amperage4 ,motor-transformer4 ,a transformer which is operated by a motor4 ,a dynamo-electric machine provided with two armature windings1 one serving to receive current1 as a motor1 the other to deliver current1 as a generator1 to a secondary circuit4 ,n ,n4 ,an abbreviation for the north-seeking pole in a magnet4 ,natural ,magnet4 ,a loadstone4 ,needle4 ,a term applied to a bar-magnet poised horizontally upon a vertical point4 ,a magnetic needle1 or the magnet in a mariner's compass4 ,negative4 ,opposed to positive4 ,negative ,electricity4 ,the kind of electricity with which a piece of amber is charged by friction with flannel4 ,in a galvanic battery or cell the surface of the zinc is charged with negative electricity4 ,negative electricity1 according to the theory of some scientists1 really means a deficiency of electricity4 ,negative ,electrode4 ,the same as ,negative ,element4 ,negative ,element4 ,the plate not dissolved by the solution in a voltaic cell2 the one which is positively charged4 ,the carbon1 platinum1 or copper plate or pole in a battery4 ,negative ,feeder4 ,the conductor which connects the negative mains with the negative poles of a generator4 ,negative ,plate4 7,see ,plate1 ,negative47 ,negative ,pole4 7,see ,pole1 ,negative47 ,neutral ,feeder4 ,the same as ,neutral ,wire4 ,neutral ,wire4 ,the central wire in a three-wire system4 ,nickel-bath4 ,a bath for the electro-deposition of nickel4 ,non-arcing ,fuse4 ,a fuse-wire which is enclosed in a tube packed with asbestos or silk1 and which does not produce an arc when it fuses or blows out4 ,it is practically noiseless1 save for a slight hissing sound1 accompanied by a light puff of smoke1 which escapes from a venthole in the side of the tube4 ,non-conductor4 ,a material or substance offering very high resistance to the passage of the electric current4 ,non-magnetic ,steel4 ,alloys of iron incapable of being magnetized4 ,they are composed of iron and manganese1 nickel1 steel1 etc4 ,normal4 ,regular4 ,the average value of observed quantities4 ,normal current is a regular current without variations4 ,the force of a current at which a system is intended to work4 ,normal ,voltage4 ,the same as ,normal ,current4 ,north ,pole4 ,the north-seeking pole of a magnet4 ,the pole of a magnet which tends to point to the north1 and whence lines of force are assumed to issue on their course to the other pole of the magnet4 ,o ,o4 ,an abbreviation for ,ohm4 ,oersted's ,discovery4 ,oersted discovered1 in #ahbj1 that a magnetic needle tended to place itself at right angles to a current of electricity4 ,this fundamental principle is the basis of the galvanometer1 the dynamo1 and the motor4 ,ohm4 ,the practical unit of resistance4 ,a legal ohm is the resistance of a column of mercury one square millimetre in cross-sectional area and #ajf4bd centimetres in length4 ,ohm1 ,true4 ,the true ohm is the resistance of a column of mercury #ajf4bd centimetres long and one square millimetre in cross-sectional area4 ,an ohm may be measured by a ,no4 #cj copper wire nine feet and nine inches long4 ,if larger size wire is used the piece must be proportionately longer1 since the resistance is less4 ,ohmic ,resistance4 ,true resistance as distinguished from spurious resistance1 or counter electro-motive force4 7,see also ,resistance1 ,ohmic47 ,ohm's ,law4 ,the basic law which expresses the relations between current1 electro-motive force1 and resistance in active circuits4 ,it is formulated as follows3 #a4 ,the current strength is equal to the electro-motive force divided by the resistance4 #b4 ,the electro-motive force is equal to the current strength multiplied by the resistance4 #c4 ,the resistance is equal to the electro-motive force divided by the current strength4 ,o4 ,k4 ,a telegraphic signal meaning yes1 or all right4 ,it is supposed to be a misspelled form of all correct1 8,oll ,kerrekt40 ,okonite4 ,a form of insulation for wires and conductors2 a trade name applied to insulations1 and protected by copyright4 ,open ,arc4 ,a voltaic arc not enclosed4 ,open ,circuit4 7,see ,circuit1 ,open47 ,oscillating ,current4 7,see ,current1 ,oscillating47 ,outlet4 ,that part of an electrolier or electric light fixture out of which the wires are led for attachment to incandescent light sockets4 ,outside ,wiring4 ,the wiring for an electric circuit which is located outside a building or other structure4 ,overhead ,feeders4 ,the same as overhead conductors4 ,overhead ,trolley4 ,the system in which the current for the propulsion of trolley-cars is taken from overhead feeders or wires4 ,overhead ,trolley-wire4 ,a naked1 hard copper wire drawn at high tension1 and suspended over or at the side of a car-track1 and from which the trolley-wheel takes its current4 ,overload4 ,in an electric motor1 an excess of mechanical load prevents economical working1 causing the armature to revolve slowly and the wiring to heat4 ,in this case heating implies waste of energy4 ,overload ,switch4 ,a switch which operates automatically to open a circuit in line with a motor1 and so save the motor from overheating or burning in the event of an overload4 ,p ,paper ,cable4 ,a cable insulated with waxed or paraffined paper4 ,paraffine4 ,a residuum of petroleum oil1 valuable as an insulating medium in electrical work4 ,a hydro-carbon composition of the highest resistance known4 ,it is extensively used in condensers and other electrical apparatus as a dielectric and insulator4 ,parallel ,distribution4 ,a distributing system for electricity wherein the receptive contrivances are adjusted between every two of a number of parallel conductors running to the limits of the system4 ,when two or more conductors connect two mains of comparatively large size and low resistance1 they are said to be in parallel or in multiple4 ,this order is easily pictured by imagining the mains to be the sides of a ladder and the conductors the rungs4 ,in the latter the lamps are placed4 ,it follows that the current flows from one main to the other through the conductors and lamps4 ,paramagnetic4 ,substances which have magnetic properties1 or those which are attracted by magnetic bodies4 ,a paramagnetic substance has high multiplying power for lines of force1 therefore a bar of iron which is a paramagnetic substance of the highest quality becomes magnetic when placed within a circle of electric lines of force4 ,the first example of paramagnetic substance brought to the attention of man was the lodestone1 from which the ancient mariners fashioned their crude compass needles4 ,p-,c4 ,an abbreviation for porous cup4 ,pear ,push4 ,a push-button enclosed in a handle having the shape of a pear4 ,it is generally attached to the end of a flexible wire cord4 ,periodic ,current4 7,see ,current1 ,periodic47 ,permanency1 ,electric4 ,the power of conductors to retain their conductivity unaffected by the lapse of time4 ,permanent ,magnet4 7,see ,magnet1 ,permanent47 ,phase4 ,one complete oscillation4 ,the interval elapsing from the time a particle moves through the middle point of its course to the instant when the phase is to be stated4 ,simple harmonic motion4 ,oscillation4 ',phone4 ,an abbreviation for the word ,telephone4 ,phonograph4 ,an apparatus for reproducing sound4 ,it is vibratory and not electric in its action1 except that the mechanism may be driven by electricity4 ,it consists of a rotating cylinder of a waxlike material and a glass diaphragm carrying a needle-point that lightly touches the surface of the waxen cylinder4 ,if the diaphragm is agitated the needle vibrates1 making indentations in the surface of the wax4 ,if the needle is set back and the cylinder rotated so as to carry the point over the indentations1 the sound is given back through the vibration of the diaphragm4 ,pickle4 ,an acid solution used to cleanse metallic surfaces preparatory to electro-plating4 ,pilot ,wires4 ,wires brought from distant parts of electric light and power mains1 and leading to voltmeters at a central station4 ,through their agency the potential energy of every part of the system may be measured4 ,pith-balls4 ,balls made from the pith of light wood1 such as elder4 ,they are used in the construction of electroscopes and for other experiments in static electricity4 ,plant4 ,the apparatus for generating electric current1 including engines1 boilers1 dynamos1 mains1 and subsidiary apparatus4 ,plate1 ,condenser4 ,in a static apparatus1 the condenser having a flat piece of glass for a dielectric4 ,it is mounted on an axle so that it may be revolved4 ,plate1 ,ground4 ,in a lightning-arrester1 the plate connected to the earth or ground wire4 ,plate1 ,negative4 ,in a voltaic battery1 the plate which is unattacked by the fluid4 ,it is made of carbon1 platinum1 or copper4 ,plate1 ,positive4 7,see ,positive ,plate47 ,plating-bath4 ,a vessel of solution for the deposition of metal by electrolysis4 ,used in electro-plating4 ,plating1 ,electro4 ,the process of depositing metal on surfaces of metals or other substances by the aid of an electrolyte and the electric current4 ,platinum ,fuse4 ,a slender wire of platinum roused to incandescence by current1 and used to explode a charge of powder or other combustible substance4 ,plug4 ,a piece of metal1 with a handle1 used to make electric connections by being inserted between two slightly separated plates or blocks of metal4 ,a wedge of metal1 slightly tapered1 and used to thrust between two conductors to close or complete a circuit4 ,plumbago4 ,soft1 lustrous graphite2 a native form of carbon sometimes chemically purified4 ,it is used chiefly in electrotyping for dusting the wax moulds to make the surface an electric conductor4 ,plunge-battery4 7,see ,battery1 ,plunge47 ,polar4 ,pertaining to one of the poles of a magnet4 ,polarity4 ,the disposition in a body to place its axis in a particular direction when influenced by magnetism4 ,for example1 the attraction and repulsion at the opposite ends of a magnet4 ,the ,n and ,s seeking poles of a compass needle is the simplest example4 ,polarity1 ,electric4 ,the disposition in a paramagnetic body to be influenced by electric waves and lines of force4 ,the otherwise non-magnetic body or mass becomes magnetic to attract or repulse when influenced by electricity1 but ceases to retain the phenomena after the electric influence is removed4 ,a piece of soft iron wire1 a nail1 or a short rod of iron will become electro-polarized when a current of electricity is sent through a coil of insulated wire so wound that one end will be ,n the other ,s4 ,so soon as the circuit is broken the polarity ceases4 ,polarization4 ,the depriving of a voltaic cell of its proper electro-motive force4 ,this may be brought about through the solution becoming spent1 or in the event of the acid being saturated with zinc1 and so failing to act on the metallic zinc4 ,counter electro-motive force due to the accumulation of hydrogen on the negative plate4 ,polarizing-current4 7,see ,current1 ,polarizing47 ,polar ,surface4 ,the surface of a magnetic substance through which the magnetic flux passes in or out4 ,pole-changer4 ,an automatic1 oscillating switch or contact-breaker which reverses the direction of the current4 ,pole1 ,negative4 ,the ,s pole in a magnet or compass needle4 ,pole1 ,positive4 7,see ,positive ,pole47 ,pole-switch1 ,single4 ,a switch designed to open or close one lead only4 ,poles4 ,the terminals of an open electric circuit at which there necessarily exists a potential difference4 ,the terminals of an open magnetic circuit1 or the ends of a magnetized mass of iron4 ,porcelain4 ,a fine variety of earthenware1 valuable for insulators and insulating purposes4 ,porosity4 ,the state or property of having small interstices or holes4 ,the opposite of density4 ,porous ,cup or ,cell4 ,a cup or cell made of pipe-clay or of unglazed earthenware through which a current of electricity can pass when wet or in a liquid4 ,porous cups are used in cells and batteries to keep two liquids apart1 and yet permit electrolysis and electrolytic conduction4 ,positive ,currents4 ,currents which deflect the needle to the left4 ,positive ,electricity4 ,the current that flows from the active element1 the zinc in a battery1 to the carbon4 ,the negative electricity flows from the carbon to the zinc4 ,positive ,electrode4 ,the electrode which is connected with the positive pole of a source of electric energy4 ,positive ,feeders4 ,the lead or wire in a set of feeders which is connected to the positive terminal of the generator4 ,positive ,plate4 ,in a voltaic cell1 the plate which is acted upon and corroded4 ,the current from the positive plate is negative electricity4 ,positive ,pole4 ,the ,n pole in a magnet or magnetic needle4 ,so called because it seeks the north or negative pole of the earth4 ,positive ,wire1 or ,conductor4 ,the wire1 or conductor1 connected with the positive pole of any apparatus which produces electro-motive force4 ,potential1 ,electric4 ,the power to perform electric work4 ,potential ,energy4 ,capacity for doing work4 ,potential energy when liberated becomes actual energy for the performance of work4 ,power-generator4 ,any source from which power is generated4 ,power-house4 ,a station in which the plant of an electric power system is operated and the current distributed to local or long-distance points4 ,power-houses are either primary or secondary stations4 ,in the primary station the current is generated directly by the aid of mechanical power1 either the steam-engine or the steam-turbine4 ,the secondary station1 or sub-station1 is located at a distance from the main power-house1 and has no mechanical means of generating current4 ,the current1 usually of high alternating voltage1 is supplied to the sub-station from the main power-house2 and by means of transformers and converters1 the high-voltage current is transformed into one of lower ,e-,m-,f and higher amperage1 for distribution over local lines4 ,power-unit4 ,the unit of electric power is the volt-ampere or watt4 ,pressure1 ,electric4 ,electro-motive force or voltage4 ,primary4 ,a term used to designate the induction-coil in an induction-apparatus or transformer4 ,it is an abbreviation for primary coil4 ,primary ,battery4 7,see ,battery1 ,primary47 ,prime ,conductor4 7,see ,conductor1 ,prime47 ,push-button4 ,a switch for closing a circuit by means of pressure applied to a button4 ,the button is provided with a spring1 so that when pushed in and released it flies back1 reopening the circuit4 ,pyrogravure4 ,a process of engraving by the use of platinum points heated to redness by the electric current4 ,q ,q4 ,abbreviation or symbol for electric quantity4 ,quadrant4 ,the quarter of a circle or of its circumference4 ,quadruple ,circuit4 7,see ,circuit1 ,quadruple47 ,quantity4 ,the term is applied to express arrangements of electrical connections for giving the largest possible amount of current4 ,quantity1 ,electro-magnetic4 ,the electro-magnetic current measured by its intensity for a second of time4 ,quick-break4 ,a break affected in an electric current by the employment of a quick-break switch4 ,quickening4 ,the amalgamating of the surface of a metallic object before electro-plating it with silver4 ,this secures better adhesion of the deposit1 and is done by dipping the article into a solution of mercurial salts--one part of mercuric nitrate to one hundred parts of water4 ,r ,radiant ,energy4 ,energy existing in the luminiferous ether and exercised in wave transmission1 creating light or sound4 ,radium possesses the highest form of radiant energy4 ,radiate4 ,to emit or send out in direct lines from a point or points1 as radiating heat1 light1 or sound4 ,the radiations are sent out in all directions from a central point1 just as a stone thrown in a pond of still water will radiate waves or ripples from the central point4 ,radiation4 ,the travelling or motion of ether waves through space4 ,radiator1 ,electric4 ,a series of plates or wire-coils heated by current4 ,they radiate heat and so warm the surrounding air4 ,radiograph4 ,a photographic picture taken by the ,x-ray process4 ,receiver4 ,in telephony or telegraphy1 an instrument for receiving the message as distinguished from the instrument sending or transmitting the message4 ,the telephone piece held to the ear is the receiver4 ,receiving ,end4 ,the end of a line where the operative currents are received1 as opposed to the end at which they are transmitted4 ,receptacle4 ,a device for the installation of an attachment or extension plug4 ,used in connection with electric-lighting circuits4 ,recoil ,kick4 ,reaction resulting from a disruptive discharge4 ,recorder4 ,in telegraphy1 the receiving apparatus for recording the dot-and-dash signals on a strip or tape of paper4 ,reduction4 ,the influence exerted without apparent communication by a magnetic field or a charged mass upon neighboring bodies4 ,the induction-coil is a simple example of this force4 ,the current passes through the primary or inner coil about a core of soft iron1 and in doing so it develops lines of force in the secondary or outer coils1 although no current is flowing directly through them from a battery or dynamo4 ,reduction ,gear4 ,a gear which acts to reduce a speed below that of a motor in full motion without lessening its motive force4 ,refract4 ,to break the natural course of light in an elastic medium4 ,the rays of light1 as they pass from a rare into a dense medium1 are refracted4 ,register1 ,electric4 ,an apparatus for registering and recording the movements of employs about a building4 ,press-buttons are arranged throughout the building1 and when a man passes a station he presses the button1 and the time is recorded by the apparatus4 ,regulator ,magnet4 7,see ,magnet1 ,regulator47 ,relay4 ,a telegraphic or telephonic receiving instrument which opens and closes a local circuit through movements caused by the impulses of currents received4 ,the relay battery may be very delicate so as to work with weak currents4 ,the function of the relay is to open and close circuits for the admission of a new current to push on the sound or vibration to a more distant point4 ,the main battery may be of any desired power4 ,relay ,connection4 ,a connection used in telegraphy1 including a local battery1 with a short circuit1 normally open1 but closed at will by a switch and sounder1 or other appliance4 ,a very weak current will work the apparatus4 ,relay1 ,ordinary4 ,a relay that is not polarized4 ,relay1 ,repeating4 ,in telegraphy1 a relay for repeating the signals through a second line4 ,reluctance4 ,magnetic resistance4 ,repeater4 ,in telegraphy1 an instrument for repeating the signals through a second line4 ,it is virtually a relay which is controlled by the sender1 and which1 in turn1 operates the rest of the main line4 ,it is usually located at about the middle of the total distance covered4 ,repeating-station4 ,a telegraph station located on a long line1 and occupying a position at the juncture of the sections into which the line is divided4 ,the currents received through one section are repeated into the other sections by means of a repeater4 ,repulsion1 ,electric4 ,the tendency which exists between two bodies charged alike to mutually repel each other4 ,residual ,charge4 7,see ,charge1 ,residual47 ,resilience4 ,the power to spring back to a former position4 ,electricity is resilient1 although its elasticity cannot be measured accurately4 ,resin4 ,a solid inflammable substance or gum1 and a good non-conductor in electrical work4 ,it is the product obtained by distilling the sap of the pitch-pine4 ,the name is also applied to the product of distilling the sap of other trees4 ,common resin1 shellac1 lac1 ,dragon's-blood1 and other substances of a similar nature are resins4 ,they are all dielectrics1 and the source of negative frictional electricity when rubbed with cotton1 wool1 flannel1 silk1 or fur4 ,resistance4 ,that quality of an electric conductor in virtue of which it opposes the passage of an electric current1 causing the disappearance or modification of electro-motive force1 and converting electric energy into heat energy4 ,resistance-box4 ,a box filled with resistance-coils connected in series and provided with a switch1 so that any number of the coils may be cut out4 ,resistance1 ,carbon4 ,a resistance composed of carbon as a substitute for a coil of wire4 ,carbon rods are placed close together having an air space between them1 with alternate ends connected4 ,piles may be built up of carbon plates1 whose resistance is made to vary by changing the pressure4 ,resistance-coil4 ,a coil of wire metal or other substances having the power to resist a current of electricity4 ,a coil of wire used to measure an unknown resistance by virtue of its own known resistance4 7,see also ,coil1 ,resistance47 ,resistance1 ,dielectric4 7,see ,dielectric ,resistance47 ,resistance1 ,electrolytic4 ,the resistance of an electrolyte to the passage of a current decomposing it4 ,it is almost entirely due to electrolysis1 and is intensified by counter-electro-motive force4 ,when a current of a voltage so low as not to decompose an electrolyte is passed through the latter1 the resistance appears very high and sometimes almost infinite4 ,if the voltage is increased until the electrolyte is decomposed the resistance suddenly drops to a point lower than the true resistance4 ,resistance1 ,internal4 ,the resistance of a battery1 or generator1 in an electric circuit as distinguished from the resistance of the rest of the circuit4 ,resistance1 ,liquid4 ,a liquid of varying specific gravity used to create resistance to the passage of the electric current4 ,resistance effected by the use of liquid through which a current must pass to complete a circuit4 ,resistance1 ,metallic4 ,the resistance of metals to the electric current4 ,german-silver resistance as distinguished from that of water1 carbon1 or other substances4 ,resistance1 ,ohmic4 ,true resistance measured in ohms as distinguished from counter electro-motive force4 7,see also ,ohmic ,resistance47 ,resistance1 ,spurious4 ,the counter-electro-motive force4 ,in its effect of opposing a current and in resisting its formation it differs from true resistance4 ,true resistance diminishes current strength1 absorbs energy1 and develops heat4 ,spurious resistance opposes and diminishes a current without absorption of energy or production of heat4 ,resistance1 ,standard4 ,a known resistance employed to determine unknown resistances by comparison4 ,resistance1 ,true4 ,the true resistance measured in ohms as distinguished from counter-electro-motive force4 ,resonator1 ,electric4 ,a small1 open electric circuit with ends nearly touching4 ,when exposed to electric resonance1 or to a sympathetic electric oscillating discharge1 a spark passes across the gap4 ,the spark is due to inductance in the resonator4 ,retentiveness4 ,that property which enables steel to retain its magnetism4 ,return4 ,a line or conductor which carries current back to its starting-point after it has traversed a circuit4 ,the best definition of a return is a circuit on which no new apparatus is installed4 ,return-circuit4 7,see ,circuit1 ,return47 ,return-circuit1 ,railway4 ,a grounded circuit used in trolley systems for ground returns through the tracks1 they being joined by links or flexible wires so as to form perfect conductors4 ,it is the negative side of the system1 the positive being in the overhead or underground feed-wire or rail4 ,reversibility4 ,the principle by which any form of generator for producing a given form of energy may be reversed to absorb energy4 ,the dynamo of the reversible type driven to generate current may be reversed and will develop power if a current is run through it4 ,rheostat4 ,an adjustable resistance4 ,an apparatus for changing the resistance1 without opening the circuit1 by throwing a switch-bar across contact points4 ,rod ,clamp4 ,a clamp used in the lamp rod of an arc-light to hold the carbon4 ,rntgen ,effects4 ,phenomena obtained by the use of the ,x or ,rntgen rays4 ,rntgen-ray ,screen4 ,a screen whose surface is covered with fluorescent material for the purpose of receiving and displaying the ,rntgen image4 ,rntgen ,rays4 ,a peculiar form of light radiation discovered by ,rntgen1 and which is emitted from that portion of a high vacuum tube upon which the kathode rays fall4 ,rotary ,magnetic ,field4 7,see ,magnetic ,field1 ,rotary47 ,ruhmkorff ,coil4 7,see ,coil1 ,ruhmkorff47 ,s ,safety ,fuse4 ,a device to prevent overheating of any portion of a circuit by excessive current4 ,it generally consists of a strip of fusible metal which1 if the current attains too great strength1 melts and opens the circuit4 ,salt4 ,a chemical compound containing two atoms or radicals which saturate each other4 ,one is electro-positive1 the other electro-negative4 ,salts are decomposed by electrolysis1 and in separating they combine to form new molecules4 ,saturated4 ,a liquid is said to be saturated when it has dissolved all the salts it will take up4 ,search-light4 ,an apparatus for producing a powerful beam of light and projecting it in any desired direction4 ,secondary4 ,a term applied to the secondary coil of a transformer or induction-coil4 ,secondary ,battery4 7,see ,battery1 ,secondary47 ,secondary ,plates4 ,the plates of a secondary battery or storage-battery4 ,when charged1 the negative plate should be brown or deep reddish in color1 and the positive slate-colored4 ,self-excited4 ,electrified by its own current4 ,self-winding ,clock4 ,a clock which automatically winds itself by electricity4 ,it is operated by a small electro-magnetic motor which obtains its current from an outside source4 ,semaphore1 ,electric4 ,an apparatus for exhibiting signals4 ,used in the railway block system4 ,series4 ,arranged in succession4 ,when incandescent lamps are installed so that the current goes in and out of one lamp1 and so on to the next and the succeeding ones1 they are said to be arranged in series4 ,it takes high ,e-,m-,f and current1 or amperage1 to operate such lamps4 ,series batteries are arranged with the zinc pole of one connected to the carbon pole of the next4 ,series ,arc ,cut-out4 ,a device by means of which a short circuit is established past a defective lamp1 thereby securing the undisturbed operation of all the other lamps in the circuit4 ,series ,distribution4 ,a distribution of electricity in which the receptive devices are arranged in successive order upon one conductor1 extending the entire length of the circuit4 ,series ,dynamo4 ,a series-wound dynamo4 ,series ,incandescent ,lamp4 ,an incandescent lamp adapted for service in a series circuit4 ,series ,motor4 ,a motor adapted for use in a series circuit2 a motor whose field-coil winding is in series with the armature4 ,series1 ,multiple4 ,an arrangement of electric apparatus in which the parts are grouped in sets in parallel1 and these sets are connected in series4 ,series ,winding4 ,a method of winding a generator or motor in which one of the commutator brush connections is joined to the field-magnet winding4 ,the other end of the magnet winding is connected with the outer circuit1 and the second armature brush is coupled with the remaining terminal of the outer circuit4 ,service ,wires4 ,wires connected to the supply circuit or main wires1 and which run into buildings to supply current for heat1 light1 and power4 ,shellac4 ,a resin gum1 gathered from certain ,asiatic trees4 ,it is soluble in alcohol1 and is used extensively in electric work as an insulator4 ,shifting ,magnetic ,field4 7,see ,magnetic ,field1 ,shifting47 ,shock1 ,electric4 ,the effect upon the animal system of the discharge of an electric current of high potential difference4 ,the voltage is the main element in a shock4 ,shoe4 ,as applied to electric railways1 the casting employed to bear on the third rail to take in positive current and electro-motive force4 ,the cast-iron plate of an electric break1 which1 by magnetism1 adheres to another iron surface4 ,short ,circuit4 7,see ,circuit1 ,short47 ,shunt-box4 ,a resistance-box designed for use as a galvanometer shunt4 ,the box contains a series of resistance-coils which can be plugged in or out as required4 ,shunt-winding4 ,a dynamo or motor is shunt-wound when the field-magnet winding is parallel with the winding of the armature4 ,silver-bath4 ,a solution of a salt of silver used in the electro-plating process4 ,silver-plating4 ,depositing a coating of silver on a metallic surface by the acid of electro-metallurgy4 ,silver-stripping ,bath4 ,an acid solution used for stripping silver from a metallic surface before re-plating it4 ,simple ,circuit4 7,see ,circuit1 ,simple47 ,simple ,immersion4 7,see ,immersion1 ,simple47 ,simple ,magnet4 7,see ,magnet1 ,simple47 ,single-trolley ,system4 ,a trolley system employing only one overhead conducting wire1 the track and ground serving as the return-circuit4 ,single-wound ,wire4 ,wire insulated by winding or overlaying with but a single layer of material4 ,sliding-condenser4 7,see ,condenser1 ,sliding47 ,snap-switch4 ,a switch so contrived as to give a quick break4 ,a spiral spring is fastened between the handle and arm in such a manner that when the handle is drawn back the spring operates and quickly draws a knife-bar from the keeper1 breaking the contact instantly and without the formation of an arc4 ,socket4 ,a receptacle for an incandescent lamp or plug4 ,solenoid4 ,a helical coil of wire of uniform diameter or cylindrical in shape4 ,it is useful in experiments with electro-magnetism4 ,solution4 ,a fluid composed of dissolved salts2 a mixture of liquids and fluids4 ,sound ,waves4 ,waves produced in an elastic medium by sonorous vibration1 as in wireless telegraphy4 ,sounder4 ,in telegraphy1 the instrument operated on by the key at the other end of a line4 ,various devices are employed to increase their resonance--as1 for instance1 hollow boxes4 ,sounders are generally placed on local circuits and are actuated by relays4 ,sounder1 ,repeating4 ,a telegraphic instrument which repeats a message into another circuit4 ,s-,p4 ,an abbreviation for single pole4 ,spark-arrester4 ,a screen of wire-netting fitted around the carbons of arc-lamps to prevent the chips or hot sparks from flying4 ,spark-coil4 ,a coil for producing a spark from a source of comparatively low electro-motive force4 ,the induction-coil is an example4 ,spark1 ,electric4 ,the phenomenon observed when a disruptive charge leaves an accumulator or induction-coil and passes through an air gap4 ,spark-gap4 ,the space left between the ends of an electric resonator across which the spark springs4 ,sparking4 ,the production of sparks at the commutator1 between the bars and the brushes of dynamos and motors4 ,they are minute voltaic arcs1 and should not be allowed to occur1 as they cut away the metal and score the surface of the commutator4 ,spark-tube4 ,a tube used as a gauge to determine when the exhaustion of the vacuum chamber1 or bulb1 of an incandescent lamp is sufficiently high4 ,specific ,gravity4 ,the relative weight or density of a body as compared with a standard4 ,water is usually taken as a standard for solids and liquids1 and air for gases4 ,speed-counter4 ,an instrument which records the number of revolutions a shaft makes in a given time4 ,spent ,acid4 ,acid which has become exhausted4 ,in a battery the acid becomes spent from combination with zinc2 it also loses its depolarizing power4 ,spring-contact4 ,a spring connected to one lead of an electric circuit4 ,it is arranged to press against another spring or contact1 which it opens or closes by the introduction of a plug or wedge4 ,spring-jack4 ,an arrangement of spring-arm conductors under which plugs with wires attached can be slipped to make a new connection or to cut out certain circuits4 ,spurious ,resistance4 7,see ,resistance1 ,spurious47 ,standard ,candle4 7,see ,candle1 ,standard47 ,standard ,resistance4 7,see ,resistance1 ,standard47 ,starting-box4 ,a resistance or shunt box used for letting current pass gradually into motors1 instead of throwing on the full current at once4 ,static ,electricity4 ,electricity generated by friction2 frictional electricity1 such as lightning2 electricity of high electro-motive force and practically uncontrollable for commercial purposes4 ,static ,shock4 ,a term used in electro-therapeutics for describing the discharge from a small condenser or ,leyden-jar2 also the effect produced by the action of the vibrator of the induction-coil4 ,station1 ,central4 ,the building or place in which the electrical apparatus is installed for the generation of current2 the headquarters of telephone lines4 ,steady ,current4 ,an electric current whose strength is fixed or invariable4 ,stock-ticker4 ,an instrument employed to give quotations of stocks by telegraphic record4 ,a paper tape runs through an electrical machine which prints on it the figures and letters that stand for stocks and their values4 ,the whole system is operated from a station located in the ,stock-exchange4 ,storage ,accumulator4 7,see ,accumulator1 ,storage47 ,storage-battery4 7,see ,battery1 ,storage47 ,strength of ,current4 ,amperage2 the quantity of current in a circuit4 ,stripping4 ,the process of removing electro-plating1 or thin metal coatings1 from an object before it is re-electro-plated4 ,stripping ,liquid4 ,the liquid in a stripping-bath used for removing metals from surfaces before re-plating them4 ,submarine ,cable4 ,a telegraphic cable laid at the bottom of the sea or any body of water4 ,submarine ,search-light4 ,an incandescent light which works under water4 ,sub-station4 ,a generating or converting plant subsidiary to a central station1 and placed so as to supply current in a district situated at a distance from the main power-house4 ,subway1 ,electric4 ,an underground passageway utilized for carrying cables and wires4 ,sweating4 ,a process by which the ends of cables are brought together and soldered4 ,s-,w-,g4 ,an abbreviation for standard wire gauge4 ,switch4 ,a device for opening and closing an electric circuit4 ,made in a great variety of forms1 such as push-button1 telegraph-key1 knife switch1 automatic switch1 lever switch1 rheostat1 etc4 ,switch-bell4 ,a combined bell and switch4 ,the bell is operated when the switch is opened or closed4 ,switch-blade4 ,the blade of a switch2 a conducting strip connecting two contact-jaws4 ,switch-board4 ,a board or table to which wires are led and connected with cross-bars or other devices by which connections can be made4 ,synchronize4 ,to agree in point of time2 to effect concurrence of phase in two alternating-current machines1 in order to combine them electrically4 ,t ,table-push4 ,a push-button connected with a call-bell and fixed on a table for convenience in using4 ,tamadine4 ,a form of cellulose used for making the filaments of incandescent lamps4 ,the material is cut into proper shapes1 carbonized1 and flashed4 ,tangent ,galvanometer4 7,see ,galvanometer1 ,tangent47 ,tape1 ,insulating4 ,prepared tape used in covering the bared ends of wires or joints4 ,tap-wires4 ,the conductors in trolley systems that at stated intervals1 take the current from the mains and supply it to the bare feed-wires4 ,telegraph4 ,a system of electric communication invented by ,s4 ,f4 ,b4 ,morse1 in which the dot-and-dash characters are used4 ,there are various modifications of the system--double 7or duplex71 multiplex1 and quadruplex--by means of which a number of messages may be sent out over the same wires at one time4 ,communication from place to place is had over wires mounted on poles1 or by underground or submarine cables4 ,telegraphy1 ,wireless4 ,a system of telegraphy carried on without the aid of wires1 using instead the ether waves of the atmosphere to conduct the vibrations overhead1 and the ground1 or earth1 as a return4 ,the present limit of its working is about four thousand miles4 ,telephone4 ,an instrument and apparatus for the transmission of articulate speech by the electric current4 ,a magnet is encased in a tube and is encircled at one end by a coil of fine1 insulated wire4 ,a diaphragm of thin iron is fixed in front of the coil and close to the end of the magnet4 ,the ends of the coil-wires are connected with a line1 at the other end of which another and similar instrument is installed4 ,the voice causes the sending diaphragm to vibrate1 and these waves are transmitted to the other instrument1 where they can be heard through contra-vibrations of the receiving diaphragm4 ,telephone1 ,long-distance4 ,a telephone of modern construction1 in which the sound-recording mechanism is so sensitive as to make the vibrations of the voice audible at long distances4 ,it will work satisfactorily at one thousand or even fifteen hundred miles4 ,terminal4 ,the end of any open electric circuit1 or of any electric apparatus1 as the electrodes of a battery4 ,thermostat1 ,electric4 ,an apparatus similar in some respects to a thermometer1 and used for closing an electric circuit when the latter becomes heated4 ,it is used in connection with automatic fire-alarms to give warning of fire4 ,for this purpose the metal coil is arranged to close the contact at a temperature of #abe ,f4 ,it usually consists of a compound strip of metal wound in the form of a spiral and fastened at one end4 ,to this end one terminal of a circuit is connected4 ,the expansion of the coil causes its loose end to touch a contact-point and close the circuit4 ,third ,rail4 ,a railway motive system which employs a third rail instead of an overhead trolley feed-wire4 ,the rail is laid on or under the surface of the ground and properly insulated4 ,a shoe from the car bears on the rail and takes up the current4 ,three-wire ,circuit4 ,a system invented by ,edison for the distribution1 from two dynamos1 of current for multiple arc or constant potential service4 ,one wire or lead starts from the positive pole of one dynamo1 another from the negative pole of the other dynamo1 and between the two dynamos the central or neutral lead is made fast4 ,illustration ,now the dynamos may generate a current of #bbj volts1 and send it1 at this strength1 through the outer wires2 but if lamps are connected between either of the outer and the neutral wires1 the current1 passing through the lamps1 will be reduced to #aaj volts4 ,time-ball1 ,electric4 ,a ball which1 by means of electricity1 is made to drop from the top of a high pole1 giving a visual signal for twelve o'clock or any other hour that may be designated4 ,traction1 ,electric4 ,the propulsion of a car or conveyance by means of electricity4 ,transformer4 ,in alternating-current systems1 the induction-coil by means of which the primary current1 with high initial electro-motive force1 is changed into a secondary current with low initial electro-motive force4 ,transmission4 ,the conveyance of electric energy and currents from one point to another by the proper means of conduction4 ,transmitter4 ,an instrument which originates the signals which are sent through a line or circuit4 ,the ,morse key in telegraphy and the ,blake transmitter in telephony are examples4 ,tri-phase4 ,three-phase4 ,trolley4 ,a contact-wheel of bronze which rolls under the supply-wire in an overhead traction system and takes off the current necessary to run the car motors4 ,trolley-wheel4 ,the same as ,trolley4 ,trolley-wire4 ,the overhead wire in a traction system which feeds the current through a trolley-wheel and pole to the motors of a car running underneath4 ,true ,ohm4 7,see ,ohm1 ,true47 ,true ,resistance4 7,see ,resistance1 ,true47 ,two-wire ,circuit4 ,the single system universally used for light and power transmission of current4 ,u ,undulating ,current4 7,see ,current1 ,undulating47 ,uniform ,magnetic ,field4 7,see ,magnetic ,field1 ,uniform47 ,unipolar4 ,having but one pole4 ,unit4 ,the single standard of force1 light1 heat1 magnetism1 attraction1 repulsion1 resistance1 etc4 ,v ,vacuum4 ,a space empty or void of all matter2 a space from which all gases have been exhausted4 ,vacuum ,tubes4 ,tubes of glass through which electric discharges are passed after the gases have been partially removed2 for example1 the ,x-ray tube of ,rntgen and the ,crooke tubes4 ,vibrator1 ,electro-magnetic4 ,the make-and-break mechanism used on induction-coils1 or other similar apparatus1 in which1 through alternate attractions1 an arm or spring is kept in motion4 ,vitriol1 ,blue4 ,a trade name for copper sulphate4 7,bluestone47 ,vitriol1 ,green4 ,a trade name for ferrous sulphate4 7,copperas47 ,vitriol1 ,white4 ,a trade name for zinc sulphate4 7,salts of zinc47 ,volt4 ,the practical unit of electro-motive force2 the volume and pressure of an electric current4 ,voltage4 ,electric-motive force expressed in volts--as1 a voltage of #ajj volts4 ,voltaic4 ,a term derived from the name of the ,italian scientist ,volta1 and used in many ways as applied to electrical current and devices4 ,formerly the term galvanic was commonly employed4 ,voltaic ,electricity4 7,see ,electricity1 ,voltaic47 ,voltimeter4 ,an instrument for measuring the voltage of a current4 ,vulcanite4 ,vulcanized rubber4 ,valuable for its insulating properties and inductive capability4 ,w ,watt4 ,the practical unit of electrical activity2 the rate of work or rate of energy4 ,it is a unit of energy or of work represented by a current of one ampere urged on by one volt of electro-motive force4 ,the volt-ampere4 ,the standard of electrical energy corresponding to horse-power in mechanics4 ,watt-hour4 ,a unit of electric energy or work2 one watt exerted or expended through one hour4 ,waves1 ,electro-magnetic4 ,ether waves caused by electro-magnetic disturbances affecting the luminiferous ether4 ,welding1 ,electric4 ,welding by the use of the electric current4 ,wimshurst ,electric ,machine4 ,an influence machine for producing high potential or static electricity4 ,thin disks of glass are mounted on insulated bearings and revolved by power4 ,brushes collect the frictional electricity1 which is discharged into a ,leyden-jar or other form of accumulator4 ,it is of no practical use excepting in electro-therapeutics4 ,wire1 ,flexible4 ,a cord of fine wire strands laid together and insulated so that it may be easily bent or wrapped4 ,wiring4 ,installing wires so as to form a circuit for the conveyance of current for light1 heat1 and power4 ,x ,x-rays4 ,a curious phenomenon involving the radiation of invisible rays of light1 which have the power to travel through various opaque bodies4 ,the rays are used in detecting foreign substances in the human body and for photographing invisible or hidden objects without disturbing their surroundings4 ,x-ray ,lamp4 ,a high vacuum tube lamp whose interior walls are covered with crystals of calcium or other fluorescent substances1 and which1 when exposed to the ,x-rays1 give out a luminous light4 ,y ,yoke4 ,a piece of soft iron which connects the ends of two portions of a core on which wire coils are wound4 ,it is located at the ends farthest from the poles4 ,the soft-iron bar placed across the ends of a horseshoe magnet to retain its magnetism4 ,z ,zinc-battery4 ,a battery which decomposes zinc in an electrolyte1 thereby producing a current4 ,zinc ,currents4 ,negative currents4 ,zinc-plating4 ,the employment of zinc in electro-plating4 ,,the ,,end ,transcriber's ,notes ,inconsistent spelling1 hyphenation1 etc4 have been retained1 unless mentioned under ,changes ,made below4 ,technical descriptions have been kept as printed1 even when they seem doubtful1 wrong or dangerous4 ,depending on the hard- and software and their settings used to read this text1 not all elements may display as intended4 ,changes ,made ,footnotes and illustrations have been moved outside text paragraphs4 ,where letters 7such as ,v or ,l7 are used to denote a shape rather than the letter1 they have been transcribed as ,v or ,l for consistency with other1 similarly used letters such as ,u4 ,some minor obvious typographical errors have been corrected silently4 ,page #ajh3 called ,nobile's pair changed to called ,nobili's pair4 ,page #ahb3 shallacked changed to shellacked4 ,page #ahd3 7,a1 ,b1 and ,c7 and ,a ,a1 ,b ,b1 and ,c ,c7 changed to 7,a1 ,b1 and ,c and ,a ,a1 ,b ,b1 and ,c ,c74 ,dictionary3 several entries have been moved to their proper alphabetical position4 ,page #ccd3 modern applications of phenonema changed to applications of phenomena ,page #cgb3 ,coil1 ,ruhmkoff changed to ,coil1 ,ruhmkorff4 ,page #chb3 ,daniells changed to ,daniell4 ,page #cif3 graphite a native2 form of carbon changed to graphite2 a native form of carbon4 ,page #dja3 ,ruhmkoff ,coil4 7,see ,coil1 ,ruhmkoff47 changed to ,ruhmkorff ,coil4 7,see ,coil1 ,ruhmkorff47