,this file was produced from page images at the ,internet ,archive4 ,transcriber's ,note ,this book was transcribed from scans of the original found at the ,internet ,archive4 ,the page scans were done by ,google4 ,the original book was done as three volumes1 but the edition ,i have transcribed put all three volumes together as a clothbound book4 ,as a result it had three identical prefaces and duplicated ads4 ,i have included one preface1 at the beginning1 and put the ads at the end of the book4 ,i have rotated a couple of illustrations4 ,arts and ,science ,series ,no4 #g ,home-made ,electrical ,apparatus ,a ,practical ,handbook for ,amateur ,experimenters ,in ,three ,parts 99,volume ,i99 ,second ,edition 99,,by99 99,a4 ,m4 ,powell99 ,,published ,,by ,,cole ,,morgan1 ,inc4 ,publishers of the ,arts and ,science ,series ,p4,o4 ,,box #dgc ,,city ,,hall ,,station ,,new ,,york1 ,n4 ,y4 ,printed in ,u4 ,s4 ,a4 ,copyright #aiah by ,,cole ,,morgan1 ,inc4 ,,preface ,the purpose of this book is to aid the young experimenter in building and operating his own electrical apparatus and instruments4 ,every boy of now-a-days experiments with electricity and the right sort of book which furnishes him with ideas gets close to his heart4 ,of books upon electricity there is no end4 ,that is granted4 ,but there are very few practical books for the young experimenter who wishes to construct miscellaneous electrical apparatus for his own amusement and instruction which really amounts to something and which is worth his pains when the labor has been finished4 ,this book is therefore offered as a volume of instruction for making all sorts of batteries1 rectifiers1 motors1 etc41 which are entirely out of the toy class and yet are not so elaborate that they cannot be easily constructed at home by the average boy who is willing to put a little care into his work4 ,the materials required are such that they can he procured without any great expense4 ,it has been planned to present the material in such a manner that it will aid the judgment of the young experimenter and assist him in developing his own ideas4 ,without exception1 all of the apparatus described in the following pages has been actually constructed by the author1 not only once but many times and put to a practical test before being embodied into the book4 ,you may therefore be sure that if you follow the instructions carefully1 that the result will in each case be a substantial piece of apparatus which is capable of fulfilling all of your expectations4 ,the drawings have all been reproduced on a large scale and in almost every case the dimensions of even the smallest details have been given4 ,some of the apparatus has been described in the pages of the ,boys' ,magazine and since its publication the readers of that magazine have written to the author asking questions about the apparatus which have enabled him when rewriting the material for publication in book form to clear up many questions and further explain in a little more detail many of the problems which naturally occur to the boy who likes to build his own electrical devices4 ,,the ,,author4 ,,preface 4444444444444444444444444444444444444444 4444444444444444444 ,,chapter ,i4 ,,static ,,electrical ,,apparatus 4444444444444444444444444444 ,how to ,build a ,wimshurst ,machine4 4444444444444444444444444444444 ,experiments with ,static ,electrical ,apparatus4 4444444444444444444 ,,chapter ,,ii4 ,,cells ,,and ,,batteries4 4444444444444444444444444444444444 ,the ,voltaic ,cell4 4444444444444444444444444444444444444444 4444444 ,homemade ,batteries4 4444444444444444444444444444444444444444 44444 ,battery ,solutions or ,electrolytes4 444444444444444444444444444444 ,connecting ,cells4 4444444444444444444444444444444444444444 4444444 ,storage or ,secondary ,cells4 4444444444444444444444444444444444444 ,an ,experimental ,storage ,cell4 44444444444444444444444444444444444 ,a ,homemade ,storage ,cell4 4444444444444444444444444444444444444444 ,recharging and ,caring for ,storage ,cells4 444444444444444444444444 ,,chapter ,,iii4 ,,how ,,to ,,reduce ,,the #aaj ,v4 ,d4,c4 ,,or ,a4,c4 ,,to ,a ,,lower ,,voltage ,,for ,,experimental ,,purposes4 44444444444444444444444444444444 ,,chapter ,,iv4 ,,how ,,an ,,alternating ,,current ,,may ,,be ,,changed ,,into ,,direct ,,current ,,by ,,means ,,of ,,an ,,electrolytic ,,rectifier4 44444444444444444444 ,,chapter ,v4 ,,how ,,to ,,build ,a ,,step-,,down ,,transformer ,,for ,,reducing ,,the #aaj ,,volt ,a4 ,c4 ,,for ,,experimental ,,purposes4 44444444444444444444444444444 ,,chapter ,,vi4 ,,electric ,,measuring ,,instruments 444444444444444444444444 ,galvanometers1 ,ammeters1 ,voltmeters4 ,how to ,make a ,galvanometer4 4 ,the ,construction of ,ammeters and ,voltmeters4 44444444444444444444 ,,chapter ,,vii4 ,,current ,,control ,,devices4 44444444444444444444444444444 ,how to ,make a ,pole ,changing ,switch or ,current ,reverses ,how to ,reverse a ,small ,motor4 4444444444444444444444444444444444444444 44 ,how to ,make a ,small ,battery ,rheostat for ,regulating the ,speed of ,small ,motors1 ,etc4 4444444444444444444444444444444444444444 444444 ,,chapter ,,viii4 ,,how ,,to ,,make ,a ,,telegraph ,,key ,,and ,,sounder ,,and ,,install ,a ,,telegraph ,,line4 4444444444444444444444444444444444444444 44444444444 ,,chapter ,,ix4 ,,how ,,to ,,make ,,and ,,install ,a ,,telephone4 444444444444444444 ,,chapter ,x4 ,,medical ,,coils ,,and ,,shocking ,,coils4 4444444444444444444444 ,,chapter ,,xi4 ,,the ,,construction ,,of ,,spark ,,coils4 4444444444444444444444 ,experiment #a--;,an ,imitation ,gassiot's ,cascade4 44444444444444444444 ,experiment #b--;,a ,ghostly ,light 444444444444444444444444444444444444 ,experiment #c--,lighting ,geissler ,tubes4 444444444444444444444444444 ,experiment #d--;,flickering ,light4 4444444444444444444444444444444444 ,experiment #e--,rotating a ,geissler ,tube4 44444444444444444444444444 ,experiment #f--;,fluorescent ,writing4 4444444444444444444444444444444 ,experiment #g--;,an ,electric ,bomb4 4444444444444444444444444444444444 ,experiment #h--;,electrifying the ,garbage ,can4 4444444444444444444444 ,experiment #i--;,how to ,make an ,electric ,spark ,photograph ,itself4 444 ,,chapter ,,xii4 ,,how ,,to ,,make ,a ,,dynamo-,,motor 444444444444444444444444444 ,,chapter ,,xiii4 ,,an ,,electric ,,battery ,,motor4 44444444444444444444444444 ,,chapter ,,xiv4 ,,how ,,to ,,build ,,an ,,electric ,,engine4 444444444444444444444 ,,chapter ,,xv4 ,,miniature ,,battery ,,lighting4 444444444444444444444444444 ,,chapter ,,xvi4 ,,coherer ,,outfits ,,for ,,wireless ,,telegraphy4 4444444444444 ,,chapter ,,xvii4 ,,how ,,to ,,build ,a ,,tesla ,,high ,,frequency ,,coil4 44444444444 ,,chapter ,,xviii4 ,,an ,,experimental ,,wireless ,,telephone4 4444444444444444 ,,chapter ,,xix4 ,,miscellaneous ,,experiments ,,and ,,apparatus4 4444444444444 ,,electrolysis4 4444444444444444444444444444444444444444 44444444444 ,,electroplating4 4444444444444444444444444444444444444444 444444444 ,,electric ,,current ,,generated ,,by ,,heat4 44444444444444444444444444444 ,a ,,handy ,,light4 4444444444444444444444444444444444444444 4444444444 ,,an ,,experimental ,,arc ,,lamp4 444444444444444444444444444444444444444 ,a ,,magnetic ,,diver4 4444444444444444444444444444444444444444 4444444 ,,the ,,magnetic ,,fish4 4444444444444444444444444444444444444444 444444 ,a ,,magnetic ,,clown4 4444444444444444444444444444444444444444 4444444 ,,an ,,electric ,,breeze4 4444444444444444444444444444444444444444 44444 ,a ,,static ,,motor4 4444444444444444444444444444444444444444 444444444 ,,fig4 #a4--;,a simple ,wimshurst ,machine which any boy can easily make4 ,p ,p1 ,plates2 ,,br1 ,neutralizes2 ,c ,r1 ,collectors2 ,,dr1 ,discharge ,rods2 ,j ,j1 ,leyden ,jars2 ,h ,h1 ,insulating ,handles2 ,c1 ,crank2 ,u1 ,upright2 ,b1 ,belt4 4444444444444444444444444444444444444444 444444444444444444444 ,,fig4 #b4--,the plates for the ,static ,machine are made of hard rubber and are #g inches in diameter4 ,each plate carries sixteen tinfoil sectors4 4444444444444444444444444444444444444444 444444444444444444 ,,fig4 #c4--,the details of the ,tinfoil ,sector4 ,sixteen are required for each plate4 ,they are stuck to the plates with shellac4 444444444444 ,,fig4 #d4--;,details of the ,grooved ,pulley1 attached to each plate4 ,the ,pulleys are turned out of wood4 44444444444444444444444444444444444 ,,fig4 #e4--,the base of the ,wimshurst ,machine4 ,all woodwork about the machine should be carefully dried and then shellaced so that it cannot absorb any moisture4 444444444444444444444444444444444444444 ,,fig4 #f4--;,details of one of the ,uprights which support the ,plates1 ,driving ,pulleys1 etc4 ,these1 being made of wood1 should also be dried and shellaced so that they cannot absorb moisture4 4444444444 ,,fig4 #g4--,showing the ,two ,uprights in position on the ,base4 444444444 ,,fig4 #h4--,the ,driving ,pulleys4 ,these are turned out of wood and mounted on a shaft having a ,crank at one end4 444444444444444444444 ,,fig4 #i4--,the ,crank is bent out of a piece of #c_/af rod1 #g inches long1 into the shape shown4 4444444444444444444444444444444444444444 44444 ,,fig4 #aj4--,the ,collector with the ,discharge ,rods1 etc1 in position4 ,a is the ,brass ,ball forming one terminal of the gap across which the sparks jump4 ,b is another ,brass ,ball screwed onto the end of the ,collector ,rod and having a hole in it1 through which the ,discharge ,rod slips4 ,,cc are two threaded ,washers used to clamp the ,discharge ,rod in place4 4444444444444444444444444444444444444444 4444444444444 ,,fig4 #aa4--,showing how ,binding ,posts may be substituted for ,round ,balls on the ,collector ,rods4 44444444444444444444444444444444444444 ,,fig4 #ab4--;,details of the ,discharger ,rods4 44444444444444444444444444 ,,fig4 #ac4--,the ,supporting ,bar upon which the ,collector ,rods are mounted4 ,made of hard rubber so as to be a perfect ,insulator4 44444 ,,fig4 #ad4--,the ,neutralizers4 ,two are required4 ,they are bent out of ,brass ,rod and fitted with a ,tinsel ,tuft at each end4 ,the centre piece upon which the ,rod is mounted should be of ,hard ,rubber4 4444 ,,fig4 #ae4--;,details of the ,leyden ,jars4 ,they are simply small ,test ,tubes1 coated inside and outside with tinfoil for about two-thirds their height and fitted with a ,brass ,rod connected with the inside coating4 4444444444444444444444444444444444444444 444444444444444444 ,,fig4 #af4--;,a ,large ,leyden ,jar for experimental purposes4 444444444444 ,,fig4 #ag4--,showing how to ,discharge a ,leyden ,jar with a curved piece of stiff wire fitted to a ,wooden ,handle4 44444444444444444444444444 ,,fig4 #ah4--,the ,lightning ,board is simply a ,strip of ,glass covered with small ,tinfoil ,squares4 ,it may be insulated by mounting on a ,bottle4 ,the two ,wires attached to the wide ,tinfoil ,strips at the ends of the ,board are for connection to the ,static ,machine or ,leyden ,jar4 4444444444444444444444444444444444444444 444444444444444 ,,fig4 #ai4--;,a very pretty effect can be produced by arranging small tinfoil strips on the ,glass in a ,pattern4 ,each strip should be separated from the other just far enough for a ,spark to pass4 44444 ,,fig4 #bj4--;,a very pretty design made by arranging the ,strips in the form of a ,seven-pointed ,star4 ,flowers1 initials or almost any pattern may be made in the same way4 444444444444444444444444444444 ,,fig4 #ba4--,the ,electric ,parasol4 ,the upper right-hand corner shows a piece of ,tissue ,paper cut into ,strips4 7#a7 ,is the apparatus before the ,tissue ,paper is fastened to the ,cork4 7#b7 ,shows the completed ,parasol and 7#c71 the ,parasol when connected to the machine and the latter is set in operation4 444444444444444444444444444444444444444 ,,fig4 #bb4--;,electric ,birds4 ,the ,birds are made of ,tissue ,paper and should be about the size and shape shown in the lower right-hand corner of the illustration above4 444444444444444444444444444444444 ,,fig4 #bc4--;,electric ,acrobats4 ,the ,acrobats are made of paper4 ,the little figure in the upper right-hand part of the illustration is the proper size4 4444444444444444444444444444444444444444 4444444444 ,,fig4 #bd4--,the ,electric ,mortar4 ,c is the ,mortar1 ,p the ,powder1 ,b a ,small ,ball and ,w ,w the two ,wires between which the ,spark igniting the powder takes place4 4444444444444444444444444444444444444444 444 ,,fig4 #be4--;,an ,electric ,whirligig4 44444444444444444444444444444444444 ,,fig4 #bf4--;,a ,voltaic ,cell4 ,a ,voltaic ,cell consists of a ,strip of ,copper and a ,strip of ,zinc immersed in a dilute solution of ,sulphuric ,acid4 4444444444444444444444444444444444444444 44444444444 ,,fig4 #bg4--,ordinary ,jelly ,glasses1 ,tumblers1 ,fruit ,jars1 etc1 make good ,jars for small cells by cutting off the tops4 4444444444444444 ,,fig4 #bh4--;,a ,simple ,home-made ,cell4 444444444444444444444444444444444 ,,fig4 #bi4--;,a ,home-made ,battery having two ,carbon ,plates with a ,zinc ,rod between4 4444444444444444444444444444444444444444 44444444444444 ,,fig4 #cj4--,the ,elements for a ,simple ,home-made ,cell composed of two ,carbon ,rods and one ,zinc ,rod clamped between two ,wooden ,strips4 444 ,,fig4 #ca4--;,four ,carbon ,rods and one ,zinc ,rod arranged to form the ,elements of a ,cell4 4444444444444444444444444444444444444444 4444444 ,,fig4 #cb4--;,a ,battery of ,three ,cells arranged so that they can all be lifted out of the solution at once4 4444444444444444444444444444444 ,,fig4 #cc4--,showing how ,cells are arranged when they are connected in ,series4 ,the ,voltage of ,six ,dry ,cells connected in series as above would be approximately #f x #a4e or #i ,volts4 444444444444444444444444 ,,fig4 #cd4--,showing ,six ,dry ,cells connected in ,multiple4 ,the ,voltage of such an arrangement would only be #a4e1 but the ,amperage available would be six times that possible from ,cells connected as in ,figure #cc4 4444444444444444444444444444444444444444 44444444444444444444444 ,,fig4 #ce4--,showing how to connect a ,battery of ,cells in ,series-,multiple4 4444444444444444444444444444444444444444 4444444444 ,,fig4 #cf4--;,battery ,connectors like that shown above can be obtained for #a #a_/b cents each and will be found to be very handy4 4444444444 ,,fig4 #cg4--;,a ,simple ,experimental ,storage ,battery consisting of two ,lead ,plates immersed in ,dilute ,sulphuric ,acid4 44444444444444444444 ,,fig4 #ch4--,showing how to charge a ,simple ,storage ,cell composed of two ,lead ,plates immersed in ,sulphuric ,acid by connecting it to two ,bichromate of ,potash ,cells4 444444444444444444444444444444444444444 ,,fig4 #ci4--,showing how the ,plates for a ,storage ,cell may be made from ,sheet ,lead by boring it full of holes and filling with paste4 44444 ,,fig4 #dj4--;,a set of three ,plates composed of ,one ,positive and ,three ,negatives assembled to form a ,cell4 4444444444444444444444444444444 ,,fig4 #da4--;,glass and ,rubber ,storage ,cell ,jars which are on the market for the ,electrical ,experimenter and may be purchased very reasonably4 4444444444444444444444444444444444444444 444444444444444 ,,fig4 #db4--;,an empty ,storage ,cell ,grid and also a ,pasted ,plate both of which are on the market for experimenters who wish to build their own ,cells4 4444444444444444444444444444444444444444 4444444444444444 ,,fig4 #dc4--,two ,negative ,plates burned together and the ,connecting ,lug used4 4444444444444444444444444444444444444444 44444444444444444 ,,fig4 #dd4--,the ,elements of a ,storage ,cell composed of two ,negative ,plates and one ,positive ,plate in their proper position4 44444444444 ,,fig4 #de4--,three different sizes of ,storage ,cells which may be purchased ready made or built by the experimenter out of prepared materials as explained4 4444444444444444444444444444444444444444 444 ,,fig4 #df4--;,a ,hydrometer for preparing and testing the ,acid ,solution for ,storage ,batteries4 4444444444444444444444444444444444444444 4444 ,,fig4 #dg4--,the proper way of ,recharging ,storage ,cells from the #aaj ,volts ,d4 ,c4 ,supply in series with a set of ,lamps4 44444444444444444 ,,fig4 #dh4--;,a ,lamp ,bank consisting of a ,set of #aaj-,volt ,lamps connected ,multiple and arranged to be placed in series with any device it is desired to use on the #aaj-,volt ,current4 444444444444444444444444444 ,,fig4 #di4--;,a ,single ,cell of ,electrolytic ,rectifier4 44444444444444444 ,,fig4 #ej4--;,an ,electrode cut out of ,sheet ,metal4 ,the top is bent over at right angles and drilled so that it can be mounted on the underside of the cover4 4444444444444444444444444444444444444444 444 ,,fig #ea4--;,a ,cast ,electrode will last much longer than one cut from ,sheet ,metal4 ,cast ,electrodes like that above are on the market and can be purchased very reasonably4 444444444444444444444444444444444 ,,fig4 #eb4--;,a completed single ,cell ,rectifier4 ,the right hand sketch shows how the ,electrodes are mounted on the underside of the cover4 ,,fig4 #ec4--;,a ,diagram showing how a ,rectifier cuts off one-half of the ,alternating ,current ,wave and changes it into ,pulsating ,direct ,current4 4444444444444444444444444444444444444444 444444444444444444 ,,fig4 #ed4--;,circuit showing how a ,single ,cell of ,rectifier should be connected in series with a ,lamp ,bank to ,recharge a ,storage ,cell4 ,a is the ,aluminum ,plate and ,l the ,lead or ,iron ,plate4 444444444444444 ,,fig4 #ee4--;,diagram showing the ,difference in ,current after it has been passed through a ,single ,cell or ,rectifier and after passing through a ,four-,cell ,rectifier4 4444444444444444444444444444444444444444 4444 ,,fig4 #ef4--;,diagram showing how a ,four-,cell ,rectifier is connected4 ,the ,alternating ,current ,source is connected to ,c and ,d4 ,the ,direct ,current is taken off at ,a and ,b4 ,the ,electrodes marked ,a1 ,a1 ,a1 ,a are the ,aluminum ,electrodes4 ,l1 ,l1 ,l1 ,l may be ,lead or ,iron4 444444 ,,fig4 #eg--;,a ,complete ,four-,cell ,rectifier connected together and ,mounted in a ,tray4 4444444444444444444444444444444444444444 44444444 ,,fig4 #eh4--;,details of the two different ,pieces of ,sheet ,iron used in building up the ,core4 ,sufficient of each piece are required to form a pile of each three-quarters of an inch thick4 4444444444444444444 ,,fig4 #ei4--,the ,method used in piling up the ,strips to ,assemble the ,core4 4444444444444444444444444444444444444444 444444444444444444444 ,,fig4 #fj4--;,assembly of the ,core4 444444444444444444444444444444444444 ,,fig4 #fa4--;,details of the ,primary and ,secondary ,windings4 44444444444 ,,fig4 #fb4--,showing the ,core completely assembled with the ,primary and ,secondary in position4 ,p1 ,p are the ,primary ,terminals4 #a1 #b and #c are the ,secondary ,terminals4 44444444444444444444444444444444444444 ,,fig4 #fc4--,the ,step-down ,transformer mounted on a ,wooden ,base4 444444 ,,fig4 #fd4--;,a detailed ,drawing showing how the ,sides of the ,case are formed by bending a long strip of ,sheet ,iron at four points4 444444 ,,fig4 #fe4--;,details of the ,top and ,bottom of the ,case4 444444444444444 ,,fig4 #ff4--,the completed ,transformer4 4444444444444444444444444444444 ,,fig4 #fg4--;,a ,simple ,galvanometer4 44444444444444444444444444444444444 ,,fig4 #fh4--;,details of the ,bobbin4 44444444444444444444444444444444444 ,,fig4 #fi4--;,details of the ,armature1 ,bearings and ,pointer4 44444444444 ,,fig4 #gj4--;,a complete ,voltmeter having the ,scale at the top4 44444444 ,,fig4 #ga--;,an ,ammeter so constructed that the ,scale is at the bottom4 4 ,,fig4 #gb4--,showing how the ,armature1 ,shaft and ,pointer are assembled for a ,meter having the ,scale at the bottom4 44444444444444444444444 ,,fig4 #gc4--;,details of the ,wooden ,parts which form the ,case4 444444444 ,,fig4 #gd4--,showing how the ,apparatus is arranged and connected for calibrating the ,ammeter4 4444444444444444444444444444444444444444 44 ,,fig4 #ge4--,showing how the ,apparatus is arranged and connected for calibrating the ,voltmeter4 4444444444444444444444444444444444444444 ,,fig4 #gf4--;,a ,pole changing ,switch for reversing ,small ,motors or the direction of an ,electric ,current4 444444444444444444444444444444444 ,,fig4 #gg4--,top view of a small ,battery ,rheostat 444444444444444444444 ,,fig4 #gh4--;,details of the ,rheostat ,base4 ,the lower part of the illustration is a cross section4 4444444444444444444444444444444444 ,,fig4 #gi4--,looking at the ,base from the bottom showing the grooves in which the ,wires are laid4 4444444444444444444444444444444444444444 4 ,,fig4 #hj4--,the ,german-silver ,resistance ,wire is wound around a ,fibre ,strip4 4444444444444444444444444444444444444444 44444444444444444444 ,,fig4 #ha4--,the ,lever1 ,knob1 ,binding ,posts1 etc4 444444444444444444444 ,,fig4 #hb4--,the completed ,rheostat4 4444444444444444444444444444444444 ,,fig4 #hc4--,key ,frame4 4444444444444444444444444444444444444444 4444444 ,,fig4 #hd4--,sounder ,frame4 4444444444444444444444444444444444444444 444 ,,fig4 #he4--,the ,electro ,magnets4 4444444444444444444444444444444444444 ,,fig4 #hf--,the ,sounder ,armature4 4444444444444444444444444444444444444 ,,fig4 #hg4--,sounder ,frame with ,lever in ,position4 44444444444444444444 ,,fig4 #hh4--,top ,view of ,completed ,instrument 4444444444444444444444444 ,,fig4 #hi4--,side ,view of ,key4 4444444444444444444444444444444444444444 ,,fig4 #ij4--,key and ,circuit ,closing ,levers4 44444444444444444444444444 ,,fig4 #ia4--;,american ,morse ,code4 4444444444444444444444444444444444444 ,,fig4 #ib4--;,circuit for ,two ,instruments4 44444444444444444444444444444 ,,fig4 #ic4--,the ,wooden ,back for the ,telephone4 44444444444444444444444 ,,fig4 #id4--,the ,complete ,telephone4 4444444444444444444444444444444444 ,,fig4 #ie4--;,details of the ,receiver ,hook4 4444444444444444444444444444 ,,fig4 #if4--,showing how the ,push ,button is arranged4 44444444444444444 ,,fig4 #ig4--;,circuit showing how to connect two ,telephone ,stations to the ,line4 4444444444444444444444444444444444444444 44444444444444444 ,,fig4 #ih4--;,bobbin for ,medical ,coil4 444444444444444444444444444444444 ,,fig4 #ii4--;,bobbin with ,winding4 4444444444444444444444444444444444444 ,,fig4 #ajj4--;,construction of the ,core4 4444444444444444444444444444444 ,,fig4 #aja4--,vibrator ,parts and ,core ,cap4 4444444444444444444444444444 ,,fig4 #ajb4--,regulator ,tube4 4444444444444444444444444444444444444444 4 ,,fig4 #ajc4--,the ,base with ,location of ,holes4 444444444444444444444444 ,,fig4 #ajd4--,top ,view of ,finished ,coil4 444444444444444444444444444444 ,,fig4 #aje4--,side ,view of ,completed ,coil4 4444444444444444444444444444 ,,fig4 #ajf4--,vibrator ,parts4 4444444444444444444444444444444444444444 4 ,,figs4 #ajg and #ajh4--,two ,types of ,handles4 44444444444444444444444444 ,,fig4 #aji4--;,induction or ,spark ,coil4 44444444444444444444444444444444 ,,fig4 #aaj4--,the ,primary and ,core4 44444444444444444444444444444444444 ,,fig4 #aaa4--,the ,secondary ,winding4 4444444444444444444444444444444444 ,,fig4 #aab4--,the ,fixed ,condenser4 444444444444444444444444444444444444 ,,fig4 #aac4--;,details of the ,wooden ,coil ,heads4 44444444444444444444444 ,,fig4 #aad4--;,details of the ,wooden ,base4 44444444444444444444444444444 ,,fig4 #aae4--;,details of the ,interrupter4 ,the ,spring and ,standard for the ,one inch coil should be made one-quarter of an inch longer4 444 ,,fig4 #aaf4--,the tube4 4444444444444444444444444444444444444444 4444444 ,,fig4 #aag4--,the ,bridge4 4444444444444444444444444444444444444444 44444 ,,fig4 #aah4--,section of the ,spark ,coil showing the arrangement of the ,parts4 4444444444444444444444444444444444444444 44444444444444444444 ,,fig4 #aai4--;,end ,view of the ,complete ,coil4 44444444444444444444444444 ,,fig4 #abj4--,side ,view of the ,completed ,coil4 444444444444444444444444 ,,fig4 #aba4--;,diagram of ,connections4 444444444444444444444444444444444 ,,fig4 #abb4--,perspective view of ,coil showing names of the various parts4 4444444444444444444444444444444444444444 44444444444444444444 ,,fig4 #abc--;,front view of the ,field ,casting4 4444444444444444444444444 ,,fig4 #abd4--,side elevation of the ,field ,casting4 44444444444444444444 ,,fig4 #abe4--;,details of the ,armature4 44444444444444444444444444444444 ,,fig4 #abf4--,the ,commutator4 4444444444444444444444444444444444444444 4 ,,fig4 #abg4--,the ,armature and ,commutator ,assembled on the ,shaft ready for winding4 4444444444444444444444444444444444444444 44444444444444 ,,fig4 #abh4--;,details of the ,wooden ,base4 44444444444444444444444444444 ,,fig4 #abi4--;,details of the ,bearings4 44444444444444444444444444444444 ,,fig4 #acj4--,the ,pulley4 4444444444444444444444444444444444444444 44444 ,,fig4 #aca4--,the ,brushes4 4444444444444444444444444444444444444444 4444 ,,fig4 #acb4--,the ,completed ,dynamo4 44444444444444444444444444444444444 ,,fig4 #acc4--,the completed ,electric ,motor4 444444444444444444444444444 ,,fig4 #acd4--;,details of the ,field ,frame4 44444444444444444444444444444 ,,fig4 #ace4--,the ,assembled ,field ready for ,winding4 444444444444444444 ,,fig4 #acf4--;,details of the ,armature ,lamination4 444444444444444444444 ,,fig4 #acg4--,the ,armature assembled on the ,shaft ready to ,wind4 444444 ,,fig4 #ach4--,the ,commutator4 4444444444444444444444444444444444444444 4 ,,fig4 #aci4--;,diagram showing how the ,armature ,coils are connected to the ,commutator ,sections4 4444444444444444444444444444444444444444 44 ,,fig4 #adj4--,the ,bearings4 4444444444444444444444444444444444444444 444 ,,fig4 #ada4--,the ,brushes4 4444444444444444444444444444444444444444 4444 ,,fig4 #adb4--,the ,fibre ,block for supporting each ,brush4 44444444444444 ,,fig4 #adc4--;,completed ,electric ,engine4 444444444444444444444444444444 ,,fig4 #add4--,the ,engine ,base4 4444444444444444444444444444444444444444 ,,fig4 #ade4--;,details of the ,electromagnet ,bobbin4 44444444444444444444 ,,fig4 #adf4--;,details of the ,engine ,frame4 4444444444444444444444444444 ,,fig4 #adg--,the ,bearings4 4444444444444444444444444444444444444444 4444 ,,fig4 #adh4--;,details of the ,shaft4 44444444444444444444444444444444444 ,,fig4 #adi4--,the ,armature1 ,armature ,bearing and ,connecting ,rod4 444444 ,,fig4 #aej4--,the ,brushes4 4444444444444444444444444444444444444444 4444 ,,fig4 #aea4--;,a ,flywheel may be cut from sheet iron4 444444444444444444 ,,fig4 #aeb4--,small ,tungsten ,battery ,lamps4 444444444444444444444444444 ,,fig4 #aec4--;,a ,simple ,lighting ,arrangement4 44444444444444444444444444 ,,fig4 #aed4--,showing the differences between the ,candelabra1 ,single ,ediswan and ,double ,ediswan ,types of ,lamp ,bases4 4444444444444444444 ,,fig4 #aee4--,miniature ,sockets of the types known as ,flat ,base ,porcelain1 ,pin and ,weatherproof4 44444444444444444444444444444 ,,fig4 #aef4--;,connections for a #b4h ,volt ,lamp4 444444444444444444444444 ,,fig4 #aeg4--;,a ,miniature ,base ,tungsten ,filament ,battery ,lamp for small lighting4 4444444444444444444444444444444444444444 44444444444444444 ,,fig4 #aeh4--;,a ,tungsten ,automobile ,lamp with ,ediswan ,base4 44444444444 ,,fig4 #aei4--,lamps ,controlled by ,one ,switch4 4444444444444444444444444 ,,fig4 #afj4--,lamps ,controlled by ,separate switches4 444444444444444444 ,,fig4 #afa4--;,double ,control ,system4 4444444444444444444444444444444444 ,,fig4 #afb4--,the ,coherer ,details4 444444444444444444444444444444444444 ,,fig4 #afc4--,the ,complete ,coherer4 44444444444444444444444444444444444 ,,fig4 #afd4--,pony ,type ,relay4 4444444444444444444444444444444444444444 ,,fig4 #afe4--;,connections for the ,receiving ,set4 4444444444444444444444 ,,fig4 #aff4--;,coherer1 ,decoherer and ,relay ,connections4 444444444444444 ,,fig4 #afg4--;,how the ,transmitter is ,connected4 44444444444444444444444 ,,fig4 #afh4--,the ,complete ,spark ,gap4 444444444444444444444444444444444 ,,fig4 #afi4--;,details of ,spark ,gap4 44444444444444444444444444444444444 ,,fig4 #agj4--,tesla ,coil ,circuits4 444444444444444444444444444444444444 ,,fig4 #aga4--,secondary ,tube4 4444444444444444444444444444444444444444 4 ,,fig4 #agb4--;,details of the ,secondary ,heads4 4444444444444444444444444 ,,fig4 #agc4--;,details of the ,primary ,head4 4444444444444444444444444444 ,,fig4 #agd4--,primary ,cross ,bar4 44444444444444444444444444444444444444 ,,fig4 #age4--;,front ,view of the completed ,tesla ,coil4 44444444444444444 ,,fig4 #agf--,side ,view of the completed ,tesla ,coil4 4444444444444444444 ,,fig4 #agg4--;,diagram of connections for operating the ,coil4 4444444444 ,,fig4 #agh4--,plate ,glass ,condenser4 4444444444444444444444444444444444 ,,fig4 #agi4--,when a ,bar ,magnet is plunged into a ,hollow ,coil of ,wire1 a ,momentary ,current of ,electricity is ,generated4 44444444444444444444 ,,fig4 #ahj4--,magnetic ,phantom showing the ,lines of ,force about a ,bar ,magnet4 4444444444444444444444444444444444444444 4444444444444444444 ,,fig4 #aha4--,magnetic ,phantom about a ,coil of ,wire carrying a current4 ,,fig4 #ahb4--;,illustrating the ,principle of the ,induction ,wireless ,telephone4 4444444444444444444444444444444444444444 4444444444444444 ,,fig4 #ahc4--,showing how the ,coils may be formed by winding around nails set in a circle in the ,floor4 4444444444444444444444444444444 ,,fig4 #ahd4--;,circuit ,diagram showing how the ,coil is connected so as to serve for either transmitting or receiving4 44444444444444444444444 ,,fig4 #ahe4--;,apparatus for ,electrolysis ,experiment4 444444444444444444 ,,fig4 #ahf4--;,electroplating ,tank4 444444444444444444444444444444444444 ,,fig4 #ahg4--;,generating ,electric ,current by ,heat4 44444444444444444444 ,,fig4 #ahh4--;,a ,handy ,light4 4444444444444444444444444444444444444444 44 ,,fig4 #ahi4--;,experimental ,arc ,lamp4 4444444444444444444444444444444444 ,,fig4 #aij4--,the ,magnetic ,diver4 4444444444444444444444444444444444444 ,,fig4 #aia4--,the ,magnetic ,fish4 44444444444444444444444444444444444444 ,,fig4 #aib4--,the ,magnetic ,clown4 4444444444444444444444444444444444444 ,,fig4 #aic4--;,an ,electric ,breeze4 4444444444444444444444444444444444444 ,,fig4 #aid4--,the ,static ,motor4 444444444444444444444444444444444444444 ,,chapter ,i4 ,,static ,,electrical ,,apparatus 99,static ,electricity4 ,how to ,build a ,wimshurst ,machine4 ,experiments with ,static ,electrical ,apparatus499 99,static ,electricity99 is an extremely interesting subject for the amateur experimenter1 in view of the many spectacular experiments which may be performed with it4 ,the number of such experiments is almost unlimited4 ,static electricity was the first evidence of the wonderful force which in the present day moves trains1 lights our homes1 etc41 to come to the notice of man4 ,long before the days of batteries1 dynamos1 telegraphs1 electric lights and before1 perhaps1 such things were even dreamed of1 static electricity absorbed the attention of scientists1 and the names of some of the world's greatest men such as for instance1 ,aristotle1 ,roger ,bacon1 ,gilbert1 ,boyle1 ,newton1 ,franklin1 etc41 are closely linked with its history4 ,it is probably safe to say that experiments with static electricity led the famous ,italian1 ,galvani1 to the discovery of the sort of electricity called 99galvanic99 currents1 and to the battery4 ,galvanic current is the sort of electricity produced by batteries and has the same properties in many ways as that generated by huge dynamos in the power houses of to-day4 ,the modern boy can duplicate these old experiments far more easily and on a larger scale than any of the old scientists could1 owing to the fact that he is supplied with explicit directions and can easily obtain the necessary materials at a neighboring hardware or electrical store1 whereas men like ,newton and ,franklin not only had to 99devise99 or 99invent99 their own apparatus but make their materials as well4 ,how to ,build a ,wimshurst ,machine4 ,static electricity and lightning are the same thing4 ,a boy can produce static electricity in small quantities by rubbing a glass rod with a piece of flannel or silk4 ,illustration3 ,,fig4 #a4--;,a simple ,wimshurst ,machine which any boy can easily make4 ,p ,p1 ,plates2 ,,br1 ,neutralizes2 ,c ,r1 ,collectors2 ,,dr1 ,discharge ,rods2 ,j ,j1 ,leyden ,jars2 ,h ,h1 ,insulating ,handles2 ,c1 ,crank2 ,u1 ,upright2 ,b1 ,belt4 ,rub the rod briskly and then hold it over some tiny bits of paper or specks of dust and watch them jump up to meet the rod1 just as if the latter were a magnet attracting small tacks or nails4 ,it is static electricity which gives the rod this wonderful power4 ,if you rub the rod briskly and then hold it close to your cheek1 you will feel a slight tickling and hear a faint crackling sound4 ,if this is done in the dark you may be able to see a very faint phosphorescent light or even small sparks4 ,the quantity of electricity produced in this manner by rubbing a glass rod is extremely limited and while a number of very interesting and instructive experiments may be performed in this manner1 the most spectacular ones are only possible with the aid of a static-machine4 ,illustration3 ,,fig4 #b4--,the plates for the ,static ,machine are made of hard rubber and are #g inches in diameter4 ,each plate carries sixteen tinfoil sectors4 ,the most practical form of static machine is that known as the ,wimshurst4 ,it consists of two circular plates made of glass or hard rubber arranged so that by turning a crank1 they may be revolved in opposite directions4 ,on these plates are a number of small strips of tinfoil4 ,the static electricity is generated on these tinfoil strips and collected by two metal rods having small pins arranged along them in a row4 ,a simple form of ,wimshurst machine which any boy can easily make is illustrated in ,figure #a4 ,it will generate considerable static electricity and will make sparks two inches long4 99,the ,plates99 on these machines are hard rubber4 ,they are illustrated in ,figure #b4 ,glass is usually used for static machine plates1 but has the disadvantage of breaking easily4 ,it is also hard for the young experimenter to cut out circular glass plates and drill them4 ,the author has had very good success with hard rubber4 ,illustration3 ,,fig4 #c4--,the details of the ,tinfoil ,sector4 ,sixteen are required for each plate4 ,they are stuck to the plates with shellac4 ,two plates are required for the machine4 ,they should be in the form of circles seven inches in diameter and be perfectly true4 ,they need to be only one-sixteenth of an inch thick4 ,the rubber should be perfectly flat and not warped at any point4 99,the ,sectors991 as the tinfoil strips are called1 are wedge shaped pieces having rounded ends as shown in ,figure #c4 ,they should be cut of heavy tinfoil4 ,thirty-two sectors are required1 sixteen for each plate4 ,they are seven-sixteenths of an inch wide at the top1 one inch long and five-sixteenth of an inch wide at the bottom4 ,the plates should be very carefully cleaned by rubbing with a dry cloth and then laid on a flat surface all ready to receive the sectors4 ,the sectors should be stuck to the plates with thick shellac4 ,they should be arranged all on one face1 symmetrically and at equal distances apart1 with the inner ends resting on a circle four and one-half inches in diameter4 ,each sector should be carefully pressed down on the rubber so that it sticks smoothly without any air bubbles or creases4 ,both plates should be treated in the same manner4 ,illustration3 ,,fig4 #d4--;,details of the ,grooved ,pulley1 attached to each plate4 ,the ,pulleys are turned out of wood4 99,the ,pulley99 illustrated in ,figure #d is one inch in diameter and eleven-sixteenths of an inch thick4 ,two of these pulleys will be required4 ,the hole through the centre should be about three-sixteenths of an inch in diameter4 ,one pulley should be attached to each of the rubber plates4 ,the large face of the pulley should be against the face of the plate upon which the tinfoil sectors are mounted4 ,the hole in the centre of the pulley should line up perfectly with a hole of the same size in the centre of each one of the plates4 ,the plates are fastened to the pulleys by three small brass nails driven into the wood through small holes in the rubber4 99,the ,base99 of the machine is a rectangular shaped piece of wood six inches long1 four inches wide and three-quarters of an inch thick4 ,a notch1 one inch wide and one-half an inch deep is cut in the centre of the front and back as shown in ,figure #e4 ,the purpose of these notches is to receive the uprights4 99,the ,uprights99 are strips of wood1 seven inches long1 one inch wide and one-half an inch thick4 ,the tipper end of each of the uprights is rounded as shown in ,figure #f4 ,illustration3 ,,fig4 #e4--,the base of the ,wimshurst ,machine4 ,all woodwork about the machine should be carefully dried and then shellaced so that it cannot absorb any moisture4 ,two holes should be bored through each of the uprights from front to back4 ,the lower hole is three-sixteenths of an inch in diameter and two and one-quarter inches from the bottom4 ,the upper hole is six and one-half inches from the bottom and is between one-eighth and three-sixteenths of an inch in diameter so that a three-sixteenth rod driven into it will fit tightly4 ,the uprights should be mounted in position in the base and fastened with screws4 ,the plates are mounted between the upper ends of the uprights in the position shown in ,figure #a1 by driving a short piece of #c_/af round brass rod through the uprights into the holes in the centre of the pulleys4 ,the rod used to mount the back plate should be one and one-half inches long and that used for the front plate one and five-eighths inches long4 ,the #c_/af hole in the pulleys should be large enough so that the latter will revolve freely4 ,the plates are revolved by two driving pulleys provided with a crank for turning4 99,the ,driving ,pulleys99 are shown in ,figure #h4 ,they are not so easy to make as the small pulleys attached to the plates4 ,they are turned out of wood and should be both alike4 ,the exact shape and dimensions are shown in the illustration4 ,the hole through the centre should be a scant three-sixteenths of an inch so that the pulleys will force onto a #c_/af rod very tightly4 99,the ,crank99 is bent out of a piece of brass or steel rod about seven inches long4 ,the straight portion1 forming the shaft upon which the pulleys are mounted1 is three and seven-eighths inches long4 ,the portion at right angles to this1 forming what is known as the throw of the crank1 is one inch and seven-eighths4 ,the part forming the crank handle is one inch and one-quarter long4 ,illustration3 ,,fig4 #f4--;,details of one of the ,uprights which support the ,plates1 ,driving ,pulleys1 etc4 ,these1 being made of wood1 should also be dried and shellaced so that they cannot absorb moisture4 ,the driving pulleys are placed between the two standards with the small projecting portions or bosses nearest the uprights4 ,the straight portion of the crank should then be slipped through the hole in the front upright and driven tightly into the driving pulleys4 ,the driving pulleys should fit so tightly onto the shaft that they will not slip4 ,the end of the shaft should project through the pulleys far enough so that is rests in the hole in the rear standard4 ,the holes in the uprights or standards should be just large enough so that the shaft will turn freely4 ,the driving pulleys should be lined up so that the groove in each comes directly under the groove in the corresponding pulley attached to the plate above4 99,the ,belts99 consist simply of heavy cotton cord4 ,the rear belt should be crossed so that the rear plate runs in the opposite direction from the front plate when the crank is turned4 ,the electricity is collected from the sectors on the plates by two 99,collectors499 ,these are illustrated in ,figure #aj and consists of a piece of #e_/cb brass rod1 about six inches long1 bent into the shape shown4 ,two small tufts of tinsel are soldered to the ,u-shaped portion of the collector so that when the latter is placed in its proper position on the machine1 they will brush against the tinfoil-sectors as they pass when the plates revolve4 ,illustration3 ,,fig4 #g4--,showing the ,two ,uprights in position on the ,base4 ,the other end of the rod is threaded to fit into a hole in a small brass ball about three-eighths or one-half inch in diameter4 ,many experimenters may have difficulty in securing a suitable brass ball for this purpose4 ,an ordinary binding post may be used instead4 ,the hole in the bottom of a binding post is usually threaded to fit an #h-cb screw4 ,the end of the rod is just the right size to receive an #h-cb thread and so there should be no trouble in getting the parts to fit4 ,the brass ball is marked ,a in the illustration4 ,the ball is preferable to the binding because it has no sharp corners from which the electricity might leak4 ,static electricity leaks from sharp edges or corners and they must always be avoided as far as possible in the construction of static apparatus4 ,the end of the rod where it screws into the ball or binding post should be threaded back for a distance of about three-quarters of an inch and two brass nuts screwed onto the rod4 ,these nuts are marked ,c in the illustration4 ,illustration3 ,,fig4 #h4--,the ,driving ,pulleys4 ,these are turned out of wood and mounted on a shaft having a ,crank at one end4 ,the collectors are held in position by the supporting bar illustrated in ,figure #ac4 ,this bar is made of a strip of hard rubber1 five and one quarter inches long1 five-eighths of an inch wide and three-sixteenths of an inch thick4 ,three holes1 each five-thirty-seconds of an inch in diameter1 should be bored in the bar4 ,one hole should be exactly in the centre and the other holes seven-sixteenths of an inch back from the end4 ,the centre hole is slipped over the end of the shaft which projects through the front standard supporting the plate and the bar fastened across the support at right angles like a cross by driving in two small brass nails or screws through holes made in the rubber for that purpose4 ,the threaded portion of the collector rods should be slipped through the holes near the ends of the hard rubber bar and clamped firmly in position by placing one of the nuts ,c on the back and the other on the front and tightening them up4 ,the exact position of the collectors is best understood from ,figure #a4 ,they are lettered ,c ,r in the illustration4 ,the brass balls ,b are screwed onto the ends of the rods after the nuts have been tightened4 ,each of these balls should have a hole1 one-eighth of an inch in diameter drilled through it at right angles to the collector rod4 ,the hole provided in the binding post for the accommodation of the wire may be used in case binding posts are employed instead of the rods4 ,these holes are to accommodate the ,discharge ,rods1 which are two round brass rods1 one-eighth of an inch in diameter and three and one-half inches long4 ,one end of each of the rods is fitted with a small brass ball4 ,illustration3 ,,fig4 #i4--,the ,crank is bent out of a piece of #c_/af rod1 #g inches long1 into the shape shown4 ,the other end of each is provided with a small insulating handle4 ,a ,no4 #hjjc ,electrose ,knob is just the thing4 ,these knobs are provided with a threaded bushing so that they may be screwed onto the rod4 ,the proper position for the discharge rods is shown in ,figure #a4 ,by sliding the rods back and forth in the balls on the ends of the collectors1 the distance between the balls on the ends of the rods may be varied4 ,the spark discharge from the machine1 when the latter is completed1 takes place between these balls4 ,the machine still remains to be fitted with the neutralizers and a set of ,leyden jars4 99,the ,neutralizers99 are illustrated in ,figure #ad4 ,two are required4 ,they consist of a piece of one-eighth inch brass rod1 six inches long1 having the ends bent over at right angles so as to form a shallow ,u4 ,the distance between the ends when bent should be about three and five-eights inches4 ,a tuft of tinsel should be soldered to the ends of each of the neutralizers4 ,illustration3 ,,fig4 #aj4--,the ,collector with the ,discharge ,rods1 etc1 in position4 ,a is the ,brass ,ball forming one terminal of the gap across which the sparks jump4 ,b is another ,brass ,ball screwed onto the end of the ,collector ,rod and having a hole in it1 through which the ,discharge ,rod slips4 ,,cc are two threaded ,washers used to clamp the ,discharge ,rod in place4 ,each neutralizer rod is supported by a hard rubber washer three-quarters of an inch in diameter and five-sixteenths of an inch thick4 ,in the centre of the washer a hole should be drilled1 which will fit snugly onto the rods upon which the plates are mounted and revolve4 ,the neutralizer rod passes through a hole in the upper part of the washer as shown in the illustration4 ,before the neutralizers can be put into position it will be necessary to pull out the rods which support the plates so that the plates can be removed4 ,the hard rubber washers supporting the neutralizers are then slipped over the rods so that one will come between each support and plate when the latter is put back into position4 ,the rods should be turned so that the tinsel tufts touch the sectors4 ,the rubber washers should fit snugly on the rods so that the neutralizer will stay in any position in which it is placed4 ,the proper position for the front neutralizer is a little less than half way between vertical and horizontal as shown in ,figure #a4 ,the neutralizer behind the rear plate should be at right angles to that in front4 ,illustration3 ,,fig4 #aa4--,showing how ,binding ,posts may be substituted for ,round ,balls on the ,collector ,rods4 ,the machine is now all ready for operation4 ,in order for it to operate satisfactorily it is necessary for it to be warm and dry4 ,it is1 therefore1 a very good idea to thoroughly dry the woodwork and give it a coat of varnish or shellac so that it cannot absorb any moisture4 ,it may be necessary to start the machine by rubbing a glass rod with a piece of flannel or silk and then touching the rod to some of the sectors4 ,the handle of the machine should be turned from left to right1 that is1 in such a direction that the front plate revolves in the same direction as the hands of a clock4 ,if the machine is in proper working order a stream of small sparks should flow between the spark balls on the ends of the discharger rods1 provided they are not over a half inch apart1 when the crank is turned4 ,the spark can be intensified and lengthened by fitting the machine with two small ,leyden jars4 99,the ,leyden ,jars99 are made from small test tubes three inches long4 ,the inside of the tube should be coated with tinfoil to within about one inch from the top4 ,the outside of the tube should be coated in the same manner for the same distance4 ,the tinfoil can be secured to the glass with shellac4 ,the top of the ,leyden jars is closed with an ordinary cork4 ,a piece of heavy brass wire bent into the form of a hook should pass through the cork and make connection with the tinfoil on the inside of the tube4 ,one ,leyden ,jar should be hung over each of the collector rods by means of the hook4 ,the tinfoil coatings on the outside of the jars should be connected together by a piece of wire running across from one tube to the other4 ,illustration3 ,,fig4 #ab4--;,details of the ,discharger ,rods4 ,the machine is now complete and ready for performing a number of very interesting experiments4 ,experiments with ,static ,electrical ,apparatus4 99,a ,leyden ,jar99 is a very simple device for accumulating and storing static electricity4 ,it consists simply of a wide mouthed jar or bottle coated with tinfoil part way up on both the outside and the inside in exactly the same manner as the small test tubes used on the static machine4 ,not all glass jars are suitable for making ,leyden ,jars4 ,the quality of the glass varies considerably and some will be found far superior to the rest4 ,the glass vessels used by chemists and called beaker glasses usually make excellent ,leyden ,jars4 ,it is not very difficult to make a good ,leyden ,jar4 ,after you have selected the jar or bottle you wish to use1 clean and dry it very thoroughly4 ,then give the inside a thorough brushing over with shellac4 ,cut a strip of tinfoil which is long enough to go all the way around the inside of the jar and about two-thirds its height4 ,before the shellac is thoroughly dry but is still sticky1 insert the tinfoil strip carefully into the jar and press it smoothly against the glass4 ,illustration3 ,,fig4 #ac4--,the ,supporting ,bar upon which the ,collector ,rods are mounted4 ,made of hard rubber so as to be a perfect ,insulator4 ,the outside of the jar should also be given a coat of shellac and covered with tinfoil in exactly the same manner4 ,the tinfoil on the outside of the jar should be the same height as that on the inside4 ,the bottom of the jar should be coated1 both inside and out by cutting two circular pieces out of the tinfoil and sticking them on with shellac4 ,the jar should be provided with a wooden cover which will fit snugly into the top4 ,the wood should be dried and then given a coat of shellac so that it cannot absorb any moisture4 ,illustration3 ,,fig4 #ad4--,the ,neutralizers4 ,two are required4 ,they are bent out of ,brass ,rod and fitted with a ,tinsel ,tuft at each end4 ,the centre piece upon which the ,rod is mounted should be of ,hard ,rubber4 ,it may perhaps be well at this point to emphasize how highly important it is to always keep all static electrical apparatus thoroughly dry and to construct it so that it will not collect or absorb any moisture4 ,a small hole should be bored through the centre of the cover so as to permit a brass rod to pass through4 ,a piece of spring wire bent into a spiral should be attached to the lower end of the rod4 ,when the cover is in position1 the spring wire should make contact with the tinfoil on the inside of the jar4 ,it is a very good idea to fit the top of the rod with a small brass ball4 ,this will prevent the electricity from leaking from the sharp corners on the end of the rod4 ,static electricity leaks very easily from sharp corners or points1 but does not escape so readily from round corners or balls4 ,illustration3 ,,fig4 #ae4--;,details of the ,leyden ,jars4 ,they are simply small ,test ,tubes1 coated inside and outside with tinfoil for about two-thirds their height and fitted with a ,brass ,rod connected with the inside coating4 ,the ,leyden jar may be charged with electricity from the static machine by connecting a wire from one of the discharge rods to the outside tinfoil coating on the jar4 ,another wire should be connected from the other discharge rod to the rod on the jar which connects with the inside tinfoil coating4 ,turning the handle of the machine rapidly for ten or fifteen seconds will charge the jar4 ,disconnect the wires as promptly as possible so that the electricity in the jar will not have a chance to leak back into the machine4 ,be very careful while doing this1 however1 because if you should happen to touch the tinfoil on the outside of the jar and the rod which connects with the inside coating at the same time you will get one of the surprises of your life4 ,illustration3 ,,fig4 #af4--;,a ,large ,leyden ,jar for experimental purposes4 ,the shock won't really hurt you any but it will be very uncomfortable and somewhat surprising4 ,you can discharge a ,leyden jar by bringing a piece of wire which is connected to the outside coating1 near to the knob on the rod4 ,when the wire is close to the ball the electricity will jump across the space in the shape of a snapping white spark4 ,the ,leyden jar can be used in connection with a number of experiments described later on4 ,illustration3 ,,fig4 #ag4--,showing how to ,discharge a ,leyden ,jar with a curved piece of stiff wire fitted to a ,wooden ,handle4 99,bottled ,lightning499 ,a very pretty effect can be obtained by passing the spark from a ,leyden jar or a static machine over a lightning board4 ,a lightning board consists of a pane of glass having a number of small squares of tinfoil stuck on it so that when the electrical discharge is passed over it1 sparks take place between the little tinfoil squares and produce an effect something like miniature lightning4 ,a lightning board suitable for the static machine just described may be made from a strip of ordinary window glass about nine inches long and two inches wide4 ,clean the glass thoroughly and then give it a coat of shellac on one side4 ,as soon as the shellac becomes sticky1 lay on a strip of tinfoil the same size as the glass and rub it down smoothly4 ,when the shellac has thoroughly dried so that the tinfoil is stuck tightly to the glass1 the board is ready to be cut up into squares4 ,this can be best accomplished by means of a sharp knife and a ruler4 ,use care in doing the work so as not to tear the tinfoil and be sure that the knife cuts all the way through to the glass4 ,leave two solid strips of tinfoil at each end to which to make connections4 ,illustration3 ,,fig4 #ah4--,the ,lightning ,board is simply a ,strip of ,glass covered with small ,tinfoil ,squares4 ,it may be insulated by mounting on a ,bottle4 ,the two ,wires attached to the wide ,tinfoil ,strips at the ends of the ,board are for connection to the ,static ,machine or ,leyden ,jar4 ,the lightning board should be mounted by cementing it in a slot in a cork in a bottle so that the glass bottle serves as an insulated support4 ,if one of the tinfoil strips left solid at the end of the board is connected to one of the discharge rods on the static machine and the other end is connected likewise to the other discharge rod innumerable little sparks will zig-zag between the tinfoil squares when the machine is set in operation4 ,the effect is quite pretty if the experiment is performed in a dark room4 ,the ,leyden jar can be charged by the static machine and discharged through the lightning board4 ,the sparks produced by the ,leyden jar will be much more brilliant than those of the static machine above4 ,a very pretty effect can be produced by arranging the tinfoil in the form of a pattern or design as for example that illustrated in ,figure #ai4 ,a strip of glass about the same size as that used for the lightning board may be employed4 ,the glass is coated with shellac and as soon as it becomes sticky1 small rectangular pieces of tinfoil arranged in a zig-zag pattern and having small spaces between them1 are stuck in position4 ,the end pieces are made larger than the other strips so as to afford means for connecting the wires4 ,the strip should then be insulated and mounted by cementing it in a slot in the cork of a glass bottle4 ,illustration3 ,,fig4 #ai4--;,a very pretty effect can be produced by arranging small tinfoil strips on the ,glass in a ,pattern4 ,each strip should be separated from the other just far enough for a ,spark to pass4 ,the apparatus shown in ,figure #bj is made according to the same plan but the glass in this case is in the form of a square instead of a strip4 ,the tinfoil strips are arranged in the form of a seven pointed star or any other pattern which may be desirable4 ,the two large strips ,a and ,b are the ones to which the wires should be connected4 99,the ,electric ,parasol99 is illustrated in ,figure #ba4 ,it is made by pasting some narrow strips of tissue paper1 about three-sixteenths of an inch wide and three or four inches long1 to a small cork which has previously been covered with tinfoil4 ,the strips can be made most easily by cutting a small sheet of tissue paper into strips like the teeth of a comb as shown in the upper right hand corner of ,figure #ba4 ,the tinfoil covered cork should be mounted on the upper end of a stiff copper or brass wire supported in a bottle4 ,if this wire is then connected to one of the discharge rods on the static machine and the hand held to the other1 the paper strips will spread out like a parasol or umbrella1 as soon as the machine is set in operation4 ,illustration3 ,,fig4 #bj4--;,a very pretty design made by arranging the ,strips in the form of a ,seven-pointed ,star4 ,flowers1 initials or almost any pattern may be made in the same way4 ,a novel experiment somewhat similar in principle to the electric parasol is that shown in ,figure #bb4 ,three small paper birds about the size of that shown at the right hand side of the illustration should be cut out of tissue paper and each one attached to a piece of cotton thread about six inches long4 ,the threads are then tied to one end of a ,t-shaped frame bent out of copper wire and supported on a bottle4 ,if the wire frame is then connected to one of the discharge rods and the hand held to the other while the machine is set in operation1 the birds will rise in the air and fly around as far as the threads will let them4 ,illustration3 ,,fig4 #ba4--,the ,electric ,parasol4 ,the upper right-hand corner shows a piece of ,tissue ,paper cut into ,strips4 7#a7 ,is the apparatus before the ,tissue ,paper is fastened to the ,cork4 7#b7 ,shows the completed ,parasol and 7#c71 the ,parasol when connected to the machine and the latter is set in operation4 99,electric ,acrobats499 ,the apparatus shown in ,figure #bc consists of a circular metal plate about four inches in diameter suspended by a wire from a wire ,t stuck in a cork in a bottle4 ,another circular metal plate of the same size is laid on the table below the other4 ,the distance between the two plates should be about one inch or an inch and one-half4 ,cut three or four little figures1 the same size as that shown in the upper right hand part of the illustration1 out of tissue paper and lay them on the bottom plate4 ,illustration3 ,,fig4 #bb4--;,electric ,birds4 ,the ,birds are made of ,tissue ,paper and should be about the size and shape shown in the lower right-hand corner of the illustration above4 ,the circular metal plates may be made of sheet tin1 copper1 brass or galvanized iron4 ,even cardboard1 provided that it is covered with tinfoil1 will serve4 ,the upper plate should be connected to one discharge rod on the static machine and the lower plate to the other4 ,then as soon as the machine is set in operation the little paper figures will begin to dance up and down1 stand on their heads1 hang by one foot or hand1 turn somersaults and perform all sorts of stunts4 99,gunpowder99 may be ignited by the spark from a ,leyden jar4 ,a miniature mortar may be made from a piece of broom handle about an inch and one-half in diameter with a hole one inch deep in one end as shown by ,c ,figure #bd4 ,the mortar should be fastened to a small wooden base which will support it in an inclined position as in the illustration4 ,illustration3 ,,fig4 #bc4--;,electric ,acrobats4 ,the ,acrobats are made of paper4 ,the little figure in the upper right-hand part of the illustration is the proper size4 ,bore two small holes through the wall of the mortar1 near the bottom and exactly opposite to each other ,insert two short pieces of coper wire1 ,w1 ,w1 in the holes and fasten them tightly in position4 ,the ends of the wires should be about one-eighth of an inch apart4 ,a small pinch of gunpowder is then placed in the bottom of the mortar4 ,charge the ,leyden jar and then discharge it through the mortar by connecting it to the two wires ,w1 ,w4 ,as soon as the spark passes1 the powder will explode4 ,an experiment such as this should be performed cautiously and the face and hands should be kept away from the powder4 ,do not put more than a pinch of powder in the mortar at a time and by all means keep the reserve supply out of the way so that there will be no danger of exploding it by accident4 99,an ,electric ,whirligig99 is an interesting piece of apparatus which may be built by following the suggestions contained in ,figure #be4 ,illustration3 ,,fig4 #bd4--,the ,electric ,mortar4 ,c is the ,mortar1 ,p the ,powder1 ,b a ,small ,ball and ,w ,w the two ,wires between which the ,spark igniting the powder takes place4 ,mount four pieces of dowel about three inches long at the corners of a wooden base about eight inches long and two inches wide so that they form four vertical posts as shown by ,a1 ,b1 ,c1 ,d4 ,the dowels1 as well as the wooden base should be carefully dried and shellaced so that they will not absorb any moisture4 ,stretch two pieces of straight stiff wire between the posts ,a ,c and ,b ,d1 near the top4 ,the wires should be perfectly straight and level4 ,the whirligig itself is made by passing a sewing needle through the axis of a small cork4 ,four small wires having the ends bent over at right angles should then be stuck in the cork as shown in the upper left hand part of ,figure #be4 ,all of the wires should point in the same direction4 ,illustration3 ,,fig4 #be4--;,an ,electric ,whirligig4 ,the four wires should all be the same length so that the whirligig is perfectly balanced4 ,the cork is then covered with tinfoil so that there will be an electrical connection between the four small wires and the needle forming the shaft4 ,the two wires ,a ,c and ,b ,d are connected together by a wire ,a ,b and a piece of flexible wire led to the ,wimshurst machine4 ,the opposite side of the ,wimshurst machine is then grounded or touched with the hand4 ,if the whirligig is laid on the wires ,a ,c and ,b ,d as shown in the illustration and it is perfectly balanced it will commence to revolve and roll along the wires just as soon as the ,wimshurst machine is set in operation4 ,it is the escape of the electricity from the points of the four wires on the whirligig which causes this4 ,other interesting experiments in static electricity may be performed with the aid of a ,wimshurst machine and the experimenter who is sufficiently interested to continue farther is referred to any good book on physics or some such volume as ,the ,boy ,electrician4 ,,chapter ,,ii4 ,,cells ,,and ,,batteries4 ,sources of ,current4 ,one of the chief difficulties of the average young experimenter is to secure a satisfactory source of current for operating his apparatus4 ,there are three means at his disposal and he may draw his electricity from #a4 ,a power or lighting circuit2 #b4 ,a dynamo2 #c4 ,batteries4 ,illustration3 ,,fig4 #bf4--;,a ,voltaic ,cell4 ,a ,voltaic ,cell consists of a ,strip of ,copper and a ,strip of ,zinc immersed in a dilute solution of ,sulphuric ,acid4 ,only those who are so fortunate as to live in a house wired for light and power service and supplied from the street mains1 are likely to be able to utilize the first named4 ,those experimenters who live in towns where there are no commercial power wires or whose homes are not wired for such service will have to therefore depend upon a dynamo or a battery4 ,a dynamo is a very satisfactory source of current1 provided some sort of power1 such as a windmill1 water motor or small engine is available for driving it4 ,a hand dynamo is unsatisfactory for some purposes because the experimenter is usually unable to drive the dynamo and attend to other work at the same time4 ,batteries are the most expensive source of current but for many reasons1 as explained above1 are all that is available to the average experimenter4 ,there are two classes of batteries1 known as #a4 ,primary batteries2 #b4 ,secondary or storage batteries4 99,primary ,batteries99 are those which generate their own current by the action of some chemical such as1 for example1 an acid upon a metal4 99,secondary ,batteries99 derive their current from a dynamo or other source of electricity and store it away in the form of 99,chemical energy99 until it is used up4 ,a storage battery might be likened to a pail1 which can be carried to a dynamo and filled full of electricity4 ,those who possess a storage battery can recharge it themselves from the #aaj-volt lighting or power circuit1 from a dynamo or by taking it to an automobile garage where recharging is done4 ,homemade batteries are not as practical as those which can be purchased ready made1 but the knowledge and experience gained in making your own are so valuable that every experimenter is urged to start in this way4 ,various materials such as zinc1 copper1 carbon1 etc41 can be used to make some very interesting and valuable batteries4 ,one of the most common mistakes made in reference to cells and batters is in calling a single cell a 99battery994 ,one cell is a cell4 ,more than one cell connected together is a 99battery of cells99 or simply a 99battery994 ,the ,voltaic ,cell4 ,the first practical cell was invented in #aghf by an ,italian professor named ,volta and it is1 therefore usually called the ,voltaic cell4 ,a ,voltaic cell may be easily made by the experimenter1 by placing some water1 mixed with sulphuric acid1 in a glass tumbler or a jelly jar and then immersing therein a strip of zinc and a strip of copper1 each about four inches long and one inch wide4 ,the strips must be kept separate from one another and should be scraped clean and bright before they are placed in the solution4 ,a copper wire is fastened to the top of each one of the strips4 ,the acid solution should be composed of one part of acid1 mixed with ten parts of water4 ,when mixing acid and water1 always remember to pour the acid into the water and never pour water into acid4 ,otherwise the solution will suddenly become very hot and is liable to crack the jar4 ,acid should always be mixed in a glass or earthenware vessel and never in any sort of a wooden or metal receptacle1 because it will attack and dissolve metals and wood4 ,as soon as the acid has been prepared for the ,voltaic cell fill a tumbler about three quarters full and then immerse the zinc and copper strips therein4 ,as soon as the strips are in the acid1 bubbles will commence to rise from the zinc4 ,these bubbles are a gas called hydrogen and are evidence of a chemical action which takes place in a battery4 ,the zinc is being dissolved by the acid and during the process1 sets free hydrogen gas4 ,it will probably be noticed that very few bubbles arise from the copper plate and that there seems to be little chemical action there4 ,it will also be noticed that if the two wires connected to the strips are brought together the bubbles will arise from the zinc much faster than before4 ,that is because1 when the wires are connected together1 a complete electrical circuit is formed3 ,the zinc is really being oxidized or slowly burned4 ,if zinc is burned in the open air or in a fire it will give out its energy in the form of heat but when it is burned in an acid solution in the presence of another metal it gives out its energy in the form of electricity4 ,the zinc strip in a ,voltaic battery is known as the 99negative99 pole or cathode1 and the copper strip1 as the positive pole or anode4 ,when the electrical circuit is completed by touching the two wires connected to the poles together1 the current is supposed to flow from the positive pole through the wires and back into the solution through the negative pole4 ,if the two wires1 instead of being connected together1 are connected to an electrical instrument called a voltmeter the needle or pointer on the meter will swing over and point to about one volt4 99,a ,voltmeter99 is an instrument for measuring electrical pressure or 99potential994 ,the pressure of an electric current is measured in 99volts99 just as the pressure of water may be measured in 99pounds994 ,if the copper strip is lifted out of the solution and a carbon plate or rod also having a wire attached is substituted in its place it will be found that the voltage or potential has increased to one and one-half volts4 ,zinc and carbon are said to have a greater potential difference than zinc and copper and inasmuch as it is usually desirable for a battery to have the greatest potential difference possible1 zinc and carbon are employed in the batteries of to-day instead of zinc and copper4 ,if the wires are then disconnected from the voltmeter and connected to an electrical instrument called an 99ammeter991 the needle or pointer will probably swing over until it indicates a current of perhaps ten amperes4 ,an 99ammeter99 is an instrument for measuring the volume of an electric current4 ,an 99ampere99 is a unit of current and is used to designate the rate of flow just as feet per second are used to denote rate of flow in the case of water in a pipe4 ,if the meter is allowed to remain connected to the cell for a short time it will be noticed that the pointer will commence to slowly drop back towards zero4 ,the cell is then becoming 99polarized991 which is to say that small bubbles of hydrogen which are liberated by the chemical action1 collect on the carbon and cause the strength of the battery to fall off4 ,if the battery is agitated or the carbon is lifted out and scraped it will be found that the current will immediately rise again to its first strength4 ,it would be a nuisance if it were continually necessary to scrape the carbon or shake the battery so as to avoid 99polarization99 and so another means is employed to secure the desired result4 ,this is accomplished by introducing certain chemicals into the solution which will give forth 99oxygen994 ,when oxygen and hydrogen meet under proper conditions they combine and form ordinary 99water994 99,bichromate of potash99 or as it is also often called 99potassium bichromate99 is the chemical most commonly employed for this purpose4 ,illustration3 ,,fig4 #bg4--,ordinary ,jelly ,glasses1 ,tumblers1 ,fruit ,jars1 etc1 make good ,jars for small cells by cutting off the tops4 ,homemade ,batteries4 99,the materials99 required for making batteries1 suitable as a source of current for the experimenter1 will not be found expensive in most cases4 99,carbon rods99 and 99plates99 may be purchased from an electrical supply house but they can also be easily and cheaply obtained from old dry cells4 ,dry cells may be split open with a cold chisel and a hammer4 ,care should be exercised not to break the carbon in removing it4 ,the round carbon rods used in arc lamps may be used for making batteries provided that if they are copper plated1 the copper is first removed by immersing the rod in a bath of nitric acid4 ,if this precaution is not taken there will be a local action set up between the copper and the carbon and the battery will not be as efficient as it will be if the copper is removed4 ,carbon rods and plates are easily drilled with an ordinary hand drill4 ,carbon is quite brittle and breaks easily1 therefore only very light pressure should be used4 ,while zinc rods and plates may also be purchased they are easily made by the experimenter who possesses a little ingenuity4 ,the melting point of zinc is quite low4 ,it can be melted in a small iron pot and cast into the form of rods or plates in plaster-of-,paris moulds4 ,plates may also be cut out of heavy sheet zinc4 ,illustration3 ,,fig4 #bh4--;,a ,simple ,home-made ,cell4 ,ordinary jelly-glasses1 tumblers1 fruit jars1 etc41 make good jars for small cells4 ,the tops of fruit jars and batteries can be cut off so as to make the opening larger4 ,the cutting can be done with an ordinary glass cutter or by filling a scratch completely around the jar or bottle1 at the place it is desired to cut it off1 with a three cornered file4 ,if a hot poker or wire is then held against the scratch it will commence to crack along the line and follow the hot poker as it is drawn around4 ,illustration3 ,,fig4 #bi4--;,a ,home-made ,battery having two ,carbon ,plates with a ,zinc ,rod between4 ,figure #bh shows a simple arrangement consisting of a carbon and a zinc plate mounted upon a wooden strip4 ,the strip is used to support the plates and rests across the top of the jar so that the plates hang below in the solution4 ,most chemicals attack wood and for that reason it is well to dip the strip in some hot paraffin4 ,the carbon and zinc plates are fastened on opposite sides of the wooden strip by means of a round headed screw and a washer4 ,a wire lead should be placed under the washer on each plate4 ,if the screw and washer are then smeared with some hot paraffin or vaseline they will be protected from corrosion4 ,care should be used so that the two screws employed to fasten the plates to the strip do not touch each other in the wood4 ,if they should1 the battery will be short circuited and the current will flow through the screws instead of the wires4 ,figure #bi shows an arrangement consisting of two carbon plates mounted upon a wooden strip4 ,the zinc element consists of a rod set in a whole in the strip between the two carbon plates4 ,it will be found that two carbon plates will form a better cell than one with only one plate or rod4 ,the arrangement illustrated in ,figure #cj shows two carbon rods and one zinc rod clamped between two wooden strips4 ,the zinc rod is placed in the center and the carbons to either side4 ,illustration3 ,,fig4 #cj4--,the ,elements for a ,simple ,home-made ,cell composed of two ,carbon ,rods and one ,zinc ,rod clamped between two ,wooden ,strips4 ,the wooden strips are cut away a bit at the points where they clamp the rods so as to form sort of a groove into which the rods fit without slipping or twisting4 ,the strips are drawn together tightly at the ends by two wood screws4 ,when more than one carbon rod or plate is used in a cell1 the carbons should all be connected together so as to form a single unit4 ,the drawing in ,figure #cj shows a wire twisted around the carbons so as to connect them together but it would be a far better connection if the wire was clamped between the carbons and the wood so that it is held firmly4 ,four carbon rods may be utilized by following the suggestion shown by the drawing in ,figure #ca4 ,this consists of a square piece of wood about #d x #d inches and one-half of an inch thick4 ,illustration3 ,,fig4 #ca4--;,four ,carbon ,rods and one ,zinc ,rod arranged to form the ,elements of a ,cell4 ,a zinc rod is set in a hole in the center4 ,four carbon rods are set in a circle around the zinc and held in place by screws4 ,all the carbon rods should be connected together4 ,the wooden top not only serves to support the carbon and zinc rods1 but will also act as a cover for the cell and prevent the solution from evaporating4 ,battery ,solutions or ,electrolytes4 ,it has already been shown how cells become polarized when the solution consists simply of sulphuric acid and water4 ,an ordinary acid solution also has the further disadvantage that the zinc element is continually consumed by the acid when it is in the solution1 regardless of whether current is being drawn from the cell or not4 ,it is of course consumed more rapidly when the circuit is complete and current is flowing than when it is not1 but the action is still nevertheless sufficiently rapid to entirely consume the zinc even in the latter case in a very short time4 ,if an ordinary acid solution is used therefore as the liquid or 99electrolyte991 as it is technically termed1 it is always necessary to lift the elements out of their solutions whenever the cells are not in use4 ,they should be lifted out and carefully washed so as to remove all traces of acid4 ,illustration3 ,,fig4 #cb4--;,a ,battery of ,three ,cells arranged so that they can all be lifted out of the solution at once4 ,a milder chemical which does not attack the zinc so rapidly as an acid is often used wherever a battery is to be employed for ringing bells1 operating sounders1 telephoning1 etc41 and only a small amount is required4 ,sal-ammoniac or chloride of ammonium1 as it is also called1 is a good chemical for this purpose4 ,it is very cheap and only requires to be dissolved in water4 ,a good strong solution should be made and an element consisting of several carbons and one zinc such as those shown in ,figures #bi1 #cj and #ca used4 ,such a cell will give about #a4e volts and #c or #d amperes4 ,if the current is drawn from the battery continuously or too rapidly1 it will also 99polarize99 and the current will begin to fall off4 ,the advantage of a sal-ammoniac cell is that the elements may be left in the solution when the cell is not in use1 without appreciable waste of the zinc4 ,a very powerful cell of the non-polarizing type capable of delivering a heavy current and having an ,e4 ,m4 ,f4 of two volts can be made by adding some potassium bichromate to a sulphuric acid solution4 ,an electrolyte of this sort may be prepared by dissolving four ounces of bichromate of potash in sixteen ounces of water4 ,add to this1 four ounces of sulphuric acid4 ,the acid should be added slowly and the solution stirred at the same time4 ,this solution will be found an excellent one to use with cells having carbon and zinc elements4 ,the current and voltage are much higher than those of an ordinary acid solution4 ,this type of cell also has the disadvantage that the zincs waste away rapidly when in the solution1 regardless of whether current is being drawn or not4 ,this can be partly overcome by 99amalgamating99 the zincs with mercury4 ,in order to amalgamate your battery zincs1 procure a little 99mercuric nitrate99 from a druggist or chemical house4 ,dissolve the mercuric nitrate in a small amount of water and then rub the zincs with a wad of cotton or cloth which has been dipped in the mercuric nitrate solution4 ,the arrangement shown in ,figure #cb is a very convenient one to follow in arranging a battery of three or more cells4 ,the elements of three cells are all mounted upon a strip of paraffined wood and connected in series4 ,the three battery jars are placed in a row so that each pair of elements will dip into their proper jar when the strip is laid across the tops4 ,such an arrangement is not only more compact than one having the elements composing each cell mounted upon separate strips1 but will be found very convenient when an electrolyte composed of bichromate of potash and acid is used1 because all the elements may then be raised out of the solutions at the same time4 ,it is possible to place the jars in a frame and arrange a windlass fitted with a crank so that the elements may be easily raised or lowered from and to the solution4 ,such an arrangement is called a plunge battery4 ,connecting ,cells4 ,cells may be connected either in 99series991 in 99multiple991 or in 99series-multiple991 depending upon the number of cells to be used and the amperage and voltage desired4 ,illustration3 ,,fig4 #cc4--,showing how ,cells are arranged when they are connected in ,series4 ,the ,voltage of ,six ,dry ,cells connected in series as above would be approximately #f x #a4e or #i ,volts4 ,cells are in series when they are connected with a wire leading from the negative pole of one of the positive pole of another1 so that the current flows through each one in turn4 ,figure #cc shows six cells connected in series4 ,cells are placed in series when voltage is the most important factor4 ,the total voltage of the battery is then equal to the sum of the voltages of the cells4 ,for example1 the voltage of the ordinary dry cell is about #a4e and therefore if four dry cells are connected in series the total voltage of the battery will be six4 ,if six dry cells are connected in series the voltage at the terminals will be about nine4 ,when a heavy amperage is desired1 cells are connected in multiple4 ,figure #cd shows six cells connected in multiple4 ,it will be noticed that all the negative poles are connected together to form one terminal1 while all the positive poles form another4 ,the amperage of the average dry cell is about #bj4 ,the amperage of a battery of cells connected in multiple is equal to the sum of the amperages of the separate cells4 ,the amperage of four cells connected in multiple will be about #hj and about #abj in the case of six cells4 ,illustration3 ,,fig4 #cd4--,showing ,six ,dry ,cells connected in ,multiple4 ,the ,voltage of such an arrangement would only be #a4e1 but the ,amperage available would be six times that possible from ,cells connected as in ,figure #cc4 ,the life of the average dry cell is about twenty ampere hours under normal conditions4 ,if however the cell is discharged at a high rate1 say for instance1 five amperes1 it will be found that the life is less than twenty ampere hours4 ,on the other hand1 if the discharge rate is very low1 as for example1 one-quarter of an ampere1 the capacity of the cell will be greater4 ,in order to get the most economical service from a battery it is therefore advisable to lighten the load as far as possible1 and cells are consequently often connected in 99series-multiple99 with that result in view4 ,in a case1 for illustration1 where it might be desirable to secure a current #d #a_/b volts and five amperes from dry cells1 the series-multiple arrangement could be recommended4 ,three dry cells connected in series will furnish #d #a_/b volts and five amperes1 but by using two sets as in ,figure #ce1 the load is divided between them and each set will only have to furnish amperes to the circuit4 99,two sets of cells used in series-multiple will therefore last more than twice as long as either set would alone499 ,the series-multiple arrangement is recommended where cells are to be used for operating toy trains1 induction coils1 motors1 etc41 as being the most economical4 ,always be sure to use large wire in connecting cells4 ,fine wire offers considerable resistance to the electrical current and the full benefit of the batteries cannot be secured when it is used4 ,illustration3 ,,fig4 #ce4--,showing how to connect a ,battery of ,cells in ,series-,multiple4 ,use care to scrape all connections so that they are clean and bright4 ,tighten the binding posts with a pair of pliers so that there is no chance of their becoming loose4 ,another wise precaution is to always arrange batteries so that there is a small space between two cells and no likelihood of any of the wires or binding posts coming into contact with one another so as to form a short circuit4 ,after the connections have been carefully made a little vaseline smeared over them will prevent corrosion4 ,illustration3 ,,fig4 #cf4--;,battery ,connectors like that shown above can be obtained for #a #a_/b cents each and will be found to be very handy4 ,storage or ,secondary ,cells4 ,storage or secondary cells 7also sometimes called accumulators71 differs from primary cells in that they will not give forth an electric current until they have been 99charged99 by passing an electric current through them4 ,illustration3 ,,fig4 #cg4--;,a ,simple ,experimental ,storage ,battery consisting of two ,lead ,plates immersed in ,dilute ,sulphuric ,acid4 ,the ,storage ,cell is therefore a very convenient means of taking electric energy at one time or place and storing it up for future use4 ,from this it must not be implied that electricity is actually stored in such a battery4 ,the energy of the electric current is really changed into chemical energy and this energy produces electricity when the cell is again discharged4 ,the superiority of the storage cell over any other form of battery is universally recognized4 ,the dry cell has an ,e4 ,m4 ,f4 of only #a4e volts and deteriorates rapidly with age4 ,the ,e4 ,m4 ,f4 of a storage cell is #b volts1 or #cc #a_/c per cent higher4 ,storage cells will operate almost any electrical device with increased power over any other form of battery4 ,a wireless set will send farther1 lamps will turn steadier and a motor will give more power4 ,illustration3 ,,fig4 #ch4--,showing how to charge a ,simple ,storage ,cell composed of two ,lead ,plates immersed in ,sulphuric ,acid by connecting it to two ,bichromate of ,potash ,cells4 ,if properly cared for1 a storage cell will last indefinitely4 ,it may be recharged an unlimited number of times and is exactly as good as new each time4 ,a dry cell must be thrown away when discharged4 ,storage cells are rated by their output in 99,ampere ,hours499 ,an 99,ampere ,hour99 is the amount of current represented by one ampere flowing for one hour4 ,a #aj ampere hour cell will give #b amperes for five hours1 #a ampere for #aj hours1 #a_/b ampere for #bj hours1 etc4 ,the ampere hour capacity of a cell divided by the amount of current being used will determine how long that current can be drawn before recharging is necessary4 ,storage cells may be recharged from any source of 99direct99 current1 that is1 from the lighting circuit1 in series with a lamp1 from a small shunt wound dynamo1 from dry cells or other primary batteries1 or from alternating current by using a 99,rectifier994 ,an ,experimental ,storage ,cell4 ,storage cells consist of lead plates immersed in an electrolyte of dilute sulphuric acid4 ,cut two strips1 one inch wide and five inches long1 out of sheet lead about one-eighth of an inch thick4 ,attach a wire to each one of the plates and then immerse them in a jar full of 99electrolyte99 composed of3 #a4 ,ten parts of water4 #b4 ,one part of sulphuric acid4 ,connect the wire leading from the plates to a voltmeter and you will notice that the pointer will not move away from zero4 ,disconnect the wires and mark one plate as the 99positive991 by means of a little cross2 mark the other plate 99negative991 with a straight line4 ,connect two good bichromate cells in series and lead the positive terminal to the lead plate marked with a cross4 ,connect the negative pole of the battery to the other lead plate4 ,bubbles of gas will immediately begin to arise from the lead plates4 ,let the batteries remain connected for about five minutes and then remove them4 ,if you then connect the two lead plates to the voltmeter again you will find that the needle now swings nearly to two volts4 ,you will also find that your storage cell1 for the two lead plates are now a storage cell1 will also ring a bell or run a small motor for a few seconds4 ,the two lead plates became 99charged99 when the current from the bichromate cells was passed through them4 ,this little experiment illustrates the principle of the storage cell very well4 ,a storage cell made of lead plates in the manner just described would not possess sufficient capacity to make it worth while as a practical cell4 ,it has been found that if instead of a solid flat plate1 a framework or grid is used1 consisting of a set of bars crossing one another at right angles1 leaving spaces between1 which are filled with a paste made of lead oxides1 there will be a considerable gain in the capacity of the cell4 ,a ,homemade ,storage ,cell4 ,the storage cell illustrated in the accompanying illustrations is very simple to make and a battery of them capable of delivering six or eight volts will prove a very convenient source of current for performing all sorts of electrical experiments4 ,illustration3 ,,fig4 #ci4--,showing how the ,plates for a ,storage ,cell may be made from ,sheet ,lead by boring it full of holes and filling with paste4 ,the plates are cut from sheet lead from one-quarter to five-sixteenths of an inch thick4 ,the height and width will depend upon the size of the jars used4 ,there are several sizes of rectangular glass storage cell jars on the market1 and if the plates are made about three inches wide and three and one-half inches high1 they will fit the smallest size of jar4 ,a lug about one inch and one-half long and three-quarters of an inch wide is left projecting at the top4 ,three plates are used in each cell4 ,each cell will have an ,e4 ,m4 ,f4 of two volts when fully charged4 ,in order therefore to have a battery capable of delivering six volts1 three cells will be necessary4 ,nine plates will be required for three cells4 ,the body of the plates should then be drilled full of holes about one-eighth of an inch in diameter as shown by ,b in ,figure #ci4 ,the plates are now ready for pasting4 ,select three of the plates and mark them with a small cross4 ,these are to be 99positive99 plates when finished4 ,the paste for these plates is made by mixing red lead with diluted sulphuric acid4 ,the paste should form a good stiff mixture4 ,lay the three plates upon a smooth board and press the paste carefully into the holes with a flat stick4 ,they are then laid aside to dry and harden4 ,illustration3 ,,fig4 #dj4--;,a set of three ,plates composed of ,one ,positive and ,three ,negatives assembled to form a ,cell4 ,the six remaining plates are to be 99negatives99 when finished and they are pasted in identically the same manner as the positives except that the paste is made of a mixture of yellow lead and dilute sulphuric acid instead of red lead4 ,a pasted plate is shown at the right in ,figure #ci4 ,cut six rectangular pieces1 three by three and one-half inches1 of heavy blotting paper or thin whitewood4 ,the thin wood used in the construction of fruit baskets may be used for this purpose4 ,these rectangles are to be used as separators between the plates4 ,illustration3 ,,fig4 #da4--;,glass and ,rubber ,storage ,cell ,jars which are on the market for the ,electrical ,experimenter and may be purchased very reasonably4 ,the plates should then be assembled in groups of three1 as shown in ,figure #dj4 ,the positive plate is placed in the centre with a separator on either side4 ,two negative plates are then placed on the outside4 ,the lugs on the negative plates should come opposite to each other4 ,a square lead block having a hole bored through the centre may be placed between the two negative lugs4 ,the lugs are then clamped together with a binding post and a screw4 ,the plates are held in a compact bundle by two heavy rubber bands passing around them4 ,each group of plates is then placed in its proper jar and the jar filled full of a mixture composed of3 #a4 ,four parts of water1 and #b4 ,one part of sulphuric acid4 ,the plates are now ready for forming4 ,the cells are connected in series by leading a wire from the negative of one to the positive of another and so on4 ,the terminals of the battery are then connected to a steady source of direct current of at least ten volts4 ,the positive pole of the battery should be connected to the positive of the current source and the negative to the negative4 ,the source of current may be 7#a7 the #aaj volt ,d4 ,c4 supply in series with a lamp bank as described in ,chapter ,,iv2 7#b7 the #aaj volt ,a4 ,c4 supply after it has passed through a rectifier2 7#c7 another battery1 or 7#d7 a shunt wound dynamo4 ,illustration3 ,,fig4 #db4--;,an empty ,storage ,cell ,grid and also a ,pasted ,plate both of which are on the market for experimenters who wish to build their own ,cells4 ,the current passed through the storage cells during the forming process should be about one ampere for cells of the size described above4 ,as soon as the positive plates of the storage cells have changed to a dark chocolate-brown color and the negatives to a gray-slate1 disconnect the storage battery from the source of current and proceed to use it just as you would any ordinary battery4 ,use it until it is exhausted and then connect to the charging current again1 taking care to make certain that the positive pole of the battery is connected to the positive pole of the current source4 ,after the cells have been recharged and discharged in this manner about ten times they will be completely formed and ready for permanent service4 ,complete directions for recharging storage cells and instructions for their care and maintenance will be found further on4 ,the only objection to the storage cells just described is that the paste is liable to fall out of the plates in time4 ,the plates or grids as they are called used in commercial storage cells are cast in elaborate moulds which make it possible to overcome this difficulty4 ,such grids cannot however be made by the experimenter4 ,jars1 pasted plates and empty grids may be purchased from well known firms dealing in apparatus for the experimenter1 and with their aid it is possible to construct a very substantial and durable storage cell at home4 ,the empty grids or fully formed plates may be purchased in the following sizes3 ,positive or ,negative ,plate1 size #b #g_/h x #b #a_/b #c #a_/h x #b #g_/h #c #e_/h x #e #c_/d #d #c_/d x #b #g_/h #d #c_/d x #e #c_/d ,glass jars will be found satisfactory for stationary batteries4 ,rubber jars are however advisable for portable batteries4 ,jars of the following sizes may be easily obtained3 ,glass ,jar1 outside #c #c_/d x #d x #a #a_/b inches ,glass ,jar1 outside #c #c_/d x #e x #a #a_/b inches ,hard ,rubber ,jar1 outside4 #f #a_/b x #c #a_/b x #a #a_/b inches ,hard ,rubber ,jar1 outside4 #f #a_/b x #f #a_/b x #a #a_/b inches ,if the empty grids are purchased1 they should be pasted in the same manner as those plates just described4 ,an empty grid of this type is shown in ,figure #db4 ,a pasted plate is shown along side of it4 ,the two negative plates in cells of this type are fastened together by burning into a lug1 ,the lugs for this purpose may also be purchased and will be found inexpensive4 ,the long lugs on the negative plates are cut off so that they will only just project through the rectangular holes in the connecting lug when the latter is in place1 as shown by ,a in ,figure #dc4 ,the plates are burned into the connecting lug by using a red hot soldering iron to melt the lead until they flow together at those points4 ,this is a job requiring a little skill and the experimenter had better practice burning some odd bits of lead together first so as to avoid all possibility of spoiling his plates4 ,illustration3 ,,fig4 #dc4--,two ,negative ,plates burned together and the ,connecting ,lug used4 ,the positive plate is placed in position1 as shown in ,figure #dd4 ,wooden separators of the same size as the plates are placed between the plates and the whole strapped together with heavy rubber bands near the top and bottom4 ,the cells are then placed in their jars and the latter poured full of electrolyte1 providing that the batteries are to be of the stationary or open type4 ,if it is desirable that they be portable and arranged so that the acid will not easily spill1 it will be necessary to seal them at the top4 ,the sealing is accomplished by cutting a cover strip out of thin wood which will slip down over the lugs into the jar so that it comes about one-half an inch below the top4 ,a small hole should be bored in the centre of the cover strip to receive a short piece of hard rubber or lead tubing1 which will act as a vent and permit the gases formed during charging to escape or the electrolyte to be emptied at will4 ,illustration3 ,,fig4 #dd4--,the ,elements of a ,storage ,cell composed of two ,negative ,plates and one ,positive ,plate in their proper position4 ,the cover strip should fit into the jar tightly so that when the sealing mixture is poured in it will not run down around the plates or into the jar4 ,the top of the battery is then poured full of a molten compound of asphaltum and pitch4 ,no attempt should be made to seal the batteries when they contain acid4 ,the inside of the jar should be clean and dry4 ,after the cells are sealed and filled with electrolyte they are ready for either forming or charging1 depending upon whether the empty grids were purchased and pasted by the experimenter or the plates were bought already pasted and formed4 ,if they require forming1 they must be put through the same forming process which has already been described4 ,the finished cells when sealed will appear like those shown in ,figure #de1 according to the sizes of plates and jars used4 ,illustration3 ,,fig4 #de4--,three different sizes of ,storage ,cells which may be purchased ready made or built by the experimenter out of prepared materials as explained4 ,recharging and ,caring for ,storage ,cells4 ,storage cells are especially affected by the usage given them4 ,if they are mistreated they will quickly go to pieces1 whereas1 on the other hand if well treated they will last indefinitely4 ,it is important that the electrolyte used in the cells should always be of the proper strength4 ,the only accurate method of preparing the electrolyte is with the aid of a 99hydrometer994 ,a hydrometer is an instrument for determining the specific gravity of solutions4 ,it is a little device which looks somewhat like a thermometer4 ,it is placed in the solution and allowed to float4 ,there is a numbered scale along the upper part of the hydrometer and the 99specific gravity99 or strength of the solution is indicated on the scale by the point which is level with the surface of the solution4 ,the normal specific gravity for a storage battery solution should be about #a4bej4 ,the strength can be increased by adding more acid and decreased by adding water4 ,ordinary commercial or technical grades of sulphuric acid and ordinary water are satisfactory for primary batteries1 but the acid and water used in making the electrolyte for storage cells must be 99chemically pure99 if you wish to obtain good results and desire your batteries to hold their charge while standing4 ,storage cells can be recharged with ,,direct current only4 ,a dynamo for recharging storage cells must be ,,shunt wound4 ,the voltage of the charging current must be greater than that of the storage cells4 ,about three volts of charging current will be required for each cell of the storage battery4 ,cells may be connected in multiple when recharging so as to bring the voltage of the cells below that of the charging current4 ,it will of course1 however1 take much longer to recharge cells connected in multiple than the same cells connected in series1 provided that the amperage of the current is the same4 ,storage cells must not be recharged too rapidly4 ,it is better to recharge them slowly rather than too rapidly4 ,two amperes is plenty for small cells of #aj-ae ampere hours capacity4 ,three amperes is sufficient for cells of #ae-be ampere hours capacity4 ,five to six amperes is the right charging rate for a #dj ampere hour battery and #h amperes in the case of a #fj ampere hour battery4 ,illustration3 ,,fig4 #df4--;,a ,hydrometer for preparing and testing the ,acid ,solution for ,storage ,batteries4 ,storage cells should never be allowed to stand discharged for any length of time or the plates are liable to become hardened and sulphated4 ,they turn white when they are sulphated4 ,it will take a great deal of charging and recharging to get them back in shape when once they get in that condition4 ,never short circuit a storage cell or discharge it too rapidly4 ,whenever any great amount of sediment collects in the bottom of the jars1 pour out the acid solution and wash the cell out thoroughly with some pure water4 ,the plates of a storage cell should always be raised up off the bottom of the jar1 so that any sediment which collects will fall below4 ,illustration3 ,,fig4 #dg4--,the proper way of ,recharging ,storage ,cells from the #aaj ,volts ,d4 ,c4 ,supply in series with a set of ,lamps4 ,it is a very good plan to keep the terminals of a storage cell or battery smeared with vaseline so that they will not become corroded4 ,you can tell when a storage cell or battery is fully recharged by the color of the plates4 ,the positives will in that case be a dark chocolate brown and the negatives a light slate gray color4 ,a cell which is fully recharged will indicate #b #a_/b volts on a voltmeter connected across its terminals while the charging current is still on4 ,,chapter ,,iii4 ,,how ,,to ,,reduce ,,the #aaj ,v4 ,d4,c4 ,,or ,a4,c4 ,,to ,a ,,lower ,,voltage ,,for ,,experimental ,,purposes4 ,it is often desirable to operate experimental apparatus and other electrical devices from the #aaj volt lighting circuit4 ,such a circuit may be either direct or alternating1 commonly spoken of as ,d4,c4 and ,a4,c4 ,the easiest method of reducing the voltage of the #aaj volt circuit to a value where it can be used in place of an ordinary battery is to use a step-down transformer4 ,a transformer will1 however1 operate only on alternating current and it is impossible to use it on a direct current circuit4 ,illustration3 ,,fig4 #dh4--;,a ,lamp ,bank consisting of a ,set of #aaj-,volt ,lamps connected ,multiple and arranged to be placed in series with any device it is desired to use on the #aaj-,volt ,current4 ,it is therefore necessary to secure the desired result by placing an adjustable resistance in the circuit and the most practical method of accomplishing this is to use a lamp bank4 99,a ,lamp ,bank99 consists of a number of incandescent lamps arranged on a board so that any desired number may be quickly included in or withdrawn from the circuit4 ,figure #dh illustrates such an arrangement4 ,it consists of a number of ,edison sockets of the type known as flat-base porcelain receptacles1 mounted in two rows upon a suitable baseboard4 ,six or ten receptacles will usually prove sufficient for the ordinary lamp bank4 ,the lamps are connected in series-multiple4 ,the diagram in the upper left hand corner of ,figure #dh shows just how this is done4 ,four binding posts should be mounted upon one end of the board and marked ,a1 ,b1 ,b and ,c as shown4 ,b and ,b are connected together1 or to use an electrical term1 are in common4 ,the #aaj volt supply is connected to the posts ,b and ,c4 ,if any electrical device is then connected to ,a and ,b and a lamp placed in each one of the receptacles1 the lamps will be in series with the apparatus and lower the voltage of the #aaj volt circuit to a value where it may be used for recharging storage cells1 operating toy motors1 electroplating1 lighting miniature lamps1 running toy railways1 etc4 #aaj volt carbon lamps should be used on a lamp bank operated on a #aaj volt circuit4 ,carbon lamps consume more current than tungsten lamps and it will therefore not be necessary to use as many4 ,each #af c4p4 #aaj volt lamp used will allow about one-half of an ampere to pass through the circuit4 ,thirty-two candle power bulbs of the same voltage will pass about one ampere1 while an #h c4p4 bulb will only permit one-quarter of an ampere to flow4 ,it is therefore very easy to regulate the amount of current flowing by using lamps of different sizes and screwing them in or out of the receptacles4 ,a lamp bank such as this may of course be used on either the #aaj volt ,a4 ,c4 or ,d4 ,c4 circuit4 ,,chapter ,,iv4 ,,how ,,an ,,alternating ,,current ,,may ,,be ,,changed ,,into ,,direct ,,current ,,by ,,means ,,of ,,an ,,electrolytic ,,rectifier4 ,oftentimes the only source of electrical energy for experimental work is the #aaj volt alternating current supply4 ,this may be reduced to a voltage suitable for operating small battery motors1 trains1 lamps1 etc41 by means of a lamp bank resistance or a step-down transformer4 ,direct current is 99necessary99 however in order to recharge storage batteries and to operate many other devices4 ,the electrolytic rectifier is a device for changing alternating current into direct current and will be found satisfactory for this purpose1 provided too much is not demanded of it4 ,it is fairly efficient if used only to rectify small amounts of current4 ,it is not efficient when large amounts of currents are passed through it and quickly becomes very hot in such a case4 ,an electrolytic rectifier consists of an electrode of iron or lead and one of aluminum immersed in a solution of sodium phosphate4 ,illustration3 ,,fig4 #di4--;,a ,single ,cell of ,electrolytic ,rectifier4 ,an ordinary glass battery jar may be used to hold the solution1 preferably one measuring #e x #g inches4 ,the electrodes are supported by a wooden cover which also serves to prevent the solution from evaporating4 ,the cover may be circular in form and simply rest on the top of the jar or may have a groove turned on the underside so that it fits the rim of the jar snugly4 ,it is a wise precaution to thoroughly saturate the cover with paraffin by immersing it in a molten bath of that material4 ,if the cover is allowed to remain in the molten paraffin until all bubbles have ceased to rise1 the paraffin will thoroughly permeate the wood and protect it from the action of the ,chemical solution used in the rectifier4 ,illustration3 ,,fig4 #ej4--;,an ,electrode cut out of ,sheet ,metal4 ,the top is bent over at right angles and drilled so that it can be mounted on the underside of the cover4 ,as stated above1 one electrode may be made of iron or lead4 ,the other should be aluminum4 ,the electrode may be cut out of sheet metal and made in the form of a strip about one and one-half inches wide and six inches long4 ,the top of each electrode is bent over at right angles and bored with a small drill and an #h-cb brass machine screw is passed through the hole and through the cover into the bottom of the binding post mounted on the top of the cover1 thereby serving not only to fasten the electrode securely in place to the underside of the cover1 but also to establish connection between the electrode and the binding post itself4 ,electrodes which are cut out of sheet metal possess the disadvantage that they are not quite as efficient and will not last as long as electrodes which are cast4 ,cast electrodes are much heavier and far more efficient in many other ways4 ,they cannot be easily made by the young experimenter1 but may be procured from any one of several firms dealing in supplies for experimenters4 ,the right hand sketch in ,figure #eb shows how the electrodes should appear when they are mounted in position on the underside of the cover4 ,they are placed about two and one-half inches to three inches apart4 ,the solution is formed by dissolving sodium-phosphate in water until a saturated solution is formed1 that is1 until the water will not dissolve any more4 ,sodium-phosphate dissolves rather slowly and it will be necessary to stir the solution and crush the lumps which form with a stick or glass rod4 ,fill the jars nearly to the top and then place the electrodes into position4 ,illustration3 ,,fig #ea4--;,a ,cast ,electrode will last much longer than one cut from ,sheet ,metal4 ,cast ,electrodes like that above are on the market and can be purchased very reasonably4 ,the action of the electrolytic rectifier1 in changing alternating current into direct current1 is interesting and peculiar4 ,the rectifier acts much like a valve which opens one way and closes the other4 ,if a battery is connected to the electrodes of a rectifier1 the positive pole of the battery being connected to the lead or iron electrode and the negative of the battery to the aluminum electrode of the rectifier1 the current from the battery will flow through the rectifier and nothing unusual will happen4 ,if1 however1 the poles are reversed so that the positive pole is connected to the aluminum electrode1 oxygen gas will form on the aluminum4 ,the action of the oxygen gas is to combine with the aluminum and form a coating of 99aluminum oxide99 all over the electrode4 ,aluminum oxide is an insulator and it therefore quickly forms an insulating coating which shields the electrode from the solution and stops the passage of the current4 ,this action is almost instantaneous4 ,illustration3 ,,fig4 #eb4--;,a completed single ,cell ,rectifier4 ,the right hand sketch shows how the ,electrodes are mounted on the underside of the cover4 ,if the rectifier is connected to an alternating current supply it will act just like a valve permitting the current to flow in one direction but stopping it whenever the aluminum electrode is 99positive994 ,the resulting current is therefore1 under proper conditions1 an intermittent current flowing only in one direction4 ,an alternating current may be represented by a wavy line drawn above and below a straight line4 ,every time that the wavy line crosses the straight line it represents an alternation or a reversal of the direction in which the current flows4 ,illustration3 ,,fig4 #ec4--;,a ,diagram showing how a ,rectifier cuts off one-half of the ,alternating ,current ,wave and changes it into ,pulsating ,direct ,current4 ,the direct current from an electrolytic rectifier working under proper conditions is practically one-half of the alternating current wave and may be represented by the series of waves marked by ,c in the lower part of the illustration in ,figure #ec4 ,it will be noticed that these lines do not cross the straight line and the current therefore does not reverse but flows in one direction only4 ,when a single cell of rectifier is used on the #aaj volt current supply1 it should be placed in series with a lamp bank or a step-down transformer so that the current is reduced to lower voltage4 ,figure #ed shows how to connect a storage cell in series with a single cell of rectifier and a lamp bank so that the storage cell may be recharged from the alternating current4 ,a step-down transformer will be found more efficient and not quite so wasteful of current as a lamp bank4 ,the rectifier and the storage cell are simply connected in series with the secondary of the step-down transformer in order to secure this result4 ,illustration3 ,,fig4 #ed4--;,circuit showing how a ,single ,cell of ,rectifier should be connected in series with a ,lamp ,bank to ,recharge a ,storage ,cell4 ,a is the ,aluminum ,plate and ,l the ,lead or ,iron ,plate4 ,illustration3 ,,fig4 #ee4--;,diagram showing the ,difference in ,current after it has been passed through a ,single ,cell or ,rectifier and after passing through a ,four-,cell ,rectifier4 ,the negative pole of the storage cell must always be connected to the aluminum electrode of the rectifier4 ,the series of little curved lines at the bottom of ,figure #ec which represent the alternating current after it has been changed into direct current by the action of the rectifier1 have a space between each two1 showing that there are periods during which no current flows but that the current is intermittent and made up of a number of short impulses4 ,one-half of the alternating current is therefore really wasted4 ,it is possible1 by means of four cells of rectifier1 to so connect them that both halves of the alternating current wave are utilized and the spaces are filled up as shown in the lower part of ,figure #ee4 ,illustration3 ,,fig4 #ef4--;,diagram showing how a ,four-,cell ,rectifier is connected4 ,the ,alternating ,current ,source is connected to ,c and ,d4 ,the ,direct ,current is taken off at ,a and ,b4 ,the ,electrodes marked ,a1 ,a1 ,a1 ,a are the ,aluminum ,electrodes4 ,l1 ,l1 ,l1 ,l may be ,lead or ,iron4 ,the current which would normally be in a reverse direction1 and therefore below the straight line1 has been completely reversed so that it flows in the same direction as that above the line4 ,figure #ef shows how to connect four cells of rectifier in order to secure this result4 ,an electrolytic rectifier composed of cells approximately #e x #g inches1 as described1 will not efficiently handle a current of over two to two and one-half amperes4 ,a four cell rectifier will operate to the best advantage on a voltage over #ej1 and for that reason it is always best to use a lamp bank or step-down transformer in connection with it4 ,when the solution in a rectifier becomes hot it will not operate as efficiently as when cold4 ,the solution becomes exhausted after a certain amount of usage and requires renewal4 ,this condition will be indicated by the failure of the rectifier to operate properly4 ,the old solution should then be thrown away and the jars and electrodes washed and cleaned thoroughly before the new solution is poured in4 ,illustration3 ,,fig4 #eg--;,a ,complete ,four-,cell ,rectifier connected together and ,mounted in a ,tray4 ,,chapter ,v4 ,,how ,,to ,,build ,a ,,step-,,down ,,transformer ,,for ,,reducing ,,the #aaj ,,volt ,a4 ,c4 ,,for ,,experimental ,,purposes4 ,a ,step-,down ,transformer will reduce the #aaj volt alternating current to a low voltage4 ,these low voltage currents are still alternating but will operate almost all sorts of direct current apparatus with the exception of permanent magnet type motors which are now practically obsolete4 ,a suitable step-down transformer may be used to operate electrical toys1 such as small fans1 motors and miniature electric railway trains1 ring bells1 light small lamps1 operate spark coils1 etc41 in fact the different uses are practically unlimited1 depending only upon the ingenuity of the experimenter4 ,illustration3 ,,fig4 #eh4--;,details of the two different ,pieces of ,sheet ,iron used in building up the ,core4 ,sufficient of each piece are required to form a pile of each three-quarters of an inch thick4 ,a step-down transformer cannot be used to recharge storage cells or for electro-plating unless the current is first passed through a rectifier4 ,a transformer is both in principle and construction really very simple4 ,it consists simply of two coils of wire wound around an iron core4 ,one coil consists of many turns of fine wire and is connected to the #aaj volt alternating current4 ,this coil is called the 99primary994 ,the other coil consists of a smaller number of turns of larger wire and is called the 99secondary994 ,the lower voltage currents are obtained from the secondary4 ,the first step to take in making a transformer is to procure some sheet iron of the sort used for making stove pipes4 ,it is called stove pipe iron4 ,this iron will have to be cut into a number of pieces like ,a and ,b in ,figure #eh4 ,the exact shape and dimensions are most easily understood from the illustration4 ,a somewhat resembles a three-pronged fork1 while ,b is simply a strip #b #e_/h inches long and #a_/b inch wide4 ,illustration3 ,,fig4 #ei4--,the ,method used in piling up the ,strips to ,assemble the ,core4 ,a sufficient quantity of each piece will be required to make a pile three-quarters of an inch thick when tightly compressed4 ,the best method of procedure is to lay out one piece like ,a very accurately and then cut it out4 ,hammer it out perfectly flat and use it as a pattern to lay out the other pieces with4 ,the cutting can be done with a pair of ordinary tin snips4 ,the pieces should all be cut very accurately and truly so that they will match when piled up4 ,the rough edges of the iron can be smoothed up with a file4 ,figure #fj shows how the core should look when it is assembled4 ,it should form a rectangle three and three-quarters inches long and two and five-eighths inches wide4 ,the method of piling up the 99laminations991 as the pieces forming the core are called1 is illustrated in ,figure #ei4 ,one of the strips ,b is placed against the open end of ,a4 ,the next set of strips is arranged in the same manner except that the position is reversed so that the strip ,b is at the opposite end of the pile4 ,this method is continued1 reversing each alternate set of strips until the pile is complete as shown in ,figure #fj4 ,after the core has been assembled1 examine it carefully and make certain that none of the strips are of the wrong size so that some protrude farther than others4 ,the next step in the work is to make the windings1 ,the windings are each made on a cardboard tube having an inside diameter of about #a #a_/af inches4 ,the tubes may be made by rolling a strip of wrapping paper around a piece of broom handle or some other round object of the proper size4 ,the edges of the tube should be glued so that it cannot unroll4 ,illustration3 ,,fig4 #fj4--;,assembly of the ,core4 ,the 99secondary winding99 is an inch and nine-sixteenths long and one and thirteen-sixteenths of an inch in diameter4 ,it is composed of #abj turns of ,no4 #ag ,b4 ,s4 gauge single cotton covered wire wound in six layers4 ,a tap is led out at the end of the second layer4 ,the 99primary99 is one and nine-sixteenths inches in diameter and one and one-sixteenth long4 ,it is composed of #ajdj turns of wire wound in #ac layers4 ,illustration3 ,,fig4 #fa4--;,details of the ,primary and ,secondary ,windings4 ,illustration3 ,,fig4 #fb4--,showing the ,core completely assembled with the ,primary and ,secondary in position4 ,p1 ,p are the ,primary ,terminals4 #a1 #b and #c are the ,secondary ,terminals4 ,the windings must be carefully made and every care taken to see that they are properly insulated4 ,it is a very good plan to insert a layer of paper between each two layers of wire4 ,after the windings are finished they are ready to assemble on the core4 ,in order to put them in place1 the core must be taken apart first4 ,the primary and secondary go along side of each other on the centre tongue of the ,a strips4 ,the core is put together again with the windings in position by slipping each alternate ,a strip through from the opposite direction so that when it is all assembled the result is like that shown in ,figure #fb4 ,the transformer is now ready for mounting4 ,the usual method of mounting a step-down transformer is to place it in an iron box or case4 ,this is of course the best way because the windings and core are then protected4 ,the experimenter who wishes to go to the trouble of building an iron box for his transformer will find it worth the time4 ,for the benefit of those however who may wish to mount the transformer on a switchboard or as part of some apparatus1 the scheme shown in ,figure #fc is suggested4 ,the base consists simply of a rectangular piece of hardwood which has been given a coat of shellac4 ,illustration3 ,,fig4 #fc4--,the ,step-down ,transformer mounted on a ,wooden ,base4 ,the transformer core rests on two wooden strips marked ,s and ,s in the illustration4 ,it is clamped to the base by two strips1 ,t and ,t1 held in position by round head wood screws at each end4 ,the terminals of the primary winding are led to the two binding posts1 marked ,p ,p4 ,the secondary terminals are connected to three binding posts1 marked #a1 #b and #c4 ,the #aaj volt ,a4 ,c is connected to the primary posts ,p ,p by means of a flexible wire and plug which can be screwed into the nearest lamp socket4 ,the low voltage is secured from the binding posts #a1 #b and #c4 ,binding ,posts #a and #b will give #b volts ,binding ,posts #b and #c will give #h volts ,binding ,posts #a and #c will give #ab volts ,illustration3 ,,fig4 #fd4--;,a detailed ,drawing showing how the ,sides of the ,case are formed by bending a long strip of ,sheet ,iron at four points4 ,the drawings in ,figures #fd1 #fe and #ff will be of assistance to those who wish to enclose the transformer in an iron case instead of mounting it on a board4 ,the case is made of sheet iron4 ,the sides are composed of a strip of sheet iron fifteen and seven-eighths inches long and two and three-quarters inches wide4 ,the strip should be bent at four points so as to form a rectangular box1 the sides of which are four and three-sixteenth inches long and the front and back1 three and nine-sixteenths4 ,the ends of the strip should overlap about three-eighths of an inch and be riveted or soldered4 ,the bottom may be fastened to the sides with a couple of rivets or by soldering at one or two points4 ,the bottom and top of the case should both be the same4 ,they are made from a rectangular shaped piece of sheet iron four and seven-eighths inches long and four and one-quarter inches wide4 ,a notch five-sixteenths of an inch square is cut out of each corner and the sides and ends then folded down along the dotted lines as indicated in ,figure #fe4 ,illustration3 ,,fig4 #fe4--;,details of the ,top and ,bottom of the ,case4 ,the transformer is laid in the case with a small block of wood under the core at either side so as to raise the windings up off the bottom4 ,the secondary terminals are connected to binding posts marked #a1 #b and #c in ,figure #ff4 ,these binding posts are mounted on insulating bushings which pass through the holes marked ,no4 #a1 ,no4 #b and ,no4 #c in ,figure #fd4 ,the insulating bushings consist simply of fibre washers so that the binding posts will not short circuit on the metal case4 ,one end of a piece of double conductor lamp cord is led through a hole in the back of the case and soldered to the two primary coil terminals4 ,the other end of the lamp cord is connected to an attachment plug which may be screwed into a lamp socket4 ,illustration3 ,,fig4 #ff4--,the completed ,transformer4 ,the transformer case is then poured full of molten coil wax so that the space around the transformer is entirely filled4 ,after the wax has cooled1 fasten the cover on and it is complete4 ,arts and ,science ,series ,no4 #h ,home-made ,electrical ,apparatus ,a ,practical ,handbook for ,amateur ,experimenters ,in ,three ,parts 99,volume ,,ii99 ,second ,edition 99,,by99 99,a4 ,m4 ,powell99 ,,published ,,by ,,cole ,,morgan1 ,inc4 ,publishers of the ,arts and ,science ,series ,p4,o4 ,,box #dgc ,,city ,,hall ,,station ,,new ,,york1 ,n4 ,y4 ,printed in ,u4 ,s4 ,a4 ,copyright #aiah by ,,cole ,,morgan1 ,inc4 ,,chapter ,,vi4 ,,electric ,,measuring ,,instruments ,galvanometers1 ,ammeters1 ,voltmeters4 ,how to ,make a ,galvanometer4 ,if several turns of wire are wrapped about a compass1 and a current of electricity sent through the coil1 the compass needle will be deflected4 ,such an instrument is called a 99galvanometer99 and may be used for detecting very feeble currents4 ,figure #fg shows a very simple form of galvanometer which may be made by winding about fifty turns of ,no4 #cf ,b4 ,s4 ,gauge single silk covered wire around an ordinary pocket compass4 ,the compass is set on a block of wood and the wire wound around both the compass and the block4 ,the terminals of the wire are connected to two binding posts4 ,illustration3 ,,fig4 #fg4--;,a ,simple ,galvanometer4 ,a galvanoscope of this sort may also be used for a polarity indicator to distinguish between positive and negative poles4 ,connect an ordinary dry cell to the galvanometer and the needle will immediately swing to one side or the other1 depending upon which way the current flows4 ,the carbon of the dry cell is 99positive99 and the zinc is 99negative994 ,note which way the needle swings1 whether toward the binding post connected to the positive pole or the one connected to the negative pole4 ,it will swing towards the corresponding pole when any other source of current is connected to it and by knowing whether it points towards positive or negative it is very easy to determine the polarity4 ,the ,construction of ,ammeters and ,voltmeters4 ,the experimenter will find a voltmeter and an ammeter to be very useful instruments about the workshop and laboratory4 ,a 99voltmeter99 is an instrument designed to measure electro-motive force or electrical pressure4 ,an instrument designed to measure rate of flow of current is called an 99ammeter994 ,ammeters and voltmeters are really1 in principle1 galvanometers1 the scales of which have been calibrated to read in amperes or volts1 as the case may be4 ,the little meters described below are very simple but quite sensitive4 ,illustration3 ,,fig4 #fh4--;,details of the ,bobbin4 ,the wooden bobbin which holds the wire is shown in ,figure #fh4 ,the exact dimensions are best understood from the illustration4 ,the wood can be easily secured from an old cigar box4 ,in laying out the work1 scratch the lines on the wood with the point of a darning needle4 ,pencil lines are too thick to permit of accuracy in small work4 ,the bobbin should be perfectly square and true when finished4 ,finish by rubbing with fine sandpaper and then give it a coat of shellac4 ,two bobbins will be required1 one for the voltmeter and one for the ammeter4 ,do not use any nails in putting the bobbins together4 ,use strong glue only4 ,the bobbin for the ammeter should be wound full of ,no4 #ad ,b4 ,s4 ,gauge double cotton covered magnet wire4 ,the voltmeter requires much smaller wire4 ,no4 #cg ,b4 ,s4 ,gauge single silk covered wire will serve the purpose satisfactorily1 but a finer size such as ,no4 #ch or #dj1 is better4 ,such fine sizes will probably1 however1 prove more difficult for the experimenter to obtain4 ,sufficient wire should be used to fill the bobbin up4 ,the wire should be wound on carefully in smooth even layers4 ,a small hole should be bored in one of the flanges1 through which to pass the end of the wire when starting the first layer4 ,about six inches of wire should be left at both ends of the coils to make connection to the terminals with4 ,the whole winding should be given a coat of shellac when finished4 ,illustration3 ,,fig4 #fi4--;,details of the ,armature1 ,bearings and ,pointer4 ,the armature is a piece of soft steel1 one and one-eighth inches long1 and one-quarter of an inch thick4 ,a one-sixteenth inch hole is bored1 slightly above the centre of the armature1 to receive the shaft4 ,the centre of gravity is thus thrown below the centre of mass and the pointer attached to the armature will always return to zero if the instrument is level4 ,the shaft is a piece of one-sixteenth inch bessemer steel rod1 three-eighths of an inch long4 ,the ends are filed to a sharp point as shown in the upper pert of ,fig4 #fi4 ,a small hole is bored in the top of the armature almost directly over the shaft as shown in ,fig1 #fi to receive the lower end of the pointer1 which is a piece of ,no4 #af aluminum wire1 three and one-quarter inches long4 ,the other end of the pointer should be flattened slightly by tapping with a hammer and then filed into a shape resembling a spear head4 ,illustration3 ,,fig4 #gj4--;,a complete ,voltmeter having the ,scale at the top4 ,after all the holes have been bored and before the shaft and the pointer are in place1 the armature must be tempered so that it will retain its magnetism4 ,in order to temper the armature1 heat it to a bright red and drop it immediately into a basin of strong salt water4 ,it may then be magnetized by rubbing one end against the pole of a strong magnet4 ,the bearings are formed by two #f-cb brass screws1 one-half an inch long and having a small hole in the end to accommodate the end of the shaft4 ,these screws pass through the upper flange of the bobbin from the opposite sides4 ,the holes in the flanges should be slightly smaller than the outside of the screw so that the latter will fit snugly and take hold as if the wood were threaded4 ,figures #gj and #ga show two different methods of assembling and completing the instruments4 ,in one1 the bobbin is mounted on the base and the scale is at the top4 ,in the other1 this relation is just turned abound and the bobbin is at the top and the scale at the bottom4 ,in the latter case the pointer must be attached to the bottom of the armature instead of the top4 ,illustration3 ,,fig4 #ga--;,an ,ammeter so constructed that the ,scale is at the bottom4 ,figure #gc shows the shapes and dimensions of the wooden parts which compose the case4 ,a glass front slides in two shallow grooves cut in the wooden sides1 one-eighth of an inch from the front4 ,glue and brass screws should be used in putting the case together4 ,do not use iron or iron screws4 ,illustration3 ,,fig4 #gb4--,showing how the ,armature1 ,shaft and ,pointer are assembled for a ,meter having the ,scale at the bottom4 ,the two binding posts connected to the terminals of the wire on the bobbin should be mounted on the base4 ,a small1 round-headed brass screw1 long enough to pass all the way through the base will serve to level the instrument and bring the pointer exactly at zero4 ,if a little brass strip is placed in the slot in the screw head and soldered there so as to form what is known as a winged screw1 the adjustment may be made with the fingers and without the aid of a screw driver4 ,the scale is formed on a piece of stiff white cardboard directly under the pointer4 ,the scale is supported by gluing it to two small wooden blocks4 ,the various values are marked on the scale with a pen and ink4 ,the glass front should therefore not be put in place until the instrument has been calibrated4 ,to properly calibrate the meters1 they must be compared with a suitable standard4 ,the zero value on the meters is normally in the centre of the scale4 ,when a current is passed through the bobbins1 the armature tends to swing around at right angles4 ,but since the armature is pivoted above its centre of mass1 the centre of gravity is displaced when it swings and exerts a pull in opposition to that of the bobbin4 ,the amount of swing will be greater as the current is correspondingly stronger4 ,the pointer will swing either to the right or to the left1 depending upon the direction in which the current passes through the coil of wire on the bobbin4 ,illustration3 ,,fig4 #gc4--;,details of the ,wooden ,parts which form the ,case4 ,the zero point on the two instruments shown in the accompanying illustration is at the extreme left of the scales4 ,the pointers are bent to the left so that the current may be passed through the meters in only one direction and the scales will have a greater range of values4 ,in order to calibrate the ammeter1 place it in series with a standard ammeter having a calibrated scale which is known to be correct4 ,a set of strong batteries and a rheostat should be included in the circuit4 ,the arrangement is illustrated in ,figure #gd4 ,the rheostat is adjusted so that various current readings are obtained4 ,the positions of the pointer on the standard meter are carefully noted and corresponding graduations made on the scale of the other meter for each value4 ,illustration3 ,,fig4 #gd4--,showing how the ,apparatus is arranged and connected for calibrating the ,ammeter4 ,illustration3 ,,fig4 #ge4--,showing how the ,apparatus is arranged and connected for calibrating the ,voltmeter4 ,in order to calibrate the voltmeter it must be compared to a standard voltmeter4 ,the voltmeters must be placed in parallel or shunt with each other as shown in ,figure #ge4 ,a switch is connected to the battery so that the voltage of a varying number of cells may be passed through the meters4 ,in order to secure a close adjustment of the voltage1 a rheostat is placed across the battery and switch so that it shunts the cells which are in circuit4 ,by adjusting both the rheostat and the switch1 any voltage within the maximum range of the battery may be secured4 ,after the meters have been calibrated and assembled1 they are ready for service and will form a very useful and valuable part of the experimenter's laboratory4 ,when using the meters remember that it is always necessary that the ammeter shall be in series and the voltmeter in parallel or shunt with the circuit4 ,,chapter ,,vii4 ,,current ,,control ,,devices4 ,how to ,make a ,pole ,changing ,switch or ,current ,reverses ,how to ,reverse a ,small ,motor4 ,the switch shown in ,figure #gf is a very simple device which will be found very handy for many purposes4 ,it consists of two brass levers mounted alongside of each other and connected together with an insulating strip or yoke bearing a handle so that they can both be moved together4 ,the levers are pivoted at their back ends and provided with binding posts marked ,b4 ,p4 and ,b4 ,p4 in the illustration4 ,the front ends of the levers swing over three switch contact points properly spaced so that the levers touch the adjoining contacts at the same time4 ,the contacts are marked #a1 #b1 and #c4 ,illustration3 ,,fig4 #gf4--;,a ,pole changing ,switch for reversing ,small ,motors or the direction of an ,electric ,current4 ,we will suppose that the experimenter has some device operated by a battery and desires to arrange the apparatus so that he can quickly reverse the terminals of the battery so as to send the current through the device in either direction quickly and at will4 ,the apparatus to be operated should be connected to the two binding posts mounted on the switch levers and marked ,b4 ,p4 and ,b4 ,p4 ,connect the negative pole of the battery to the contact marked #b 7the center one71 and the positive pole to both #a and #c 7the outside ones74 ,when the switch is thrown to the right so that the levers rest on the contacts #b and #c1 the right hand lever will be positive and the left hand one negative4 ,when the switch is thrown to the left so that the levers rest on #a and #b1 the left hand lever will be positive and the right hand one negative4 ,the current has been reversed4 ,illustration3 ,,fig4 #gg4--,top view of a small ,battery ,rheostat ,a switch such as this makes it possible to quickly reverse the running direction of small motors4 ,in order to accomplish this1 connect the two brushes on the motor to the two switch levers4 ,connect the contracts #a and #c 7the two outside ones7 together and lead the wire to one terminal of the battery used for operating the motor4 ,in case the motor is operated by a generator or from the #aaj volt current1 connect the wire to one terminal of the power source4 ,the middle contact on the switch 7marked #b7 should be connected to one end of the field winding on the motor4 ,the other end of the field winding should be connected to the remaining battery terminal or power source4 ,moving the switch back and forth will send the current through the commutator in opposite directions and cause the motor to run in either direction as desired4 ,how to ,make a ,small ,battery ,rheostat for ,regulating the ,speed of ,small ,motors1 ,etc4 99,a ,rheostat99 is a variable resistance for regulating the amount of current flowing in a circuit4 ,it is a very useful device about the experimental laboratory4 ,it may be used1 for regulating the speed of small motors1 the amount of current flowing into a storage battery when recharging1 the brilliancy of a lamp1 etc4 ,illustration3 ,,fig4 #gh4--;,details of the ,rheostat ,base4 ,the lower part of the illustration is a cross section4 ,figure #gg shows a form of small rheostat which may be easily built by the experimenter4 ,it consists of a coil of ,german silver resistance wire wound around a fibre form and set in a groove in a wooden base4 ,a brass lever slides over the edge of the resistance coil so that the portion included in the circuit may be increased or decreased easily at will4 ,the dimensions shown in the several drawings which follow are for a rheostat having a resistance of approximately ten ohms and suitable for general experimental work4 ,it is possible to use the same plans and by doubling the dimensions1 make a rheostat which is much larger and may be used to carry heavier currents or which possesses more resistance4 ,illustration3 ,,fig4 #gi4--,looking at the ,base from the bottom showing the grooves in which the ,wires are laid4 ,the details of the wooden base are given in ,figures #gh and #gi4 ,the outside diameter of the base is four inches4 ,it is five-eighths of an inch thick4 ,the lower #g part of ,figure #gh shows a cross section of the base4 ,the groove is three and one-eighth inches in diameter inside1 five-sixteenths of an inch thick and five thirty-seconds of an inch wide4 ,the hole in the centre of the base is to accommodate the shaft of the switch lever1 ,two holes1 seven-eighths of an inch apart are drilled at the back of the base to accommodate the binding posts4 ,the binding posts' holes and also the hole in the centre of the base for the shaft are countersunk at the bottom as shown in ,figure #gi4 ,the fibre strip which supports the ,german silver resistance wire is shown in ,figure #hj4 ,it is eight inches long1 three-eighths of an inch wide and one-eighth of an inch thick4 ,if the experimenter has access to a lathe it is possible to wind the wire on the fibre strip under tension with the aid of the screw feed so that the wire will go on very tightly and with a small air space between the turns4 ,when a lathe is not available it will be necessary to groove the top and bottom of the fibre strip with the aid of a three-cornered file4 ,the grooves should be evenly spaced and as close together as possible4 ,they serve to prevent the wire from slipping and the adjacent turns becoming short circuited4 ,the wire used to wind the strip should be ,no4 #bd ,b4 ,s4 ,gauge ,german ,silver wire and should be bare4 ,wind the wire tightly into the grooves in the strip and fasten both ends by looping through a small hole bored in the ends of the fibre for that purpose4 ,the fibre strip can be bent so that it will fill in the groove in the wooden base by heating it in the flame of a bunsen burner4 ,it should not1 of course1 be heated too hot or the fibre will burn4 ,warm it thoroughly and bend into a circle of the same diameter as the groove in the base4 ,then force the strip into the groove with the two ends opposite the two binding post holes4 ,the strip should fit into the groove tightly so that there is no danger of it shifting or slipping out4 ,illustration3 ,,fig4 #hj4--,the ,german-silver ,resistance ,wire is wound around a ,fibre ,strip4 ,the details of the switch lever1 knob and binding posts1 are shown in ,figure #ha4 ,the lever is made of sheet brass cut into the shape shown and is one and three-quarter inches long4 ,the knob is similar to those used on typewriters for turning the paper roller4 ,it is fitted with a threaded stem moulded into the head4 ,these knobs may be obtained at almost any supply house carrying goods for experimenters4 ,the lever is slipped over the stem and clamped tightly against the knob by a nut on the under side4 ,the end of the stem or shaft fits into the hole in the centre of the wooden base4 ,slip a washer over the end and then thread on a brass washer4 ,tighten the nut up until the end of the lever makes firm contact with the resistance wire but is not so tight that it binds and cannot be easily moved by turning the knob4 ,when the right position for the nut is found1 solder it to the stem so that it cannot change its adjustment4 ,illustration3 ,,fig4 #ha4--,the ,lever1 ,knob1 ,binding ,posts1 etc4 ,the completed rheostat is shown in ,figure #hb4 ,the right hand terminal of the ,german ,silver wire is connected to the right hand binding post4 ,the other binding post is connected to the washer around the lever shaft on the under side of the base4 ,the wires should be laid in grooves cut in the bottom of the base for that purpose4 ,drive a brass headed upholsterer's nail into the base near the left hand terminal of the resistance so that when the lever is swung around in that direction as far as it will go1 the tack will raise the lever up off the resistance wire and break the circuit completely4 ,two small nails should be driven into the base in such a position that they will limit the swing of the lever and prevent it from moving so far that it passes over the ends of the resistance unit4 ,the rheostat may be connected in a circuit by attaching two wires to the binding posts4 ,it should be placed in series with any device which it is desired to regulate4 ,the carrying capacity is limited to two amperes owing to the fact that a heavier current than this will cause the wire to overheat4 ,turning the knob so that the lever moves towards the upholsterer's nail1 which raises it up off the wire1 increases the amount of resistance in the circuit and cuts down the current1 until the lever slides up on the nail when the circuit is broken entirely4 ,moving the knob in the other direction decreases the resistance and increases the current until the lever has moved as far as it may1 when the current will be at a maximum4 ,illustration3 ,,fig4 #hb4--,the completed ,rheostat4 ,,chapter ,,viii4 ,,how ,,to ,,make ,a ,,telegraph ,,key ,,and ,,sounder ,,and ,,install ,a ,,telegraph ,,line4 ,the modern telegraph consists essentially of four things3 #a4 ,a battery which produces the electric current4 #b4 ,a wire to conduct the current from one point to another4 #c4 ,a key or switch for turning the current off and on4 #d4 ,an electro-magnetic receiving apparatus1 which changes the pulsations of the electric current into sounds4 ,illustration3 ,,fig4 #hc4--,key ,frame4 ,its operation is not1 as many suppose1 complicated and difficult to understand1 but is quite simple4 ,the key is really a form of switch and is simply a contrivance for controlling the electric current4 ,it consists of a steel lever1 pivoted in the centre1 and provided with a rubber knob1 which the operator grasps lightly with the thumb and forefinger4 ,when the lever is pressed downwards1 a platinum point on the under side is brought into contact with another similar point set into a rubber bushing in the base of the key1 so that there is no electrical connection between the two points unless the key is pressed down or closed as it is usually termed4 ,the receiving device1 or sounder1 consists of two electro-magnets mounted on a base under a flat strip or iron1 called the armature1 which is attracted by the magnetism of the electro-magnets when a current flows through them1 and is withdrawn by a spring when no magnetism is produced by the windings4 ,illustration3 ,,fig4 #hd4--,sounder ,frame4 ,the armature is usually mounted on a strip of brass or aluminum called the lever4 ,the lever strikes against an anvil and produces the clicks which form the dots and dashes of the telegraph alphabet4 ,every time the key is pressed1 an electric current goes through the line1 causing the magnets to draw the armature downward and produce a click4 ,when the key lever is released1 the current is shut off and the lever flies up and clicks against the top of the anvil4 ,the time between the first and second clicks may be easily varied at will1 by changing the length of time that the key lever is held down4 ,two clicks very close together1 made by pressing the key and immediately releasing it1 are called a dot4 ,a dash is made by pressing the key down and holding it down for a fraction of a second so that the interval between the first and second clicks is about three times as long as that between the clicks of a dot4 ,illustration3 ,,fig4 #he4--,the ,electro ,magnets4 ,any boy can make a simple telegraph set quite easily4 ,the only drawback of such an apparatus1 however1 is that it is usually not practical for long lines but may only be used for ticking messages from one room to another4 ,it is equally possible for the young experimenter to make a perfectly practical telegraph outfit which will operate over a line a mile long1 if he is willing to give the time and labor necessary to the work4 ,the telegraph set-described below is one which1 because of its simplicity1 particularly lends itself to construction by the young experimenter whose tools are rather limited4 ,in order to make a really practical telegraph outfit1 it is almost essential that the key and sounder frame be made out of cast iron so as to give the instruments the requisite stiffness4 ,it is easier to use castings than to attempt to bend the parts out of metal4 ,in order to secure the proper castings it will be necessary to first make a set of patterns4 ,this is not very difficult4 ,the key frame is shown in ,figure #hc and the ,sounder frame in ,figure #hd4 ,the patterns should be cut out of wood according to the exact shape and dimensions shown in the illustrations4 ,omit all the holes1 however1 because no holes should appear in the patterns but only in the finished castings4 ,illustration3 ,,fig4 #hf--,the ,sounder ,armature4 ,the patterns should be made perfectly smooth and be a good1 clean job throughout4 ,after they are finished1 give them each a coat of shellac and they are ready for the foundry4 ,almost any iron foundry will make up the castings if supplied with the patterns4 ,if a number of experimenters chip in and make up a set of patterns from which several sets of castings are ordered at the same time1 the cost will be very slight4 ,after the castings are secured1 they should be cleaned up with a file and drilled according to the illustration in ,figures #hc and #hd4 ,several of the holes should be tapped to receive an #h-cj machine screw4 ,such holes are marked in the illustrations4 ,the holes not marked ,tap should be just large enough to allow an #h-cb screw to slip through4 ,illustration3 ,,fig4 #hg4--,sounder ,frame with ,lever in ,position4 99,the ,electro-magnets99 are illustrated in ,figure #he4 ,the magnet core is made of a piece of #e-af inch round iron rod an inch and a quarter long4 ,a fibre washer1 three-quarters of an inch in diameter is fitted over each end of the core4 ,one end of the core is drilled and tapped to receive an #h-cb screw4 ,the magnet bobbin1 before winding is shown at the left of the illustration and a finished magnet at the right4 ,two magnets are required4 ,they should both be wound in the same direction with ,no4 #be single cotton covered wire4 ,the wire should be wound in smooth1 even layers and the terminals led out through two small holes in the fibre heads4 99,the ,sounder ,armature99 is a piece of steel or iron rod1 five-sixteenths of an inch square and three and three-eighths inches long4 ,it serves both as the armature and the sounder lever4 ,the exact location of the holes is shown in ,figure #hf4 ,the holes h and i should be tapped to receive an #h-cb screw4 ,the hole j should pass a screw of the same size4 ,this screw serves as the pivot for the armature4 ,figure #hg shows how the sounder frame should appear when the lever is in position4 ,the screw ,a controls the distance which the armature moves on its upward stroke4 ,the screw ,b strikes the anvil on the downward stroke and controls the distance between the armature and the electro-magnets4 ,illustration3 ,,fig4 #hh4--,top ,view of ,completed ,instrument ,the armature is pushed upwards and held away from the magnets against the screw ,a by a small spiral spring4 ,the lower end of the spring sets in the hole ,c in the sounder frame and the upper end rests against the end of the screw ,c so that the tension of the spring can be regulated by moving the screw up and down4 ,the armature should be free to move up and down on the pivot screw but should not move sideways4 99,the ,base99 of the instrument is a rectangular piece of hardwood1 four and one-half inches long1 three and three-quarter inches wide and one-half inch thick4 ,the sounder is mounted on the base in the position shown in ,figure #hh1 which is a top view of the complete instrument4 ,two long #h-cb machine screws pass upwards through the wooden base1 through the holes e and f in the sounder frame and into the bottom of the magnets1 thus serving not only to hold the magnets in position but also the sounder frame to the base4 ,illustration3 ,,fig4 #hi4--,side ,view of ,key4 ,figure #hi is a side view of the completed key4 ,the key lever and the circuit closing lever are illustrated in ,figure #ij4 ,the lever is four and three-eighths inches long and five-sixteenths of an inch wide4 ,it should be made from spring brass4 ,the circuit closing lever is a strip of brass of the same width4 ,all the holes in both levers1 with the exception of the centre hole in the key lever should be large enough to pass an #h-cb screw4 ,the centre hole should be tapped to receive an #h-cb screw4 ,the key lever is fastened to the frame by means of a round headed #h-cb machine screw4 ,the screw should be tightened so that the lever cannot move from side to side4 ,the circuit closing lever is pivoted to the back end so that it can swing4 ,the key lever should be fitted with a regular key knob and the circuit closing lever with a small knob such as is generally used for the purpose4 ,both of these styles of knobs can be purchased from almost any electrical supply house4 ,the contact points are best made of silver4 ,silver makes a better contact metal than almost anything else1 with the exception of platinum4 ,if silver cannot be obtained a piece of large german-silver wire may be used4 ,illustration3 ,,fig4 #ij4--,key and ,circuit ,closing ,levers4 ,one contact is soldered to the under side of the key lever4 ,the other contact should be mounted on the head of a screw and pass through a hole in the iron key frame and through the wooden base underneath4 ,this lower contact should be directly underneath the upper contact and be thoroughly insulated from the base4 ,several thicknesses of well shellaced paper will form a first class insulating medium4 ,the length of the contacts should be such that there is a distance of about #c-cb of an inch between them when the lever is horizontal4 ,the circuit closing lever should make contact with a small strip of spring brass under the lower contact point so that the contact is connected to the frame of the key through the circuit closing lever when the latter is closed4 ,the adjustment screw on the key frame is used to regulate the upward stroke of the key lever4 ,the adjustment screw on the key lever is used to regulate the spring tension of the lever4 ,the lower end rests against the top of a small spiral spring made of brass wire4 ,illustration3 ,,fig4 #ia4--;,american ,morse ,code4 ,connecting the outfit is a very simple mater4 ,the two inside terminals of the sounder magnets should be connected together4 ,one of the outside terminals is led to a binding post mounted on the back of the base4 ,the other terminal is connected to the lower key contact4 ,the frame of the key is connected to a second binding post at the back of the base4 ,the connecting wires should pass through small holes and along the under side of the base4 ,the ,morse ,telegraph ,code is shown in ,figure #ia4 ,a single dry cell will provide sufficient current for practising the ,code4 ,the cell should be connected to the two binding posts and the circuit closing lever should be kept open at all times or the battery will become exhausted4 ,illustration3 ,,fig4 #ib4--;,circuit for ,two ,instruments4 ,the number of batteries required on a long line will depend upon the resistance of the line and cannot easily be pre-determined4 ,figure #ib shows a circuit for connecting two instruments on a line4 ,when the double contact switch is on point ,a the batteries are out of circuit4 ,throwing the switch on ,b puts the batteries into circuit4 ,they should be kept out of circuit when the stations are not in use4 ,the circuit closer at ,station #a must be kept closed when ,station #b is telegraphing and vice versa4 ,,chapter ,,ix4 ,,how ,,to ,,make ,,and ,,install ,a ,,telephone4 ,not many years ago1 the telephone was the wonder of the times just as the aeroplane and the wireless are to-day4 ,the original telephone apparatus was an exceedingly crude and simple arrangement which has gradually developed into a wonderful and complex system which makes it possible to carry on a conversation with almost any other point in the ,united ,states as easily as it is face to face4 ,illustration3 ,,fig4 #ic4--,the ,wooden ,back for the ,telephone4 ,many of my young readers have undoubtedly already constructed a set of telegraph instruments and rigged up a line with some nearby chum4 ,like the telegraph1 the principle of the telephone is that of a current of electricity flowing over a line wire into a pair of electro-magnets1 and it is not any more difficult to install a short telephone line than a telegraph4 ,of course there are many important differences between a telephone and a telegraph but they are not intricate or complex4 ,the telephone is exceedingly sensitive when compared to the telegraph4 ,an ordinary telegraph relay requires about one hundredth of an ampere to operate it1 whereas a telephone receiver will produce an audible sound on a current of less than one millionth of an ampere4 ,illustration3 ,,fig4 #id4--,the ,complete ,telephone4 ,the telephone may be defined as an apparatus for transmitting speech to a distance by means of electricity4 ,the part of the apparatus which takes up the sounds and changes them into electric currents is the transmitter4 ,where words are spoken into the mouth-piece of the transmitter1 they strike a thin metal diaphragm1 to the back of which is fastened a small cup-shaped piece of carbon4 ,a second cup is mounted in a rigid position directly back of the first and the space between is filled with small polished granules of carbon4 ,when the granules are undisturbed and are lying loosely together their resistance to an electric current is so great that they allow almost none to flow4 ,when the vibrations of the voice strike the diaphragm they move it back and forth and cause the carbon cup mounted on its back to move and exert a varying pressure on the granules4 ,when the granules are compressed their resistance is greatly lowered and they permit current to pass4 ,that part of the apparatus which transforms the pulsating current back into sound waves is called the receiver4 ,it consists of a thin iron disk1 placed very near but not quite touching the end of a small permanent magnet about which is wound a coil of fine insulated wire4 ,illustration3 ,,fig4 #ie4--;,details of the ,receiver ,hook4 ,if the transmitter and receiver are connected together in series with a battery and words are spoken into the transmitter1 the little carbon granules are immediately thrown into motion1 and being alternately compressed and released cause corresponding changes in the current flowing through the receiver from the battery4 ,the strength of the magnetic pull exerted by the combined permanent magnet and coil of wire varies with each change in the electric current and thus by alternately attracting and repelling the diaphragm causes it to vibrate and emit sounds4 ,this is the general principle of the telephone4 ,the telephones in actual service to-day are complicated with bells1 induction coils1 condensers and relays1 which render them more efficient1 but the general principle of the transmission of the speech is the same4 ,i would not advise the young experimenter to attempt to build his own transmitter and receiver except for the knowledge and experience gained thereby4 ,homemade instruments of this sort are not likely to prove sensitive enough for practical purposes over a long line4 ,a first class telephone receiver can be purchased for #ij cents and an equally good transmitter for #b4be ,these1 together with an ordinary electric bell can be built into a first class telephone instrument which will give excellent service over a long line4 ,illustration3 ,,fig4 #if4--,showing how the ,push ,button is arranged4 ,any boys can easily build and install such an arrangement4 ,when completed it will prove invaluable as a source of communication from one part of the house to another1 from the house to the barn or between two chums living in the same neighborhood4 ,figure #ic shows the wooden back of the instrument4 ,it is made from a piece of board #ab inches long and #g inches wide1 by cutting into the shape shown4 ,this back serves to mount the transmitter1 receiver1 bell1 etc4 99,the ,bell99 is for the purpose of giving an audible signal so that the person hearing it will know that some one at the other end of the line wishes1 to talk4 ,figure #id is a front view of the completed instrument4 ,the bell is mounted on the upper part of the back as shown in the illustration4 99,the ,receiver ,hook99 is shown in detail in ,figure #ie4 ,it should be cut out of heavy sheet brass and finished in the shape shown4 ,the receiver hook is mounted directly under the bell as shown in ,figure #id4 ,the hook should project out to the left beyond the edge of the back4 ,the hook is mounted by a round headed brass screw passing through the hole in the right hand end4 ,illustration3 ,,fig4 #ig4--;,circuit showing how to connect two ,telephone ,stations to the ,line4 ,the hook should move freely up and down between two contacts 7marked #a and #b in ,figure #id74 ,these contacts are simply two small brass strips bent at right angles and fastened about an inch apart along the left hand edge of the wooden back by means of two small round headed brass wood screws4 ,the position of the contacts should be such that the hook is in a horizontal position when it is half way between the two4 ,a small spring is arranged so as to pull the hook up against the upper contact 7,no4 #a7 when the receiver is lifted off4 ,when the receiver is hung on the hook1 it should overcome the lift of the spring and pull the hook down against the lower contact 7,no4 #b74 99,the ,receiver99 may be purchased at almost any reliable electrical supply house4 ,it should be provided with a ring so that it can be hung onto the hook4 99,the ,transmitter99 is preferably of the solid back long distance type4 ,it also can be purchased ready made from almost any electrical supply house4 ,the transmitter is mounted on the wooden back directly under the hook4 ,it is marked ,t in ,figure #id4 99,a ,push ,button991 made out of two round headed brass wood screws and a strip of spring brass as shown in ,figure #if1 is mounted to the right of the transmitter4 ,one end of the spring is fastened down firmly with a screw1 the other end is bent so that it is directly over but does not touch the second screw mounted about seven-eighths of an inch away4 ,four binding posts should be arranged along the bottom of the wooden back and two more just to the left of the transmitter4 ,the set is now ready to wire or connect4 ,the connections can be understood best by following the diagrams in ,figures #id and #ig4 ,starting with the four binding posts along the bottom of the back1 mark the left hand one ,b#a1 mark the next one ,b#b1 the third ,e and the fourth ,l4 ,connect a wire from binding post ,b#a to the post ,p#a directly above it4 ,run the wire from ,p#a to the brass strip on the push button4 ,connect binding posts ,b#b and ,e together and from ,e run a wire to the right hand binding post on the bell4 ,connect a wire from the left hand post on the bell to the lower contact #b4 ,the hook should be connected to binding post ,l4 ,the upper contact #a is connected to one terminal of the transmitter4 ,the other terminal of the transmitter goes to binding post ,p#b4 ,the telephone receiver should be connected to the posts ,p#a and ,p#b by means1 of flexible wire4 ,the contact on the push button should be connected to the upper hook contact #a4 ,the set is now complete1 ready to connect to a similar outfit4 ,the battery is connected to the binding posts marked ,b#a and ,b#b4 ,e and ,l are the line posts to which the wires connecting the two sets are led4 ,the wire connecting the two outfits should not be smaller than ,no4 #ah ,b4 ,s4 gauge4 ,no4 #ad will prove better if the line is a long one4 ,the wire should be very carefully insulated4 ,ordinary porcelain knobs will serve as suitable insulators4 ,if desirable1 only one wire need be used1 the circuit being completed by connecting the post ,e on each instrument to the ground or earth4 ,the gas or water pipes will form the most suitable ground connection4 ,the number of batteries required will depend upon the length of the line4 ,the actual number necessary to ring the bell properly can be best ascertained by experiment4 ,it should be noticed that the battery connections at each station are reversed so that the batteries will be series4 ,the negative of the battery at one station is connected to ,e and the positive pole of the other battery at the other station to the similar post4 ,when the stations are not in use the receivers should be left hanging on the hooks4 ,in order to call the other station1 lift the receiver off the hook4 ,this throws the transmitter1 receiver and battery into the circuit4 ,the resistance of the receiver and transmitter1 however1 are so great that they will prevent enough current from flowing to ring the bell at the other station4 ,pressing the push button will short circuit the transmitter and receiver and allow enough current to flow to ring the bell at the other station4 ,the other person has merely to lift up his receiver in order that the two parties may talk back and forth4 ,when the receivers are on the hooks both bells are in circuit ready for either party to call up4 ,,chapter ,x4 ,,medical ,,coils ,,and ,,shocking ,,coils4 ,medical coils and shocking coils are the same4 ,the term shocking coil is usually applied to the low priced medical coils which most boys are familiar with for giving shocks4 ,illustration3 ,,fig4 #ih4--;,bobbin for ,medical ,coil4 ,a medical coil is nothing more or less than a small induction coil for raising the voltage of a battery high enough to produce a shock4 ,the human body possesses so much resistance that the voltage of one or two cells of ordinary battery is not sufficient to pass enough current through to be felt except under exceptional conditions1 as for instance when contact is made directly with a nerve through an open cut or a metal filling in a tooth4 ,a small lathe will be of much assistance in making some of the parts and fittings for the medical coil1 although it is not absolutely essential and the ingenious young experimenter can undoubtedly find some method of doing without it4 ,it is not necessary to follow the dimensions given here exactly1 and a very good coil can be built by adapting spools1 binding posts1 etc41 which may already be on hand1 although1 of course1 they should be used with some sense of proportion in mind so that nothing is carried to an extreme4 ,the first part which will be required is the bobbin4 ,this is shown in ,fig4 #ih and consists of a wooden spool1 two and seven-sixteenth inches long and one inch in diameter4 ,it has a three-eighths inch hole running all the way through the center4 ,the dimensions of the flanges1 etc41 can probably be best understood by referring directly to the illustration4 ,the flanges are flattened slightly on one side so that when the bobbin is mounted the flat portion will rest on the base and give a better support4 ,illustration3 ,,fig4 #ii4--;,bobbin with ,winding4 99,the ,primary ,winding99 consists of two layers of ,no4 #bd ,b4 ,s4 ,gauge single cotton covered wire4 ,the terminals of the winding should be led out through two small holes in the right hand head of the bobbin4 ,cover the winding with two or three layers of thin shellaced paper and then wind on the secondary4 ,the secondary is composed of ten layers of ,no4 #cf ,b4 ,s4 ,gauge single cotton covered wire4 ,the inside end of the secondary should be connected to the outside end of the primary4 ,the outside terminal is led out through a small hole in the head at the opposite end from the primary leads4 ,the wire on both the primary and secondary should be wound on in smooth even layers4 ,the illustration in ,figure #ii shows the bobbin after the windings are finished4 99,the ,core99 is made out of thin sheet iron rolled up into a cylinder two and three-sixteenths inches long and nine-thirty-seconds inches in diameter4 ,the core should be rolled up just as tightly as possibly1 because the more iron there is in the core1 within of course reasonable limit1 the better the coil will work4 ,thin tin plated iron cut from a cracker box may be used for the core4 ,the thinner it is the better4 ,a core of this sort1 rolled up out of sheet iron will give much better results than a core composed of a solid bar of iron4 ,illustration3 ,,fig4 #ajj4--;,construction of the ,core4 ,the end of the core is slipped into an iron core cap4 ,this is shown in ,figure #aja4 ,it consists of a small cylinder1 seven-sixteenths of an inch in length1 cut from a piece of iron rod1 three-eighths of an inch in diameter4 ,a hole nine-thirty-seconds of an inch in diameter and five-sixteenths of an inch deep should be drilled in one end4 ,this cap is slipped over one end of the core4 ,it should fit very tightly so that it will not pull out4 ,the core is then slipped into the bobbin with the outside end of the core cap projecting about one-sixteenth of an inch out of the end at which the primary terminals lead out4 ,the cap should fit into the bobbin very snugly so that the core is held firmly in place4 ,since the hole through the bobbin is three-eighths of an inch in diameter and the core is only nine-thirty-seconds of an inch in diameter there should be a space all around the core1 except at the end where the cap is1 so that a thin brass regulator tube can be slipped in and out over the tube4 ,illustration3 ,,fig4 #aja4--,vibrator ,parts and ,core ,cap4 99,the ,regulator ,tube99 should be two and seven-sixteenths inches long and have an inside diameter of five-sixteenths of an inch4 ,in case the experimenter has any difficulty in securing a tube of this size he can easily make one by rolling a piece of sheet brass around a suitable sized rod and soldering the edges4 ,when the tube is slipped over the core and moved in and out of the bobbin1 after the coil has been finished and set in operation1 it will regulate the strength of the secondary or shocking current4 ,when the tube is completely out of the bobbin1 the current will be the strongest4 ,if a paper scale1 divided into sixteenths of an inch and bearing numbers1 is pasted around the tube it will act as an indicator of the current strength4 ,the base is wood and measures four and five-eighths inches long1 two and three-quarters inches wide and is one-half an inch thick4 ,the proper location of the various holes can be found by referring to the illustration in ,figure #ajc4 ,the corners of the base should be slightly rounded so as to improve the appearance4 ,figure #ajd is a top view of the coil after it has been assembled4 ,the bobbin is mounted a little back of the centre of the base so that the core cap will be opposite the armature of the vibrator4 ,illustration3 ,,fig4 #ajb4--,regulator ,tube4 99,the ,vibrator ,parts99 are illustrated in ,figures #aja and #ajf4 ,the vibrator spring is a piece of thin steel or phosphor bronze1 one-quarter of an inch wide and one and three-sixteenths inches long4 ,a soft iron armature1 five-sixteenths of an inch in diameter and one-eighth of an inch thick is fastened to one end of the spring4 ,a five-thirty-seconds inch hole is drilled in the other end and it is then mounted in the vibrator posts4 ,this consists of a small brass pillar1 one-quarter of an inch in diameter and five-eighths of an inch long4 ,the lower end is drilled1 and tapped to receive a #d-cf screw which fastens it to the base4 ,a saw slot one-quarter of an inch deep is made in the top to receive the vibrator spring4 ,the post which holds the adjustment screw is identical with that which supports the vibrator spring1 except that a threaded hole is drilled through the saw slot1 fifteen-thirty-seconds of an inch from the bottom1 through which the screw passes4 ,the end of the adjustment screw1 which may be an ordinary knurled thumbscrew from a binding post1 should be fitted with a contact point4 ,the best contact point is a piece of platinum1 but a small piece of silver can be made to serve the purpose very well4 ,illustration3 ,,fig4 #ajc4--,the ,base with ,location of ,holes4 ,illustration3 ,,fig4 #ajd4--,top ,view of ,finished ,coil4 ,the vibrator spring should also be fitted with a similar contact point4 ,illustration3 ,,fig4 #aje4--,side ,view of ,completed ,coil4 ,the medical coil is very easy to connect4 ,run the inside primary terminal to the binding post on the rear left hand corner of the base4 ,connect the other terminal to the vibrator post4 ,a wire should be led from the adjustment screw post to the binding post mounted on the forward left hand corner of the base4 ,illustration3 ,,fig4 #ajf4--,vibrator ,parts4 ,one or two cells of battery should be sufficient to operate the coil4 ,connect the battery to the two binding posts4 ,adjust the thumbscrew until the contact on the end just touches the contact point on the vibrator spring4 ,the current will then flow through the primary winding and magnetize the core4 ,the magnetism of the core will draw the armature towards it1 thus pulling the contacts apart and interrupting the current4 ,the process will repeat itself very rapidly at a speed depending upon the adjustment of the thumbscrew and as long as the battery remains connected4 ,illustration3 ,,figs4 #ajg and #ajh4--,two ,types of ,handles4 ,the handles for the coil are very easily made out of a piece of brass tubing about two and one-half inches long and five-eighths of an inch in diameter4 ,they can also be made by rolling a piece of sheet brass or tin into a tube and soldering the edges together4 ,the illustration shows two methods of making the handles and attaching the cords4 ,the handle in the upper part of the illustration is made from a piece of tubing4 ,a wooden plug or cork is fitted into one end4 ,the wire passes through a hole in the centre of the plug and is turned back over the edge so that when the plug is forced into the tube1 the wire will make contact with it4 ,the handle in the lower part of the illustration is made from one of the brass cylinders in which the indelible ink for rubber stamps is supplied4 ,a hole is bored in the bottom through which the wire passes4 ,the end of the wire is soldered to a piece of stiff brass wire bent into the shape of a hairpin4 ,the ends of the wire are spread apart so that they will spring against the inside of the tube4 ,the connector is then pulled up inside of the handle4 ,the flexible wires or cords as they are sometimes called1 attached to the handles1 should be about eighteen inches long4 ,the opposite ends to the handles should be led through two holes in the base1 in front of the bobbin4 ,the left hand cord should be connected to the vibrator post and the right hand cord to the outside secondary terminal4 ,the coil is now complete1 ready for operation4 ,connect the battery to the binding posts4 ,start the interrupter and grasp one of the handles in each hand4 ,draw the regulator tube out of the bobbin gradually and the current will gradually grow stronger and stronger until it is impossible to hold the handles4 ,when the regulator tube is all the way in the bobbin it is practically impossible to feel the current4 ,of course any intermediate strength between the two extremes can easily be secured4 ,the shock from the coil is harmless4 ,when the regulator is all the way out1 the shock is very strong4 ,the only result1 however1 is to make the person receiving it drop the handles4 ,the current from medical coils is often prescribed by physicians for rheumatism and nervous disorders1 but it must be properly applied in order to be of benefit4 ,,chapter ,,xi4 ,,the ,,construction ,,of ,,spark ,,coils4 ,a ,spark ,coil is one of the most interesting pieces of apparatus that an experimenter can possess4 ,not only can it be used to transmit wireless messages1 but numerous and various experiments may be performed with its aid4 ,the purpose of a spark coil is to generate enormously high voltages which are able to send sparks across an air space which ordinary battery currents of low voltage could not possibly pierce4 ,illustration3 ,,fig4 #aji4--;,induction or ,spark ,coil4 ,it consists of an iron core surrounded by a coil of heavy wire known as the primary and a second outside winding of finer wire known as the secondary4 ,the primary is connected to a few cells of dry battery in series with an interrupter4 ,every time that the interrupter shuts off the battery current in the primary1 currents are induced in the secondary which are of sufficiently high voltage or pressure to leap across a space in the shape of sparks4 ,a spark coil is not very hard to construct1 but it requires careful workmanship and patience4 ,it is not usually a job which can be finished in a day1 but will take quite a little time1 especially in winding the secondary4 ,in describing the construction of a spark coil in this chapter1 directions and dimensions have been given for a one-quarter inch coil4 ,the general method of procedure is the same for all sizes of coils1 the dimensions only1 are different4 ,the experimenter may therefore easily build a larger coil than the one-quarter inch by consulting the tables of dimensions4 ,parts for spark coils are for sale by many electrical houses and it is possible to purchase the complete parts for less than the separate materials would cost4 ,such parts are made by special machinery and therefore are produced quite cheaply4 ,the ,core is made of soft iron core wire about ,no4 #bj or #bb ,b4 ,s4 ,gauge4 ,each piece should be four and three-quarters inches long4 ,iron wire may be bought already cut to length from various houses dealing in experimenter's supplies4 ,considering the amount of labor that is required to cut each piece to length arid then straighten it out1 it is cheaper to purchase the wire already cut4 ,illustration3 ,,fig4 #aaj4--,the ,primary and ,core4 ,size of ,coil4 ,o ,length of ,p ,diameter of ,primary ,wire ,core ,core #a_/d inch #d #c_/d inches #a_/b inch #ah ,b4 ,s4 #a_/b inch #e inches #e_/h inch #ah ,b4 ,s4 #a inch #g inches #e_/h inch #ah ,b4 ,s4 ,core wire is a special grade of wire which is very soft and has been annealed4 ,if ordinary iron wire is used in making a core1 it must first be annealed4 ,this is accomplished by tying the wire in a compact bundle and placing it in a wood fire until it is red hot4 ,after the wire is hot1 cover it with ashes and allow the fire to die away4 ,when the fire has gone out and the wire has cooled the annealing process is complete4 ,enough wires each four and three-quarters inches long to form a compact bundle one-half inch in diameter will be required4 ,illustration3 ,,fig4 #aaa4--,the ,secondary ,winding4 ,l ,size ,l ,length of ,m ,no4 of ,m ,size ,no4 of ,turns ,wire of ,coil ,secondary ,sections of ,hole per ,section #a_/d in4 #b #c_/h in4 #a #a #a_/ah #e1jjj #cg in4 en4 #a_/b in4 #b #c_/h in4 #a #a #a_/h #aj1jjj #cg in4 en4 #a in4 #b #b_/h in4 #a #a #a_/h #aj1jjj #cg in4 en4 ,there are two sections of secondary used on the #a-;inch coils4 ,cut a piece of tough wrapping paper about six inches long and four and one-half inches wide4 ,roll it up in the form of a tube so that it is six inches long and one-half inch in diameter inside4 ,glue the inside and outside edges of the paper so that the tube cannot unroll and then slip the core wires into it until the tube is packed tightly and no more can be slipped in4 ,the core is now ready for the primary1 which consists of two layers of ,no4 #ah ,b4 ,s4 ,gauge cotton covered wire wound over the core for a distance of three and three-quarters inches4 ,the winding should start five-eighths of an inch from one end of the core4 ,the wire must be wound very smoothly and carefully4 ,the inside end of the wire can be fastened so that it will not become loose by placing a short piece of tape lengthwise of the core and winding two or three turns over it4 ,then double the end back and complete the winding over it4 ,the end of the wire can be fastened by imbedding a piece of tape under the winding with a small loop projecting and then passing the wire through the loop4 ,figure #aaj shows the complete core with primary winding in position4 99,the ,secondary99 is a much more tedious job than the primary and must be very carefully made4 ,whenever it is possible for the experimenter to purchase a secondary already wound he is advised to do so4 ,the secondary consists of #e1jjj-f1jjj turns of ,no4 #cg ,b4 ,s4 ,gauge1 enameled wire wound in smooth1 even layers1 with two layers of paper between every two layers of wire4 ,the primary winding is wrapped with six layers of empire cloth or paper4 ,empire cloths and papers are a yellow insulating material made by treating linen or paper with linseed oil4 ,roll up a paper tube of five or six layers of paper so that the finished tube is two and one-half inches long and of proper inside diameter to just slip over the primary winding when the empire cloth or paper is in position4 ,the secondary is wound over this paper tube4 ,it will be necessary to mount the tube on a round wooden mandrel fitted with a small crank or handle so that the tube may be revolved4 ,a winder may be very easily made by mounting a round wooden stick of the same diameter as the inside of the paper tube in a pair of wooden supports4 ,bore a hole in one end of the stick and bend a piece of stiff wire in it so as to form a crank4 ,illustration3 ,,fig4 #aab4--,the ,fixed ,condenser4 ,size ,length ,width ,length ,width ,no4 of ,no4 of of of of of of ,paper ,tinfoil ,coil ,paper ,paper ,tinfoil ,tinfoil ,sheets ,sheets #a_/d #cj in4 #d #c_/h #cj in4 #d in4 #e #d in4 in4 #a_/b #cj in4 #d #c_/h #cj in4 #d in4 #e #d in4 in4 #a in4 #cj in4 #d #c_/h #cj in4 #d in4 #g #f in4 ,the paper placed between each two layers of the secondary winding should be the special waxed paper which is made for that purpose4 ,start and end each layer of wire one-half inch from the edges of the paper4 ,wind the wire in smooth1 even layers1 permitting each turn to touch the other1 but none to lap over4 ,wind on two layers of waxed paper between each layer of wire and the next4 ,the paper must be put on smoothly and evenly so as to afford a firm foundation for the next layer of wire4 ,the wire should never come nearer to the edges of the paper than one-half inch or the insulation of the secondary will be weak and the coil not liable to give a long spark4 ,the utmost care should be used not to break the wire4 ,if it should break1 the ends must be very carefully connected4 ,the number of turns that each layer averages should be carefully noted so that by keeping a record of the number of layers it is possible to tell how many turns have been wound on4 ,when five to six thousand turns have been wound on the secondary it is sufficiently large1 and the outside end of the wire should be fastened and prevented from unwinding by securing it with a drop of sealing wax4 ,when winding a secondary remember that if at any point in the work1 you allow the winding to become irregular or uneven1 the irregularity will be much exaggerated on the succeeding layers4 ,for this reason do not allow any irregularities to occur and if the wire tends to go unevenly1 wind on two or three extra layers of the waxed paper to smooth it out4 ,illustration3 ,,fig4 #aac4--;,details of the ,wooden ,coil ,heads4 ,size of ,coil ,d ,k ,j #a_/d in4 #c in4 #b #a_/b in4 #a_/b in4 #a_/b in4 #c in4 #b #a_/b in4 #e_/h in4 #a in4 #c #a_/b in4 #c in4 #e_/h in4 99,the ,condenser99 consists of alternate layers of tinfoil and paraffined paper piled on top of each other and then rolled up4 ,four sheets of tinfoil1 thirty-six inches by two and three-quarters inches wide will be required4 ,eight strips of waxed condenser paper1 three and one-quarter inches wide and thirty-six inches long are necessary4 ,lay one sheet of paper out flat on a table or board and place a sheet of tinfoil over it4 ,the tinfoil should be along the centre of the paper strip so that there is a one-quarter inch paper margin along the sides4 ,one end of the tinfoil should project over the end of the paper about two inches4 ,lay two sheets of waxed paper over the tinfoil making them line up with the first paper sheet all around4 ,then place another strip of tinfoil on the paper4 ,it should be directly above the first sheet of tinfoil1 but the end of the tinfoil must overlap the paper by two inches at the opposite end from the first sheet4 ,place two more sheets of paper over the tinfoil and on top of that a third strip of foil4 ,the third strip of foil should line up exactly with the first strip4 ,then lay two more sheets of waxed paper over the third sheet of foil and place the fourth sheet of tinfoil in position making it exactly line up with the second sheet4 ,place a single sheet of paper on top4 ,the result should consist of four sheets of tinfoil insulated from each other with two strips of paper between each two strips of foil4 ,connect the first and third sheets together with a wire and the second and fourth sheets likewise4 ,cut out a piece of cardboard1 one and one-quarter inches wide and three and one-quarter inches long4 ,lay the cardboard on one end of the condenser and roll the condenser up around it very tightly4 ,tie it with a piece of string to keep it from unrolling1 and dip it in some melted paraffine4 ,then place it between two boards with a weight on top so as to press it out flat4 99,the ,coil ,heads99 are made from two hardwood blocks three inches square and one-half an inch thick4 ,a circular groove1 two and one-half inches in diameter and one-quarter of an inch deep is turned in each block to receive a cardboard tube of the same diameter4 ,the two upper corners of each of the blocks are rounded slightly to improve their appearance4 ,one of the heads has a round hole one-half inch in diameter bored through the centre so that one end of the core may be passed through4 ,the core should project through about one-eighth of an inch4 ,the other head is bored with a hole of the same diameter but the hole should not pass all the way through1 and serves merely to receive and support the other end of the core4 ,illustration3 ,,fig4 #aad4--;,details of the ,wooden ,base4 ,size of ,coil ,a ,b ,c #a_/d in4 #h in4 #d in4 #a #a_/h in4 #a_/b in4 #h #a_/d in4 #d #a_/b in4 #a #a_/h in4 #a in4 #aj #a_/d in4 #d #a_/b in4 #a #a_/d in4 99,the ,base99 of the coil is a box eight inches long1 four inches wide and one and one-eighth inches deep4 ,it is made in the form of a hollow box4 ,give the base a coat of stain1 preferably some dark color1 such as mahogany1 and then a coat of shellac or varnish4 ,the wooden heads should be stained black4 ,the parts of the interrupter are shown in ,figure #aae4 ,they cannot be made by every experimenter on account of the tools required1 but can be purchased very cheaply from concerns dealing in material for experimenters4 99,the ,standard99 is a piece of hexagonal brass rod one and three-sixteenths inches long and three-eighths of an inch in diameter4 ,the lower end of the standard is tapped to receive an #h-cb machine screw4 ,a hole is bored at right angles to the axis of the standard1 one inch from the lower end and tapped to receive an #h-cb thumbscrew4 ,illustration3 ,,fig4 #aae4--;,details of the ,interrupter4 ,the ,spring and ,standard for the ,one inch coil should be made one-quarter of an inch longer4 ,the ,thumbscrew should be about seven-eighths of an inch long and be provided with a lock nut so that it can be fastened in position4 ,the end of the thumb-screw is drilled with a small hole and a contact point driven in tightly4 ,the contact point is usually a piece of platinum wire1 but in the case of a small coil may be a piece of the special contact wire which is sold for just this purpose4 ,illustration3 ,,fig4 #aaf4--,the tube4 ,size of ,coil ,length of ,tube ,diameter of ,tube #a_/d inch #d #a_/d inch #b #a_/b inch #a_/b inch #d #a_/b inch #b #a_/b inch #a inch #f #a_/b inch #c inch 99,the ,spring99 is a piece of thin steel1 three-eighths of an inch wide and two and one-eighth inches long4 ,several holes are drilled in it4 ,the illustration shows the exact location of these holes4 ,the holes ,a and ,c should be just large enough to allow an #h-cb machine screw to slip through4 ,the hole ,b is just large enough to receive a piece of contact wire4 99,the ,contact99 wire should be about three-thirty-seconds of an inch long and be slipped in the hole and riveted in place4 99,the ,armature99 is a piece of soft iron cut out of a rod one-half an inch in diameter4 ,it should be about one-quarter of an inch thick1 but should have a small stud left on one face so that the stud may be slipped into the hole marked ,c in the steel spring and the armature then riveted firmly to the spring by flattening out the stud4 ,illustration3 ,,fig4 #aag4--,the ,bridge4 ,size of ,coil ,e ,length ,i ,width #a_/d inch #d #g_/h inch #c_/d inch #a_/b inch #e #a_/h inch #c_/d inch #a inch #g #a_/h inch #c_/d inch ,the spring is bent at right angles about one-half inch from the end as shown by the dotted line in ,figure #aae4 99,a ,cardboard ,tube991 two and one-half inches in diameter and four and one-quarter inches long1 is used to inclose the primary and secondary windings when they are in position4 ,the tube may be given a very fine appearance by gluing a single layer of black bookbinders' cloth over it4 99,the ,bridge99 shown in ,figure #aag is a strip of wood about one-eighth of an inch thick1 four and seven-eighths inches long and three-quarters of an inch wide4 ,it is stained to match the base and is then given a coat of shellac or varnish4 ,two holes are bored in1 the bridge1 one inch from each end4 ,the coil is now ready for assembling4 ,figure #aah4 shows a cross-section of the complete coil4 ,slip the secondary over the insulating cloth or paper wrapped around the primary4 ,pass one end of the core through the hole in the coil head making sure that the groove is on the side towards the secondary4 ,the secondary should be exactly in the centre of the primary4 ,illustration3 ,,fig4 #aah4--,section of the ,spark ,coil showing the arrangement of the ,parts4 ,slide the cardboard tube over the primary and secondary into the groove4 ,lead the secondary terminals out through small holes in the cardboard tube at opposite ends so that the wires are separated as far as possible4 ,slip the other coil head over the end of the core and the tube and then mount the coil on the top of the base4 ,the coil should be in the centre of the base when considered from front to back4 ,it should be to the left of centre1 however1 when viewed from side to side4 ,the two primary heads should be four inches apart ,when the coil is assembled4 ,the primary wires are led down close to the wooden head and through the base under the coil4 ,they should be kept as far away from the secondary as is possible4 ,the coil is fastened to the base by a wood screw passing through the base into each of the wooden heads4 ,figure #abb will show best how the interrupter is arranged4 ,the brass spring carrying the armature at its upper end is mounted in front of the core end projecting through the wooden head4 ,the standard carrying the thumbscrew and the lock nut are mounted directly behind the spring in such a position that the contacts touch each other and line up perfectly4 ,illustration3 ,,fig4 #aai4--;,end ,view of the ,complete ,coil4 ,size of ,coil ,b ,width of ,base ,d ,width of ,head #a_/d inch #d inch #c inch #a_/b inch #d inch #c inch #a inch #d #a_/b inch #c #a_/b inch ,a small brass washer is placed between the standard and the base so that it will not bite into the wood when the screw is tightened4 ,the standard and the spring are both mounted by #h-cb brass machine screws passing through the base4 ,two binding posts are mounted on the corners of the base near the interrupter4 ,illustration3 ,,fig4 #abj4--,side ,view of the ,completed ,coil4 ,size of ,a ,c ,d ,e ,f ,g ,h ,q ,coil #a_/d in4 #h in4 #a #c #d #c #a #e_/h #d #a_/h in4 #g_/h in4 #g_/af in4 #a_/d in4 in4 in4 in4 #a_/b in4 #h #a_/d #a #c #e #c #a #e_/h #d in4 #a_/h in4 #a_/h in4 #g_/af in4 #a_/b in4 in4 in4 in4 #a in4 #aj #a #c #g #d #a #e_/h #f #a_/d #a_/d #a_/b #a_/h in4 #g_/af in4 #a_/b in4 in4 in4 in4 in4 in4 ,the condenser is fastened to the under side of the base by means of a wooden strip passing across it and secured to the base by means of two small wood screws4 ,one of the binding posts is connected to one of the primary wires4 ,the other primary wire is connected to the spring4 ,the other binding post is connected to the standard4 ,the condenser is connected directly across the interrupter1 that is1 one wire is connected to the spring and the other wire to the standard4 ,two binding posts are mounted on the wooden bridge and then the bridge is fastened across the top of the coil by means of two brass nails4 ,the secondary terminals are connected to these binding posts4 ,the ,coil is now ready for operation4 ,connect two pieces of wire to the secondary binding posts and bring them toward each other until they almost touch4 ,the space between should be about one-quarter of an inch long4 ,illustration3 ,,fig4 #aba4--;,diagram of ,connections4 ,connect three or four good dry cells to the primary posts and turn the thumbscrew until the contact point on the end touches the contact on the spring4 ,the interrupter should immediately commence to buzz and if the coil has been properly constructed and connected1 a stream of sparks will jump between the wires connected to the secondary4 ,it may be possible that the action of the interrupter and consequently the strength of the sparks at the secondary can be improved by bending the spring' either away or towards the core4 ,a little experimenting will soon show just how much tension the spring should have4 ,when the proper position of the thumb-screw is found1 tighten the lock nut so that it cannot change its adjustment4 ,illustration3 ,,fig4 #abb4--,perspective view of ,coil showing names of the various parts4 ,details and instructions for building and experimenting with larger spark coils are given in our books ,experimental ,wireless ,construction and ,induction ,coils4 ,,experiments ,,with ,,spark ,,coils4 ,experiment #a--;,an ,imitation ,gassiot's ,cascade4 ,wrap a piece of copper wire around a small glass jar and connect it to one of the secondary terminals of the coil4 ,fill the jar up with water and dip a wire connected to the other secondary terminal into the water4 ,if the coil is then set into operation1 the entire outside of the jar will be covered with sparks starting from the wires and rushing upwards into the neck of the jar4 ,if the coil used for this experiment is a very small one1 the glass jar should also be very small1 as for example1 a small medicine vial4 ,this experiment shows off the best when performed in the dark4 ,experiment #b--;,a ,ghostly ,light ,grasp the bulb of an old incandescent electric light bulb in one hand and touch the base of the lamp to one of the secondary terminals of the coil4 ,set the coil in operation and the bulb will glow with a weird greenish light4 ,this experiment will work best in the dark4 ,experiment #c--,lighting ,geissler ,tubes4 ,the most beautiful and wonderful effects may be obtained from ,geissler tubes operated from a spark coil in a dark room4 ,these tubes come in an almost endless variety of styles and shapes4 ,they are exhausted of air and fitted with metallic wires1 sealed into the ends1 a portion of the wire projecting outside in the form of small rings1 so that the connections are easily established4 ,some of the tubes are of ordinary glass1 while others are made of glass having in its composition certain metallic oxides4 ,some of the tubes are filled with various gases in a highly rarified state4 ,others have a double wall with the outside filled with a fluorescent liquid1 such as an aqueous solution of sulphate of quinine or an alcoholic solution of strammonium1 and other compounds4 ,the tubes are not very expensive4 ,they can be obtained in a great variety of sizes4 ,most well stocked electrical houses carrying goods for the electrical experimenter have them on hand4 ,such tubes are of necessity very fragile articles and should be handled with extreme care4 ,it is a good plan to keep them wrapped in cotton and to put them away in a strong wooden box1 so as to reduce the danger of breakage4 ,the very smallest coil1 even the one-quarter inch size1 will serve to light a large tube4 4 ,in fact1 if too large a coil is used1 there is danger of spoiling the tube4 ,the tubes are connected to the spark coil by running a wire from each of the small rings at the ends of the tubes to the secondary terminals4 ,several tubes may be connected in series when a or #a-;inch coil is available4 ,to show the best effects1 the room should be in perfect darkness and the tubes should be placed against a background of black velvet4 ,experiment #d--;,flickering ,light4 ,spread your fingers out and move your hand rapidly back and forth over a lighted ,geissler tube in a darkened room4 ,your hand will appear to have ten or twelve fingers instead of five4 ,this is due to the fact that the light from a ,geissler tube is flickering and not at all steady4 ,each time the interrupter of the coil opens1 the current is sent through the tube and lights it momentarily4 ,the flickering is almost too rapid to be perceived by the naked eye until you have something like the fingers or a pencil in front of it4 ,experiment #e--,rotating a ,geissler ,tube4 ,an extremely pretty effect can be secured by rotating a ,geissler tube at high speed while it is lighted4 ,this may be accomplished by means of an electric motor of small size4 ,the tube is tied tightly to a stick of wood which has a hole drilled exactly in its center into which the motor shaft fits tightly4 ,two rings of metal are mounted on the motor shaft1 and a wire is led from each to a terminal of the tube4 ,a copper strip rests on each ring1 and these two copper strips are connected to the secondary of the spark coil4 ,when the motor is started and the coil set into operation1 the tube will appear like the spokes of a wheel4 ,the intermittent light will make the tube visible for a fraction of a second in various positions around the circle as it rotates1 and this gives the effect which is much like that of a pinwheel4 ,experiment #f--;,fluorescent ,writing4 ,dissolve some sulphate of quinine in water and then draw a picture or design or write a sentence on a piece of white paper with it1 and allow it to dry4 ,the writing will be invisible1 but if you hold it up to a lighted ,geissler tube in a dark room1 it will appear as if written with a beautiful blue ink4 ,experiment #g--;,an ,electric ,bomb4 ,this is a very interesting experiment from which there is no danger if it is performed carefully4 ,the mortar is nothing more or less than a piece of wood which is hard and well seasoned1 and has a small hole bored in its axis about three-eighths of an inch in diameter and an inch deep4 ,two short lengths of stiff copper wire should be inserted through the sides near the bottom of the hole so as to form a small spark gap between the ends4 ,put a little gunpowder in the mortar and connect two wires from the secondary terminals of the spark coil to the spark gap4 ,place a cork loosely in the muzzle of the mortar and then1 standing well away1 close the switch in the primary circuit of the coil1 so that a spark passes through the mortar4 ,the spark will ignite the powder and it will explode with a loud report4 99,caution994--,do not use more than a pinch of powder at a time as this is sufficient to cause a sharp explosion4 ,experiment #h--;,electrifying the ,garbage ,can4 ,if you are ever annoyed by dogs or cats that knock the cover off the garbage can in their search for canine and feline delicacies1 you can give them the surprise of their lives with the aid of a spark coil upon the occasion of their next visit4 ,set the can upon a thick piece of perfectly dry wood and run a wire from the can to one secondary terminal of the spark coil4 ,connect the other secondary terminal to the ground or to a water or gas pipe4 ,the next time you see a dog with his nose in the can1 close the switch connected to the primary circuit4 ,what happens will not hurt the dog1 but he will travel for home as fast as four legs can carry him4 ,experiment #i--;,how to ,make an ,electric ,spark ,photograph ,itself4 ,this experiment must be conducted in a dark room with the aid of a photographer's ruby lamp so that the photographic plates used will not become light struck and spoiled4 ,place an ordinary photographic plate on a piece of sheet metal with the coated or sensitive side up4 ,connect the piece of sheet metal to one of the secondary terminals of the spark coil by means of a wire4 ,then sift some dry starch powder1 flour of sulphur or talcum powder through a thin piece of gauze on to the plate4 ,lead a sharp pointed wire from the other secondary terminal of the coil4 ,complete the primary circuit of the coil just long enough to make one single spark4 ,wipe the powder off the plate thoroughly and develop it in the usual manner4 ,the negative will show a peculiar electric discharge looking very much like sea moss4 ,no two photographs will be alike4 ,the test results are obtained when only one or two sparks are allowed to pass4 ,arts and ,science ,series ,no4 #i ,home-made ,electrical ,apparatus ,a ,practical ,handbook for ,amateur ,experimenters ,in ,three ,parts 99,volume ,,iii99 ,second ,edition 99,,by99 99,a4 ,m4 ,powell99 ,,published ,,by ,,cole ,,morgan1 ,inc4 ,publishers of the ,arts and ,science ,series ,p4,o4 ,,box #dgc ,,city ,,hall ,,station ,,new ,,york1 ,n4 ,y4 ,printed in ,u4 ,s4 ,a4 ,copyright #aiah by ,,cole ,,morgan1 ,inc4 ,,chapter ,,xii4 ,,how ,,to ,,make ,a ,,dynamo-,,motor ,it is very difficult to construct a first class dynamo without resort to the materials and methods employed in the manufacture of commercial machines4 ,the necessity for careful workmanship in every detail1 can hardly be overestimated4 ,poor workmanship and poor materials will always result in an inefficient machine4 ,telegraph instruments1 toy motors1 etc41 may be constructed from all sorts of odds and ends of materials1 and they will work fairly well1 but in order to make a real dynamo it will be necessary to use certain materials for which nothing can be substituted4 ,illustration3 ,,fig4 #abc--;,front view of the ,field ,casting4 ,the field casting must be soft gray cast iron and the magnet wire should be of good quality4 ,both the field and the armature of the small dynamo described in the following pages are cast iron and patterns will be necessary in order to form the moulds for the castings4 ,it may be possible for several experimenters to club together and make the patterns1 or have them made1 for building this dynamo4 ,the dynamo described has an output of about ten watts4 ,it may also be used as a motor and as such will develop considerable power4 ,the castings for this machine are already on the market and may be obtained from the publishers of this book4 ,illustration3 ,,fig4 #abd4--,side elevation of the ,field ,casting4 99,the ,field99 is shown in ,figures #abc and #abd4 ,the details in both illustrations are fully dimensioned and probably no comment in that direction will be necessary4 ,if the experimenter decides to make his own patterns he should use every care to make certain that they are carefully and accurately made4 ,they should be made of wood and finished by rubbing with fine sandpaper until perfectly smooth and then given a coat of shellac4 ,the parts should also be given a slight draft or taper toward one side so that the pattern may be easily withdrawn from the mould4 ,illustration3 ,,fig4 #abe4--;,details of the ,armature4 ,the easiest way to bore out the tunnel of the field is to perform the work on a lathe4 ,if no lathe is handy1 the work can be accomplished with nothing more than the aid of a file and a little patience4 ,it should be cleaned out until it is perfectly round and measures one and five-sixteenths of an inch in diameter4 ,any rough spots on the casting should be smoothed up with a file4 99,the ,armature99 is illustrated in ,figure #abe4 ,the centre of the armature should be bored out to fit a three-sixteenths inch shaft4 ,the shaft is a piece of steel rod four inches long4 ,the outside of the armature should be turned down to a diameter of one and one-quarter inches1 making it one-sixteenth of an inch smaller in diameter than the tunnel in the field4 99,the ,commutator99 is illustrated in ,figure #abf4 ,it has two sections and consists of a short piece of brass tubing fitted on a fibre core and split lengthwise on two opposite sides so that each section is insulated from the other4 ,it is not very difficult to make such a commutator4 ,a hole is drilled through the fibre1 which fits very tightly on the shaft4 ,the shaft is then placed in a lathe with the fibre in position and the latter turned down until a piece of seven-sixteenths inch brass tubing can be driven on4 ,the tube should be five-eighths of an inch long4 ,then mark two lines along the tube at points diametrically opposite4 ,bore two small holes to receive two small screws1 a short distance away from each side of these lines and on each side of them4 ,make certain that the screws do not go into the fibre far enough to touch the shaft4 ,the commutator may then be split along each side of the lines with a hacksaw1 continuing the cut right through the brass and slightly into the insulating core4 ,the heads of the screws should be filed off flush with the surface of the commutator and the latter trued up and made perfectly smooth4 ,illustration3 ,,fig4 #abf4--,the ,commutator4 ,if each section of the commutator is provided with a small brass machine screw near the back edge as shown in ,figure #abf1 it will greatly facilitate connection with the ends of the armature windings4 ,the armature1 shaft and commutator1 as they should appear when assembled are shown in ,figure #abg4 ,those portions of the armature and shaft which will come into contact with the armature wire should be insulated with shellaced paper4 ,soak the paper in the shellac until it is soft and it can be very easily pressed into proper shape to fit the armature4 ,allow the shellac to dry and harden before winding on the wire4 ,illustration3 ,,fig4 #abg4--,the ,armature and ,commutator ,assembled on the ,shaft ready for winding4 ,the armature will not need to be fastened on the shaft if it is a tight fit and cannot be twisted4 ,if it is loose1 it may be fastened by means of a small set screw or pin4 ,the commutator should fit the shaft very tightly so that it will not slip or twist4 99,the ,armature ,winding99 is ,no4 #bj ,b4 ,s4 ,gauge single-cotton covered magnet wire4 ,sufficient wire should be put on to fill up the winding space completely4 ,do not1 however1 put on too much wire or it will interfere with the field magnets and prevent the armature from revolving4 ,test the winding after it is finished to see that the wire is not grounded or connected to the armature at any point4 ,if the insulation is perfect1 give the winding a good coat of shellac and allow it to dry4 ,the ends of the winding are each connected to one of the commutator sections as shown in ,figure #abg4 99,the ,field ,winding99 is ,no4 #bj ,b4 ,s4 ,gauge single cotton covered wire4 ,the wire should be wound on in smooth1 even layers1 and the winding space between the flanges completely filled up4 ,the winding space in the field frame should be insulated with shellaced paper by covering the core and the flanges4 ,the flanges are best insulated with paper disks cut in two halves so that they will slip around the core4 ,illustration3 ,,fig4 #abh4--;,details of the ,wooden ,base4 ,the details of the wooden base are shown in ,figure #abh4 ,it is a rectangular shaped piece of wood1 five inches long1 four inches wide and five-eighths of an inch thick4 ,the corners are slightly rounded4 99,the ,bearings99 are small brass castings4 ,they are both alike4 ,the details are illustrated in ,figure #abi4 ,it will be necessary to make a wooden pattern and send it to a brass foundry for castings4 ,the castings should be smoothed up with a file and then drilled4 ,the shaft hole should be three-sixteenths of an inch in diameter and the screw holes just large enough to pass an #h-cb screw4 ,the bearings are fastened to the projecting arms on the field casting by means of round headed #h-cb brass machine screws4 ,the armature should revolve exactly in the centre of the tunnel in the field and should be free in the bearings so that it runs easily and without binding4 99,the ,brushes99 are illustrated in ,figure #aca4 ,they are cut out of spring copper and bent according to the shape and dimensions shown4 ,the field is fastened to the base by means of two large machine screws passing upwards through the base into threaded holes in the bottom of the casting4 ,the brushes are bent at right angles and mounted on the base on either side of the commutator with small round headed wood screws4 ,they should bear firmly against the commutator4 ,the commutator should be in such a position on the shaft1 in relation to the armature1 that the dividing lines between the two sections are directly opposite the centre of the iron faces of the armature as shown in ,figure #abg4 ,illustration3 ,,fig4 #abi4--;,details of the ,bearings4 ,illustration3 ,,fig4 #acj4--,the ,pulley4 ,illustration3 ,,fig4 #aca4--,the ,brushes4 ,the shaft should be fitted with a small grooved pulley to accommodate a small round belt4 ,the completed dynamo is shown in ,figure #acb4 ,the dynamo is connected in what is known as shunt4 ,one terminal of the field magnet is connected to one brush and the other terminal to the other brush4 ,a wire is then led from each one of the brushes to a binding post4 ,before the dynamo will generate current it will be necessary to magnetize the field by connecting the terminals to several strong batteries and allowing the current to flow through for several seconds4 ,a shunt wound dynamo will only generate when run in a certain direction4 ,in order to make it generate when run in the opposite direction1 it is necessary to reverse the field connections to the brushes4 ,illustration3 ,,fig4 #acb4--,the ,completed ,dynamo4 ,the dynamo will be found to operate as a very powerful little motor1 but on account of having only a two pole armature1 it must be started when the current is turned on by giving the shaft a twist4 ,the dynamo may be driven by a small water motor or from the driving wheel of a sewing machine4 ,it may be used as a generator for lighting lamps1 ringing bells1 electroplating1 etc4 ,,chapter ,,xiii4 ,,an ,,electric ,,battery ,,motor4 ,,an electric motor has two essential parts4 ,these are a field magnet for furnishing a strong magnetic field and a revolving armature4 ,it is an easy matter to make a strong electric motor suitable to operate on batteries by the exercise of a little careful workmanship4 ,the field frame and armature of the motor shown in ,figure #acc are laminated1 that is1 built up of separate sheets of iron4 ,they may be made out of sheet tin or ordinary stove pipe iron4 ,the cheapest and simplest method of securing good flat material is to get some old scrap from a tinner's or plumbing shop4 99,the ,details of the ,field99 are shown in ,figure #acd4 ,the exact shape and dimensions can be understood by reference to the illustration4 ,lay out one lamination very carefully as a pattern4 ,cut it out and smooth up the edges1 making certain that it is perfectly true to size and shape4 ,then use it as a template to lay out the other laminations by placing it on the metal and scribing a line around the edges with a sharp pointed needle4 ,enough laminations should be cut out to make a pile five-eighths of an inch high when tightly pressed together4 ,illustration3 ,,fig4 #acc4--,the completed ,electric ,motor4 99,the ,armature99 is made in exactly the same manner as the field frame1 that is1 by cutting out a pattern according to the shape and dimensions shown in ,figure #acf and using it as a template to lay out the other laminations4 ,enough should be cut to make a pile five-eighths of an inch high when tightly squeezed together4 ,illustration3 ,,fig4 #acd4--;,details of the ,field ,frame4 ,illustration3 ,,fig4 #ace4--,the ,assembled ,field ready for ,winding4 ,the armature is one and three-sixteenths inches in diameter4 ,the hole in the field frame which accommodates the armature is one inch and one-quarter in diameter so that there is a space in between for the armature to revolve in4 ,the hole through the center for the shaft should be of such diameter that the laminations will force very tightly on a shaft one-eighth of an inch in diameter4 ,the laminations should be very carefully flattened and then forced over the steel shaft which is two and one-eighth inches long4 ,clean up all the rough edges with a file and smooth the outside so that it will revolve properly in the field without scraping4 ,illustration3 ,,fig4 #acf4--;,details of the ,armature ,lamination4 ,illustration3 ,,fig4 #acg4--,the ,armature assembled on the ,shaft ready to ,wind4 ,figure #acg illustrates the armature assembled on the shaft and ready to be wound4 99,the ,armature ,windings99 consist of four layers of ,no4 #bb ,b4 ,s4 ,gauge double cotton covered magnet wire wound around each leg4 ,the iron should be very carefully insulated with shellaced paper before the wire is put in position so that there will not be any danger of short circuit due to the sharp edges of the metal cutting through the insulation4 ,each leg should contain the same number of turns of wire and all should be wound in the same direction4 ,the ,commutator is illustrated in ,figure #ach4 ,it consists of a piece of brass tubing seven-sixteenths of an inch long1 five-sixteenths inside and three-eighths of an inch outside4 ,it should be forced onto a piece of fibre five-sixteenths of an inch in diameter and seven-sixteenths of an inch long4 ,split the tube into three equal parts by dividing it longitudinally with a hack-saw4 ,make a fibre ring which will force onto the tube very tightly when it is in position on the fibre core and so hold the three commutator sections firmly in position4 ,the sections should be so arranged that there is a small space between each two and they are perfectly insulated from each other4 ,the fibre core should have a one-eighth inch hole through the centre so that it may be forced tightly onto the shaft and up against the armature after the windings are in position4 ,the commutator should be in such a position that the split between each two sections come directly opposite the centre of each winding4 ,suppose that the windings are lettered ,a1 ,b1 and ,c1 the commutator section between ,a and ,b is numbered #a1 that between ,a and ,c is ,no4 #b1 and the one between ,c and ,b is ,no4 #c4 ,then the inside terminal of ,b is connected to the outside terminal of ,a and soldered to the end of commutator section ,no4 #a close to the winding4 ,the inside end of ,b is connected to the outside terminal of ,c and to commutator section ,no4 #b4 ,the inside end of winding ,c is connected to the outside of ,b and to commutator section ,no4 #c4 ,the connection of the armature windings to the commutator are represented by the diagram in ,figure #aci4 ,illustration3 ,,fig4 #ach4--,the ,commutator4 ,illustration3 ,,fig4 #aci4--;,diagram showing how the ,armature ,coils are connected to the ,commutator ,sections4 ,illustration3 ,,fig4 #adj4--,the ,bearings4 99,the ,field ,winding99 consists of five layers of ,no4 #ah ,b4 ,s4 double cotton covered wire4 ,a much neater job may be made of this part of the work if two fibre heads are cut to slip over the field and support the ends of the winding as shown in the illustration in ,figure #acc4 99,the ,bearings99 are illustrated in ,figure #adj4 ,they are made out of three-eighths inch brass strip one-sixteenth of an inch thick by bending and drilling as shown in the illustration4 ,the location of the holes is best understood from the drawing4 ,the larger bearing is assembled on the field at the side towards the commutator4 ,assembling the motor is a comparatively easy matter if it is done properly and carefully4 ,the bearings are mounted on the field frame by screws passing through the holes ,b and ,b into a nut on the outside of the bearing at the opposite side of the field4 ,the armature should revolve freely without binding and without any danger of scraping against the field4 ,slip some small fibre washers over the ends of the shaft between the armature and the bearings so as to take up all end play4 99,the ,brushes99 are made of spring copper according to the shape and dimensions shown in ,figure #ada4 ,they can be cut out with a pair of snips4 ,each brush is mounted on a small fibre block supported on the large motor bearing4 ,the holes marked ,a and ,c in the illustration should be threaded with a #d-cf tap4 ,the hole ,b should be made one-eighth of an inch in diameter and drilled all the way through the block4 ,the holes ,a and ,c are used to fasten the blocks to the bearing4 ,the brushes are fastened to the blocks by means of a #f-cb screw with a nut on the lower end4 99,the ,base99 is a rectangular block1 three inches wide1 three and one-half inches long and three-eighths of an inch thick4 ,the motor is fastened to the base by four small right angled brackets bent out of strip brass and secured to the field frame by two machine screws passing through the holes ,h and ,h into a nut at the opposite end4 ,illustration3 ,,fig4 #ada4--,the ,brushes4 ,one terminal of the field winding is connected to a binding post mounted on the base4 ,the other terminal of the field is connected to the right hand brush4 ,the end of the wire should be placed under the head of the screw which holds the brush to the fibre block4 ,the brush should be on the under side of the block so that it bears against the under side of the commutator4 ,the left hand brush bears against the upper side of the commutator and is connected to a second binding post on the base of the motor4 ,this makes it a series motor1 that is1 the armature and the field are connected in series4 ,illustration3 ,,fig4 #adb4--,the ,fibre ,block for supporting each ,brush4 ,the motor is now ready to run4 ,put a drop of oil on each bearing and make certain that the curved portion of the brushes bear firmly against the centre of the commutator on opposite sides4 ,the armature having three poles1 should start without assistance and run at high speed as soon as the current is applied4 ,two cells of dry or other battery should be sufficient4 ,the motor may be fitted with a small pulley so that its power may be utilized for driving small models4 ,,chapter ,,xiv4 ,,how ,,to ,,build ,,an ,,electric ,,engine4 ,an ,electric engine is really a form of electric motor but differs from the most common form of the latter in that the armature1 instead of revolving1 oscillates back and forth1 like the piston of a steam or gasoline engine4 ,electric engines are not as efficient as electric motors from the standpoint of the amount of power delivered in proportion to the current used1 but they make very interesting models and the young experimenter will derive fully as much pleasure in constructing one as from the construction of an electric motor4 ,various forms of electric engines were made before the first practical electric motor was invented4 ,they amounted to little more than curiosities1 however1 and could only be used where the expense of electric current was not to be regarded4 ,illustration3 ,,fig4 #adc4--;,completed ,electric ,engine4 ,the engine illustrated in ,figure #adc is of the double action type4 ,it is provided with two electromagnets arranged so that one pulls the armature forward and the other pulls it back4 ,the motion of the armature is transmitted to the shaft by means of a connecting rod and crank4 ,it is very simple to build and the design is such that it will operate equally well whether it is made large or small4 ,if you do not happen to have all the necessary materials to build an engine according to the dimensions shown in the drawings you can make it just one-half that size and it will work equally well although it will of course not give as much power4 ,the complete engine is shown in ,figure #adc4 ,all the various parts have been marked so that you can easily identify them in the other drawings4 ,it is well to study this illustration carefully first so that you will understand just how all the parts are arranged4 99,the ,base99 is illustrated in ,figure #add4 ,it is made of a piece of hardwood1 seven inches long1 three and one-half inches wide and one-half an inch thick4 ,illustration3 ,,fig4 #add4--,the ,engine ,base4 99,the ,magnets994 ,the size of the electromagnets will largely determine the dimensions of the rest of the engine4 ,the magnets shown in ,figure #ade are made of three-eighths inch round iron1 two and one-half inches long1 provided with two fibre washers one and one-eighth inches in diameter4 ,one end of each of the steel cores is drilled and tapped to receive an #h-cb iron screw4 ,the experimenter may possibly be able to secure some old magnet cores fitted with fibre heads from an old telephone bell or ringer as they are sometimes called4 ,a suitable bolt can be made to serve the purpose by cutting it off to the right dimensions with a hack saw4 ,if a drill and a tap are not available for drilling and tapping the end so that the core can be properly mounted in the frame of the engine it is possible by the exercise of a little ingenuity to use the threaded portion of a bolt to good advantage4 ,the hole in the frame should then be made larger so that the end of the bolt will slip through instead of an #h-cb screw and the core clamped in position by a nut on each side4 ,the fibre washers are spaced two and one-sixteenth inches apart4 ,the space in between should be wound full of ,no4 #ah ,b4 ,s4 ,gauge cotton covered magnet wire4 ,before winding in the wire1 cover the core with a layer of paper so that the wire does not touch the metal4 ,the ends of the wire should be led out through small holes in the fibre heads4 ,illustration3 ,,fig4 #ade4--;,details of the ,electromagnet ,bobbin4 ,it is not absolutely necessary to use ,no4 #ah ,b4 ,s4 ,gauge wire in winding the magnets but this is the size which will give the best results on the average battery4 ,illustration3 ,,fig4 #adf4--;,details of the ,engine ,frame4 ,if you use larger wire1 the engine will require more current from the battery4 ,if you use finer wire1 a battery of a higher voltage will be necessary4 ,the current consumption will1 however1 be less4 99,the ,frame499--,the electromagnets are mounted in the frame of the engine by means of two screws passing through the holes ,e and ,d4 ,the details of the frame are illustrated in ,figure #adf4 ,it is made of a strip of wrought iron or cold rolled steel1 nine and one-quarter inches long1 an inch or an inch and one-eighth wide and one-eighth of an inch thick4 ,the material for making this part of the engine and also the bearings can probably best be obtained at some blacksmith shop or hardware store4 ,heavy galvanized iron can be used but it is not usually thick enough and it may be necessary use two thicknesses4 ,the ends of the strip are rounded and bent at right angles so as to form a ,u-shaped piece with sides one and three-quarters inches high4 ,the holes ,d and ,e should be large enough to pass an #h-cb screw4 ,the holes ,a1 ,b and ,c should be about one-eighth of an inch in diameter4 ,they are used to pass the screw which hold the frame of the engine to the wooden base4 ,illustration3 ,,fig4 #adg--,the ,bearings4 99,the ,bearings99 are shown in ,figure #adg4 ,they are ,u-shaped and are made out of a strip of iron or steel in the same manner as the frame of the engine but are three-quarters of an inch wide instead of an inch and one-eighth4 ,the dimensions will be understood best by referring to the drawing4 ,the #c_/cb inch holes near the top of each side are the bearing holes for each end of the shaft4 ,the one-eighth inch holes below are used to fasten the brush holder in position4 ,the holes in the bottom serve to fasten the bearings to the base4 ,illustration3 ,,fig4 #adh4--;,details of the ,shaft4 99,the ,shaft99 will probably prove the most difficult part of the engine to make properly4 ,the details are given in ,figure #adh4 ,it is made of a piece of one-eighth inch steel rod bent so that it has a throw of one-half an inch1 that is1 is offset one-quarter of an inch so that the connecting rod moves back and forth a distance of one half an inch4 ,the finished shaft should be three inches long4 ,the piece of steel used should be longer than this1 so that it can be cut off to exact dimensions after the shaft is finished4 ,a second crank should be bent in one end of the shaft so as to form an offset contact for the brushes4 ,this second crank will have to be at right angles to the first one and should be much smaller4 ,the ends of the shaft are turned or filed down to a diameter of three-thirty second of an inch for a distance of about the same amount so that they will fit in the bearing holes and turn freely but not allow the whole shaft to slip through4 ,the work of making the shaft will require a small vice1 a light hammer1 files and a couple of pairs of pliers4 ,one pair of pliers should be of the round nosed type and the other a pair of ordinary square jawed side cutters4 ,it may require two or three attempts before a perfect shaft is secured4 ,when finished it should be perfectly true and turn freely in the holes4 ,the bearings can be adjusted slightly by bending so that the shaft will fit in the holes and be free but yet not be loose enough to slip out4 99,the ,armature99 is a strip of soft iron1 two and one-eighth inches long1 seven-sixteenths of an inch wide and three-sixteenths of an inch thick4 ,a one-sixteenth inch slot1 three-eighths of an inch long is cut in one end4 ,a one-sixteenth inch hole is drilled through from one side to the other1 one-eighth of an inch from each end4 ,the hole which passes through the slot is used to pass the pin which pivots the armature to the connecting rod4 ,the other hole is used to mount the armature in its bearing4 ,the armature bearing is a small edition of the one which is used to support the engine shaft4 ,the details and the dimensions are given in the lower left hand side of ,figure #adi4 ,the armature is shown in the centre of the same illustration4 ,the connecting rod is illustrated at the right4 ,this is made from a strip of three-sixty-fourths inch brass1 three-sixteenths of an inch wide and one and five-eighths inches long4 ,a one-eighth inch hole should be drilled close to one end and a one-sixteenth inch hole close to the other4 ,illustration3 ,,fig4 #adi4--,the ,armature1 ,armature ,bearing and ,connecting ,rod4 99,the ,brushes99 are two strips of thin phosphor bronze sheet1 two and three-sixteenths inches long and nine-thirty-seconds of an inch wide4 ,they are illustrated in ,figure #aej4 ,the block upon which they are mounted is hard fibre4 ,it is one and five-eighths inches long and three-eighths of an inch square4 ,illustration3 ,,fig4 #aej4--,the ,brushes4 99,the ,flywheel994 ,it may be possible to secure a flywheel for the engine from some old toy4 ,it should be about three and one-half inches in diameter4 ,a flywheel can be made out of sheet iron or steel by following the suggestion in ,figure #aea1 which shows a wheel cut out of one-eighth inch sheet steel4 ,it is given the appearance of having spokes by boring six three-quarter inch holes through the face as shown4 ,the hole in the centre of the wheel should be one-eighth of an inch in diameter4 ,the wheel is slipped over the shaft and fastened in position by soldering4 ,the parts are now all ready to assemble into the complete engine4 ,mount the electromagnets in the frame and fasten the frame down to the wooden base so that one end of the frame comes practically flush with the left hand edge of the base4 ,fasten the bearing across the frame at right angles by a screw passing through the centre hole in the bottom of the bearing1 through the hole ,a and into the base4 ,the bottom of the bearing should be bent slightly so as to straddle the frame4 ,the bearings should be secured and prevented from turning or twisting by two screws passed through the other two holes in the bottom4 ,use round-headed wood screws in mounting the bearing and the frame4 ,the armature bearing should be mounted on the frame directly between the two electromagnets4 ,then place the armature in position by slipping a piece of one-sixteenth inch brass rod through the bearing holes and the hole in the lower part of the armature4 ,illustration3 ,,fig4 #aea4--;,a ,flywheel may be cut from sheet iron4 ,solder the flywheel in position on the shaft and snap the latter into the bearings4 ,adjust the bearings so that the shaft will turn freely4 ,the connecting rod should be slipped over the shaft before it is placed in the bearings4 ,fasten the other end of the connecting rod to the armature by means of a piece of one-sixteenth inch brass rod which passes through the small holes bored for that purpose4 ,when the flywheel is spun with the fingers1 the armature should move back and forth between the two electromagnets and almost but not quite touch the two magnet poles4 ,all the moving parts should be fitted firmly together but be free enough so that there is no unnecessary friction and so that the engine will continue to run for a few seconds when the flywheel is spun with the fingers4 ,the brushes1 supported on their fibre block should be mounted on the bearing by means of two screws passing through the holes in the bearing into the block4 ,the position of the brushes should be such that the shaft passes between the two upper ends but does not touch them unless the small contact crank mentioned above is in proper position to do so4 ,the proper adjustment of the brushes1 so that they make contact with the shaft at the proper moment1 will largely determine the speed and power which the finished engine will develop4 ,two binding posts should be mounted on the right hand end of the base so that the engine can be easily connected to a battery4 ,connect one terminal of the right hand electromagnet to one of the binding posts4 ,run the other terminal of the electromagnet to the brush on the opposite side of the shaft4 ,connect one terminal of the left hand electromagnet to the other binding post and run the other terminal to the brush on the opposite side of the shaft4 ,save for a few minor adjustments1 the engine is now ready to run4 ,connect two or three cells of dry battery to the two binding posts and turn the flywheel so that it moves from right to left across the top4 ,just as the crank passes dead centre and the armature starts to move back away from the left hand magnet1 the small contact crank should touch the left hand brush and send the current through the right hand magnet4 ,this will draw the armature over to the right4 ,just before the armature gets all the way over to the right1 the contact should break connection with the left hand brush and interrupt the current so that the inertia of the flywheel will cause it to keep moving and the armature to start to move over towards the left hand magnet at which point the contact on the shaft should commence to bear against the right hand brush1 thus throwing the left hand magnet into circuit and drawing the armature over to that side4 ,if the brushes and the cranks are in proper relation to each other the engine will continue to repeat this operation and gradually gain speed until it is running at a good rate4 ,the appearance of the engine can be improved by painting the metal parts black and the flywheel red4 ,the magnets can be wrapped with a piece of bright red cloth to protect the wire against injury and brighten the appearance of the engine4 ,,chapter ,,xv4 ,,miniature ,,battery ,,lighting4 ,the tungsten lamp has opened wonderful possibilities in the field of electric lighting by means of miniature lamps operated from batteries4 ,the tungsten lamp uses less than one third the amount of current required by the old-fashioned carbon filament lamps in producing the same candle power4 ,this means that the battery will last three times as long4 ,miniature lighting is one of the most practical phases of experimental electricity to which the experimenter can apply his time4 ,battery operated lamps will be found invaluable in many places for lighting dark corners1 hallways1 barns1 garages1 camps1 bungalows1 workshops1 etc4 99,tungsten ,battery ,lamps99 are made in a great many different styles and sizes4 ,the smallest sizes are used for flashlights1 hand-lanterns1 etc4 ,these are not rated according to their candlepower1 but to the voltage which they should be operated on4 ,flashlight lamps will be found satisfactory as a means of illuminating closets1 cellars1 stairways1 etc41 but do not give sufficient light for reading or any purpose of that sort4 ,the light which they give varies from one to three candle-power according to the size of the lamp4 ,they are made for #a4e1 #b4h1 #c4h and #e4h volts or respectively one1 two1 three and four dry cells4 ,flashlight lamps are provided with what is known as a miniature base only4 ,a very simple lighting arrangement which will prove exceedingly useful for illuminating a dark closet1 a coal bin or the face of a clock1 etc41 consists of a #a4e volt lamp1 a single cell of dry battery and a suitable switch and wire4 ,such an installation may be made at a cost of less than seventy-five cents4 ,illustration3 ,,fig4 #aeb4--,small ,tungsten ,battery ,lamps4 ,the lamp is mounted in what is known as a miniature porcelain base receptacle4 ,the switch may most conveniently be the type termed a wood base switch4 ,in case the lamp is installed for illuminating a clock1 a pear push and a flexible cord may be substituted for turning the light off and on in place of the switch4 ,it can then be suitably hung alongside of the clock or bed as desired4 ,the wire should not be smaller than ,no4 #ah ,b4 ,s4 ,gauge or else it will offer too much resistance to the electric current and full benefit of the candle-power of the lamp will not be secured4 ,annunciator wire is preferable4 ,it has good insulation and at the same time is not too large to be easily run through corners1 cracks1 etc4 ,the diagram in ,figure #aec shows how to connect the lamp to the battery and switch4 ,figure #aef shows two dry cells connected in series for use with a #b4h volt lamp4 ,illustration3 ,,fig4 #aec4--;,a ,simple ,lighting ,arrangement4 ,when more illumination is desired than that furnished by flashlight lamps greater candle-power will be required4 ,the following table shows the voltages and candle-powers of those lamps which are most suitable in such an instance3 ,g#f4444d volts #d candle-power ,g#f4444f volts #d candle-power ,g#h #f volts #f candle-power ,they may also be operated from dry cells4 ,if they are intended to be in use for other than a few minutes at a time it will be well to use a battery consisting of two sets of cells connected in series multiple4 ,the method of connecting cells in series multiple has already been illustrated in ,figure #ce4 ,this will lighten the strain on the battery and it will be found that two sets of batteries used in series multiple will last 99more than twice99 as long as one set used alone4 ,illustration3 ,,fig4 #aed4--,showing the differences between the ,candelabra1 ,single ,ediswan and ,double ,ediswan ,types of ,lamp ,bases4 ,six volt lamps of more than six candle-power are best operated on storage batteries because the current required is too great for dry cells to give efficient service in such a case4 ,the tungsten lamps made for automobiles are ideal for miniature lighting plants operated by storage batteries4 ,the list below shows some of the sizes on a current of six to eight volts4 ,the bases are made of brass and come in four different styles1 miniature1 candelabra1 single ,ediswan and double ,ediswan4 ,the single and double ,ediswan are used on automobiles because the construction of the base and the socket or the receptacle into which it fits is such that the lamp cannot jar loose4 ,illustration3 ,,fig4 #aee4--,miniature ,sockets of the types known as ,flat ,base ,porcelain1 ,pin and ,weatherproof4 ,the candelabra base is probably the type best adapted to miniature lighting elsewhere than on an automobile4 ,the letter ,g and the number in the first column indicates the size of the glass globe or bulb of the lamps4 ,you can compute the approximate amount of current drawn from a battery by a tungsten lamp1 by dividing the candle-power by the voltage4 ,the result is the current in amperes4 ,for example1 a #f volt1 #ab candle-power lamp will consume #ab divided by #f1 or #b amperes4 ,illustration3 ,,fig4 #aef4--;,connections for a #b4h ,volt ,lamp4 ,storage batteries are rated by their output in 99ampere hours994 ,an ampere hour is the amount of current represented by one ampere flowing for one hour4 ,a forty ampere hour cell will deliver one ampere for forty hours1 #d amperes for ten hours or #e amperes for eight hours4 ,the ampere hour capacity of a storage cell divided by the amount of current being used will determine how long that current can be drawn before recharging is necessary4 ,the maximum amount of current it is safe to draw from a storage cell without impairing its life and efficiency is the maximum current which that cell can deliver continuously for eight hours4 ,in order to determine this current simply divide the manufacturer's rating of the battery in ampere hours by eight4 ,the answer is the maximum current you should require from the battery if you wish to obtain good service from it4 ,for example1 the maximum safe discharge rate of a #dj ampere hour battery is #dj divided by #h or #e amperes4 ,illustration3 ,,fig4 #aeg4--;,a ,miniature ,base ,tungsten ,filament ,battery ,lamp for small lighting4 ,the method of computing the current required by a lamp and the method for determining the maximum safe discharge rate of a battery will enable you to figure the size of the smallest battery it is desirable to use in a lighting plant4 ,suppose that you intend to use three #f volt #ab candlepower lamps4 ,each lamp will require two amperes or a total of six when all three lamps are burning at the same time4 ,six amperes multiplied by eight ampere hours equals #dh ampere hours4 ,this is the smallest size of battery which should be used4 ,if it is larger1 it will be advantageous1 because it will supply the lamps a correspondingly longer time without recharging4 ,figure #aee shows some of the sockets or receptacles which are on the market4 ,the illustration to the left is a flat base receptacle4 ,it will be found most useful when the lamp is to be mounted directly on the wall or ceiling4 ,the weatherproof type of socket may be secured with either a fibre or a porcelain shell4 ,illustration3 ,,fig4 #aeh4--;,a ,tungsten ,automobile ,lamp with ,ediswan ,base4 ,the brass shell socket is the best wherever appearance counts4 ,it is patterned after the standard ,edison sockets and is made so that it will screw onto several different sizes and styles of brackets which may be mounted on either the ceiling or the wall4 ,this type of socket is also made with a small switch built inside so that the lamp may be turned on or off directly at the socket4 99,the ,wire99 used to connect the system will depend upon where the lamps are located4 ,annunciator or office wire as it is sometimes called will serve in most cases where the wires are to be run entirely indoors4 ,the largest size made is ,no4 #af ,b4 ,s4 ,gauge4 ,this is the size which should be used4 ,annunciator wire is made in various colors so that it can be more easily concealed4 ,if the wires are run outdoors1 or somewhat exposed to the weather1 as on a porch or in a barn1 it is advisable to use weatherproof or rubber covered wire4 ,lead covered twin conductor is recommended for use aboard boats or wherever the wire is liable to abrasion4 ,illustration3 ,,fig4 #aei4--,lamps ,controlled by ,one ,switch4 ,if the lamps are larger than eight candle-power1 or several are to be used on the same line1 the wires should be larger than ,no4 #af4 ,when a battery is connected to a system of wires1 the voltage at the end of the line is much lower than it is at the battery terminals4 ,this is due to the resistance of the wire and is called voltage drop4 ,the lamps at the end of the line will not burn as brilliantly as those close to the battery4 ,this can be partially overcome by using large wire4 ,the lamps may be either connected in series or in multiple4 ,when a six volt battery is used1 it will be necessary to connect them in multiple4 ,figure #aei shows how several lamps may be connected in multiple and controlled by one switch4 ,figure #afj shows the same lamps with three separate switches so that each lamp may be turned on or off individually4 ,illustration3 ,,fig4 #afj4--,lamps ,controlled by ,separate switches4 ,it is possible to arrange a lamp and two switches so that it can be turned on or off at either switch independently of the other4 ,this is a very convenient method of installing a light on a stairway or in a hall4 ,one switch may be placed at the top of the stairs and the other at the bottom4 ,a person going either up or down stairs can light the lamps ahead and turn it out as he passes the last switch regardless of its position at the other end4 ,the switches must be of the type called two point or double throw single pole and the levers must always rest on one of the contacts and never be left in between4 ,illustration3 ,,fig4 #afa4--;,double ,control ,system4 ,,chapter ,,xvi4 ,,coherer ,,outfits ,,for ,,wireless ,,telegraphy4 ,making a ,coherer4 ,how to ,adjust the ,instruments4 ,,many experimenters desire some device by which wireless signals may be made clearly audible without the necessity of holding a telephone receiver to the ear4 ,it is not possible for the amateur to make such an arrangement which will receive signals over long distances4 ,it is1 however1 possible to arrange a coherer so that signals coming from a nearby station may be indicated by the ringing of a bell4 ,illustration3 ,,fig4 #afb4--,the ,coherer ,details4 ,such a coherer outfit will receive messages coming within a radius of one mile and may also be used for demonstrating the principles of wireless telegraphy when both the receiving and transmitting station are located in the same room or building4 ,in order to secure these results it will be necessary to substitute a device called a coherer for the detector in the receiving apparatus4 ,a coherer consists essentially of a few metal filings between two metal plugs4 ,the filings are made part of a circuit which includes a relay and a battery4 ,under ordinary conditions the filings lie loosely together and their resistance to an electric current is so great that they will not allow enough energy to flow to operate the relay4 ,if1 however1 the two plugs are connected to the aerial and ground so that the currents of the incoming wireless signals also pass through the filings1 they will suddenly cohere or stick together and permit sufficient current to pass to operate the relay4 ,illustration3 ,,fig4 #afc4--,the ,complete ,coherer4 ,a tapper1 or as it is also sometimes called a decoherer1 is also arranged in the circuit so as to automatically shake the filings up and restore them to their loose state as soon as each signal is received4 ,the decoherer consists simply of an ordinary bell mounted so that the hammer will strike the coherer and jar it4 ,the first thing required in order to make a coherer is a pair of double binding posts4 ,these should be mounted on a wooden base six inches long and four inches wide as shown in ,figure #afc4 ,a piece of glass tubing about one and one-half inches long and one-eighth of an inch in diameter inside together with some brass rod which will just slip into the tube tightly will be required4 ,cut two pieces of the brass rod one and three-quarters inches long and face off the ends perfectly square and smooth4 ,slip these rods through the upper holes in the binding posts and into the glass tube as shown in ,figure #afc4 ,be sure that everything lines up perfectly and then remove one of the plugs4 ,before putting the plug back in place put some nickel and silver filings in the tube so that when the rods are pushed almost together1 with only a distance of three-sixty-fourths to one-sixteenth of an inch between1 the filings will about half fill the space4 ,illustration3 ,,fig4 #afd4--,pony ,type ,relay4 ,the filings are a mixture of silver and nickel and must be very carefully prepared4 ,the mixture should be nine-tenths nickel and one-tenth silver4 ,the filings may be secured by holding a five cent piece over a clean sheet of paper and filing it with a coarse file4 ,the silver filings are made in the same way by using a ten cent piece or a quarter in place of the nickel4 ,do not use the fine dust and powder which is formed1 but only the coarse filings4 ,the success of the coherer will depend upon its adjustment and it will probably be necessary for the beginner to experiment considerably to find out just the right amount of filings to place in the tube and how far apart the brass plugs should be placed4 ,the decoherer is made by removing the gong from an old electric bell and mounting the bell on the base in the position shown in ,figure #afc4 ,the hammer should be bent so that it will tap the coherer lightly when a battery is connected to the bell binding posts4 ,the only thing required to complete the apparatus is a relay4 ,a relay of the ,pony type such as that shown in ,figure #afd will serve for ordinary work4 ,it should be wound to at least #aej ohms1 for to a certain extent1 the higher the resistance1 the more sensitive it will be4 ,when it is desired to secure the maximum possible distance with the coherer a polarized relay will be necessary4 ,a polarized relay is much more sensitive than the ordinary sort4 ,the polarized relay should be wound to #ajjj ohms4 ,illustration3 ,,fig4 #afe4--;,connections for the ,receiving ,set4 ,figure #afe illustrates how the coherer1 decoherer and relay should be connected4 ,two wires connected to the coherer posts lead to the magnets of the relay in series with a single dry cell4 ,the contact posits of the relay are connected to the decoherer in series with another dry cell4 ,when wireless signals pass through the relay they will cause the resistance to drop and allow sufficient current from the dry cell to pass through the coherer to energize the magnets of the relay and draw the armature in1 thus closing the decoherer circuit4 ,when the armature of the relay is drawn in towards the magnets the relay contacts are brought together4 ,this closes the decoherer circuit and starts the hammer to tapping the coherer1 thus restoring the filings to their former loose state4 ,the decoherer will tap the coherer as long as the incoming signals continue4 ,by breaking the signals up into dots and dashes of the telegraph code a message may be easily transmitted and read from the tapping of the decoherer4 ,illustration3 ,,fig4 #aff4--;,coherer1 ,decoherer and ,relay ,connections4 ,the best results are secured from a coherer outfit if it is connected to the aerial and ground by substituting it for the detector in a circuit employing a double slide tuning coil and a fixed condenser4 ,the two wires that would ordinarily be connected to the detector terminals are simply connected to the coherer posts4 ,when the apparatus is to be used for demonstration or experiment and the transmitting and receiving stations are both located in the same room or house it will not be necessary to use an aerial and ground but merely to attach two copper wires about #ah or #bd inches long to the opposite sides of the coherer as shown in ,figure #afc4 ,in such a case the transmitter should be arranged as in ,figure #afg4 ,a spark gap made especially for this purpose is illustrated in ,figure #afh4 ,some of the details of the gap are shown in ,figure #afi4 ,illustration3 ,,fig4 #afg4--;,how the ,transmitter is ,connected4 ,the ball may be made in the form of a complete sphere or else consist simply of half of one as illustrated4 ,it should have a radius of about five-eighths of an inch and arranged so that it may be mounted upon the end of a catch-wire4 ,illustration3 ,,fig4 #afh4--,the ,complete ,spark ,gap4 ,the catch-wires are mounted in two standards similar in construction to a large binding post three and one-quarter inches high4 ,the standards should be mounted by screwing them on top of the secondary terminals of the spark coil4 ,the spark balls should be adjusted so that the distance between them is not over one-eighth of an inch4 ,the coherer apparatus will probably require to be very accurately adjusted before it will work properly4 ,patience and a little experience will soon enable one to overcome the difficulties and to put the apparatus in sensitive condition without much trouble4 ,illustration3 ,,fig4 #afi4--;,details of ,spark ,gap4 ,the coherer will be found to be the most sensitive when only a very few filings are used4 ,the adjustment desired in the relay is the one in which the armature is given the smallest possible amount of motion and the spring which pulls the armature away from the magnets1 the least tension4 ,the best method of finding the most sensitive adjustment for the apparatus is to place the transmitting and receiving stations only a few feet apart from each other in the same room4 ,after you learn how to adjust the coherer and relay properly you will then find that you can move the transmitter quite a distance away from the coherer and it will still operate4 ,of course a coherer outfit is not very satisfactory and reliable for the regular reception of wireless signals even over short distances because of its irregular working4 ,it is1 however1 very useful for sort of a calling or signal outfit4 ,it may be connected to the tuning coil by means of a double-pole1 double-throw switch and left in the circuit so as to indicate by the working of the tapper when any of the other stations in the near neighborhood are sending4 ,the detector can then be quickly inserted in the circuit in place of the coherer by throwing the switch in the opposite direction and the signals read in the telephone receiver4 ,,chapter ,,xvii4 ,,how ,,to ,,build ,a ,,tesla ,,high ,,frequency ,,coil4 ,,if the discharge from a ,leyden jar or a condenser is passed through a coil of wire acting as a primary and the primary is provided with a secondary coil of a larger number of turns1 a peculiar current known as high frequency electricity is generated in the secondary4 ,such a device is known as a ,tesla ,coil or ,transformer4 ,illustration3 ,,fig4 #agj4--,tesla ,coil ,circuits4 ,when a ,leyden jar or a condenser discharges through a coil of wire1 the spark which takes place does not consist simply of a single spark passing in one direction only1 but is really made of a number of separate sparks passing alternately in opposite directions at the tremendous rate of from one hundred thousand to one million times per second4 ,a ,tesla high frequency coil opens a field of wonderful possibilities to the amateur experimenter and brings innumerable weird and fascinating experiments within his reach4 ,the ,tesla coil described in the following pages will give sparks of high frequency electricity two or three inches long from the secondary1 when used in connection with a two inch spark induction coil4 ,if used in connection with a small high potential wireless transformer1 the high frequency discharge can be increased to six or eight inches4 ,a ,tesla coil1 suitable for use with a smaller spark coil1 say one capable of giving sparks from one-half to one inch in length can be made by following the same plans but cutting all of the dimensions in half4 ,make the secondary six inches long and one and one-half inches in diameter instead of twelve inches long and three inches in diameter1 etc4 ,illustration3 ,,fig4 #aga4--,secondary ,tube4 99,the ,secondary99 winding consists of a single layer of ,no4 #bh ,b4 ,s4 ,gauge double cotton covered wire wound over a cardboard tube1 twelve inches long and and three inches in diameter4 ,the tube must be thoroughly dried before using it1 by baking in an oven4 ,a coat of shellac1 both inside and out1 will avoid the possibility of having to rewind the tube because of the wire becoming loose1 due to drying out of the tube later4 ,the wire should be wound on in a smooth1 even layer to within about one-quarter of an inch from the ends and given a coat of hot paraffine when finished4 ,the ends of the tube are fitted with circular wooden heads having a half inch flange4 99,the ,base99 is a rectangular piece of wood1 fifteen inches long and six inches wide4 ,the secondary is supported in position by two hard rubber uprights1 four inches high1 seven-eighths of an inch wide and one-half an inch thick4 ,a round-headed brass wood screw is passed through the top part of each of the supports into the centre of each one of the wooden secondary heads4 ,high frequency currents are very hard to insulate and wood does not possess sufficient insulating value to fit it for use as supports4 ,hard rubber or glass are the most satisfactory materials for the supports4 ,illustration3 ,,fig4 #agb4--;,details of the ,secondary ,heads4 ,the secondary terminals are connected to two brass rods1 five inches long and having a small brass ball at the upper end1 mounted on the top of each of the hard rubber supports4 ,the lower ends of the hard rubber supports are fastened to the base by means of screws passing upwards through the base into a threaded hole in the bottom of each support4 ,illustration3 ,,fig4 #agc4--;,details of the ,primary ,head4 ,the secondary passes through the centre of the primary4 ,the primary consists of eight turns of heavy copper wire wound around a wooden drum or frame4 ,the wire should be ,no4 #h or ,no4 #aj ,b4 ,s4 ,gauge4 ,flat copper or brass ribbon one-quarter of an inch wide can be used in place of the wire4 ,the stranded copper wire1 consisting of seven ,no4 #bb ,b4 ,s4 ,gauge wires twisted together and commonly employed for wireless aerials can be used to good advantage in winding the primary1 the idea of using a large wire1 stranded wire1 or ribbon being to obtain a conductor having as much surface as possible4 ,high frequency currents travel only on the surface of wires and conductors4 ,a hollow tube is just as good a conductor for high frequency currents as a solid rod of the same diameter4 ,illustration3 ,,fig4 #agd4--,primary ,cross ,bar4 ,illustration3 ,,fig4 #age4--;,front ,view of the completed ,tesla ,coil4 ,illustration3 ,,fig4 #agf--,side ,view of the completed ,tesla ,coil4 ,the heads of the primary drum are wooden rings1 seven inches in diameter outside1 four and one-half inches inside and one-half an inch thick4 ,six cross bars1 two and one-half inches long1 three-quarters of an inch thick and one-half an inch wide are required to support the wire4 ,they are spaced equidistantly around the rings and held in position by means of brass screws passing through the rings4 ,do not use iron screws1 because iron is magnetic and should be entirely avoided in the construction of a ,tesla coil4 ,small notches should be cut in the outside edge of the cross bars to accommodate the wires4 ,the wires should pass around the drum in the form of a spiral with one-quarter to five-sixteenths of an inch space between the turns4 ,the completed drum will somewhat resemble a squirrel cage4 ,the ends of the primary winding should terminate in two large binding posts mounted on the primary heads4 ,the heads are fastened to the centre of the base by a couple of large wood screws passing upwards though the bottom4 ,illustration3 ,,fig4 #agg4--;,diagram of connections for operating the ,coil4 ,the illustration in ,figure #agg shows how to connect the ,tesla coil4 ,the primary should be in series with a condenser and a spark gap4 ,the condenser should consist of two or three ,leyden jars or several glass plates coated with tinfoil4 ,it is impossible to determine just how much capacity the condenser should have in advance1 because the length of the conducting wires1 adjustment of the spark gap1 etc41 will have considerable effect4 ,the condenser is connected directly across the terminals of the spark coil4 ,the spark gap may consist of two one-eighth inch brass rods supported by two double binding posts mounted on a small wooden block4 ,the induction coil should be as large as possible4 ,when the coil is set in operation it will charge the condenser and a white1 snappy spark should pass across the gap4 ,if the fingers are brought near to one of the secondary terminals of the ,tesla coil1 a small1 reddish purple spark will jump out to meet them4 ,it will be necessary to adjust the apparatus very carefully before a spark of any considerable length can be obtained4 ,changing the length of the spark gap and the size of the condenser will undoubtedly produce results4 ,it may also be possible to lengthen the high frequency spark by disconnecting one of the wires from the primary binding posts on the ,tesla coil and connecting the wire directly to some one of the primary turns4 ,a very small change in some one of the connections may produce considerable result4 ,the purpose of the adjustments is to tune the circuit in the same manner that a wireless outfit is tuned by altering the capacity of the condenser or varying the number of turns in the helix4 ,illustration3 ,,fig4 #agh4--,plate ,glass ,condenser4 ,there are many interesting experiments which may be performed with the aid of a ,tesla coil which space does not permit of describing here4 ,the weird and strange beauty of the ,tesla discharge is most evident when it takes place in the dark4 ,high frequency currents do not produce a shock4 ,if you hold a piece of metal in your hand and bring it near one of the secondary terminals1 you can take the shock of a high-frequency coil1 throwing a spark several inches long without feeling any sensation except that of a slight warmth4 ,,chapter ,,xviii4 ,,an ,,experimental ,,wireless ,,telephone4 ,many of the readers of this book are probably wireless experimenters who have constructed their own wireless telegraph apparatus1 but not many have ever built a wireless telephone set4 ,the arrangement described in the following chapter may be built by almost any boy and will prove a very interesting and instructive piece of apparatus4 ,it is of no real practical value as a wireless telephone1 owing to the fact that the distance over which it will transmit intelligible speech is limited to #aej to #cjj feet4 ,however if you have a chum who lives next door or across the street or within the distance named above1 it is easily possible for you to construct a wireless telephone which will enable you to remain in your own rooms and hold a conversation with each other1 without any connecting wires4 ,illustration3 ,,fig4 #agi4--,when a ,bar ,magnet is plunged into a ,hollow ,coil of ,wire1 a ,momentary ,current of ,electricity is ,generated4 ,the instruments depend for operation upon what is known as magnetic induction4 ,michael ,faraday1 who was a famous ,english scientist1 discovered in #ahca that if a magnet is suddenly plunged into a hollow coil of wire1 a momentary current of electricity is generated in the coil4 ,you can try this experiment for yourself by connecting a galvanometer with a hollow coil of wire and then suddenly plunging a bar magnet into the coil4 ,if you observe closely you will notice that the needle of the galvanometer is deflected1 this indicating that a current has passed through the circuit4 ,the galvanometer should of course be far enough away so that the needle is not affected directly by the magnetism of the bar magnet itself4 ,illustration3 ,,fig4 #ahj4--,magnetic ,phantom showing the ,lines of ,force about a ,bar ,magnet4 ,as long as the bar magnet is motionless1 it will not induce any current in the coil4 ,as soon as it is moved however1 the currents are set up4 ,the mechanical work done in moving the magnet is really the source of electrical energy4 ,the medium which changes the mechanical energy into electricity is called the magnetic field4 ,the real nature of a magnetic field is very hard to explain and not easily understood4 ,it is a peculiar state or condition of the space in the immediate neighborhood of a magnet4 ,it is possible to show its existence by placing a sheet of cardboard over a magnet and then sprinkling iron filings over the surface of the cardboard4 ,if the cardboard is tapped slightly1 the filings will settle down in curving lines1 forming a magnetic phantom4 ,the curved lines into which the filings form themselves1 represent the paths of the lines of force which make up the magnetic field4 ,the illustration in ,figure #ahj shows the magnetic phantom about a bar magnet4 ,when the space in the neighborhood of a wire or a coil of wire through which a current of electricity is passing is examined by means of some iron filings sprinkled on a sheet of cardboard1 it is found that a similar state of affairs exists there and that it also possesses a magnetic field4 ,this can be readily shown by punching a small hole in the centre of a sheet of cardboard or stiff paper and passing a wire which is carrying a strong current of electricity through the hole at right angles to the surface of the cardboard4 ,sprinkle some iron filings on the cardboard and they will arrange themselves in circles around the wire1 forming a magnetic phantom giving definite proof to the eyes of the existence of the magnetic field4 ,some of my readers may have begun to wonder what a magnetic field has to do with the operation of the wireless telephone4 ,it has already been explained that this particular type of wireless telephone depends upon magnetic induction for its operation4 ,it is necessary to have some sort of a conception of the magnetic field before you will be able to understand magnetic induction4 ,illustration3 ,,fig4 #aha4--,magnetic ,phantom about a ,coil of ,wire carrying a current4 ,in order that you may gain an idea of how the instruments work1 suppose that two coils of wire1 ,a and ,b1 are connected as shown in ,figure #ahb4 ,the coil ,a is connected in series with a set of batteries and a telegraph key4 ,the other coil ,b is connected to a telephone receiver4 ,the coils are placed parallel to each other and only a few inches apart4 ,when the key is pressed so that the circuit is complete and the battery current flows through the coil ,a1 it creates a magnetic field in the vicinity of the coil and lines of force are set up in the immediate neighborhood4 ,the lines of force will travel through and about coil ,b and 99induce in it a current of electricity994 ,the electric current will cause a sound like a click in the telephone receiver4 ,when a telephone transmitter is substituted for the key and words are spoken into the mouthpiece1 the current passing through the coil from the battery will be varied in accordance with the vibrations of the voice4 ,the changes in the current will produce changes in the magnetic field set up by the coil and the changes in the magnetic field will produce a varying current in the coil ,b so that the words will be distinctly repeated by the receiver connected to ,b4 ,illustration3 ,,fig4 #ahb4--;,illustrating the ,principle of the ,induction ,wireless ,telephone4 ,this experiment is very easy to perform and may be carried out by almost any boy with the materials he probably already has around his shop4 ,twenty-five to thirty turns of magnet wire of almost any size wound around one end of a cardboard tube three or four inches in diameter will serve as the coil ,a4 ,a similar coil wound around the tube five or six inches away1 an ordinary telephone transmitter and receiver and two or three dry cells form all the rest of the equipment desired4 ,words spoken into the transmitter connected to the coil ,a will be distinctly heard in the telephone receiver connected to the coil ,b1 although there is no connection between the two coils other than the 99magnetic field994 ,such an outfit as this is of course only experimental and intended solely for the purpose of demonstrating the principles of operation of the larger outfit4 ,if it is desired to make a practical set for talking over a considerable distance it will be necessary to make coils much larger in diameter and to build them so they contain a larger number of turns4 ,illustration3 ,,fig4 #ahc4--,showing how the ,coils may be formed by winding around nails set in a circle in the ,floor4 ,large coils can be made by drawing a circle about four feet in diameter on the floor of your shop4 ,then drive a number of small nails around the circle about three inches apart4 ,this arrangement will serve as a form to wind the coil4 ,after the winding is completed you can pull a few of the nails out and lift it off and you will have a circular coil four feet in diameter4 ,two coils will be required4 ,they should be made of ,no4 #bj ,b4 ,s4 ,gauge cotton covered wire4 ,each coil should contain about seventy-five turns of wire4 ,about three pounds of wire will be required for each coil4 ,after winding the coils should be tied with string or tape about every six inches so that they will not come apart4 ,the nails can then be pulled out of the floor and the coil is ready for use4 ,if it is intended to subject the coils to any amount of handling1 it is a good idea to secure two large hoops such as girls use for rolling along the sidewalk1 about four feet in diameter4 ,then make the coils exactly the same diameter as the hoops and when they are finished bind them to the hoops with tape4 ,two binding posts may be mounted on each of the hoops and the terminals of the coil connected to them4 ,two coils are required in order to establish a complete wireless telephone system1 one at each station4 ,each coil may be used for both sending and receiving messages4 ,each station should be arranged as in ,figure #ahd4 ,the transmitter should be of the type known as long distance4 ,the switch is a two point switch4 ,illustration3 ,,fig4 #ahd4--;,circuit ,diagram showing how the ,coil is connected so as to serve for either transmitting or receiving4 ,it is a good plan to use two telephone receivers mounted on a head band so that both ears can be used and the hands left free to manipulate the switch4 ,if a set of telephone receivers wound to a high resistance for wireless telegraph purposes is used it will greatly increase the range of the outfit4 ,six to eight first class dry cells will be required to form the battery4 ,a push button is placed in series with the transmitter so that the battery current will be consumed only when the button is pressed4 ,this makes it necessary to push the button when sending a message4 ,when the lever of the two point switch rests on the contact ,a the circuit is completed for transmitting4 ,when the lever rests on ,b the telephone receivers are connected to the coil and the apparatus is ready for receiving a message4 ,if the apparatus is used only for demonstrating purposes1 a camera tripod will be found very convenient for supporting the coils4 ,the transmitter and switch can be fastened to the top of the tripod and the batteries placed in a box on the ground4 ,it is absolutely necessary that the coils be perfectly parallel to each other when messages are being transmitted back and forth4 ,it is well to start with the coils comparatively close to each other1 say ten or twelve feet at first1 and then gradually increase the distance4 ,coils approximately four feet in diameter and containing about seventy-five turns of wire will transmit and receive messages about one hundred and fifty feet4 ,the range can be increased slightly by using more batteries4 ,if too much battery is used1 however1 the telephone transmitter will become very hot and is liable to burn out4 ,it is impossible1 of course1 to call up over a set of wireless phones such as these4 ,if you succeed in getting your set to work satisfactorily with your chum across the street and wish to talk to him it will be necessary for you to arrange some predetermined time4 ,in order to operate your phone place the switch lever on the contact ,a4 ,hold your finger tightly against the push button so that the circuit is completed and talk slowly and distinctly into the transmitter4 ,the transmitter will operate the best when the mouthpiece points on a level with your mouth4 ,the lips should be about one inch away from the mouthpiece4 ,speak in a low even tone4 ,the switch at your friend's station should be resting on ,b4 ,when you finish speaking throw your switch to ,b and listen in your telephone receivers4 ,the operator at the other station should throw his switch to ,a and push the button4 ,he may then talk to you4 ,,chapter ,,xix4 ,,miscellaneous ,,experiments ,,and ,,apparatus4 ,,electrolysis4 ,liquid which will conduct a current of electricity is called an 99electrolyte994 ,all electrolytes are compounds1 that is1 they consist of more than one substance4 ,when an electric current passes through a liquid it decomposes it4 ,this process of decomposition is called 99electrolysis994 ,pure water is not a conductor of electricity4 ,if sulphuric acid is added to water1 the mixture become an electrolyte and will conduct4 ,if an electric current is passed through water containing sulphuric acid1 it will decompose the water4 ,illustration3 ,,fig4 #ahe4--;,apparatus for ,electrolysis ,experiment4 ,water is composed of oxygen and hydrogen and so bubbles of oxygen and hydrogen gas will rise from the liquid4 ,figure #ahe illustrates a very simple arrangement for decomposing acidulated water into oxygen and hydrogen gases4 ,it consists of a bottle with the bottom broken out1 and provided with a cork fitted snugly into the neck4 ,two glass tubes pass through the cork4 ,a small piece of platinum wire is sealed into the inside end of each glass tube4 ,the platinum wires are connected to copper wires leading out of the lower ends of the tubes4 ,if the bottle is inverted and filled with a dilute solution of sulphuric acid1 the current from two or three dry cells will decompose the water4 ,the battery should be connected to the wires running through the glass tubes4 ,bubbles of gas will rise from the platinum wires4 ,oxygen gas will rise from the positive wire or electrode and hydrogen gas from the negative electrode4 ,if two test tubes are filled with acidulated water and then inverted over the wires1 the tubes will collect the gas4 ,in a few minutes it will be noticed twice as much hydrogen as oxygen has been generated4 ,if copper or brass electrodes re used the acid will attack the positive one and a chemical action will take place which will prevent the liberation of any appreciable amount of oxygen1 unless an excessive amount of current is passed through4 ,,electroplating4 ,electroplating consists of coating bodies with metal by means of an electric current4 ,the proper chemicals1 a small tank and a suitable source of current are the only apparatus required4 ,the process may be outlined as follows3 ,thoroughly clean the article to be electroplated so as to remove all grease and dirt4 ,attach it to the negative pole of the battery and suspend it in an electrolyte composed of some chemical salt of the metal to be deposited4 ,in order to maintain the strength of the solution1 a piece of metal of the kind to be deposited is attached to the positive electrode4 ,a tank for plating small articles such as keys1 rings1 knives1 etc41 may be made out of a square glass battery jar by providing it with a wooden moulding fitted around the top edge to support the conductor rods4 ,the rods are made of brass or copper and are threaded at one end so as to be provided with binding posts4 ,the centre rod is the one from which the articles to be plated are suspended4 ,they should be attached to it by means of a thin copper wire4 ,the two outside rods support the anodes4 ,the anodes are sheets of metal of the kind to be deposited which1 in the case of copper plating1 would be copper1 in a case of silver plating silver1 nickel for nickel plating1 etc4 ,illustration3 ,,fig4 #ahf4--;,electroplating ,tank4 ,objects which are to be plated must be free from all traces of dirt or grease or the plating will not be uniform because it will not stick to the dirty spots4 ,articles made of plaster1 wax1 etc41 which are not conductors of electricity can be plated by first covering with powdered graphite4 ,articles of iron1 steel1 zinc and tin cannot be silver or gold plated unless first covered with a thin coating of copper4 ,a single storage cell is an excellent source of current for electroplating4 ,a rheostat should be placed in the circuit so that the current can be regulated4 ,the negative pole should be connected to the centre rod from which the articles are suspended4 ,the positive pole is connected to the rods supporting the anodes4 ,the tank should be filled with electrolyte to within about an inch of the top4 ,the articles to be plated and also the anodes should be completely submerged4 ,the electrolyte used for copper plating is simply a solution of copper sulphate in water4 ,the electrolyte for nickel plating is composed of one part of nickel sulphate dissolved in twenty parts of water to which one part of sodium bisulphate is added4 ,articles which have been electroplated must be buffed to give them a bright polish4 ,,electric ,,current ,,generated ,,by ,,heat4 ,if the point of contact between two dissimilar metals is heated1 a current of electricity will be generated4 ,this principle was discovered nearly one hundred years ago by a scientist named ,seebeck1 and has resulted in many attempts on the part of inventors to utilize the heat of the sun's rays in producing electricity4 ,illustration3 ,,fig4 #ahg4--;,generating ,electric ,current by ,heat4 ,an interesting experiment illustrating the production of electricity by heat can be easily performed with very simple apparatus4 ,an alcohol lamp1 candle or source of heat1 a piece of copper1 a steel needle and a galvanometer or a telephone receiver are all that are necessary4 ,the galvanometer or the telephone receiver1 whichever is used1 is for the purpose of detecting the electric current4 ,connect the needle and the piece of copper1 which should preferably be a small sheet1 to the galvanometer or telephone receiver4 ,hold the copper sheet over the flame of the alcohol lamp until it is quite hot and then touch the hottest portion with the point of the needle4 ,enough current will be generated to produce a click ,in the telephone receiver or to cause the galvanometer needle to move4 ,the needle should be pressed against the copper tightly enough so that the point cuts through the scale or oxide on the surface and makes a good electrical contact with the metal underneath4 ,various devices for the production of electricity consisting of a large number of strips of dissimilar metals in contact with one another and arranged so that they can be easily heated have been invented4 ,they are called thermopiles4 ,a ,,handy ,,light4 ,figure #ahh shows a simple and handy form of light which utilizes the current from a home made primary cell4 ,it consists of a glass fruit jar1 fitted with a tight wooden top4 ,a miniature porcelain socket and a #a4e volt tungsten lamp are mounted on top4 ,the battery is arranged so that the zinc element can be drawn up out of the solution when the light is not in use and any waste thereby prevented4 ,the zinc electrode consists of a strip of that metal fastened onto the lower end of a brass rod by means of two threaded nuts4 ,the upper end of the rod passes through a small metal collar on the top of the cover1 provided with a thumb-screw so that when the electrode is lifted up out of the solution it may be clamped firmly in that position4 ,the zinc strip should not be so long that it will not clear the solution when raised up if the jar is about half filled4 ,illustration3 ,,fig4 #ahh4--;,a ,handy ,light4 ,the positive electrode is a battery carbon mounted on the lower end of a brass rod4 ,the brass rod in this case is not movable because the carbon can remain in the solution indefinitely without any waste4 ,the joint between the brass rods and the electrode should be coated with paraffine so that the chemicals in the solution will not cause any corrosion4 ,the rods should be connected to the lamp socket4 ,when the zinc is lowered into the solution1 the lamp will be lighted by the current generated4 ,the electrolyte should be that described as the bichromate solution on page #cd of ,vol4 ,i of this book4 ,,an ,,experimental ,,arc ,,lamp4 ,an arc lamp is operated by causing an electric current to pass between two carbon rods4 ,if the voltage is high enough1 carbon vapor will form between the rods when they are separated a short distance4 ,it requires an ,e4 ,m4 ,f4 of approximately fifty volts to produce and maintain an arc4 ,a six volt storage battery will heat a pair of sharp pointed carbons to incandescence and produce a light somewhat similar to the electric arc4 ,illustration3 ,,fig4 #ahi4--;,experimental ,arc ,lamp4 ,ordinary carbon rods such as those used in flashlight batteries will serve very nicely for a battery arc lamp4 ,the ends should be filed to sharp points4 ,figure #ahi shows a simple method of mounting the carbons4 ,the lower one is soldered to a piece of brass strip by taking advantage of the brass cap pressed over the upper end of flashlight battery carbons4 ,the upper carbon is mounted on the forward end of a brass lever which is pivoted near the back end so that an adjustable counterweight may be used to regulate the pressure on the point of contact between the two carbons4 ,if the carbons are touching lightly and are connected to a strong battery of six volts or more1 the point of contact will be heated to incandescence and will produce a dazzling white light4 ,a real arc lamp for operation on the #aaj volt current1 in series with a bank of lamps1 may be constructed on this same scheme by using larger carbons and eliminating the counterweight4 ,the upper arm should be pivoted in the same manner but should move stiffly so that it will remain in any position in which it is set4 ,if the #aaj volt current is used1 the carbons should be brought together and then separated a short distance4 ,the current will continue to flow across and will form an arc producing a very powerful purplish white light4 ,the arc will consume the carbons quite rapidly and also generate a great deal of heat4 ,therefore if it is intended to use the light for any length of time it is advisable to fasten the carbons by means of a clamp so that they may be easily replaced4 ,a ,,magnetic ,,diver4 ,this is a mystifying piece of apparatus to those who do not know its secret4 ,the little diver apparently travels up and down from the bottom of a jar full of water to the surface at a word of command4 ,the diver consists of a small glass test tube about two inches long having the figure of a man painted upon it4 ,the lower end is closed by a very small cork through which is pushed a large iron tack with the head on the outside4 ,the test tube contains just enough water to float head up even with the surface of the water4 ,the exact amount of water required to just permit enough buoyancy for the diver to rise again to the surface after he has been to the top will have to be determined by careful experiment4 ,the jar containing the diver should be set on a table having a drawer in which a pair of powerful electromagnets can be placed directly under the jar4 ,the electro-magnets are connected to a strong battery and a switch located under the rug or carpet and so arranged that it may be closed by stepping on it lightly and without attracting attention4 ,if the diver does not have too much bouyancy the attraction between the tack and the electro-magnets when the switch is closed should be sufficient to cause him to descend to the bottom of the jar4 ,when the current is turned off the diver should rise again4 ,illustration3 ,,fig4 #aij4--,the ,magnetic ,diver4 ,,the ,,magnetic ,,fish4 ,the same sort of a scheme employed in the ,magnetic ,diver may be used for producing a magnetic fish which will swim around and around a pan of water4 ,illustration3 ,,fig4 #aia4--,the ,magnetic ,fish4 ,it consists of a small wooden fish having a magnetised sewing needle attached to the under side4 ,the fish is placed in a bowl of water on a table having a drawer in which a pair of electro-magnets mounted on a rotating wooden arm may be placed so that they swing around directly underneath4 ,a piece of strong twine wrapped around an empty spool and attached to the centre of the arm makes it possible to rotate the magnets by pulling on the string4 ,when the magnets are connected to a battery they will exert a strong magnetic pull upon the needle fastened to the fish and if slowly rotated will cause the latter to follow slowly around the bowl4 ,a ,,magnetic ,,clown4 ,small figures of men or animals cut out of sheet iron will perform many amusing acrobatic feats when under the influence of a magnet4 ,illustration3 ,,fig4 #aib4--,the ,magnetic ,clown4 ,such figures are easily cut out of an old tin cracker box with a pair of snips or strong shears4 ,a realistic appearance may be secured with the aid of a little paint4 ,a tin clown having a sharply pointed hat1 hands and feet will do all sorts of stunts when hanging from the poles of a horseshoe magnet4 ,if several clowns are made they can be caused to hold hands1 stand on each others heads1 jump up in the air1 etc4 ,,an ,,electric ,,breeze4 ,if a sewing needle is connected to one of the discharge rods of a static machine and the point of the needle is presented to the flame of the candle while the machine is in operation1 the flame will be repelled just as if a breeze or current of air were issuing from the needle4 ,this is caused by the brush discharge which takes place whenever high voltage electricity has a chance to escape from a sharp point or edge4 ,the brush discharge will be much more marked if the condensers or ,leyden ,jars are not connected to the discharge rods4 ,the electric breeze can be felt if the point of the needle is brought near to the side of the face4 ,it is necessary that the needle and the wire connecting it to the static machine be very carefully insulated from all surrounding objects which might dissipate the electricity before it has an opportunity to escape from the needle point4 ,illustration3 ,,fig4 #aic4--;,an ,electric ,breeze4 ,a ,,static ,,motor4 ,this is a motor operated by the electricity from a static machine4 ,it does not possess any appreciable amount of power and must be very carefully built and balanced in order to operate4 ,it consists of four celluloid ping-pong balls1 ,b1 ,b1 ,b1 ,b1 covered with tinfoil and mounted on opposite ends of two wooden spokes4 ,the balls should be at right angles to each other as shown in the illustration4 ,the spokes pass through a cork4 ,the cork is mounted on a wire spoke or knitting needle passing through its centre and supported in small notches in the top of two upright wooden bearings4 ,the device must be very carefully balanced so that the slightest impulse will cause it to spin and so that there will not be any dead centre4 ,the upright bearings are mounted on a wooden base4 ,two other tinfoil covered balls ,a1 ,a1 are supported on glass or rubber insulating rods at opposite ends of the base on a level with the axle and in such a position that the balls ,b1 ,b1 ,b1 ,b1 almost touch ,a and ,a as they swing past4 ,illustration3 ,,fig4 #aid4--,the ,static ,motor4 ,connect ,a and ,a each to one discharger rod on the ,wimshurst machine4 ,start the machine and give the axle of the static motor a twist4 ,as the balls ,b1 ,b go past ,a and ,a they will receive a charge of electricity which will cause them to repel each other until they have swung past the other ball on the opposite side and discharge their electricity in return for a charge of the opposite sign4 ,any of the ,following ,practical ,books 99will be sent ,at ,once1 ,post-paid on receipt of price499 ,there is very little danger of losing currency in a letter if the following directions are observed3 ,cut a circular hole the diameter of the coin in a piece of cardboard1 of sufficient size to fit closely in the envelope4 ,the cardboard should be no thicker than the coin4 ,insert the coin in the hole and paste a piece of paper on both sides of the cardboard to prevent the coin from falling out4 ,,cole ,,morgan ,publishers of the ,arts and ,sciences ,series ,p4,o4 ,box #dgc ,new ,york1 ,n4 ,y4 99,the ,boy ,electrician99 ,practical ,plans for ,electrical ,toys and ,apparatus1 with an ,explanation of the ,principles of ,everyday ,electricity4 99,by ,,alfred ,p4 ,,morgan499 ,author of ,wireless ,telegraph ,construction for ,amateurs and ,wireless ,telegraphy and ,telephony1 etc4 99,with full-page ,illustrations and #cbd ,working ,drawings and ,diagrams99 99by the author4 #hvo41 ,cloth1 ,net ,price1 #b4jj499 ,this is the age of electricity4 ,the most fascinating of all books for a boy must therefore be one dealing with the mystery of this ancient force and modern wonder1 even a mere list of whose services is impossible4 ,the best qualified of experts to instruct boys1 ,alfred ,p4 ,morgan1 has in a book far superior to any other of its kind told not only how to make all kinds of motors1 telegraphs1 telephones1 batteries1 etc41 and to do so economically1 but has explained the principles upon which these depend for operation1 and how the same thing is done in the every-day world be well presented and so attractive is this really great book that it will be an education for any bright boy to have it1 as well as the best kind of a moral safeguard1 by leaving no time or thought for evil1 and a means of future benefit beyond the power of any one to reckon4 ,glancing over the pages of this book1 one cannot but be impressed by the excellent illustrations1 clearness of expression and the large number of subjects that are covered4 ,it is beyond doubt the best book in this line that has ever been written or published4 ,it is a book that will delight every boy who has a leaning towards electrical experiments4 ,the author writes in a clear and chatty style and while he has a thorough technical knowledge of his subject he has succeeded in treating it in a simple manner so that it is readily intelligible to his young readers4 99,among the ,chapter ,headings and ,contents are399 ,magnets and ,magnetism--,static ,electricity--,static ,electric ,machines--,cells and ,batteries--,electro-,magnetism and ,magnetic ,induction--,electrical ,units--,electrical ,appurtenances--,electrical ,measuring ,instruments--,bells1 ,alarms and ,annunciators--,electric ,telegraphs--,microphones and ,telephones--,induction ,coils--,transformers--,wireless ,telegraphy--,wireless ,telephony--,electric ,motors--,dynamos--,an ,electric ,railway--,miniature ,lighting--,miscellaneous ,electrical ,apparatus4 99,,read ,,what ,,has ,,been ,,said ,,of ,,it499 ,even a casual glance through the many pages of the book does not fail to emphasize the fact that ,mr4 ,alfred ,p4 ,morgan has indeed succeeded well in giving the juvenile electricians a work that has long been sought4--,popular ,electricity4 ,we have no hesitation in commending the book to the attention of the juvenile audience for which it is intended4--,boston ,post4 ,a great book for enterprising boys4 ,bright boys will highly appreciate it and feel like thanking the wideawake publishers for putting such a reliable and interesting work in the field4--,new ,haven ,journal4 ,the book covers the subject of electricity thoroughly in all its phases and is a splendid acquisition to any boy's library4--,detroit ,times4 ,in this age of electricity a book like the present one is both fascinating and valuable especially to boys4 ,the book is attractive with its many illustrations and will prove of much educational value for any bright boy4--,zion's ,herald4 ,this is an admirably complete and explicit handbook for young boys who fall under the spell of tinkering with electrical apparatus4--,boston ,transcript4 ,well presented and attractive this book will be a source of great benefit and delight for any bright boy4--,new ,orleans ,times-,picayune4 99,price1 #b4jj1 ,postpaid99 ,,countless ,,other ,,magazines1 ,,newspapers ,,and ,,libraries ,,have ,,endorsed ,,this ,,great ,,book4 ,,send ,,for ,a ,,copy ,,now4 99,if you are interested in this great book1 write for our #h-page special99 99descriptive circular499 99,experimental ,wireless ,construction99 99,,eighty-,,six ,,pages ,,ninety-,,three ,,illustrations99 99,only #be ,cents1 ,postpaid99 ,here at last is the book which every young experimenter interested in constructing his own wireless apparatus has been looking for4 ,a book which tells how to build apparatus which anyone would be proud to own4 ,it is a more advanced book than ,wireless ,construction and ,installation for ,beginners1 and describes apparatus which is much more elaborate and sensitive4 ,the instruments have all been the subject of considerable experimental work and study4 ,all the apparatus has been put to practical test and carefully improved by clever experts4 ,by purchasing this book you get the benefit of vast knowledge and experience and are enabled to build far better instruments than by following your own designs and haphazard methods4 ,,the ,,tremendous ,,popularity ,,of ,,this ,,valuable ,,little ,,book ,,is ,,only ,,an ,,indication ,,of ,,its ,,great ,,worth4 ,it has only been on the market a short time1 yet the sales will undoubtedly soon reach a point which would indicate that experimenters unquestionably consider1 that in proportion to its size1 it is the best book on the market4 ,it does not describe any old or obsolete forms of wireless apparatus but only the latest types of aerials1 spark coils1 keys1 gaps1 condensers1 helixes1 oscillation transformers1 loose couplers1 tuning coils1 detectors1 loading coils1 variable condensers1 aerial switches1 etc4 ,,it ,,is ,,one ,,of ,,the ,,most ,,detailed ,,and ,,thorough ,,books ,,ever ,,published4 ,the information is all intensely practical4 ,complete directions and dimensions are given4 ,nothing is left to be guessed at4 ,the book must really be seen to be appreciated4 99,partial ,contents99 ,chapter ,i4--,,the ,,aerial4 ,the ,location of the ,station4 ,the ,construction of an ,operating ,bench4 ,the ,aerial and ,ground4 ,the ,supports or ,masts4 ,types of ,aerials4 ,how to ,erect an ,aerial4 ,protection from ,lightning1 ,etc4 ,chapter ,,ii4--,,spark ,,coils4 ,the ,construction of ,spark ,coils4 ,a #a_/d-;inch ,spark ,coil4 ,a #a_/b-;inch ,spark ,coil4 ,a #a-;inch ,spark ,coil4 ,a #a #a_/b-;inch ,coil4 ,a #b-;inch ,coil4 ,sources of ,current4 ,dry ,cells4 ,storage ,cells4 ,wireless ,keys1 ,etc4 ,chapter ,,iii4--,,transmitting ,,apparatus ,,and ,,its ,,construction4 ,step-down ,transformers4 ,spark ,gaps4 ,the ,oscillation ,condenser4 ,leyden ,jars4 ,helixes4 ,oscillation ,transformers1 ,etc4 ,chapter ,,iv4--,,the ,,receiving ,,apparatus ,,and ,,its ,,construction4 ,a ,silicon ,detector4 ,a ,galena ,detector4 ,the ,double ,slide ,tuning ,coil4 ,how to ,make a ,fixed ,condenser4 ,building a ,loose ,coupler4 ,the ,loading ,coil4 ,how to ,make a ,variable ,condenser1 ,etc4 ,chapter ,v4--,,arrangement ,,and ,,operation ,,of ,,the ,,apparatus4 ,aerial ,switches4 ,the ,buzzer ,test4 ,using ,more ,than ,one ,detector4 ,shunting the ,detector4 ,complete ,outfits4 ,portable ,sets4 ,the ,operation of the ,station1 ,etc4 99,,lessons ,,in ,,wireless ,,telegraphy99 ,,fourth ,,edition #gb ,pages #ff ,illustrations ,a systematic course in the elementary principles4 ,written so you can understand it4 ,in #ce lessons4 #a4--,magnetism4 #b4--,magnetic ,induction4 #c4--,primary and ,secondary ,cells4 #d4--;,electric ,currents4 #e4--;,electromagnetism4 #f4--;,dynamo-,electric ,machinery4 #g4--,the ,induction ,coil4 #h4--,the ,transformer4 #i4--,leyden ,jars and ,condensers4 #aj4--;,electromagnetic ,theory4 #aa4--;,electric ,waves4 #ab4--,principles of ,wave ,telegraphy4 #ac4--,the ,aerial4 #ad4--,the ,wireless ,coil4 #ae4--,the ,high ,potential ,transformer4 #af4--,the ,oscillation ,condenser4 #ag4--,the ,helix4 #ah4--,spark ,gaps4 #ai4--,the ,key4 #bj4--;,aerial ,switches4 #ba4--;,anchor ,gaps4 #bb4--;,detectors4 #bc4--,tuning ,coils4 #bd4--,loose ,couplers4 #be4--;,fixed ,condensers4 #bf4--,variable ,condensers4 #bg4--,telephone ,receivers4 #bh4--;,hot ,wire ,ammeter4 #bi4--,potentiometer4 #cj4--;,dead ,end ,losses and ,switches4 #ca4--;,distributed ,capacity4 #cb4--,poulsen ,arc4 #cc4--,receiving ,undamped ,waves4 #cd4--,the ,audion ,amplifier4 #ce4--;,hook-,ups4 99,price1 #be ,cents1 ,postpaid99 ,if you want to understand your apparatus and how it works1 you will need this book--over #ae1jjj copies in use4 99,price1 #be ,cents1 ,postpaid99 99,model ,flying ,machines99 99,,how ,,to ,,build ,,and ,,fly ,,them99 ,will prove interesting and valuable4 ,have you ever built and flown a ,model ,racer8 ,if not1 you have missed something4 ,price1 #be ,cents1 ,postpaid4 ,model ,aeroplaning is one of the most fascinating and instructive of sports4 ,thousands of young men and boys have formed ,model ,aero ,clubs and organized ,flying ,contests throughout the country4 ,,model ,,flying ,,machines of the ,arts and ,sciences series is the only book giving reliable data and instructions for the construction of practical ,model ,aeroplanes4 ,,if ,,you ,,are ,a ,,beginner1 this is the book that you ought to have4 ,it will start you right4 ,it tells how to build seven different types of machines1 starting with the simplest ,monoplane and finishing with several ,long ,distance ,racing ,models4 ,,if ,,you ,,are ,,interested ,,in ,,model ,,aeroplaning1 this book will prove the one you have been looking for4 ,gives valuable ,kinks4 ,tells how to carve propellers1 make winders1 adjust and fly machines1 etc4 ,fully illustrated with large size1 detailed working drawings1 showing the exact size of each part4 ,twelve full-page plates4 ,printed on first-class paper4 ,heavy cover in three colors4 ,sent postpaid by return mail upon receipt of #be cents4 99,,every ,,model ,,aviator ,,ought ,,to ,,have ,a ,,copy99 99,wireless ,construction and ,installation for ,beginners99 ,,seventy-,,three ,,pages ,,sixty-,,seven ,,illustrations4 7,second ,edition47 ,a ,practical ,handbook giving detailed instructions for the ,construction and ,operation of a ,boy's ,wireless ,outfit4 99,only #be;c4 ,prepaid99 ,an indispensible book for the young wireless experimenter4 ,it not alone shows how to build the various instruments but describes their actual workings and tells how to operate them4 99,,every ,,boy ,,is ,,advised ,,to99 99,,send ,,for ,a ,,copy99 ,written in a very clear and simple style1 the book is invaluable to a beginner4 ,he will be able with its aid to construct simple apparatus of the latest and approved type4 ,the instruments described in the book have been the subject of considerable experimental work and special study4 ,they are modeled along simple lines so that they will be easy and inexpensive to construct1 but at the same time combine features which make them very sensitive and capable of receiving or transmitting messages greater distances than some more complicated apparatus4 99,,this ,,book1 ,,considering ,,its ,,worth1 ,,is ,a ,,gift ,,at #be;c499 ,there are no old or obsolete forms of wireless apparatus discussed1 but only the latest types of tuning coils1 receiving transformers1 fixed condensers1 keys1 spark coils1 detectors1 etc4 ,the book is illustrated by numerous detailed working drawings giving all dimensions4 ,several full-page views of the apparatus enable the beginner to fully comprehend the text4 99,,the ,,most ,,thorough ,,and ,,complete ,,elementary ,,wireless99 99,,construction ,,book ,,published99 ,the pages on the construction and installation of aerials will be found to be of considerable help to the experimenter1 for it is here that the most trouble is experienced by the beginner4 ,the practical and helpful information on this subject is alone worth several times the cost of the book4 99,,partial ,,contents99 ,chapter ,i4--99,,wireless ,,telegraphy994 ,an intensely interesting subject2 amateur wireless telegraphy2 the purpose of the aerial and ground2 the apparatus used to send messages2 the apparatus used to receive messages4 ,chapter ,,ii4--99,,aerials ,,and ,,grounds994 ,where to put up the aerial2 types of aerials2 the ,t aerial2 the masts2 the wire2 insulators2 leading in the wires2 the ground4 ,chapter ,,iii4--99,,how ,,to ,,build ,,and ,,operate ,,the ,,simplex ,,double ,,slide ,,receiving ,,outfit994 ,the tuning coil2 the tube2 the sliders2 the fixed condenser2 the detector parts2 assembling the set2 connecting the instruments2 operation4 ,chapter ,,iv4--99,,how ,,to ,,build ,,the ,,simplex ,,loose ,,coupler1 ,,detector ,,and ,,condenser994 ,the base2 the primary2 the secondary2 the pillar2 the switch2 ,how to make the ,simplex cat whisker detector2 ,how to make the ,simplex fixed condenser2 ,how to connect the apparatus2 ,how to tune with the loose coupler2 ,how to adjust the detector4 ,chapter ,v4--99,,telephone ,,receivers ,,and ,,headbands499 ,chapter ,,vi4--99,,how ,,to ,,build ,,the ,,simplex ,,spark ,,coil499 ,the core2 the secondary2 the condenser2 the coil heads2 the base2 the interrupter parts2 the bridge4 ,chapter ,,vii4--99,,how ,,to ,,make ,,the ,,simplex ,,key994 ,chapter ,,viii4--99,,how ,,to ,,connect ,,and ,,operate ,,the ,,apparatus994 ,how to connect and operate a complete wireless station2 ,how to operate2 the code1 etc4 99,three ,new ,books on ,home ,made99 99,electrical ,apparatus99 ,the ,book you are now reading is only the first volume of ,home-made ,electrical ,apparatus4 ,written in a very clear and simple style1 the other volumes are invaluable to the young experimenter4 ,there are no old or obsolete forms of apparatus described but only the latest electrical devices1 making them 99,the ,most ,thorough and ,complete ,books for99 99the ,young ,electrical ,experimenter ,published99 ,the partial ,table of ,contents below only gives a small idea of the interesting matter contained in these volumes4 ,,volume ,,ii #gb ,pages #ee ,illustrations ,table of ,contents ,chapter ,,vi--,,electrical ,,measuring ,,instruments4 ,galvanometers1 ,ammeters1 ,voltmeters1 etc4 ,chapter ,,vii--,,current ,,control ,,devices4 ,how to ,make a ,pole ,changing ,switch or ,current ,reverser4 ,how to ,reverse ,small ,motors4 ,battery ,rheostats4 ,chapter ,,viii--,,how ,,to ,,make ,a ,,telegraph ,,key ,,and ,,sounder4 ,how to ,install a ,telegraph ,line and ,learn to ,operate4 ,learning the ,morse ,code4 ,chapter ,,ix--,,how ,,to ,,make ,,and ,,install ,a ,,telephone4 ,chapter ,x--,,medical ,,coils ,,and ,,shocking ,,coils4 ,chapter ,,xi--,,the ,,construction ,,of ,,spark ,,coils4 ,a one-quarter inch ,coil1 a one-half inch ,coil1 a one inch ,coil4 ,experiments with ,spark ,coils4 ,,volume ,,iii #hj ,pages #gc ,illustrations ,chapter ,,xii--,,how ,,to ,,make ,a ,,dynamo-,,motor4 ,chapter ,,xiii--,,how ,,to ,,make ,a ,,toy ,,battery ,,motor4 ,chapter ,,xiv--,,how ,,to ,,build ,,an ,,electric ,,engine4 ,chapter ,,xv--,,miniature ,,battery ,,lamp ,,lighting4 ,chapter ,,xvi--,,coherer ,,outfits ,,for ,,wireless ,,telegraphy4 ,chapter ,,xvii--,,how ,,to ,,build ,a ,,tesla ,,high ,,frequency ,,coil4 ,experiments with ,high ,frequency ,currents4 ,chapter ,,xviii--,,an ,,experimental ,,wireless ,,telephone4 ,chapter ,,xix--,,miscellaneous ,,apparatus4 ,electrolysis of ,water4 ,electro-,plating4 ,electricity from ,heat4 ,a ,handy ,light4 ,an ,experimental ,arc ,lamp4 ,a ,magnetic ,diver4 ,magnetic ,fish4 ,a ,magnetic ,clown4 ,an ,electric ,breeze4 ,a ,static ,motor4 99,price ,postpaid1 #be ,cents per ,volume99 ,all three volumes can be supplied bound together with handsome cloth cover for #a4be postpaid4 99,parts and ,materials99 ,for ,building the ,apparatus ,described in this ,book ,we have received so many requests from our customers for information as to where they may obtain some of the materials required to build the apparatus described in this book1 that we have made arrangements to supply same4 ,our business is essentially publishing1 and we do not intend to go into the manufacture of1 or to push the sale of apparatus or parts4 ,knowing1 however1 that many of our customers live where they are remote from cities or suitable supply houses1 where they might obtain the necessary materials1 we believe that the value of our books will be increased ten fold to the reader if we are in a position to furnish parts1 etc4 99,m#ejj99 ,complete ,set of ,parts for ,dynamo illustrated in ,figure #acb 99#c4ge99 ,shipping ,weight1 #e lbs4 99,m#fca99 ,complete ,set of ,parts for ,tesla ,coil 99#d4ej99 ,shipping ,weight1 #d lbs4 99,m#fca;,a99 ,completed ,tesla ,coil 99#f4jj99 ,shipping ,weight1 #aj lbs4 99,m#fca;,b99 ,complete ,tesla ,coil ,outfit1 consisting of ,tesla ,coil1 two-inch ,spark ,coil1 ,spark ,gap and ,leyden ,jars 99#be4jj99 ,shipping ,weight1 #be lbs4 ,please use list number when ordering4 ,include postage to pre-pay mailing charges1 or we will ship by ,express ,collect4 ,no parts supplied other than listed above4 ,all prices subject to change without notice4 ,send for latest price list4 99,,cole ,,morgan1 ,inc499 ,p4,o4 ,box #dgc1 ,city ,hall ,sta4 ,new ,york1 ,n4 ,y4