file which includes the original illustrations4 ,see #bhcce-;h4htm or #bhcce-;h4zip3 7https3_/_/www4gutenberg4org_/dirs_/#b_/ h_/c_/c_/bhcce_/bhcce-;h_/#bhcce-;h4htm7 or 7https3_/_/www4gutenberg4org_/dirs_/#b_/ h_/c_/c_/bhcce_/bhcce-;h4zip7 ,transcriber's ,note ,the punctuation and spelling from the original text have been preserved faithfully4 ,only obvious typographical errors have been corrected4 ,,how ,,two ,,boys ,,made ,,their ,,own ,,electrical ,,apparatus by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 99 99 99 99 99 ,,how ,,two ,,boys ,,made ,,their ,,own ,,electrical ,,apparatus ,by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,,eighth ,,edition ,price1 postpaid1 #a4jj ,this book contains #ada pages1 #abe illustrations1 and directions for making #aeb pieces of apparatus4 ,size1 #ex#g-a_/b2 red cloth4 ,,contents3 ,chapter ,i4 ,cells and ,batteries4--,,ii4 ,battery ,fluids and ,solutions4--,,iii4 ,miscellaneous ,apparatus and ,methods of ,construction4--,,iv4 ,switches and ,cut-,outs4--,v4 ,binding-,posts and ,connectors4--,,vi4 ,permanent ,magnets4--,,vii4 ,magnetic ,needles and ,compasses4--,,viii4 ,yokes and ,armatures4--,,ix4 ,electro-,magnets4--,x4 ,wire-,winding ,apparatus4--,,xi4 ,induction ,coils and ,their ,attachments4--,,xii4 ,contact ,breakers and ,current ,interrupters4--,,xiii4 ,current ,detectors and ,galvanometers4--,,xiv4 ,telegraph ,keys and ,sounders4--,,xv4 ,electric ,bells and ,buzzers4--,,xvi4 ,commutators and ,current ,reversers4--,,xvii4 ,resistance ,coils4--,,xviii4 ,apparatus for ,static ,electricity4--,,xix4 ,electric ,motors4--,,xx4 ,odds and ,ends4--,,xxi4 ,tools and ,materials4 ,the author of this book is a teacher and writer of great ingenuity1 and we imagine that the effect of such a book as this falling into juvenile hands must be highly stimulating and beneficial4 ,it is full of explicit details and instructions in regard to a great variety of apparatus1 and the materials required are all within the compass of very modest pocket-money4 ,moreover1 it is systematic and entirely without rhetorical frills1 so that the student can go right along without being diverted from good helpful work that will lead him to build useful apparatus and make him understand what he is about4 ,the drawings are plain and excellent4 ,we heartily commend the book4--,electrical ,engineer4 ,those who visited the electrical exhibition last ,may cannot have failed to notice on the south gallery a very interesting exhibit1 consisting1 as it did1 of electrical apparatus made by boys4 ,the various devices there shown1 comprising electro-magnets1 telegraph keys and sounders1 resistance coils1 etc41 were turned out by boys following the instructions given in the book with the above title1 which is unquestionably one of the most practical little works yet written that treat of similar subjects1 for1 with but a limited amount of mechanical knowledge1 and by closely following the instructions given1 almost any electrical device may be made at very small expense4 ,that such a book fills a long-felt want may be inferred from the number of inquiries we are constantly receiving from persons desiring to make their own induction coils and other apparatus4--,electricity4 ,at the electrical show in ,new ,york last ,may one of the most interesting exhibits was that of simple electrical apparatus made by the boys in one of the private schools in the city4 ,this apparatus1 made by boys of thirteen to fifteen years of age1 was from designs by the author of this clever little book1 and it was remarkable to see what an ingenious use had been made of old tin tomato-cans1 cracker-boxes1 bolts1 screws1 wire1 and wood4 ,with these simple materials telegraph instruments1 coils1 buzzers1 current detectors1 motors1 switches1 armatures1 and an almost endless variety of apparatus were made4 ,in his book ,mr4 ,st4 ,john has given directions in simple language for making and using these devices1 and has illustrated these directions with admirable diagrams and cuts4 ,the little volume is unique1 and will prove exceedingly helpful to those of our young readers who are fortunate enough to possess themselves of a copy4 ,for schools where a course of elementary science is taught1 no better text-book in the first steps in electricity is obtainable4--,the ,great ,round ,world4 ,exhibit of ,experimental ,electrical ,apparatus ,,at ,,the ,,electrical ,,show1 ,,madison ,,square ,,garden1 ,,new ,,york4 ,while only #dj pieces of simple apparatus were shown in this exhibit1 it gave visitors something of an idea of what young boys can do if given proper designs4 ,illustration3 ,,how ,,two ,,boys ,,made ,,their ,,own ,,electrical ,,apparatus ,gives ,proper ,designs--,designs for over #aej ,things4 ,,by ,,the ,,same ,,author--7,,list ,r7 ,,list ,,no4 ,,list ,,price ,r#a--;,,fun ,,with ,,magnetism4 ,a book and complete outfit of apparatus for sixty-one experiments4 ,weight #d ounces4 ,price #j4ce ,r#b--;,,fun ,,with ,,electricity4 ,a book and complete outfit of apparatus for sixty experiments4 ,weight #a pound4 ,price #j4fe ,r#c--;,,fun ,,with ,,puzzles4 ,a book and complete outfit for four hundred puzzles with key to them4 ,one pound4 ,price #j4ce ,r#d--;,,fun ,,with ,,soap-,,bubbles4 ,a book and complete outfit of apparatus for fancy bubbles and films4 ,one pound4 ,price #j4ce ,r#e--;,,fun ,,with ,,shadows4 ,a book and complete outfit of apparatus for shadow pictures1 pantomimes1 etc4 ,one pound4 ,price #j4ce ,r#f--;,,fun ,,with ,,photography4 ,a book and complete outfit of apparatus for amateur work4 ,one pound4 ,price #j4fe ,r#g--;,,fun ,,with ,,chemistry4 ,a book and complete outfit of apparatus for forty-one experiments4 ,one pound4 ,price #j4fe ,r#da--;,,electric ,,shooting ,,game4 ,absolutely harmless2 fascinating4 ,paper bullets shot by electricity4 ,one pound4 ,price #j4ce ,r#db--;,,electric ,,air-,,ships ,,and ,,other ,,games4 ,great fun4 ,get into the game2 be an aviator at home2 for two players4 ,one pound4 ,price #j4ce ,r#dc--;,,electric ,,fortune-,,teller tells a lot4 ,mysteriously electric4 ,comic and otherwise4 ,in preparation4 ,one pound4 ,price #j4ce ,r#ea--;,,how ,,two ,,boys ,,made ,,their ,,own ,,electrical ,,apparatus4 ,a book containing complete directions for making many kinds of electrical apparatus4 ,seventh edition2 #ada pages2 cloth4 ,price #a4jj ,r#eb--,,the ,,study ,,of ,,elementary ,,electricity ,,and ,,magnetism ,,by ,,experiment4 ,a text-book for students and others4 ,systematic course for home or school4 #bbj pages2 #bjj experiments2 cloth2 fourth edition4 ,price #a4be ,this book with #aje pieces of apparatus complete1 by express #f4be ,r#ec--,,things ,a ,,boy ,,should ,,know ,,about ,,electricity explains in simple language things a boy wants to know1 things he should know4 ,seventh edition4 #ahj pages2 cloth4 ,price #a4jj ,r#ed--,,real ,,electric ,,toy-,,making ,,for ,,boys contains complete directions for making and using many electrical toys4 ,over #ajj original drawings1 diagrams and plates4 ,second edition2 #adj pages1 cloth4 ,price #a4jj ,r#ee--,,wireless ,,telegraphy ,,for ,,amateurs ,,and ,,students contains theoretical and practical information1 together with directions for performing numerous experiments on wireless with simple home-made apparatus4 ,third and enlarged edition in preparation4 ,price #a4jj ,r#ef--;,,electrical ,,handicraft contains complete directions for making and using nearly #aej pieces of electrical apparatus1 including various devices and outfits for experimental purposes4 ,new ideas and inexpensive supplies4 ,cloth2 #beb pages2 #bej drawings4 ,second edition4 ,price #a4jj ,r#eg;,c--,,the ,,study ,,of ,,electric ,,motors ,,by ,,experiment contains sixty experiments that bear directly upon the construction1 operation and explanation of electric motors1 together with much helpful information upon the apparatus required4 ,over #ajj pages2 paper cover4 ,price #j4ce ,r#eh--,,things ,a ,,boy ,,should ,,know ,,about ,,wireless contains much practical and some theoretical information on the operation and explanation of wireless outfits1 together with numerous wiring-diagrams4 ,third edition2 #abf pages2 cloth4 ,price #a4jj ,ask your ,bookseller1 ,toy-dealer or ,electrical ,store for our ,books1 ,games1 ,toys and ,electrical ,apparatus4 ,write for ,catalogue4 ,,thomas ,m4 ,,st4 ,,john1 ,cascade ,ranch1 ,east ,windham1 ,n4,y4 99 99 99 99 99 ,,how ,,two ,,boys ,,made ,,their ,,own ,,electrical ,,apparatus ,containing ,complete ,directions for ,making ,all ,kinds of ,simple ,apparatus for the ,study of ,elementary ,electricity by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,author of ,fun ,with ,magnetism1 ,fun ,with ,electricity1 ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment1 ,things ,a ,boy ,should ,know ,about ,electricity1 etc4 ,eighth ,edition ,thomas ,m4 ,st4 ,john ,cascade ,ranch ,east ,windham ,new ,york ,copyright1 #ahih1 by ,thomas ,m4 ,st4 ,john ,how ,two ,boys ,made ,their ,own ,electrical ,apparatus4 ,,table ,,of ,,contents4 ,,chapter4 ,,page4 ,i4 ,cells and ,batteries1 #e ,,ii4 ,battery ,fluids and ,solutions1 #ae ,,iii4 ,miscellaneous ,apparatus and ,methods of ,construction1 #bj ,,iv4 ,switches and ,cut-,outs1 #bh ,v4 ,binding-,posts and ,connectors1 #cb ,,vi4 ,permanent ,magnets1 #cg ,,vii4 ,magnetic ,needles and ,compasses1 #dj ,,viii4 ,yokes and ,armatures1 #de ,,ix4 ,electro-,magnets1 #ea ,x4 ,wire-,winding ,apparatus1 #fj ,,xi4 ,induction ,coils and ,their ,attachments1 #fd ,,xii4 ,contact ,breakers and ,current ,interrupters1 #ge ,,xiii4 ,current ,detectors and ,galvanometers1 #gh ,,xiv4 ,telegraph ,keys and ,sounders1 #ib ,,xv4 ,electric ,bells and ,buzzers1 #ajd ,,xvi4 ,commutators and ,current ,reversers1 #aaj ,,xvii4 ,resistance ,coils1 #aad ,,xviii4 ,apparatus for ,static ,electricity1 #aag ,,xix4 ,electric ,motors1 #abb ,,xx4 ,odds and ,ends1 #acc ,,xxi4 ,tools and ,materials1 #acg-ada ,a ,,word ,,to ,,boys4 ,the author is well aware that the average boy has but few tools1 and he has kept this fact constantly in mind4 ,it is a very easy matter for a skilled mechanic to make1 with proper tools1 very fine-looking pieces of apparatus4 ,it is not easy to make good apparatus with few tools and a limited amount of skill1 unless you follow simple methods4 ,by following the methods given1 any boy of average ability can make the apparatus herein described4 ,most of the illustrations have been made directly from apparatus constructed by young boys4 ,it is impossible to describe the different pieces of apparatus in any special or logical order4 ,it is taken for granted that you have some book of simple experiments and explanations to serve as a guide for the order1 and to give you an idea of just the apparatus needed for the special experiments4 ,it would be foolish to start in and make all the apparatus described1 without being able to intelligently use it in your experiments4 ,take up a systematic course of simple experiments1 and make your own apparatus1 as needed4 ,before making any particular piece of apparatus1 read what is said about the other pieces of the same general nature4 ,this will often be a great help1 and it may suggest improvements that you would like to have4 ,in case your apparatus does not work as expected1 read the directions again1 and see if you have followed them4 ,wrong connections1 poor connections1 short circuits1 broken wire1 etc41 will make trouble4 ,with a little patience and care you will be able to locate and correct any troubles that may come up in such simple apparatus4 ,,thomas ,m4 ,,st4 ,,john4 ,how ,two ,boys ,made ,their ,own ,electrical ,apparatus ,,chapter ,i4 ,,cells ,,and ,,batteries4 ,,apparatus #a4 #a4 ,carbon-,zinc ,cell4 ,fig4 #a4 ,if you have some rubber bands you can quickly make a cell out of rods of zinc and carbon4 ,the rods are kept apart by putting a band1 ,b1 around each end of both rods4 ,the bare wires are pinched under the upper bands4 ,the whole is then bound together by means of the bands1 ,a1 and placed in a tumbler of fluid1 as given in ,app4 #ae4 ,this method does not make first-class connections between the wire and rods4 7,see ,sec4 #c47 ,illustration3 ,fig4 #a4 ,,apparatus #b4 ,illustration3 ,fig4 #b4 #b4 ,carbon-,zinc ,cell4 ,fig4 #b4 ,in case you want to make your cell out of carbon and zinc rods1 and do not have any means of making holes for them in the wood1 as in ,app4 #c and #d1 you will find this method useful4 ,cut grooves1 ,g1 into one side of the wood1 ,a1 which should be about #d-a_/b x #a x #a_/b in4 ,the grooves should be quite deep1 and so placed that the rods will be about #a_/d in4 apart4 ,a strip of tin1 ,t1 #a_/b in4 wide1 should be bent around each rod4 ,the screw1 ,s1 put through the two thicknesses of tin will hold the rod in place4 ,another screw1 ,x1 acts as a binding-post4 ,the zinc rod only is shown in ,fig4 #b4 ,the carbon rod is arranged in the same way4 ,use the fluid of ,app4 #ae4 #c4 ,note4 ,when the bichromate solution of ,app4 #ae is used for cells1 the strong current is given1 among other reasons1 because the zinc is rapidly eaten up4 ,this action goes on even when the circuit is broken1 so always remove and wash the zinc as soon as you have finished4 ,,apparatus #c4 #d4 ,carbon-,zinc ,cell4 ,fig4 #c4 ,the wooden cross-piece1 ,a1 is #d-a_/b x #a x #a_/b in4 ,the carbon and zinc rods1 ,c and ,z1 are #d in4 long x #a_/b in4 in diameter4 ,the holes are bored1 if you have a brace and bit1 so that they are #c_/d in4 apart1 center to center4 ,this makes the rods #a_/d in4 apart4 ,to make connections between the rods and outside wires1 cut a shallow slot at the front side of each hole1 so that you can put a narrow strip of tin or copper1 ,b1 in the hole by the side of each rod4 ,setscrews1 ,s1 screwed in the side of ,a1 will hold the rods in place1 and at the same time press the strips1 ,b1 against them4 ,connections can easily be made between wire and ,b by using a spring binding-post1 ,d1 or by fastening the wire direct to the strips1 as shown in ,app4 #d4 ,illustration3 ,fig4 #c4 ,use the battery fluid given in ,app4 #ae1 and use a tumbler for the battery jar4 ,this cell will run small1 well-made motors1 induction coils1 etc4 7,see ,sec4 #c47 ,,apparatus #d4 #e4 ,carbon-,zinc ,cell4 ,fig4 #d4 ,the general construction of this cell is the same as that of ,app4 #c4 ,there are #b carbons1 ,c1 each #d x #a_/b in4 ,the holes for these are bored in ,a #a-a_/d in4 apart1 center to center4 ,the zinc rod1 ,z1 is a regular battery zinc1 #f x #c_/h in41 and has a binding-post1 ,y1 of its own4 ,the rods1 ,c1 are held in ,a1 and connections are made as explained in ,app4 #c4 ,illustration3 ,fig4 #d4 ,the wire1 ,x1 is fastened direct to the strips1 ,b1 as shown4 ,when ready to use this cell1 be sure that the wire connecting the carbons does not touch ,z4 7,why87 ,the other wire is connected to ,y4 ,the wooden piece is #d-a_/b x #a x #a_/b in4 ,use the battery fluid of ,app4 #ae in a tumbler4 ,this cell will run small motors1 and is good for induction coils1 etc4 7,see ,sec4 #c47 ,,apparatus #e4 ,illustration3 ,fig4 #e4 #f4 ,experimental ,cell4 ,fig4 #e4 ,cut a strip each of copper1 ,c1 and zinc1 ,z4 7,see list of materials47 ,they should be about #b in4 wide and #d in4 long4 ,punch a hole through each1 one side of the center1 for screws1 ,e4 ,the wooden cross-piece1 ,a1 should be #d-a_/b x #a x #g_/h in4 ,the battery-plates1 or elements1 should be screwed to this1 taking care that the screws1 ,e1 do not touch each other4 ,if the holes are made in the position shown in ,fig4 #e1 the screws can be arranged some distance apart4 ,the wires leading from the cell may be fastened under the screws with copper burs1 or spring binding-posts 7,app4 #db7 can be slipped on the top of the plates4 ,the solution to be used will depend upon what the cell is to do4 ,for simple experiments use the dilute acid 7,app4 #ad74 ,if for small motors1 use the formula given in ,app4 #ae4 ,the zinc should be well amalgamated4 7,app4 #bj47 ,,apparatus #f4 ,illustration3 ,fig4 #f4 #g4 ,experimental ,cell4 ,fig4 #f4 ,in some experiments a comparison is made between cells with large plates and cells with small ones4 ,this form will be convenient to use where narrow plates are desired4 ,those shown are #d x #a_/b in4 ,they are screwed to the cross-piece1 which is #d-a_/b x #a x #g_/h in4 ,do not let the screws touch each other4 ,the wires are fastened under the screw-heads4 ,,apparatus #g4 ,illustration3 ,fig4 #g4 #h4 ,experimental ,two-fluid ,cell4 ,fig4 #g4 ,this cell has a zinc strip1 ,z1 and copper cylinder1 ,c1 for the elements4 ,the porous cup1 ,p ,c1 is fully described in ,app4 #aa4 ,z is #e x #a in41 and should be well amalgamated 7,app4 #bj74 7,study reasons for amalgamation47 ,a zinc rod1 like that shown in ,fig4 #d1 may be used instead of the strip4 ,the copper cylinder1 ,c1 nearly surrounds ,p ,c1 and is made from a piece of thin sheet-copper1 #f x #b in4 ,the narrow strip1 or leader1 ,a1 is #e x #a_/b in4 ,to fasten it to ,c1 punch two small holes in ,c and ,a1 put short lengths of stout copper wire through the holes1 and hammer them down so that they will act as rivets1 ,r4 ,c can be hung centrally in the tumbler by bending ,a as shown4 ,y and ,x are spring binding-posts 7,app4 #db74 ,the battery wires can be fastened directly to ,z and ,a1 as suggested in ,fig4 #d4 #i4 ,setting up the ,cell4 ,arrange as in ,fig4 #g1 but remove ,z from ,p ,c4 ,pour some of the acid solution of ,app4 #ad into ,p ,c until it stands about #b-a_/b in4 deep1 and at once pour the copper solution of ,app4 #af in the tumbler1 on the outside of ,p ,c1 until it stands at the same height as the liquid in ,p ,c4 ,as soon as the liquids have soaked into ,p ,c1 you can put ,z in place1 when the cell will be ready for use4 ,remove and wash ,z1 when you have finished1 and if you wish to use this cell occasionally1 remove the liquids and wash ,p ,c thoroughly in water4 ,when dry it will be as good as new4 ,the acid rapidly acts upon ,z1 so it is better to remove ,z if you wish to leave the experimenting even for a few minutes only4 ,put a few crystals of copper sulphate 7blue vitriol7 in the tumbler under the copper1 to keep the copper solution saturated4 7,see text-book for the chemical action in this two-fluid cell47 ,,apparatus #h4 #aj4 ,two-fluid ,battery4 ,fig4 #h4 ,when two or more cells are joined together the combination is called a battery4 ,fig4 #h shows two experimental cells joined in series4 7,study methods of joining cells47 ,for convenience1 and to keep them from being easily overturned1 a frame has been made for them4 ,the base1 ,b1 is #h x #d x #g_/h in4 ,to the back of this is nailed the upright board1 ,a1 #h x #d-a_/b x #a_/b in4 ,on the top of ,a are #c binding-posts1 #a1 #b1 #c1 which consist of metal strips #a-a_/d x #a_/b in4 ,at the lower ends are screws which are connected with the cells1 as shown4 ,spring binders can be easily slipped on and off the upper ends of the strips1 so that one or two cells can be used at will4 ,bent strips1 ,c1 are nailed to ,b1 to hold the tumblers firmly in place4 ,this framework is not necessary1 of course1 to the proper working of the battery1 but with it you are much less liable to upset the cells4 ,illustration3 ,fig4 #h4 ,,apparatus #i4 #aa4 ,gravity ,cell4 ,fig4 #i4 ,in the two-fluid cell of ,app4 #g the fluids were kept apart by the porous cup4 ,the gravity cell is really a two-fluid cell in which the two liquids are kept separate by the joint action of the current and the force of gravity4 ,this cell is used for telegraph lines and for other closed-circuit work4 #ab4 ,construction4 ,the zinc and copper1 ,z and ,c1 ,fig4 #i1 can be purchased about as cheaply as you can make them4 ,there are many forms of the zincs1 the one shown being called the crow-foot shape4 ,the copper may be star-shaped1 or as shown4 ,if you wish to make ,c1 use thin sheet-copper4 ,brush copper1 #a-c_/d in4 wide1 is excellent for the purpose4 ,use a piece #ab or #ae in4 long1 and fasten to one end of it a copper wire1 ,w1 which must be covered with paraffined paper1 or with rubber or glass tubing1 where it passes up through the zinc sulphate solution and near ,z4 ,the glass jar1 ,j1 may be made from a large glass bottle4 7,see index for battery jars47 #ac4 ,to ,set ,up the ,cell4 7,a7 ,place ,c upon the bottom of ,j1 with ,w in the position shown4 7,b7 ,put in enough copper sulphate crystals to cover the bottom of ,j1 but do not try to entirely cover ,c4 ,at the start #a_/b lb4 will be enough4 7,c7 ,pour in clean water until ,j is half full4 7,d7 ,in another vessel dissolve #a or #b oz4 of zinc sulphate in enough water to complete filling1 ,j4 7,e7 ,hang ,z in place 7,fig4 #i74 ,z must never touch ,c4 ,they should be about #c in4 apart4 ,a wire is attached to ,z by the screw1 ,s1 and the hole1 ,h4 7,f7 ,pour the zinc sulphate solution into ,j until it is within an inch of the top4 ,it should cover ,z4 ,illustration3 ,fig4 #i4 7,g7 ,connect the wires leading from ,z and ,c to your sounder and key4 7,see diagram47 ,the cell will be weak at first1 and it may not be able to run your sounder4 ,if this is the case1 short-circuit it by allowing the current to run around and around through the sounder and key1 the switch being closed4 ,you may also short-circuit the cell by joining the two wires together4 ,this will1 in a few hours1 make the dividing line between the blue and white quite distinct1 when the cell will be stronger4 ,if you have a short line only1 the battery may be short-circuited through your sounder or other coils of wire for #e or #f hours a day1 without working it too much4 ,it may be necessary to draw off some of the clear zinc sulphate1 replacing it with clear water1 if the blue line gets too low4 ,add water occasionally to make up for evaporation4 #ad4 ,regulating4 ,the two solutions are kept apart by gravity1 as the copper sulphate is heavier than the zinc sulphate4 ,the dividing line between the blue and white solutions is fairly clear when the battery works well1 and it should be about half way between ,c and ,z1 or about at ,j1 ,fig4 #i4 ,never allow the blue to get as high as ,z1 as this indicates that the cell is not worked enough4 ,the dividing line can be lowered by allowing it to run a buzzer or bell for a few hours1 or by simply short-circuiting it4 ,if the blue gets much below ,j it indicates that you are working the cell too hard1 or that you need more copper sulphate4 ,the harder the cell works1 the more zinc sulphate is formed1 and the lower the dividing line becomes4 #ae4 ,gravity ,batteries of two more cells are needed when used on telegraph lines4 ,you will need #a cell to each sounder2 that is1 for a short line in the house with two sounders1 use #b cells4 ,if you use a few hundred feet of wire running to a friend's house1 use #c cells4 ,they must be joined in series2 that is1 the copper of one to the zinc of the other4 7,see diagram of complete telegraph line47 ,do not use ground connections for short lines and home-made sounders2 use a return wire4 ,do not use different kinds of cells upon the same line4 ,,apparatus #aj4 #af4 ,storage ,battery4 ,to show the principle of storage batteries it is only necessary to use two plates of lead dipped in the battery fluid of ,app4 #ad4 ,the cell may be made as in ,app4 #e1 ,fig4 #e1 the only difference being that both plates are of sheet-lead4 ,it will be an advantage to make the plates rough by hammering against them a coarse file4 7,see explanations and experiments with this form of cell in text-book47 ,,apparatus #aa4 ,illustration3 ,fig4 #aj #ag4 ,porous ,cups for ,two-fluid ,cells4 ,fig4 #aj4 ,very good porous cups can be made from ordinary blotting-papers1 the average ones measuring #i-a_/b x #d in4 ,white ones should be used1 so that you will not be bothered with the color coming out4 ,soak the edge along one end of the blotter in paraffine 7,index7 for about #a_/d in4 ,when this is cold1 roll the blotter into the form of a cylinder that is a little over #a in4 inside diameter1 and have the paraffined end on the outside4 ,this will make #b thicknesses of paper all around1 and a little to spare4 ,rub a hot nail over the paraffine to melt it1 and stick the end to the cylinder4 ,by putting on a little more paraffine along the edge where the end laps over1 a good solid cylinder can be made4 ,the cylinder should be strengthened still more by dipping each end into melted paraffine for about #a_/h in4 ,the dark stripes around the ends and down the front of the cylinder 7,fig4 #aj7 are to represent the paraffine4 ,cut out a bottom about #a_/d in4 larger all around than the cylinder4 ,this may be paraffined to make it stiff4 ,it should be fastened to the cylinder with paraffine4 ,paraffine is not acted upon or softened by water or acid1 as is the case with glue4 ,,apparatus #ab4 #ah4 ,porous ,cups for ,two-fluid ,cells4 ,instead of the blotters of ,app4 #aa1 you can use short lengths of mailing-tubes1 which are used to protect pictures1 etc41 when sent by mail4 ,if you find that the particular tube tends to unwind when soaked1 you can use a little paraffine along the edges of the spiral1 as suggested in ,app4 #aa4 ,bottoms can be made for the cups as before4 ,,apparatus #ac4 #ai4 ,porous ,cups for ,two-fluid ,cells4 ,ordinary unglazed earthen flower-pots make good cups4 ,the hole in the bottom should be closed with a cork1 or by fastening a piece of pasteboard over the hole with paraffine4 ,the pasteboard may be fastened to the under side of the bottom more easily than to the upper side4 #bj4 ,note4 ,it is a good idea to soak the top edge of porous cups for about #a_/d in4 in paraffine to keep the solutions from crawling up by capillary attraction4 ,if the solutions constantly evaporate from the soaked tops of the cups1 they not only waste but they get the whole thing covered with crystals4 ,,chapter ,,ii4 ,,battery ,,fluids ,,and ,,solutions4 #ba4 ,sulphuric ,acid4 ,,this ,,acid ,,must ,,be ,,handled ,,with ,,great ,,care1 as it 7the concentrated7 is very strong1 and will burn the hands1 eat holes in clothing1 carpets1 etc42 it will even char wood4 ,do not let any of it drop anywhere accidentally4 ,if you wish to pour concentrated acid into a bottle1 place the bottle to be filled upon a plate1 and wipe all drops of acid from the outside of it afterward4 ,the concentrated acid should be kept in tightly-corked bottles1 as it absorbs moisture from the air very rapidly4 ,ordinary corks should be paraffined if they are to be used in acid bottles1 or they will be soon eaten up4 #bb4 ,mixing4 ,when sulphuric acid and water are mixed1 considerable heat is produced4 ,never pour water into the acid1 as the heat would be produced so rapidly that the vessel containing the mixture might break4 ,always pour the acid into the water1 and thoroughly stir the mixture at the same time4 ,earthen vessels do not break when heated as easily as glass ones4 ,the mixing may be done in ordinary glass fruit-jars1 if care be taken to pour the acid slowly into the water4 ,the jars should be set in some larger dish1 or in the sink1 before adding the acid4 ,if they get too hot1 allow them to cool a little before proceeding with the mixing4 ,as the acid is much heavier than water1 it will immediately sink to the bottom of the jar1 unless constantly stirred4 #bc4 ,there are different grades of acid upon the market4 ,for battery purposes you do not need the chemically pure 7,c ,p7 acid4 ,the ordinary commercial acid is all right1 even though it is a little dark in color4 ,you can get this at any drug-store4 ,get #e or #aj cents' worth at a time4 ,,apparatus #ad4 #bd4 ,battery ,fluid for ,simple ,cells4 ,for the simple cell 7,app4 #e71 when it is to be used for experiments with detectors or in the study of polarization1 etc41 a very dilute acid is best4 ,mix #a fluid ounce of commercial acid with #a pint of water4 ,this will make #ag fluid ounces 7,see ,app4 #ai71 and your mixture will be one-seventeenth acid4 ,make up a pint or quart bottle of this at a time1 and label it with the date3 ,dilute sulphuric acid4 #a part acid1 #af parts water4 ,apparatus #ad4 #be4 ,note4 ,do not fail to paste a label on all bottles as soon as you have put anything into them4 ,give the date1 contents1 and any other information that will help you to reproduce the mixture again4 ,do not write on them any abbreviations or other things that you will soon forget4 ,,apparatus #ae4 #bf4 ,battery ,fluid2 ,bichromate ,solution4 ,for running small motors1 shocking coils1 etc41 this solution will be found good when used with the zinc and carbon elements given in ,app4 #c and #d4 ,the bichromate destroys the hydrogen bubbles which help to polarize cells so rapidly when the plain dilute acid 7,app4 #ad7 is used4 7,study polarization47 ,the zinc used in this fluid must be well amalgamated 7,app4 #bj74 ,directions4 ,with #a quart of cold water placed in a glass or earthen dish1 slowly mix #d fluid ounces of commercial sulphuric acid4 ,read ,sec4 #bb carefully4 ,when this gets about cold1 add #d ounces of bichromate of potash4 ,powdered bichromate will dissolve more quickly than the lump4 ,keep this fluid in corked bottles1 labelled1 with date3 ,bichromate ,battery ,fluid4 ,apparatus #ae4 #bg4 ,always take the zinc from this fluid as soon as you have finished experimenting1 or even if you have no use for the cell for a few minutes4 ,the zinc and fluid are rapidly destroyed in bichromate cells even when the circuit is open4 ,always wash the carbon and zinc as soon as you take them from the fluid4 ,,apparatus #af4 #bh4 ,battery ,fluid4 ,for #b-;fluid cells 7,app4 #g71 a saturated solution of copper sulphate 7blue vitriol7 is needed4 ,place some of the crystals in a glass jar1 with water1 stir them around1 and add the sulphate as long as it is dissolved4 ,a few extra crystals should be left in the stock bottle so that the solution will always be saturated4 ,,apparatus #ag4 #bi4 ,vinegar ,battery ,fluid4 ,for a few of the experiments with detectors1 etc41 good strong vinegar does well as the exciting fluid4 ,this may be used with the copper and zinc or carbon and zinc elements4 ,the amount of current given with vinegar and ,app4 #d or #e is sufficient to show many of the simpler experiments4 ,,apparatus #ah4 #cj4 ,battery ,fluid4 ,strong brine1 made by dissolving ordinary salt in water1 will produce quite a little current with ,app4 #d or #e4 ,the presence of the current is easily shown with the astatic detectors4 ,,apparatus #ai4 #ca4 ,measures for ,water1 ,acids1 etc4 ,if you do not own a graduated glass1 such as druggists use for measuring liquids1 the following plan will be found useful4 ,in the mixing of battery fluids1 etc41 while it is not necessary to be absolutely exact1 it is necessary to know approximately what you are doing4 ,an ordinary glass pint fruit jar may be taken as the standard4 ,this holds #af fluid ounces1 or #b ordinary teacupfuls4 ,a teacupful may then be taken as #a_/b pint1 or #h fluid ounces4 ,you can probably find a small bottle that will hold #a or #b oz41 and you can easily tell how much it holds by filling it and counting the number of times it is contained in the pint can4 ,a slim bottle holding #a_/b pint can be made into a convenient measuring glass by scratching lines on it with the sharp edge of a hard file4 ,the lines should be placed1 of course1 so that they will show how much liquid you must put into it to make #a oz41 #b oz41 etc4 ,instead of the file marks1 a narrow strip of paper may be pasted upon the bottle1 and the divisions shown by lines drawn upon the paper4 ,,apparatus #bj4 #cb4 ,to ,amalgamate ,battery ,plates4 ,to keep the zinc plates or rods in cells from being eaten or dissolved when the circuit is opened1 they should be amalgamated2 that is1 they should have a coating of mercury4 ,the local currents 7see text-book7 aid in rapidly destroying the zinc1 unless it is amalgamated4 ,do not amalgamate copper plates--merely the zinc ones4 #cc4 ,place a few drops of mercury in a butter dish4 ,dip the zinc into the solution of ,app4 #ad1 then lay it upon a flat board4 ,this is necessary with thin sheet-zinc1 as it becomes very brittle when coated with mercury1 and will not stand hard rubbing4 ,if you also dip a very narrow piece of tin into the dilute sulphuric acid1 you can use this as a spoon and lift one drop of mercury at a time from the butter dish to the zinc4 ,by tapping the tin upon the zinc1 the mercury will leave the tin4 ,put the mercury only where the zinc will be under the solutions in the cell1 then rub the drops around with a small cloth that has been dipped in the acid4 ,the zinc will become very bright and silvery1 due to the mercury4 ,do not get too much mercury on it1 just enough to give it a thin coat1 as it will make the thin zinc so brittle that it will very easily break4 ,amalgamate both sides of the zinc4 ,,chapter ,,iii4 ,,miscellaneous ,,apparatus ,,and ,,methods ,,of ,,construction4 ,,apparatus #ba4 #cd4 ,for ,annealing and ,hardening ,steel4 7,see text-book for reasons why some parts of electrical apparatus should be made of hard steel1 while other parts should be made of soft iron47 #ce4 ,to anneal or soften spring steel so that you can bend it without breaking it1 heat it in a candle1 gas1 or alcohol flame until it is red-hot2 allow the steel to cool in the air slowly4 #cf4 ,to harden steel1 heat as before1 then suddenly plunge the red-hot piece into cold water4 ,this will make the steel very hard and brittle4 ,small pieces may be held by pinching them between two pieces of wood4 ,needles and wires may be stuck in a cork1 which will serve as a handle4 7,see text-book47 ,,apparatus #bb4 ,illustration3 ,fig4 #aa4 #cg4 ,alcohol ,lamp4 ,fig4 #aa4 ,an alcohol lamp is very useful in many experiments1 and it is better than a candle for annealing or hardening steel needles when making small magnets 7,app4 #ba74 ,you can make a good lamp by using a small bottle with a wide opening4 ,a vaseline bottle or even an ink bottle will do4 ,make a hole about #a_/d in4 in diameter through the cork with a small round file1 or burn it through with a hot nail4 ,make a cylinder of tin about #a-a_/b in4 long and just large enough to push through the hole4 ,the tin may be simply rolled up4 ,if you have glass tubing1 use a short length of that instead of the tin4 ,for the wick1 roll up some flannel cloth4 ,this should not fit the inside of the tin tube too tightly4 ,the alcohol should be put into the lamp when you want to use it1 and that left should be put back into the supply-bottle when you have finished1 as alcohol evaporates very rapidly4 ,the flame of this lamp is light-blue in color1 and very hot4 ,caution4 ,do not have your supply-bottle of alcohol near the lamp when you light the latter1 or near any other flame4 ,the vapor of alcohol is explosive4 ,,apparatus #bc4 #ch4 ,spool ,holder for ,wire4 ,fig4 #ab4 ,when winding magnets it is necessary to have the spool of wire so arranged that it will take care of itself and not interfere with the winding4 ,if you have a brace and bit1 bore a hole in a base #g_/h in4 thick for a #a_/d in4 dowel4 ,the dowel should fit the hole tight4 ,the spools of wire purchased can then be placed upon the dowel1 where they will unwind evenly4 ,the base may be nailed or clamped to a table4 ,illustration3 ,fig4 #ab4 ,,apparatus #bd4 #ci4 ,spool ,holder for ,wire4 ,if you have no brace and bit to make ,app4 #bc1 nail a spool to a wooden base1 place a short length of dowel in the spool1 and use this combination as a spool holder4 ,make the dowel fit the spool by winding paper around it4 ,,apparatus #be4 #dj4 ,to ,make ,holes in ,wood4 ,if you have a brace and a set of bits1 or even a small hand-drill1 it will be an easy matter to bore holes in wood4 ,an awl should be used to make holes for screws1 such as those used in making binding-posts1 etc41 as the wood is very liable to split if a screw is forced into it without a previously-made hole4 ,red-hot nails1 needles1 etc41 are easily made to burn holes of desired diameters4 ,they may be heated in a gas flame or by means of the alcohol lamp 7,app4 #bb74 ,flat pieces of hot steel will burn narrow slots1 and small1 square holes may be made with hot nails4 ,,apparatus #bf4 #da4 ,to ,make ,holes in ,sheet-,metal4 ,fig4 #ac4 ,holes may be punched in sheet-tin1 copper1 zinc1 etc41 in the following manner3 ,set a block of hard wood1 ,w1 on end2 that is1 place it so that you will pound directly against the end of the grain4 ,lay the metal1 ,t1 to be punched1 upon this1 and use a flat-ended punch4 ,a sharp blow upon a good punch with a hammer will make a fairly clean hole2 that is1 it will cut out a piece of metal1 and push it down into the wood4 ,a sharp-pointed punch will merely push the metal aside1 and leave a very ragged edge to the hole4 ,a punch may be made of a nail by filing its end flat4 ,illustration3 ,fig4 #ac4 ,,apparatus #bg4 #db4 ,to ,punch ,holes through ,thick ,yokes1 etc4 ,as soon as #e or #f layers are to be punched at one operation1 the process becomes a little more difficult than that given in ,app4 #bf4 ,if you have an anvil1 you can place the yoke over one of the round holes in it1 and punch the tin right down into the hole1 the ragged edges being afterward filed off4 ,hold the yoke as in ,app4 #gi or #hj for filing4 ,as you will probably have no anvil1 lay an old nut from a bolt upon the end of the block of wood 7,app4 #bf71 place the metal to be punched over the hole1 and imagine that you have an anvil4 ,very good results may be obtained by this method4 ,the size of nut used will depend upon the size of hole wanted4 ,,apparatus #bh4 #dc4 ,to ,straighten ,wires4 ,it is often necessary to have short lengths of wires straight1 where they are to be made into bundles1 etc4 ,to straighten them1 lay one or two at a time upon a perfectly flat surface1 place a flat piece of board upon them1 then roll them back and forth between the two4 ,the upper board should be pressed down upon the wires while rolling them4 ,if properly done1 the wires can be quickly made as straight as needles4 #dd4 ,push-,buttons4 ,nearly every house has use for one or more push-buttons4 ,the simple act of pressing your finger upon a movable button1 or knob1 may ring a bell a mile away1 or do some other equally wonderful thing4 ,,apparatus #bi4 #de4 ,push-,button4 ,fig4 #ad4 ,this is made quickly1 and may be easily fastened to the window or door-casing4 ,one wire is joined to ,a and the other to ,c4 ,b is a strip of tin or other metal1 about #e_/h in4 wide and #b in4 long4 ,it is bent so that it will not touch ,a unless it is pressed down4 ,this may be placed anywhere1 in an electric-bell circuit or other open circuit1 where it is desired to let the current pass for a moment only at a time4 ,illustration3 ,fig4 #ad4 ,,apparatus #cj4 #df4 ,push-,button4 ,fig4 #ae and ,fig4 #af4 ,by placing ,app4 #bi in a box1 we can make something that looks a little more like a real push-button4 ,fig4 #ae shows a plan with the box-cover removed1 and ,fig4 #af shows a view of the inside of it1 a part of the box being cut away4 ,c1 ,fig4 #ae1 is a wooden pill-box #a in4 high and #a-c_/d in4 in diameter4 ,make a #a_/d in4 hole in the cover of ,c for the button1 ,g1 which is a short piece of #a_/d in4 dowel4 ,this rests upon a single thickness of tin1 ,d1 which is cut into a strip #c_/h in4 wide and about #a-a_/d in4 long4 ,in the bottom of ,c are two holes just large enough to allow the screws ,e and ,f to pass through4 ,the wires1 ,a and ,b1 pass from the binding-posts1 ,x and ,y1 through small holes burned through the sides of the box1 and are fastened under the screw-heads4 ,the whole box is screwed to the wooden base1 which is #c x #d x #g_/h in41 by the screws1 ,e and ,f4 ,d should have enough spring in it to raise itself and ,g when the pressure of the finger is removed4 ,the circuit will be closed only when you press the button4 ,illustration3 ,fig4 #ae4 ,illustration3 ,fig4 #af4 ,,apparatus #ca4 #dg4 ,push-,button4 ,figs4 #ag1 #ah1 #ai4 ,fig4 #ag shows a top view or plan of the apparatus4 ,fig4 #ah is a sectional view2 that is1 we suppose that the button has been cut into two parts along its length and through the center line4 ,fig4 #ai is an enlarged detail drawing of the underside of the spool1 ,c4 ,the same part is marked by the same letter in all of the figures4 ,illustration3 ,fig4 #ag4 ,illustration3 ,fig4 #ah4 ,illustration3 ,fig4 #ai4 ,saw an ordinary spool1 ,c1 into two parts4 ,one-half of ,c will serve as the outside case for the button4 ,the part to be pressed with the finger is a short length of #a_/d in4 dowel4 ,to keep this from falling out of the hole in ,c1 a short piece of wire nail1 ,n1 has been put through a small hole in its lower end4 ,a slot1 ,f1 has been burned or cut into the underside of ,c1 so that ,n can pass up and down in it when ,d is raised and lowered4 ,the rod1 ,d1 rests upon ,a1 one of the contacts4 ,this is a straight piece of tin1 cut as shown in ,fig4 #ag1 the narrow part being #a_/d in4 wide and #a-a_/d in4 long4 ,the wide part is #c_/d in4 wide and #a in4 long4 ,the other contact1 ,b1 is the same size as ,a4 ,a deep groove1 a little over #a_/d in4 wide1 is cut into the base so that the narrow part of ,b can be bent down below the end of ,a4 ,the base shown is #d x #b-a_/b x #g_/h in4 ,the spool1 ,c1 is fastened to the base by #b screws or wire nails put up through the base1 their positions being shown by the dots at ,e1 ,fig4 #ag4 ,x and ,y1 ,fig4 #ah1 are #b screw binding-posts4 ,it is evident that the current cannot pass from ,x to ,y1 unless the button1 ,d1 be pressed down so that the end of ,a will touch ,b4 ,,apparatus #cb4 #dh4 ,sifter for ,iron ,filings4 ,fig4 #bj4 ,in making magnetic figures with iron filings1 it is an advantage to have the particles of iron fairly small and uniform in size4 ,a simple sifter may be made by pricking holes in the bottom of a pasteboard pill-box with a pin4 ,the sifter may be put away with the filings in it1 provided you turn it upside down4 ,illustration3 ,fig4 #bj4 ,,apparatus #cc4 #di4 ,sifter for ,iron ,filings4 ,fig4 #ba4 ,punch small holes in the cover of a tin box with a small wire nail4 ,if you have occasion to use sifters for other purposes1 the different sizes can be made by using larger and smaller nails to punch the different tin covers4 ,but one size of nail should be used for one sifter4 ,illustration3 ,fig4 #ba4 ,,apparatus #cd4 #ej4 ,sifters may be made by pricking holes in an envelope4 ,a sifter with very small holes can be made of a piece of muslin cloth4 ,this can be used in the form of a little bag1 or a piece of it can be pasted over the open bottom of a pill-box4 ,,apparatus #ce4 #ea4 ,to ,cut ,wires1 ,nails1 etc4 ,if you have no wire-cutters1 or large shears1 you can cut large or small wires by hammering them against the sharp edge of another hammer1 an anvil1 or a piece of iron4 ,do not let the hammer itself hit upon the edge of the anvil4 ,the above process will make a ,v-shaped dent on one side of even large wires1 or nails1 when they may be broken by bending back and forth4 ,,chapter ,,iv4 ,,switches ,,and ,,cut-,,outs4 #eb4 ,switches1 ,cut-,outs4 ,where apparatus is to be used frequently1 such as for telephone and telegraph lines1 it pays to make your switches1 etc41 carefully4 ,the use of these switches1 etc41 will be shown in the proper place4 ,their construction only will be given here4 ,,apparatus #cf4 #ec4 ,cut-,out4 ,fig4 #bb4 ,details4 ,x1 ,y1 and ,z represent #c binding-posts like ,app4 #db4 ,these are fastened to a wooden base that is about #c x #e x #c_/d4 ,the ends of the wires shown come from and go to the other pieces of apparatus4 ,q shows a stout wire or strip of #b or #c thicknesses of tin4 ,suppose we have an apparatus1 as1 for example1 an electric bell1 which we want to have ring when someone at a distance desires to call us4 ,if we use a telephone or telegraph instrument we shall want to cut the bell out of the circuit as soon as we hear the call and are ready to talk4 ,suppose the current comes to us through the wire1 ,a1 ,fig4 #bb4 ,it can pass by the wire1 ,c1 through the bell and back to ,x4 ,if we wanted simply to have the bell ring1 the current could pass directly from ,x into the earth1 or over a return wire back to the push-button at our friend's house4 ,if1 however1 we are to use some other instrument1 by lifting the end of ,q out of ,x and pushing it into ,y1 the bell will be cut out1 and the current can pass on wherever we need it4 ,illustration3 ,fig4 #bb4 ,,apparatus #cg4 #ed4 ,cut-,out4 ,fig4 #bc4 ,the main features of this are like those of ,app4 #cf4 ,the three binding-posts are like ,app4 #df4 ,instead of a band of metal to change connections1 as ,q in ,app4 #cf1 a stout copper wire is used4 ,this can be easily changed from one of the upper binding-posts to the other1 thereby throwing in or cutting out any piece of apparatus joined with the upper connectors4 ,illustration3 ,fig4 #bc4 ,,apparatus #ch4 ,illustration3 ,fig4 #bd4 #ee4 ,switch4 ,fig4 #bd4 ,this simple switch has but one contact point1 ,d1 which is a screw-head4 ,this switch may be used anywhere in the circuit by simply cutting the wire carrying the current1 and joining the ends of the wire to the binding-posts ,x and ,y4 ,the metal strip1 ,e1 is made of #b or #c thicknesses of tin4 ,it is #e_/h in4 wide and about #e in4 long1 and presses down upon ,d1 when swung to the left1 thus closing the circuit4 ,the short metal strips shown are #e_/h x #a-a_/d in4 ,the upper strip is joined to the end of ,e by a coiled copper wire1 ,c ,w4 7,see ,app4 #ej47 ,if the current enters by the wire1 ,a1 it will pass through ,c ,w1 ,e1 ,d and out at ,b4 ,the strip ,e is pivoted at ,f by a small screw4 ,the base may be #c or #d x #e x #g_/h in4 ,,apparatus #ci4 #ef4 ,switch4 ,fig4 #be4 ,by increasing the number of contact points and the wires leading from them1 a switch may be made to throw in one or more pieces of apparatus4 ,this variety of switch is useful in connection with resistance coils 7,index74 ,by joining the ends of the coils with the points #a1 #b1 #c1 etc41 more or less resistance can be easily thrown in by simply swinging the lever1 ,e1 around to the left or right4 ,the uses of this will be again referred to4 ,illustration3 ,fig4 #be4 ,details4 ,the base of the one shown in ,fig4 #be is #d x #e x #g_/h in4 thick4 ,the switch1 ,e1 is a band of #b thicknesses of tin #e_/h in4 wide4 ,it is pivoted at ,f with a screw4 ,to the end of ,e is fastened a copper wire1 which leads to the upper binding-post1 ,x 7,app4 #df74 ,the apparatus has #e contact points1 marked #a1 #b1 #c1 etc4 ,these consist of brass screws and copper washers4 ,with ,f as a center draw the arc of a circle that has a radius of #d in4 ,place the screws #a1 #b1 etc41 along this arc1 and about #e_/h in4 apart1 center to center2 that is1 the screws are all #d in4 from ,f1 and are1 therefore1 in the form of a curve4 ,the last screw forms a part of the binding-post1 ,y4 ,suppose #d pieces of apparatus1 marked ,a1 ,b1 ,c1 and ,d1 be connected with #a1 #b1 etc41 as shown4 ,these may be1 for example1 coils of wire to be used as resistance coils4 ,if the current enters at ,x1 it will pass along at ,e and be ready to leave at ,y1 as soon as ,e touches one of the contact points4 ,if ,e be placed upon #a1 the current will be obliged to pass through all of the coils1 ,a1 ,b1 etc41 before it can get to ,y4 ,in this case the resistance will be greatest4 ,if ,e be now moved on to #b1 only ,a will be cut out1 and the total resistance reduced4 ,by placing ,e upon #d1 but one coil1 ,d1 will be in the circuit4 ,when ,e is upon #e the current will pass through the switch with practically no resistance4 ,this is the principle upon which current regulators work4 7,study resistance in text-book47 ,when ,e is in the position shown in ,fig4 #be no current can pass4 ,,chapter ,v4 ,,binding-,,posts ,,and ,,connectors4 #eg4 ,binding-,posts are used to make connections between two pieces of apparatus1 between two or more wires1 between a wire and any apparatus1 etc41 etc4 ,they are used simply for convenience1 so that the wires can be quickly fastened or unfastened to the apparatus4 ,there are many ways of making them at home4 ,the following forms will be found useful and practical4 ,although some that are given are really connectors instead of binding-posts1 we shall give them the general name of binding-posts4 ,,apparatus #dj4 #eh4 ,binding-,post4 ,about the simplest form is a screw1 or a nail with a flat head4 ,the bare wire may be placed under the head of the screw or nail before forcing it entirely into the wood4 ,this will keep the end of the wire in place1 and another wire may be joined electrically to the first by merely touching it to the screw-head1 or by placing it under the screw-head4 ,,apparatus #da4 #ei4 ,binding-,post4 ,fig4 #bf4 ,this consists of a screw and a copper washer or bur4 ,the screw is a round-headed brass one1 #e_/h in4 long1 number #e or #g4 ,the copper burs are ,no4 #h1 and fit nicely around the screws4 ,by using #b burs instead of #a1 several wires may be easily joined together at one point4 ,scrape the covering from the ends of the wires1 and place them between the burs4 ,illustration3 ,fig4 #bf4 ,,apparatus #db4 #fj4 ,binding-,post4 ,fig4 #bg4 ,a coiled spring serves very well as a connector4 ,one end should be fastened to the apparatus1 as shown1 by clamping it under a screw-head4 ,the other end of the coil should be pulled out a little1 away from the other turns1 so that you can stretch the spring in order to put the bare ends of wires between the turns4 ,any number of wires placed between these turns will be pinched and electrically connected4 ,the coil should be about #a_/b in4 long and less than #a_/b in4 in diameter4 ,you can make a coil by tightly wrapping stiff iron wire around a pencil4 ,the steel wire springs taken from old window-shades are excellent for this purpose4 ,they may be cut into lengths with tinner's shears4 ,,apparatus #dc4 #fa4 ,binding-,post4 ,fig4 #bh4 ,two copper or tin strips fastened at one end by a screw1 the upper strip being bent a little at one end1 make a connector that is useful for some purposes1 where you want to make and break the connection frequently4 ,the bare end of the wire which belongs to the apparatus is fastened under the screw-head4 ,the outside wire1 or wires1 to be connected are pushed between the strips of metal4 ,another way is to fasten the outside wire to a strip of metal about #a_/b in4 wide1 and then push this between the strips shown in the figure4 ,the strips shown should be about #c_/d in4 wide and #a-a_/d in4 long4 ,illustration3 ,fig4 #bg4 ,illustration3 ,fig4 #bh4 ,illustration3 ,fig4 #bi4 ,,apparatus #dd4 #fb4 ,binding-,post4 ,fig4 #bi4 ,a combination made between ,app4 #db and #dc does well4 ,fasten a metal strip1 #c_/d in4 x #a-a_/d in41 to the apparatus by means of a screw4 ,the apparatus wire should be fastened under the screw-head4 ,a short length of spring may be pushed upon the upright part of the strip1 as shown4 ,into this you can quickly fasten the outside wires4 ,,apparatus #de4 #fc4 ,binding-,post4 ,fig4 #cj4 ,this makes a very simple and practical binding-post for home-made apparatus4 ,it consists of a screw-eye1 preferably of brass4 ,the circle or eye should be about #c_/h or #a_/b in4 in diameter4 ,the thread on such a screw-eye will be about #a_/b in4 long4 ,two copper burs are used to pinch the wires4 ,,apparatus #df4 #fd4 ,binding-,post4 ,fig4 #ca4 ,this consists of a screw1 screw-eye1 bur and a metal strip1 #c_/d x #a-a_/d in4 ,the apparatus wire should be fastened under the screw-head4 ,any outside wires which are to be joined to the apparatus should be clamped under the bur by turning the screw-eye4 ,a small hole should be made in the wood before putting in the screw-eye4 7,see ,app4 #be47 ,do not turn the screw-eye too hard1 or you will spoil the thread made in the wood4 ,illustration3 ,fig4 #cj4 ,illustration3 ,fig4 #ca4 ,illustration3 ,fig4 #cb4 ,,apparatus #dg4 #fe4 ,binding-,post4 ,fig4 #cb4 ,the size of the bolt used in this form of binding-post will depend somewhat upon the thickness of the base of the apparatus4 ,in general1 a #c_/d or #g_/h in4 base should be used where screws or screw-eyes are necessary4 ,with this kind 7,fig4 #cb7 a thin base can be used4 ,the head is shown counter-sunk into the bottom of the base4 ,this is not necessary1 provided at least #c heads are placed far enough apart to form legs for the apparatus to stand on4 ,strips of wood may be nailed upon the underside of the base to make room for the heads in case they are not used as legs4 ,the wires should be pinched between the nut and the copper bur shown4 ,if the bolt is too large for a bur1 an iron washer may be used4 ,a washer may be made of tin1 or two nuts may be used4 ,,apparatus #dh4 #ff4 ,binding-,post4 ,fig4 #cc4 ,this is a suggestion for a combination of ,app4 #dd and #dg4 ,it is useful in school apparatus4 ,wires may be permanently fastened on the right1 under the nut1 and a spring1 as in ,app4 #dd1 may be slipped on the metal strip at the left1 which is held under the head of the bolt4 ,illustration3 ,fig4 #cc4 ,,apparatus #di4 #fg4 ,mercury ,connector4 ,a cup of mercury may be used as a connector4 ,make a small hole about #a_/d in4 in diameter and depth1 in a piece of wood1 and place #b or #c drops of mercury in this4 ,the ends of wires dipped in this will be electrically connected4 ,,apparatus #ej4 ,illustration3 ,fig4 #cd4 #fh4 ,connector4 ,fig4 #cd4 ,this shows how a wire may be fastened to one end of a short strip of tin4 ,at the other end of the strip a slot is cut4 ,this may straddle the body of a screw1 or when left plain may be used to slip between the two metal strips shown in ,app4 #dc4 ,,apparatus #ea4 #fi4 ,binding-,post4 ,fig4 #ce4 ,the ends of two or more wires may be quickly joined electrically by placing them between the nuts of a short bolt4 ,by using #c nuts the bolt will more easily connect a large number of wires4 ,illustration3 ,fig4 #ce4 ,make ,additional ,notes and ,sketches ,here4 ,,chapter ,,vi4 ,,permanent ,,magnets4 #gj4 ,permanent ,magnets may be made in many ways and from many different kinds of steel4 ,the steel used for needles1 watch and clock springs1 files1 cutting tools1 etc41 is generally of good quality1 and it is already hard enough to retain magnetism4 7,see ,retentivity in text-book47 ,,apparatus #eb4 #ga4 ,bar ,magnet4 ,a straight magnet is called a bar magnet4 ,magnetize a sewing-needle4 ,for some experiments a needle-magnet1 as we may call it1 is better than a large magnet4 ,,apparatus #ec4 #gb4 ,bar ,magnet4 ,a harness-needle1 which is thicker and stronger than a sewing-needle1 makes an excellent bar magnet4 ,,apparatus #ed4 #gc4 ,bar ,magnet4 ,for long slim magnets use a knitting-needle4 ,some knitting-pins1 as they are sometimes called1 break off short when bent1 but most of them will bend considerably before breaking4 ,these slim magnets are excellent for the study of ,consequent ,poles4 7,see text-book47 ,,apparatus #ee4 #gd4 ,flexible ,bar ,magnets4 ,it is often necessary to have flexible magnets so that they may be bent into different shapes4 ,these may be made from watch or clock springs1 as such steel1 called spring steel1 will straighten out again as soon as the pressure is removed from it4 ,corset steels1 dress steels1 hack-saw blades1 etc41 make good thin flexible bar magnets4 ,,apparatus #ef4 #ge4 ,strong ,bar ,magnets may be made from flat files4 ,the handle end may be broken off so that the two ends of the file shall be nearly alike in size4 ,these should be magnetized upon an electro-magnet4 ,,apparatus #eg4 #gf4 ,compound ,bar ,magnets are made by first magnetizing several thin pieces of steel1 and then riveting them together so that their like poles shall be together1 and pull together4 ,to make a small compound bar magnet1 magnetize several harness-needles1 or even sewing-needles1 and then bind them into a little bundle with all the ,n poles at the same end4 ,melted paraffine dropped in between them will hold them together4 ,rubber bands may be used also1 or1 if but one end is to be experimented with1 the points may be stuck into a cork1 and the heads used to do the lifting4 ,,apparatus #eh4 #gg4 ,small ,horseshoe ,magnets may be made from needles or from other pieces of steel used for bar magnets4 ,they should be annealed 7,app4 #ba7 at their centers at least1 so that you can bend them into the desired shape4 ,in the case of bright needles1 like harness-needles1 the part annealed will become blackened4 ,if you heat the center only1 and the ends remain bright for about #a_/b inch1 you will not need to harden the needle again4 ,it is an advantage to have the center of the magnet a little soft1 as it is not then liable to break4 ,the ends alone may be hardened by holding the bent portion away from the candle or gas flame1 while heating the ends4 ,the bent steel should be magnetized by drawing its ends across the poles of a horseshoe magnet4 ,,apparatus #ei4 #gh4 ,flexible ,horseshoe ,magnets may be made of thin spring steel4 ,the distance between the poles can be regulated at will by bending the steel more or less4 ,the poles may be held at any desired distance apart by thread or wire1 which should be wound around the legs of the magnet a little above the poles4 ,this will keep the steel from straightening out4 ,,apparatus #fj4 #gi4 ,horseshoe ,magnet4 ,fig4 #cf and #cg4 ,magnetize two harness-needles1 and stick them into a cork so that the poles shall be arranged as shown4 ,the distance between the poles can be regulated to suit4 ,this forms a very simple and efficient magnet1 with the advantages of a real horseshoe magnet4 ,illustration3 ,fig4 #cf4 ,illustration3 ,fig4 #cg4 ,,apparatus #fa4 #hj4 ,armatures4 ,all home-made magnets should be provided with armatures1 or keepers4 ,these are made of soft iron on the regular magnets1 and tend to keep the magnet strong4 7,see text-book47 ,for the bar magnets described1 a piece of sheet-tin1 upon which to lay them1 is all that is needed for an armature4 ,the lines of force will pass through this4 ,for the horseshoe magnets described1 strips of tin1 soft iron wires1 or even a wire nail placed across the poles will greatly aid in keeping in the strength4 ,the little magnets should not be dropped or jarred4 7,study the theory of magnetism in text-book47 ,,chapter ,,vii4 ,,magnetic ,,needles ,,and ,,compasses4 #ha4 ,magnetic ,needles and ,compasses consist chiefly of a short bar-magnet4 ,when used to tell the directions1 north1 east1 etc41 the apparatus is generally called a compass4 ,when we speak of the needle1 we really mean the compass-needle4 ,the little magnet may be almost any piece of magnetized steel1 provided it is arranged so that it can easily swing around4 ,there are several ways of supporting the compass-needle4 ,it may rest upon a pivot1 it may be hung from a fine thread1 or it may be floated upon water with the aid of a cork1 etc4 #hb4 ,uses4 ,we all know that compasses are used to point to the north and south1 and we speak of the points of the compass4 ,this1 of course1 is the most important use of the compass1 and it has been known for centuries4 ,in the laboratory it is used to show or detect the presence of currents of electricity1 and1 in connection with coils of wire1 it may show the relative strengths of two currents1 etc4 ,when used for such purposes it generally has special forms and sizes4 7,see ,galvanometers and ,detectors47 ,,apparatus #fb4 #hc4 ,compass4 ,an oily sewing-needle will float upon the surface of water1 when it is carefully let down to the water4 ,a little butter may be rubbed upon the previously-magnetized needle to make it float better4 ,illustration3 ,fig4 #ch4 ,,apparatus #fc4 #hd4 ,compass4 ,fig4 #ch shows a magnetized sewing-needle floated upon a cork4 ,the needle may be permanently fastened to the cork with a few drops of melted paraffine4 ,,apparatus #fd4 #he4 ,compass4 ,fig4 #ci4 ,with a sharp knife make a cut part way through a flat cork4 ,into the cut push a short length of magnetized watch-spring4 ,in the illustration the spring is shown partly removed from the cut4 ,float the cork4 ,,apparatus #fe4 #hf4 ,compass4 ,fig4 #dj4 ,stick a pin1 ,p1 into a pasteboard1 cork1 or wooden base1 ,b4 ,bend a piece of stiff paper double1 as shown1 and then stick through it1 on each side1 a magnetized sewing-needle1 ,s ,n4 ,the north poles of the needles should be at the same end of the paper4 ,why8 ,balance the paper upon the pin-pivot1 and see it fly around to the north and south4 ,illustration3 ,fig4 #ci4 ,illustration3 ,fig4 #dj4 ,illustration3 ,fig4 #da4 ,,apparatus #ff4 #hg4 ,compass4 ,fig4 #da4 ,it is an advantage to have a magnetic needle that is always ready for use4 ,the support is made by driving a pin through the top of a wooden pill-box1 which should be about #a-c_/d in4 in diameter4 ,this gives plenty of room under and around the needle4 ,if the pin be left too long1 it will not be possible to put the bottom and top of the box together when you want to put the compass away4 ,cut the pin off 7,app4 #ce7 at the right length1 so that the magnetic needle can be safely put away in the closed pill-box4 #hh4 ,the ,needle1 that is the short bar magnet1 may be made of watch-spring4 ,as the spring is already quite hard and brittle1 it may be easily broken into desired lengths4 ,it is always better to make #c or #d needles at a time1 as some will swing more easily than others1 and time will be saved in making them4 ,break off #c or #d pieces of thin spring1 each about #a-a_/b in4 long4 ,bend them as in ,fig4 #db4 ,a good dent1 not a hole1 should be made at the center of each to keep them upon the support or pin-point4 ,a center punch1 not too sharp1 is the best tool to use1 but a slight dent may be made with a sharp wire nail1 provided the watch-spring is first annealed or softened4 7,see ,app4 #ba47 ,do not place the spring directly upon iron or steel when making the dent1 as these might injure the point of the punch1 and the dent would not be deep enough4 ,fig4 #db shows a good way to make dents in steel springs4 ,place #b or #c layers of copper or lead between the anvil and the spring4 ,a hammer or hatchet will do for the anvil4 ,as the copper will give easily1 a good dent may be made by striking the punch or nail with a hammer4 ,if the spring has been annealed before denting it1 it should be hardened again 7,app4 #ba7 before magnetizing it1 so that it will retain magnetism well4 7,see ,residual ,magnetism in text-book47 ,illustration3 ,fig4 #db4 #hi4 ,balancing4 ,after a dent has been made1 place the spring upon its support so that the pin-point shall be in the dent4 ,it will1 no doubt1 need balancing4 ,if one end is but slightly heavier than the other1 the spring may be balanced by magnetizing it so that the lighter end shall become a north pole4 ,this will then tend to dip and make the needle swing horizontally4 ,if one end is much heavier than the other1 it should first be magnetized and then balanced by cutting little pieces from the heavier end with tinners' shears1 or by weighting the lighter end with thread1 which may be wound around it4 ,the finished compass-needle should swing very freely1 and should finally come to rest in an ,n and ,s line after vibrating back and forth several times4 ,,apparatus #fg4 #ij4 ,glass-,covered ,compass4 ,a perspective view of this apparatus is shown in the tangent galvanometer4 7,see ,index47 ,the outside band1 ,e1 is made of thick paper1 #a in4 wide1 and with such a diameter that it just fits around the glass4 ,in this model1 the glass from an old alarm-clock was used1 it being #d in4 in diameter4 ,four pasteboard strips were sewed to the inside of the paper band ,e4 ,they were made #g_/h in4 long1 so that the glass1 when resting upon them1 would be near the top of ,e4 ,the needle should be not over #a in4 long1 if it is to be used in the galvanometer4 ,a long slender paper pointer should be stuck to the top of the needle4 ,be careful to have the combined needle and pointer well balanced1 so that it will swing freely4 ,a circle graduated into #e-;degree spaces should be fastened under the needle4 #ia4 ,astatic ,needles4 ,in the magnetic needles so far described1 the pointing-power has been quite strong4 ,by pointing-power we mean the tendency to swing around to the ,n and ,s4 ,in ,app4 #fe the #b needle magnets had considerable pointing-power1 because they helped each other4 ,for some experiments in electricity a magnetic needle is required which has but little pointing-power2 in fact1 to detect the presence of very feeble currents by means of the needle1 the less the pointing-power the better4 ,can you think of any way to arrange ,app4 #fe so that it shall have very little pointing-power8 ,,apparatus #fh4 #ib4 ,astatic ,needle4 ,fig4 #dc4 ,turn one of the needle magnets of ,app4 #fe end for end1 so that the ,n pole of one shall be at the same end of the paper as the ,s pole of the other4 ,you can see that by this arrangement one needle pulls against the other4 ,the magnetic field still remains about the little magnets1 otherwise this combination would be of no value in the construction of galvanometers4 ,the more nearly equal the magnets are in strength1 the less the pointing-power of the combination4 ,illustration3 ,fig4 #dc4 ,illustration3 ,fig4 #dd4 ,,apparatus #fi4 #ic4 ,astatic ,needle4 ,fig4 #dd4 ,magnetize two sewing-needles as equally as possible1 by rubbing them over the pole of a magnet an equal number of times4 ,remove the covering from a piece of fine copper wire1 say ,no4 #cj1 and use the bare wire to wind about the needles1 as shown4 ,be sure to place the poles of the little magnets as in the ,fig4 ,this combination may be supported by a fine thread4 ,it is used for ,astatic ,detectors4 7,see ,index47 ,,chapter ,,viii4 ,,yokes ,,and ,,armatures4 #id4 ,yokes are used to fasten two straight electro-magnets together to form a horseshoe electro-magnet4 ,the reasons for using them should be understood4 ,soft iron should be used for yokes and armatures1 as this is the best conductor of lines of magnetic force4 ,sheet-tin is made of thin iron1 which is coated with tin4 7,try a magnet upon a tin can47 ,this soft iron is very easily handled1 bent1 and punched1 and is very useful for many purposes4 ,the tin from old tomato cans1 cracker boxes1 etc41 is just as good as any4 ,the method of making your yokes will depend entirely upon the tools at your command4 ,several ways are given4 ,y1 ,fig4 #dg1 shows the position of the yoke4 ,,apparatus #gj4 #ie4 ,yoke4 ,for the experimental magnets 7,app4 #hi7 a fairly large yoke is required in order to have the magnets far enough apart4 ,if you have only a nail punch 7,app4 #bf7 with which to make holes in tin1 you will be obliged to punch but one thickness at a time4 7,see method of punching sheet-metal1 ,app4 #bf47 ,cut #e or #f pieces of the tin1 #c-a_/d x #a in4 ,with a center punch 7tools7 or sharp-pointed nail make small dents 7#b in4 apart7 in each piece to mark the places where the holes are to be punched4 ,punch #e_/af in4 holes in each piece4 ,if you do this carefully1 the holes in the different pieces will match1 and the bolts can be pushed or screwed into these4 ,when screwing in the bolt magnets turn them by their heads2 do not pinch the coils1 as this loosens the wire4 ,if you have a good punch1 it is better to make the yoke as in ,app4 #bg1 instead of using separate pieces of tin4 ,,apparatus #ga4 #if4 ,yoke4 ,fig4 #de and #df4 ,cut a strip of tin #f in4 long by #c-a_/d in4 wide4 ,bend one end of it so that it will lap over #c_/d in4 7,fig4 #df72 hammer it down gently1 then bend this over and over until the whole tin is used4 ,the final result will be a flat roll1 #c-a_/d by about #a in4 ,this should be hammered flat4 ,illustration3 ,fig4 #de4 ,illustration3 ,fig4 #df4 ,if you have the tools it is easy to drill two #e_/af holes in this strip4 ,they should be #b in4 apart2 that is1 #b in4 from the center of one to that of the other4 ,start the holes with a center punch4 #ig4 ,if you have no way of drilling the holes1 they must be punched4 7,see ,app4 #bg47 ,this will make the strip bulge out on the underside around the holes4 ,this bur1 or most of it1 should be filed off4 7,see ,app4 #gi for method of filing thin pieces of metal47 ,the resulting yoke may be held firmly to the magnets by the use of #b extra nuts1 as in ,fig4 #fg4 ,remember that the magnets must be held firmly in the yoke4 ,,apparatus #gb4 #ih4 ,yoke4 ,the best way of making this1 of course1 is to cut a piece of bar-iron the right size4 ,for #e_/af bolts the strip of wrought iron should be about #c_/d in4 wide and #c_/af or #a_/d in4 thick4 ,any blacksmith can make this and punch or drill the holes4 ,if taps and dies 7tools7 are at hand1 the hole may be drilled and tapped to fit the thread on the bolt4 ,it is very easy to make good looking apparatus if you have1 and can use1 a whole machine shop full of tools4 ,the lengths of yokes will depend upon the special uses to be made of them4 ,,apparatus #gc4 #ii4 ,yoke4 ,fig4 #dg4 ,the yoke1 ,y1 is a part of a carriage4 ,this can be bought at a blacksmith's4 ,the holes are already in1 but it may require some filing before the nuts of the bolt magnets will fit down firmly4 ,illustration3 ,fig4 #dg4 ,,apparatus #gd4 #ajj4 ,tin ,armatures may be made by bending together #e or #f thicknesses of tin4 ,different forms of tin armatures are shown under telegraph sounders2 these should have a hole punched at the center2 through this is put a screw4 ,the length of the armature will depend upon the distance the magnets are placed apart2 they should be about #c_/d in4 wide4 ,,apparatus #ge4 #aja4 ,nail ,armatures4 ,fig4 #dh4 ,a nail1 ,n1 placed through a piece of wood1 ,a1 will serve as a very simple armature4 ,to make it a little heavier1 if necessary1 a piece of annealed iron wire1 ,w1 may be wound around ,n4 ,care should be taken to have the two parts fairly alike in size and weight4 ,illustration3 ,fig4 #dh4 ,,apparatus #gf4 #ajb4 ,wire ,armatures4 ,fig4 #di4 ,annealed iron wires make good armatures4 ,the short lengths of wire should be straightened 7,see ,app4 #bh7 before binding them into a bundle4 ,they may be held together with thread or paraffine1 until they are in place1 as1 for example1 in a wooden piece1 ,a1 ,fig4 #di4 ,the bundle of wires should fit snugly into the hole made through ,a1 and the wires should be bound together at each end with wire4 ,illustration3 ,fig4 #di4 ,,apparatus #gg4 #ajc4 ,trembling ,armature4 ,fig4 #ej4 ,armatures to be used upon electric bells1 automatic current interrupters1 buzzers1 etc41 may be called trembling armatures4 ,they may be made entirely of sheet-tin4 ,the part1 ,f1 which gives it the spring1 should be about #e_/h in4 wide4 ,its length will depend upon the particular apparatus to be made4 ,it is made of #b thicknesses of thin tin4 ,see ,fig4 #ej for dimensions4 ,the part ,n projects beyond ,l4 ,this may be used to tap against a regulating screw1 or to fasten a hammer on for an electric bell4 ,the part1 ,l1 should have about #d layers of tin on each side of ,f1 and it should pinch ,f tightly4 ,illustration3 ,fig4 #ej4 ,,apparatus #gh4 #ajd4 ,trembling ,armature4 ,fig4 #ea4 ,when very rapid motions are desired in a trembling armature1 ,app4 #gg will be a little heavy4 ,a light and quick-acting armature can be made of sheet-tin4 ,the exact dimensions will depend upon the use to be made of it1 but you will find the following a guide4 ,cut the part1 ,b1 ,e1 out of thin tin4 ,the covers and bottoms of tin cans are thinner than their bodies4 ,the narrow part1 ,b1 should be about #a_/d in4 wide and #b in4 long for a small apparatus1 while ,e may be #c_/d in4 square4 ,through ,e is a screw1 which holds it firmly to a wooden piece1 ,d1 about #c_/d in4 square4 ,the part1 ,e1 can be made longer than its width1 so that two screws can be used2 this will keep ,a from jarring up or down4 ,illustration3 ,fig4 #ea4 ,,apparatus #gi4 ,illustration3 ,fig4 #eb4 #aje4 ,to ,file ,thin ,metal ,strips4 ,fig4 #eb4 ,when sheet-metal is punched by the methods usually employed by boys1 a bulge or bur is made on the underside around the hole4 ,if this bur be hammered to flatten it1 the hole is distorted and made smaller4 ,it is better to file the bur down1 at least part way4 ,it is not convenient to file a piece of thin metal when it is held in a vise4 ,it is better to use either a metal or a wooden clamp1 as shown in ,fig4 #eb2 then the filing can be quickly and easily done4 ,y is the yoke to be filed4 ,it is well to place a piece of metal1 ,i1 between the table and the end of the screw4 ,,apparatus #hj4 #ajf4 ,clamp4 ,fig4 #ec4 ,if you have no clamp to hold metal strips while filing them1 you can put a screw1 ,s1 through one hole to hold the strip down fairly tight4 ,drive a nail1 ,n1 behind the strip4 ,this will keep it from turning while you file the free end4 ,illustration3 ,fig4 #ec4 99 99 99 99 99 ,electro-,magnetic ,armatures4 ,a description of this form of armature is given in the chapter on electric motors4 7,see ,index47 ,,chapter ,,ix4 ,,electro-,,magnets4 #ajg4 ,electro-,magnets are absolutely necessary in the construction of most pieces of electrical apparatus4 ,there are several ways of making them at home4 ,to quickly make a good-looking one1 a winder 7,app4 #ic7 is required4 ,we shall divide our electro-magnets into four parts3 ,core1 washers1 insulation1 and coil4 ,of course1 you know that when a current of electricity passes through a wire1 a magnetic field is produced around the wire4 ,a coil of wire1 or helix1 has a stronger field than a straight wire carrying the same current1 because each turn or convolution adds its field to that of the other turns4 ,by having the center of the helix made of iron1 instead of air1 wood1 or other non-magnetic bodies1 the strength of the magnet is greatly increased4 ,this central core may be fixed permanently in the coil1 or be removable4 ,for our purposes fixed cores are just as good as movable ones1 and the coils are easily wound upon them4 ,when wire is wound by hand from a spool into a coil1 or around a core1 it soon becomes twisted and tangled4 ,make a winder4 ,this will keep the wire straight and save much time4 ,,apparatus #ha4 ,illustration3 ,fig4 #ed4 #ajh4 ,electro-,magnet4 ,fig4 #ed4 ,drive a nail into a board so that it will project about #c_/d of an inch4 ,a soft1 or wrought-iron1 nail is best1 but a short1 thick wire-nail will do4 ,if you do not have a thick nail1 use an iron screw4 ,wind #c or #d layers of insulated copper wire around it1 and fasten the bare ends of the wire down with bent pins4 ,number #bd wire will be found a good size for experimental purposes4 ,touch the wires leading from the battery to the ends of the coil1 and see if the nail will lift pieces of iron4 #aji4 ,note4 ,always leave at least #f in4 of wire at the ends of all coils and windings4 ,this is needed for connections and repairs1 as the wire is liable to get broken at any time around the binding-posts4 #aaj4 ,note4 ,after you have wound wire upon a core or spool1 keep it from untwisting by taking a loop or hitch around it with the wire4 ,fig4 #ee shows how this is done4 ,pull the end of the wire enough to make the loop stay in place4 ,,apparatus #hb4 #aaa4 ,electro-,magnet4 ,fig4 #ef4 ,cut annealed iron wire into pieces1 #c inches long1 straighten them 7,app4 #bh71 and tie them with thread into a bundle about #e_/af in4 in diameter4 ,melted paraffine run in between the wires will hold them in together1 but stout thread will do4 ,wind #c or #e layers of ,no4 #bd insulated copper wire upon the soft iron core4 ,this is useful for simple experiments1 and this idea may be applied to magnets to be used in pieces of apparatus4 ,hold the bundle of wires in a vise1 and file the ends smooth1 before winding on the wire4 ,paraffine should be used to hold the turns of insulated wire together4 ,illustration3 ,fig4 #ee4 ,illustration3 ,fig4 #ef4 ,illustration3 ,fig4 #eg4 ,,apparatus #hc4 #aab4 ,electro-,magnet4 ,fig4 #eg4 ,an electro-magnet with a removable core may be made by winding the wire on a spool4 ,the core is made1 as in ,app4 #hb1 of soft iron wires1 bound together with stout thread4 ,a bolt may be used instead of the wire1 but the wire loses its magnetism much quicker than a soft steel bolt would4 7,study residual magnetism47 ,this magnet is strong enough for many purposes1 but the wire is too far from the core1 on account of the thickness of the wood1 to make it efficient4 ,the wire may be wound on by hand1 but a winder 7,app4 #ic7 will do much better and quicker work4 ,,apparatus #hd4 ,illustration3 ,fig4 #eh4 ,illustration3 ,fig4 #ei4 #aac4 ,horseshoe ,electro-,magnet4 ,fig4 #eh4 ,bend soft iron wires1 and make a bundle of them4 ,if you wish to wind the wire around spools1 the bundle cannot be very large4 ,it will be found best to make the bundle about #c_/h in4 in diameter1 and not to use the spools4 ,strong paper should be wrapped once or twice around the legs of the horseshoe1 and the insulated wire1 say #d layers1 can then be wound directly upon this4 7,see ,sec4 #aae for method of making connection between the coils47 ,it is a little troublesome to wind wire upon a horseshoe like this1 and for ,app4 #he4 ,spools are handier1 because each can be wound separately1 and then be slipped in place4 ,the ends of the horseshoe should be filed smooth4 ,,apparatus #he4 #aad4 ,electro-,magnet4 ,fig4 #ei4 ,an ordinary iron staple is useful as the core of a small magnet4 ,one like this is shown also in ,fig4 #id1 used as a telegraph sounder4 ,it takes some time to wind #d layers of wire on to each leg of the staple1 so be sure to see ,sec4 #aae about the method of winding4 ,in ,fig4 #ei the half-hitches 7,sec4 #aaj7 are not shown4 ,coat the finished coils with paraffine4 #aae4 ,method of ,joining ,coils4 ,fig4 #fj4 ,if ,a and ,b represent the two cores of a horseshoe electro-magnet1 the coils must be joined in such a manner that the current will pass around them in opposite directions1 in order to make them unlike poles4 ,the current is supposed to pass around ,b1 ,fig4 #fj1 in the direction taken by clock hands1 while it passes around ,a in an anti-clockwise direction4 ,the inside ends1 ,sec4 #abc1 of the coils may be twisted together1 or fastened under a screw-head4 ,in ,fig4 #fj one coil is shown to be a continuation of the other4 ,illustration3 ,fig4 #fj4 ,,apparatus #hf4 ,illustration3 ,fig4 #fa4 ,illustration3 ,fig4 #fb4 #aaf4 ,electro-,magnet4 ,fig4 #fa4 ,wind #f layers of ,no4 #bd or #be insulated copper wire around a #e_/af machine-bolt that is #b-a_/b in4 long4 ,fig4 #fa shows one method of holding the bolt solidly in an upright position1 so that magnetic figures can be easily made and the magnet studied4 ,two nuts are used1 the lower one being counter-sunk1 so that the base will stand flat upon the table4 ,this bolt is shown without washers 7,sec4 #aai71 and will do fairly well to show the action of electro-magnets4 ,the ends of the wire should always be left #e or #f in4 long1 and be led out to binding-posts4 ,the coil may be held in place1 and its turns kept from untwisting by coating it with paraffine4 ,the base may be of any desired size4 ,,apparatus #hg4 #aag4 ,electro-,magnet ,core4 ,fig4 #fb4 ,this shows another method of fastening a bolt-core in an upright position4 ,this is done without the use of two nuts4 ,a strip of tin1 ,t1 #a in4 wide1 is punched and slipped onto the #e_/af bolt before the nut is screwed on and the coil wound4 ,this is fastened to the base by screws1 ,s4 ,washers1 ,w1 are here shown4 7,see ,sec4 #aai for washers47 ,,apparatus #hh4 #aah4 ,bolt ,electro-,magnets are easy to make1 according to the directions given1 and they are1 when finished1 more like the regular purchased magnets than any of the other forms described4 ,with proper batteries 7,app4 #c1 #d1 etc417 they can be used for a great variety of purposes1 as will be seen4 ,there are many forms of bolts in the market1 but the ordinary machine bolt1 #e_/af in4 in diameter1 is best for our purposes4 ,the ones #b and #b-a_/b in4 long are used4 #aai4 ,washers or coil ends are used on the bolt magnets so that considerable wire can be wound on closely and evenly4 ,these are made out of thick pasteboard1 which cuts smoother if it has been soaked in melted paraffine4 ,unless you know how1 you will find it a hard job to make the hole in the exact center of the washer4 ,the method of easily making washers is illustrated in ,fig4 #fc4 ,first place a spool 7the end of which is #g_/h or #a in4 in diameter7 upon the table1 and lay the pasteboard upon this4 ,push a large round nail through the pasteboard into the hole in the spool4 ,the nail should be nearly as large as the hole4 ,use the large nail as a handle1 and with the shears cut around the edge of the spool end4 ,cut the washer as round as possible1 and be careful not to cut into the spool4 ,the holes in the washers will be a little smaller than the #e_/af bolt4 ,this will make the washers hold tightly to the bolt when you force them on4 ,fig4 #fd shows the bolt-core1 with the washers in place4 ,if you cannot get a large nail1 a lead-pencil1 or sharpened dowel1 will do to force through the pasteboard4 ,illustration3 ,fig4 #fc4 #abj4 ,insulation of ,cores4 ,while the covering on the wire would probably be all that is necessary to thoroughly insulate the coil from the core1 it is better to wind a layer or two of paraffine paper around the bolt 7,fig4 #fe7 before winding4 ,illustration3 ,fig4 #fd4 ,illustration3 ,fig4 #fe4 ,illustration3 ,fig4 #fe-a_/b4 #aba4 ,the ,coils of wire to be used upon the bolt-cores should be put on with the winder 7,app4 #ic74 ,for all ordinary purposes ,no4 #bd or #be single or double cotton covered copper wire will do4 ,it is better to put on an even number of layers4 ,the winding 7,see ,fig4 #gj7 begins at the nut-end of the bolt1 and by using #f or #h layers of wire1 instead of #e or #g1 both coil ends will be at the same end of the bolt4 #abb4 ,method of ,winding the ,coils4 ,the winders used for bolt magnets are described in ,app4 #ia1 etc4 ,we shall suppose that the washer1 ,w1 ,fig4 #gj1 and the insulation1 ,i1 are upon the bolt before screwing it into the winder-nut1 ,w ,n4 ,make a pinhole1 ,p ,h1 in the right-hand washer1 as near the bolt-nut1 ,b ,n1 as possible4 ,stick about #f in4 of the wire through ,p ,h1 and wind this end around ,w ,n1 as shown1 to hold the wire4 ,the supply of wire should be upon a spool slipped onto some stationary rod 7,app4 #bc71 so that you can give your entire attention to winding4 ,begin to turn the winder slowly at first4 ,turn the handle towards you when it is at the bottom1 as in ,fig4 #gj2 that is1 if you look at it from the side1 turn the handle clockwise4 ,let the wire slip through your left hand as the turns are made1 and guide it so that the turns will be close together4 ,if they go on crooked1 unwind at once1 then rewind properly4 ,you can guide the wire best by holding your left hand about #h or #aj inches from the bolt4 ,as soon as you reach the left side or head end of the bolt1 feed the wire towards the right4 ,if at any time the layers become rough on account of one turn slipping down between turns of the previous layer1 fasten a piece of paraffine paper around the coil as soon as the imperfect layer is completed4 ,wind on #h layers1 and count the number of turns in one or two of them1 so that you can tell about how many turns in all you have around the core4 ,make a half-hitch 7see ,sec4 #aaj7 with the wire when the last layer is finished1 to keep it from unwinding1 and leave a #f in4 end4 ,the coil should be protected by fastening around it a piece of dark-colored stiff paper4 ,paraffine paper is good for this purpose4 ,with a little practice you will be able to rapidly and neatly wind on the wire4 ,the winder-nut1 ,w ,n1 must hold the bolt solidly to keep it from wobbling4 #abc4 ,we shall call the starting end of the wire which passes through ,p ,h1 the inside end1 and the end of the last layer the outside end4 ,this can pass out between the washer and the paper covering4 ,,apparatus #hi4 #abd4 ,experimental ,horseshoe ,electro-,magnet4 ,fig4 #ff4 ,among the most useful pieces of apparatus for home use1 is a good horseshoe electro-magnet4 ,fig4 #ff shows a very convenient and practical form4 ,with this1 alone1 can be shown all the principles of telegraph sounders1 electric bells1 etc4 ,they are excellent for making magnetic figures 7,see text-book74 ,you are supposed to be looking down on the ,app4 in ,fig4 #ff4 ,the bolts are #b in4 apart center to center4 ,illustration3 ,fig4 #ff4 ,the bolt magnets are fully described in ,app4 #hh2 the binding-posts1 as ,app4 #df2 the yoke1 as ,app4 #ga2 the method of fastening to the base1 as ,app4 #ij2 the base is #e x #d x #g_/h in42 the magnets are made of #e_/af bolts1 #b-a_/b in4 long4 #abe4 ,to ,join the ,coils1 fasten the two inside ends 7,sec4#abc7 of the wire to a middle binding-post1 and carry the outside ends to the two outside binding-posts4 ,in this way you can use either magnet alone1 if desired 7,see experiments in text-book71 or change the polarity at will by changing the connections4 7,see ,sec4 #aae and #abc47 ,,apparatus #ij4 #abf4 ,fastenings for ,electro-,magnet4 ,fig4 #fg4 ,when both electro-magnets are to be permanently fastened to a base1 especially if tin yokes are to be used1 as in ,app4 #hi1 it is best to use a nut on each side of the yoke4 ,it is important to have a perfectly tight connection between bolt and yoke4 ,several ways of fastening the bolts and yokes are shown2 but it will be found best to cut holes in the base for the lower nuts1 and to screw the yoke directly to the base4 ,this makes a solid and pleasing arrangement4 ,for the experimental magnets 7,app4 #hi7 make the yoke #c-a_/d in4 long1 and place the magnets #b in4 apart center to center4 ,illustration3 ,fig4 #fg4 ,,chapter ,x4 ,,wire ,,winding ,,apparatus4 ,,apparatus #ia4 #abg4 ,winder4 ,fig4 #fh4 ,in case you do not have any means of making a smooth hole for the bearings of the winders of ,app4 #ic and #id1 you can use a spool for the purpose4 ,b is the end of a piece of board about #a in4 thick1 #c in4 wide1 and #f in4 long4 ,the spool1 ,a1 is laid upon this1 a band of tin1 ,t1 being used to hold it down firmly upon the end of ,b4 ,screws1 ,s1 hold ,t down4 ,a stove-bolt axle 7,see ,app4 #ic7 is shown1 and by using a nut1 as explained1 bolt magnets may be wound4 ,by using the handle of ,app4 #ib1 this arrangement can be used to wind almost anything1 when used together with the attachment of ,app4 #ie4 ,illustration3 ,fig4 #fh4 ,illustration3 ,fig4 #fi4 ,,apparatus #ib4 #abh4 ,crank for ,winders1 etc4 ,fig4 #fi4 ,this form of crank or handle will be found easier to make than the one in which a wire is expanded in the slot of a stove bolt1 and it can be used for many purposes1 especially where dowels serve as axles4 ,wrap a little paper around the end of the #a_/d in4 dowel1 ,d1 and push it part way into the spool1 ,a1 then put in a set-screw1 ,s1 to keep ,a from twisting upon ,d4 ,the straight end of the wire1 ,h1 should be put into a hole1 ,b1 and another set-screw used to fasten it into the spool4 ,,apparatus #ic4 #abi4 ,winder4 ,fig4 #gj4 ,for winding bolt magnets1 this form of winder is very useful4 ,it consists of a stove bolt1 ,s ,b1 #b in4 long 7total length7 and #e_/af in4 in diameter4 ,illustration3 ,fig4 #gj4 #acj4 ,handle or ,crank1 ,h1 is made of a stout wire1 #d in4 long1 bent at the lower end as shown4 ,h is fastened into the slot of ,s ,b4 ,to do this the end of ,h is hammered flat until it will just slip into the slot4 ,it may be soldered there1 or be made to fit by expanding it so that it will press out against the sides of the slot4 ,to do this1 place ,s ,b into a hole in an anvil1 or hold it in a vise1 being careful not to injure the thread4 ,place the flattened end of ,h in the slot1 and strike it on top so that it will expand and be pinched in the slot2 but do not pound it so hard that you split the bolt head4 ,three or four good center-punch dents upon the wire over the slot will help to expand it4 #aca4 ,the ,framework is made of wood1 the dimensions being shown in ,fig4 #gj4 ,a #e_/af hole should be made for ,s ,b1 the thread of which will stick through about #a_/d in4 so that the winder-nut1 ,w ,n1 can be turned onto it4 ,w ,n should be on but #b or #c threads of ,s ,b4 ,this will leave part of it for the thread of the bolt magnet1 and when this and ,s ,b meet in center of ,w ,n they will bind against each other and hold the bolt tight4 ,the winder can be nailed or screwed at ,s to the edge of a table or held in a vise4 ,,apparatus #id4 ,illustration3 ,fig4 #ga4 #acb4 ,winder4 ,fig4 #ga4 ,this shows a winder that can be used for several purposes by arranging different attachments4 ,it will be first described as shown in ,fig4 #ga1 where it is being used to wind a bolt magnet4 ,the principal dimensions are shown in the figure4 ,it is made of #c_/d in4 wood about #c in4 wide1 the two outer parts ,x and ,z being nailed to the center one1 ,y1 which is to be held in a vise1 or fastened to the edge of a table4 ,a #e_/af in4 hole should be made through the upper part ,x and ,z at one side of the center1 so that a long #e_/af bolt can be put through and used as described in ,app4 #ic1 if desired4 ,a smaller hole1 #a_/d in41 should be made on the other side of the center for a #a_/d in4 dowel4 ,the dowel1 ,d1 is shown1 and this size is a little smaller than the hole in ordinary spools1 shown at ,a and ,b4 ,one-quarter in4 dowels can be made to fit fairly tight into the holes by wrapping paper around them4 ,five-sixteenth bolts can be screwed into the spool holes1 shown by the bolt magnet in ,fig4 #ga4 ,to firmly hold a spool from twisting around upon the dowel-axle1 a set-screw1 ,s ,s1 is needed4 ,these are small screws1 say #e_/h in4 long1 ,no4 #e4 ,a small hole should be made into the spool before forcing in the screw4 7,app4 #be47 ,the spools ,a and ,b are fastened in this way1 by set-screws1 to ,d4 ,the handle1 ,h1 is made as in ,app4 #ic1 in this case a short stove bolt1 ,s ,b1 being used and screwed into ,b4 ,fig4 #fi shows a very simple form of handle for all such purposes1 which may be used instead of the one here shown4 ,the details of winding on the wire are given under ,app4 #hh4 ,,apparatus #ie4 #acc4 ,attachment for ,winder4 ,fig4 #gb4 ,by using this addition to ,app4 #ic or #id1 almost any ordinary kind of windings can be made4 ,the wooden block1 ,a1 may be about #b in4 square and #g_/h in4 thick4 ,a set-screw1 ,s1 binds it to the dowel-axle1 ,d1 which is made to turn by one of the forms of cranks given1 and which is held in one of the frameworks4 ,windings like that shown in ,app4 #aab1 ,fig4 #he1 can easily be done with this1 the upright part1 with the two spools1 being screwed right to ,a of ,fig4 #gb4 ,illustration3 ,fig4 #gb4 ,,chapter ,,xi4 ,,induction ,,coils ,,and ,,their ,,attachments4 #acd4 ,induction ,coils1 or shocking coils1 are rather expensive to buy1 and altogether too complicated for boys to make by the methods usually given in books4 ,the method here given is simple1 the materials are cheap1 and if you make them according to directions1 you will have an apparatus that will1 be able to make your friends dance to a rather lively tune4 ,the amount of shock can be regulated perfectly 7,app4 #ajc74 ,winding4 ,full instructions have been given for making bolt magnets 7,app4 #hh74 ,the winding of our induction coils is done in the same way by the same winder as the bolt magnets 7,app4 #ic71 or by hand4 ,you will find it a very tiresome and troublesome job1 however1 to wind on #ab or #ae hundred turns of fine wire by hand4 ,make a winder4 ,several different forms of induction coils are shown4 ,the coil is the most important feature1 however1 and we shall consider that separately4 ,when you understand the construction of one coil1 you can readily apply this to the different forms4 ,some form of contact breaker1 or current interrupter1 is needed also4 ,these will be treated by themselves4 ,the connections will be discussed under each form of apparatus4 ,,apparatus #if4 #ace4 ,induction ,coil2 ,construction of ,coil ,proper4 ,figs4 #gc1 #gd4 ,an induction coil is a peculiar and wonderful apparatus4 ,there are at least two coils to each one4 ,these are both wound upon the same core4 ,they are made of different sizes of wire1 are wound separately1 and the strangest thing of all is1 that these two coils are not connected with each other in any way4 ,if they were not thoroughly insulated from each other1 the coil would be of no value4 7,study induction47 ,the winding of the two coils is done as explained in ,app4 #hh4 ,illustration3 ,fig4 #gc4 ,illustration3 ,fig4 #gd4 #acf4 ,the ,core is made of a #e_/af machine bolt1 #b-a_/b in4 long4 ,leave but #b or #c threads at the end1 just enough to fasten it solidly to the winder 7,app4 #ic74 ,the washers should be about #a-e_/h in4 apart inside1 and they should be made around a spool 7,sec4 #aai7 that is fully #a in4 in diameter4 #acg4 ,the ,inside or ,primary ,coil could be wound directly upon the bolt2 but it is much better to cover the bolt with one or two thicknesses of paraffined paper1 ,i 7,index71 as shown4 ,a pinhole1 ,h1 in the washer is for the inside end 7see ,sec4 #abc7 of the primary coil1 and the hole1 ,j1 is for the outside end of it4 ,the primary coil should be made of #c layers of wire1 which should be coarser than that used for the secondary coil4 ,for our purposes it is best not to use a wire coarser than ,no4 #bj1 and not finer than ,no4 #bd4 ,use ,no4 #bd insulated copper wire if you are going to connect ordinary batteries with it4 ,a bichromate cell 7,app4 #d7 is best4 ,put about #f in4 7see ,sec4 #aji7 of wire through ,h1 and with ,app4 #ic wind on #c layers of say ,no4 #bd wire4 ,there being an odd number of layers1 the winding will stop at the head end of the bolt1 where a half hitch 7see ,sec4 #aaj7 should be taken before passing the wire through the hole1 ,j4 ,cut the wire #f in4 from the hole4 ,write down the number of turns of wire to each layer and the total number of turns4 ,you now have a #c-layer coil1 and a current passed through this will magnetize the bolt2 you have--so far--merely an electro-magnet4 ,cover the primary coil with #b layers of paraffined paper1 ,k 7,fig4 #gd71 and put some paraffine between the edges of ,k and the washers1 so that the wire of the secondary coil cannot possibly come in contact with that already wound on4 #ach4 ,the ,secondary ,coil should be made of a large number of turns of fine wire4 ,do not use anything coarser than ,no4 #cj4 ,this is a good size1 as finer wire is very easily broken by unskilled hands4 ,for the size of bolt mentioned put on #ac layers4 ,there will be about #ajj turns to each layer1 making a total of about #a1cjj turns of ,no4 #cj wire4 ,write down the total number of turns in your coil4 ,to start the secondary coil1 make a pinhole1 ,l1 just outside of the insulation1 ,k1 of the primary coil4 ,put #f in4 of wire through this1 wind the end around the nut 7,app4 #ic1 ,fig4 #gj71 and wind on as evenly as possible #ac layers4 ,if the layers become rough1 it is well to put a band of paper around after each #c or #d4 ,when you have finished take a half hitch 7,sec4 #aaj71 and leave a #f-;in4 length free4 ,cover the secondary coil with strong paper4 ,this coil may be used on any of the forms of shockers given4 ,,apparatus #ig4 #aci4 ,induction ,coil4 ,fig4 #ge4 ,the base is made of a piece of board1 #g x #e x #g_/h in4 ,the locations of the different parts are shown in the figure4 ,the coil is explained in detail in ,app4 #if4 ,it is fastened to the base by a thin copper strip1 #d1 which is bent over the coil and held down by screws1 #c4 ,if you haven't any copper you can use a narrow strip of tin4 ,do not use a wide piece of tin or iron4 ,the coil may be held down firmly by strong twine placed around each end of it4 ,the twine should pass through holes in the base1 and be tied on the underside of the base4 ,the binding-posts are like ,app4 #df4 #adj4 ,the ,current ,interrupter consists of a tin or copper strip1 ,r1 #f in4 long and #a_/b or #c_/d in4 wide4 ,at one end of ,r is a screw1 ,s1 which is used as a binding-post for the outside end1 ,b1 of the primary coil4 7,see ,sec4 #acg47 ,along the center line of the strip1 ,r1 are driven #a-;in4 wire nails1 ,q4 ,these are placed #a_/d in4 apart1 and they should go into the wood enough only to make them solid4 7,see ,fig4 #ha47 ,do not drive them in so far that they will split the base4 ,a stout wire1 ,p1 fastened at one end only completes the interrupter4 ,illustration3 ,fig4 #ge4 #ada4 ,the ,connections4 ,the binding-posts1 ,w and ,x1 should be connected with the wires leading from a battery4 ,use the bichromate batteries of ,app4 #c or #d4 ,a dry battery will do4 ,if the current enters at ,x1 it will pass around the primary coil 7,sec4 #acg7 and out through ,b into ,r4 ,it can go no farther until the free end of ,p is made to touch ,r1 or one of the nails1 ,q1 when the circuit will be closed4 ,the current will fly around and around through the battery1 primary coil1 and interrupter as long as the end of ,p touches a nail4 ,the battery current does not get into the secondary coil at all4 ,you can see1 then1 that the primary circuit1 that is1 the one passing through the coarse wire1 will be rapidly opened and closed by bumping the free end of ,p along upon the row of nails4 ,the wires1 ,c and ,d1 coming from the secondary coil 7,sec4 #ach7 are in connection with ,y and ,z1 to which are connected the wires leading from the handles 7,app4 #aja7 held by the person receiving the shock4 #adb4 ,to use the coil1 arrange as explained4 ,let your friend hold the handles 7,app4 #aja7 while you scrape the end of ,p back and forth along the row of nails4 ,for those who cannot stand much of a shock1 use a regulator 7,app4 #ajc74 ,,apparatus #ih4 #adc4 ,induction ,coil4 ,fig4 #gf4 ,in case you wish to make the interrupter as a separate piece of apparatus1 as ,app4 #ajd1 this arrangement will be found good4 ,the base is #e x #d x #g_/h in4 ,the coil is explained in ,app4 #if1 and the methods of holding it to the base are given in ,app4 #ig4 ,the binding-posts are like ,app4 #df4 ,illustration3 ,fig4 #gf4 ,the ,connections4 ,we shall suppose that you have the interrupter of ,app4 #ajd1 ,fig4 #ha4 ,the ends of the primary coil 7,sec4 #acg7 are fastened under the screws of ,x and ,w1 and those of the secondary coil to ,y and ,z4 ,connect one battery wire with ,x and the other battery wire to the interrupter at ,s1 ,fig4 #ha4 ,fasten the end of a stout wire to ,w1 and leave the other end free to scrape along on the nails1 ,q1 of the interrupter4 ,this will then open and close the primary circuit4 ,the handles 7,app4 #aja7 are connected with ,y and ,z1 as explained in ,app4 #ig4 ,use the battery of ,app4 #c or #d4 ,,apparatus #ii4 #add4 ,induction ,coil4 ,fig4 #gg4 ,if you wish to fasten your coil in an upright position the apparatus will look like ,fig4 #gg4 ,the base may be #e x #d x #g_/h in4 ,the binding-posts are like ,app4 #df4 ,the coil is made as explained in ,app4 #if2 but to have all the ends of the coils come out at the bottom1 as shown1 an even number of layers of wire will be necessary4 ,it will be just as well to have an odd number of layers as before1 and to bring the wire ends down the side of the coil4 ,the coil is fastened to the base with screws1 ,s1 passing through a tin strip1 ,t1 which has a hole punched for the bolt4 ,t is squeezed between the regular nut on the bolt and an extra one on the underside of it4 ,see ,fig4 #fa for suggestion of another method of holding bolts upright4 ,the connections should be made with an outside interrupter1 battery1 and handles1 as explained in ,app4 #ih4 ,illustration3 ,fig4 #gg4 ,,apparatus #ajj4 #ade4 ,induction ,coil4 ,fig4 #gh1 #gh-;,a1 #gh-;,b4 ,in case you wish to make a larger coil than those already described1 the following will be found practical4 ,it is made in the same general way as before1 an automatic interrupter1 however1 being added4 ,the ,core is a machine-bolt1 #d-a_/b in4 long and #e_/af in4 in diameter4 ,you may use a carriage-bolt of the same dimensions1 if you file away the square shoulder at the head end1 so that it will be the same size as the body of the bolt4 ,paste a piece of thick paper upon the head1 so that ,a will strike the paper instead of the iron4 ,the ,washers should be made around a spool that is fully #a in4 in diameter4 7,see ,sec4 #aai47 ,the core should be insulated with paraffine paper before winding on the primary coil4 7,see ,app4 #hh47 ,the washers are #c-g_/h in4 apart1 inside4 ,the winding of the coils should be done with ,app4 #ic1 or some other winder4 ,the winder-nut1 ,w ,n1 ,fig4 #gj1 must hold the long core perfectly tight1 to avoid wobbling4 ,the base is #h x #e x #g_/h in4 ,the different parts are placed as shown4 ,the coil is fastened to the base as in ,app4 #ig4 ,for binding-posts see ,app4 #df4 ,illustration3 ,fig4 #gh4 #adf4 ,the ,primary ,coil 7,sec4 #acg7 is made by winding #c layers of ,no4 #bd insulated copper wire upon the insulated core4 ,one end1 #f1 is fastened to ,w 7,see ,sec4 #aji71 and the other end1 #e1 is held under the screw-head1 ,r4 ,wind at least two layers of paraffined paper around this coil before winding on the secondary coil4 #adg4 ,the ,secondary ,coil 7,sec4 #ach7 is made of ,no4 #cj insulated copper wire1 there being #aa or #ac layers1 each having about #bjj turns4 ,this makes1 in all1 about #b1ejj turns of fine wire4 ,if your winder works properly and the long core is strongly held by the winder-nut1 you will have no trouble1 although it takes a little time to wind on so many turns4 ,the ends of this coil1 #g and #h1 are fastened to ,y and ,z1 which are made like ,app4 #df4 ,it will be found best to wrap a piece of thin paper around the coil after every #c or #d layers are wound on4 ,this makes better insulation1 and makes the winding easier4 ,protect the coil by covering it with thick paper4 ,the whole coil1 when completed1 is about #a in4 in diameter4 ,illustration3 ,fig4 #gh-;,a4 ,illustration3 ,fig4 #gh-;,b4 #adh4 ,the ,automatic ,interrupter 7,figs4 #gh1 #gh-;,a1 #gh-;,b7 consists of several parts4 ,b1 ,e1 ,c is a piece of thin tin1 all in one piece4 ,the part1 ,b1 is #a_/d in4 wide and #a-c_/d in4 long4 ,its exact height above the base will depend upon the diameter of your coil4 ,for the coil here described1 #a in4 in diameter1 the top edge of ,b is #e_/h in4 above the base4 ,see ,fig4 #gh-;,b for shape of ,b1 ,e1 ,c before bending it1 and for its dimensions4 ,around the end of ,b are tightly wound several turns of tin1 making the armature or hammer1 ,a1 which should not be allowed to strike against the head of the bolt on account of residual magnetism4 7,see text-book47 ,a piece of thick paper pasted on the head for ,a to strike upon is best4 ,a will probably not get near enough to the bolt to strike it1 but this will depend upon how you arrange the parts4 ,d is a wooden piece1 #a in4 high1 #a in4 wide1 and #c_/h or #a_/b in4 thick2 it is nailed to the base4 ,through its center is a hole for the screw-eye1 ,s ,i1 which is the regulating-screw4 ,f is a piece of copper1 brass1 or tin1 #e_/h x #a-c_/d in4 ,it is held to the base by the screw1 ,s1 and is bent so that it presses tightly against ,s ,i4 ,through ,f is a screw1 ,r1 to hold one end of the primary coil4 #adi4 ,adjustment and ,use4 ,the battery wires should be joined to ,w and ,x1 and the handles to the secondary coil at ,y and ,z1 unless a regulator 7,app4 #ajc7 is used4 ,let us consider the primary circuit4 ,if the current enters at ,w it will pass through the primary coil and out at ,x1 after going through #e1 ,r1 ,f1 ,s ,i1 ,b1 ,e1 and ,c4 ,the instant that the current passes1 the bolt becomes magnetized2 this attracts ,a1 which pulls ,b away from the end of ,s ,i1 thus automatically opening the circuit4 ,b at once springs back to its former position against ,s ,i1 as ,a is no longer attracted2 the circuit is closed and the operation is rapidly repeated4 ,b should press gently against ,s ,i1 which must be screwed back and forth1 until the best results are obtained4 ,while not in use ,a should be about #a_/h or #c_/af in4 from the bolt-head4 ,the armature1 ,a1 should vibrate back and forth very rapidly4 ,if this coil gives too much shock with one cell of ,app4 #c or #d1 put a regulator 7,app4 #ajc7 between ,y and one of the handles 7,app4 #aja74 ,,apparatus #aja4 #aej4 ,handles for ,shocking ,coils4 ,fig4 #gi4 ,ordinary sheet-tin makes good handles4 ,cut #b pieces1 each #f x #d-a_/b in41 and connect a stout copper wire to each4 ,this may be done as suggested in ,fig4 #gi1 where the tin laps tightly over the bare end of the wire1 or by punching #d or #e holes through the tin1 and weaving the wire back and forth through the holes4 ,be sure that a tight and permanent connection is made4 ,the wires joined to the handles should be about ,no4 #bj1 and be #d or #e feet long4 ,roll the tin into a cylinder1 so that the connection will be on the inside4 ,illustration3 ,fig4 #gi4 ,,apparatus #ajb4 #aea4 ,handles for ,shocking ,coils4 ,very neat handles may be made from #d-;in4 lengths of brass tubing that is about #c_/d in4 in diameter4 ,the wires leading to the coil may be soldered to the handles4 ,,apparatus #ajc4 #aeb4 ,current ,regulator for ,induction ,coils4 ,fig4 #hj4 ,if your coil gives too much of a shock with one cell of ,app4 #c or #d1 you can pull the carbon and zinc partly out of the solution to weaken the shock1 or you can use a water regulator4 ,t is an ordinary tin tomato can nearly filled with water1 ,l is a lamp chimney4 ,one wire1 ,a1 is fastened to ,t directly1 or by a spring binding-post4 ,the other wire1 ,b1 is fastened to a piece of copper1 ,c1 which may be raised or lowered inside of ,l4 ,d is a piece of pasteboard with a small hole in its center4 #aec4 ,use4 ,if this apparatus be put anywhere in the primary circuit1 the amount of shock can be regulated by raising or lowering ,c4 ,when ,c is raised1 the current has to pass through a longer column of water than it does when ,c is near the bottom of ,l4 ,when ,c touches ,t1 the current passes easily4 ,if it were not for the chimney1 the current would pass to the sides of ,t4 ,illustration3 ,fig4 #hj4 ,,chapter ,,xii4 ,,contact ,,breakers ,,and ,,current ,,interrupters4 #aed4 ,contact ,breakers2 ,current ,interrupters4 ,it is often necessary to make and break the electric current at frequent intervals4 ,this can be done by an ordinary key 7,app4 #aah7 by rapidly raising and lowering it4 ,it is more convenient1 however1 to use some other form of apparatus4 ,the current may be interrupted automatically2 that is1 it may be made to do the work itself 7,app4 #ajj71 or each make and break in it may be governed by the student4 ,,apparatus #ajd4 ,illustration3 ,fig4 #ha4 #aee4 ,interrupter4 ,fig4 #ha4 ,the body of this consists of a strip of wood1 #f or #g in4 long1 #a-a_/b in4 wide1 and #g_/h in4 thick4 ,cut a strip of tin #a in4 wide and long enough to bend down over the ends of the wood4 ,fasten the tin to the wood with small wire nails1 driving the nails into the ends as well as into the top of the strip4 ,make a center line along the tin as a guide1 and then drive #a-;in4 wire nails through the tin into the wood1 so that they will make a row the length of the wood1 and stand about #a_/d in4 apart4 ,on one end make a hole through the tin1 and put in a screw-eye binding-post 7,app4 #de74 ,it is evident that if a wire from one pole of a battery be connected with the binding-post1 it will also be electrically connected with the tin strip and nails4 ,by touching the wire from the other battery-pole to the tin or to any nail1 the circuit will be closed4 ,if this last-mentioned wire be drawn along entirely above the tin1 so that its end can bump along from one nail to another1 you can see that the current will be closed every time a nail is touched1 and be opened every time it jumps through the air4 ,this apparatus can be connected with shocking coils1 induction apparatus1 etc41 etc4 ,its use will be more clearly shown in connection with such apparatus4 ,,apparatus #aje4 ,illustration3 ,fig4 #hb4 #aef4 ,interrupter4 ,fig4 #hb4 ,the nails in this apparatus are placed in a circle about #d in4 in diameter4 ,they are electrically connected to each other by a bare copper wire1 which is wound around each nail several times1 and then led out to one of the binding-posts4 ,in the center of the circle is a nail1 or screw1 which is connected by a wire to the other binding-post1 care being taken not to allow the two wires to touch each other4 ,around the central screw is wound one end of a stout wire1 the other end of which reaches out from the screw far enough to touch the nails4 ,when this stout wire touches any nail1 a current entering one binding-post can pass through nails1 screw1 etc41 and out at the other binding-post4 ,when the end of the stout wire is between two nails1 the current cannot flow4 ,by placing the finger against this stout wire and turning it around rapidly1 the current can be interrupted as desired4 ,the base should be about #e x #f x #g_/h in4 ,,apparatus #ajf4 #aeg4 ,interrupter4 ,wind the end of the wire from one pole of the battery around the handle of the file4 ,scrape the other wire along the rough file4 ,as it jumps from one ridge to another the current will be rapidly interrupted4 ,,apparatus #ajg4 #aeh4 ,interrupter4 ,hold the end of the wire from one pole of a battery upon a saw-blade4 ,draw the other wire along over the teeth of the saw4 ,as the wire jumps from one tooth to the next the current will be broken4 ,,apparatus #ajh4 #aei4 ,automatic ,interrupter4 ,an ordinary electric bell1 or buzzer1 may be used as an interrupter4 ,every time the vibrating armature swings1 the circuit is opened4 ,the combination of a battery1 induction coil1 and electric bell makes a very good outfit for medical purposes4 ,the automatic interrupter used on ,app4 #ajj should be studied4 ,,chapter ,,xiii4 ,,current ,,detectors ,,and ,,galvanometers4 #afj4 ,current ,detectors2 ,galvanometers4 ,when a wire carrying a current of sufficient strength is properly brought near a magnetic needle1 the latter will be deflected from its ,n and ,s line4 ,the conducting wire has a magnetic field while the current passes through it1 and this gives the wire the power to act upon a magnetic needle just as another magnet would4 ,the action of detectors1 etc41 depends upon this fact2 and1 strange to say1 the magnetic field about the wire disappears the instant the current ceases to pass4 ,the combination1 thus1 of a coil of wire and a magnetic needle1 properly arranged1 makes an instrument with which the presence of electricity can be detected4 ,when the strength of a current is to be measured1 or the strengths of two currents are to be compared1 the apparatus is called a galvanometer4 ,the method of making these pieces of apparatus will depend upon the strength of current to be tested or measured4 ,,apparatus #aji4 #afa4 ,current ,detector4 ,figs4 #ch and #dj show magnetic needles4 ,these may be used to detect a current by holding the conducting wire near them and parallel to the needle4 ,this form is not sensitive to weak currents4 ,the delicacy of the apparatus is increased by allowing the wire to pass above and below the needle several times as in the next apparatus4 ,,apparatus #aaj4 #afb4 ,current ,detector4 ,fig4 #hc consists1 like all detectors1 of a coil and a magnetic needle4 ,the other parts are merely for convenience4 ,each turn of the coil helps to move the needle when the current passes4 ,illustration3 ,fig4 #hc4 #afc4 ,the ,coil is made by winding #aj feet of ,no4 #cj insulated copper wire around the end of a broom-handle or other cylinder that is about #a inch in diameter4 ,this length of wire makes about #cb turns around such a cylinder4 ,the exact length of wire for this makes no difference4 ,after winding it1 the coil should be slipped from the handle1 being careful to hold it in such a way that it cannot uncoil and spring away from you4 ,tie the coil together with thread1 in #c or #d places1 to keep it in shape1 and leave #e or #f in4 of wire free at each end1 so that connections can be made with other pieces of apparatus4 ,after this is done press the coil into the shape shown1 ,fig4 #hc4 ,this brings the wire near the needle and allows a longer needle to be used4 ,the coil may be fastened to a pasteboard base4 ,to do this1 prick #d holes in the base near the ends of the oval coil1 and pass a strong thread through these with the aid of a sewing-needle4 ,tie the thread on the underside of the base at each end4 ,if this is well done1 the coil will be held firmly in an upright position4 ,paraffine may be used instead of the thread4 ,the ends of the wire should be made bare1 and these may be sewed to the base to keep them in place4 #afd4 ,the ,needle may be supported upon a pin or needle-point4 ,the piece of needle should be stuck through a cork which has a slot cut into its underside1 so that it will straddle the lower part of the coil4 ,the height of the needle-point should be fixed so that the horizontal ends of the magnetic needle will be near the axis of the coil1 that is1 along its central line4 #afe4 ,to ,use the ,detector1 turn its base around until the coil is in the ,n and ,s line--that is1 until the magnetic needle is parallel to the length of the coil and wholly inside of it4 ,touch the ends of the coil with the two ends of the wire1 which is supposed to carry a current4 ,the needle will fly around until it is nearly perpendicular to its former position1 if the current is strong enough4 ,,apparatus #aaa4 ,illustration3 ,fig4 #hd4 #aff4 ,current ,detector4 ,fig4 #hd4 ,to make a more substantial detector than ,app4 #aaj1 the coil should be fastened to a wooden base4 ,the coil may be made of #aj ft4 ,no4 #cj wire1 as explained4 7,sec4 #afc47 ,a hole should be made in the base with a small awl or with a hot wire1 and into this should be set a pin1 head down4 ,the hole need not be larger than the pin-head1 and when you find out how high the pin-point should be above the base1 the pin may be fastened in place with a little paraffine1 which should be pressed into the hole around the pin4 ,the coil may be fastened in place with paraffine4 ,the ends of the coil may be connected with binding-posts1 described in ,app4 #df1 as shown1 or with any other desired form4 ,the base should be #d x #e x #g_/h inches4 ,the coil looks well when placed about #a in4 from the edge of the base4 ,the binding-posts may be about #a in4 from the edges4 ,,apparatus #aab4 #afg4 ,current ,detector4 ,fig4 #he4 ,this is more troublesome to make than ,app4 #aaa1 but perhaps it looks more scientific4 #afh4 ,the ,coil is wound around #b ordinary spools which are glued to a vertical piece1 which1 in turn1 is screwed to a base4 ,you should not use iron nails or screws in the construction of electrical apparatus1 when a magnetic needle is to be used in connection with it1 as these would attract the needle4 ,the spools may be pushed onto dowels which are fastened into the vertical piece4 ,small brass screws are good for the purpose also1 if you haven't good glue or the dowels4 ,this coil1 etc41 may be used in connection with an astatic needle4 ,the coil may be wound with ,app4 #ic or #id1 if you make the attachment of ,app4 #ie1 and screw the upright carrying the spools to the attachment4 ,illustration3 ,fig4 #he4 ,the binding-posts1 shown in ,fig4 #he1 are not to be advised4 ,it will be better to use those of ,app4 #de4 ,the magnetic needle is supported by a sewing-needle stuck through a cork4 ,this may be fastened to the base with paraffine4 #afi4 ,it is often troublesome to turn the apparatus around until the needle becomes parallel to the length of the coil4 ,to avoid this1 a small bar magnet1 shown in the ,fig4 #he1 may be laid on top of the coil4 ,a magnetized sewing-needle will do1 and this will keep the magnetic needle quiet and parallel to it when the current is not passing through the coil4 ,of course1 it takes a little more current to move the magnetic needle when the bar magnet is in place1 than it does without the magnet4 #agj4 ,by allowing the current to enter the right-hand binding-post1 as you look at it from the front 7,fig4 #he71 it will go around the coil in the direction of the hands of a clock1 that is1 from left to right on top4 ,this1 of course1 is not necessary to merely detect the presence of a current4 ,in order1 however1 to determine the direction of currents by means of a magnetic needle1 study the effect with a single turn of wire at first4 7,see text-book47 #aga4 ,dimensions4 ,the base is #e x #d x #e_/h in4 ,the upright piece is #e x #c-a_/b x #e_/h in4 ,the spools are #b-a_/b in4 apart center to center4 ,,apparatus #aac4 ,illustration3 ,fig4 #hf4 #agb4 ,astatic ,current ,detector4 ,fig4 #hf4 ,the ordinary magnetic needle points to the north quite strongly4 ,it is evident1 then1 that this pointing-power must be overcome by the magnetic field around the coil of wire1 before the needle can be forced from the ,n and ,s line4 ,very weak currents will not visibly move the magnetic needle in the detectors so far described4 ,you should remember that no action will take place unless the magnetic field around the magnetic needle is acted upon by that around the coil4 ,in order to make an instrument that will be very sensitive1 we must have strong fields about the needle and coil1 and we must1 at the same time1 decrease the pointing-power of the needle4 ,we can increase the strength of the field about the needle1 and at the same time decrease its pointing-power by using an astatic needle4 7,see ,app4 #fi47 ,the arrangement shown in ,fig4 #hf is a very simple one1 and it is quite sensitive4 #agc4 ,details of ,construction4 ,the base is #d x #e x #g_/h in4 ,the coil is made from #aj ft4 of ,no4 #cj insulated copper wire4 7,see ,sec4 #afc for details about coil making47 ,the binding-posts are like ,app4 #da4 ,the ,astatic ,needle is described for ,app4 #fi4 ,the needles may be broken off1 if too long for the coil4 ,they are supported by a fine thread hung from a screw-eye1 which may be turned to adjust the position of the needles4 ,this is not necessary1 as the thread may be hung from a plain wire arm that reaches out from the upright rod4 ,this rod is a #f-;in4 piece of dowel1 #a_/d or #e_/af in4 in diameter4 ,it stands in an ordinary spool which should be glued to the base4 ,do not nail it to the base4 ,the wire arm may be of iron1 as it is some distance above the needle2 but it is better to use a stiff brass or copper one4 ,in the figure one end of the wire is twisted around the screw-eye1 making a nut for the screw-eye to turn in4 ,hang the astatic needle so that the wire between the two parts will not quite touch the coil4 ,the needles should be parallel to the coil before testing for currents4 ,they will fly around very decidedly with even fairly weak currents4 ,,apparatus #aad4 ,illustration3 ,fig4 #hg4 #agd4 ,astatic ,current ,detector4 ,fig4 #hg4 ,for a description of the wood-work1 coil1 etc41 see ,app4 #aab2 for the astatic needle see ,app4 #fi2 for the method of supporting the needle see ,app4 #aac1 ,fig4 #hf4 ,the top part of the coil is spread apart a little to allow the lower needle to be dropped through the opening thus made1 and to allow the wire joining the two needles to be free to turn4 ,the needles may be broken off a little1 if necessary1 or an opening may be cut into the vertical part of the frame1 so that they can swing more freely4 ,this detector will indicate quite feeble currents4 ,,apparatus #aae4 #age4 ,astatic ,detector4 ,fig4 #hh4 ,as previously ,stated1 the sensitiveness of a detector can be made greater by increasing the strength of the coil-field for a given current4 ,this may be done by increasing the number of turns of wire in the coil4 ,the most convenient way will be to use two coils1 one on each side of the astatic needle4 #agf4 ,the ,support1 or framework1 is a lamp chimney4 ,by this the astatic needle is suspended and protected from air currents4 ,the chimney should be at least #c in4 in diameter at the bottom1 about #aj in4 high1 with a plain round top4 ,upon the top of the chimney is placed the cover of a wooden pill-box1 #b in4 in diameter4 #agg4 ,the ,coils should be made separately1 for convenience4 ,each should be of #aj ft4 ,no4 #cj wire4 7,see details ,sec4 #afc47 ,cut out a round piece of stiff pasteboard1 just large enough to go inside of the bottom of the chimney4 ,fasten the coils to this by sewing 7,sec4 #afc71 or with paraffine1 so that they shall be symmetrically located and #c_/h in4 apart4 ,the pasteboard circle may be fastened to the base with small brass screws4 ,do not use any iron nails or tacks4 ,in this1 all four ends of wire are brought out under the edge of the chimney 7,fig4 #hh74 ,cut little grooves in the base for the wire to sink into1 so that the chimney will rest firmly upon the base all around4 ,the ends of the wires are fastened to three binding-posts4 ,illustration3 ,fig4 #hh4 #agh4 ,joining the ,coils4 ,the end of one coil must be joined to the beginning of the other properly1 or the action of one will destroy that of the other4 ,fig4 #hi shows the two coils1 ,a and ,b4 ,if the current enters at the binding-post1 ,x1 it will pass through the turns of coil ,a1 in the direction of clock-hands1 then out to ,y1 where ,b begins1 around ,b in the same way1 and then to ,z4 ,y may be simply a screw-eye binding-post 7,app4 #da74 ,by this arrangement one or both coils can be used at a time4 ,if the current is very weak1 use both coils2 that is1 connect the ends of wires to be tested with the two outside binding-posts4 ,if they are joined to the middle and one outside post1 one coil only will be in the circuit4 #agi4 ,the ,base should be about #g x #e x #g_/h in4 ,fasten three bent brass or copper strips to the base with brass screws to hold the chimney steady4 ,by bending them in more or less you can make a snug fit around the chimney4 #ahj4 ,adjusting the ,needle4 ,in the center of the box-cover is a small hole4 ,the thread from the needle passes through this4 ,the upper end of the thread is wound around a screw-eye1 which is screwed into the cover near one edge4 ,by turning the cover around1 the needle can be made to hang parallel to the coils1 and by turning the screw-eye1 the needle can be raised or lowered4 ,a small hole should be made in the cover before putting in the screw-eye1 or you will be liable to split the wood4 ,illustration3 ,fig4 #hi4 #aha4 ,use4 ,this apparatus will indicate very slight currents2 in fact1 as feeble ones as the student will have occasion to experiment with1 such as induced currents1 currents of thermo-electricity1 and currents produced by exceedingly weak batteries4 7,see text-book47 ,,apparatus #aaf4 #ahb4 ,tangent ,galvanometer4 ,fig4 #ij4 ,for the uses of this form of galvanometer see text-book4 ,do not use any iron in making this apparatus4 ,the base is #e x #d x #g_/h in4 ,at its front end are three binding-posts4 ,the pasteboard band1 ,g1 is #a-a_/d in4 wide and #f in4 in diameter4 ,cut the pasteboard #ba in4 long and #a-a_/d in4 wide1 then bend it into the form of a circle4 ,there will be a lap of about #c in41 and you can make it solid by sewing the two ends together at the lap4 ,illustration3 ,fig4 #ij4 #ahc4 ,the ,coils maybe made of ,no4 #bd insulated copper wire1 which should be wound on before fastening ,g to the base4 ,there are two separate coils1 one having five turns and the other ten turns4 ,leaving a #f-;in4 length1 ,a1 for connections1 wind five turns of wire on to ,g1 putting them on clockwise2 that is1 pass them over the top of ,g from left to right4 ,tie thread around ,g and the wire to hold them together after you have five turns on1 and cut a #f-;in4 end1 ,b4 ,now begin with ,c1 and wind on ten turns1 bringing the end of them out at ,d4 ,punch holes1 ,f1 through ,g on each side of the coils1 run twine1 ,t1 through them1 and tie ,t on the outside of ,g4 ,do this in three or four places1 to firmly hold the coils4 #ahd4 ,fastening ,coils to ,base4 ,the band and coils will not rest squarely upon the base1 so cut two pieces of wood1 ,e1 about #b x #a_/d x #a_/d in41 to be put under ,g1 one being on each side of the coil4 ,make holes through the base1 pass strong cord1 ,h1 through them1 and over the inside of ,g1 then tie under the base4 ,this should tightly squeeze ,e1 and hold ,g upright and firm4 #ahe4 ,the ,connections4 ,a and ,b are the ends of the five-turn coil2 ,c and ,d are the ends of the ten-turn coil4 ,if the battery-wires are connected with ,x and ,y1 the current will pass through five turns of wire2 if connected with ,y and ,z1 it will pass through ten turns2 if with ,x and ,z1 the current will pass through the entire fifteen turns4 ,in this way the strength of the magnetic field about the coil can be regulated1 and its effect upon the magnetic needle1 ,m1 changed4 #ahf4 ,to ,support the ,needle1 glue or sew two strips1 ,i1 to ,g4 ,they must be in such a position that the poles of ,m will be as nearly as possible in a horizontal line drawn through the center of the circle1 ,g4 ,after you have made ,m 7,app4 #ff71 and have found where the pieces1 ,i1 should be1 fasten them to ,g1 and then to ,i glue a pasteboard strip1 ,j1 about #a-a_/d in4 wide4 ,run a pin1 ,p1 up through the center of ,j to support ,m4 #ahg4 ,the ,magnetic ,needle1 ,m1 should not be over #a in4 long for this kind of an instrument4 7,see ,app4 #ff for full directions for making it47 ,on the top of ,m should be fastened a light paper pointer or index1 ,l4 ,the short end should be made large1 so that the long slim end will not over-turn ,m2 that is1 the pointer should balance itself4 ,it may be fastened to ,m with paraffine or a drop of sealing-wax4 ,if carefully balanced1 the pointer can be made quite long4 #ahh4 ,the ,graduated ,circle1 ,k1 is described4 7,index47 ,with this you can tell through how many degrees the needle is deflected1 when the current passes4 ,the strength of different currents can be compared1 and many interesting experiments performed with the tangent galvanometer4 ,for clearness1 the circle1 ,k1 is shown small4 ,in order to have the divisions on it far enough apart1 ,k should be about #d in4 in diameter4 ,the zero points should be at the front and back of the instrument1 when a pointer is used on the needle4 #ahi4 ,how to ,use ,it4 ,for full explanations1 and for the study of experimental cells1 etc41 by means of the tangent galvanometer1 see text-book4 ,it will be impossible for you to get ,m exactly in the center of ,g2 you cannot get the pointer exactly at right angles with ,m2 hence1 if you pass a certain current through the coils1 and the pointer reads #bj degrees1 you will find1 if you reverse the current1 making it go through the coil in an opposite direction1 that the pointer may read #bd degrees on the opposite side of the zero4 ,to get the true reading1 then1 take the average of the two1 which in the case mentioned would be #bb degrees4 7,see current reversers47 ,,apparatus #aag4 #aij4 ,tangent ,galvanometer4 ,fig4 #ia4 ,the base consists of #b parts1 ,a and ,b4 ,it is not necessary to use two pieces if you have wood that is at least #g_/h in4 thick4 ,this is given as a suggestion in case you have nothing but thin boards4 ,by screwing ,b to ,a the base is made thick enough to take the screws for binding-posts4 ,the base proper1 ,a1 is #h-a_/b x #e x #a_/b in4 ,if you make this of #g_/h in4 stuff1 you will not need ,b4 ,the ,back1 ,c1 is #aj x #h-a_/b x #a_/b in4 ,it is screwed to the base4 ,do not use nails1 as these affect the magnetic needle4 ,find the center of ,c1 and with this as a center1 draw two circles1 7that is1 the circumferences of two circles17 one #e in4 in diameter to show where to cut out a hole1 ,h1 and the other #g in4 in diameter to serve as a guide for fastening on the spools1 ,f4 ,illustration3 ,fig4 #ia4 ,the ,spools1 ,f1 are glued to ,c4 ,if you have brass screws1 these may be used instead of the spools2 they should be left sticking out from ,c about #a in4 ,around the spools or screws1 fasten a pasteboard band1 ,g1 on which to wind the wire4 ,g may be about #a in4 wide2 it should be kept in the circular form by sewing the ends together where they lap4 7,read directions in ,app4 #aaf47 #aia4 ,the ,coils on this model are #d in number4 7,see ,app4 #aaf for the method of winding47 ,the first coil is made of coarse wire1 ,no4 #ah1 its ends being joined to the binding-posts1 ,v and ,w4 ,the second coil has #e turns of ,no4 #bd insulated copper wire1 its ends being joined to ,w and ,x4 ,the third coil has #aj turns of the same size wire1 ,no4 #bd1 and is joined to ,x and ,y4 ,the fourth coil has #bj turns of the same joined to ,y and ,z4 ,if you want to use the galvanometer for quite weak currents1 it would be well to make a fifth coil of #bj turns of ,no4 #cj wire1 and join it with ,z and a new binding-post4 ,the ends of the coils are run through small screw-eyes before passing to ,x1 ,y1 etc4 ,this is not necessary1 it merely keeps them in place4 ,the ,binding-,posts are like ,app4 #dc4 ,any other desired style may be used1 those of ,app4 #df being preferred4 ,the ,hole1 ,h1 is #e in4 in diameter4 ,it should be cut out about #a_/b in4 below the center of the circles to allow for ,d1 and for the pin-point which supports the magnetic needle1 the poles of which should be in the line passing through the center of the coils4 ,the method of cutting the hole1 ,h1 through ,c1 will depend upon the tools at your service4 ,d is the front edge of an adjustable table1 like that explained4 7,index47 ,it is #d-a_/d in4 wide4 ,it supports the magnetic needle which is inside of ,e4 ,e is the outside of a glass-covered compass4 7,see ,app4 #fg for details47 ,the needle should not be over #a in4 long4 ,,chapter ,,xiv4 ,,telegraph ,,keys ,,and ,,sounders4 ,,apparatus #aah4 ,illustration3 ,fig4 #ib4 #aib4 ,telegraph ,keys4 ,fig4 #ib4 ,telegraph keys are merely pieces of apparatus by which the circuit can be conveniently and rapidly opened or closed at the will of the operator4 ,an ordinary push-button may be used to turn off and on the current1 but it is not so convenient as a key4 ,fig4 #ib shows a side view of a simple key4 ,c is a metal strip about #c_/d in4 wide and #d or #e in4 long4 ,at the left end it is fastened to the base with a screw1 ,a4 ,another screw1 ,x1 serves as one binding-post4 ,y is another screw binding-post4 ,w is a short wire1 used to regulate the amount of spring to the key4 ,this is done by moving ,w to the right or left4 ,if the current enters at ,x1 it will pass along ,c and out at ,y1 when ,c is pressed down4 ,by moving ,c up and down according to a previously arranged set of signals1 messages can be sent by means of the electric current4 7,see telegraph alphabet47 ,this apparatus is not a good one where the line is to be run with a closed circuit battery1 or where it is to be used very often4 ,it will do1 however1 for places where a push-button would be too tiresome to use4 ,the right end of ,c is curved4 ,this curve serves as a handle4 ,d and ,e are wires leading from ,x and ,y4 ,,apparatus #aai4 #aic4 ,telegraph ,key4 ,fig4 #ic4 ,the base is #e x #d x #g_/h in4 ,the key1 ,c1 is made of two thicknesses of tin4 ,it is made into a strip #e-a_/b x #c_/d in41 then the front end is bent up for a handle1 as suggested in ,fig4 #ib1 the front end being above the base so that it will not touch the strap1 ,d1 unless it is pressed down4 ,c is fastened to the base by a screw1 ,h1 which also binds one end of the copper wire1 ,c ,w4 ,about #c_/d in4 from ,h is placed ,x1 which is a screw-eye binding-post4 ,under ,c is the wire1 ,w1 which is used to regulate the amount of spring in ,c1 by moving it forward or backward4 ,s ,i shows the position of a screw-eye1 or of an ordinary screw put into the base through ,c4 ,the hole in ,c should be made so that ,c can move up and down easily around the screw4 ,this is used to make a click when the key is allowed to spring up4 ,the downward click is made when ,c strikes ,d at each depression4 ,illustration3 ,fig4 #ic4 ,the ,strap1 ,d1 is made of tin4 ,it is #d x #a_/b in4 before bending up the right end a little4 ,it is fastened to the base by the screw1 ,f1 and by the other binding-post1 ,y4 ,its right end is raised enough to allow the arm1 ,e1 to pass under it1 but it must press down well upon ,e when ,e is forced toward ,f4 ,the ,swinging ,arm or ,switch1 ,e1 is also made of tin1 and measures1 finished1 #d-a_/b x #a_/b in4 ,its front end should be bent up a little for convenience in handling it4 7,see ,fig4 #ib47 ,e is pivoted at ,g by a screw1 which also binds the wire1 ,c ,w4 ,fig4 #bd shows another way to make the pivot and connection4 #aid4 ,operation4 ,see ,fig4 #ii for the details of the connections of a home-made telegraph line4 ,when you are using the line and telegraphing to your friend1 the switch1 ,e1 of your instrument must be open1 as in ,fig4 #ic1 and the corresponding switch on his instrument must be closed2 that is1 the circuit must be opened and closed at but one place at a time4 ,as soon as you have finished1 your switch must be closed4 ,he will open his and proceed4 ,when you have both finished1 both switches must be closed4 ,if your friend left his switch open1 you could not call him over the line1 as no current could pass into his sounder4 #aie4 ,batteries4 ,as the circuit has to be left closed for hours and perhaps days at a time1 so that either operator can call the other1 a closed-circuit battery is necessary4 7,see ,app4 #i47 ,a dry cell1 ,leclanche1 or other open-circuit cell would not be at all suitable for a telegraph line1 as it would soon polarize4 ,large ,daniel cells1 which are #b-;fluid cells like ,app4 #g1 or gravity cells 7,app4 #i7 are the best for your line4 ,,apparatus #abj4 #aif4 ,telegraph ,sounder4 ,fig4 #id4 ,the wood-work consists of #b parts2 the base1 ,b1 is #f x #d x #c_/d in41 and the back1 ,a1 is #f x #e x #a_/b in4 ,a is nailed or screwed to ,b4 ,the ,magnet1 ,m1 is fully described in ,app4 #he4 ,m is held firmly to ,a by cord or wire1 which should pass around it near the poles and at the curved part4 ,the wire should pass through small holes in ,a1 and be tied at the back4 ,wire nails driven into ,a at the sides of ,m will keep it from moving about4 ,the wires from the magnet coils are led to two spring binding-posts1 ,x and ,y4 ,illustration3 ,fig4 #id4 #aig4 ,the ,armature1 ,c1 is made of a narrow piece of thin iron1 about #e-a_/b x #a_/d x #a_/h in4 ,it may be made by bending up #c or #d thicknesses of tin into that shape4 ,this is the part which will be attracted by ,m1 when the current passes1 and which will make the clicks by which the message can be read4 7,see telegraph alphabet47 ,there are many ways by which ,c can be held near ,m4 ,the figure shows how it can be done entirely with #a-;in4 wire nails4 ,at the right end of ,c two nails are driven into ,a above and below ,c4 ,they are just far enough apart to allow the left end of ,c to be raised and lowered without binding2 in other words1 these nails make a pivot for ,c to swing upon1 and they help to support it at the same time4 ,the left end of ,c must not quite touch the poles of ,m when the current passes1 because the residual magnetism would keep ,c from dropping back into place4 ,to adjust the armature1 pass the current through ,m1 hold ,c so that it will not quite touch the poles1 then drive in the upper nail1 #b4 ,put another nail1 #a1 below ,c1 so that ,m will not have to lift ,c more than #a_/h or #c_/af in4 ,try the nails in different positions until ,c quickly rises and falls when the circuit is closed and opened4 ,a nail1 #c1 driven in front of ,c1 will keep its right end in place4 ,no springs are needed1 as gravity acts upon ,c instantly1 bringing it to the lowest position as soon as the current ceases to flow4 #aih4 ,the ,battery will depend upon how much you want to use the sounder4 ,if just to show the principle of it1 almost any cell of medium strength will do1 like that of ,app4 #c1 #d or #e4 ,a dry battery will do1 but if you use the sounder much1 an open-circuit battery will soon use itself up4 ,where much work is needed of the battery use ,app4 #i4 ,illustration3 ,fig4 #ie4 ,the ,key like ,app4 #aai is best4 ,push-buttons are handy where used only for experiments1 and not for the actual sending of messages4 ,,apparatus #aba4 #aii4 ,telegraph ,sounder4 ,fig4 #ie4 ,this makes a simple and efficient sounder for short lines4 ,the base1 ,b1 is #g x #d-a_/b x #g_/h in4 ,the back1 ,a1 is #g x #d-a_/b x #a_/b in42 it is nailed to ,b4 ,the piece ,d is #d x #c_/d x #c_/d in42 it is nailed to ,a4 ,c is a wooden piece #a-a_/b x #c_/d x #c_/d in42 it is nailed to ,a1 and in its top is a screw1 ,e1 which is used as a regulating-screw to keep the armature1 ,l1 from touching the poles4 #bjj4 ,the ,armature1 ,l1 is explained as ,app4 #gg4 ,the two thicknesses of tin at ,f must not be too thick1 or it will take too much battery power to work the sounder4 ,if you find that it is too stiff to bend down1 when the current is on1 try the arrangement of ,app4 #abb1 which is easier to make and regulate4 ,the whole point depends upon the tin you have4 ,the end of ,l must tap against ,e4 ,a hole is punched in the part ,f1 and a screw1 ,g1 holds it to ,d4 ,l should rest about #a_/h in4 above the poles and gently press against a screw or nail1 ,v4 #bja4 ,the ,magnets are like ,app4 #hi4 ,they are made as in ,app4 #hh1 and held down like ,app4 #ij4 ,these should be placed very near the back1 ,a1 so that the armature will be over them4 ,if your yoke is not too wide the coils may rest against ,a4 ,y and ,z are binding-posts like ,app4 #df4 #bjb4 ,connections4 ,join the coils as explained in ,sec4 #abe and see ,sec4 #aae4 ,instead of a third or middle binding-post1 as in ,fig4 #ff1 hold the two inside ends between a screw-head and a copper bur4 ,the method of joining the wires for a line with two outfits1 is shown in ,app4 #abd4 ,if you have but one key1 sounder1 and battery1 simply join the line wire to the return wire there shown4 ,a gravity cell is best4 7,see ,app4 #i47 #bjc4 ,hints ,about ,adjusting4 ,if you have the right spring to the part ,f1 of the armature1 you will have no trouble4 ,it must not be so weak that it allows ,l to strike upon the poles1 as the residual magnetism 7,text-book7 will hold ,l down after the current has ceased to pass4 ,no springs are necessary1 if your tin is right4 ,do not have ,l too far away from the poles4 ,the distance is regulated by the position of ,v4 ,if you have trouble in getting it to work see ,app4 #abb4 ,the poles must be opposite in nature4 ,,apparatus #abb4 ,illustration3 ,fig4 #if4 #bjd4 ,telegraph ,sounder4 ,fig4 #if4 ,the magnets1 connections1 etc41 are like those of ,app4 #aba1 no binding-posts1 etc41 being here shown4 ,the armature is straight1 however1 the part ,f resting upon ,d4 ,a hole is made in the end of ,f1 and through this is a screw or nail1 ,s4 ,the hole must be large enough to allow ,s to pass through easily4 ,this acts as a bearing or pivot4 ,l is kept up against ,v by the rubber-band1 ,j1 one end of which passes around the end of ,l2 to the other end of ,j is a thread1 which is tied around a screw-eye1 ,k4 ,by turning the screw-eye1 the band may be made to pull more or less upon ,l4 ,in this way the apparatus may be regulated according to your battery4 ,the general dimensions and explanations are given in ,app4 #aba4 ,d is made of such a height that it will bring ,l about #a_/h or #c_/af in4 above the poles4 ,,apparatus #abc4 ,illustration3 ,fig4 #ig4 #bje4 ,telegraph ,sounder4 ,figs4 #ig and #ih4 ,this apparatus looks a little more like a regular sounder than ,app4 #aba and #abb1 but it is much harder to make and adjust4 ,in this the lower nuts of the bolts are not sunk into the base1 and the magnets are made of #b-;in4 bolts4 ,if you change this and fasten them like ,app4 #hi and #ij1 it will simply change the dimensions of the small parts4 ,the sizes given are for this particular instrument4 ,fig4 #ig shows a perspective view1 and ,fig4 #ih is a plan or top-view of it1 with dimensions4 ,illustration3 ,fig4 #ih4 #bjf4 ,the ,base1 ,b1 is #f x #d x #g_/h in4 ,the magnet1 ,m1 is explained in ,app4 #hi4 ,its wires are attached to the binding-posts like ,app4 #df4 ,the armature1 ,a1 is #b-a_/b x #c_/d x #a_/h in41 and made as described in ,app4 #ga4 ,the piece1 ,d1 is #b-a_/b x #a-c_/h x #a_/b in41 and is screwed to ,b from below1 after the two uprights1 ,c1 are nailed to it4 ,the uprights1 ,c1 are #b-c_/d x #g_/h x #a_/b in4 ,they are nailed to ,d4 ,the nail1 ,n1 runs through both uprights1 and acts as the bearing for ,f to rock up and down upon4 ,the hole for ,n is #b in4 above ,b4 ,it must not be too loose in the holes1 or ,f will rock sidewise1 and allow ,a to touch one of the magnets4 ,the upright1 ,e1 is #b-c_/d x #c_/d x #c_/d in41 and is screwed or nailed to ,b from below4 ,a screw1 ,g1 is put into the side of ,e near the top4 ,this screw has the underside of the head filed flat1 and against this the screw1 ,l1 taps when the armature is attracted4 ,the arm1 ,f1 which carries the armature1 ,a1 is #d-a_/b x #a_/b x #a_/b in41 and is pivoted by means of ,n1 which passes through it and the uprights ,c4 ,f must swing up and down freely4 ,the hole for ,n1 in this model1 is #a-c_/d in4 from the armature end4 #bjg4 ,the armature is fastened to ,f by a screw1 ,s4 ,a copper bur is put under the head of ,s to aid in keeping ,a from rocking sidewise4 ,through ,f1 and about half way between ,c and ,l1 is put a screw1 ,i1 the lower end of which taps against the head of a screw1 ,h1 which is put into ,d4 ,by unscrewing ,h a little1 ,f will be raised1 and ,a will be brought nearer the poles of ,m4 ,the rubber-band1 ,j1 is placed over the head of ,i1 and has tied to it a thread1 ,o1 which in turn is tied to a screw-eye1 ,k4 ,k screws into the end of ,b1 and by turning it one way or the other1 the tension1 or pull1 on ,j may be increased or diminished4 ,there must be enough spring in ,j to pull ,a up after the current ceases2 it must not pull so much that the magnet cannot draw ,a down hard enough to make a good click between ,l and ,g4 ,the ,magnet1 ,m1 is explained in ,app4 #hi1 and the construction of one bolt magnet is given in detail in ,app4 #hh4 ,in this particular sounder the bolts are #b in4 long under the heads1 thus bringing the tops of the bolt-heads about #b-a_/d in4 above ,b4 ,m is held to the base by a band of tin1 ,t4 ,the yoke may be screwed to ,b1 as suggested in ,app4 #ij4 ,this is the better plan4 #bjh4 ,adjustment4 ,you will find1 although you make all of the parts with the dimensions given1 that you will have to try1 and change1 and adjust before everything will work perfectly4 ,a must not be allowed to touch the poles of ,m when it is pulled down1 on account of the residual magnetism1 which would keep it pulled down4 ,adjust this with ,f4 ,the armature must not be pulled too far up from the poles of ,m by the tension in ,j2 adjust this with ,i and ,h4 ,if your battery is weak1 the pull of ,j must be small1 just enough to raise ,a4 ,the ,battery4 ,it is supposed1 if you make an instrument like this1 that you expect to use it for a line4 ,in that case make a regular gravity battery like the cell of ,app4 #i4 ,see ,fig4 #ii for line connections1 and ,fig4 #ih for plan view of this sounder4 ,,apparatus #abd4 #bji4 ,telegraph ,line2 ,connections4 ,fig4 #ii shows the complete connections for our telegraph line1 with two complete outfits4 ,the capital letters are used on the right side1 ,r1 and small letters are on the left side1 ,l4 ,the batteries1 ,b1 b1 are like ,app4 #i4 ,the keys1 ,k1 k1 are like ,app4 #aai4 ,the sounders1 ,s1 s1 are like ,app4 #aba or #abb4 ,illustration3 ,fig4 #ii4 #baj4 ,the two stations1 ,r and ,l1 may be near each other1 or in different houses4 ,the return wire1 ,r ,w1 passes from the copper of b to the zinc of ,b4 ,this is important4 ,if the cells are not joined properly1 they will not work4 ,it is better to have the cells together1 on a short line1 joined in series4 ,the line wire1 ,l ,w1 and the return wire1 ,r ,w1 may be made of insulated copper wire for short lines in the house4 ,ordinary annunciator wire1 ,no4 #bj1 is good and cheap4 ,the kind that is double cotton wrapped1 waxed1 and paraffined1 has about #bce ft4 to the pound4 ,you should get at least #e ft4 for #a cent4 ,if your line stretches from one house to another you will find it better to use iron wire4 ,galvanized iron or steel wire ,no4 #ad is good4 ,this size weighs about #ajj lbs4 to the mile4 ,the return and line wires must not touch each other at any point2 they must not touch any pipe or other piece of metal that will short circuit your batteries4 ,it is best to use porcelain or glass insulators to support your wires if the line is long2 but for short lines1 where you use a return wire1 you may support the wires upon poles or trees by means of loops made of strong cord or wire4 #baa4 ,operation4 ,suppose ,r 7right7 and ,l 7left7 have a line4 ,by studying ,fig4 #ii you will see that ,r's switch1 ,e1 is open while e is closed4 ,the whole system1 then1 has but one place where the circuit is open4 ,as soon as ,r presses his key1 ,k1 the circuit is closed1 the current from both cells rushes around through ,k1 ,s1 ,l ,w1 s1 k1 b1 ,r ,w1 and ,b4 ,this magnetizes the bolts of both ,s and s1 and their armatures come down with a click upon the regulating-screws1 where they remain as long as the current passes4 ,as soon as ,r raises his key the armatures rise1 making the up-click4 ,r can1 in this way1 regulate the time between the two clicks4 ,if he presses ,k down and lets it up quickly1 the two clicks that his friend ,l hears from s are close together2 this makes what is called a dot4 ,if ,r holds ,k down longer1 it makes a longer time between the clicks for ,l to hear1 and this makes a dash4 ,r1 of course1 hears his own sounder1 which is making the dots and dashes also4 ,as soon as ,r has finished1 he closes his switch1 ,e4 ,l then opens his switch and proceeds to answer4 ,both ,e and e should be left closed when you are through talking4 7,read ,sec4 #aid1 #aie1 and study what is said in ,app4 #i about the gravity cell to be used on such a line47 #bab4 ,telegraph ,alphabet4 ,the letters are represented by combinations of dots1 dashes and spaces4 ,a dot is made by pressing the key down1 and raising it at once2 that is1 the key is raised as soon as it strikes4 ,this makes the letter ,e4 ,the dash is made by pressing down the key1 and allowing the current to pass about as long as it takes to make #c dots2 this makes the letter ,t4 ,a long dash for ,l should take about as long as for #e dots4 ,spaces occur in a letter and between words4 ,to make a dash you hesitate while the lever of the key is down1 to make a space1 you hesitate while the key is up4 ,h is made with #d dots without hesitation or space4 ,by putting a space between the dots the letter 1 ,y or ,z is made according to the position of the space4 ,notice that letters containing dashes do not contain spaces4 ,a space is really the opposite of a dash4 ,the letters ,c1 ,e1 ,h1 ,i1 ,o1 ,p1 ,r1 ,s1 ,y1 ,z1 and are made entirely of dots or of dots and spaces4 ,you should notice that several letters are the reverse of others2 ,a is the reverse of ,n1 ,b of ,v1 ,d of ,u1 ,c of ,r1 ,q of ,x1 and ,z of 4 ,the student should study some book upon telegraphy1 if he desires to become expert4 ,punctuation marks are left out of the alphabet here given1 as boys will find very little use for them4 ,a ,b ,c ,d ,e ,f ,g ,h ,i ,j ,k ,l ,m ,n ,o ,p ,q ,r ,s ,t ,u ,v ,w ,x ,y ,z #a #b #c #d #e #f #g #h #i #j ,,chapter ,,xv4 ,,electric ,,bells ,,and ,,buzzers4 ,,apparatus #abe4 #bac4 ,electric ,buzzer4 ,fig4 #ajj4 ,a buzzer is1 in construction1 very similar to an electric bell2 in fact1 you will have a buzzer by removing the bell from any ordinary electric bell4 ,they are used in places where the loud sound of a bell would be objectionable4 ,as the buzzer is easier to make than a bell1 we shall discuss it first4 #bad4 ,the arrangement of the parts1 7,fig4 #ajj71 is very much like that of the sounder of ,app4 #aba1 ,fig4 #ie4 ,the armature is1 in this case1 a vibrating one and acts on the same principle as the automatic interrupter on ,app4 #ajj1 which you should study4 7,see ,sec4 #adh47 ,the general dimensions may be taken from ,app4 #aba4 ,the base1 ,b1 in this case is about #a in4 wide4 ,d also is made #a in4 wide4 ,h is #a x #a x #a_/b in41 and is nailed to ,a4 ,through its center is a hole for the regulating screw-eye1 ,i4 ,the end of ,i presses against ,f4 ,the exact position of ,h will have to be determined after the magnets are in place4 ,the armature1 ,l1 should be about #a_/h or #c_/af in4 above the poles4 ,they are not allowed to strike the poles1 as a screw1 ,e1 regulates that4 7,see ,sec4 #bjc74 ,y and ,z are two binding-posts1 like ,app4 #df4 ,to these are connected the battery wires4 ,the strip of tin or copper1 which forms ,y1 is cut like a letter ,t there being three holes in it1 one near the end of each arm4 ,the screw-eye1 #b1 and the screw1 #c1 are put through the horizontal part of the ,t1 and the regulating-screw1 ,i1 passes through the hole in the vertical part which springs up against ,i1 thus forming an electrical connection between ,y and ,i4 ,the magnets are made and fastened as in ,app4 #hi4 #bae4 ,connections4 ,the inside ends of the magnet coils1 7,sec4 #abc71 are fastened between a screw-head and a copper bur1 ,s4 ,one outside end goes to ,z1 and the other under the screw1 ,g1 which holds ,f to ,d4 ,illustration3 ,fig4 #ajj4 #baf4 ,adjustment4 ,the part1 ,f1 and the screw1 ,e1 must be just high enough to keep ,l from striking the poles of ,m4 ,if ,f is too weak1 it will bend down to ,m4 ,if ,f is too strong1 it will take too much battery power to run it4 ,in case there is not strength enough in ,f to quickly raise ,l when the current ceases to pass1 arrange a screw-eye and rubber band as shown in ,fig4 #if4 ,i should be slowly turned one way or the other1 until it touches ,f just right to allow ,l to vibrate back and forth rapidly4 #bag4 ,operation4 ,we shall suppose that you have all parts adjusted and the battery wires joined to ,y and ,z4 ,if the current enters at ,z1 it will fly around through the coils1 through ,g1 ,f1 up ,i1 through the ,t-shaped tin and out at ,y4 ,the current was in ,l1 but it could not get out at any other place than at ,y4 ,as soon as the bolts were magnetized1 ,l was forcibly drawn down1 pulling ,f away from ,i1 thus opening the circuit4 ,as the bolts were no longer magnets1 ,f sprang right back to ,i1 the current passed long enough to re-magnetize the bolts4 ,this operation was rapidly repeated4 #bah4 ,use4 ,if you wish to use the buzzer simply to call some one occasionally1 a dry battery or ,leclanche cell is best4 ,this apparatus is good to work a gravity cell when it needs regulating4 ,,apparatus #abf4 ,illustration3 ,fig4 #aja4 #bai4 ,electric ,bell4 ,fig4 #aja4 ,before making this bell1 carefully read the directions and explanations given for the electric buzzer1 ,app4 #abe4 ,the parts are very much alike in the two instruments1 and most of the lettering of them has been made the same in the illustrations4 ,if you look at ,fig4 #aja from the side1 with the letters ,m and ,q at the bottom1 you will see that this bell is merely a modified form of ,app4 #abe4 ,the ,base is #g x #e x #a_/b in4 ,to the upper end of this is nailed the cross piece1 ,d4 ,to ,d are fastened the binding-posts4 ,the ,parts1 ,f1 ,g1 ,h1 ,i1 ,j1 ,k1 ,l1 ,m1 ,n1 ,p1 ,q1 are the same as explained in ,app4 #aba and #abe4 ,the ,magnet is fastened to the base by a tin strip1 ,c1 which is screwed down at both ends4 ,by nailing a strip1 like ,d1 along the left side of the base1 the magnet may be fastened to this4 ,this strip would take the place of the base of ,app4 #abe4 ,the piece1 ,f1 of two thicknesses of tin1 is made longer than it was in ,app4 #abe2 in fact1 it projects through ,l and forms the part ,n4 ,to the lower end of ,n is fastened a large bullet4 ,hold the cutting-edge of a strong knife-blade upon the bullet1 and with a few taps of a hammer drive the blade into it to make a gash4 ,put the end of ,n into the cut1 then hammer the bullet so that ,n will be pinched4 ,if you have no bullet1 cut a long strip of tin1 about #c_/h in4 wide1 and wind this about the end of ,n to serve as a ball4 ,the ,bell1 ,e1 may be taken from an old alarm-clock4 ,this is not screwed directly to the base1 as it would not ring well4 ,after you have the ball1 ,o1 properly fixed1 hold ,e1 so that ,o will strike it near its rim2 then cut a piece of wood about #e_/h x #e_/h1 and long enough to put under ,e1 to raise its rim to the right place4 ,this piece must be screwed to the base from the underside1 and on to its top is placed the screw which passes through the bell4 ,in other words1 ,e is mounted upon a rod which is fastened to the base4 ,the ,adjustments are made as in ,app4 #abe4 ,by bending ,n a little1 ,o can be made to tap ,e properly4 ,the ,battery for a bell that is to be used much should be an open circuit one1 such as the ,leclanche1 or the ordinary dry batteries4 ,it is cheaper to buy a dry battery than it is to make one suitable for bells4 ,a and ,b show wires that lead to the bell from the battery4 ,one of the wires should be passed through a push-button4 ,,apparatus #abg4 #bbj4 ,electric ,bell4 ,by arranging the buzzer of ,app4 #abe with a bell1 you can use the same for an electric bell4 ,the part1 ,f1 should be made long enough to extend entirely through ,l1 and project beyond ,l for about #b in4 ,to the end of this is fastened a large bullet1 or a band of tin4 7,see ,app4 #abf47 ,illustration3 ,fig4 #ajb4 ,,apparatus #abh4 #bba4 ,combination ,buzzer and ,telegraph ,sounder4 ,fig4 #ajb4 ,this apparatus is good for experimental purposes1 where you do not wish to go to the trouble to make two separate pieces4 ,for the dimensions and explanations see ,app4 #aba and #abe4 ,there is but a slight change in ,app4 #abe to make this4 #bbb4 ,connections4 ,the inside ends 7,sec4 #abc7 of the magnet wires are fastened together at ,s4 ,the outside ends are joined to the two binding-posts1 ,y and ,z1 made like ,app4 #df4 ,a wire1 ,p1 joins ,y with the screw in ,t1 which is a piece of stiff tin or copper1 which presses down upon the top of ,i4 ,in this way a connection may always be had between ,i and ,t4 ,a wire1 ,r1 joins ,f electrically with ,x2 it is held under the head of the screw1 ,g4 7,see ,app4 #abe about adjustments47 #bbc4 ,operation4 ,when you wish to use the apparatus as a buzzer1 join your battery wires to ,x and ,z4 ,if the current enters ,z1 it will pass through the magnet coils out to ,y1 through ,p1 ,t1 ,i1 ,f1 and ,r to ,x4 ,if you use it as a telegraph sounder1 join the battery wires to ,y and ,z4 ,the current will then pass simply through the coils2 it will not bother to go into ,p1 ,f1 etc41 as it has no place it can escape4 ,if used simply for experimental purposes almost any cell of sufficient strength will do4 ,if for telegraph1 use ,app4 #i2 if for buzzer1 use an open circuit cell1 as1 for example1 a dry cell4 ,,chapter ,,xvi4 ,,commutators ,,and ,,current ,,reversers4 #bbd4 ,commutators and ,current ,reversers are useful in some experiments1 as1 for example1 those with tangent galvanometers 7,app4 #aaf1 #aag71 in which readings are made with the current passing around the coil in one direction1 and again made at once with the current reversed4 ,the use of commutators on motors and dynamos should be understood4 ,the reversers herein shown are1 of course1 not at all like those used on motors4 ,current reversers are used in connection with the needle-telegraph and many other instruments4 ,illustration3 ,fig4 #ajc4 ,,apparatus #abi4 #bbe4 ,current ,reverser4 ,fig4 #ajc4 ,the base is #e x #d x #g_/h in4 ,to this are fastened four metal straps1 ,a1 ,b1 ,c1 and ,d4 ,these may be made of brass1 aluminum1 or even of tin4 ,if made of tin1 use one thickness of metal for ,c and ,d1 and two thicknesses for ,a and ,b4 ,each strap has two #a_/h in4 holes punched in it1 their positions being shown by the screw-heads and screw-eye binding-posts4 ,construction4 ,c is #c-c_/d x #a_/b in4 ,fasten this to the base first4 ,at the left end is a small screw1 while the right end is held down by the binding-post1 ,w4 ,the keys1 ,a and ,b1 should have quite a little spring to them4 ,these are cut #e x #c_/d in4 ,the front end of each is bent over a little 7see the key ,app4 #aah1 ,fig4 #ib7 so that they may be more easily grasped4 ,the length after bending will be less than #e in4 ,the front ends should be raised from the base 7,fig4 #ib7 so that they will not touch ,c1 unless pressed down4 ,the #a_/h in4 holes in the end of ,a are about #c_/d in4 apart1 one being used for a screw to hold it to the base1 and the other for the binding-post1 ,y4 ,the strap1 ,d1 is #c-c_/d x #a_/b in4 ,it is fastened at one end by a screw1 and at the other end by ,x4 ,d is bent about #c_/d in4 from each end1 so that its middle part stands above the base about #a_/d in4 ,the straps1 ,a and ,b1 press up against ,d1 unless they are held down with the hand4 #bbf4 ,connections4 ,w and ,x are joined to the poles of the battery to be used4 ,y and ,z are joined to the apparatus in which the current must be passed in one direction1 and then in the opposite direction4 ,a tangent galvanometer1 or a needle-telegraph instrument1 for example1 may be connected with ,y and ,z4 #bbg4 ,operation4 ,suppose that the battery current enters at ,w4 ,as long as both keys are raised1 the current can go no farther4 ,now1 imagine that we press ,a down solidly upon ,c1 the current will pass along ,a1 which does not now touch ,d1 out through ,y into the galvanometer1 back to ,z1 into ,d1 and to the battery again2 that is1 the current will enter the galvanometer from ,y4 ,now1 suppose that we let ,a spring up against ,d again1 and press ,b down1 the current still coming into ,w from the battery2 the current will pass along ,b1 out through ,z1 into the galvanometer1 back to ,y1 through ,d1 and back to the battery4 ,it is evident1 then1 that the current can be made to pass out of ,y or ,z to the galvanometer at will by pressing down ,a or ,b4 ,,apparatus #acj4 ,illustration3 ,fig4 #ajd4 #bbh4 ,current ,reverser4 ,fig4 #ajd4 ,the wooden base is #g x #e x #g_/h in4 ,to this are fastened two brass or tin straps1 ,c and ,d1 #e x #a_/b in4 ,they are fastened at the front ends by screws1 ,s1 while the binding-posts1 ,y and ,z1 hold the other ends solid4 ,x and ,w are two screw-eye binding-posts 7,app4 #de74 ,the small square piece of wood1 ,t1 is #c x #c x #a_/b in4 ,through the corners of ,t1 and in positions so that they will be directly over ,c and ,d1 are put four screw binding-posts1 #a1 #b1 #c1 #d 7,app4 #da74 ,the screws1 however1 pass entirely through ,t1 and stick out about #a_/d in4 on the underside of it4 ,the wire1 ,a1 connects ,w1 #a and #d1 while the wire1 ,b1 connects ,x1 #b and #c4 ,a and ,b must not touch each other where they cross on the top of ,t4 ,n is a wire nail that serves as a handle4 ,if we were to place ,t1 holding the four corner screws1 upon the straps1 ,c and ,d1 it is evident that all the screws would touch the straps1 if they were properly adjusted4 ,we must fix things so that two only can touch the straps at a time4 ,put a screw1 ,q1 through the center of ,t1 from the bottom1 so that it will stick out of the bottom more than the screws1 #a1 #b1 etc4 ,the screws1 #b and #d1 will be lifted from ,c and ,d when the handle1 ,n1 is pressed down4 ,by raising ,n1 the top1 ,t1 can be made to rock up and down upon ,q as a pivot4 ,by lifting ,n far enough1 #b and #d will be pressed against ,c and ,d1 while #a and #c will be raised4 ,a spring1 ,r1 is shown joined to ,t and to the base4 ,this will hold the screws1 #b and #d1 down upon ,c and ,d1 unless ,n is pressed down4 #bbi4 ,operation4 ,we shall first suppose that the spring1 ,r1 is holding #b and #d in contact with ,c and ,d2 #a and #c will1 of course1 be held up in the air4 ,imagine that we have a galvanometer connected with ,y and ,z4 ,if the battery current enters at ,w1 it will pass along ,a to #d1 before it can find a chance to escape4 ,it will pass through #d into ,d1 and into the galvanometer by way of ,z1 then back by way of ,y1 up #b1 and out to the battery from ,x4 ,if we now press the handle1 ,n1 down1 the current will pass from ,w to #a1 down #a through ,c and ,y to the galvanometer4 ,it will return to the battery by way of ,z1 ,d1 #c1 ,b1 and ,x4 ,the current can then be rapidly reversed by raising and lowering ,n4 ,,chapter ,,xvii4 ,,resistance ,,coils4 ,,apparatus #aca4 #bcj4 ,resistance ,coils4 ,fig4 #aje4 ,for experiments in resistance 7,see text-book71 a set of standard resistances is necessary4 ,there are many ways in which the resistances may be made2 you can arrange them upon a long board1 upon a rack1 or wind the wires around spools4 ,we generally speak of resistance coils4 ,the ,ohm is taken as the standard4 ,if you use copper wire1 you may take #i ft4 #i in4 of ,no4 #cj insulated wire as your standard ,ohm4 ,you could1 of course1 take any other length of any size as your standard1 but it will be best to make your coils with a certain number of ,ohms resistance4 ,if you have no ,no4 #cj wire1 you may use #ci ft4 #a in4 of ,no4 #bd insulated copper wire for #a ,ohm4 7,see wire tables in text-book47 ,illustration3 ,fig4 #aje4 #bca4 ,to avoid the magnetic effect 7,see resistance coils1 in text-book71 the wire should be measured off1 then doubled1 before winding it upon the spools4 ,the wire may be held to the spool with paraffine4 ,fig4 #aje shows how the doubled wire looks on the spool1 a few turns only being shown4 ,do not use any nails or other iron in connection with the coils proper4 #bcb4 ,by making #d coils having1 respectively1 #a1 #b1 #b1 and #e ,ohms resistance1 you will be able to use any number of ,ohms from #a to #aj4 ,these will be very handy in connection with a ,wheatstone's bridge for comparing resistances4 7,see text-book for experiments74 ,the coils should be mounted upon a base with proper binding-posts1 so that one or more coils can be used at a time4 7,see ,app4 #acb47 ,for the #b-,ohm coil use1 of course1 twice as much of the same kind of wire as for the #a-,ohm coil4 ,,apparatus #acb4 ,illustration3 ,fig4 #ajf4 #bcc4 ,resistance ,coils4 ,fig4 #ajf4 ,the construction of one coil is given in ,app4 #aca4 ,to have the set of coils so that they can be easily used1 place the spools upon a base which1 in the model1 is #h-a_/b x #d x #g_/h in4 ,the spools are #a-c_/d in4 apart1 center to center1 and should be glued to the base4 ,fig4 #ajf is a plan of the apparatus4 ,u1 ,v1 etc41 are binding-posts like ,app4 #df4 ,the figures between them show how many ,ohms resistance there are in the coil above4 ,the coils ,a1 ,b1 ,c1 ,d1 and ,e are wound respectively for #a1 #b1 #b1 #e and #aj ,ohms4 #bcd4 ,connections4 ,if you join a ,wheatstone's bridge1 for example1 with ,u and ,v 7,fig4 #ajf71 the resistance added will be but #a ,ohm2 if you join with ,u and ,w1 the coils ,a and ,b will be in the circuit and make #c ,ohms resistance2 if ,v and ,x1 #d ,ohms2 if ,v and ,y1 #i ,ohms2 if ,u and ,z1 the whole1 or #bj ,ohms4 ,,apparatus #acc4 #bce4 ,resistance ,coils4 ,for use in some experiments in comparing the resistance1 diameter1 lengths1 etc41 of wires 7,see text-book71 it is very handy to have coils made a certain number of meters long4 7,the meter is a ,french unit of measure and represents #ci4cgje of our inches74 ,german-silver wire has a much greater resistance than copper wire of the same size and length4 7a7 ,make a coil 7,see ,app4 #aca for method7 containing #a meter of ,no4 #cj ,german-silver wire4 7b7 ,make a coil with #b meters ,no4 #cj ,german-silver wire4 7c7 ,make one with #b meters of ,no4 #bh ,german-silver wire4 7d7 ,make one with #bj meters of ,no4 #cj copper wire4 ,the above wire must be insulated if it is to be wound upon spools4 ,bare wire may be arranged on boards or racks so that the current may not be short circuited4 ,,chapter ,,xviii4 ,,apparatus ,,for ,,static ,,electricity4 #bcf4 ,static or ,frictional ,electricity4 ,there are many interesting and instructive experiments in this branch of electricity4 ,all that can be done here is to explain a few pieces of simple apparatus to show the presence of static electricity1 it being taken for granted that you know how to produce it1 and that you have some book of simple experiments4 #bcg4 ,electroscopes are instruments for showing the presence of static electricity4 ,,apparatus #acd4 #bch4 ,thread ,electroscope4 ,a piece of ordinary thread may be used for this purpose4 ,tie one end of it to the back of a chair or other support4 ,,apparatus #ace4 #bci4 ,pith-,ball ,electroscope4 ,fig4 #ajg4 ,the pith from elder1 corn-stalk1 milk-weed1 etc41 is very light and porous4 ,when this is tied to the end of a silk thread1 we get the pith-ball electroscope1 so much talked about in nearly every text-book on physics4 ,the upper end of the thread may be tied to any suitable support4 ,fig4 #aag shows a book1 lead pencil1 and a small weight to hold the pencil steady4 ,the thread is tied to one end of the pencil4 ,illustration3 ,fig4 #ajg4 ,,apparatus #acf4 #bdj4 ,support for ,electroscopes1 etc4 ,fig4 #ajh4 ,glue or nail a spool1 ,s1 to a wooden base1 ,b1 measuring about #d x #e in4 ,wrap some paper around a #g in4 length of #a_/d in4 dowel1 ,d1 to make it fit the hole in ,s4 ,wind one end of a wire1 ,w1 around the top end of ,d4 ,to the outer end of ,w tie a silk thread1 ,s ,t1 on the lower end of which may be tied a piece of pith or material to serve as an electroscope4 ,illustration3 ,fig4 #ajh4 ,,apparatus #acg4 #bda4 ,carbon ,electroscope4 ,carbon will be found to make a most excellent electroscope1 as it is light and a good conductor of electricity4 ,light an ordinary match and let it burn until it is charred through and through4 ,the black substance remaining is carbon4 ,tie a small piece of the carbon1 about #a_/d in4 long1 to one end of a silk thread1 and support the thread as in ,fig4 #ajg or #ajh4 ,,apparatus #ach4 #bdb4 ,pivoted ,electroscope4 ,fig4 #aji and #aaj4 ,fold a piece of stiff paper double1 then cut it into the shape shown4 ,it should be about #c in4 long and #a in4 wide when opened out4 ,a hole1 ,b1 about #a_/b in4 in diameter should be cut in it while folded4 ,a piece of paper1 ,c1 should be pasted to ,a1 so that its top1 where it is creased1 will be about #a_/h in4 above the top of ,a4 ,the support consists of a pin1 ,e1 stuck through a cork1 ,d4 ,balance the paper on the pin1 which passes up through the hole1 ,b4 ,an electrified body brought near this apparatus will make it whirl around very decidedly4 ,illustration3 ,fig4 #aji4 ,illustration3 ,fig4 #aaj4 ,,apparatus #aci4 #bdc4 ,fancy ,electroscope4 ,fig4 #aaa4 ,fold a piece of stiff paper double1 then cut out some fancy-shaped figure1 as suggested1 and draw the face1 clothes1 etc41 to suit4 ,this being folded through the center for cutting1 it can be balanced upon a pin-point as explained in ,app4 #ach4 ,illustration3 ,fig4 #aaa4 ,illustration3 ,fig4 #aab4 ,,apparatus #adj4 #bdd4 ,box-,cover ,electroscope4 ,fig4 #aab4 ,a pasteboard box-cover1 balanced upon a pin1 makes a fairly good electroscope1 although it is not nearly so sensitive as ,app4 #ach4 ,the pin may be stuck in the upper end of the dowel1 ,d1 shown in ,fig4 #ajh4 ,,apparatus #ada4 #bde4 ,leaf ,electroscope4 ,fig4 #aac4 ,this is a very sensitive instrument1 and can be used to tell the kind of static electricity on a body1 as well as the mere presence of it4 7,see experiments in text-book47 ,the lamp chimney acts as a support for the leaves1 ,l1 and it protects them from currents of air4 ,a tin box-cover1 ,c1 has a small hole punched through its center4 ,through this is pushed one end of a wire1 ,w4 ,this may be a hairpin1 straightened4 ,the upper end is bent over at right angles1 after passing it through the hole4 ,the lower end is bent as shown4 ,on this horizontal part is fastened the leaf4 ,these should be made of aluminum leaf1 or of ,dutch metal4 ,the former will stand more rough handling than the latter4 ,goldleaf is used for very sensitive instruments4 ,it is a little too delicate for unskilled hands4 ,illustration3 ,fig4 #aac4 ,illustration3 ,fig4 #aad4 #bdf4 ,to cut the aluminum leaf1 place it between two pieces of paper1 then cut paper and all into the desired shape4 ,the piece should be about #c in4 long and #a in4 wide4 ,fold this across the middle1 and stick it to the underside of the wire 7,fig4 #aac74 ,saliva will make it adhere to the wire1 if you have nothing better4 ,,apparatus #adb4 #bdg4 ,to ,show ,where a ,charge of ,static ,electricity ,resides4 ,fig4 #aad4 ,this shows a tin baking-powder box placed upon a hot tumbler4 ,a moist cotton thread is hung over the edge of the box4 7,see experiments in text-book47 ,the box will become charged by touching it with a charged body4 ,the thread will show whether the charge resides upon the inside or upon the outside of the box4 ,,apparatus #adc4 ,illustration3 ,fig4 #aae4 #bdh4 ,support for ,electrified ,combs4 ,fig4 #aae4 ,in the study of static electricity1 ordinary ebonite combs can be used to great advantage4 ,a bent hairpin will serve as a cradle to support them4 ,a silk thread may be tied to the wire1 but a narrow silk ribbon is better than thread1 as it will hold the comb steady4 ,,chapter ,,xix4 ,,electric ,,motors4 #bdi4 ,an ,electric ,motor is really a machine4 ,if it be supplied with a proper current of electricity1 its armature will revolve2 and1 if a pulley or wheel be fastened to the revolving shaft1 a belt can be attached1 and the motor made to do work4 ,there are many kinds of motors1 and many simple experiments which aid in understanding them4 ,all that can be done here1 however1 is to show how to make simple motors4 7,see text-book for experiments47 ,,apparatus #add4 #bej4 ,electric ,motor4 ,fig4 #aaf1 #aag4 ,fig4 #aaf shows a plan or top view1 and ,fig4 #aag shows a side view1 with a part of the apparatus removed1 for clearness4 ,the base1 ,b1 is #e x #d x #g_/h in4 ,the upright1 ,u1 is #c-a_/b x #a-a_/b x #a_/b in41 and is nailed or screwed to ,b4 ,the binding-posts1 ,x and ,y are like ,app4 #df4 #d is a screw binding-post4 #bea4 ,the ,field-,magnets1 as the large electro-magnets on a motor are called1 are made of #e_/af machine-bolts1 #b-a_/b in4 long4 ,the washers are #a-a_/b in4 apart inside4 7,see ,app4 #hh for full directions47 ,the bolt cores are #b in4 apart1 center to center4 7,see ,app4 #hi47 ,the tin yoke1 ,d1 is made like ,app4 #ga1 and it is fastened to the base1 like ,app4 #ij4 ,the hole for the screw1 however1 is made a little to one side of the center1 so that a dent can be made at the center for the bottom of the shaft1 #h1 to turn in4 ,make the dent with a center punch4 ,the yoke is fastened to ,b1 so that one edge of it is #a-a_/b in4 from the back edge of ,b4 7,fig4 #aaf74 #beb4 ,the ,armature1 ,a1 is made of #f or #h thicknesses of tin1 #b-a_/b in4 long and #c_/d wide4 7,see ,app4 #ga47 ,in its center is punched or drilled a #a_/d in4 hole1 so that it can be slipped onto the #a_/d in4 sink-bolt1 #h4 ,if you have taps you can make the hole a little smaller than #a_/d in41 and thread it so that it will screw onto #h4 ,a must be heavy enough to revolve a few times when once started4 ,it is pinched between two nuts1 #i and #aa1 so that it just clears the poles when it turns4 7,see ,app4 #ade for another form of armature47 ,illustration3 ,fig4 #aaf4 #bec4 ,the shaft or axle1 #h1 is made of a sink-bolt that is #c in4 long and #a_/d in4 in diameter4 ,these sink-bolts are threaded over their entire length1 and are furnished with two nuts1 #i and #aa1 ,fig4 #aag4 ,file or grind the end of #h to a point1 so that it will turn easily in a dent made for it in the yoke1 ,d1 or in a dent made in another piece of tin fastened over the yoke4 ,the shaft is held in a vertical position by the arm1 ,c4 #bed4 ,the ,arm1 ,c1 is made of #b or #c thicknesses of tin4 ,it is #c x #c_/d in42 it has in one end a hole for the shaft to revolve in easily1 and in its other end a slot is cut4 ,a screw-eye and bur are used to hold ,c to the upright1 ,u4 ,by this means the shaft can be moved and regulated as to position4 ,illustration3 ,fig4 #aag4 #bee4 ,the ,commutator1 #i1 7,fig4 #aag71 is made of one of the nuts furnished with the shaft4 ,two of its corners are filed or ground off1 so that it has the shape shown at the right1 in ,fig4 #aag4 ,the copper wire1 #aj1 rubs against #i1 as the pointed part of it comes around4 #aj is really a brush1 and carries the current into #i at the right time4 #bef4 ,connections4 ,join the two inside ends 7,sec4 #abc7 of the coils to #d4 ,the outside end of #b is joined to ,x2 the outside end1 #g1 of the other coil1 #f1 is carried up under or around the screw-eye1 ,s ,i1 and then its bare end reaches out and gently scrapes against the top of the shaft1 #h4 ,the wire1 #aj1 leads from ,y to the back of the base1 where it is carried up to a screw1 #ab1 which holds it to ,u4 ,its bare end reaches out to gently scrape against the commutator1 #i1 when it swings around4 ,this wire1 #aj1 should not press against #i during the entire revolution4 #beg4 ,adjustment4 ,suppose the current enters at ,x4 ,when the brush1 #aj1 presses against the commutator1 #i1 the current passes through ,x1 #a1 #b1 #c1 #d1 #e1 #f1 #g1 down #h to #i1 and out through #aj to ,y4 7,the current1 of course1 goes down into ,d and into the bolt-cores also2 but it can go no farther1 if the coils are properly insulated1 and ,a is not allowed to touch the cores4 ,it is better to have the end of the shaft rest upon a piece of glass1 having a slight depression made with a file1 or in a dent made in tin which rests upon wood1 the tin having no connection with ,d47 ,if #aj should continue to press against #i1 the current would continue to pass1 and ,a would be held firmly in place1 directly over #b and #f1 and1 of course1 the shaft could not revolve4 ,if1 however1 the brush leaves #i 7,see plan of #i at side of ,fig4 #aag71 just as ,a gets over the coils1 or an instant before it gets there1 the weight of ,a will carry it beyond the coils4 ,no current should pass again1 until ,a is at least at right angles to a line drawn through the center of the coils4 ,if the current again passes1 the ends of ,a will be attracted by the bolt-cores4 ,in other words1 the current should pass a little less than one-half of the time1 and this is divided into two parts4 ,suppose you start ,a with your finger2 the current should be shut off automatically just before the center of ,a gets over the center of the bolt-cores4 ,a makes #a_/d of a revolution without current1 and just after it gets beyond this1 the current passes for nearly #a_/d of a revolution1 which brings the ends over the poles again4 ,the next #a_/d of a turn it has no current1 because the flat side of #i is opposite the brush1 #aj1 as during the first #a_/d4 ,the last #a_/d the current passes again4 ,the exact position of the commutator will depend upon the way you arrange the brush4 ,the positions of #i and #aj can be found by trial1 so that the circuit will be promptly opened and closed at the proper moment4 ,start the motor by turning the armature4 #beh4 ,batteries4 ,the amount of power needed will depend upon how well you make the motor4 ,one cell of ,app4 #c or #d will run a well made one1 but it is better to use #b cells4 ,join the wires to ,x and ,y4 ,illustration3 ,fig4 #aah4 ,,apparatus #ade4 #bei4 ,armature for ,motors4 ,fig4 #aah shows another form of armature that may be used for small motors like ,app4 #add2 in fact1 you may find that this form is easier to make than that of ,app4 #add4 ,m is a #e_/af machine screw1 #a-a_/b in4 long1 #i being the nut furnished with it4 #i is filed as explained in ,sec4 #bee1 and forms the commutator4 ,c is the arm 7,sec4 #bed74 ,a is the armature 7,sec4 #beb74 ,a is held firmly in place between the spool1 ,e1 and #i4 ,s is a set-screw which passes through ,e1 and holds the piece of #a_/d in4 dowel1 ,f1 in place4 ,n is a needle-point fastened in the end of ,f4 ,n revolves in a dent made in a piece of tin1 ,h1 which rests upon a wooden strip1 ,g4 ,g is cut away on its underside1 so that it will straddle the yoke1 ,d1 ,fig4 #aag2 it is nailed to the base4 ,this is given as a suggestion4 ,by making ,f a little longer1 ,n can turn in a dent made in the yoke1 below ,g4 #bfj4 ,adjustments4 ,m1 being #e_/af in4 in diameter1 will screw solidly into the hole in ,e4 ,place #i upon it first1 then ,a1 and screw it about #a_/b way into ,e4 #i will serve as a lock-nut by turning it so that it will pinch ,a and hold it firmly against the top of ,e4 ,f should reach half way into ,e4 ,put ,n in place after you have ,h and ,g arranged4 ,you can then cut the upper end of ,f at such a place that it will bring ,a about #a_/h in4 from the top of the magnet-cores4 ,paper wrapped around ,f will make a good fit in ,e4 ,the current should enter ,m and leave #i1 as fully explained in ,app4 #add4 7,see ,sec4 #beg74 ,,apparatus #adf4 #bfa4 ,electric ,motor4 ,fig4 #aai1 #abj1 #aba1 #abb4 ,fig4 #aai shows a front view1 and ,fig4 #abj a side view of the whole motor4 ,fig4 #aba shows the part that revolves1 and includes the shaft1 armature and commutator4 ,fig4 #abb shows a section of the commutator4 ,all the dimensions are taken from a model4 ,you can modify the size to suit4 #bfb4 ,wood-work4 ,the base is #g x #e x #g_/h in4 ,the uprights1 ,u1 are #c-a_/b x #a x #c_/d in4 ,they are screwed or nailed to the base from below1 their #a-;in4 sides being towards you in ,fig4 #aai4 ,they are #d-a_/d in4 apart1 inside1 in this model4 ,the piece1 ,a1 is #b-a_/b x #g_/h x #e_/h in41 and is cut away on the underside to straddle the yoke4 ,fig4 #aah is a suggestion as to its shape4 ,a is screwed or nailed to ,b4 #bfc4 ,tin-work4 ,the horizontal arm1 ,t1 is made of #c thicknesses1 and holds the shaft in a vertical position4 ,t is #f-a_/d x #c_/d4 ,in its ends are slots1 and in its center is a hole so that the #a_/d in4 shaft can revolve easily1 but not too loosely4 ,the slots allow an adjustment1 the screws1 ,s1 holding ,t to ,u4 ,the shaft rests in a dent made in a piece of tin which is tacked to ,a4 ,the yokes are elsewhere described4 ,illustration3 ,fig4 #aai4 #bfd4 ,field-,magnets4 ,in this model they were made of #e_/af bolts1 #b in4 long1 placed #b in4 apart center to center4 ,the washers are #a-a_/h in4 apart inside4 7,see ,app4 #hh for full directions47 ,app4 #hi and #ga should be studied4 ,except in size1 they are made as in ,app4 #add4 ,they have #h layers of ,no4 #bd or #be wire4 #bfe4 ,the ,armature1 ,fig4 #aba1 on this style of motor consists of a regular horseshoe electro-magnet1 made in the same general way as the field-magnets4 ,the electro-magnets1 #ab and #af1 are smaller1 however1 than the field-magnets4 ,the cores are #a_/d in4 stove-bolts1 #a-a_/d in4 long under the head4 ,they are placed #b in4 apart1 center to center4 ,they are insulated and wound as fully explained in ,app4 #hh4 ,these #a_/d in4 bolts require a change in your winder4 7,see ,app4 #adg for this47 ,if you wish to use #e_/af bolts1 you may use the same axle for your winder as before4 ,the washers are #e_/h in4 apart1 inside4 ,the cores are wound with #d or #f layers of ,no4 #bd or #be wire4 ,this makes them about #c_/d in4 in diameter4 ,they are held in a tin yoke1 #ad1 made of #e or #f thicknesses of tin4 #ad is #c x #c_/d in41 and has #c holes punched in it4 ,the two outside holes are #b in4 apart4 ,through these pass the bolts1 which are held firmly by the #b nuts4 ,the shaft1 ,s ,b1 is a sink-bolt1 #c in4 long1 and #a_/d in4 in diameter4 7,see ,sec4 #bec47 ,the inside ends 7,sec4 #abc7 of the coils should be firmly twisted together or held under the top nuts to make a good connection between them4 ,illustration3 ,fig4 #abj4 #bff4 ,the ,commutator is in two parts1 which must be insulated from each other4 ,the #b sections are made out of thin tin or copper in the shape of an inverted ,t1 as shown at #aj1 ,fig4 #aba4 ,the arms of the ,t are about #c_/h in4 wide1 the horizontal ones reaching about half around the spool1 ,e4 ,the vertical arm reaches over the top of ,e1 and is held down by a small screw1 ,j4 ,the sections1 #aj1 must not touch the shaft4 ,the outside wires 7,sec4 #abc7 of #ab and #af are fastened under these screws1 ,j1 and they must not touch the shaft4 ,bend the tin sections so that they will be as nearly round as possible4 ,the spool1 ,e1 has been sawed off so that it will go between the field-magnets4 ,wind paper around the shaft to make it fit solidly into ,e4 ,s is a small screw that holds ,e in place1 if the paper does not hold it tight enough4 ,illustration3 ,fig4 #aba4 ,illustration3 ,fig4 #abb4 ,fig4 #abb shows a section of the spool and tin sections with the brushes pressing against them4 ,the sections do not touch each other1 and the brushes touch opposite sections4 ,it is evident1 then1 that the current must pass through the coils #ab and #af in order to get from one section of the commutator to the other1 provided you have no short circuits through the shaft or elsewhere4 ,the slots in the commutator must be directly under the center line of the yoke1 #ad1 as seen in ,fig4 #aba4 #bfg4 ,the brushes1 #i and #ai1 ,fig4 #abj1 are made of very thin tin or copper4 ,they are cut to the shape shown1 the narrow part being about #a_/h in4 wide1 and long enough to reach at least to the center-line of the apparatus4 ,the foot1 or bottom part of the brushes1 should be about #a-a_/d x #c_/d in4 ,these are used to fasten them to the base and to make connections4 ,if you have no thin metal for brushes1 use copper wires1 and arrange them so that they will press gently against the commutator4 #bfh4 ,connections4 ,the inside ends 7,sec4 #abc7 of the field-magnets are held at #d4 ,the outside end of coil #b is joined to ,x1 and that of coil #f to #h1 the foot of the brush which presses against #aj4 ,the section1 #aj1 of the commutator is joined to #aa1 the outside end of coil #ab1 its inside end being fastened to the inside end of coil1 #af1 either by twisting them together1 or by fastening them under the top nuts of the armature yoke1 #ad4 ,the outside end of coil #af is joined to the other commutator section1 #ah4 ,the brush1 #ai1 completes the circuit4 ,in the foot of #ai is the binding-post1 ,y4 ,if the current enters at ,x1 it will pass through #a1 #b1 #c1 #d1 #e1 #f1 #g1 #h1 #i1 #aj1 #aa1 #ab1 #ac1 #ad1 #ae1 #af1 #ag1 #ah1 #ai1 and out at ,y1 provided #aj and #ah are in contact with #i and #ai4 ,be careful not to have any short circuits4 ,if1 for example1 the wire #g touches #d1 or if #c touches #h1 or if the wires #aa and #ag touch the shaft1 your current will not pass where you expect1 and you will have trouble4 #bfi4 ,adjustment4 ,the armature cores should just clear the poles of the field-magnets as they turn4 ,this must be regulated by the thickness of ,a and the position of the nuts on the shaft1 ,s ,b4 ,the slots in the commutator must be under the center of the yoke1 #ad4 ,the brushes1 #i and #ai1 must touch #aj and #ah1 but not so hard that they will stop the motor4 ,wire brushes are more easily adjusted than tin or sheet-copper ones4 ,the tin arm1 ,t1 must hold the shaft properly4 ,the point of the shaft must allow it to turn easily4 ,the motor will turn clockwise if the attachments are made as shown4 ,use #a or #b good bichromate cells1 like ,app4 #c or #d4 #bgj4 ,operation4 ,the current will pass through the field-coils in the same direction1 as long as the battery wires are not changed4 ,the current is reversed in the armature-coils every time the brushes change from one section to the other of the commutator2 that is1 it flows in one direction during one-half of a revolution1 and in the opposite direction during the other half4 ,this reverses the poles of the armature-magnets every #a_/b revolution4 7,see text-book for full explanations and for simple experiments with electric motors47 ,,apparatus #adg4 #bga4 ,attachment for ,winder4 ,in winding small electro-magnets for armature1 etc41 in which cores are used that are not #e_/af in4 in diameter1 your winder will have to be slightly changed4 ,its #e_/af stove-bolt will have to be removed1 and a #a_/d in4 one put in instead4 ,this may be done by making a handle for the #a_/d in4 bolt4 ,to keep this from wobbling in the #e_/af hole1 wind stiff paper around the bolt until it fits quite tightly4 ,the whole winder is explained as ,app4 #ic4 ,,chapter ,,xx4 ,,odds ,,and ,,ends4 ,,apparatus #adh4 #bgb4 ,graduated ,circles4 ,fig4 #abc4 ,for compasses 7,app4 #fg71 and for use in connection with tangent galvanometers 7,app4 #aaf71 a graduated circle is necessary4 ,fig4 #abc is a reduced drawing from an original that is #d in4 in diameter4 ,the long lines are #aj degrees apart1 the smallest divisions shown being #e degrees apart4 ,single degrees can be determined with considerable accuracy with the eye4 ,illustration3 ,fig4 #abc4 ,to divide the circle4 ,divide the circumference into #d equal parts2 these will be #ij degrees from each other1 there being #cfj degrees in every circle4 ,divide each quarter into nine equal parts with a pair of dividers2 these will be for the long lines1 #aj degrees apart4 ,divide each of these into two equal parts4 ,if you are used to drawing1 you can divide the circle still more1 but #e-;degree divisions will do4 ,,apparatus #adi4 #bgc4 ,adjustable ,table4 ,fig4 #abd4 ,a table that can be raised or lowered is useful4 ,the one shown at ,d1 ,fig4 #abd1 is used for the galvanometer of ,app4 #aag4 ,the dimensions are given in the figure4 ,the upright piece1 ,u1 is fastened to ,d with brass screws1 not with nails1 as these would affect the needle4 ,it is placed at one side of ,d so that the compass needle placed in the center of ,d will also be in the center of the wire coils when used in ,app4 #aag4 ,the table is fastened in any position by a screw-eye1 ,s ,i1 which presses a copper washer1 ,w1 against ,u4 ,s ,i works through a narrow slot1 ,s1 and screws into the back of the galvanometer4 ,by making ,s longer1 the table may be used for other laboratory purposes1 if it is joined with some other form of standard4 ,illustration3 ,fig4 #abd4 ,,apparatus #aej4 #bgd4 ,glue ,pot4 ,if you have occasion to use glue1 you can make a good glue pot out of #b tin cans1 one being placed inside the other4 ,put #a_/d teacupful of glue in the inside can4 ,if you have time1 cover it with cold water1 and let it soften4 ,if you are in a hurry1 cover it with hot water4 ,set this inside can into the other1 in which you have boiling water4 ,do not let the water boil over4 ,the solder will not melt from ordinary tomato cans1 if you keep water in them4 ,thin the glue with a little hot water until it drips from the brush in drops4 ,have the glue hot and fairly thin1 and apply quickly4 ,hold the pieces of wood together by pressure until the glue hardens4 ,,apparatus #aea4 #bge4 ,paraffine ,paper and ,cardboard are extremely useful for insulating purposes4 ,the paraffine used in candles will do1 if you cannot get it in block form4 ,while ordinary paper will do for simple apparatus to wind about coils1 etc41 you will find that paraffine paper can be handled very rapidly4 ,to melt the paraffine you should use a double boiler1 or one made of a shallow basin set in a pan of water4 ,the water should be boiled4 ,this will melt the paraffine in the basin4 ,strips of paper just passed through the melted paraffine will become soaked1 and the paraffine will quickly harden in the air4 ,allow thick cardboard to soak for a minute or two1 to drive out all the air4 ,this makes excellent washers for electro-magnets4 7,see ,sec4 #aai47 ,to make one piece of this paper stick to another1 merely pass a clean hot nail over the two where they lap4 ,to hold coils of wire together1 or to wooden bases1 use a few drops of paraffine applied with a large hot nail4 #bgf4 ,caution4 ,do not heat paraffine directly upon the fire or over a burner1 unless you watch it constantly4 ,it will burn if its temperature is raised too much4 ,it is better to heat it with steam1 as you do glue4 ,,apparatus #aeb4 #bgg4 ,battery ,jars4 ,for small cells1 use glass tumblers4 ,ordinary glass fruit jars are good4 ,even earthen bowls may be used1 and for large cells--if you have nothing better--you can use small earthen crocks or jars4 #bgh4 ,glass ,bottles can be cut off so that they will make excellent jars4 ,if you have thin bottles1 you can cut them with strong cord4 ,tie one end of the cord1 which should be #e or #f feet long1 to a door knob or to a solid post4 ,tie the other end around your body4 ,make one complete turn of the cord around the bottle where you wish to cut it2 draw the cord tight by stepping back1 and with both hands draw the bottle back and forth vigorously many times1 so that the cord will rub it hard and make it very hot4 ,do not let the cord move lengthwise upon the bottle4 ,this will make a circle around the bottle that is very hot4 ,immediately plunge the bottle into cold water1 the colder the better4 ,use ice-water1 if you have it4 ,if you produce heat enough1 the bottle should crack all the way around very neatly4 ,file off any sharp corners and edges with a wet file4 #bgi4 ,a hot iron can be used with success to cut off a bottle4 ,file a deep groove first1 hold the red-hot iron first on one side of file mark and then on the other to start the crack4 ,you can lead the crack wherever you wish by keeping the iron about #a_/h in4 ahead of it4 #bhj4 ,a small gas-flame will be much better than a hot iron1 and you may easily use it1 if you have glass tubing1 rubber tubing1 etc41 in your shop4 ,draw out the glass so that the gas will burn in a fine needle-like flame about #a in4 long4 ,keep the point of the flame about #a_/d in4 ahead of the crack4 ,the glass tube should be held in a rubber tube connected with the gas pipe4 ,,chapter ,,xxi4 ,,tools ,,and ,,materials4 #bha4 ,your ,workshop4 ,if possible1 keep all your work1 tools and apparatus in one room1 and lock the door when you leave4 ,the work-bench may be made of an old kitchen table1 or of a strong1 large box4 ,the tool chest may be made of any clean box about the size of a soap box4 ,shelves can be made by setting soap or starch boxes on their sides1 one above the other4 #bhb4 ,the tools needed are generally mentioned in the proper places1 under the directions for construction4 ,it is better to buy your tools as required1 than to buy too many at once1 some of which you may not need4 ,if you have absolutely no tools1 not even a saw or hammer1 you will be obliged to buy or borrow1 although a great deal can be done with a good knife4 ,do not be satisfied with rough-looking pieces of apparatus4 ,there are a few important tools needed for this work4 ,while substitutes can be found for most of them1 the boy who has access to a wood-working bench and tools will be able to do better and more rapid work than the boy who has no such tools4 #bhc4 ,list of tools4 ,the following tools are needed1 if rapid1 accurate work is desired3 7#a47 ,lead pencil4 7#b47 ,a rule1 divided into sixteenths for measuring4 ,a straight foot rule will do1--cost one cent4 7#c47 ,steel point for scratching lines on tin and copper4 ,a stout needle-point is just the thing4 7#d47 ,an awl for making holes in wood2 one that is a little less than #a_/h in4 in diameter is best4 7,see ,app4 #be47 7#e47 ,a try-square with a #f in4 blade1 so that you can mark out your apparatus with square corners4 ,you can use a square-cornered box or piece of pasteboard1 if you have no try-square4 7#f47 ,chisels are very useful1 but you can do wonders with a good sharp knife4 7#g47 ,screw-driver4 ,do not use a good knife-blade for a screw-driver4 7#h47 ,a saw1 one with teeth that are not too coarse is to be preferred4 7#i47 ,a plane is extremely useful to make your wood-work smooth and neat2 but a great deal can be done with the sharp edges of broken glass1 followed by a good rubbing with fine sand-paper4 7#aj47 ,a brace and a set of bits may be needed in #b or #c cases1 but nearly all of the holes can be made as in ,app4 #be4 7#aa47 ,punches for sheet-tin1 etc41 will save much time4 7,see ,app4 #bf1 #bg47 ,for small holes in binding-posts1 etc41 use a flat-ended punch1 #a_/h in4 in diameter4 ,you should have one #a_/d or #e_/af in4 in diameter1 if you make your yokes1 armatures1 etc41 as in ,chapter ,,viii4 ,a blacksmith will help you out with this4 7#ab47 ,a center-punch or sharp-pointed punch for making dents in metal4 ,a sharp-pointed wire nail will do for tin and copper4 7#ac47 ,files for metal4 7#ad47 ,some sort of a vice or clamp4 7,see ,app4 #gi1 #hj47 7#ae47 ,shears for cutting sheet-tin1 etc4 ,a pair of old shears will do4 7#af47 ,an anvil or piece of old iron that may be used to hammer on to flatten tin1 etc4 ,an old flat-iron makes a good anvil4 7#ag47 ,hammer4 ,the small hollow handle tool sets are very handy1 and they contain small chisels1 awls1 screw-driver1 etc4 ,these sets cost from #ej cents up4 #bhd4 ,materials4 ,for wood you will find the sides and ends of clean soap or starch boxes about the right thickness2 they are fairly smooth to begin with4 ,for thin wood use cigar boxes4 ,the pieces from old boxes should be removed with care1 and saved in one place1 which may be called your lumber yard4 ,all nails should be removed with a claw-hammer4 ,look out for nails when using a saw1 plane or other edged tool4 7,see ,sec4 #big47 ,the edges of bases1 etc41 may be bevelled as shown in ,fig4 #ie4 ,this is not necessary1 but it adds greatly to the appearance4 #bhe4 ,screw-,eyes4 ,brass screw-eyes1 with copper burs1 make excellent binding-posts4 7,app4 #de1 #df47 ,those that are #c_/h in4 in diameter inside the circle are about right4 ,these are about #a-a_/d in4 long in all1 with a #a_/b in4 thread4 #bhf4 ,copper ,burs1 such as are used with rivets1 are very handy4 ,the size that is #a_/b in4 in diameter1 with a #a_/h in4 hole1 is good4 ,illustration3 ,fig4 #abe4 #bhg4 ,copper ,wire4 ,this can be bought at an electrician's4 ,the only trouble1 however1 in buying small quantities is that you may have to pay a large price in proportion4 ,if you get it on #a_/b lb4 spools you can handle it much better 7see ,app4 #bc7 than you can if you have it in a tangle4 ,it is well to have #a_/b lb4 of ,no4 #bd or #be for electro-magnets1 current-detectors1 etc41 etc4 #a_/b lb4 of ,no4 #cj will not be too much1 if you make induction coils4 ,if you handle your wire carefully1 single cotton-covered will do4 ,double cotton-covered is better than single1 but it costs more4 ,be careful not to injure the covering4 7,see below for splicing wire47 ,look out for broken wire4 #bhh4 ,splicing ,wire4 ,fig4 #abe4 ,do not simply touch two wires together and imagine that you have a good connection2 a mere twist is not sufficient4 ,clean the ends of old wire thoroughly with a file or knife-blade1 and join them as shown in ,fig4 #abe4 #bhi4 ,copper4 ,sheet-copper can be purchased at a tinsmith's or at a hardware store4 ,electricians usually have a thin variety of copper called brush copper1 which makes good battery-plates1 binding-posts1 etc4 ,you can cut this thin copper with an ordinary pair of shears4 #bij4 ,iron4 ,for thin sheet-iron1 nothing is better than sheet-tin4 7,see tin47 ,hoop iron is thicker than tin1 and makes good yokes1 etc4 ,in many cases1 ordinary nails may be used where a magnetic substance is needed4 ,annealed iron wire is extremely soft4 7,see text-book for experiments with steel and iron47 #bia4 ,steel4 ,old files1 watch-springs1 clock-springs1 corset-steels1 knitting-needles1 harness-needles1 hack-saw blades1 sewing-needles1 etc41 are generally made of a good quality of steel4 #bib4 ,zinc1 in the sheet form1 can be bought at a hardware store4 ,for a few cents you can get quite a large piece4 ,get the thick pieces for heavy battery-plates of an electrician4 ,you do not need anything that is thicker than #a_/h in4 ,the zinc rods are usually amalgamated4 #bic4 ,lead can be bought at a plumber's1 tinsmith's1 or hardware store4 ,you may want some for a storage cell4 #bid4 ,nails4 ,wire nails are best for light work4 ,get an assortment from #a_/b in4 long up to #a-a_/b in4 #bie4 ,screws4 ,it is better to use brass screws around electrical apparatus4 ,for the small work1 for binding-posts1 etc41 use #e_/h ,no4 #e4 ,another handy size is ,no4 #g1 from #c_/d to #a-a_/d in4 long4 ,the round-headed screws are best1 unless you want to countersink them4 #bif4 ,tin4 ,this is really thin sheet-iron1 covered with tin4 ,save up tomato-cans1 cracker-boxes1 condensed-milk cans1 etc4 ,the cracker-boxes are just as good as sheet-tin1 as the pieces are large and clean4 ,you can remove the solder from cans by heating them in the kitchen fire4 ,knock out the bottoms with a poker when the solder gets soft4 ,clean the tin with sand-paper4 #big4 ,carbons4 ,you can get carbon rods or plates at an electrician's4 ,if you have arc electric lights in your city1 you will be able to pick up carbons2 these1 however1 generally have a coating of copper1 which must be eaten off with dilute nitric acid4 ,this is a bother4 ,you will find it cheaper to buy the #a_/b in4 rods that are #ab in4 long1 and uncoated4 #bih4 ,shellac4 ,your wood-work will be much improved by using shellac upon it after you have thoroughly sand-papered it4 ,you can get it1 all prepared1 at a paint store4 ,wood-alcohol is used to thin it if it gets too thick4 ,keep it in a wide-mouth bottle4 ,paint it on quickly and evenly with a brush1 and do not go over it again when it is partly dry4 ,wait until it is thoroughly hard before putting on a second coat4 ,it should be fairly thin to spread well4 ,clean your brush in wood-alcohol before putting it away1 and keep the shellac bottle tightly corked4 ,a small tin can or a teacup is best to hold the shellac when using it4 99 99 99 99 99 ,,things ,a ,,boy ,,should ,,know ,,about ,,electricity4 ,by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,the book contains #ahj pages1 and #bfj illustrations2 it measures #e x #g-a_/b in41 and is bound in cloth4 ,seventh ,edition ,price1 postpaid1 #a4jj ,,contents3 ,chapter ,i4 ,about ,frictional ,electricity4--,,ii4 ,about ,magnets and ,magnetism4--,,iii4 ,how ,electricity is ,generated by the ,voltaic ,cell4--,,iv4 ,various ,voltaic ,cells4--,v4 ,about ,push-,buttons1 ,switches and ,binding-,posts4--,,vi4 ,units and ,apparatus for ,electrical ,measurements4--,,vii4 ,chemical ,effects of the ,electric ,current4--,,viii4 ,how ,electroplating and ,electrotyping are ,done4--,,ix4 ,the ,storage ,battery and ,how it ,works4--,x4 ,how ,electricity is ,generated by ,heat4--,,xi4 ,magnetic ,effects of the ,electric ,current4--,,xii4 ,how ,electricity is ,generated by ,induction4--,,xiii4 ,how the ,induction ,coil ,works4--,,xiv4 ,the ,electric ,telegraph1 and ,how it ,sends ,messages4--,,xv4 ,the ,electric ,bell and ,some of its ,uses4--,,xvi4 ,the ,telephone1 and ,how it ,transmits ,speech4--,,xvii4 ,how ,electricity is ,generated by ,dynamos4--,,xviii4 ,how the ,electric ,current is ,transformed4--,,xix4 ,how ,electric ,currents are ,distributed for ,use4--,,xx4 ,how ,heat is ,produced by the ,electric ,current4--,,xxi4 ,how ,light is ,produced by the ,incandescent ,lamp4--,,xxii4 ,how ,light is ,produced by the ,arc ,lamp4--,,xxiii4 ,x-,rays1 and ,how the ,bones of the ,human ,body are ,photographed4--,,xxiv4 ,the ,electric ,motor and ,how it ,does ,work4--,,xxv4 ,electric ,cars1 ,boats and ,automobiles4--,,xxvi4 ,a ,word ,about ,central ,stations4--,,xxvii4 ,miscellaneous ,uses of ,electricity4 ,this book explains1 in simple1 straightforward language1 many things about electricity2 things in which the ,american boy is intensely interested2 things he wants to know2 things he should know4 ,it is free from technical language and rhetorical frills1 but it tells how things work1 and why they work4 ,it is brimful of illustrations--the best that can be had--illustrations that are taken directly from apparatus and machinery1 and that show what they are intended to show4 ,this book does not contain experiments1 or tell how to make apparatus2 our other books do that4 ,after explaining the simple principles of electricity1 it shows how these principles are used and combined to make electricity do every-day work4 99 99 99 99 99 ,everyone ,should ,know ,about ,electricity4 99 99 99 99 99 ,a ,,very ,,appropriate ,,present ,things a ,boy ,should ,know ,about ,wireless ,by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,author of ,things a ,boy ,should ,know about ,electricity1 ,fun with ,electricity1 ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment1 ,the ,study of ,electric ,motors by ,experiment1 ,electrical ,handicraft1 ,etc41 ,etc4 #abf ,pages--#aji ,illustrations and ,diagrams ,bound in ,cloth--,net #a4jj ,this book contains much practical and some theoretical information regarding the operation and explanation of wireless outfits4 ,it discusses enough of the theoretical side to make the student sure of himself and to give a well-rounded knowledge of this most practical subject4 ,the author has explained the various pieces of apparatus needed in a wireless station in such a clear manner that the student can not fail to understand how they work and why they work4 ,the numerous drawings and diagrams simplify the discussions to such an extent that the reader will not want to skip a single paragraph4 ,things a ,boy ,should ,know ,about ,wireless will be welcomed by thousands of enthusiasts and it should find its way into every library4 ,from ,,thomas ,m4 ,,st4 ,,john ,cascade ,ranch4 ,east ,windham1--,n4,y4 ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment ,by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,,fourth ,,edition ,price1 postpaid1 #a4be4 ,the book contains #bbj pages and #afh illustrations4 ,it measures #e x #g-a_/b in41 and it is bound in green cloth4 ,,contents3 ,part ,i4 ,magnetism4--,chapter ,i4 ,iron and ,steel4--,,ii4 ,magnets4--,,iii4 ,induced ,magnetism4--,,iv4 ,the ,magnetic ,field4--,v4 ,terrestrial ,magnetism4 ,part ,,ii4 ,static ,electricity4--,,vi4 ,electrification4--,,vii4 ,insulators and ,conductors--,,viii4 ,charging and ,discharging ,conductors4--,,ix4 ,induced ,electrification4--,x4 ,condensation of ,electrification4--,,xi4 ,electroscopes4--,,xii4 ,miscellaneous ,experiments4--,,xiii4 ,atmospheric ,electricity4 ,part ,,iii4 ,current ,electricity4--,,xiv4 ,construction and ,use of ,apparatus4--,,xv4 ,galvanic ,cells and ,batteries4--,,xvi4 ,the ,electric ,circuit4--,,xvii4 ,electromotive ,force4--,,xviii4 ,electrical ,resistance4--,,xix4 ,measurement of ,resistance4--,,xx4 ,current ,strength4--,,xxi4 ,chemical ,effects of the ,electric ,current4--,,xxii4 ,electromagnetism4--,,xxiii4 ,electromagnets4--,,xxiv4 ,thermo electricity4--,,xxv4 ,induced ,currents4--,,xxvi4 ,the ,production of ,motion by ,currents4--,,xxvii4 ,applications of ,electricity4--,,xxviii4 ,wire ,tables4--,apparatus ,list4--,index4 ,this is a text-book for amateurs1 students1 and others who want to take up a systematic course of electrical experiments at home or in school4 ,it will give a practical and experimental knowledge of elementary electricity1 and thoroughly prepare students for advanced work4 ,full directions are given for ,,two ,,hundred ,,experiments4 ,the experiments and discussions are so planned that the student is always prepared for what follows4 ,although the experiments may be performed with the apparatus that is usually found in school laboratories1 the author has designed a complete set of apparatus for those who want to have their own outfit4 99 99 99 99 99 ,if you want to take up a systematic course of experiments--experiments that will build a lasting foundation for your electrical knowledge--this book will serve as a valuable guide4 ,jan4 #a1 #aiah ,,student',s ,,discount ,,discontinued ,,price ,,to ,,all1 #f4be ,owing to greatly increased costs of labor and materials the discount of #fe;c formerly allowed on this set has been discontinued4 ,complete sets only now sold4 ,shipping weight on improved sets #aj lbs4 securely packed in wooden box4 ,sent by parcel post if proper postage is included in your remittance2 otherwise by express charges collect4 ,fun ,with ,magnetism and ,fun ,with ,electricity have started more young men upon electrical careers than any other scientific outfits ever placed before the public4 ,the thousands upon thousands that have been sold in all parts of the world have furnished fun and science for people of all ages1 and the mere fact that they are listed by the ,new ,york ,board of ,education1 and recommend to the pupils and teachers of the ,new ,york public and private schools is a guarantee of their value4 ,were it not for the fact that these are made in such large quantities and sold by stores1 agents and mail-order houses1 the price would be much higher4 ,don't fail to get these4 ,they have a national reputation4 ,,fun ,,with ,,magnetism ,this outfit contains a #cb-page book of instructions1 with #de illustrations1 together with a complete set of apparatus for performing #fa fascinating experiments4 ,it will give you some new ideas about magnetism and start you at the right place in your study of electricity4 ,think what that means--to start right6 ,the book contains experiments with the horseshoe magnet1 with bar magnets1 with floating magnets1 etc41 etc41 thus giving a practical knowledge of the subject2 and it is all done in such an interesting way that one can't help remembering it4 ,every experiment clinches some fact and every fact is important4 ,amusing ,experiments4--,something for ,nervous ,people to ,try4--,the ,jersey ,mosquito4--,the ,stampede4--,the ,runaway4--,the ,dog-fight4--,the ,whirligig4--,the ,naval ,battle4--,a ,string of ,fish4--,a ,magnetic ,gun4--,a ,top ,upside down4--,a ,magnetic ,windmill4--,a ,compass ,upside down4--,the ,magnetic ,acrobat4--,the ,busy ,ant-hill4--,the ,magnetic ,bridge4--,the ,merry-go-,round4--,the ,tight-rope ,walker4--,a ,magnetic ,motor ,using ,attractions and ,repulsions4--,and #dc ,others4 ,no4 ,r#a--;,fun with ,magnetism1 ,complete ,outfit1 postpaid #j4ce ,illustration ,,fun ,,with ,,electricity ,the author of this ,fun with ,science series has spent a great deal of time and money in experimenting to devise apparatus that will do the proper work and be1 at the same time1 simple and cheap1 and in no outfit has he succeeded better than in ,fun with ,electricity4 ,when you think of an outfit retailing for #ej;c4 and covering the whole subject of ,static ,electricity1 giving #fj scientific experiments upon its production1 conduction and induction1 with a #ee-page book of instructions with #ch drawings1 and a complete set of apparatus of #bj articles for performing these #fj experiments1 you will understand why the sales of this outfit have been enormous4 ,as the subject is presented in a fascinating way--and not as mere dry science--every one likes to do the experiments4 ,no wonder these sets are highly praised by parents and educators in every part of the country6 ,there is ,fun in these ,experiments3 ,chain ,lightning4--,an ,electric ,whirligig4--,the ,baby ,thunderstorm4--,a ,race with ,electricity4--,an ,electric ,frog ,pond4--,an ,electric ,ding-,dong4--,the ,magic ,finger4--,daddy ,long-,legs4--,jumping ,sally4--,an ,electric ,kite4--,very ,shocking4--,condensed ,lightning4--,an ,electric ,fly-,trap4--,the ,merry ,pendulum4--,an ,electric ,ferry-,boat4--,a ,funny ,piece of ,paper4--,a ,joke on the ,family ,cat4--,electricity ,plays ,leap-,frog4--,lightning ,goes ,over a ,bridge4--,electricity ,carries a ,lantern4--,and #dj ,others4 ,there isn't an outfit anywhere at any price that gives better value for the money4 ,an ideal present for a boy4 ,no4 ,r#b--;,fun with ,electricity1 ,complete ,outfit1 postpaid #j4fe ,,fun ,,with ,,puzzles ,here is an outfit that every boy and girl should have1 for it is amusing1 instructive and educational4 ,it is real fun to do puzzles and to puzzle your friends1 and this book contains some real brain-teasers that will make you think4 ,the book contains #ae chapters1 #hj pages1 and #abh illustrations1 and measures #ex#g-a_/b inches4 ,if you can't do any particular puzzle you will find its solution in the key1 which is bound with the book4 ,if you want to win prizes by doing the puzzles in the magazines1 you will find this book of four hundred puzzles a regular school of puzzles that will give you a thorough training for this kind of work4 ,the book alone is well worth the price1 to say nothing of the outfit of numbers1 counters1 pictures1 etc4 ,contents of ,book3 ,chapter 7#a7 ,secret ,writing4 7#b7 ,magic ,triangles1 ,squares1 ,rectangles1 ,hexagons1 ,crosses1 ,circles1 etc4 7#c7 ,dropped ,letter and ,dropped ,word ,puzzles4 7#d7 ,mixed ,proverbs1 ,prose and ,rhyme4 7#e7 ,word ,diamonds1 ,squares1 ,triangles1 and ,rhomboids4 7#f7 ,numerical ,enigmas4 7#g7 ,jumbled ,writing and ,magic ,proverbs4 7#h7 ,dissected ,puzzles4 7#i7 ,hidden and ,concealed ,words4 7#aj7 ,divided ,cakes1 ,pies1 ,gardens1 ,farms1 etc4 7#aa7 ,bicycle and ,boat ,puzzles4 7#ab7 ,various ,word and ,letter ,puzzles4 7#ac7 ,puzzles with ,counters4 7#ad7 ,combination ,puzzles4 7#ae7 ,mazes and ,labyrinths4 ,secret ,writing is explained in this book1 and it shows how you can write letters to your friends and be sure that no one can read them unless they are also in the secret4 ,this one thing alone will give you a great deal of enjoyment4 ,get this outfit and have some fun4 ,no4 ,r#c--;,fun with ,puzzles1 ,complete ,outfit1 postpaid #j4ce 99 99 99 99 99 ,,fun ,,with ,,soap-,,bubbles ,fancy ,bubbles and ,films are not easily blown without special apparatus1 and even with the proper outfit one must know how4 ,that's why we furnish a #af-page book with every set to show just how to do it4 ,with the aid of the #ba illustrations and the directions you can produce remarkable results that will surprise and entertain your friends4 ,a child can do it as well as a grown person4 ,illustration ,soap-,bubble ,parties using these outfits create real sensations4 ,why not be the first in your town to give a ,fun with ,soap-,bubbles ,party8 ,just write and ask about the price for any special number of them--say six or a dozen4 ,contents of ,book3 ,twenty-one ,illustrations4--,introduction4--,the ,colors of ,soap-,bubbles4--,the ,outfit4--,soap ,mixture4--,useful ,hints4--,bubbles ,blown with ,pipes4--,bubbles ,blown with ,straws4--,bubbles ,blown with the ,horn4--,floating ,bubbles4--,baby ,bubbles4--,smoke ,bubbles4--,bombshell ,bubbles4--,dancing ,bubbles4--,bubble ,games4--,supported ,bubbles4--,bubble ,cluster4--,suspended ,bubbles4--,bubble ,lamp ,chimney4--,bubble ,lenses4--,bubble ,basket4--,bubble ,bellows4--,to ,draw a ,bubble ,through a ,ring4--,bubble ,acorn4--,bubble ,bottle4--,a ,bubble ,within a ,bubble4--,another ,way4--,bubble ,shade4--,bubble ,hammock4--,wrestling ,bubbles4--,a ,smoking ,bubble4--,soap ,films4--,the ,tennis ,racket ,film4--,fish-net ,film4--,pan-shaped ,film4--,bow and ,arrow ,film4--,bubble ,dome4--,double ,bubble ,dome4--,pyramid ,bubbles4--,turtle-back ,bubbles4--,soap-,bubbles and ,frictional ,electricity4 ,there is nothing more beautiful than the airy-fairy soap-bubble with its everchanging colors4 ,this outfit gives the best possible amusement for old and young4 ,no4 ,r#d--;,fun with ,soap-,bubbles1 ,complete ,outfit1 postpaid #j4ce ,three extra packages of prepared soap1 postpaid 4#aj ,,fun ,,with ,,shadows ,no wonder shadow-making has been popular for several centuries6 ,what could give keener delight than comical shadow-pictures1 pantomimes1 entertainments1 etc48 ,professional shadowists use wires1 forms1 and various devices to aid them1 and that is why they get such wonderful results on the stage4 ,do you want to do the same thing right in your own home and entertain your friends with all kinds of fancy shadows8 ,you can do it with this outfit1 for the book contains #ajj illustrations and diagrams with directions for using the numerous articles included in the box4 ,you will be surprised to see how easily you can make these funny shadows with the aid of the outfit4 ,better get one now and make shadows like a professional4 ,illustration ,the ,outfit contains everything necessary for all ordinary shadow pictures1 shadow entertainments1 shadow plays1 etc4 ,the following articles are included3 ,one book of ,instructions called ,fun with ,shadows2 #a ,shadow ,screen2 #b ,sheets of ,tracing ,paper2 #a ,coil of ,wire for ,movable ,figures2 #a ,cardboard ,frame for ,circular ,screen2 #a ,cardboard ,house for ,stage ,scenery2 #a ,jointed ,wire ,fish-pole and ,line2 #b ,bent ,wire ,scenery ,holders2 #d ,clamps for ,screen2 #a ,wire ,figure ,support2 #a ,wire for ,oar2 #b ,spring ,wire ,table ,clamps2 #a ,wire ,candlestick ,holder2 #e ,cardboard ,plates containing the following printed figures that should be cut out with shears2 #ab ,character ,hats2 #a ,boat2 #a ,oar-blade2 #a ,fish2 #a ,candlestick2 #a ,cardboard ,plate containing printed parts for making movable figures4 ,no4 ,r#e--;,fun with ,shadows1 ,complete ,outfit1 postpaid #j4ce 99 99 99 99 99 ,,fun ,,with ,,photography ,popular ,pastimes are numerous1 but to many there is nothing more fascinating than photography4 ,the magic of sunshine1 the wonders of nature1 and the beauties of art are tools in the hands of the amateur photographer4 ,if you want to get a start in this up-to-date hobby1 this outfit will help you4 ,you will enjoy the work and be delighted with the beautiful pictures you can make4 ,the ,outfit contains everything necessary for making prints--together with other articles to be used in various ways4 ,the following things are included3 ,one ,illustrated ,book of ,instructions1 called ,fun ,with ,photography2 #a ,package of ,sensitized ,paper2 #a ,printing ,frame1 including ,glass1 ,back1 and ,spring2 #a ,set of ,masks for ,printing ,frame2 #a ,set of ,patterns for ,fancy ,shapes2 #a ,book of ,negatives 7,patented7 ,ready for ,use2 #f ,sheets of ,blank ,negative ,paper2 #a ,alphabet ,sheet2 #a ,package of ,card ,mounts2 #a ,package of ,folding ,mounts2 #a ,package of ,fixo4 ,illustration ,contents of ,book3 ,chapter ,i4 ,introduction4--,photography4--,magic ,sunshine4--,the ,outfit4--,,ii4 ,general ,instructions4--,the ,sensitized ,paper4--,how the ,effects are ,produced4--,negatives4--,prints4--,prin ting ,frames4--,our ,printing ,frame4--,putting ,negatives in ,printing ,frame4--,printing4--,developing4--,fixi ng4--,drying--- ,trimming4--,fancy ,shapes4--,mounting4--,,iii4 ,negatives and ,how to ,make ,them4--,the ,paper4--,making ,transparent ,paper4--,making the ,negatives4--,printed ,negatives4--,perforated ,negatives4--,negatives ,made from ,magazine ,pictures4--,ground ,glass ,negatives4--,,iv4 ,nature ,photography4--,aids to ,nature ,study4--,ferns and ,leaves4--,photographing ,leaves4--,perforating ,leaves4--,drying ,leaves1 ,ferns1 etc41 for ,negatives4--,flowers4--,v4 ,miscellaneous ,photographs4--,magnetic ,photographs4--,combination ,pictures4--,initial ,pictures4--,name ,plates4--,christmas1 ,easter and ,birthday ,cards4 ,no4 ,r#f--;,fun with ,photography1 ,complete ,outfit1 ,postpaid #j4fe ,,fun ,,with ,,chemistry ,illustration3 ,fun ,with ,chemistry ,chemistry is universally considered to be an interesting subject1 even in school1 and it is certainly an important one in these days of scientific progress4 ,this outfit starts you at the right place and presents the elements of the subject in a most interesting fashion4 ,the experiments are so enjoyable that you will take pleasure in doing them over and over again1 and you will want to do them for your friends4 ,you can have a lot of fun with this set1 and even if you have taken advanced courses in the subject you will find something new in these experiments4 ,the more you know about chemistry the more you will enjoy it1 for then you can more easily appreciate what a splendid outfit this is for the money4 ,the ,outfit contains over #bj different articles1 including chemicals1 test-tubes1 adjustable ring-stand1 litmus paper1 filter paper1 glass tubing1 etc42 in fact1 everything needed for the forty-one experiments4 ,the ,book of ,instructions is fully illustrated1 and measures #ex#g-a_/b inches4 ,fun ,found ,here3 ,from ,white to ,black1 or the ,phantom ,ship4--,yellow ,tears4--,smoke ,pearls4--,an ,ocean of ,smoke4--,a ,tiny ,whirlwind4--,a ,smoke ,cascade4--,an ,explosion in a ,teacup4--,a ,gas ,factory in a ,test-,tube4--,making ,charcoal4--,flame ,goes ,over a ,bridge4--,a ,smoke ,toboggan-,slide4--,fountains of ,flame4--,making an ,acid4--,making an ,alkali4--,a ,chemical ,fight4--,through ,walls of ,flame4--,an ,artificial ,gas ,well4--,a ,lampblack ,factory4--,steam from a ,flame4--,the ,flame that ,committed ,suicide4--,chemical ,soup4--,a ,baby ,skating-,rink4--,a ,magic ,milk-,shake4--,the ,wizard's ,breath4--,a ,chemical ,curtain4--,scrambled ,chemicals4--,and ,many ,other ,experiments4 ,no4 ,r#g--;,fun with ,chemistry1 ,complete ,outfit1 postpaid #j4fe 99 99 99 99 99 ,,electric ,,shooting ,,game ,shooting ,animals by electricity is certainly a most original game1 and it will furnish a vast amount of amusement to all4 ,the game is patented and copyrighted--because it is really a brand-new idea in games--and it brings into use that most mysterious something called electricity4 ,while the electricity is perfectly harmless1 there being no batteries1 acids or liquids1 it is very active and you will have plenty to laugh at4 ,it is so simple that the smallest child can play it and so fascinating that grandpa will want to try it4 ,the game-preserve is neatly printed in colors1 and the birds and wild animals are well worth hunting4 ,each has a fixed value--and some of them must not be shot at all--so there is ample chance for skill4 ,tissue-paper bullets are actually shot from the electric gun by electricity1 and it is truly a weird sight to see them shoot through the air impelled by this unseen force4 ,the ,outfit contains the ,game-,preserve1 the ,electric ,gun1 the ,shooting-,box1 and the ,electric ,bullets1 together with complete illustrated directions1 all placed in a neat box4 ,no4 ,r#da--;,electric ,shooting ,game1 complete1 postpaid #j4ce 99 99 99 99 99 ,,new ,,idea ,,tit-,,tat-,,toe ,splendid game for two1 three1 or four players2 great improvement upon the good old game2 fascinating game instantly learned2 nothing better for children's parties and progressive birthday parties2 box with game-board1 #ab men1 directions2 discount for party orders4 ,no4 ,r#ba--,new ,idea ,tit-,tat-,toe1 sample1 postpaid #j4ae ,electric ,air-,ships and ,other ,games 7patented7 ,illustration ,this is the age of air-ships and electricity1 so what could be more up-to-date than electric air-ships that will float and dive and race around at the will of the operator8 ,in this game ,mr4 ,st4 ,john has again made use of a scientific principle1 the air-ships being actually controlled by electricity4 ,they are made to act in a most peculiar manner1 with no wires1 no fuss1 no danger4 ,they are under perfect control and can be made to ascend to the ceiling1 drop to the floor or race across the room1 as desired4 ,you simply can't imagine how entertaining it is to see a lot of excited people managing these aerial racers1 each eager to win4 ,the outfit contains illustrated directions and materials for two players1 including the apparatus for producing the electricity and the repeller for managing the air-ships in mid-air4 ,the little air-ships are actually made of metal and they can be instantly formed4 ,here's the latest sport for all ages1 because the little ones can play too4 ,get into the game and be an aviator4 ,no4 ,r#db--;,electric ,air-,ships and ,other ,games1 postpaid #j4ce ,,aviation ,,tournaments ,,at ,,home ,,real ,,electric ,,toy-,,making ,,for ,,boys ,by ,,thomas ,m4 ,,st4 ,,john4 ,met4 ,e4 ,this book contains #adj pages and over one hundred original drawings1 diagrams1 and full-page plates4 ,it measures #ex#g-a_/b in41 and is bound in cloth4 ,,second ,,edition ,price1 postpaid1 #a4jj ,,contents3 ,chapter ,i4 ,toys ,operated by ,permanent ,magnets4--,,ii4 ,toys ,operated by ,static ,electricity4--,,iii4 ,making ,electromagnets for ,toys4--,,iv4 ,electric ,batteries4--,v4 ,circuits and ,connections4--,,vi4 ,toys ,operated by ,electromagnets4 ,,vii4 ,making ,solenoids for ,toys4--,,viii4 ,toys ,operated by ,solenoids4--,,ix4 ,electric ,motors4--,x4 ,power1 ,speed1 and ,gearing4--,,xi4 ,shafting and ,bearings4--,,xii4 ,pulleys and ,winding-,drums4--,,xiii4 ,belts and ,cables4--,,xiv4 ,toys ,operated by ,electric ,motors4--,,xv4 ,miscellaneous ,electric ,toys4--,,xvi4 ,tools4--,,xvii4 ,materials4--,,xviii4 ,various ,aids to ,construction4 ,while planning this book1 ,mr4 ,st4 ,john definitely decided that he would not fill it with descriptions of complicated1 machine-made instruments and apparatus1 under the name of ,toy-,making1 for it is just as impossible for most boys to get the parts for such things as it is for them to do the required machine work even after they have the raw materials4 ,great care has been taken in designing the toys which are described in this book1 in order to make them so simple that any boy of average ability can construct them out of ordinary materials4 ,the author can personally guarantee the designs1 for there is no guesswork about them4 ,every toy was made1 changed1 and experimented with until it was as simple as possible2 the drawings were then made from the perfected models4 ,as the result of the enormous amount of work and experimenting which were required to originate and perfect so many new models1 the author feels that this book may be truly called ,real ,electric ,toy-,making for ,boys4 99 99 99 99 99 ,every ,boy ,should ,make ,electrical ,toys4 ,a ,,motor ,,that ,,can ,,do ,,things ,the ,st ,j4 ,motor ,no4 #a 7,list ,no4 #bbja7 is designed for students and others who want a small motor for experimental purposes as well as for all of the work that any small motor can do4 ,we believe this to be the best small motor made1 and we know that it can be used in more ways than any other motor of equal cost ever built4 ,it has four binding-posts1--making it possible to energize the field or armature separately1--and so it can be used in circuits with reversers and rheostats for experiments4 ,the speed and direction of rotation can be changed at will1 thus adapting it for running toys1 etc4 ,as the binding-posts are mounted upon the frame1 this motor can be taken from the base for remounting and using in many ways1 and as it has a three-pole armature it will start promptly in any position4 ,the shaft carries a pulley1 and a fan can be added at any time4 ,one cell will give a high speed1 and more cells may be added1 according to the work it has to do4 ,motor ,no4 #a stands #c-a_/b inches high4 ,it is finished in black enamel with nickel-plated trimmings1--strong and well made4 ,with it are furnished three nickel-plated connecting-straps1 which are to be used for connecting the field and armature in series or shunt4 ,so much can be done with this motor that it is simply impossible to tell it here2 in fact1 it is used as the basis for a whole book of #fj experiments called ,the ,study of ,electric ,motors by ,experiment1 and1 when used in connection with the other parts of the ,motor ,outfits1 it will give a practical knowledge of motors that no other plan can give4 ,illustration3 ,no4 #bbja ,these motors and motor outfits have been highly praised by electrical experts and educators as being invaluable to students4 ,they can do everything the big motors can do1 and if used with the rheostats1 reversers and other apparatus in the outfits1 the student will have a whole motor laboratory4 ,why not get a motor that has brains and that can do tricks and experiments8 ,any good motor will go when you turn on the power2 but that doesn't mean much when it comes to understanding things4 ,no4 #bbja--,st4 ,j4 ,motor ,no4 #a1 with ,wiring-,diagrams #a4ce ,if sent by mail1 postage extra1 shipping weight one pound4 ,,st4 ,j4 ,,electric ,,motor ,,outfit ,these outfits have been designed for students and others who want to do real experimental work with motors1 so as to get right down to the bottom of the matter and thoroughly master the foundation principles of the subject4 ,it is simply astonishing to see how much can be learned with one of these outfits1 especially if the work be done as fully detailed in ,the ,study of ,electric ,motors by ,experiment4 ,every electrical laboratory should have one of these sets1 and the more you know about motors the more you will appreciate an outfit of this kind4 ,don't simply read about motors--get right down to the practical part of it and experiment for yourself4 ,every experiment will settle an important point in your mind4 ,,electric ,,motor ,,outfit ,no4 #bbbf,x contains everything needed for sixty interesting and profitable experiments4 ,with the improved apparatus that we now give we feel that this is the most complete set ever sold for the money4 ,the following articles are included1 packed in a wooden box3 ,,the ,,st4 ,j4 ,,motor1 fully described on another page1 is well called ,a motor that can do things4 ,,the ,,five-,,point ,,rheostat is used as a starting-box in the armature-circuit and in various other ways to regulate speed4 7,see cut47 ,,the ,,eleven-,,point ,,rheostat is used to regulate the field-magnetism1 as one method of speed-regulation1 and for other purposes4 7,see cut47 ,,the ,,double-,,key ,,current ,,reverser is1 really1 a key1 a two-point switch1 and a current-reverser combined4 ,on this account it can be used in many ways1 shown in numerous wiring-diagrams4 7,see cut47 ,,the ,,handy ,,current-,,detector is used as a current-detector and as a device for studying the counter-electromotive force of motor while running4 ,,the ,,two-,,point ,,switch is useful in quickly switching the current wherever it is needed1 and for many other experiments4 ,,the ,,strap ,,key protects the batteries and closes the circuit4 ,,the ,,miniature ,,electric ,,lamp ,,and ,,socket are used in the motor-circuit to prove certain things and form an attractive addition to the outfit4 ,,the ,,magnetic ,,needle in the new outfits is nickel-plated and serves as a compass for studying the magnetism of the poles1 etc4 ,,in ,,addition to the articles mentioned above1 the outfit contains a ,set of ,wires for ,connections1 a ,box of ,iron-,filings for studying lines of force1 an ,experimental ,package containing ,iron1 ,steel1 etc41 three ,connecting-,wires1 and ,,the ,,book ,,of ,,instructions1 called ,the ,study of ,electric ,motors by ,experiment4 ,this contains #aj chapters1 #aaj pages1 and over #gj illustrations and diagrams4 ,bound in stiff paper4 ,,batteries are not included1 unless ordered extra4 ,three of our ,no4 #aaja batteries cost #cf;c41 and extra postage for #b lbs4 ,no4 #bbbf,x--,complete ,motor ,outfit1 as above 7,p4 weight1 #c lbs47 #c4ge 99 99 99 99 99 ,,the ,,study ,,of ,,electric ,,motors ,,by ,,experiment contains ,sixty ,experiments that ,bear ,directly upon the ,construction1 ,operation1 and ,explanation of ,electric ,motors1 together with ,much ,helpful ,information upon the ,experimental ,apparatus ,required4 ,this book will be a great help to those who want to do real experimental work with motors4 ,it contains #aj chapters1 #aaj pages1 over #gj illustrations and diagrams1 and you can not afford to be without it4 ,no4 ,r#eg,p--,study of ,motors1 bound in paper1 postpaid #j4ce ,no4 ,r#eg;,c--,study of ,motors1 bound in cloth1 postpaid #j4fj ,fun ,with ,telegraphy 7,,patented7 ,,two ,,great ,,outfits ,,for ,,students ,illustration ,these two outfits are similar in construction1 although they differ in details1 each being designed for its special work4 ,the keys1 sounders and binding-posts are neatly mounted upon ebonized bases measuring #f-a_/bx#c-c_/d in41 these also serving as sounding-boards4 ,fun with ,telegraphy is the original low-price telegraph outfit for students that has sold by the thousands and given universal satisfaction4 ,it is considered the best #ej-;cent outfit ever produced1 and1 although we have made several improvements lately1 the price is the same as before4 ,in connection with a peculiar oscillating electro-magnet and a queer anvil1 the sounding-board aids in giving out a loud1 clear click that is found elsewhere only in noisy railroad sounders4 ,this outfit is best adapted for a learner's set of one instrument and a battery to be used on the table for practising1 either with or without the codegraph1 and not for telegraphing over wires to other stations4 ,outfit3 ,illustrated ,book of ,instructions1 called ,fun with ,telegraphy2 ,telegraph ,key2 ,telegraph ,sounder2 ,nickel-,plated ,binding-,posts2 ,insulated ,wires for ,connections4 ,no4 ,r#h--;,fun with ,telegraphy1 without battery1 postpaid #j4ej ,no4 ,r#h1 ,r#h;,b--,fun with ,telegraphy1 with one dry battery1 postpaid1 4#fe ,improved ,telegraphy ,no4 #b4--;,in answer to a number of requests for an improved outfit for regular line work between two stations a few hundred feet apart1 we now offer this set1 which is1 in general1 similar in plan to our first ,telegraphy ,no4 #b4 ,we have replaced the single electro-magnet of the old set1 as shown in the cut1 with two larger ones of superior construction1 thus making the instrument much more sensitive4 ,the key has also been greatly improved1 and we now have a fine set at low cost4 ,no expensive gravity batteries are needed with this ingenious arrangement1 as it is designed to work with dry batteries which are clean and cheap4 ,by means of a peculiar switch1 either station may call the other at any time1 even though the line is kept on open circuit4 ,there is absolutely no waste of current when the line is not in use--and1 even then1 only at the instant the dots and dashes are made4 ,this is certainly a great advantage over the old-fashioned methods with gravity batteries which amateurs have heretofore been obliged to use4 ,with this instrument you have a learner's set as well as one that can be used to send messages to another station4 ,if you do not care for the superior advantages of ,semi-,wireless1 this outfit will give entire satisfaction for ordinary work4 ,outfit3 ,illustrated ,book of ,instructions called ,telegraphy ,number ,two2 ,improved ,telegraph ,key2 ,telegraph ,sounder with ,double ,electromagnets3 ,special ,switch for controlling the batteries2 ,nickel-plated ,screw ,binding-posts2 ,insulated ,wires for connections4 ,no4 #bcjg--;,improved ,telegraphy ,number ,two 7no batteries71 postpaid1 #a4jj ,no4 #bcjg;,b--,same as ,no4 #bcjg1 but with two dry batteries1 postpaid1 #a4ce ,the ,codegraph 7,,patented7 ,,note--,continental ,code sent unless otherwise ordered4 ,illustration ,the ,codegraph is a brand-new scheme for thoroughly and rapidly learning the telegraphic code1 and it has been worked out with the beginner in mind4 ,this code-learning system really adapts itself to the beginner1 and it gives a personal touch to each individual student according to his needs4 ,no other system can do so much1 for the student sees1 hears and feels every letter and signal4 ,the greatest trouble that every one has in learning by listening to regular messages is in separating the letters and words as they come in so fast4 ,there is no time to think1 and letters pile up in the mind4 ,the codegraph avoids all confusion because every letter is under perfect control and may be repeated as many times as desired2 hard things can be made easy2 words and sentences can be built at will4 ,we guarantee that any one of average ability can make rapid improvement with the codegraph4 ,what ,it ,is4 ,a complete codegraph outfit1 as shown in the cut1 has three main parts3 7#a7 ,the plate and pen1 7#b7 some form of key and sounder and 7#c7 two batteries4 ,while any key and sounder can be used with the plate1 we wish to call especial attention to the duplex sounder shown1 as this has been designed to do double work4 ,if you already have ,fun with ,telegraphy1 for example1 and want to order the ,codegraph ,plate and ,pen1 we will include1 free of charge1 an extra attachment for connecting up your instrument4 ,the ,plate and ,pen4 ,when the pen is lightly drawn over the plate1 the sounder responds and shows exactly how every letter and signal should sound4 ,the student can then practise each letter until perfect4 ,the surface of the plate is covered with a special insulating enamel1 bare spots corresponding to correct dots and dashes4 ,the polished brass plate measures about #fx#h inches and has a most elegant appearance4 ,the book tells all about practising1 etc4 ,duplex ,codegraph ,key and ,sounder1 as shown1 has a double action and is the latest thing in code-learning devices4 ,by the mere turning of a switch you can have the ordinary telegraph clicks or the wireless buzzes1 making two sounders in one and at the cost of one4 ,the combination sounder and a substantial key are mounted upon a finely finished base with nickel-plated trimmings1 binding-posts1 switch1 etc4 ,if you want to become an operator in the shortest possible time1 no matter whether you have ever tried before or not1 get one of these outfits and begin at once4 ,you will be pleased right from the start1 because you will make rapid progress right from the start4 ,no4 #bcej--;,codegraph ,plate and ,pen1 with ,book of ,instructions #a4jj ,if sent by mail1 postage extra 4#ab ,no4 #bcea--;,duplex ,codegraph ,key and ,sounder 7no batteries7 #a4jj ,if sent by mail1 postage extra 4#aj ,no4 #aajb--,two ,dry ,batteries1 as shown 4#be ,if sent by mail1 postage extra 4#aj ,special--,complete ,codegraph ,outfit1 as in cut1 postpaid #b4ej ,,telegraph ,,and ,,telephone ,,sets 7,,list ,t7 ,,original ,,outfits that are worthy of your attention and that give fine results2 products of hundreds of experiments and models that give best value for least money4 ,a complete line of outfits beginning with ,fun with ,telegraphy and ending with combined ,semi-,wireless ,telegraph1 ,telephone and ,electric ,light ,signal ,sets1 with endless possibilities4 ,don't forget to add postage according to weight and zone4 ,list ,no4 ,list ,price #bcjb--,,new ,,fun ,,with ,,telegraphy4 ,a ,book1 ,key1 ,sounder1 ,wires4 ,nicely mounted1 sensitive1 adjustable1 improved1 practical4 7,p4 ,wt4 #a lb47 #j4ce #bcjb;,b#a--,same as ,no4 #bcjb1 but with #a dry battery4 7,p4 ,wt4 #a lb47 #j4ej #bcjh--,,new ,,telegraphy ,,number ,,two4 ,for regular line-work3 has ingenious switch2 uses dry batteries4 ,key1 ,sounder1 ,book1 ,wires4 7,p4 ,wt4 #a lb47 #j4ge #bcjh;,b#b--,same as ,no4 #bcjh but with two dry batteries4 7,p4 ,wt4 #b lbs47 #a4jj #bcjd--;,,clickerbuzz ,,two-,,station ,,telegraph ,,outfit4 ,special value2 loud1 resonant1 substantial1 very neat and does several things4 ,complete with two separate ,no4 #behj ,,wonderbuzz ,instruments1 ,morse ,code1 ,continental ,code1 ,wire for short ,line1 ,pkg4 small ,telegraph blanks1 ,instructions and ,wiring ,diagrams4 7,p4 ,wt4 #b lbs47 #b4jj #bcjd;,b#d--,same as ,no4 #bcjd but with four dry batteries4 7,p4 ,wt4 #c lbs47 #b4ej #bcej--;,,codegraph ,,plate1 ,,pen ,,and ,,book4 ,teaches ,continental ,wireless ,code1 giving correct sounds on your buzzer or on ours4 ,original1 practical1 solves home study4 7,weight #a pound47 ,price #a4jj #bcee--;,,codegraph ,,outfit ,,mounted on ebonized base with ,high-pitch ,nickel-plated ,buzzer1 ,binding-posts and ,key1 ,books and ,wires4 ,fine set for practice and study4 ,continental ,code4 7,weight1 #b lbs47 ,price #b4ge #bcee;,b#b--,same as #bcee1 but with #b batteries4 7,wt4 #c lbs47 ,price #c4jj #behj--,,semi-,,wireless ,,wonderbuzz1 a real wonder that can actually be used in #dj hookups4 ,a basic instrument around which to build ,code-teaching ,devices1 ,blinker ,signal ,systems1 numerous ,click ,telegraphs1 ,buzz ,telegraphs1 ,semi-wireless ,telegraphs1 several ,telephone ,plans1 combined ,telegraph and ,telephone schemes over the same wire1 actual ,room-to-room ,wireless1 etc41 etc4 ,can't begin to tell it all here4 ,an all-useful instrument with directions4 7,weight1 #a lb47 ,price #a4jj #begf--,,the ,,wonderphone is a practical1 inexpensive telephone set2 sensitive1 strong and well made4 ,outfit for one station3 ,receiver1 ,carbon ,grain ,transmitter1 both with flexible wires1 ,combination ,binding-post and ,instrument ,support1 ,battery ,box1 ,wire for ,connections1 #ej ft4 of ,line ,wire1 ,directions4 7,weight1 #a lb47 ,price #a4ej #begf;,b#b--,same as ,no4 #begf1 but with #b batteries1 7,wt4 #b lbs47 ,price #a4ge #behb--,,semi-,,wireless ,,telegraph1 ,,telephone1 ,,and ,,electric ,,light ,,signal ,,set4 ,a ,combination of the ,wonderbuzz1 the ,wonderphone1 ,night ,signal ,attachment1 and a ,lot of ,extras1 ,line ,wire1 ,etc4 ,a set that beats them all and does most4 ,no other system does so much for the money and no other can do so much for ten times the money4 ,a wonder combination of usefulness4 ,please read about the ,wonderbuzz and the ,wonderphone4 ,the latest word in telegraphy from ,cascade ,ranch4 7,weight1 #b lbs47 ,price #b4ge #behb;,b#b--,same as ,no4 #behb but with #b batteries4 7,wt4 #c lbs47 #c4jj ,no4 ,,stjc--,,save-,,time-,,jiffy-,,code4 ,learn to send and receive slowly in an hour or less4 ,in a day you can telegraph in a jiffy1 any message1 punctuation1 numbers1 sentence-signals and the whole business4 ,every boy a telegrapher4 ,fun to make your own ,cipher ,codes on this as a basis4 ,complete1 postpaid #f;c41 two for #j4aj #bdbe--;,,dandy ,,handiphone4 ,an inexpensive house-to-house telephone4 ,sensitive1 attractive1 practical1 efficient4 ,rings bell or buzzer to call1 using dry batteries4 ,will work as far as any battery-phone1 and farther than many of them4 ,a dandy ,handiphone4 ,in preparation4 ,be sure to add postage according to weight and zone4 ,,thomas ,m4 ,,st4 ,,john1 ,cascade ,ranch1 ,east ,windham1 ,n4,y4