file which includes the original illustrations4 ,see #ddffe-;h4htm or #ddffe-;h4zip3 7https3_/_/www4gutenberg4org_/cache_/epu b_/#ddffe_/pg#ddffe-;images4html7 or 7https3_/_/www4gutenberg4org_/files_/#dd ffe_/ddffe-;h4zip7 ,images of the original pages are available through ,internet ,archive4 ,see https3_/_/archive4org_/details_/thingsbo yshouldk#jjstjo ,transcriber's note3 ,text enclosed by underscores is in italics 7italics74 ,text enclosed by equal signs is in bold face 7bold74 ,characters enclosed by curly brackets after an underscore are subscripts 7example3 ,cu,s,o#d the chemical formula of copper sulfate74 ,,things ,a ,,boy ,,should ,,know ,,about ,,electricity ,illustration 99 99 99 99 99 ,,by ,,the ,,same ,,author4 ,,fun ,,with ,,magnetism4 ,a book and complete outfit of apparatus for ,sixty-,one ,experiments4 ,,fun ,,with ,,electricity4 ,a book and complete outfit of apparatus for ,sixty ,experiments4 ,,fun ,,with ,,puzzles4 ,a book1 key and complete outfit for ,four ,hundred ,puzzles4 ,,fun ,,with ,,soap-,,bubbles4 ,a book and complete outfit of apparatus for ,fancy ,bubbles and ,films4 ,,fun ,,with ,,shadows4 ,including book of instructions with one hundred illustrations and a complete outfit of apparatus for ,shadow ,pictures1 ,pantomimes1 ,entertainments1 etc41 etc4 ,,hustle-,,ball4 ,an ,american game4 ,played by means of magic wands and polished balls of steel4 ,,jingo4 ,the great war game1 including ,,jingo ,,junior4 ,,how ,,two ,,boys ,,made ,,their ,,own ,,electrical ,,apparatus4 ,a book containing complete directions for making all kinds of simple apparatus for the study of elementary electricity4 ,,the ,,study ,,of ,,elementary ,,electricity ,,and ,,magnetism ,,by ,,experiment4 ,this book is designed as a text-book for amateurs1 students1 and others who wish to take up a systematic course of simple experiments at home or in school4 ,,things ,a ,,boy ,,should ,,know ,,about ,,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 ,,ans41 ,,or ,,accuracy1 ,,neatness ,,and ,,speed4 ,for teachers and pupils4 ,containing study-charts1 practice devices and special methods for accurate1 rapid work with figures4 ,ask ,your ,bookseller1 ,stationer1 or ,toy ,dealer for our ,books1 ,games1 ,puzzles1 ,educational ,amusements1 ,etc4 ,,catalogue ,,upon ,,application ,thomas ,m4 ,st4 ,john1 #djg ,west #east ,st41 ,new ,york4 99 99 99 99 99 ,,things ,a ,,boy ,,should ,,know ,,about ,,electricity by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,author of ,fun ,with ,magnetism1 ,fun ,with ,electricity1 ,how ,two ,boys ,made ,their ,own ,electrical ,apparatus1 ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment1 etc4 ,,second ,,edition ,illustration ,new ,york ,thomas ,m4 ,st4 ,john #djg ,west #east ,street #aijc ,copyright1 #aijj4 ,by ,thomas ,m4 ,st4 ,john4 ,,things ,a ,,boy ,,should ,,know ,,about ,,electricity ,,table ,,of ,,contents ,,chapter ,,page ,i4 ,about ,frictional ,electricty #g ,,ii4 ,about ,magnets and ,magnetism #ba ,,iii4 ,how ,electricity is ,generated by the ,voltaic ,cell1 #cb ,,iv4 ,various ,voltaic ,cells1 #cf ,v4 ,about ,push-,buttons1 ,switches and ,binding-,posts1 #dc ,,vi4 ,units and ,apparatus for ,electrical ,measurements1 #dh ,,vii4 ,chemical ,effects of the ,electric ,current1 #eh ,,viii4 ,how ,electroplating and ,electrotyping are ,done1 #fj ,,ix4 ,the ,storage ,battery1 and ,how it ,works1 #fc ,x4 ,how ,electricity is ,generated by ,heat1 #fh ,,xi4 ,magnetic ,effects of the ,electric ,current1 #ga ,,xii4 ,how ,electricity is ,generated by ,induction1 #gg ,,xiii4 ,how the ,induction ,coil ,works1 #hj ,,xiv4 ,the ,electric ,telegraph1 and ,how it ,sends ,messages1 #hd ,,xv4 ,the ,electric ,bell and ,some of its ,uses1 #ia ,,xvi4 ,the ,telephone and ,how it ,transmits ,speech1 #ie ,,xvii4 ,how ,electricity is ,generated by ,dynamos1 #aja ,,xviii4 ,how the ,electric ,current is ,transformed1 #aji ,,xix4 ,how ,electric ,currents are ,distributed for ,use1 #aad ,,xx4 ,how ,heat is ,produced by the ,electric ,current1 #abd ,,xxi4 ,how ,light is ,produced by the ,incandescent ,lamp1 #abi ,,xxii4 ,how ,light is ,produced by the ,arc ,lamp1 #ace ,,xxiii4 ,x-,rays1 and ,how the ,bones of the ,human ,body are ,photographed1 #ada ,,xxiv4 ,the ,electric ,motor1 and ,how it ,does ,work1 #adg ,,xxv4 ,electric ,cars1 ,boats and ,automobiles1 #aed ,,xxvi4 ,a ,word ,about ,central ,stations1 #afb ,,xxvii4 ,miscellaneous ,uses of ,electricity1 #afe ,,to ,,the ,,reader ,for the benefit of those who wish to make their own electrical apparatus for experimental purposes1 references have been made throughout this work to the ,apparatus ,book2 by this is meant the author's ,how ,two ,boys ,made ,their ,own ,electrical ,apparatus4 ,for those who wish to take up a course of elementary electrical experiments that can be performed with simple1 home-made apparatus1 references have been made to ,study2 by this is meant ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment4 ,,the ,,author4 ,things ,a ,boy ,should ,know ,about ,electricity ,,chapter ,i4 ,,about ,,frictional ,,electricity4 #a4 ,some ,simple ,experiments4 ,have you ever shuffled your feet along over the carpet on a winter's evening and then quickly touched your finger to the nose of an unsuspecting friend8 ,did he jump when a bright spark leaped from your finger and struck him fairly on the very tip of his sensitive nasal organ8 ,illustration3 ,fig4 #a4 ,did you ever succeed in proving to the pussy-cat1 ,fig4 #a1 that something unusual occurs when you thoroughly rub his warm fur with your hand8 ,did you notice the bright sparks that passed to your hand when it was held just above the cat's back8 ,you should be able to see1 hear1 and feel these sparks1 especially when the air is dry and you are in a dark room4 ,did you ever heat a piece of paper before the fire until it was real hot1 then lay it upon the table and rub it from end to end with your hand1 and finally see it cling to the wall8 ,were you ever in a factory where there were large belts running rapidly over pulleys or wheels1 and where large sparks would jump to your hands when held near the belts8 ,if you have never performed any of the four experiments mentioned1 you should try them the first time a chance occurs4 ,there are dozens of simple1 fascinating experiments that may be performed with this kind of electricity4 #b4 ,name4 ,as this variety of electricity is made1 or generated1 by the friction of substances upon each other1 it is called frictional electricity4 ,it is also called static electricity1 because it generally stands still upon the surface of bodies and does not flow in currents as easily as some of the other varieties4 ,static electricity may be produced by induction as well as by friction4 ,illustration3 ,fig4 #b4 #c4 ,history4 ,it has been known for over #b1jjj years that certain substances act queerly when rubbed4 ,amber was the first substance upon which electricity was produced by friction1 and as the ,greek name for amber is elektron1 bodies so affected were said to be electrified4 ,when a body1 like ebonite1 is rubbed with a flannel cloth1 we say that it becomes charged with electricity4 ,just what happens to the ebonite is not clearly understood4 ,we know1 however1 that it will attract light bodies1 and then quickly repel them if they be conductors4 ,fig4 #b shows a piece of tissue-paper jumping toward a sheet of ebonite that has been electrified with a flannel cloth4 #d4 ,conductors and ,non-,conductors4 ,electricity can be produced upon glass and ebonite because they do not carry or conduct it away4 ,if a piece of iron be rubbed1 the electricity passes from the iron into the earth as fast as it is generated1 because the iron is a conductor of electricity4 ,glass is an insulator or non-conductor4 ,frictional electricity resides upon the outside1 only1 of conductors4 ,a hollow tin box will hold as great a charge as a solid piece of metal having the same outside size and shape4 ,when frictional electricity passes from one place to another1 sparks are produced4 ,lightning is caused by the passage of static electricity from a cloud to the earth1 or from one cloud to another4 ,in this case air forms the conductor4 7,for experiments1 see ,study1 ,chapter ,,vii47 ,illustration3 ,fig4 #c4 #e4 ,electroscopes4 ,a piece of carbon1 pith1 or even a small piece of damp tissue-paper will serve as an electroscope to test the presence of static electricity4 ,the pith is usually tied to a piece of silk thread which is a non-conductor4 ,fig4 #c shows the ordinary form of pith-ball electroscope4 ,the leaf electroscope is a very delicate apparatus4 ,gold-leaf is generally used1 but aluminum-leaf will stand handling and will do for all ordinary purposes4 ,fig4 #d shows a common form1 the glass being used to keep currents of air from the leaves and at the same time to insulate them from the earth4 ,electroscopes are used to show the presence1 relative amount1 or kind of static electricity on a body4 7,see ,study1 ,chapter ,,xi47 ,illustration3 ,fig4 #d4 #f4 ,two ,kinds of ,electrification4 ,it can be shown that the electrification produced on all bodies by friction is not the same2 for example1 that generated with glass and silk is not the same as that made with ebonite and flannel4 ,it has been agreed to call that produced by glass and silk positive1 and that by ebonite and flannel negative4 ,the signs and - are used for positive and negative4 #g4 ,laws of ,electrification4 7#a7 ,charges of the same kind repel each other2 7#b7 charges of unlike kinds attract each other2 7#c7 either kind of a charge attracts and is attracted by a neutral body4 #h4 ,static ,electric ,machines4 ,in order to produce static electricity in quantities for experiments1 some device is necessary4 ,the electrophorus 7e-lec-troph-o-rus7 is about the simplest form of machine4 ,fig4 #e shows a simple electrophorus in which are two insulators and one conductor4 ,the ebonite sheet ,e ,s is used with a flannel cloth to generate the electricity4 ,the metal cover ,e ,c is lifted by the insulating handle ,e ,r4 ,the cover ,e ,c is placed upon the thoroughly charged sheet ,e ,s1 and then it is touched for an instant with the finger1 before lifting it by ,e ,r4 ,the charge upon ,e ,c can then be removed by bringing the hand near it4 ,the bright spark that passes from ,e ,c to the hand indicates that ,e ,c has discharged itself into the earth4 ,the action of the electrophorus depends upon induction4 7,for experiments1 details of action1 induced electrification1 etc41 see ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment1 ,chapters ,,viii4 and ,,ix47 ,illustration3 ,fig4 #e4 ,the first electric machine consisted of a ball of sulphur fastened to a spindle which could be turned by a crank4 ,by holding the hands or a pad of silk upon the revolving ball1 electricity was produced4 ,illustration3 ,fig4 #f4 ,illustration3 ,fig4 #g4 #i4 ,the ,cylinder ,electric ,machine consists1 as shown in ,fig4 #f1 of a glass cylinder so mounted that it can be turned by a crank4 ,friction is produced by a pad of leather ,c1 which presses against the cylinder as it turns4 ,electric sparks can be taken from the large conductors which are insulated from the earth4 ,the opposite electricities unite with sparks across ,d and ,e4 ,if use is to be made of the electricity1 either the rubber or the prime conductor must be connected with the ground4 ,in the former case positive electricity is obtained2 in the latter1 negative4 #aj4 ,the ,plate ,electrical ,machine4 ,fig4 #g also shows an old form of machine4 ,such machines are made of circular plates of glass or ebonite1 two rubbing pads being usually employed1 one on each side of the plate4 ,one operator is seen on an insulated stool 7,fig4 #g71 the electricity passing through him before entering the earth by way of the body of the man at the right4 ,illustration3 ,fig4 #h4 #aa4 ,the ,toepler-,holtz ,machine1 in one form1 is shown in ,fig4 #h4 ,the electricity is produced by the principle of induction1 and not by mere friction4 ,this machine1 used in connection with condensers1 produces large sparks4 #ab4 ,the ,wimshurst ,machine is of recent date1 and not being easily affected by atmospheric changes1 is very useful for ordinary laboratory work4 ,fig4 #i shows one form of this machine4 #ac4 ,influence ,machines for ,medical ,purposes are made in a large variety of forms4 ,a ,wimshurst machine is generally used as an exciter to charge the plates of the large machine when they lose their charge on account of excessive moisture in the atmosphere4 ,fig4 #aj shows a large machine4 ,illustration3 ,fig4 #i4 #ad4 ,uses of ,electrical ,machines4 ,static electricity has been used for many years in the laboratory for experimental purposes1 for charging condensers1 for medical purposes1 etc4 ,it is now being used for ,x-ray work1 and considerable advancement has been made within a few years in the construction and efficiency of the machines4 ,illustration3 ,fig4 #aj4 ,with the modern machines large sparks are produced by merely turning a crank1 enough electricity being produced to imitate a small thunderstorm4 ,the sparks of home-made lightning will jump several inches4 ,do not think that electricity is generated in a commercial way by static electric machines4 ,the practical uses of static electricity are very few when compared with those of current electricity from batteries and dynamos4 #ae4 ,condensation of ,static ,electricity4 ,by means of apparatus called condensers1 a terrific charge of static electricity may be stored4 ,fig4 #aa shows the most common form of condenser1 known as the ,leyden jar4 ,it consists of a glass jar with an inside and outside coating of tin-foil4 ,illustration3 ,fig4 #aa4 ,illustration3 ,fig4 #ab4 ,to charge the jar it is held in the hand so that the outside coating shall be connected with the earth1 the sparks from an electric machine being passed to the knob at the top1 which is connected by a chain to the inside coating4 ,to discharge the jar1 ,fig4 #ab1 a conductor with an insulating handle is placed against the outside coat2 when the other end of the conductor is swung over towards the knob1 a bright spark passes between them4 ,this device is called a discharger4 ,fig4 #ac shows a discharge through ether which the spark ignites4 ,illustration3 ,fig4 #ac4 #af4 ,the ,leyden ,battery1 ,fig4 #ad1 consists of several jars connected in such a way that the area of the inner and outer coatings is greatly increased4 ,the battery has a larger capacity than one of its jars4 7,for ,experiments in ,condensation1 see ,study1 ,chapter ,x47 ,illustration3 ,fig4 #ad4 #ag4 ,electromotive ,force of ,static ,electricity4 ,although the sparks of static electricity are large1 the quantity of electricity is very small4 ,it would take thousands of galvanic cells to produce a spark an inch long4 ,while the quantity of static electricity is small1 its potential1 or electromotive force 7,e4 ,m4 ,f471 is very high4 ,we say that an ordinary gravity cell has an ,e4 ,m4 ,f4 of a little over one volt4 ,five such cells joined in the proper way would have an ,e4 ,m4 ,f4 of a little over five volts4 ,you will understand1 then1 what is meant when we say that the ,e4 ,m4 ,f4 of a lightning flash is millions of volts4 #ah4 ,atmospheric ,electricity4 ,the air is usually electrified1 even in clear weather1 although its cause is not thoroughly understood4 ,in #ageb it was proved by ,benjamin ,franklin 7,fig4 #ae71 with his famous kite experiment1 that atmospheric and frictional electricities are of the same nature4 ,by means of a kite1 the string being wet by the rain1 he succeeded1 during a thunderstorm1 in drawing sparks1 charging condensers1 etc4 ,illustration3 ,fig4 #ae4 ,illustration3 ,fig4 #af4 #ai4 ,lightning may be produced by the passage of electricity between clouds1 or between a cloud and the earth 7,fig4 #af71 which1 with the intervening air1 have the effect of a condenser4 ,when the attraction between the two electrifications gets great enough1 a spark passes4 ,when the spark has a zigzag motion it is called chain lightning4 ,in hot weather flashes are often seen which light whole clouds1 no thunder being heard4 ,this is called heat lightning1 and is generally considered to be due to distant discharges1 the light of which is reflected by the clouds4 ,the lightning flash represents billions of volts4 ,illustration3 ,fig4 #ag4 #bj4 ,thunder is caused by the violent disturbances produced in the air by lightning4 ,clouds1 hills1 etc41 produce echoes1 which1 with the original sound1 make the rolling effect4 #ba4 ,lightning-,rods1 when well constructed1 often prevent violent discharges4 ,their pointed prongs at the top allow the negative electricity of the earth to pass quietly into the air to neutralize the positive in the cloud above4 ,in case of a discharge1 or stroke of lightning1 the rods aid in conducting the electricity to the earth4 ,the ends of the rods are placed deep in the earth1 ,fig4 #ag4 #bb4 ,st4 ,elmo's ,fire4 ,electrification from the earth is often drawn up from the earth through the masts of ships1 ,fig4 #ah1 to neutralize that in the clouds1 and1 as it escapes from the points of the masts1 light is produced4 ,illustration3 ,fig4 #ah4 #bc4 ,aurora ,borealis1 also called ,northern ,lights1 are luminous effects1 ,fig4 #ai1 often seen in the north4 ,they often occur at the same time with magnetic storms1 when telegraph and telephone work may be disturbed4 ,the exact cause of this light is not known1 but it is thought by many to be due to disturbances in the earth's magnetism caused by the action of the sun4 ,illustration3 ,fig4 #ai4 ,,chapter ,,ii4 ,,about ,,magnets ,,and ,,magnetism4 #bd4 ,natural ,magnets4 ,hundreds of years ago it was discovered that a certain ore of iron1 called lodestone1 had the power of picking up small pieces of iron4 ,it was used to indicate the north and south line1 and it was discovered later that small pieces of steel could be permanently magnetized by rubbing them upon the lodestone4 #be4 ,artificial ,magnets4 ,pieces of steel1 when magnetized1 are called artificial magnets4 ,they are made in many forms4 ,the electromagnet is also an artificial magnet2 this will be treated separately4 ,illustration3 ,fig4 #bj #bf4 ,the ,horseshoe ,magnet1 ,fig4 #bj1 is1 however1 the one with which we are the most familiar4 ,they are always painted red1 but the red paint has nothing to do with the magnetism4 ,the little end-piece is called the keeper1 or armature2 it should always be kept in place when the magnet is not in use4 ,the magnet itself is made of steel1 while the armature is made of soft iron4 ,steel retains magnetism for a long time1 while soft iron loses it almost instantly4 ,the ends of the magnet are called its poles1 and nearly all the strength of the magnet seems to reside at the poles1 the curved part having no attraction for outside bodies4 ,one of the poles of the magnet is marked with a line1 or with the letter ,n4 ,this is called the north pole of the magnet1 the other being its south pole4 ,illustration3 ,fig4 #ba4 #bg4 ,bar ,magnets are straight magnets4 ,fig4 #ba shows a round bar magnet4 ,the screw in the end is for use in the telephone1 described later4 #bh4 ,compound ,magnets4 ,when several thin steel magnets are riveted together1 a compound magnet is formed4 ,these can be made with considerable strength4 ,fig4 #bb shows a compound horseshoe magnet4 ,fig4 #bc shows a form of compound bar magnet used in telephones4 ,the use of the coil of wire will be explained later4 ,a thick piece of steel can not be magnetized through and through4 ,in the compound magnet we have the effect of a thick magnet practically magnetized through and through4 ,illustration3 ,fig4 #bb4 ,illustration3 ,fig4 #bc4 #bi4 ,magnetic and ,diamagnetic ,bodies4 ,iron1 and substances containing iron1 are the ones most readily attracted by a magnet4 ,iron is said to be magnetic4 ,some substances1 like nickel1 for example1 are visibly attracted by very strong magnets only4 ,strange as it may seem1 some substances are actually repelled by strong magnets2 these are called diamagnetic bodies4 ,brass1 copper1 zinc1 etc41 are not visibly affected by a magnet4 ,magnetism will act through paper1 glass1 copper1 lead1 etc4 ,illustration3 ,fig4 #bd4 #cj4 ,making ,magnets4 ,one of the strangest properties that a magnet has is its power to give magnetism to another piece of steel4 ,if a sewing-needle be properly rubbed upon one of the poles of a magnet1 it will become strongly magnetized and will retain its magnetism for years4 ,strong permanent magnets are made with the aid of electromagnets4 ,any number of little magnets may be made from a horseshoe magnet without injuring it4 ,illustration3 ,fig4 #be4 #ca4 ,magnetic ,needles and ,compasses4 ,if a bar magnet be suspended by a string1 or floated upon a cork1 which can easily be done with the magnet made from a sewing-needle1 ,fig4 #bd1 it will swing around until its poles point north and south4 ,such an arrangement is called a magnetic needle4 ,in the regular compass1 a magnetic needle is supported upon a pivot4 ,compasses have been used for many centuries by mariners and others4 ,fig4 #be shows an ordinary pocket compass1 and ,fig4 #bf a form of mariner's compass1 in which the small bar magnets are fastened to a card which floats1 the whole being so mounted that it keeps a horizontal position1 even though the vessel rocks4 ,illustration3 ,fig4 #bf4 #cb4 ,action of ,magnets ,upon ,each ,other4 ,by making two small sewing-needle magnets1 you can easily study the laws of attraction and repulsion4 ,by bringing the two north poles1 or the two south poles1 near each other1 a repulsion will be noticed4 ,unlike poles attract each other4 ,the attraction between a magnet and iron is mutual2 that is1 each attracts the other4 ,either pole of a magnet attracts soft iron4 ,in magnetizing a needle1 either end may be made a north pole at will2 in fact1 the poles of a weak magnet can easily be reversed by properly rubbing it upon a stronger magnet4 #cc4 ,theory of ,magnetism4 ,each little particle of a piece of steel or iron is supposed to be a magnet1 even before it touches a magnet4 ,when these little magnets are thoroughly mixed up in the steel1 they pull in all sorts of directions upon each other and tend to keep the steel from attracting outside bodies4 ,when a magnet is properly rubbed upon a bar of steel1 the north poles of the little molecular magnets of the steel are all made to point in the same direction4 ,as the north poles help each other1 the whole bar can attract outside bodies4 ,by jarring a magnet its molecules are thoroughly shaken up2 in fact1 most of the magnetism can be knocked out of a weak magnet by hammering it4 #cd4 ,retentivity4 ,the power that a piece of steel has to hold magnetism is called retentivity4 ,different kinds of steel have different retentivities4 ,a sewing-needle of good steel will retain magnetism for years1 and it is almost impossible to knock the magnetism out by hammering it4 ,soft steel has very little retentivity1 because it does not contain much carbon4 ,soft iron1 which contains less carbon than steel1 holds magnetism very poorly2 so it is not used for permanent magnets4 ,a little magnetism1 however1 will remain in the soft iron after it is removed from a magnet4 ,this is called residual magnetism4 #ce4 ,heat and ,magnetism4 ,steel will completely lose its magnetism when heated to redness1 and a magnet will not attract red-hot iron4 ,the molecules of a piece of red-hot iron are in such a state of rapid vibration that they refuse to be brought into line by the magnet4 #cf4 ,induced ,magnetism4 ,a piece of soft iron may be induced to become a magnet by holding it near a magnet1 absolute contact not being necessary4 ,when the soft iron is removed1 again1 from the influence of the magnet1 its magnetism nearly all disappears4 ,it is said to have temporary magnetism2 it had induced magnetism4 ,if a piece of soft iron be held near the north pole of a magnet1 as in ,fig4 #bg1 poles will be produced in the soft iron1 the one nearest the magnet being the south pole1 and the other the north pole4 ,illustration3 ,fig4 #bg4 ,illustration3 ,fig4 #bh4 #cg4 ,magnetic ,field4 ,if a bar magnet be laid upon the table1 and a compass be moved about it1 the compass-needle will be attracted by the magnet1 and it will point in a different direction for every position given to the compass4 ,this strange power1 called magnetism1 reaches out on all sides of a magnet4 ,the magnet may be said to act by induction upon the compass-needle4 ,the space around the magnet1 in which this inductive action takes place1 is called the magnetic field4 ,fig4 #bh shows some of the positions taken by a compass-needle when moved about on one side of a bar magnet4 ,illustration3 ,fig4 #bi4 ,illustration3 ,fig4 #cj4 #ch4 ,magnetic ,figures can be made by sprinkling iron filings upon a sheet of paper under which is placed a magnet4 ,fig4 #bi shows a magnetic figure made with an ordinary bar magnet4 ,the magnet was placed upon the table and over this was laid a piece of smooth paper4 ,fine iron filings were sifted upon the paper1 which was gently tapped so that the filings could arrange themselves4 ,as each particle of iron became a little magnet1 by induction1 its poles were attracted and repelled by the magnet2 and when the paper was tapped they swung around to their final positions4 ,notice that the filings have arranged themselves in lines4 ,these lines show the positions of some of the lines of magnetic force which surrounded the magnet4 ,these lines of force pass from the north pole of a magnet through the air on all sides to its south pole4 ,illustration3 ,fig4 #ca4 ,fig4 #cj shows a magnetic figure made from two bar magnets placed side by side1 their unlike poles being next to each other4 ,fig4 #ca shows the magnetic figure of a horseshoe magnet with round poles1 the poles being uppermost4 #ci4 ,the ,use of ,armatures4 ,a magnet attracts iron most strongly at its poles1 because it is at the poles that the greatest number of lines of force pass into the air4 ,lines of force pass easily through soft iron1 which is said to be a good conductor of them4 ,air is not a good conductor of the lines of force2 in order1 then1 for the lines of force to pass from the north pole of a magnet to its south pole1 they must overcome this resistance of the air1 unless the armature is in place4 ,a magnet will gradually grow weaker when its armature is left off4 #dj4 ,terrestrial ,magnetism4 ,as the compass-needle points to the north and south1 the earth must act like a magnet4 ,there is a place very far north1 about a thousand miles from the north pole of the earth1 which is called the earth's north magnetic pole4 ,compass-needles point to this place1 and not to the earth's real north pole4 ,you can see1 then1 that if a compass be taken north of this magnetic pole1 its north pole will point south4 ,lines of force pass from the earth's north magnetic pole through the air on all sides of the earth and enter the earth's south magnetic pole4 ,the compass-needle1 in pointing toward the north magnetic pole1 merely takes the direction of the earth's lines of force1 just as the particles of iron filings arrange themselves in the magnetic figures4 #da4 ,declination4 ,as the magnetic needle does not point exactly to the north1 an angle is formed between the true north and south line and the line of the needle4 ,in ,fig4 #cb the line marked ,n ,s is the true north and south line4 ,the angle of variation1 or the declination1 is the angle ,a between the line ,n ,s and the compass-needle4 ,illustration3 ,fig4 #cb4 ,illustration3 ,fig4 #cc4 #db4 ,dip or ,inclination4 ,if a piece of steel be carefully balanced upon a support1 and then magnetized1 it will be found that it will no longer balance4 ,the north pole will dip or point downward4 ,fig4 #cc shows what happens to a needle when it is held in different positions over a bar magnet4 ,it simply takes the directions of the lines of force as they pass from the north to the south pole of the magnet4 ,as the earth's lines of force pass in curves from the north to the south magnetic pole1 you can see why the magnetic needle dips1 unless its south pole is made heavier than its north4 ,magnetic needles are balanced after they are magnetized4 ,illustration3 ,fig4 #cd4 ,fig4 #cd shows a simple form of dipping needle4 ,these are often used by geologists and miners4 ,in the hands of the prospector1 the miner's compass1 or dipping needle1 proves a serviceable guide to the discovery and location of magnetic iron ore4 ,in this instrument the magnetic needle is carefully balanced upon a horizontal axis within a graduated circle1 and in which the needle will be found to assume a position inclined to the horizon4 ,this angle of deviation is called the inclination or dip1 and varies in different latitudes1 and even at different times in the same place4 #dc4 ,the ,earth's ,inductive ,influence4 ,the earth's magnetism acts inductively upon pieces of steel or iron upon its surface4 ,if a piece of steel or iron1 like a stove poker1 for example1 be held in a north and south line with its north end dipping considerably1 it will be in the best position for the magnetism of the earth to act upon it2 that is1 it will lie in the direction taken by the earth's lines of force4 ,if the poker be struck two or three times with a hammer to shake up its molecules1 we shall find1 upon testing it1 that it has become magnetized4 ,by this method we can pound magnetism right out of the air with a hammer4 ,if the magnetized poker be held level1 in an east and west direction1 it will no longer be acted upon to advantage by the inductive influence of the earth1 and we can easily hammer the magnetism out of it again4 7,for experiments on magnets and magnetism see ,study1 ,part ,i47 ,,chapter ,,iii4 ,,how ,,electricity ,,is ,,generated ,,by ,,the ,,voltaic ,,cell4 #dd4 ,early ,experiments4 ,in #aghf ,galvani1 an ,italian physician1 made experiments to study the effect of static electricity upon the nervous excitability of animals1 and especially upon the frog4 ,he found that electric machines were not necessary to produce muscular contractions or kicks of the frog's legs1 and that they could be produced when two different metals1 ,fig4 #ce1 like iron and copper1 for example1 were placed in proper contact with a nerve and a muscle and then made to touch each other4 ,galvani first thought that the frog generated the electricity instead of the metals4 ,illustration3 ,fig4 #ce4 ,volta proved that the electricity was caused by the contact of the metals4 ,he used the condensing electroscope as one means of proving that two dissimilar metals become charged differently when in contact4 ,volta also carried out his belief by constructing what is called a ,voltaic ,pile4 ,he thought that by making several pairs of metals so arranged that all the little currents would help each other1 a strong current could be generated4 ,fig4 #cf shows a pile1 it being made by placing a pair of zinc and copper discs in contact with one another1 then laying on the copper disc a piece of flannel soaked in brine1 then on top of this another pair1 etc41 etc4 ,by connecting the first zinc and the last copper1 quite a little current was produced4 ,this was a start from which has been built our present knowledge of electricity4 ,strictly speaking1 electricity is not generated by combinations of metals or by cells2 they really keep up a difference of potential1 as will be seen4 ,illustration3 ,fig4 #cf4 ,illustration3 ,fig4 #cg4 ,illustration3 ,fig4 #ch4 #de4 ,the ,simple ,cell4 ,it has been stated that two different kinds of electrifications may be produced by friction2 one positive1 the other negative4 ,either can be produced1 at will1 by using proper materials4 ,fig4 #cg shows a section of a simple cell2 ,fig4 #ch shows another view4 ,cu is a piece of copper1 and ,zn a piece of zinc4 ,when they are placed in dilute sulphuric acid1 it can be shown by delicate apparatus that they become charged differently1 because the acid acts differently upon the plates4 ,they become charged by chemical action1 and not by friction4 ,the zinc is gradually dissolved1 and it is this chemical burning of the zinc that furnishes energy for the electric current in the simple cell4 ,the electrification1 or charge1 on the plates tends to flow from the place of higher to the place of lower potential1 just as water tends to flow down hill4 ,if a wire be joined to the two metals1 a constant current of electricity will flow through it1 because the acid continues to act upon the plates4 ,the simple cell is a single-fluid cell1 as but one liquid is used in its construction4 #de;a4 ,plates and ,poles4 ,the metal strips used in voltaic cells are called plates or elements4 ,the one most acted upon by the acid is called the positive 77 plate4 ,in the simple cell the zinc is the plate1 and the copper the negative 7-7 plate4 ,the end of a wire attached to the - plate is called the pole1 or electrode4 ,fig4 #cg shows the negative 7-7 electrode as the end of the wire attached to the plate4 #df4 ,direction of ,current4 ,in the cell the current passes from the zinc to the copper2 that is1 from the positive to the negative plate1 where bubbles of hydrogen gas are deposited4 ,in the wire connecting the plates1 the current passes from the copper to the zinc plate4 ,in most cells1 carbon takes the place of copper4 7,see ,study1 #bfh47 #dg4 ,local ,currents2 ,amalgamation4 ,ordinary zinc contains impurities such as carbon1 iron1 etc41 and when the acid comes in contact with these1 they form with the zinc a small cell4 ,this tends to eat away the zinc without producing useful currents4 ,the little currents in the cell from this cause are called local currents4 7,see ,study1 ,exp4 #aaa1 #bgc47 ,this is largely overcome by coating the zinc with mercury4 ,this process is called amalgamation4 ,it makes the zinc act like pure zinc1 which is not acted upon by dilute sulphuric acid when the current does not pass4 7,see ,study1 #beg1 #bgd47 #dh4 ,polarization of ,cells4 ,bubbles of hydrogen gas are formed when zinc is dissolved by an acid4 ,in the ordinary simple cell these bubbles collect on the copper plate1 and not on the zinc plate1 as might be expected4 ,the hydrogen is not a conductor of electricity1 so this film of gas holds the current back4 ,the hydrogen acts like a metal and sets up a current that opposes the zinc to the copper current4 ,several methods are employed to get rid of the hydrogen4 7,see ,study1 #bgh1 #bgi1 #bhj47 ,,chapter ,,iv4 ,,various ,,voltaic ,,cells4 #di4 ,single-,fluid and ,two-,fluid ,cells4 ,the simple cell 7 #de7 is a single-fluid cell4 ,the liquid is called the electrolyte1 and this must act upon one of the plates2 that is1 chemical action must take place in order to produce a current4 ,the simple cell polarizes rapidly1 so something must be used with the dilute sulphuric acid to destroy the hydrogen bubbles4 ,this is done in the bichromate of potash cell4 ,in order to get complete depolarization--that is1 to keep the carbon plate almost perfectly free from hydrogen1 it is necessary to use two-fluid cells1 or those to which some solid depolarizer is added to the one fluid4 #ej4 ,open and ,closed ,circuit ,cells4 ,if we consider a voltaic cell1 the wires attached to it1 and perhaps some instrument through which the current passes1 we have an electric circuit4 ,when the current passes1 the circuit is closed1 but when the wire is cut1 or in any way disconnected so that the current can not pass1 the circuit is open or broken4 7,see ,study1 #bff47 ,open ,circuit ,cells are those which can give momentary currents at intervals1 such as are needed for bells1 telephones1 etc4 ,these must have plenty of time to rest1 as they polarize when the circuit is closed for a long time4 ,the ,leclanch and dry cells are the most common open circuit cells4 ,closed ,circuit ,cells4 ,for telegraph lines1 motors1 etc41 where a current is needed for some time1 the cell must be of such a nature that it will not polarize quickly2 it must give a strong and constant current4 ,the bichromate and gravity cells are examples of this variety4 7,see ,study1 #bhf47 #ea4 ,bichromate of ,potash ,cells are very useful for general laboratory work4 ,they are especially useful for operating induction coils1 small motors1 small incandescent lamps1 for heating platinum wires1 etc4 ,these cells have an ,e4,m4,f4 of about #b volts4 ,dilute sulphuric acid is used as the exciting fluid1 and in this is dissolved the bichromate of potash which keeps the hydrogen bubbles from the carbon plate4 7,see ,apparatus ,book1 #bf47 ,zinc and carbon are used for the plates1 the pole being the wire attached to the carbon4 ,illustration3 ,fig4 #ci4 ,fig4 #ci shows one form of bichromate cell4 ,it furnishes a large quantity of current1 and as the zinc can be raised from the fluid1 it may be kept charged ready for use for many months1 and can be set in action any time when required by lowering the zinc into the liquid4 ,two of these cells will burn a one candle-power miniature incandescent lamp several hours4 ,the carbon is indestructible4 ,note4 ,for various forms of home-made cells1 see ,apparatus ,book1 ,chapter ,i41 and for battery fluids see ,chapter ,,ii4 #eb4 ,the ,grenet ,cell4 ,fig4 #dj is another form of bichromate cell4 ,the carbon plates are left in the fluid constantly4 ,the zinc plate should be raised when the cell is not in use1 to keep it from being uselessly dissolved4 ,illustration3 ,fig4 #dj4 ,illustration3 ,fig4 #da4 #ec4 ,plunge ,batteries4 ,two or more cells are often arranged so that their elements can be quickly lowered into the acid solution4 ,such a combination1 ,fig4 #da1 is called a plunge battery4 ,the binding-posts are so arranged that currents of different strengths can be taken from the combination4 ,the two binding-posts on the right of the battery will give the current of one cell2 the two binding-posts on the left of the battery will give the current of two cells1 and the two end binding-posts will give the current of all three cells4 ,when not in use the elements must always be hung on the hooks and kept out of the solution4 #ed4 ,large ,plunge ,batteries4 ,fig4 #db1 are arranged with a winch and a bar above the cells2 these afford a ready and convenient means of lifting or lowering the elements and avoiding waste4 ,in the battery shown1 ,fig4 #db1 the zincs are #df inches2 the carbons have the same dimensions1 but there are two carbon plates to each zinc1 thus giving double the carbon surface4 ,illustration3 ,fig4 #db4 #ee4 ,the ,fuller ,cell1 ,fig4 #dc1 is another type of bichromate cell1 used largely for long-distance telephone service1 for telephone exchange and switch service1 for running small motors1 etc4 ,it consists of a glass jar1 a carbon plate1 with proper connections1 a clay porous cup1 containing the zinc1 which is made in the form of a cone4 ,a little mercury is placed in the porous cup to keep the zinc well amalgamated4 ,either bichromate of potash or bichromate of soda can be used as a depolarizer4 ,illustration3 ,fig4 #dc4 ,illustration3 ,fig4 #dd4 #ef4 ,the ,gravity ,cell1 sometimes called the bluestone or crowfoot cell1 is used largely for telegraph1 police1 and fire-alarm signal service1 laboratory and experimental work1 or whenever a closed circuit cell is required4 ,the ,e4,m4,f4 is about one volt4 ,this is a modified form of the ,daniell cell4 ,fig4 #dd shows a home-made gravity cell4 ,a copper plate is placed at the bottom of the glass jar1 and upon this rests a solution of copper sulphate 7bluestone74 ,the zinc plate is supported about four inches above the copper1 and is surrounded by a solution of zinc sulphate which floats upon the top of the blue solution4 ,an insulated wire reaches from the copper to the top of the cell and forms the positive pole4 7,see ,apparatus ,book1 #aa to #ae1 for home-made gravity cell1 its regulation1 etc4 ,for experiments with two-fluid ,daniell cell1 see ,study1 ,exp4 #aac1 #bha to #bhf47 ,illustration3 ,fig4 #de4 #ef;a4 ,bunsen ,cells1 ,fig4 #de1 are used for motors1 small incandescent lamps1 etc4 ,a carbon rod is inclosed in a porous cup1 on the outside of which is a cylinder of zinc that stands in dilute sulphuric acid1 the carbon being in nitric acid4 #eg4 ,the ,leclanch ,cell is an open circuit cell4 ,sal ammoniac is used as the exciting fluid1 carbon and zinc being used for plates4 ,manganese dioxide is used as the depolarizer2 this surrounds the carbon plate1 the two being either packed together in a porous cup or held together in the form of cakes4 ,the porous cup1 or pressed cake1 stands in the exciting fluid4 ,the ,e4 ,m4 ,f4 is about #a4e volts4 ,illustration3 ,fig4 #df4 ,illustration3 ,fig4 #dg4 ,illustration3 ,fig4 #dh4 ,illustration3 ,fig4 #di4 ,fig4 #df shows a form with porous cup4 ,the binding-post at the top of the carbon plate forms the electrode1 the current leaving the cell at this point4 ,the ,gonda ,prism ,cell 7,fig4 #dg71 is a form of ,leclanch in which the depolarizer is in the form of a cake4 #eh4 ,dry ,cells are open circuit cells1 and can be carried about1 although they are moist inside4 ,the pole is the end of the carbon plate4 ,zinc is used as the outside case and plate4 ,fig4 #dh shows the ordinary forms4 ,fig4 #di shows a number of dry cells arranged in a box with switch in front1 so that the current can be regulated at will4 ,illustration3 ,fig4 #ej4 #ei4 ,the ,edison-,lelande ,cells1 ,fig4 #ej1 are made in several sizes and types4 ,zinc and copper oxide1 which is pressed into plates1 form the elements4 ,the exciting fluid consists of a #be per cent4 solution of caustic potash in water4 ,they are designed for both open and closed circuit work4 ,,chapter ,v4 ,,about ,,push-,,buttons1 ,,switches ,,and ,,binding-,,posts4 #fj4 ,electrical ,connections4 ,in experimental work1 as well as in the everyday work of the electrician1 electrical connections must constantly be made4 ,one wire must be joined to another1 just for a moment1 perhaps1 or one piece of apparatus must be put in an electric circuit with other apparatus1 or the current must be turned on or off from motors1 lamps1 etc4 ,in order to conveniently and quickly make such connections1 apparatus called push-buttons1 switches and binding-posts are used4 ,illustration3 ,fig4 #ea4 ,illustration3 ,fig4 #eb4 #fa4 ,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 ,fig4 #ea shows a simple push-button1 somewhat like a simple key in construction4 ,if we cut a wire1 through which a current is passing1 then join one of the free ends to the screw ,a and the other end to screw ,c1 we shall be able to let the current pass at any instant by pressing the spring ,b firmly upon ,a4 ,push-buttons are made in all sorts of shapes and sizes4 ,fig4 #eb gives an idea of the general internal construction4 ,the current enters ,a by one wire1 and leaves by another wire as soon as the button is pushed and ,b is forced down to ,a4 ,the bottom of the little button rests upon the top of ,b4 ,fig4 #ec shows a ,table ,clamp-,push for use on dining-tables1 card-tables1 chairs1 desks1 and other movable furniture4 ,fig4 #ed shows a combination of push-button1 speaking-tube1 and letter-box used in city apartment houses4 ,fig4 #ee shows an ,indicating ,push4 ,the buzzer indicates1 by the sound1 whether the call has been heard2 that is1 the person called answers back4 ,illustration3 ,fig4 #ec4 ,illustration3 ,fig4 #ed4 ,modifications of ordinary push-buttons are used for floor push-buttons1 on doors1 windows1 etc41 for burglar-alarms1 for turning off or on lights1 etc41 etc4 7,see ,apparatus ,book1 ,chapter ,,iii41 for home-made push-buttons47 ,illustration3 ,fig4 #ee4 #fb4 ,switches have a movable bar or plug of metal1 moving on a pivot1 to make or break a circuit1 or transfer a current from one conductor to another4 ,fig4 #ef shows a single point switch4 ,the current entering the pivoted arm can go no farther when the switch is open1 as shown4 ,to close the circuit1 the arm is pushed over until it presses down upon the contact-point4 ,for neatness1 both wires are joined to the under side of the switch or to binding-posts4 ,illustration3 ,fig4 #ef4 ,fig4 #eg shows a knife switch4 ,copper blades are pressed down between copper spring clips to close the circuit4 ,the handle is made of insulating material4 ,pole-changing switches1 ,fig4 #eh1 are used for changing or reversing the poles of batteries1 etc4 ,fig4 #ei shows a home-made switch1 useful in connection with resistance coils4 ,by joining the ends of the coils ,a1 ,b1 ,c1 ,d1 with the contact-points #a1 #b1 #c1 etc41 more or less resistance can be easily thrown in by simply swinging the lever ,e around to the left or right4 ,if ,e be turned to #a1 the current will be obliged to pass through all the coils ,a1 ,b1 etc41 before it can pass out at ,y4 ,if ,e be moved to #c1 coils ,a and ,b will be cut out of the circuit1 thus decreasing the resistance to the current on its way from ,x to ,y4 ,current regulators are made upon this principle4 7,see ,apparatus ,book1 ,chapter ,,iv41 for home-made switches47 ,illustration3 ,fig4 #eg4 ,illustration3 ,fig4 #eh4 ,illustration3 ,fig4 #ei4 ,switchboards are made containing from two or three to hundreds of switches1 and are used in telegraph and telephone work1 in electric light stations1 etc41 etc4 7,see ,chapter on ,central ,stations47 ,fig4 #fj shows a switch used for incandescent lighting currents4 ,illustration3 ,fig4 #fj4 ,illustration3 ,fig4 #fa4 #fc4 ,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 allow the wires to be quickly fastened or unfastened to the apparatus4 ,a large part of the apparatus shown in this book has binding-posts attached4 ,fig4 #fa shows a few of the common forms used4 7,see ,apparatus ,book1 ,chapter ,v41 for home-made binding-posts47 ,,chapter ,,vi4 ,,units ,,and ,,apparatus ,,for ,,electrical ,,measurements4 #fd4 ,electrical ,units4 ,in order to measure electricity for experimental or commercial purposes1 standards or units are just as necessary as the inch or foot for measuring distances4 #fe4 ,potential2 ,electromotive ,force4 ,if water in a tall tank be allowed to squirt from two holes1 one near the bottom1 the other near the top1 it is evident that the force of the water that comes from the hole at the bottom will be the greater4 ,the pressure at the bottom is greater than that near the top1 because the head is greater4 ,when a spark of static electricity jumps a long distance1 we say that the charge has a high potential2 that is1 it has a high electrical pressure4 ,potential1 for electricity1 means the same as pressure1 for water4 ,the greater the potential1 or electromotive force 7,e4,m4,f47 of a cell1 the greater its power to push a current through wires4 7,see ,study1 #bif to #cje1 with experiments47 #ff4 ,unit of ,e4,m4,f42 the ,volt4--,in speaking of water1 we say that its pressure is so many pounds to the square inch1 or that it has a fall1 or head1 of so many feet4 ,we speak of a current as having so many volts2 for example1 we say that a wire is carrying a #aaj-volt current4 ,the volt is the unit of ,e4,m4,f4 ,an ordinary gravity cell has an ,e4,m4,f4 of about one volt4 ,this name was given in honor of ,volta4 #fg4 ,measurement of ,electromotive ,force4 ,there are several ways by which the ,e4,m4,f4 of a cell1 for example1 can be measured4 ,it is usually measured relatively1 by comparison with the ,e4 ,m4 ,f4 of some standard cell4 7,see ,study1 ,exp4 #adj1 for measuring the ,e4 ,m4 ,f4 of a cell by comparison with the two-fluid cell47 ,illustration3 ,fig4 #fb4 ,voltmeters are instruments by means of which ,e4 ,m4 ,f4 can be read on a printed scale4 ,they are a variety of galvanometer1 and are made with coils of such high resistance1 compared with the resistance of a cell or dynamo1 that the ,e4 ,m4 ,f4 can be read direct4 ,the reason for this will be seen by referring to ,ohm's law 7,study1 #cef72 the resistance is so great that the strength of the current depends entirely upon the ,e4 ,m4 ,f4 ,illustration3 ,fig4 #fc4 ,voltmeters measure electrical pressure just as steam gauges measure the pressure of steam4 ,fig4 #fb shows one form of voltmeter4 ,fig4 #fc shows a voltmeter with illuminated dial4 ,an electrical bulb behind the instrument furnishes light so that the readings can be easily taken4 #fh4 ,electrical ,resistance4 ,did you ever ride down hill on a hand-sled8 ,how easily the sled glides over the snow6 ,what happens1 though1 when you strike a bare place1 or a place where some evil-minded person has sprinkled ashes8 ,does the sled pass easily over bare ground or ashes8 ,snow offers very little resistance to the sled1 while ashes offer a great resistance4 ,illustration3 ,fig4 #fd4 ,all substances do not allow the electric current to pass through them with the same ease4 ,even the liquid in a cell tends to hold the current back and offers internal resistance4 ,the various wires and instruments connected to a cell offer external resistance4 7,see ,study1 ,chapter ,,xviii41 for experiments1 etc47 #fi4 ,unit of ,resistance4 ,the ,ohm is the name given to the unit of resistance4 ,about #i ft4 #i in4 of ,no4 #cj copper wire1 or #ci feet #a in4 of ,no4 #bd copper wire1 will make a fairly accurate ohm4 ,resistance coils1 having carefully measured resistances1 are made for standards4 7,see ,apparatus ,book1 ,chapter ,,xvii41 for home-made resistance coils47 ,fig4 #fd shows a commercial form of a standard resistance coil4 ,the coil is inclosed in a case and has large wires leading from its ends for connections4 ,fig4 #fe gives an idea of the way in which coils are wound and used with plugs to build up resistance boxes1 ,fig4 #ff4 #gj4 ,laws of ,resistance4 #a4 ,the resistance of a wire is directly proportional to its length1 provided its cross-section1 material1 etc41 are uniform4 #b4 ,the resistance of a wire is inversely proportional to its area of cross-section2 or1 in other words1 inversely proportional to the square of its diameter1 other things being equal4 ,illustration3 ,fig4 #fe4 #c4 ,the resistance of a wire depends upon its material1 as well as upon its length1 size1 etc4 #d4 ,the resistance of a wire increases as its temperature rises4 7,see ,study1 ,chapters ,,xviii4 and ,,xix41 for experiments on resistance1 its measurement1 etc47 ,illustration3 ,fig4 #ff4 #ga4 ,current ,strength4 ,the strength of a current at the end of a circuit depends not only upon the electrical pressure1 or ,e4 ,m4 ,f41 which drives the current1 but also upon the resistance which has to be overcome4 ,the greater the resistance the weaker the current at the end of its journey4 #gb4 ,unit of ,current ,strength2 ,the ,ampere4 ,a current having an ,e4 ,m4 ,f4 of one volt1 pushing its way through a resistance of one ohm1 would have a unit of strength1 called one ampere4 ,this current1 one ampere strong1 would deposit1 under proper conditions1 4#jjjcbgg gramme of copper in one second from a solution of copper sulphate4 #gc4 ,measurement of ,current ,strength4 ,a magnetic needle is deflected when a current passes around it1 as in instruments like the galvanometer4 ,the galvanoscope merely indicates the presence of a current4 ,galvanometers measure the strength of a current1 and they are made in many forms1 depending upon the nature and strength of the currents to be measured4 ,galvanometers are standardized1 or calibrated1 by special measurements1 or by comparison with some standard instrument1 so that when the deflection is a certain number of degrees1 the current passing through it is known to be of a certain strength4 ,illustration3 ,fig4 #fg4 ,fig4 #fg shows an astatic galvanometer4 ,fig4 #fh shows a tangent galvanometer1 in which the strength of the current is proportional to the tangent of the angle of deflection4 ,fig4 #fi shows a ,d',arsonval galvanometer1 in which a coil of wire is suspended between the poles of a permanent horseshoe magnet4 ,the lines of force are concentrated by the iron core of the coil4 ,the two thin suspending wires convey the current to the coil4 ,a ray of light is reflected from the small mirror and acts as a pointer as in other forms of reflecting galvanometers4 ,illustration3 ,fig4 #fh4 #gd4 ,the ,ammeter1 ,fig4 #gj1 is a form of galvanometer in which the strength of a current1 in amperes1 can be read4 ,in these the strength of current is proportional to the angular deflections4 ,the coils are made with a small resistance1 so that the current will not be greatly reduced in strength in passing through them4 ,illustration3 ,fig4 #fi4 #ge4 ,voltameters measure the strength of a current by chemical means1 the quantity of metal deposited or gas generated being proportional to the time that the current flows and to its strength4 ,in the water voltameter1 ,fig4 #ga1 the hydrogen and oxygen produced in a given time are measured4 7,see ,study1 ,chapter ,,xxi47 ,illustration3 ,fig4 #gj4 ,the copper voltameter measures the amount of copper deposited in a given time by the current4 ,fig4 #gb shows one form4 ,the copper cathode is weighed before and after the current flows4 ,the weight of copper deposited and the time taken are used to calculate the current strength4 ,illustration3 ,fig4 #ga4 #gf4 ,unit of ,quantity2 ,the ,coulomb is the quantity of electricity given1 in one second1 by a current having a strength of one ampere4 ,time is an important element in considering the work a current can do4 ,illustration3 ,fig4 #gb4 #gg4 ,electrical ,horse-power2 ,the ,watt is the unit of electrical power4 ,a current having the strength of one ampere1 and an ,e4 ,m4 ,f4 of one volt has a unit of power4 #gdf watts make one electrical horse-power4 ,watts amperes volts4 ,fig4 #gc shows a direct reading wattmeter based on the international volt and ampere4 ,they save taking simultaneous ammeter and voltmeter readings1 which are otherwise necessary to get the product of volts and amperes1 and are also used on alternating current measurements4 ,illustration3 ,fig4 #gc4 ,there are also forms of wattmeters1 ,fig4 #gd1 in which the watts are read from dials like those on an ordinary gas-meter1 the records being permanent4 ,fig4 #ge shows a voltmeter ,v1 and ammeter ,a1 so placed in the circuit that readings can be taken4 ,d represents a dynamo4 ,a is placed so that the whole current passes through it1 while ,v is placed between the main wires to measure the difference in potential4 ,the product of the two readings in volts and amperes gives the number of watts4 ,illustration3 ,fig4 #gd4 #gh4 ,chemical ,meters also measure the quantity of current that is used2 for example1 one may be placed in the cellar to measure the quantity of current used to light the house4 ,illustration3 ,fig4 #ge4 ,fig4 #gf shows a chemical meter1 a part of the current passing through a jar containing zinc plates and a solution of zinc sulphate4 ,metallic zinc is dissolved from one plate and deposited upon the other4 ,the increase in weight shows the amount of chemical action which is proportional to the ampere hours4 ,knowing the relation between the quantity of current that can pass through the solution to that which can pass through the meter by another conductor1 a calculation can be made which will give the current used4 ,a lamp is so arranged that it automatically lights before the meter gets to the freezing-point2 this warms it up to the proper temperature1 at which point the light goes out again4 ,illustration3 ,fig4 #gf4 ,,chapter ,,vii4 ,,chemical ,,effects ,,of ,,the ,,electric ,,current4 #gi4 ,electrolysis4 ,it has been seen that in the voltaic cell electricity is generated by chemical action4 ,sulphuric acid acts upon zinc and dissolves it in the cell1 hydrogen is produced1 etc4 ,when this process is reversed1 that is1 when the electric current is passed through some solutions1 they are decomposed1 or broken up into their constituents4 ,this process is called electrolysis1 and the compound decomposed is the electrolyte4 7,see ,study1 #cfi1 etc41 with experiments47 ,illustration3 ,fig4 #gg4 ,fig4 #gg shows how water can be decomposed into its two constituents1 hydrogen and oxygen1 there being twice as much hydrogen formed as oxygen4 ,fig4 #gh shows a glass jar in which are placed two metal strips1 ,a and ,c1 these being connected with two cells4 ,in this jar may be placed various conducting solutions to be tested4 ,if1 for example1 we use a solution of copper sulphate1 its chemical formula being ,cu,s,o#d1 the current will break it up into ,cu 7copper7 and ,,so#d4 ,the ,cu will be deposited upon ,c as the current passes from ,a to ,c through the solution4 ,a is called the anode1 and ,c the cathode4 ,illustration3 ,fig4 #gh4 ,fig4 #gi shows another form of jar used to study the decomposition of solutions by the electric current4 ,illustration3 ,fig #gi4 #hj4 ,ions4 ,when a solution is decomposed into parts by a current1 the parts are called the ,ions4 ,when copper sulphate 7,cu ,,so#d7 is used1 the ions are ,cu1 which is a metal1 and ,,so#d1 called an acid radical4 ,when silver nitrate 7,ag ,,no#c7 is used1 ,ag and ,,no#c are the ions4 ,the metal part of the compound goes to the cathode4 ,,chapter ,,viii4 ,,how ,,electroplating ,,and ,,electrotyping ,,are ,,done4 #ha4 ,electricity and ,chemical ,action4 ,we have just seen1 ,chapter ,,vii41 that the electric current has the power to decompose certain compounds when they are in solution4 ,by choosing the right solutions1 then1 we shall be able to get copper1 silver1 and other metals set free by electrolysis4 #hb4 ,electroplating consists in coating substances with metal with the aid of the electric current4 ,if we wish to electroplate a piece of metal with copper1 for example1 we can use the arrangement shown in ,fig4 #gh1 in which ,c is the cathode plate to be covered1 and ,a is a copper plate4 ,the two are in a solution of copper sulphate1 and1 as explained in #gi1 the solution will be decomposed4 ,copper will be deposited upon ,c1 and the ,,so#d part of the solution will go to the anode ,a1 which it will attack and gradually dissolve4 ,the ,,so#d1 acting upon the copper anode1 makes ,cu,s,o#d again1 and this keeps the solution at a uniform strength4 ,the amount of copper dissolved from the copper anode equals1 nearly1 the amount deposited upon the cathode4 ,the metal is carried in the direction of the current4 ,if we wish to plate something with silver or gold1 it will be necessary to use a solution of silver or gold for the electrolyte1 a plate of metallic silver or gold being used for the anode1 as the case may be4 ,great care is used in cleaning substances to be plated1 all dirt and grease being carefully removed4 ,fig4 #hj shows a plating bath in which several articles can be plated at the same time by hanging them upon a metal bar which really forms a part of the cathode4 ,if1 for example1 we wish to plate knives1 spoons1 etc41 with silver1 they would be hung from the bar shown1 each being a part of the cathode4 ,the vat would contain a solution of silver1 and from the other bar would be hung a silver plate having a surface about equal to that of the combined knives1 etc4 ,illustration3 ,fig4 #hj4 ,most metals are coated with copper before they are plated with silver or gold4 ,when plating is done on a large scale1 a current from a dynamo is used4 ,for experimental purposes a ,gravity cell will do very well4 7,see ,study1 #cgd to #chj with experiments47 #hc4 ,electrotyping4 ,it was observed by ,de ,la ,rue in #ahcf that in the ,daniell cell an even coating of copper was deposited upon the copper plate4 ,from this was developed the process of electrotyping1 which consists in making a copy in metal of a wood-cut1 page of type1 etc4 ,a mould or impression of the type or coin is first made in wax1 or other suitable material4 ,these moulds are1 of course1 the reverse of the original1 and as they do not conduct electricity1 have to be coated with graphite4 ,this thin coating lines the mould with conducting material so that the current can get to every part of the mould4 ,these are then hung upon the cathode in a bath of copper sulphate as described in #hb4 ,the electric current which passes through the vat deposits a thin layer of metallic copper next to the graphite4 ,when this copper gets thick enough1 the wax is melted away from it1 leaving a thin shell of copper1 the side next to the graphite being exactly alike in shape to the type1 but made of copper4 ,these thin copper sheets are too thin to stand the pressure necessary on printing presses1 so they are strengthened by backing them with soft metal which fills every crevice1 making solid plates about in4 thick4 ,these plates or electrotypes are used to print from1 the original type being used to set up another page4 ,,chapter ,,ix4 ,,the ,,storage ,,battery1 ,,and ,,how ,,it ,,works4 #hd4 ,polarization4 ,it has been stated that a simple cell polarizes rapidly on account of hydrogen bubbles that form upon the copper plate4 ,they tend to send a current in the opposite direction to that of the main current1 which is thereby weakened4 ,illustration3 ,fig4 #ha4 #he4 ,electromotive ,force of ,polarization4 ,it has been shown1 ,fig4 #ga1 that water can be decomposed by the electric current4 ,hydrogen and oxygen have a strong attraction or chemical affinity for each other1 or they would not unite to form water4 ,this attraction has to be overcome before the water can be decomposed4 ,as soon as the decomposing current ceases to flow1 the gases formed try to rush together again2 in fact1 if the water voltameter be disconnected from the cells and connected with a galvanoscope1 the presence of a current will be shown4 ,this voltameter will give a current with an ,e4 ,m4 ,f4 of nearly #a4e volts2 so it is evident that we must have a current with a higher voltage than this to decompose water4 ,this ,e4 ,m4 ,f41 due to polarization1 is called the ,e4 ,m4 ,f4 of polarization4 #hf4 ,secondary or ,storage ,batteries1 also called accumulators1 do not really store electricity4 ,they must be charged by a current before they can give out any electricity4 ,chemical changes are produced in the storage cells by the charging current just as they are in voltameters1 electroplating solutions1 etc42 so it is potential chemical energy that is really stored4 ,when the new products are allowed to go back to their original state1 by joining the electrodes of the charged cell1 a current is produced4 ,fig4 #ha shows two lead plates1 ,a and ,b1 immersed in dilute sulphuric acid1 and connected with two ordinary cells4 ,a strong current will pass through the liquid between ,a and ,b at first1 but it will quickly become weaker1 as chemical changes take place in the liquid4 ,this may be shown by a galvanometer put in the circuit before beginning the experiment4 ,by disconnecting the wires from the cells and joining them to the galvanometer1 it will be shown that a current comes from the lead plates4 ,this arrangement may be called a simple storage cell4 ,regular storage cells are charged with the current from a dynamo4 7,see ,study1 ,exp4 #aea47 ,illustration3 ,fig4 #hb4 ,the first storage cells were made of plain lead plates1 rolled up in such a way that they were close to each other1 but did not touch4 ,these were placed in dilute sulphuric acid4 ,they were charged in alternate directions several times1 until the lead became properly acted upon1 at which time the cell would furnish a current4 ,a great improvement was made in #ahha1 by ,faure1 who coated the plates with red lead4 ,illustration3 ,fig4 #hc4 ,the method now generally practiced is to cast a frame of lead1 with raised right-angled ribs on each side1 thus forming little depressed squares1 or to punch a lead plate full of holes1 which squares or holes are then filled with a pasty mixture of red oxide of lead in positive plates1 and with litharge in negatives4 ,in a form called the chloride battery1 instead of cementing lead oxide paste into or against a lead framing in order to obtain the necessary active material1 the latter is obtained by a strictly chemical process4 ,fig4 #hb shows a storage cell with plates1 etc41 contained in a glass jar4 ,fig4 #hc shows a cell of #da plates1 set up in a lead-lined wood tank4 ,fig4 #hd shows three cells joined in series4 ,many storage cells are used in central electric light stations to help the dynamos during the rush hours at night4 ,they are charged during the day when the load on the dynamos is not heavy4 ,fig4 #he shows another form of storage cell containing a number of plates4 ,illustration3 ,fig4 #hd4 #hg4 ,the ,uses of ,storage ,batteries are almost numberless4 ,the current can be used for nearly everything for which a constant current is adapted1 the following being some of its applications3 ,carriage propulsion2 electric launch propulsion2 train lighting2 yacht lighting2 carriage lighting2 bicycle lighting2 miners' lamps2 dental1 medical1 surgical1 and laboratory work2 phonographs2 kinetoscopes2 automaton pianos2 sewing-machine motors2 fan motors2 telegraph2 telephone2 electric bell2 electric fire-alarm2 heat regulating2 railroad switch and signal apparatus4 ,by the installing of a storage plant many natural but small sources of power may be utilized in furnishing light and power2 sources which otherwise are not available1 because not large enough to supply maximum demands4 ,the force of the tides1 of small water powers from irrigating ditches1 and even of the wind1 come under this heading4 ,illustration3 ,fig4 #he4 ,as a regulator of pressure1 in case of fluctuations in the load1 the value of a storage plant is inestimable4 ,these fluctuations of load are particularly noticeable in electric railway plants1 where the demand is constantly rising and falling1 sometimes jumping from almost nothing to the maximum1 and vice versa1 in a few seconds4 ,if for no other reason than the prevention of severe strain on the engines and generators1 caused by these fluctuations of demand1 a storage plant will be valuable4 ,,chapter ,x4 ,,how ,,electricity ,,is ,,generated ,,by ,,heat4 #hh4 ,thermoelectricity is the name given to electricity that is generated by heat4 ,if a strip of iron1 ,i1 be connected between two strips of copper1 ,c ,c1 these being joined by a copper wire1 ,c ,w1 we shall have an arrangement that will generate a current when heated at either of the junctions between ,c and ,i4 ,when it is heated at ,a the current will flow as shown by arrows1 from ,c to ,i4 ,if we heat at ,b1 the current will flow in the opposite direction through the metals1 although it will still go from ,c to ,i as before4 ,such currents are called thermoelectric currents4 ,illustration3 ,fig4 #hf4 ,different pairs of metals produce different results4 ,antimony and bismuth are generally used1 because the greatest effect is produced by them4 ,if the end of a strip of bismuth be soldered to the end of a similar strip of antimony1 and the free ends be connected to a galvanometer of low resistance1 the presence of a current will be shown when the point of contact becomes hotter than the rest of the circuit4 ,the current will flow from bismuth to antimony across the joint4 ,by cooling the juncture below the temperature of the rest of the circuit1 a current will be produced in the opposite direction to the above4 ,the energy of the current is kept up by the heat absorbed1 just as it is kept up by chemical action in the voltaic cell4 #hi4 ,peltier ,effect4 ,if an electric current be passed through pairs of metals1 the parts at the junction become slightly warmer or cooler than before1 depending upon the direction of the current4 ,this action is really the reverse of that in which currents are produced by heat4 ,illustration3 ,fig4 #hg4 #ij4 ,thermopiles4 ,as the ,e4,m4,f4 of the current produced by a single pair of metals is very small1 several pairs are usually joined in series1 so that the different currents will help each other by flowing in the same direction4 ,such combinations are called thermoelectric piles1 or simply thermopiles4 ,fig4 #hg shows such an arrangement1 in which a large number of elements are placed in a small space4 ,the junctures are so arranged that the alternate ones come together at one side4 ,fig4 #hh shows a thermopile connected with a galvanometer4 ,the heat of a match1 or the cold of a piece of ice1 will produce a current1 even if held at some distance from the thermopile4 ,the galvanometer should be a short-coil astatic one4 7,see ,study1 ,chapter ,,xxiv41 for experiments and home-made thermopile47 ,illustration3 ,fig4 #hh4 ,,chapter ,,xi4 ,,magnetic ,,effects ,,of ,,the ,,electric ,,current4 #ia4 ,electromagnetism is the name given to magnetism that is developed by electricity4 ,we have seen that if a magnetic needle be placed in the field of a magnet1 its ,n pole will point in the direction taken by the lines of force as they pass from the ,n to the ,s pole of the magnet4 ,illustration3 ,fig4 #hi4 #ib4 ,lines of ,force about a ,wire4 ,when a current passes through a wire1 the magnetic needle placed over or under it tends to take a position at right angles to the wire4 ,fig4 #hi shows such a wire and needle1 and how the needle is deflected2 it twists right around from its ,n and ,s position as soon as the current begins to flow4 ,this shows that the lines of force pass around the wire and not in the direction of its length4 ,the needle does not swing entirely perpendicular to the wire1 that is1 to the ,e and ,w line1 because the earth is at the same time pulling its ,n pole toward the ,n4 ,fig4 #ij shows a bent wire through which a current passes from ,c to ,z4 ,if you look along the wire from ,c toward the points ,a and ,b1 you will see that under the wire the lines of force pass to the left4 ,looking along the wire from ,z toward ,d you will see that the lines of force pass opposite to the above1 as the current comes toward you4 ,this is learned by experiment4 7,see ,study1 ,exp4 #aeb1 #che1 etc47 ,illustration3 ,fig4 #ij4 ,illustration3 ,fig4 #ia4 ,rule4 ,hold the right hand with the thumb extended 7,fig4 #hi7 and with the fingers pointing in the direction of the current1 the palm being toward the needle and on the opposite side of the wire from the needle4 ,the north-seeking pole will then be deflected in the direction in which the thumb points4 #ic4 ,current ,detectors4 ,as there is a magnetic field about a wire when a current passes through it1 and as the magnetic needle is affected1 we have a means of detecting the presence of a current4 ,when the current is strong it is simply necessary to let it pass once over or under a needle2 when it is weak1 the wire must pass several times above and below the needle1 ,fig4 #ia1 to give the needle motion4 7,see ,apparatus ,book1 ,chapter ,,xiii41 for home-made detectors47 ,illustration3 ,fig4 #ib4 #id4 ,astatic ,needles and ,detectors4 ,by arranging two magnetized needles with their poles opposite each other1 ,fig4 #ib1 an astatic needle is formed4 ,the pointing-power is almost nothing1 although their magnetic fields are retained4 ,this combination is used to detect feeble currents4 ,in the ordinary detector1 the tendency of the needle to point to the ,n and ,s has to be overcome by the magnetic field about the coil before the needle can be moved2 but in the astatic detector and galvanoscope this pointing-power is done away with4 ,fig4 #ic shows a simple astatic galvanoscope4 ,fig4 #fg shows an astatic galvanometer for measuring weak currents4 ,illustration3 ,fig4 #ic4 #ie4 ,polarity of ,coils4 ,when a current of electricity passes through a coil of wire1 the coil acts very much like a magnet1 although no iron enters into its construction4 ,the coil becomes magnetized by the electric current1 lines of force pass from it into the air1 etc4 ,fig4 #id shows a coil connected to copper and zinc plates1 so arranged with cork that the whole can float in a dish of dilute sulphuric acid4 ,the current passes as shown by the arrows1 and when the ,n pole of a magnet is brought near the right-hand end1 there is a repulsion1 showing that that end of the coil has a ,n pole4 ,rule4 ,when you face the right-hand end of the coil1 the current is seen to pass around it in an anti-clockwise direction2 this produces a ,n pole4 ,when the current passes in a clockwise direction a ,s pole is produced4 ,illustration3 ,fig4 #id4 #if4 ,electromagnets4 ,a coil of wire has a stronger field than a straight wire carrying the same current1 because each turn adds its field to the fields of the other turns4 ,by having the central part of the coil made of iron1 or by having the coil of insulated wire wound upon an iron core1 the strength of the magnetic field of the coil is greatly increased4 ,lines of force do not pass as readily through air as through iron2 in fact1 lines of force will go out of their way to go through iron4 ,with a coil of wire the lines of force pass from its ,n pole through the air on all sides of the coil to its ,s pole2 they then pass through the inside of the coil and through the air back to the ,n pole4 ,when the resistance to their passage through the coil is decreased by the core1 the magnetic field is greatly strengthened1 and we have an electromagnet4 ,the coil of wire temporarily magnetizes the iron core2 it can permanently magnetize a piece of steel used as a core4 7,see ,study1 ,chapter ,,xxii41 for experiments47 ,illustration3 ,fig4 #ie4 #ig4 ,forms of ,electromagnets4 ,fig4 #ie shows a straight1 or bar electromagnet4 ,fig4 #if shows a simple form of horseshoe electromagnet4 ,as this form is not easily wound1 the coils are generally wound on two separate cores which are then joined by a yoke4 ,the yoke merely takes the place of the curved part shown in ,fig4 #if4 ,in ,fig4 #ig is shown the ordinary form of horseshoe electromagnet used for all sorts of electrical instruments4 7,see ,apparatus ,book1 ,chapter ,,ix41 for home-made electromagnets47 #ih4 ,yokes and ,armatures4 ,in the horseshoe magnet there are two poles to attract and two to induce4 ,the lines of force pass through the yoke on their way from one core to the other1 instead of going through the air4 ,this reduces the resistance to them4 ,if we had no yoke we should simply have two straight electromagnets1 and the resistance to the lines of force would be so great that the total strength would be much reduced4 ,yokes are made of soft iron1 as well as the cores and armature4 ,the armature1 as with permanent horseshoe magnets1 is strongly drawn toward the poles4 ,as soon as the current ceases to flow1 the attraction also ceases4 ,illustration3 ,fig4 #if4 ,illustration3 ,fig4 #ig4 ,illustration3 ,fig4 #ih4 ,beautiful magnetic figures can be made with horseshoe magnets4 ,fig4 #ih shows that the coils must be joined so that the current can pass around the cores in opposite directions to make unlike poles4 7,see ,study1 ,exp4 #afd to #agc47 ,,chapter ,,xii4 ,,how ,,electricity ,,is ,,generated ,,by ,,induction4 #ii4 ,electromagnetic ,induction4 ,we have seen that a magnet has the power to act through space and induce another piece of iron or steel to become a magnet4 ,a charge of static electricity can induce a charge upon another conductor4 ,we have now to see how a current of electricity in one conductor can induce a current in another conductor1 not in any way connected with the first1 and how a magnet and a coil can generate a current4 ,illustration3 ,fig4 #ii4 ,illustration3 ,fig4 #ajj4 #ajj4 ,current from ,magnet and ,coil4 ,if a bar magnet1 ,fig4 #ii1 be suddenly thrust into a hollow coil of wire1 a momentary current of electricity will be generated in the coil4 ,no current passes when the magnet and coil are still2 at least one of them must be in motion4 ,such a current is said to be induced1 and is an inverse one when the magnet is inserted1 and a direct one when the magnet is withdrawn from the coil4 #aja4 ,induced ,currents and ,lines of ,force4 ,permanent magnets are constantly sending out thousands of lines of force4 ,fig4 #ajj shows a bar magnet entering a coil of wire2 the number of lines of force is increasing1 and the induced current passes in an anti-clockwise direction when looking down into the coil along the lines of force4 ,this produces an indirect current4 ,if an iron core be used in the coil1 the induced current will be greatly strengthened4 ,illustration3 ,fig4 #aja4 ,it takes force to move a magnet through the center of a coil1 and it is this work that is the source of the induced current4 ,we have1 in this simple experiment1 the key to the action of the dynamo and other electrical machines4 #ajb4 ,current from two ,coils4 ,fig4 #aja shows two coils of wire1 the smaller being connected to a cell1 the larger to a galvanometer4 ,by moving the small coil up and down inside of the large one1 induced currents are generated1 first in one direction and then in the opposite4 ,we have here two entirely separate circuits1 in no way connected4 ,the primary current comes from the cell1 while the secondary current is an induced one4 ,by placing a core in the small coil of ,fig4 #aja1 the induced current will be greatly strengthened4 ,it is not necessary to have the two coils so that one or both of them can move4 ,they may be wound on the same core1 or otherwise arranged as in the induction coil4 7,see ,study1 ,chapter ,,xxv41 for experiments on induced currents47 ,,chapter ,,xiii4 ,,how ,,the ,,induction ,,coil ,,works4 #ajc4 ,the ,coils4 ,we saw1 #ajb1 that an induced current was generated when a current-carrying coil1 ,fig4 #aja1 was thrust into another coil connected with a galvanometer4 ,the galvanometer was used merely to show the presence of the current4 ,the primary coil is the one connected with the cell2 the other one is called the secondary coil4 ,illustration3 ,fig4 #ajb4 ,when a current suddenly begins to flow through a coil1 the effect upon a neighboring coil is the same as that produced by suddenly bringing a magnet near it2 and when the current stops1 the opposite effect is produced4 ,it is evident1 then1 that we can keep the small coil of ,fig4 #aja with its core inside of the large coil1 and generate induced currents by merely making and breaking the primary circuit4 ,we may consider that when the primary circuit is closed1 the lines of force shoot out through the turns of the secondary coil just as they do when a magnet or a current-carrying coil is thrust into it4 ,upon opening the circuit1 the lines of force cease to exist2 that is1 we may imagine them drawn in again4 #ajd4 ,construction4 ,fig4 #ajb shows one form of home-made induction coil1 given here merely to explain the action and connections4 ,nearly all induction coils have some form of automatic current interrupter1 placed in the primary circuit1 to rapidly turn the current off and on4 ,details of ,figs4 #ajb and #ajc4 ,wires #e and #f are the ends of the primary coil1 while wires #g and #h are the terminals of the secondary coil4 ,the primary coil is wound on a bolt which serves as the core1 and on this coil is wound the secondary which consists of many turns of fine wire4 ,the wires from a battery should be joined to binding-posts ,w and ,x1 and the handles1 from which the shock is felt1 to ,y and ,z4 ,fig4 #ajc shows the details of the interrupter4 ,illustration3 ,fig4 #ajc4 ,if the current from a cell enters at ,w1 it will pass through the primary coil and out at ,x1 after going through #e1 ,r1 ,f1 ,s ,i1 ,b1 ,e and ,c4 ,the instant 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 ,,si1 as ,a is no longer attracted2 the circuit being closed1 the operation is rapidly repeated4 ,a condenser is usually connected to commercial forms4 ,it is placed under the wood-work and decreases sparking at the interrupter4 7,see ,apparatus ,book1 ,chapter ,,xi41 for home-made induction coils47 ,illustration3 ,fig4 #ajd4 ,fig4 #ajd shows one form of coil4 ,the battery wires are joined to the binding-posts at the left4 ,the secondary coil ends in two rods1 and the spark jumps from one to the other4 ,the interrupter and a switch are shown at the left4 ,fig4 #aje shows a small coil for medical purposes4 ,a dry cell is placed under the coil and all is included in a neat box4 ,the handles form the terminals of the secondary coil4 #aje4 ,the ,currents4 ,it should be noted that the current from the cell does not get into the secondary coil4 ,the coils are thoroughly insulated from each other4 ,the secondary current is an induced one1 its voltage depending upon the relative number of turns of wire there are in the two coils4 7,see ,transformers47 ,the secondary current is an alternating one2 that is1 it flows in one direction for an instant and then immediately reverses its direction4 ,the rapidity of the alternations depends upon the speed of the interrupter4 ,coils are made that give a secondary current with an enormous voltage2 so high1 in fact1 that the spark will pass many inches1 and otherwise act like those produced by static electric machines4 ,illustration3 ,fig4 #aje4 #ajf4 ,uses of ,induction ,coils4 ,gas-jets can be lighted at a distance with the spark from a coil1 by extending wires from the secondary coil to the jet4 ,powder can be fired at a distance1 and other things performed1 when a high voltage current is needed4 ,its use in medicine has been noted4 ,it is largely used in telephone work4 ,of late1 great use has been made of the secondary current in experiments with vacuum-tubes1 ,x-ray work1 etc4 ,,chapter ,,xiv4 ,,the ,,electric ,,telegraph1 ,,and ,,how ,,it ,,sends ,,messages4 #ajg4 ,the ,complete ,telegraph ,line consists of several instruments1 switches1 etc41 etc41 but its essential parts are3 ,the ,line1 or wire1 which connects the different stations2 the ,transmitter or ,key2 the ,receiver or ,sounder1 and the ,battery or ,dynamo4 #ajh4 ,the ,line is made of strong copper1 iron1 or soft steel wire4 ,to keep the current in the line it is insulated1 generally upon poles1 by glass insulators4 ,for very short lines two wires can be used1 the line wire and the return2 but for long lines the earth is used as a return1 a wire from each end being joined to large metal plates sunk in the earth4 ,illustration3 ,fig4 #ajf4 #aji4 ,telegraph ,keys are merely instruments 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 the current off and on1 but it is not so convenient as a key4 ,fig4 #ajf shows a side view of a simple key which can be put anywhere in the circuit1 one end of the cut wire being attached to ,x and the other to ,y4 ,by moving the lever ,c up and down according to a previously arranged set of signals1 a current will be allowed to pass to a distant station4 ,as ,x and ,y are insulated from each other1 the current can pass only when ,c presses against ,y4 ,fig4 #ajg shows a regular key1 with switch1 which is used to allow the current to pass through the instrument when receiving a message4 ,illustration3 ,fig4 #ajg4 #aaj4 ,telegraph ,sounders receive the current from some distant station1 and with its electromagnet produce sounds that can be translated into messages4 ,illustration3 ,fig4 #ajh4 ,fig4 #ajh shows simply an electromagnet ,h1 the coil being connected in series with a key ,k and a cell ,d ,c4 ,the key and ,d ,c are shown by a top view4 ,the lever of ,k does not touch the other metal strap until it is pressed down4 ,a little above the core of ,h is held a strip of iron1 on armature ,i4 ,as soon as the circuit is closed at ,k1 the current rushes through the circuit1 and the core attracts ,i making a distinct click4 ,as soon as ,k is raised1 ,i springs away from the core1 if it has been properly held4 ,in regular instruments a click is also made when the armature springs back again4 ,the time between the two clicks can be short or long1 to represent dots or dashes1 which1 together with spaces1 represent letters4 7,for ,telegraph ,alphabet and complete directions for home-made keys1 sounders1 etc41 see ,apparatus ,book1 ,chapter ,,xiv47 ,illustration3 ,fig4 #aji4 ,illustration3 ,fig4 #aaj4 ,fig4 #aji shows a form of home-made sounder4 ,fig4 #aaj shows one form of telegraph sounder4 ,over the poles of the horseshoe electromagnet is an armature fixed to a metal bar that can rock up and down4 ,the instant the current passes through the coils the armature comes down until a stop-screw strikes firmly upon the metal frame1 making the down click4 ,as soon as the distant key is raised1 the armature is firmly pulled back and another click is made4 ,the two clicks differ in sound1 and can be readily recognized by the operator4 #aaa4 ,connections for ,simple ,line4 ,fig4 #aaa shows complete connections for a home-made telegraph line4 ,the capital letters are used for the right side1 ,r1 and small letters for the left side1 ,l4 ,gravity cells1 ,b and b1 are used4 ,the sounders1 ,s and s1 and the keys1 ,k and k1 are shown by a top view4 ,the broad black lines of ,s and s represent the armatures which are directly over the electromagnets4 ,the keys have switches1 ,e and e4 ,the two stations1 ,r and ,l1 may be in the same room1 or in different houses4 ,the return wire1 ,r ,w1 passes from the copper of b to the zinc of ,b4 ,this is important1 as the cells must help each other2 that is1 they are in series4 ,the line wire1 ,l ,w1 passes from one station to the other1 and the return may be through the wire1 ,r ,w1 or through the earth2 but for short lines a wire is best4 ,illustration3 ,fig4 #aaa4 #aab4 ,operation of ,simple ,line4 ,suppose two boys1 ,r 7right7 and ,l 7left7 have a line4 ,fig4 #aaa shows that ,r's switch1 ,e1 is open1 while e is closed4 ,the entire circuit1 then1 is broken at but one point4 ,as soon as ,r presses his key1 the circuit is closed1 and the current from both cells rushes around from ,b1 through ,k1 ,s1 ,l ,w1 s1 k1 b1 ,r ,w1 and back to ,b4 ,this makes the armatures of ,s and s come down with a click at the same time4 ,as soon as the key is raised1 the armatures lift and make the up-click4 ,as soon as ,r has finished1 he closes his switch ,e4 ,as the armatures are then held down1 ,l knows that ,r has finished1 so he opens his switch e1 and answers ,r4 ,both ,e and e are closed when the line is not in use1 so that either can open his switch at any time and call up the other4 ,closed circuit cells must be used for such lines4 ,on very large lines dynamos are used to furnish the current4 #aac4 ,the ,relay4 ,owing to the large resistance of long telegraph lines1 the current is weak when it reaches a distant station1 and not strong enough to work an ordinary sounder4 ,to get around this1 relays are used2 these are very delicate instruments that replace the sounder in the line wire circuit4 ,their coils are usually wound with many turns of fine wire1 so that a feeble current will move its nicely adjusted armature4 ,the relay armature merely acts as an automatic key to open and close a local circuit which includes a battery and sounder4 ,the line current does not enter the sounder2 it passes back from the relay to the sending station through the earth4 ,illustration3 ,fig4 #aab4 ,fig4 #aab gives an idea of simple relay connections4 ,the key ,k1 and cell ,d ,c1 represent a distant sending station4 ,e is the electromagnet of the relay1 and ,r ,a is its armature4 ,l ,w and ,r ,w represent the line and return wires4 ,r ,a will vibrate toward ,e every time ,k is pressed1 and close the local circuit1 which includes a local battery1 ,l ,b1 and a sounder4 ,it is evident that as soon as ,k is pressed the sounder will work with a good strong click1 as the local battery can be made as strong as desired4 ,fig4 #aac shows a regular instrument which opens and closes the local circuit at the top of the armature4 ,illustration3 ,fig4 #aac4 #aad4 ,ink ,writing ,registers are frequently used instead of sounders4 ,fig4 #aad shows a writing register that starts itself promptly at the opening of the circuit1 and stops automatically as soon as the circuit returns to its normal condition4 ,a strip of narrow paper is slowly pulled from the reel by the machine1 a mark being made upon it every time the armature of an inclosed electromagnet is attracted4 ,when the circuit is simply closed for an instant1 a short line1 representing a dot1 is made4 ,registers are built both single pen and double pen4 ,in the latter case1 as the record of one wire is made with a fine pen1 and the other with a coarse pen1 they can always be identified4 ,the record being blocked out upon white tape in solid black color1 in a series of clean-cut dots and dashes1 it can be read at a glance1 and as it is indelible1 it may be read years afterward4 ,registers are made for local circuits1 for use in connection with relays1 or for direct use on main lines1 as is usually desirable in fire-alarm circuits4 ,illustration3 ,fig4 #aad4 ,,chapter ,,xv4 ,,the ,,electric ,,bell ,,and ,,some ,,of ,,its ,,uses4 ,illustration3 ,fig4 #aae4 ,illustration3 ,fig4 #aaf4 #aae4 ,automatic ,current ,interrupters are used on most common bells1 as well as on induction coils1 etc4 7,see #ajd47 ,fig4 #aae shows a simple form of interrupter4 ,the wire #a1 from a cell ,d ,c1 is joined to an iron strip ,i a short distance from its end4 ,the other wire from ,d ,c passes to one end of the electromagnet coil ,h4 ,the remaining end of ,h is placed in contact with ,i as shown1 completing the circuit4 ,as soon as the current passes1 ,i is pulled down and away from the upper wire #b1 breaking the circuit4 ,i1 being held by its left-hand end firmly in the hand1 immediately springs back to its former position1 closing the circuit again4 ,this action is repeated1 the rapidity of the vibrations depending somewhat upon the position of the wires on ,i4 ,in regular instruments a platinum point is used where the circuit is broken2 this stands the sparking when the armature vibrates4 #aaf4 ,electric ,bells may be illustrated by referring to ,fig4 #aaf1 which shows a circuit similar to that described in #aae1 but which also contains a key ,k1 in the circuit4 ,this allows the circuit to be opened and closed at a distance from the vibrating armature4 ,the circuit must not be broken at two places at the same time1 so wires should touch at the end of ,i before pressing ,k4 ,upon pressing ,k the armature ,i will vibrate rapidly4 ,by placing a small bell near the end of the vibrating armature1 so that it will be struck by ,i at each vibration1 we should have a simple electric bell4 ,this form of electric bell is called a trembling bell1 on account of its vibrating armature4 ,illustration3 ,fig4 #aag4 ,illustration3 ,fig4 #aah4 ,fig4 #aag shows a form of trembling bell with cover removed4 ,fig4 #aah shows a single-stroke bell1 used for fire-alarms and other signal work4 ,in this the armature is attracted but once each time the current passes4 ,as many taps of the bell can be given as desired by pressing the push-button4 ,fig4 #aai shows a gong for railway crossings1 signals1 etc4 ,fig4 #abj shows a circuit including cell1 push-button1 and bell1 with extra wire for lengthening the line4 ,illustration3 ,fig4 #aai4 ,electro-,mechanical ,gongs are used to give loud signals for special purposes4 ,the mechanical device is started by the electric current when the armature of the electromagnet is attracted4 ,springs1 weights1 etc41 are used as the power4 ,fig4 #aba shows a small bell of this kind4 ,illustration3 ,fig4 #abj4 #aag4 ,magneto ,testing ,bells1 ,fig4 #abb1 are really small hand-power dynamos4 ,the armature is made to revolve between the poles of strong permanent magnets1 and it is so wound that it gives a current with a large ,e4 ,m4 ,f41 so that it can ring through the large resistance of a long line to test it4 ,magneto ,signal ,bells1 ,fig4 #abc1 are used as generator and bell in connection with telephones4 ,the generator1 used to ring a bell at a distant station1 stands at the bottom of the box4 ,the bell is fastened to the lid1 and receives current from a distant bell4 ,illustration3 ,fig4 #aba4 ,illustration3 ,fig4 #abb4 ,illustration3 ,fig4 #abc4 ,illustration3 ,fig4 #abd4 #aah4 ,electric ,buzzers have the same general construction as electric bells2 in fact1 you will have a buzzer by removing the bell from an ordinary electric bell4 ,buzzers are used in places where the loud sound of a bell would be objectionable4 ,fig4 #abd shows the usual form of buzzers1 the cover being removed4 ,,chapter ,,xvi4 ,,the ,,telephone1 ,,and ,,how ,,it ,,transmits ,,speech4 #aai4 ,the ,telephone is an instrument for reproducing sounds at a distance1 and electricity is the agent by which this is generally accomplished4 ,the part spoken to is called the transmitter1 and the part which gives sound out again is called the receiver4 ,sound itself does not pass over the line4 ,while the same apparatus can be used for both transmitter and receiver1 they are generally different in construction to get the best results4 ,illustration3 ,fig4 #abe4 ,illustration3 ,fig4 #abf4 ,illustration3 ,fig4 #abg4 #abj4 ,the ,bell or ,magneto-transmitter generates its own current1 and is1 strictly speaking1 a dynamo that is run by the voice4 ,it depends upon induction for its action4 ,illustration3 ,fig4 #abh4 ,fig4 #abe shows a coil of wire1 ,h1 with soft iron core1 the ends of the wires being connected to a delicate galvanoscope4 ,if one pole of the magnet ,h ,m be suddenly moved up and down near the core1 an alternating current will be generated in the coil1 the circuit being completed through the galvanoscope4 ,as ,h ,m approaches the core the current will flow in one direction1 and as ,h ,m is withdrawn it will pass in the opposite direction4 ,the combination makes a miniature alternating dynamo4 ,illustration3 ,fig4 #abi4 ,if we imagine the soft iron core of ,h1 ,fig4 #abe1 taken out1 and one pole of ,h ,m1 or preferably that of a bar magnet stuck through the coil1 a feeble current will also be produced by moving the soft iron back and forth near the magnet's pole4 ,this is really what is done in the ,bell transmitter1 soft iron in the shape of a thin disc 7,d1 ,fig4 #abf7 being made to vibrate by the voice immediately in front of a coil having a permanent magnet for a core4 ,the disc1 or diaphragm1 as it is called1 is fixed near1 but it does not touch1 the magnet4 ,it is under a constant strain1 being attracted by the magnet1 so its slightest movement changes the strength of the magnetic field1 causing more or less lines of force to shoot through the turns of the coil and induce a current4 ,the coil consists of many turns of fine1 insulated wire4 ,the current generated is an alternating one1 and although exceedingly small can force its way through a long length of wire4 ,illustration3 ,fig4 #acj4 ,fig4 #abg shows a section of a regular transmitter1 and ,fig4 #abh a form of compound magnet frequently used in the transmitter4 ,fig4 #abi shows a transmitter with cords which contain flexible wires4 ,illustration3 ,fig4 #aca4 #aba4 ,the ,receiver1 for short lines1 may have the same construction as the ,bell transmitter4 ,fig4 #acj shows a diagram of two ,bell receivers1 either being used as the transmitter and the other as the receiver4 ,as the alternating current goes to the distant receiver1 it flies through the coil first in one direction and then in the other4 ,this alternately strengthens and weakens the magnetic field near the diaphragm1 causing it to vibrate back and forth as the magnet pulls more or less4 ,the receiver diaphragm repeats the vibrations in the transmitter4 ,nothing but the induced electric current passes over the wires4 ,illustration3 ,fig4 #acb4 #abb4 ,the ,microphone4 ,if a current of electricity be allowed to pass through a circuit like that shown in ,fig4 #aca1 which includes a battery1 a ,bell receiver1 and a microphone1 any slight sound near the microphone will be greatly magnified in the receiver4 ,the microphone consists of pieces of carbon so fixed that they form loose contacts4 ,any slight movement of the carbon causes the resistance to the current to be greatly changed4 ,the rapidly varying resistance allows more or less current to pass1 the result being that this pulsating current causes the diaphragm to vibrate4 ,the diaphragm has a constantly varying pull upon it when the carbons are in any way disturbed by the voice1 or by the ticking of a watch1 etc4 ,this principle has been made use of in carbon transmitters1 which are made in a large variety of forms4 ,illustration3 ,fig4 #acc4 #abc4 ,the ,carbon ,transmitter does not1 in itself1 generate a current like the magneto-transmitter2 it merely produces changes in the strength of a current that flows through it and that comes from some outside source4 ,in ,fig4 #acb1 ,x and ,y are two carbon buttons1 ,x being attached to the diaphragm ,d4 ,button ,y presses gently against ,x1 allowing a little current to pass through the circuit which includes a battery1 ,d ,c1 and a receiver1 ,r4 ,when ,d is caused to vibrate by the voice1 ,x is made to press more or less against ,y1 and this allows more or less current to pass through the circuit4 ,this direct undulating current changes the pull upon the diaphragm of ,r1 causing it to vibrate and reproduce the original sounds spoken into the transmitter4 ,in regular lines1 of course1 a receiver and transmitter are connected at each end1 together with bells1 etc41 for signaling4 ,illustration3 ,fig4 #acd4 #abd4 ,induction ,coils in ,telephone ,work4 ,as the resistance of long telephone lines is great1 a high electrical pressure1 or ,e4,m4,f4 is desired4 ,while the current from one or two cells is sufficient to work the transmitter properly1 and cause undulating currents in the short line1 it does not have power enough to force its way over a long line4 ,to get around this difficulty1 an induction coil1 ,fig4 #acc1 is used to transform the battery current1 that flows through the carbon transmitter and primary coil1 into a current with a high ,e4 ,m4 ,f4 ,the battery current in the primary coil is undulating1 but always passes in the same direction1 making the magnetic field around the core weaker and stronger4 ,this causes an alternating current in the secondary coil and main line4 ,in ,fig4 #acc ,p and ,s represent the primary and secondary coils4 ,p is joined in series with a cell and carbon transmitter2 ,s is joined to the distant receiver4 ,one end of ,s can be grounded1 the current completing the circuit through the earth and into the receiver through another wire entering the earth4 ,illustration3 ,fig4 #ace4 #abe4 ,various forms of telephones are shown in ,figs4 #acd1 #ace1 #acf4 ,fig4 #acd shows a form of desk telephone2 ,fig4 #ace shows a common form of wall telephone2 ,fig4 #acf shows head-telephones for switchboard operators4 ,illustration3 ,fig4 #acf4 ,,chapter ,,xvii4 ,,how ,,electricity ,,is ,,generated ,,by ,,dynamos4 #abf4 ,the ,dynamo1 ,dynamo-,electric ,machine or ,generator1 is a machine for converting mechanical energy into an electric current1 through electromagnetic induction4 ,the dynamo is a machine that will convert steam power1 for example1 into an electric current4 ,strictly speaking1 a dynamo creates electrical pressure1 or electromotive force1 and not electricity1 just as a force-pump creates water-pressure1 and not water4 ,they are generally run by steam or water power4 ,illustration3 ,fig4 #acg4 #abg4 ,induced ,currents4 ,we have already spoken about currents being induced by moving a coil of wire in a magnetic field4 ,we shall now see how this principle is used in the dynamo which is a generator of induced currents4 ,illustration3 ,fig4 #ach4 ,fig4 #acg shows how a current can be generated by a bar magnet and a coil of wire4 ,fig4 #ach shows how a current can be generated by a horseshoe magnet and a coil of wire having an iron core4 ,the ends of the coil are to be connected to an astatic galvanoscope2 this forms a closed circuit4 ,the coil may be moved past the magnet1 or the magnet past the coil4 ,illustration3 ,fig4 #aci4 ,illustration3 ,fig4 #adj4 ,illustration3 ,fig4 #ada4 ,illustration3 ,fig4 #adb4 ,fig4 #aci shows how a current can be generated by two coils1 ,h being connected to an astatic galvanoscope and ,e to a battery4 ,by suddenly bringing ,e toward ,h or the core of ,e past that of ,h1 a current is produced4 ,we have in this arrangement the main features of a dynamo4 ,we can reverse the operation1 holding ,e in one position and moving ,h rapidly toward it4 ,in this case ,h would represent the armature and ,e the field-magnet4 ,when ,h is moved toward ,e1 the induced current in ,h flows in one direction1 and when ,h is suddenly withdrawn from ,e the current is reversed in ,h4 7,see ,study1 ,chapter ,,xxv41 for experiments47 ,illustration3 ,fig4 #adc4 #abh4 ,induced ,currents by ,rotary ,motion4 ,the motions of the coils in straight lines are not suitable for producing currents strong enough for commercial purposes4 ,in order to generate currents of considerable strength and pressure1 the coils of wire have to be pushed past magnets1 or electromagnets1 with great speed4 ,in the dynamo the coils are so wound that they can be given a rapid rotary motion as they fly past strong electromagnets4 ,in this way the coil can keep on passing the same magnets1 in the same direction1 as long as force is applied to the shaft that carries them4 ,illustration3 ,fig4 #add4 #abi4 ,field-,magnets2 ,armature2 ,commutator4 ,what we need then1 to produce an induced current by a rotary motion1 is a strong magnetic field1 a rotating coil of wire properly placed in the field1 and some means of leading the current from the machine4 ,illustration3 ,fig4 #ade4 ,illustration3 ,fig4 #adf4 ,if a loop of wire1 ,fig4 #adj1 be so arranged on bearings at its ends that it can be made to revolve1 a current will flow through it in one direction during one-half of the revolution1 and in the opposite direction during the other half1 it being insulated from all external conductors4 ,this agrees with the experiments suggested in #abg1 when the current generated in a coil passed in one direction during its motion toward the strongest part of the field1 and in the opposite direction when the coil passed out of it4 ,a coil must be cut by lines of force to generate a current4 ,a current inside of the machine1 as in ,fig4 #adj1 would be of no value2 it must be led out to external conductors where it can do work4 ,some sort of sliding contact is necessary to connect a revolving conductor with outside stationary ones4 ,the magnet1 called the field-magnet1 is merely to furnish lines of magnetic force4 ,the one turn of wire represents the simplest form of armature4 ,fig4 #ada shows the ends of a coil joined to two rings1 ,x1 ,y1 insulated from each other1 and rotating with the coil4 ,the two stationary pieces of carbon1 ,a1 ,b1 called brushes1 press against the rings1 and to these are joined wires1 which complete the circuit1 and which lead out where the current can do work4 ,the arrows show the direction of the current during one-half of a revolution4 ,the rings form a collector1 and this arrangement gives an alternating current4 ,illustration3 ,fig4 #adg4 ,in ,fig4 #adb the ends of the coil are joined to the two halves of a cylinder4 ,these halves1 ,x and ,y1 are insulated from each other1 and from the axis4 ,the current flows from ,x onto the brush ,a1 through some external circuit1 to do the work1 and thence back through brush ,b onto ,y4 ,by the time that ,y gets around to ,a1 the direction of the current in the loop has reversed1 so that it passes toward ,y1 but it still enters the outside circuit through ,a1 because ,y is then in contact with ,a4 ,this device is called a commutator1 and it allows a constant or direct current to leave the machine4 ,illustration3 ,fig4 #adh4 ,in regular machines1 the field-magnets are electromagnets1 the whole or a part of the current from the dynamo passing around them on its way out1 to excite them and make a powerful field between the poles4 ,to lessen the resistance to the lines of force on their way from the ,n to the ,s pole of the field-magnets1 the armature coils are wound on an iron core2 this greatly increases the strength of the field1 as the lines of force have to jump across but two small air-gaps4 ,there are many loops of wire on regular armatures1 and many segments to the commutator1 carefully insulated from each other1 each getting its current from the coil attached to it4 #acj4 ,types of ,dynamos4 ,while there is an almost endless number of different makes and shapes of dynamos1 they may be divided into two great types2 the continuous or direct current1 and the alternating current dynamo4 ,direct current machines give out a current which constantly flows in one direction1 and this is because a commutator is used4 ,alternating currents come from collectors or rings1 as shown in ,fig4 #ada2 and as an alternating current cannot be used to excite the fields1 an outside current from a small direct current machine must be used4 ,these are called exciters4 ,illustration3 ,fig4 #adi4 ,in direct current machines enough residual magnetism is left in the field to induce a slight current in the armature when the machine is started4 ,this immediately adds strength to the field-magnets1 which1 in turn1 induce a stronger current in the armature4 #aca4 ,winding of ,dynamos4 ,there are several ways of winding dynamos1 depending upon the special uses to be made of the current4 ,the series wound dynamo1 ,fig4 #adc1 is so arranged that the entire current passes around the field-magnet cores on its way from the machine4 ,in the shunt wound dynamo1 ,fig4 #add1 a part1 only1 of the current from the machine is carried around the field-magnet cores through many turns of fine wire4 ,the compound wound dynamo is really a combination of the two methods just given4 ,in separately-excited dynamos1 the current from a separate machine is used to excite the field-magnets4 #acb4 ,various ,machines4 ,fig4 #ade shows a hand power dynamo which produces a current for experimental work4 ,fig4 #adf shows a magneto-electrical generator which produces a current for medical use4 ,figs4 #adg1 #adh show forms of dynamos1 and ,fig4 #adi shows how arc lamps are connected in series to dynamos4 ,illustration ,,chapter ,,xviii4 ,,how ,,the ,,electric ,,current ,,is ,,transformed4 #acc4 ,electric ,current and ,work4 ,the amount of work a current can do depends upon two factors2 the strength 7amperes71 and the pressure1 or ,e4 ,m4 ,f4 7volts74 ,a current of #aj amperes with a pressure of #a1jjj volts #aj #a1jjj #aj1jjj watts4 ,this furnishes the same amount of energy as a current of #ej amperes at #bjj volts2 #ej #bjj #aj1jjj watts4 #acd4 ,transmission of ,currents4 ,it is often necessary to carry a current a long distance before it is used4 ,a current of #ej amperes would need a copper conductor #be times as large 7sectional area7 as one to carry the #aj ampere current mentioned in #acc4 ,as copper conductors are very expensive1 electric light companies1 etc41 generally try to carry the current on as small a wire as possible4 ,to do this1 the voltage is kept high1 and the amperage low4 ,thus1 as seen in #acc1 the current of #a1jjj volts and #aj amperes could be carried on a much smaller wire than the other current of equal energy4 ,a current of #a1jjj volts1 however1 is not adapted for lights1 etc41 so it has to be changed to lower voltage by some form of transformer before it can be used4 #ace4 ,transformers1 like induction coils1 are instruments for changing the ,e4 ,m4 ,f4 and strength of currents4 ,there is very little loss of energy in well-made transformers4 ,they consist of two coils of wire on one core2 in fact1 an induction coil may be considered a transformer1 but in this a direct current has to be interrupted4 ,if the secondary coil has #ajj times as many turns of wire as the primary1 a current of #ajj volts can be taken from the secondary coil when the primary current is but #a volt2 but the strength 7amperes7 of this new current will be but one-hundredth that of the primary current4 ,by using the coil of fine wire as the primary1 we can lower the voltage and increase the strength in the same proportion4 ,illustration3 ,fig4 #aej4 ,illustration3 ,fig4 #aea4 ,fig4 #aej shows about the simplest form of transformer with a solid iron core1 on which are wound two coils1 the one1 ,p1 being the primary1 and the other1 ,s1 the secondary4 ,fig4 #aea shows the general appearance of one make of transformer4 ,the operation of this apparatus1 as already mentioned1 is to reduce the high pressure alternating current sent out over the conductors from the dynamo1 to a potential at which it can be employed with convenience and safety1 for illumination and other purposes4 ,they consist of two or more coils of wire most carefully insulated from one another4 ,a core or magnetic circuit of soft iron1 composed of very thin punchings1 is then formed around these coils1 the purpose of the iron core being to reduce the magnetic resistance and increase the inductive effect4 ,one set of these coils is connected with the primary or high-pressure wires1 while the other set1 which are called the secondary coils1 is connected to the house or low-pressure wires1 or wherever the current is required for use4 ,the rapidly alternating current impulses in the primary or high-pressure wires induce secondary currents similar in form but opposite in direction in the secondary coils4 ,these current impulses are of a much lower pressure1 depending upon the ratio of the number of turns of wire in the respective coils1 it being customary to wind transformers in such a manner as to reduce from #a1jjj or #b1jjj-volt primaries to #ej or #ajj-volt secondaries1 at which voltage the secondary current is perfectly harmless4 ,illustration3 ,fig4 #aeb4 #acf4 ,motor-,dynamos4 ,fig4 #aeb4 ,these consist essentially of two belt-type machines on a common base1 direct coupled together1 one machine acting as a motor to receive current at a certain voltage1 and the other acting as a dynamo to give out the current usually at a different voltage4 ,as they transform current from one voltage to another1 motor-dynamos are sometimes called ,double ,field ,direct ,current ,transformers4 ,the larger sizes have three bearings1 one bearing being between the two machines1 while the smaller sizes have but two bearings1 the two armatures being fastened to a common spider4 ,illustration3 ,fig4 #aec4 ,applications4 ,the uses to which motor-dynamos are put are very various4 ,they are extensively used in the larger sizes as ,boosters1 for giving the necessary extra force on long electric supply circuits to carry the current to the end with the same pressure as that which reaches the ends of the shorter circuits from the station4 ,motor-dynamos have the advantage over dynamotors1 described later1 of having the secondary voltage easily and economically varied over wide ranges by means of a regulator in the dynamo field4 #acg4 ,dynamotors4 ,fig4 #aec4 ,in ,dynamotors the motor and dynamo armatures are combined in one1 thus requiring a single field only4 ,the primary armature winding1 which operates as a motor to drive the machine1 and the secondary or dynamo winding1 which operates as a generator to produce a new current1 are upon the same armature core1 so that the armature reaction of one winding neutralizes that of the other4 ,they therefore have no tendency to spark1 and do not require shifting of the brushes with varying load4 ,having but one field and two bearings1 they are also more efficient than motor-dynamos4 ,applications4 ,they have largely displaced batteries for telegraph work4 ,the size shown1 occupying a space of about #h-;inch cube1 and having an output of #dj watts1 will displace about #hjj gravity cells1 occupying a space of about #aj feet cube4 ,the cost of maintenance of such a battery per year1 exclusive of rent1 is about #hjj1 whereas the #a-f dynamotor can be operated at an annual expense of #aej4 ,dynamotors are largely used by telephone companies for charging storage batteries1 and for transforming from direct to alternating current1 for ringing telephone bells4 ,electro-cautery1 electroplating1 and electric heating also give use to dynamotors4 ,,chapter ,,xix4 ,,how ,,electric ,,currents ,,are ,,distributed ,,for ,,use4 ,illustration3 ,fig4 #aed4 ,illustration3 ,fig4 #aee4 ,illustration3 ,fig4 #aef4 #ach4 ,conductors and ,insulators4 ,to carry the powerful current from the generating station to distant places where it is to give heat1 power1 or light1 or even to carry the small current of a single cell from one room to another1 conductors must be used4 ,to keep the current from passing into the earth before it reaches its destination insulators must be used4 ,the form of conductors and insulators used will depend upon the current and many other conditions4 ,it should be remembered that the current has to be carried to the lamp or motor1 through which it passes1 and then back again to the dynamo1 to form a complete circuit4 ,a break anywhere in the circuit stops the current4 ,insulators are as important as conductors4 ,illustration3 ,fig4 #aeg4 ,illustration3 ,fig4 #aeh4 #aci4 ,mains1 ,service ,wires1 etc4 ,from the switchboard the current flows out through the streets in large conductors1 or mains1 the supply being kept up by the dynamos1 just as water-pressure is kept up by the constant working of pumps4 ,branches1 called service wires1 are led off from the mains to supply houses or factories1 one wire leading the current into the house from one main1 and a similar one leading it out of the house again to the other main4 ,illustration3 ,fig4 #aei4 ,illustration3 ,fig4 #afj4 ,in large buildings1 pairs of wires1 called risers1 branch out from the service wires and carry the current up through the building4 ,these have still other branches--floor mains1 etc41 that pass through halls1 etc41 smaller branches finally reaching the lamps4 ,the sizes of all of these wires depend upon how much current has to pass through them4 ,the mains in large cities are usually placed underground4 ,in some places they are carried on poles4 ,illustration3 ,fig4 #afa4 #adj4 ,electric ,conduits are underground passages for electric wires1 cables1 etc4 ,there are several ways of insulating the conductors4 ,sometimes they are placed in earthenware or iron tubes1 or in wood that has been treated to make it water-proof4 ,at short distances are placed man-holes1 where the different lengths are joined1 and where branches are attached4 ,illustration3 ,fig4 #afb4 ,fig4 #aed shows creosoted wooden pipes2 ,fig4 #aee shows another form of wooden pipe4 ,fig4 #aef shows a coupling-box used to join ,edison tubes4 ,the three wires1 used in the three-wire system1 are insulated from each other1 the whole being surrounded by an iron pipe of convenient length for handling4 ,fig4 #aeg shows sections of man-holes and various devices used in conduit work4 ,illustration3 ,fig4 #afc4 #ada4 ,miscellaneous ,appliances4 ,when the current enters a house for incandescent lighting purposes1 for example1 quite a number of things are necessary4 ,to measure the current a meter is usually placed in the cellar4 ,in new houses the insulated conductors are usually run through some sort of tube which acts as a double protection1 all being hidden from view4 ,fig4 #aeh shows a short length of iron tube with a lining of insulating material4 ,wires are often run through tubes made of rubber and various other insulating materials4 ,where the current is to be put into houses after the plastering has been done1 the wires are usually run through mouldings or supported by cleats4 ,fig4 #aei shows a cross-section of moulding4 ,the insulated wires are placed in the slots1 which are then covered4 ,illustration3 ,fig4 #afd4 ,illustration3 ,fig4 #afe4 ,illustration3 ,fig4 #aff4 ,illustration3 ,fig4 #afg4 ,fig4 #afj shows a form of porcelain cleat4 ,these are fastened to ceilings or walls1 and firmly hold the insulated wires in place4 ,fig4 #afa shows a wood cleat4 ,fig4 #afb shows small porcelain insulators4 ,these may be screwed to walls1 etc41 the wire being then fastened to them4 ,fig4 #afc shows how telegraph wires are supported and insulated4 ,fig4 #afd shows how wires may be carried by tree and insulated from them4 ,illustration3 ,fig4 #afh4 ,illustration3 ,fig4 #afi4 ,illustration3 ,fig4 #agj4 #adb4 ,safety ,devices4 ,we have seen that when too large a current passes through a wire1 the wire becomes heated and may even be melted4 ,buildings are wired to use certain currents1 and if from any cause much more current than the regular amount should suddenly pass through the service wires into the house1 the various smaller wires would become overheated1 and perhaps melt or start a fire4 ,an accidental short circuit1 for example1 would so reduce resistance that too much current would suddenly rush through the wires4 ,there are several devices by which the over-heating of wires is obviated4 ,illustration3 ,figs4 #aga to #age4 ,fig4 #afe shows a safety fuse1 or safety cut-out1 which consists of a short length of easily fusible wire1 called fuse wire1 placed in the circuit and supported by a porcelain block4 ,these wires are tested1 different sizes being used for different currents4 ,as soon as there is any tendency toward over-heating1 the fuse blows2 that is1 it promptly melts and opens the circuit before any damage can be done to the regular conductors4 ,fig4 #aff shows a cross-section of a fuse plug that can be screwed into an ordinary socket4 ,the fuse wire is shown black4 ,fig4 #afg shows a fuse link4 ,these are also of fusible material1 and so made that they can be firmly held under screw-heads4 ,for heavy currents fuse ribbons are used1 or several wires or links may be used side by side4 ,fig4 #afh shows a fusible rosette4 ,fig4 #afi shows two fuse wires fixed between screw-heads1 the current passing through them in opposite directions1 both sides of the circuit being included4 ,fig4 #agj shows various forms of cut-outs4 ,illustration3 ,fig4 #agf4 #adc4 ,wires and ,cables are made in many sizes4 ,figs4 #aga to #age show various ways of making small conductors4 ,they are made very flexible1 for some purposes1 by twisting many small copper wires together1 the whole being then covered with insulating material4 ,illustration3 ,fig4 #agg4 ,figs4 #agf1 #agg1 show sections of submarine cables4 ,such cables consist of copper conductors insulated with pure gutta-percha4 ,these are then surrounded by hempen yarn or other elastic material1 and around the whole are placed galvanized iron armor wires for protection4 ,each core1 or conductor1 contains a conductor consisting of a single copper wire or a strand of three or more twisted copper wires4 #add4 ,lamp ,circuits4 ,as has been noted before1 in order to have the electric current do its work1 we must have a complete circuit4 ,the current must be brought back to the dynamo1 much of it1 of course1 having been used to produce light1 heat1 power1 etc4 ,for lighting purposes this is accomplished in two principal ways4 ,illustration3 ,fig4 #agh4 ,fig4 #agh shows a number of lamps so arranged1 in series1 that the same current passes through them all1 one after the other4 ,the total resistance of the circuit is large1 as all of the lamp resistances are added together4 ,illustration3 ,fig4 #agi4 ,fig4 #agi shows lamps arranged side by side1 or in parallel1 between the two main wires4 ,the current divides1 a part going through each lamp that operates4 ,the total resistance of the circuit is not as large as in the series arrangement1 as the current has many small paths in going from one main wire to the other4 ,fig4 #agi also shows the ordinary two-wire system for incandescent lighting1 the two main wires having usually a difference of potential equal to #ej or #aaj volts4 ,these comparatively small pressures require fairly large conductors4 ,the ,three-,wire ,system1 ,fig4 #ahj1 uses the current from two dynamos1 arranged with three main wires4 ,while the total voltage is #bbj1 one of the wires being neutral1 #aaj volts can be had for ordinary lamps4 ,this voltage saves in the cost of conductors4 ,illustration3 ,fig4 #ahj4 ,illustration3 ,fig4 #aha4 ,the ,alternating ,system1 ,fig4 #aha1 uses transformers4 ,the high potential of the current allows small main wires1 from which branches can be run to the primary coil of the transformer4 ,the secondary coil sends out an induced current of #ej or #aaj volts1 while that in the primary may be #a1jjj to #aj1jjj volts4 ,,chapter ,,xx4 ,,how ,,heat ,,is ,,produced ,,by ,,the ,,electric ,,current4 #ade4 ,resistance and ,heat4 ,we have seen that all wires and conductors offer resistance to the electric current4 ,the smaller the wire the greater its resistance4 ,whenever resistance is offered to the current1 heat is produced4 ,by proper appliances1 the heat of resistance can be used to advantage for many commercial enterprises4 ,dynamos are used to generate the current for heating and lighting purposes4 ,illustration3 ,fig4 #ahb4 ,fig4 #ahb shows how the current from two strong cells can be used to heat a short length of very fine platinum or ,german-silver wire4 ,the copper conductors attached to the cells do not offer very much resistance4 ,it will be seen from the above that in all electrical work the sizes of the wires used have to be such that they do not overheat4 ,the coils of dynamos1 motors1 transformers1 ampere-meters1 etc41 etc41 become somewhat heated by the currents passing through them1 great care being taken that they are properly designed and ventilated so that they will not burn out4 ,illustration3 ,fig4 #ahc4 ,illustration3 ,fig4 #ahd4 #adf4 ,electric ,welding4 ,fig4 #ahc shows one form of electric welding machine4 ,the principle involved in the art of electric welding is that of causing currents of electricity to pass through the abutting ends of the pieces of metal which are to be welded1 thereby generating heat at the point of contact1 which also becomes the point of greatest resistance1 while at the same time mechanical pressure is applied to force the parts together4 ,as the current heats the metal at the junction to the welding temperature1 the pressure follows up the softening surface until a complete union or weld is effected2 and1 as the heat is first developed in the interior of the parts to be welded1 the interior of the joint is as efficiently united as the visible exterior4 ,with such a method and apparatus1 it is found possible to accomplish not only the common kinds of welding of iron and steel1 but also of metals which have heretofore resisted attempts at welding1 and have had to be brazed or soldered4 ,illustration3 ,figs4 #ahe to #ahi4 ,the introduction of the electric transformer enables enormous currents to be so applied to the weld as to spend their energy just at the point where heating is required4 ,they need1 therefore1 only to be applied for a few seconds1 and the operation is completed before the heat generated at the weld has had time to escape by conduction to any other part4 ,although the quantity of the current so employed in the pieces to be welded is enormous1 the potential at which it is applied is extremely low1 not much exceeding that of the batteries of cells used for ringing electric bells in houses4 ,illustration3 ,fig4 #aij4 #adg4 ,miscellaneous ,applications4 ,magneto ,blasting ,machines are now in very common use for blasting rocks1 etc4 ,fig4 #ahd shows one1 it being really a small hand dynamo1 occupying less than one-half a cubic foot of space4 ,the armature is made to revolve rapidly between the poles of the field-magnet by means of a handle that works up and down4 ,the current is carried by wires from the binding-posts to fuses4 ,the heat generated by resistance in the fuse ignites the powder or other explosive4 ,electric soldering irons1 flat-irons1 teakettles1 griddles1 broilers1 glue pots1 chafing-dishes1 stoves1 etc41 etc41 are now made4 ,figs4 #ahe to #ahi show some of these applications4 ,the coils for producing the resistance are inclosed in the apparatus4 ,illustration3 ,fig4 #aia4 ,fig4 #aij shows a complete electric kitchen4 ,any kettle or part of the outfit can be made hot by simply turning a switch4 ,fig4 #aia shows an electric heater placed under a car seat4 ,many large industries that make use of the heating effects of the current are now being carried on4 ,,chapter ,,xxi4 ,,how ,,light ,,is ,,produced ,,by ,,the ,,incandescent ,,lamp4 ,illustration3 ,fig4 #aib4 ,illustration3 ,fig4 #aic4 #adh4 ,incandescence4 ,we have just seen that the electric current produces heat when it flows through a conductor that offers considerable resistance to it4 ,as soon as this was discovered men began to experiment to find whether a practical light could also be produced4 ,it was found that a wire could be kept hot by constantly passing a current through it1 and that the light given out from it became whiter and whiter as the wire became hotter4 ,the wire was said to be incandescent1 or glowing with heat4 ,as metal wires are good conductors of electricity1 they had to be made extremely fine to offer enough resistance2 too fine1 in fact1 to be properly handled4 #adi4 ,the ,incandescent ,lamp4 ,many substances were experimented upon to find a proper material out of which could be made a filament that would give the proper resistance and at the same time be strong and lasting4 ,it was found that hair-like pieces of carbon offered the proper resistance to the current4 ,when heated in the air1 however1 carbon burns2 so it became necessary to place the carbon filaments in a globe from which all the air had been pumped before passing the current through them4 ,this proved to be a success4 ,illustration3 ,fig4 #aid4 ,illustration3 ,fig4 #aie4 ,illustration3 ,fig4 #aif4 ,fig4 #aib shows the ordinary form of lamp4 ,the carbon filament is attached1 by carbon paste1 to short platinum wires that are sealed in the glass1 their lower ends being connected to short copper wires that are joined to the terminals of the lamp4 ,when the lamp is screwed into its socket1 the current can pass up one side of the filament and down the other4 ,the filaments used have been made of every form of carbonized vegetable matter4 ,bamboo has been largely used1 fine strips being cut by dies and then heated in air-tight boxes containing fine carbon until they were thoroughly carbonized4 ,this baking of the bamboo produces a tough fiber of carbon4 ,various forms of thread have been carbonized and used4 ,filaments are now made by pressing finely pulverized carbon1 with a binding material1 through small dies4 ,the filaments are made of such sizes and lengths that will adapt them to the particular current with which they are to be used4 ,the longer the filament1 the greater its resistance1 and the greater the voltage necessary to push the current through it4 ,illustration3 ,fig4 #aig4 ,illustration3 ,fig4 #aih4 ,after the filaments are properly attached1 the air is pumped from the bulb or globe4 ,this is done with some form of mercury pump1 and the air is so thoroughly removed from the bulb that about one-millionth only of the original air remains4 ,before sealing off the lamp1 a current is passed through the filament to drive out absorbed air and gases1 and these are carried away by the pump4 ,by proper treatment the filaments have a uniform resistance throughout1 and glow uniformly when the current passes4 ,illustration3 ,fig4 #aii4 ,illustration3 ,fig4 #bjj4 #aej4 ,candle-,power4 ,a lamp is said to have #d1 #h1 #af or more candle-power4 ,a #af-;candle-power lamp1 for example1 means one that will give as much light as sixteen standard candles4 ,a standard sperm candle burns two grains a minute4 ,the candle-power of a lamp can be increased by forcing a strong current through it1 but this shortens its life4 ,the ,current used for incandescent lamps has to be strong enough to force its way through the filament and produce a heat sufficient to give a good light4 ,the usual current has #ej or #aaj volts1 although small lamps are made that can be run by two or three cells4 ,if the voltage of the current is less than that for which the lamp was made1 the light will be dim4 ,the filament can be instantly burned out by passing a current of too high pressure through it4 ,even with the proper current1 lamps soon begin to deteriorate1 as small particles of carbon leave the filament and cling to the glass4 ,this is due to the evaporation1 and it makes the filament smaller1 and a higher pressure is then needed to force the current through the increased resistance2 besides this1 the darkened bulb does not properly let the light out4 ,the current may be direct or alternating4 ,illustration3 ,fig4 #bja4 ,illustration3 ,fig4 #bjb4 #aea4 ,the ,uses to which incandescent lamps are put are almost numberless4 ,fig4 #aic shows a decorative lamp4 ,fancy lamps are made in all colors4 ,fig4 #aid shows a conic candle lamp1 to imitate a candle4 ,what corresponds to the body of the candle 7see figure ,b to ,c7 is a delicately tinted opal glass tube surmounted 7see figure ,a to ,b7 by a finely proportioned conic lamp with frosted globe4 ,c to ,d in the figure represents the regular base1 and thus the relative proportions of the parts are shown4 ,fig4 #aie shows another form of candelabra lamp4 ,fig4 #aif shows small dental lamps4 ,fig4 #aig shows a small lamp with mirror for use in the throat4 ,fig4 #aih shows lamp with half shade attached1 used for library tables4 ,fig4 #aii shows an electric pendant for several lamps1 with shade4 ,fig4 #bjj shows a lamp guard4 ,fig4 #bja shows a lamp socket1 into which the lamp is screwed4 ,fig4 #bjb shows incandescent bulbs joined in parallel to the and - mains4 ,fig4 #bjc shows how the lamp cord can be adjusted to desired length4 ,fig4 #bjd shows a lamp with reflector placed on a desk4 ,fig4 #bje shows a form of shade and reflector4 ,illustration3 ,fig4 #bjc4 ,illustration3 ,fig4 #bjd4 ,illustration3 ,fig4 #bje4 ,,chapter ,,xxii4 ,,how ,,light ,,is ,,produced ,,by ,,the ,,arc ,,lamp4 #aeb4 ,the ,electric ,arc4 ,when a strong current passes from one carbon rod to another across an air-space1 an electric arc is produced4 ,when the ends of two carbon rods touch1 a current can pass from one to the other1 but the imperfect contact causes resistance enough to heat the ends red-hot4 ,if the rods be separated slightly1 the current will continue to flow1 as the intensely heated air and flying particles of carbon reduce the resistance of the air-space4 ,fig4 #bjf shows two carbon rods which are joined to the two terminals of a dynamo4 ,the upper1 or positive1 carbon gradually wears away and becomes slightly hollow4 ,the heated crater1 as it is called1 is the hottest part4 ,the negative carbon becomes pointed4 ,the arc will pass in a vacuum1 and even under water4 ,illustration3 ,fig4 #bjf4 ,as the electric arc is extremely hot1 metals are easily vaporized in it2 in fact1 even the carbon rods themselves slowly melt and vaporize4 ,this extreme heat is used for many industrial purposes4 ,illustration3 ,fig4 #bjg4 ,illustration3 ,fig4 #bjh4 ,the phenomenon of the electric arc was first noticed by ,humphrey ,davy in #ahjj1 and its explanation appears to be the following3 ,before contact the difference of potential between the points is insufficient to permit a spark to leap across even #a_/ajjjj of an inch of air-space1 but when the carbons are made to touch1 a current is established4 ,on separating the carbons1 the momentary extra current due to self-induction of the circuit1 which possesses a high electromotive force1 can leap the short distance1 and in doing so volatilizes a small quantity of carbon between the points4 ,carbon vapor1 being a partial conductor1 allows the current to continue to flow across the gap1 provided it be not too wide2 but as the carbon vapor has a very high resistance it becomes intensely heated by the passage of the current1 and the carbon points also grow hot4 ,since1 however1 solid matter is a better radiator than gaseous matter1 the carbon points emit far more light than the arc itself1 though they are not so hot4 ,it is observed1 also1 that particles of carbon are torn away from the electrode1 which becomes hollowed out to a cup-shape1 and some of these are deposited on the - electrode4 ,illustration3 ,fig4 #bji4 #aec4 ,arc ,lamps4 ,as the carbons gradually wear away1 some device is necessary to keep their ends the right distance apart4 ,if they are too near1 the arc is very small2 and if too far apart1 the current can not pass and the light goes out4 ,the positive carbon gives the more intense light and wears away about twice as fast as the - carbon1 so it is placed above the - carbon1 to throw the light downwards4 ,illustration3 ,fig4 #baj4 ,illustration3 ,fig4 #baa4 ,arc lamps contain some device by which the proper distance between the carbons can be kept4 ,most of them grip the upper carbon and pull it far enough above the lower one to establish the arc4 ,as soon as the distance between them gets too great again1 the grip on the upper carbon is loosened1 allowing the carbon to drop until it comes in contact with the lower one1 thus starting the current again4 ,these motions are accomplished by electromagnets4 ,fig4 #bjg shows a form of arc lamp with single carbons that will burn from #g to #i hours4 ,illustration3 ,fig4 #bab4 ,illustration3 ,fig4 #bac4 ,illustration3 ,fig4 #bad4 ,fig4 #bjh shows the mechanism by which the carbons are regulated4 ,fig4 #bji shows a form of double carbon1 or all-night lamp1 one set of carbons being first used1 the other set being automatically switched in at the proper time4 ,illustration3 ,fig4 #bae4 ,figs4 #baj1 #baa show forms of short arc lamps1 for use under low ceilings1 so common in basements1 etc4 ,fig4 #bab shows a hand-feed focussing type of arc lamp4 ,in regular street lamps1 the upper carbon only is fed by mechanism1 as it burns away about twice as fast as the lower one1 thus bringing the arc lower and lower4 ,when it is desired to keep the arc at the focus of a reflector1 both carbons must be fed4 ,fig4 #bac shows a theatre arc lamp1 used to throw a strong beam of light from the balcony to the stage4 ,fig4 #bad shows the arc lamp used as a search-light4 ,the reflector throws a powerful beam of light that can be seen for miles2 in fact1 the light is used for signalling at night4 ,fig4 #bae shows how search-lights are used at night on war-vessels4 ,,chapter ,,xxiii4 ,x-,,rays1 ,,and ,,how ,,the ,,bones ,,of ,,the ,,human ,,body ,,are ,,photographed4 ,illustration3 ,fig4 #baf4 ,illustration3 ,fig4 #bag4 #aed4 ,disruptive ,discharges4 ,we have seen1 in the study of induction coils1 that a spark can jump several inches between the terminals of the secondary coil4 ,the attraction between the two oppositely charged terminals gets so great that it overcomes the resistance of the air-space between them1 a brilliant spark passes1 and they are discharged4 ,this sudden discharge is said to be disruptive1 and it is accompanied by a flash of light and a loud report4 ,the path of the discharge may be nearly straight1 or crooked1 depending upon the nature of the material in the gap between the terminals4 ,illustration3 ,fig4 #bah4 ,illustration3 ,fig4 #bai4 #aee4 ,effect of ,air ,pressure on ,spark4 ,the disruptive spark takes place in air at ordinary pressures4 ,the nature of the spark is greatly changed when the pressure of the air decreases4 ,fig4 #baf shows an air-tight glass tube so arranged that the air can be slowly removed with an air-pump4 ,the upper rod shown can be raised or lowered to increase the distance between it and the lower rod1 these acting as the terminals of an induction coil4 ,before exhausting any air1 the spark will jump a small distance between the rods and act as in open air4 ,as soon as a small amount of air is removed1 a change takes place4 ,the spark is not so intense and has no definite path1 there being a general glow throughout the tube4 ,as the air pressure becomes still less1 the glow becomes brighter1 until the entire tube is full of purple light that is able to pass the entire length of it2 that is1 the discharge takes place better in rarefied air than it does in ordinary air4 #aef4 ,vacuum-,tubes4 ,as electricity passes through rarefied gases much easier than through ordinary air1 regular tubes1 called vacuum-tubes1 are made for such study4 ,fig4 #bag shows a plain tube of this kind1 platinum terminals being fused in the glass for connections4 ,these tubes are often made in complicated forms1 ,fig4 #bah1 with colored glass1 and are called ,geissler tubes4 ,they are often made in such a way that the electrodes are in the shape of discs1 etc41 and are called ,crookes tubes1 ,fig4 #bai4 ,a slight amount of gas is left in the tubes4 ,illustration3 ,fig4 #bbj4 ,illustration3 ,fig4 #bbj-;,a4 #aeg4 ,cathode ,rays4 ,the cathode is the electrode of a vacuum-tube by which the current leaves the tube1 and it has been known for some time that some kind of influence passes in straight lines from this point4 ,shadows1 ,fig4 #bai1 are cast by such rays1 a screen being placed in their path4 #aeh4 ,x-,rays4 ,professor ,roentgen of ,wrzburg discovered that when the cathode rays are allowed to fall upon a solid body1 the solid body gives out still other rays which differ somewhat from the original cathode rays4 ,they can penetrate1 more or less1 through many bodies that are usually considered opaque4 ,the hand1 for example1 may be used as a negative for producing a photograph of the bones1 as the rays do not pass equally well through flesh and bone4 ,illustration3 ,fig4 #bba4 ,fig4 #bbj shows a ,crookes tube fitted with a metal plate1 so that the cathode rays coming from ,c will strike it4 ,the ,x-rays are given out from ,p4 ,these rays are invisible and are even given out where the cathode rays strike the glass4 ,some chemical compounds are made luminous by these rays2 so screens are made and coated with them in order that the shadows produced by the ,x-rays can be seen by the eye4 ,professor ,roentgen named these the ,x-rays4 ,fig4 #bbj-;,a shows a fluoroscope that contains a screen covered with proper chemicals4 ,illustration3 ,fig4 #bbb4 ,illustration3 ,fig4 #bbc4 #aei4 ,x-,ray ,photographs4 ,bone does not allow the ,x-rays to pass through it as readily as flesh1 so if the hand be placed over a sensitized photographic plate1 ,fig4 #bba1 and proper connections be made with the induction coil1 etc41 the hand acts as a photographic negative4 ,upon developing the plate1 as in ordinary photography1 a picture or shadow of the bones will be seen4 ,fig4 #bbb shows the arrangement of battery1 induction coil1 focus tube1 etc41 for examining the bones of the human body4 ,fig4 #bbc shows the bones of a fish4 ,such photographs have been very valuable in discovering the location of bullets1 needles1 etc41 that have become imbedded in the flesh1 as well as in locating breaks in the bones4 ,,chapter ,,xxiv4 ,,the ,,electric ,,motor1 ,,and ,,how ,,it ,,does ,,work4 #afj4 ,currents and ,motion4 ,we have seen1 ,chapter ,,xii41 that when coils of wire are rapidly moved across a strong magnetic field1 a current of electricity is generated4 ,we have now to deal with the opposite of this2 that is1 we are to study how motion can be produced by allowing a current of electricity to pass through the armature of a machine4 ,illustration3 ,fig4 #bbd4 ,illustration3 ,fig4 #bbe4 ,fig4 #bbd shows1 by diagram1 a coil ,h1 suspended so that it can move easily1 its ends being joined to a current reverser1 and this1 in turn1 to a dry cell ,d ,c4 ,a magnet1 ,h ,m1 will attract the core of ,h when no current passes4 ,when the current is allowed to pass first in one direction and then in the opposite direction1 by using the reverser1 the core of ,h will jump back and forth from one pole of ,h ,m to the other4 ,there are many ways by which motion can be produced by the current1 but to have it practical1 the motion must be a rotary one4 7,see ,study1 ,chapter ,,xxvi41 for numerous experiments47 ,illustration3 ,fig4 #bbf4 #afa4 ,the ,electric ,motor is a machine for transforming electric energy into mechanical power4 ,the construction of motors is very similar to that of dynamos4 ,they have field-magnets1 armature coils1 commutator1 etc42 in fact1 the armature of an ordinary direct current dynamo will revolve if a current be passed through it1 entering by one brush and leaving by the other4 ,there are many little differences of construction1 for mechanical and electrical reasons1 but we may say that the general construction of dynamos and motors is the same4 ,fig4 #bbe shows a coil of wire1 the ends of which are connected to copper and zinc plates4 ,these plates are floated in dilute sulphuric acid1 and form a simple cell which sends a current through the wire1 as shown by the arrows4 ,illustration3 ,fig4 #bbg4 ,we have seen that a current-carrying wire has a magnetic field and acts like a magnet2 so it will be easily seen that if a magnet be held near the wire it will be either attracted or repelled1 the motion depending upon the poles that come near each other4 ,as shown in the figure1 the ,n pole of the magnet repels the field of the wire1 causing it to revolve4 ,we see that this action is just the reverse to that in galvanometers1 where the coil is fixed1 and the magnet1 or magnetic needle1 is allowed to move4 ,as soon as the part of the wire1 marked ,a in ,fig4 #bbe1 gets a little distance from the pole1 the opposite side of the wire1 ,b1 begins to be attracted by it1 the attraction getting stronger and stronger1 until it gets opposite the ,n pole4 ,if the ,n pole were still held in place1 ,b would vibrate back and forth a few times1 and finally come to rest near the pole4 ,if1 however1 as soon as ,b gets opposite ,n the ,s pole of the magnet be quickly turned toward ,b1 the coil will be repelled and the rotary motion will continue4 ,illustration3 ,fig4 #bbh4 ,illustration3 ,figs4 #bbi to #bca4 ,illustration3 ,fig4 #bcb4 ,illustration3 ,fig4 #bcc4 ,let us now see how this helps to explain electric motors4 ,we may consider the wire of ,fig4 #bbe as one coil of an armature1 and the plates1 ,c and ,z1 as the halves of a commutator4 ,in this arrangement1 it must be noted1 the current always flows through the armature coil in the same direction1 the rotation being kept up by reversing the poles of the field-magnet4 ,in ordinary simple motors the current is reversed in the armature coils1 the field-magnets remaining in one position without changing the poles4 ,this produces the same effect as the above4 ,the current is reversed automatically as the brushes allow the current to enter first one commutator bar and then the opposite one as the armature revolves4 ,the regular armatures have many coils and many commutator bars1 as will be seen by examining the illustrations shown4 ,the ordinary galvanometer may be considered a form of motor4 ,by properly opening and closing the circuit1 the rotary motion of the needle can be kept up as long as current is supplied4 ,even an electric bell or telegraph sounder may be considered a motor1 giving motion straight forward and back4 #afb4 ,the ,uses of ,motors are many4 ,it would be impossible to mention all the things that are done with the power from motors4 ,a few illustrations will give an idea of the way motors are attached to machines4 ,fig4 #bbf shows one form of motor1 the parts being shown in ,fig4 #bbg4 ,illustration3 ,fig4 #bcd4 ,fig4 #bbh shows a fan motor run by a battery4 ,they are generally run by the current from the street4 ,figs4 #bbi-bca show other forms of fan motors4 ,fig4 #bcb shows an electric hat polisher4 ,a church organ bellows is shown in ,fig4 #bcc1 so arranged that it can be pumped by an electric motor4 ,fig4 #bcd shows a motor direct connected to a drill press4 #afc4 ,starting ,boxes4 ,if too much current were suddenly allowed to pass into the armature of a motor1 the coils would be over-heated1 and perhaps destroyed1 before it attained its full speed4 ,a rapidly revolving armature will take more current1 without being overheated1 than one not in motion4 ,a motor at full speed acts like a dynamo1 and generates a current which tends to flow from the machine in a direction opposite to that which produces the motion4 ,it is evident1 then1 that when the armature is at rest1 all the current turned on passes through it without meeting with this opposing current4 ,illustration3 ,fig4 #bce4 ,illustration3 ,fig4 #bcf4 ,fig4 #bce shows a starting1 stopping1 and regulating box1 inside of which are a number of ,german-silver resistance coils properly connected to contact-points at the top4 ,by turning the knob1 the field of the motor is immediately charged first through resistance1 then direct1 and then the current is put on the armature gradually through a series of coils1 the amount of current depending upon the distance the switch is turned4 ,fig4 #bcf shows a cross section of the same4 ,,chapter ,,xxv4 ,,electric ,,cars1 ,,boats1 ,,and ,,automobiles4 #afd4 ,electric ,cars1 as well as boats1 automobiles1 etc41 etc41 are moved by the power that comes from electric motors1 these receiving current from the dynamos placed at some central station4 ,we have already seen how the motor can do many kinds of work4 ,by properly gearing it to the car wheels1 motion can be given to them which will move the car4 ,illustration3 ,fig4 #bcg4 ,fig4 #bcg shows two dynamos which will be supposed to be at a power house and which send out a current to propel cars4 ,from the figure it will be seen that the wires over the cars1 called trolley-wires1 are connected to the positive 77 terminals of the dynamos1 and that the negative 7-7 terminals are connected to the tracks4 ,in case a wire were allowed to join the trolley-wire and track1 we should have a short circuit1 and current would not only rush back to the dynamo without doing useful work1 but it would probably injure the machines4 ,when some of the current is allowed to pass through a car1 motion is produced in the motors1 as has been explained4 ,as the number of cars increases1 more current passes back to the dynamos1 which must do more work to furnish such current4 ,trolley-poles1 fastened to the top of the cars and which end in grooved wheels1 called trolley-wheels1 are pressed by springs against the trolley-wires4 ,the current passes down these through switches to controllers at each end of the car1 one set being used at a time4 ,illustration3 ,fig4 #bch4 ,illustration3 ,fig4 #bci4 #afe4 ,the ,controllers1 as the name suggests1 control the speed of the car by allowing more or less current to pass through the motors4 ,the motors1 resistance coils and controllers are so connected with each other that the amount of current used can be regulated4 ,illustration3 ,fig4 #bdj4 ,illustration3 ,fig4 #bda4 ,when the motorman turns the handle of the controller to the first notch1 the current passes through all of the resistance wires placed under the car1 then through one motor after the other4 ,the motors being joined in series by the proper connections at the controller1 the greatest resistance is offered to the current and the car runs at the slowest speed at this first notch4 ,as more resistance is cut out by turning the handle to other notches1 the car increases its speed2 but as the resistance wires become heated and the heat passes into the air1 there is a loss of energy4 ,it is not economical to run a car at such a speed that energy is wasted as heat4 ,as soon as the resistance is all cut out1 the current simply passes through the motors joined in series4 ,this gives a fairly slow speed and one that is economical because all the current tends to produce motion4 ,by allowing the current to pass through the motors joined in parallel1 that is1 by allowing each to take a part of the current1 the resistance is greatly reduced1 and a higher speed attained4 ,this is not instantly done1 however1 as too much strain would be put upon the motors4 ,as soon as the next notch is reached1 the motors are joined in parallel and the resistance also thrown in again4 ,by turning the handle still more1 resistance is gradually cut out1 and the highest speed produced when the current passes only through the motors in parallel4 ,illustration3 ,fig4 #bdb4 ,illustration3 ,fig4 #bdc4 ,fig4 #bch represents a controller1 by diagram1 showing the relative positions of the controller cylinder1 reversing and cut-out cylinders1 arrangements for blowing out the short electric arcs formed1 etc4 ,a ratchet and pawl is provided1 which indicates positively the running notches1 at the same time permitting the cylinder to move with ease4 ,fig4 #bci shows a top view of the controller4 ,illustration3 ,fig4 #bdd4 #aff4 ,overhead and ,underground ,systems4 ,when wires for furnishing current are placed over the tracks1 as in ,fig4 #bcg1 we have the overhead system4 ,in cities the underground system is largely used4 ,the location of the conducting wires beneath the surface of the street removes all danger to the public1 and protects them from all interference1 leaving the street free from poles and wires4 ,fig4 #bdj shows a cross-section of an underground conduit4 ,the rails1 ,r ,r1 are supported by cast-iron yokes1 ,a1 placed five feet apart1 and thoroughly imbedded in concrete4 ,the conduit has sewer connections every #ajj feet4 ,conducting bars1 ,c ,c1 are placed on each side of the conduit1 and these are divided into sections of about #ejj feet4 ,insulators1 ,d ,d1 are placed every #ae feet4 ,they are attached to1 and directly under1 the slot-rails1 the stem passing through the conductor bar4 ,illustration3 ,fig4 #bde4 ,figs4 #bdj and #bda show the plow ,e4 ,the contact plates are carried on coiled springs to allow a free motion4 ,two guide-wheels1 ,f ,f1 are attached to the leg of the plow4 ,the conducting wires are carried up through the leg of the plow4 #afg4 ,appliances4 ,a large number of articles are needed in the construction of electric railroads4 ,a few1 only1 can be shown that are used for the overhead system4 ,fig4 #bdb shows a pole insulator4 ,fig4 #bdc shows a feeder-wire insulator4 ,fig4 #bdd shows a line suspension4 ,fig4 #bde shows a form of right-angle cross which allows the trolley-wheels of crossing lines to pass4 ,fig4 #bdf shows a switch4 ,in winter a part of the current is allowed to pass through electric heaters placed under the seats of electric cars4 ,illustration3 ,fig4 #bdf4 #afh4 ,electric ,boats are run by the current from storage batteries which are usually placed under the seats4 ,an electric motor large enough to run a small boat takes up very little room and is generally placed under the floor4 ,this leaves the entire boat for the use of passengers4 ,the motor is connected to the shaft that turns the screw4 ,fig4 #bdg shows one design4 #afi4 ,electric ,automobiles represent the highest type of electrical and mechanical construction4 ,the running-gear is usually made of the best cold-drawn seamless steel tubing1 to get the greatest strength from a given weight of material4 ,the wheels are made in a variety of styles1 but nearly all have ball bearings and pneumatic tires4 ,in the lightest styles the wheels have wire spokes4 ,the electric motors1 supported by the running-gear1 are geared to the rear wheels4 ,the motors are made as nearly dust-proof as possible4 ,storage batteries are put in a convenient place1 depending upon the design of the carriage1 and from these the motors receive the current4 ,these can be charged from the ordinary #aaj-volt lighting circuits or from private dynamos4 ,the proper plugs and attachments are usually furnished by the various makers for connecting the batteries with the street current1 which is shut off when the batteries are full by an automatic switch4 ,illustration3 ,fig4 #bdg4 ,controllers are used1 as on electric cars1 the lever for starting1 stopping1 etc41 being usually placed on the left-hand side of the seat4 ,the steering is done by a lever that moves the front wheels4 ,strong brakes1 and the ability to quickly reverse the motors1 allow electric carriages to be stopped suddenly in case of accidents4 ,electric automobiles are largely used in cities1 or where the current can be easily had4 ,the batteries must be re-charged after they have run the motors for a certain time which depends upon the speed and road1 as well as upon the construction4 ,where carriages are to be run almost constantly1 as is the case with those used for general passenger service in cities1 duplicate batteries are necessary1 so that one or two sets can be charged while another is in use4 ,fig4 #bdh shows one form of electric vehicle1 the storage batteries being placed under and back of the seat4 ,illustration3 ,fig4 #bdh4 ,,chapter ,,xxvi4 ,a ,,word ,,about ,,central ,,stations4 #agj4 ,central ,stations1 as the word implies1 are places where1 for example1 electricity is generated for the incandescent or arc lights used in a certain neighborhood2 where telephone or telegraph messages are sent to be resent to some other station2 where operators are kept to switch different lines together1 so that those on one line can talk to those on another1 etc41 etc4 ,there are many kinds of central stations1 each requiring a large amount of special apparatus to carry on the work4 ,fig4 #bdi gives a hint in regard to the way car lines get their power from a central power station4 ,as a large part of the apparatus required in ordinary central stations has already been described1 it is not necessary to go into the details of such stations4 ,illustration3 ,fig4 #bdi4 ,in lighting stations1 for example1 we have three principal kinds of apparatus4 ,boilers produce the steam that runs the steam engines1 and these run the dynamos that give the current4 ,besides these there are many other things needed4 ,the electrical energy that goes over the wires to furnish light1 heat1 and power1 really comes indirectly from the coal that is used to boil water and convert it into steam4 ,the various parts of the central station merely aid in this transformation of energy4 ,illustration3 ,fig4 #bej4 ,illustration3 ,fig4 #bea4 ,the dynamos are connected to the engines by belts1 or they are direct connected4 ,figs4 #bej1 #bea1 show dynamos connected to engines without belts4 ,the current from the dynamos is led to large switchboards which contain switches1 voltmeters1 ammeters1 lightning arresters1 and various other apparatus for the proper control and measurement of the current4 ,from the switchboard it is allowed to pass through the various street mains1 from which it is finally led to lamps1 motors1 etc4 ,water-power is frequently used to drive the dynamos instead of steam engines4 ,the water turns some form of water-wheel which is connected to the dynamos4 ,at ,niagara ,falls1 for example1 immense quantities of current are generated for light1 heat1 power1 and industrial purposes4 ,illustration ,,chapter ,,xxvii4 ,,miscellaneous ,,uses ,,of ,,electricity4 #aga4 ,the ,many ,uses to which the electric current is put are almost numberless4 ,new uses are being found for it every day4 ,some of the common applications are given below4 #agb4 ,automatic ,electric ,program ,clocks1 ,fig4 #beb1 are largely used in all sorts of establishments1 schools1 etc41 for ringing bells at certain stated periods4 ,the lower dial shown has many contact-points that can be inserted to correspond to given times4 ,as this revolves1 the circuits are closed1 one after the other1 and it may be so set that bells will be rung in different parts of the house every five minutes1 if desired4 ,illustration3 ,fig4 #beb4 ,illustration3 ,fig4 #bec4 #agc4 ,call ,boxes are used to send in calls of various kinds to central stations4 ,fig4 #bec shows one form4 ,the number of different calls provided includes messenger1 carrier1 coup1 express wagon1 doctor1 laborer1 police1 fire1 together with three more1 which may be made special to suit the convenience of the individual customer4 ,the instruments are provided with apparatus for receiving a return signal1 the object of which is to notify the subscriber that his call has been received and is having attention4 ,illustration3 ,fig4 #bed4 ,illustration3 ,fig4 #bee4 ,fig4 #bed shows another form of call box1 the handle being moved around to the call desired4 ,as it springs back to the original position1 an interrupted current passes through the box to the central station1 causing a bell to tap a certain number of times1 giving the call and location of the box4 #agd4 ,electric ,gas-,lighters4 ,fig4 #bee shows a ratchet burner4 ,the first pull of the chain turns on the gas through a four-way gas-cock1 governed by a ratchet-wheel and pawl4 ,the issuing gas is lighted by a wipe-spark at the tip of the burner4 ,alternate pulls shut off the gas4 ,as the lever brings the attached wire ,a1 in contact with the wire ,b1 a bright spark passes1 which ignites the gas1 the burner being joined with a battery and induction or spark coil4 ,automatic burners are used when it is desired to light gas at a distance from the push-button4 ,fig4 #bef shows one form4 ,two electromagnets are shown1 one being generally joined to a white push-button for turning on the gas and lighting it1 the other being joined to a black button which turns off the gas when it is pressed4 ,the armatures of the magnets work the gas-valve4 ,sparks ignite the gas1 as explained above4 ,illustration3 ,fig4 #bef4 ,illustration3 ,fig4 #beg4 #age4 ,door ,openers4 ,fig4 #beg shows one form4 ,they contain electromagnets so arranged that when the armature is attracted by the pushing of a button anywhere in the building1 the door can be pushed open4 #agf4 ,dental ,outfits4 ,fig4 #beh shows a motor arranged to run dental apparatus4 ,the motor can be connected to an ordinary incandescent light socket4 ,in case the current gives out1 the drills1 etc41 can be run by foot power4 ,illustration3 ,fig4 #beh4 #agg4 ,annunciators of various kinds are used in hotels1 factories1 etc41 to indicate a certain room when a bell rings at the office4 ,the bell indicates that some one has called1 and the annunciator shows the location of the call by displaying the number of the room or its location4 ,fig4 #bei shows a small annunciator4 ,they contain electromagnets which are connected to push-buttons located in the building1 and which bring the numbers into place as soon as the current passes through them4 ,illustration3 ,fig4 #bei4 ,,index4 ,numbers refer to paragraphs4 ,see ,table of ,contents for the titles of the various chapters4 ,action of magnets upon each other1 #cb4 ,adjuster1 for lamp cords1 #aea4 ,air pressure1 effect of spark upon1 #aee4 ,aluminum-leaf1 for electroscopes1 #e4 ,alternating current1 #abi1 #acj2 system of wiring for1 #add4 ,amalgamation of zincs1 #dg4 ,amber1 electrification upon1 #c4 ,ammeter1 the1 #gd2 how placed in circuit1 #gg4 ,ampere1 the1 #gb4 ,annunciators1 #agg4 ,anode1 #gi1 #hb4 ,apparatus for electrical measurements1 ,chap4 ,,vi4 ,appliances1 for distribution of currents1 #ada2 for electric railways1 #afg2 for heating by electricity1 #adg4 ,arc1 the electric1 #aeb4 ,arc lamp1 the1 #aec2 how light is produced by1 ,chap4 ,,xxii42 double carbon1 #aec2 hand-feed focussing1 #aec2 for search-lights1 #aec2 short1 for basements1 #aec2 single carbon1 #aec2 for theater use1 #aec4 ,armature1 of dynamo1 #abg1 #abi2 of electromagnets1 #ih2 of horseshoe magnet1 #bf2 of motors1 #afa2 uses of1 #ci4 ,artificial magnets1 #be4 ,astatic1 detectors1 #id2 galvanometer1 #gc2 needles1 #id4 ,aurora borealis1 #bc4 ,automatic1 current interrupters1 #ajd1 #aae2 gas lighters1 #agd2 program clocks1 #agb4 ,automobiles1 #afi2 controllers for1 #afi2 motors for1 #afi2 steering of1 #afi2 storage batteries for1 #afi4 ,bamboo filaments1 #adi4 ,bar magnets1 #bg2 magnetic figures of1 #ch4 ,batteries1 large plunge1 #ed2 plunge1 #ec2 secondary1 #hf2 storage1 and how they work1 ,chap4 ,,ix4 ,bell1 the electric1 and some of its uses1 ,chap4 ,,xv42 electric1 #aaf2 magneto testing1 #aag2 trembling1 etc41 #aaf4 ,bell transmitter1 #abj4 ,belts1 electricity generated by friction upon1 #a4 ,benjamin ,franklin1 #ah4 ,bichromate of potash cells1 #ea1 etc4 ,binding-posts1 ,chap4 ,v42 common forms of1 #fc4 ,blasting1 by electricity1 #adg2 electric machines for1 #adg4 ,bluestone cell1 #ef4 ,boats1 electric1 #afh4 ,boilers1 use of in central stations1 #agj4 ,bones1 photographed by x-rays1 ,chap4 ,,xxiii4 ,boosters1 #acf4 ,brushes1 #abi4 ,bunsen cells1 #ef;a4 ,burner1 automatic1 #agd2 for gas-lights1 #agd2 ratchet1 #agd4 ,buzzers1 electric1 #aah4 ,cables and wires1 #adc4 ,call boxes1 electric1 #agc4 ,carbon1 in arc lamps1 #aeb1 #aec2 filament1 #adi2 transmitter1 #abc4 ,carpet1 electricity generated upon1 #a4 ,cars1 electric1 #afd2 controllers for1 #afe2 heating by electricity1 #afg2 overhead system for1 #aff2 underground system for1 #aff4 ,cat1 electricity generated upon1 #a4 ,cathode1 definition of1 #gi2 rays1 #aeg4 ,cells1 ,bunsen1 #ef;a2 bichromate of potash1 #ea2 closed circuit1 #ej2 dry1 #eh2 ,edison-,lelande1 #ei2 electricity generated by1 ,chap4 ,,iii42 ,fuller1 #ee2 ,gonda1 #eg2 gravity1 #ef2 ,grenet1 #eb2 ,leclanch1 #eg2 open circuit1 #ej2 plates and poles of1 #de;a2 polarization of1 #dh2 simple1 #de1 #di2 single-fluid1 #di2 two-fluid1 #di2 various voltaic1 ,chap4 ,,iv4 ,central stations1 #agj2 a word about1 ,chap4 ,,xxvi4 ,chain lightning1 #ai4 ,chafing-dishes1 electrical1 #adg4 ,charging condensers1 #ae4 ,chemical action1 and electricity1 #ha4 ,chemical effects of electric current1 ,chap4 ,,vii4 ,chemical meters1 #gh4 ,church organs1 pumped by motors1 #afb4 ,circuits1 electric1 #ej2 for lamps1 #add4 ,cleats1 porcelain1 #ada2 wooden1 #ada4 ,clocks1 automatic electric1 #agb4 ,closed circuit cells1 #ej4 ,coils1 induction1 and how they work1 ,chap4 ,,xiii42 induction1 construction of1 #ajd2 method of joining1 #ih2 primary and secondary1 #ajc2 resistance1 #fi2 rotation of1 #ie2 of transformers1 #ace4 ,collectors on dynamos1 #abi4 ,commutators1 #abi4 ,compasses1 magnetic1 #ca4 ,compound1 magnets1 #bh2 wound dynamo1 #aca4 ,condensation of static electricity1 #ae4 ,condensers1 #ae2 for induction coils1 #ajd4 ,conductors1 and insulators1 #d1 #ach4 ,conduits1 electric1 #adj4 ,connections1 electrical1 #fj2 for telegraph lines1 #aaa4 ,controllers1 for automobiles1 #afi2 for electric cars1 #afe4 ,copper sulphate1 effects of current on1 #hb2 formula of1 #gi4 ,copper voltameters1 #ge4 ,cords1 adjustable for lamps1 #aea4 ,coulomb1 the1 #gf4 ,crater of hot carbons1 #aeb4 ,crookes tubes1 #aef1 #aeh4 ,current1 detectors1 #ic2 direction of in cell1 #df2 from magnet and coil1 #ajj2 from two coils1 #ajb2 induced1 #abg2 of induction coils1 #aje2 interrupters1 automatic1 #ajd1 #aae2 local1 #dg2 primary and secondary1 #ajb2 transformation of1 ,chap4 ,,xviii42 transmission of1 #acd4 ,currents1 and motion1 #afj2 how distributed for use1 ,chap4 ,,xix4 ,current strength1 #ga2 measurement of1 #gc2 unit of1 #gb4 ,cylinder electric machines1 #i4 ,daniell cell1 #ef4 ,d',arsonval galvanometer1 #gc4 ,declination1 #da4 ,decorative incandescent lamps1 #aea4 ,dental1 lamps1 #aea2 outfits1 #agf4 ,detectors1 astatic1 #id2 current1 #ic4 ,diamagnetic bodies1 #bi4 ,diaphragm for telephones1 #abj4 ,dip1 of magnetic needle1 #db4 ,direct current1 #abi1 #acj4 ,direction of current in cell1 #df4 ,discharging condensers1 #ae4 ,disruptive discharges1 #aed4 ,distribution of currents for use1 ,chap4 ,,xix4 ,door opener1 electric1 #age4 ,dots and dashes1 #aaj4 ,drill press1 run by motor1 #afb4 ,dry cells1 #eh4 ,dynamo1 the1 #abf2 alternating current1 #acj2 commutator of1 #abi2 compound wound1 #aca2 direct current1 #acj2 lamps connected to1 #acb2 series wound1 #aca2 shunt wound1 #aca2 used as motor1 #afa2 use of in central stations1 #agj2 used with water power1 #agj4 ,dynamos1 electricity generated by1 ,chap4 ,,xvii42 types of1 #acj2 various machines1 #acb2 winding of1 #aca4 ,dynamotors1 #acg4 ,earth1 inductive influence of1 #dc2 lines of force about1 #dj1 #db4 ,ebonite1 electricity by friction upon1 #c1 #d4 ,edison-,lelande cells1 #ei4 ,electric1 automobiles1 #afi2 bell1 and some of its uses1 ,chap4 ,,xv42 boats1 #afh2 buzzers1 #aah2 cars1 #afd2 conduits1 #adj2 fans1 #afb2 flat-irons1 #adf2 gas lighters1 #agd2 griddles1 #adg2 kitchen1 #adg2 lights1 arc1 ,chap4 ,,xxii42 lights1 incandescent1 ,chap4 ,,xxi42 machines1 static1 #g to #ac2 machines1 uses of1 #ad2 motor1 the1 #afa2 motor1 and how it does work1 ,chap4 ,,xxiv42 soldering irons1 #adf2 telegraph1 and how it sends messages1 ,chap4 ,,xiv42 telephone1 and how it transmits speech1 ,chap4 ,,xvi42 welding1 #adf4 ,electric current1 and work1 #acc2 and chemical action1 #ha2 chemical effects of1 ,chap4 ,,vii42 how distributed for use1 ,chap4 ,,xix42 magnetic effects of1 ,chap4 ,,xi42 how transformed1 ,chap4 ,,xviii4 ,electrical1 connections1 #fj2 horse-power1 #gg2 measurements1 ,chap4 ,,vi42 resistance1 #fh2 resistance1 unit of1 #fi2 units1 ,chap4 ,,vi4 ,electricity1 about frictional1 ,chap4 ,i42 and chemical action1 #ha2 atmospheric1 #ah2 heat produced by1 ,chap4 ,,xx42 history of1 #c2 how generated upon cat1 #a2 how generated by dynamos1 ,chap4 ,,xvii42 how generated by heat1 ,chap4 ,x42 how generated by induction1 ,chap4 ,,xii42 how generated by voltaic cell1 ,chap4 ,,iii42 origin of name1 #b4 ,electrification1 kinds of1 #f2 laws of1 #g4 ,electrolysis1 #gi4 ,electrolyte1 #gi4 ,electromagnetic induction1 #ii4 ,electromagnetism1 #ia4 ,electromagnets1 #if2 forms of1 #ig4 ,electro-mechanical gong1 #aaf4 ,electromotive force1 defined1 #fe1 #ga2 measurement of1 #fg2 of polarization1 #he2 of static electricity1 #ag2 unit of1 #ff4 ,electrophorus1 the1 #h4 ,electroplating1 #hb4 ,electroscopes1 #e4 ,electrotyping1 #hc4 ,experiments1 early1 with currents1 #dd2 some simple1 #a4 ,external resistance1 #fh4 ,fan motors1 #afb4 ,field1 magnetic1 #cg4 ,field-magnets1 #abi4 ,figures1 magnetic1 #ch4 ,filaments1 carbon1 #adi2 bamboo1 etc41 #adi4 ,fire1 ,st4 ,elmo's1 #bb4 ,flat-irons1 electric1 #adg4 ,floor mains1 #aci4 ,fluoroscope1 #aeh4 ,force1 and induced currents1 #aja2 lines of magnetic1 #ch2 lines of about a wire1 #ib1 #if2 lines of about a magnet1 #cg1 #ch4 ,frictional electricity1 about1 ,chap1 ,i42 location of charge of1 #d2 sparks from1 #d4 ,fuller cell1 the1 #ee4 ,fuse1 link1 #adb2 plug1 #adb2 ribbons1 #adb2 wire1 #adb4 ,fusible rosettes1 #adb4 ,galvani1 early experiments of1 #dd4 ,galvanometers1 #gc2 astatic1 #gc2 considered as motor1 #afa2 ,d',arsonval1 #gc2 tangent1 #gc4 ,galvanoscope1 #gc2 astatic1 #id4 ,gas lighters1 electric1 #agd4 ,geissler tubes1 #aef4 ,generators1 electric1 #abf4 ,glass1 electricity generated upon1 #d4 ,glue pots1 electric1 #adg4 ,gold-leaf1 for electroscopes1 #e4 ,gold plating1 #hb4 ,gonda cell1 #eg4 ,gong1 electro-mechanical1 #aaf4 ,gravity cell1 the1 #ef2 replaced by dynamotors1 #acg4 ,grenet cell1 #eb4 ,griddles1 electric1 #adg4 ,guard1 for lamps1 #aea4 ,heat1 how generated by electricity1 ,chap4 ,x42 and magnetism1 #ce2 and resistance1 #ade4 ,heat lightning1 #ai4 ,heaters1 for cars1 #afg4 ,history of electricity1 #c4 ,horse-power1 electrical1 #gg4 ,horseshoe1 permanent magnets1 #bf2 electromagnets1 #ig1 #ih4 ,human body1 bones of1 photographed by x-rays1 ,chap4 ,,xxiii4 ,hydrogen1 action of in cell1 #dh2 attraction of for oxygen1 #he4 ,incandescence1 #adh4 ,incandescent lamp1 #adi2 candle-power of1 #aej2 current for1 #aej2 light produced by1 ,chap4 ,,xxi42 construction of1 #adi2 uses of1 #aea4 ,inclination of magnetic needle1 #db4 ,indicating push-button1 #fa4 ,induced currents1 #abg2 and lines of force1 #aja2 by rotary motion1 #abh2 of induction coils1 #aje2 of transformers1 #ace4 ,induced magnetism1 #cf4 ,induction1 electricity generated by1 ,chap4 ,,xii42 electromagnetic1 #ii4 ,induction coils1 condensers for1 #ajd2 construction of1 #ajd2 currents of1 #aje2 how they work1 ,chap4 ,,xiii42 in telephone work1 #abd2 uses of1 #ajf4 ,inductive influence of earth1 #dc4 ,influence machines for medical purposes1 #ac4 ,ink writing registers1 #aad4 ,insulating tubing1 #ada4 ,insulators1 #ada2 and conductors1 #d1 #ach2 feeder-wire1 #afg2 for poles1 #afg2 porcelain1 #ada4 ,internal resistance1 #fh4 ,interrupters1 automatic current1 #ajd1 #aae4 ,ions1 #hj4 ,iron1 electricity upon1 by friction1 #d4 ,jar1 ,leyden1 #ae4 ,jarring magnets1 effects of1 #cc4 ,keeper of magnets1 #bf4 ,keys1 telegraph1 #aji4 ,kinds of electrification1 #f4 ,kitchen1 electric1 #adg4 ,knife switch1 #fb4 ,lamp1 incandescent1 candle-power of1 #aej2 cord1 adjustable1 #aea2 current for1 #aej2 dental1 #aea2 for desks1 #aea2 for throat1 #aea2 guard for1 #aea2 incandescent1 #adi2 socket1 #aea2 with half shade1 #aea4 ,lamp1 the arc1 #aec2 how light is produced by1 ,chap4 ,,xxii42 double carbon1 #aec2 hand-feed focussing1 #aec2 for search-lights1 #aec2 single carbon1 #aec2 short1 for basements1 #aec2 for theater use1 #aec4 ,lamp circuits1 alternating system1 #add4 ,lamps1 in parallel1 #add2 lamps in series1 #add2 three-wire system1 #add2 two-wire system1 #add4 ,laws1 of electrification1 #g2 of magnetic attraction1 #cb2 of resistance1 #gj4 ,leaf electroscopes1 #e4 ,leclanch cell1 #eg4 ,leyden1 battery1 #af2 jar1 #ae4 ,light1 how produced by arc lamp1 ,chap4 ,,xxii42 how produced by incandescent lamp1 ,chap4 ,,xxi4 ,lightning1 #ai2 rods1 #ba4 ,line1 telegraph1 ,chap4 ,,xiv42 connections for1 #aaa2 operation of1 #aab4 ,line suspension1 for trolley-wires1 #afg4 ,line wire1 #aaa4 ,lines of force1 conductors of1 #ci1 #if2 about the earth1 #dj1 #db2 and induced currents1 #aja2 about a magnet1 #ch2 about a wire1 #ib4 ,local currents1 #dg4 ,magnetic1 bodies1 #bi2 declination1 #da2 effects of electric current1 ,chap4 ,,xi42 field1 #cg2 figure of one bar magnet1 #ch2 figure of two bar magnets1 #ch2 figure of horseshoe magnet1 #ch2 needle1 dip of1 #db2 needles and compasses1 #ca4 ,magnetism1 and heat1 #ce2 induced1 #cf2 laws of1 #cb2 residual1 #cd2 retentivity1 #cd2 temporary1 #cf2 terrestrial1 #dj2 theory of1 #cc4 ,magneto1 signal bells1 #aag2 testing bells1 #aag2 transmitter1 #abj4 ,magnets1 action upon each other1 #cb2 artificial1 #be2 bar1 #bg2 compound1 #bh2 effects of jarring1 #cc2 electro1 #if2 electro1 forms of1 #ig2 horseshoe1 #bf2 and magnetism1 about1 ,chap4 ,,ii42 making of1 #cj2 natural1 #bd4 ,mains1 electric1 #aci4 ,man-holes1 in conduits1 #adj4 ,measurements1 electric1 ,chap4 ,,vi42 of current strength1 #gc2 of ,e4,m4,f41 #fg4 ,meters1 chemical1 #gh2 permanent record1 #gg4 ,microphone1 the1 #abb4 ,motion and currents1 #afj4 ,motor1 acting like dynamo1 #afc2 armature of1 #afa2 controlling speed of1 #afe2 electric1 #afa2 electric1 and how it does work1 ,chap4 ,,xxiv42 fans1 #afb2 for automobiles1 #afi2 for boats1 #afh2 for pumping bellows1 #afb2 for running drill press1 #afb2 parts of1 #afb2 starting boxes for1 #afc2 uses of1 #afb4 ,motor-dynamos1 #acf4 ,mouldings1 for wires1 #ada4 ,name1 electricity1 origin of1 #b4 ,natural magnets1 #bd4 ,needles1 astatic1 #id2 dipping1 #db2 magnetic1 #ca4 ,negative electrification1 #e4 ,non-conductors1 #d4 ,north pole1 magnetic of earth1 #dj2 of magnets1 #bf4 ,northern lights1 #bc4 ,ohm1 the1 #fi4 ,open circuit cells1 #ej4 ,openers1 for doors1 #age4 ,outfits1 dental1 #age4 ,overhead trolley system1 #aff4 ,oxygen1 attraction for hydrogen1 #he4 ,parallel arrangement of lamps1 #add4 ,peltier effect1 #hi4 ,pendant1 electric1 #aea4 ,pith-ball electroscope1 #e4 ,plate electrical machine1 #aj4 ,plates of cells1 #de;a4 ,plunge batteries1 #ec2 large1 #ed4 ,polarity of coils1 #ie4 ,polarization1 #hd2 electromotive force of1 #he2 of cells1 #dh4 ,pole-changing switch1 #fb4 ,poles1 of cells1 #de;a2 of horseshoe magnet1 #bf4 ,positive electrification1 #f4 ,potential1 defined1 #fe4 ,push-buttons1 ,chap4 ,v42 indicating1 #fa2 modifications of1 #fa2 table clamp1 #fa4 ,quantity of electricity1 #gf2 unit of1 #gf4 ,rays1 cathode1 #aeg2 x-rays1 #aeh4 ,receiver1 telephone1 #aba4 ,reflectors1 for lamps1 #aea4 ,registers1 ink writing1 #aad4 ,relay1 the1 #aac4 ,residual magnetism1 #cd4 ,resistance1 coils and boxes1 #fi2 electrical1 #fh2 external1 #fh2 and heat1 #ade2 internal1 #fh2 laws of1 #gj2 unit of1 #fi4 ,retentivity1 #cd4 ,risers1 in buildings1 #aci4 ,rods1 lightning1 #ba4 ,roentgen1 ,prof41 #aeh4 ,rosette1 fusible1 #adb4 ,running-gear1 of automobiles1 #afi4 ,safety1 devices1 #adb2 fuse1 #adb2 fuse link1 #adb2 fuse plug1 #adb2 fuse ribbon1 #adb2 fuse wire1 #adb4 ,search-lights1 #aec2 signals sent by1 #aec4 ,secondary batteries1 #hf2 uses of1 #hg4 ,series arrangement of lamps1 #add4 ,series wound dynamo1 #aca4 ,service wires1 #aci4 ,shunt-wound dynamo1 #aca4 ,signal bells1 magneto1 #aag4 ,simple cell1 the1 #de1 #di4 ,single-fluid cells1 #di4 ,single-point switch1 #fb4 ,single-stroke bell1 #aaf4 ,socket1 for incandescent lamps1 #aea4 ,soldering irons1 electric1 #adg4 ,sounders1 telegraph1 #aaj2 home-made1 #aaj4 ,spark1 effect of air pressure on1 #aee4 ,sparks1 from cells1 #ag2 from frictional electricity1 #d4 ,st4 ,elmo's fire1 #bb4 ,starting boxes1 for motors1 #afc4 ,static electric machines1 #h4 ,static electricity1 condensation of1 #ae2 electromotive force of1 #ag2 to test presence of1 #e2 uses of1 #ad4 ,steam engines1 in central stations1 #agj4 ,steel1 inductive influence of earth upon1 #dc2 retentivity of1 #bf4 ,storage batteries1 the1 and how they work1 ,chap4 ,,ix42 for automobiles1 #afi2 for boats1 #afh2 for natural sources of power1 #hg4 ,stoves1 electric1 #adg4 ,strength of current1 #ga2 measurement of1 #gc2 unit of1 #gb4 ,switchboards1 #fb4 ,switches1 ,chap4 ,v42 knife1 #fb2 pole-changing1 #fb2 single point1 #fb2 for trolley lines1 #afg4 ,table clamp-push1 #fa4 ,tangent galvanometer1 #gc4 ,teakettles1 electric1 #adg4 ,telegraph1 electric1 and how it sends messages1 ,chap4 ,,xiv42 ink writing registers1 #aad2 keys1 #aji2 relay1 #aac2 sounders1 #aaj4 ,telegraph line1 #ajg1 #ajh2 operation of1 #aab2 simple connections of1 #aaa4 ,telephone1 the1 and how it transmits speech1 ,chap4 ,,xvi42 receiver1 #aba2 transmitter1 #abj2 use of induction coil with1 #abd2 various forms of1 #abe4 ,temporary magnetism1 #cf4 ,terrestrial magnetism1 #dj4 ,theory of magnetism1 #cc4 ,thermoelectricity1 #hh4 ,thermopiles1 #ij4 ,three-wire system1 #add4 ,throat1 lamp for1 #aea4 ,thunder1 #bj4 ,toepler-,holtz machines1 #aa4 ,transformers1 #ace4 ,transforming electric current1 ,chap4 ,,xviii42 for electric welding1 #adf4 ,transmission of currents1 #acd4 ,transmitter1 ,bell1 #abj2 carbon1 #abc4 ,trembling bell1 #aaf4 ,trolley-wires1 #afd2 -poles1 #afd2 -wheels1 #afd4 ,tubes1 ,crookes1 #aef1 #aeh2 ,geissler1 #aef2 vacuum1 #aef4 ,two-fluid cells1 #di4 ,two-wire system1 #add4 ,underground trolley system #aff2 conduits for1 #aff4 ,unit1 of current strength1 #gb2 of electromotive force1 #ff2 of quantity1 #gf2 of resistance1 #fi4 ,units1 electrical1 ,chap4 ,,vi4 ,uses1 of armatures1 #ci2 of electricity1 miscellaneous1 ,chap4 ,,xxvii42 of induction coils1 #ajf2 of motors1 #afb2 of storage batteries1 #hg4 ,vacuum-tubes1 #aef4 ,variation1 angle of1 #da4 ,volt1 the1 #ff4 ,volta1 #ff2 early experiments of1 #dd4 ,voltaic cell1 electricity generated by1 ,chap4 ,,iii4 ,voltaic pile1 #dd4 ,voltameters1 #ge2 copper1 #ge2 water1 #ge4 ,voltmeters1 #fg1 #gg4 ,water1 decomposition of1 #gi2 power1 source of energy1 #agj2 voltameters1 #gc4 ,watt1 the1 #gg4 ,wattmeters1 #gg4 ,welding1 electric1 #adf4 ,wimshurst electric machine1 #ab4 ,wires and cables1 #adc4 ,wiring1 for alternating system1 #add2 three-wire system1 #add2 two-wire system1 #add4 ,work1 and electric current1 #acc4 ,x-ray photographs1 #aei4 ,x-rays1 #aef2 and how the bones of the human body are photographed1 ,chap4 ,,xxiii4 ,yokes1 #ig1 #ih4 ,zincs1 amalgamation of1 #dg4 ,,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 in41 and is bound in cloth4 ,,price1 ,,post-,,paid1 #a4jj4 ,,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 ,everyone ,should ,know ,about ,electricity4 ,a ,,very ,,appropriate ,,present ,,third ,,edition ,how ,two ,boys ,made ,their ,own ,electrical ,apparatus4 ,containing complete directions for making all kinds of simple electrical apparatus for the study of elementary electricity4 ,by ,,professor ,,thomas ,m4 ,,st4 ,,john1 ,new ,york ,city4 ,the book measures #e #g in41 and is beautifully bound in cloth4 ,it contains #ada pages and #abe illustrations4 ,complete directions are given for making #aeb different pieces of ,apparatus for the practical use of students1 teachers1 and others who wish to experiment4 ,,price1 ,,post-,,paid1 #a4jj4 ,the shocking coils1 telegraph instruments1 batteries1 electromagnets1 motors1 etc41 etc41 are so simple in construction that any boy of average ability can make them2 in fact1 the illustrations have been made directly from apparatus constructed by young boys4 ,the author has been working along this line for several years1 and he has been able1 with the help of boys1 to devise a complete line of simple electrical apparatus4 ,,the ,,apparatus ,,is ,,simple because the designs and methods of construction have been worked out practically in the school-room1 absolutely no machine-work being required4 ,,the ,,apparatus ,,is ,,practical because it has been designed for real use in the experimental study of elementary electricity4 ,,the ,,apparatus ,,is ,,cheap because most of the parts can be made of old tin cans and cracker boxes1 bolts1 screws1 wires and wood4 ,address1 ,,thomas ,m4 ,,st4 ,,john1 #djg ,west #east ,street1 ,new ,york4 ,how ,two ,boys ,made ,their ,own ,electrical ,apparatus4 ,,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 ,magnets1--,,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 wirier 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 for 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 made1 ,in this 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 ,fun ,with ,photography ,,book ,,and ,,complete ,,outfit4 ,illustration ,,photography is now an educational amusement1 and to many it is the most fascinating of all amusements4 ,the magic of sunshine1 the wonders of nature1 and the beauties of art are tools in the hand of the amateur photographer4 ,a great many things can be done with this outfit1 and it will give an insight into this most popular pastime4 ,,the ,,outfit contains everything necessary for making ordinary 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,patent ,pending7 ,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 ,,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--,drying4--,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 ,the ,book and ,complete ,outfit will be sent1 by mail or express1 ,charges ,prepaid1 upon receipt of #fe ,cents1 by ,,thomas ,m4 ,,st4 ,,john1 #djg ,w4 #east ,st41 ,new ,york4 ,fun ,with ,magnetism4 ,,book ,,and ,,complete ,,outfit ,,for ,,sixty-,,one ,,experiments ,,in ,,magnetism444 ,illustration ,children like to do experiments2 and in this way1 better than in any other1 a practical knowledge of the elements of magnetism may be obtained4 ,these experiments1 although arranged to amuse boys and girls1 have been found to be very useful in the class-room to supplement the ordinary exercises given in text-books of science4 ,to secure the best possible quality of apparatus1 the horseshoe magnets were made at ,sheffield1 ,england1 especially for these sets4 ,they are new and strong4 ,other parts of the apparatus have also been selected and made with great care1 to adapt them particularly to these experiments4--,from the author's preface4 ,,contents4--,experiments ,with ,horseshoe ,magnet4--,experiments ,with ,magnetized ,needles4--,experiments ,with ,needles1 ,corks1 ,wires1 ,nails1 etc4--,experiments ,with ,bar ,magnets4--,experiments ,with ,floating ,magnets4--,miscellaneous ,experiments4--,miscellaneous ,illustrations showing what very small children can do with the ,apparatus4--,diagrams showing how ,magnetized ,needles may be used by little children to make hundreds of pretty designs upon paper4 ,,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 ,upsidedown4--,a ,magnetic ,windmill4--,a ,compass ,upsidedown4--,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 ,the ,book and ,complete ,outfit will be sent1 ,post-paid1 upon receipt of #ce ,cents1 by ,,thomas ,m4 ,,st4 ,,john1 #djg ,w4 #east ,st41 ,new ,york4 ,,fun ,,with ,,shadows ,,book ,,and ,,complete ,,outfit ,,for ,,shadow ,,pictures1 ,,pantomimes1 ,,entertainments1 ,etc41 ,etc4 ,illustration ,shadow ,making has been a very popular amusement for several centuries4 ,there is a great deal of fun and instruction in it1 and its long life is due to the fact that it has always been a source of keen delight to grown people as well as to children4 ,in getting material together for this little book1 the author has been greatly aided by ,english1 ,french and ,american authors1 some of whom are professional shadowists4 ,it has been the author's special effort to get the subject and apparatus into a practical1 cheap form for boys and girls4 ,,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 shears3 #ab ,character ,hats2 #a ,boat2 #a ,oar-blade2 #a ,fish2 #a ,candlestick2 #a ,cardboard ,plate containing printed parts for making movable figures4 ,,contents ,,of ,,book3 ,one ,hundred ,illustrations and ,diagrams1 including ,ten ,full-page ,book ,plates1 together with ,six ,full-page ,plates on ,cardboard4 ,chapter ,i4 ,introduction4--,,ii4 ,general ,instructions4--,,iii4 ,hand ,shadows of ,animals4--,,iv4 ,hand ,shadows of ,heads1 ,character ,faces1 etc4--,v4 ,moving ,shadow ,figures and ,how to ,make ,them4--,,vi4 ,shadow ,pantomimes4--,,vii4 ,miscellaneous ,shadows4 ,the ,book and ,complete ,outfit will be sent1 ,,post-,,paid1 upon receipt of #ce cents1 by ,,thomas ,m4 ,,st4 ,,john1 #djg ,west #east ,st41 ,new ,york ,city4 ,fun ,with ,electricity4 ,,book ,,and ,,complete ,,outfit ,,for ,,sixty ,,experiments ,,in ,,electricity4444 ,illustration ,enough of the principles of electricity are brought out to make the book instructive as well as amusing4 ,the experiments are systematically arranged1 and make a fascinating science course4 ,no chemicals1 no danger4 ,the book is conversational and not at all schooly1 ,harry and ,ned being two boys who perform the experiments and talk over the results as they go along4 ,the book reads like a story4--,an appropriate present for a boy or girl4--,intelligent parents will appreciate ',fun ,with ,electricity4'--,very complete1 because it contains both book and apparatus4--,there is no end to the fun which a boy or girl can have with this fascinating amusement4 ,,there ,,is ,,fun ,,in ,,these ,,experiments4--,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 ,the ,,outfit contains #bj different articles4 ,the ,,book ,,of ,,instruction measures #e x #g inches1 and has #ch illustrations1 #ee pages1 good paper and clear type4 ,the ,book1 and ,complete ,outfit will be sent1 by mail or express1 ,charges ,prepaid1 upon receipt of #fe ,cents1 by ,,thomas ,m4 ,,st4 ,,john1 #djg ,w4 #east ,st41 ,new ,york4 ,fun ,with ,puzzles4 ,,book1 ,,key1 ,,and ,,complete ,,outfit ,,for ,,four ,,hundred ,,puzzles444 ,the ,,book measures #e #g inches4 ,it is well printed1 nicely bound1 and contains #ae chapters1 #hj pages1 and #abh illustrations4 ,the ,,key is illustrated4 ,it is bound with the book1 and contains the solution of every puzzle4 ,the ,,complete ,,outfit is placed in a neat box with the book4 ,it consists of numbers1 counters1 figures1 pictures1 etc41 for doing the puzzles4 ,,contents3 ,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 ,fun ,with ,puzzles is a book that every boy and girl should have4 ,it is amusing1 instructive1--educational4 ,it is just the thing to wake up boys and girls and make them think4 ,they like it1 because it is real fun4 ,this sort of educational play should be given in every school-room and in every home4 ,fun ,with ,puzzles will puzzle your friends1 as well as yourself2 it contains some real brain-splitters4 ,over #cjj new and original puzzles are given1 besides many that are hundreds of years old4 ,secret ,writing4 ,among the many things that ,f4 ,w4 ,p4 contains1 is the key to secret writing4 ,it shows you a very simple way to write letters to your friends1 and it is simply impossible for others to read what you have written1 unless they know the secret4 ,this1 alone is a valuable thing for any boy or girl who wants to have some fun4 ,the ,book1 ,key1 and ,complete ,outfit will be sent1 postpaid1 upon receipt of #ce cents1 by ,,thomas ,m4 ,,st4 ,,john1 #djg ,west #east ,st41 ,new ,york ,city4 ,fun ,with ,soap-,bubbles4 ,,book ,,and ,,complete ,,outfit ,,for ,,fancy ,,bubbles ,,and ,,films4444 ,illustration ,,the ,,outfit contains everything necessary for thousands of beautiful bubbles and films4 ,all highly colored articles have been carefully avoided1 as cheap paints and dyes are positively dangerous in children's mouths4 ,the outfit contains the following articles3 ,one ,book of ,instructions1 called ,fun ,with ,soap-,bubbles1 #a ,metal ,base for ,bubble ,stand1 #a ,wooden ,rod for ,bubble ,stand1 #c ,large ,wire ,rings for ,bubble ,stand1 #a ,small ,wire ,ring1 #c ,straws1 #a ,package of ,prepared ,soap1 #a ,bubble ,pipe1 #a ,water-proof ,bubble ,horn4 ,the complete outfit is placed in a neat box with the book4 7,extra ,horns1 ,soap1 etc41 furnished at slight cost47 ,,contents ,,of ,,book4--,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 ,,the ,,best ,,possible ,,amusement ,,for ,,old ,,and ,,young4 ,the ,book and ,complete ,outfit will be sent1 ,,post-,,paid1 upon receipt of #ce cents1 by ,,thomas ,m4 ,,st4 ,,john1 #djg ,west #east ,st41 ,new ,york ,city4 ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment4 ,by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,the book contains #bbj pages and #afh illustrations2 it measures #e #g in4 and is bound in green cloth4 ,,price1 ,,post-,,paid1 #a4be4 ,this book is designed as a text-book for amateurs1 students1 and others who wish to take up a systematic course of elementary electrical experiments at home or in school4 ,full directions are given for4444444 ,two ,hundred ,simple ,experiments4 ,the experiments are discussed by the author1 after the student has been led to form his own opinion about the results obtained and the points learned4 ,in selecting the apparatus for the experiments in this book1 the author has kept constantly in mind the fact that the average student will not buy the expensive pieces usually described in text-books4 ,the two hundred experiments given can be performed with simple apparatus2 in fact1 the student should make at least a part of his own apparatus1 and for the benefit of those who wish to do this1 the author has given1 throughout the work1 explanations that will aid in the construction of certain pieces especially adapted to these experiments4 ,for those who have the author's ,how ,two ,boys ,made ,their ,own ,electrical ,apparatus1 constant references have been made to it as the ,apparatus ,book1 as this contains full details for making almost all kinds of simple apparatus needed in ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment4 ,if you wish to take up a systematic course of experiments--experiments that may be performed with simple1 inexpensive apparatus1--this book will serve as a valuable guide4 ,condensed ,list of ,apparatus ,,for ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment4 ,number #a4 ,steel ,needles2 package of twenty-five4--#b4 ,flat ,cork4--#c4 ,candle4--#d-ae4 ,annealed ,iron ,wires2 assorted lengths4--#af4 ,horseshoe ,magnet2 best quality2 ,english4--#ag4 ,iron ,filings4--#ah4 ,parts for ,compass4--#ai1 #bj4 ,wire ,nails2 soft steel4--#ba1 #bb4 ,spring ,steel2 for bar magnets4--#bc4 ,iron ,ring4--#bd4 ,sifter2 for iron filings4--#be4 ,spring ,steel2 for flexible magnet4--#bf1 #bg4 ,ebonite ,sheets2 with special surface4--#bh4 ,ebonite ,rod4--#bi4 ,ebonite ,rod2 short4--#cj4 ,flannel ,cloth4--#ca4 ,tissue ,paper4--#cb4 ,cotton ,thread4--#cc4 ,silk ,thread4--#cd4 ,support ,base4--#ce4 ,support ,rod4--#cf4 ,support ,wire4--#cg4 ,wire ,swing4--#ch4 ,sheet of ,glass4--#ci4 ,hairpin4--#dj4 ,circular ,conductor4--#da4 ,circular ,conductor4--#db4 ,electrophorus ,cover4--#dc4 ,insulating ,table4--#dd4 ,insulated ,copper ,wire4--#de4 ,rubber ,band4--#df4 ,bent ,wire ,clamps4--#dg4 ,cylindrical ,conductor4--#dh4 ,discharger2 for condenser4--#di4 ,aluminum-,leaf4--#ej4 ,wires4 #ea4 ,dry ,cell4--#eb4 ,mercury4--#ec4 ,insulated ,copper ,wire2 for connections4--#ed4 ,spring ,connectors2 two dozen4--#ee4 ,parts for ,key4--#ef4 ,metal ,connecting ,plates4--#eg4 ,parts for ,current ,reverser4--#eh4 ,parts for ,galvanoscope4--#ei4 ,parts for ,astatic ,galvanoscope4--#fj-fc4 ,zinc ,strips4--#fd4 ,carbon ,rod4--#fe1 #ff4 ,glass ,tumblers4--#fg1 #fh4 ,copper ,strips4--#fi4 ,galvanized ,iron ,nail4--#gj1 #ga4 ,wooden ,cross-,pieces4--#gb4 ,brass ,screws2 one dozen4--#gc4 ,porous ,cup4--#gd4 ,zinc ,rod4--#ge4 ,copper ,plate4--#gf4 ,iron ,strip4--#gg1 #gh4 ,lead ,strips4--#gi4 ,parts for ,resistance ,coil4--#hj4 ,parts for ,wheatstone's ,bridge4--#ha4 ,german-,silver ,wire2 ,size ,no4 #cj4--hb4 ,german-,silver ,wire2 ,no4 #bh4--hc--he4 ,plate ,binding-,posts4--#hf4 ,copper ,sulphate4--#hg4 ,copper ,burs2 one dozen4--#hh4 ,combination ,rule4--#hi4 ,coil of ,wire2 on spool for electromagnet4--#ij4 ,coil of ,wire2 on spool for electromagnet4--#ia4 ,carbon ,rod4--#ib1 #ic4 ,soft ,iron ,cores with ,screws4--#id4 ,combined ,base and ,yoke4--#ie4 ,combination ,connecting ,plates4--#if4 ,long ,iron ,core4--#ig4 ,round ,bar ,magnet1 #e #c_/h in4--#ih4 ,thin ,electromagnet4--#ii4 ,degree-,card2 for galvanoscope4--#ajj4 ,scale for ,bridge4--#aja1 #ajb4 ,soft ,iron ,cores with ,heads4--#ajc1 #ajd4 ,flat ,bar ,magnets2 these are #f in42 highly polished steel2 poles marked4--#aje4 ,compass4 ,illustrated ,price ,catalogue upon ,application4 ,electrical ,apparatus ,for ,sale ,a ,,complete ,,electric ,,and ,,magnetic ,,cabinet ,,for ,,students1 ,,schools ,,and ,,amateurs4 ,,six ,,extraordinary ,,offers ,this ,cabinet of ,electrical ,experiments contains three main parts3 7,a7 ,apparatus2 7,b7 ,text-,book2 7,c7 ,apparatus ,list4 7,a7 ,the ,apparatus furnished consists of one hundred and five pieces4 ,over three hundred separate articles are used in making up this set4 ,most of it is ready for use when received4 ,seven pieces1 however1 are not assembled2 but the parts can be readily finished and put together4 7,sold1 also1 all pieces assembled47 7,b7 ,the ,text-,book--called ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment--gives full directions for two hundred experiments4 7,see table of contents1 etc47 ,price1 post-paid1 #a4be4 7,c7 ,the ,apparatus ,list is an illustrated book devoted entirely to this special set of apparatus4 ,not given with first offer4 ,,the ,,apparatus ,,is ,,simple because the designs and methods of construction have been worked out with great care4 ,,the ,,apparatus ,,is ,,practical because it has been designed for real use in ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment4 ,,the ,,apparatus ,,is ,,cheap because the various parts are so designed that they can be turned out in quantity by machinery4 #ast ,offer3 ,pieces #a to #ej #a4jj #b;d ,offer3 ,pieces #ea to #aje1 with part 7,c7 #c4ej #c;d ,offer3 ,pieces #a to #aje1 with part 7,c7 #d4jj #dth ,offer3 ,complete ,cabinet1 parts 7,a71 7,b71 7,c7 #e4jj #eth ,offer3 ,apparatus only1 all pieces assembled #d4fj #fth ,offer3 ,complete ,cabinet1 all pieces assembled #e4fj ,express charges must be paid by you4 ,estimates given4 ,a ,special ,catalogue1 pertaining to the above1 with complete price-list1 will be mailed upon application4 ,,thomas ,m4 ,,st4 ,,john1 #djg ,west #east ,st41 ,new ,york ,city ,fun ,with ,telegraphy ,,book ,,and ,,complete ,,outfit4 ,illustration ,,telegraphy is of the greatest importance to all civilized nations1 and upon it depend some of the world's most important enterprises4 ,every boy and girl can make practical use of telegraphy in one way or another1 and the time it takes to learn it will be well spent4 ,,the ,,outfit4--,mr4 ,st4 ,john has worked for a number of years to produce a telegraph outfit that would be simple1 cheap1 and practical for those who wish to make a study of telegraphy4 ,after making and experimenting with nearly one hundred models1 many of which were good1 he has at last perfected an instrument so simple1 original1 and effective that it is now being made in large quantities4 ,the sounders are so designed that they will work properly with any dry cell of ordinary strength1 and this is a great advantage for practice lines4 ,dry batteries are cheap and clean1 and there are no dangers from acids4 ,the outfit consists of the following articles1 placed in a neat box3 ,one ,book of ,instruction1 called ,fun ,with ,telegraphy2 one ,telegraph ,key2 one ,telegraph ,sounder2 ,insulated ,copper ,wires for connections4 ,the key and sounder are mounted1 with proper binding-posts1 upon a base of peculiar construction1 which aids in giving a large volume of sound4 ,,contents ,,of ,,book4--,telegraphy4--,the ,outfit4--,a ,complete ,telegraph ,line4--,connections4--,the ,telegraph ,key4--,the ,sounder4--,the ,battery4--,a ,practice ,line4--,a ,two-instrument ,line4--,operation of ,line4--,the ,morse ,telegraph ,alphabet4--,aids to ,learning ,alphabet4--,cautions4--,office ,calls4--,receiving ,messages4--,remember4--,extra ,parts4 ,,about ,,batteries4--,for those who cannot easily secure batteries1 we will furnish small dry cells1 post-paid1 at #ae cents each1 in order to deliver the outfits complete to our customers4 ,this price barely covers the total cost to us1 postage alone being #f cents4 ,,fun ,,with ,,telegraphy1 including ,book1 ,key1 ,sounder1 and ,wire 7no battery71 post-paid1 #ej cents1 by ,,thomas ,m4 ,,st4 ,,john1 #hdh ,ninth ,ave41 ,new ,york ,tool ,sets for ,students ,the following tool sets have been arranged especially for those who wish to make use of the designs contained in ,how ,two ,boys ,made ,their ,own ,electrical ,apparatus1 ,real ,electric ,toy-,making for ,boys1 ,electric ,instrument-,making1 etc4 ,it is very poor economy to waste valuable time and energy in order to save the cost of a few extra tools4 ,,note4--,save money by buying your tools in sets4 ,we do not pay express or freight charges at the special prices below4 ,,for #a4jj4--,one ,steel ,punch2 round1 knurled head4--,one light ,hammer2 polished1 nickel-plated1 varnished handle4--,one ,iron ,clamp2 japanned1 #b in4--,one ,screw-,driver2 tempered and polished blade1 cherry stained hardwood handle1 nickel ferrule4--,one ,wrench2 retinned skeleton frame1 gilt adjusting wheel4--,one ,awl2 tempered steel point1 turned and stained wood handle1 with ferrule4--,one ,vise2 full malleable1 nicely retinned1 #a-c_/h in4 jaws1 full malleable screw with spring4--,one pair ,steel ,pliers2 #d in4 long1 polished tool steel1 unbreakable1 best grooved jaw4--,one pair of ,shears2 carbonized steel blades1 hardened edge1 nickel-plated1 heavy brass nut and bolt4--,one ,file2 triangular1 good steel4--,one ,file ,handle2 good wood1 brass ferrule4--,one ,foot ,rule2 varnished wood1 has ,english and metric system4--,one ,soldering ,set2 contains soldering iron1 solder1 resin1 sal ammoniac1 and directions4 ,one ,center-,punch2 finely tempered steel4 ,,for #b4jj4--;,all that is contained in the #a4jj set of tools1 together with the following3 ,one pair of ,tinner's ,shears2 cut1 #b in41 cast iron1 hardened1 suitable for cutting thin metal4--,one ,hollow ,handle ,tool ,set2 very useful2 polished handle holds #aj tools1 gimlet1 brad-awls1 chisel1 etc4--,one ,try ,square2 #f-;in4 blue steel blade1 marked in #a_/hs1 strongly riveted4--,one #a-lb4 ,hammer2 full size1 polished head1 wedged varnished hardwood handle4--,one ,hack ,saw2 steel frame1 #i-;in4 polished steel blade1 black enamel handle2 very useful4 ,,for #c4ej4--,two ,steel ,punches2 different sizes1 one solid round1 knurled head1 polished2 the other1 point and head brightly polished1 full nickel1 center part knurled4--,one ,light ,hammer2 polished and nickel plated1 varnished handle4--,one regular ,machinist's ,hammer2 ball peen1 solid cast steel1 with varnished hardwood handle2 a superior article4--,two ,iron ,clamps2 one opens #b in41 the other #c in41 japanned4--,one ,screw-,driver2 tempered and polished blade1 firmly set in cherry stained hardwood handle with nickel ferrule4--,one ,wrench2 retinned1 skeleton frame1 gilt adjusting wheel4--,one ,awl2 tempered steel blade1 ground to point1 firmly set in turned and stained handle with ferrule4--,one ,steel ,vise2 #b-;in41 jaws1 steel screw1 bright polished jaws and handle2 a good strong vise4--,one pair of ,steel ,pliers2 #f in4 long1 bright steel1 flat nose1 #b wire-cutters1 practically unbreakable4--,one pair of ,shears2 carbonized steel blades1 hardened edges1 nickel plated1 heavy brass nut and bolt4--,one ,file2 triangular and of good steel4--,one ,file ,handle2 good wood1 with brass ferrule4--,one ,foot ,rule2 varnished wood1 has both the ,english and metric systems4--,one ,soldering ,set2 contains soldering iron1 solder1 resin1 sal ammoniac1 and directions2 a very handy article4--,one ,center-,punch2 finely tempered steel4--,one pair of ,tinner's ,shears2 these are best grade1 inlaid steel cutting edges1 polished and tempered1 japanned handles2 thoroughly reliable4--,one ,hollow ,handle ,tool ,set2 very useful2 the polished handle holds #aj tools1 gimlet1 chisel1 brad-awl1 etc4--,one ,try ,square2 #f-;in4 blue steel blade1 marked both sides in #a_/hs1 strongly riveted with brass rivets4--,one ,hack ,saw2 steel frame1 #i-;in4 polished steel blade1 black enamel handle2 very useful for sawing small pieces of wood4 ,,for #e4jj will be included everything in the #c4ej offer1 and the following3 ,one ,glue-,pot2 medium size1 with brush and best wood glue2 inside pot has hinge cover4--,one ,ratchet ,screw-,driver2 great improvement over ordinary screw-drivers2 well made and useful4--,one ,hand ,drill2 frame malleable iron2 hollow screw top holding #f drills2 bores from #a-af to #c-af-;in4 holes2 solid gear teeth2 #c-;jawed nickel plated chuck2 a superior tool1 and almost a necessity4 ,,give ,,the ,,boy ,a ,,set ,,of ,,tools ,,thomas ,m4 ,,st4 ,,john1 #hdh ,ninth ,ave41 ,new ,york ,,real ,,electric ,,toy-,,making ,,for ,,boys ,by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,this book contains #adj pages and over one hundred original drawings1 diagrams1 and full-page plates4 ,it measures #e x #g in41 and is bound in cloth4 ,price1 post-paid1 #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 ,every ,boy ,should ,make ,electrical ,toys4 ,the ,electric ,shooting ,game ,a ,,most ,,original ,,and ,,fascinating ,,game ,,patent ,,applied ,,for ,,and ,,copyrighted ,illustration ,,shooting ,,by ,,electricity ,the ,electric ,shooting ,game is an entirely new idea1 and one that brings into use that most mysterious something--electricity4 ,the game is so simple that small children can play it1 and as there are no batteries1 acids1 or liquids of any kind1 there is absolutely no danger4 ,the electricity is of such a nature that it is perfectly harmless--but very active4 ,the game-preserve is neat and attractive1 being printed in colors1 and the birds and animals are well worth hunting4 ,each has a fixed value--and some of them must not be shot at all--so there is ample opportunity for a display of skill in bringing down those which count most4 ,electric bullets are actually shot from the electric gun by electricity4 ,this instructive game will furnish a vast amount of amusement to all4 ,the ,game-,preserve1--the ,electric ,gun1--the ,shooting-,box1--the ,electric ,bullets1--in fact1 the entire electrical outfit1 together with complete illustrated directions1 will be sent in a neat box1 ,post-,paid1 upon receipt of #ej cents1 by ,,thomas ,m4 ,,st4 ,,john1 #hdh ,ninth ,ave41 ,new ,york 99 99 99 99 99 ,transcriber's note3 ,obvious punctuation errors were corrected4 ,page #df1 turnnd changed to turned 7be turned to #a7 ,page #ff1 word a added to text 7in a glass jar7