,,by ,,the ,,same ,,author4 ,,fun ,,with ,,magnetism4 ,a book and complete outfit for ,sixty-,one ,experiments4 ,,fun ,,with ,,electricity4 ,a book and complete outfit for ,sixty ,experiments4 ,,fun ,,with ,,puzzles4 ,a book and complete outfit for ,four ,hundred ,puzzles4 ,,fun ,,with ,,soap-,,bubbles4 ,a book and complete outfit for ,fancy ,bubbles and ,films4 ,,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 ,,in ,,preparation4 ,,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 ,ask ,your ,toy ,dealer1 ,stationer1 or ,bookseller for our ,books1 ,games1 ,puzzles1 ,educational ,amusements1 ,etc4 ,thomas ,m4 ,st4 ,john1 #djg ,west #east ,st41 ,new ,york4 ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment ,containing ,,two ,,hundred ,,experiments ,,performed ,,with ,,simple1 ,,home-,,made ,,apparatus ,,by ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,author of ,fun ,with ,magnetism1 ,fun ,with ,electricity1 ,how ,two ,boys ,made ,their ,own ,electrical ,apparatus1 ,etc4 ,illustration3 ,logo ,,new ,,york ,,thomas ,m4 ,,st4 ,,john #djg ,west #east ,street #aijj ,copyright1 #aijj1 ,by ,,thomas ,m4 ,,st4 ,,john4 ,to the ,student4 ,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 ,the student is advised to begin at the beginning1 to perform the experiments in the order given1 and to understand each step before proceeding4 ,certain principles and explanations necessarily precede the practical and perhaps more interesting applications of those principles4 ,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 simple1 inexpensive apparatus2 in fact1 the student should make at least a part of his own apparatus4 ,for the benefit of those who wish to make their own apparatus1 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 ,,thomas ,m4 ,,st4 ,,john4 ,new ,york1 ,april1 #aijj4 ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment ,,part ,i--,,magnetism ,,part ,,ii--,,static ,,electricity ,,part ,,iii--,,current ,,electricity ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment4 ,,table ,,of ,,contents4 ,,part ,i4--,,magnetism4 ,,page4 ,,chapter ,i4 ,iron and ,steel #c ,introduction4--,kinds of iron and steel4--,exp4 #a1 ,to study steel4--,discussion4--,exp4 #b1 ,to find whether a piece of hard steel can be made softer4--,annealing4--,exp4 #c1 ,to find whether a piece of annealed steel can be hardened4--,hardening2 ,tempering4--,exp4 #d1 ,to test the hardening properties of soft iron4--,discussion4 ,,chapter ,,ii4 ,magnets #g ,kinds of magnets4--,exp4 #e1 ,to study the horseshoe magnet4--,poles2 ,equator4--,exp4 #f1 ,to ascertain the nature of substances attracted by a magnet4--,magnetic ,bodies2 ,diamagnetic ,bodies4--,practical ,uses of ,magnets4--,exp4 #g1 ,to study the action of magnetism through various substances4--,magnetic ,transparency2 ,magnetic ,screens4--,exp4 #h1 ,to find whether a magnet can give magnetism to a piece of steel4--,discussion2 ,bar ,magnets4--,exp4 #i1 ,to make small magnets4--,exp4 #aj1 ,to find whether a freely-swinging bar magnet tends to point in any particular direction4--,north-seeking ,poles2 ,south-seeking ,poles2 ,pointing ,power4--,the ,magnetic ,needle2 ,the ,compass4--,exp4 #aa1 ,to study the action of magnets upon each other4--,exp4 #ab1 ,to study the action of a magnet upon soft iron4--,laws of ,attraction and ,repulsion4--,exp4 #ac1 ,to learn how to produce a desired pole at a given end of a piece of steel4--,rule for ,poles4--,our ,compass4--,review2 ,magnetic ,problems4--,exp4 #ad1 ,to find whether the poles of a magnet can be reversed4--,discussion2 ,reversal of ,poles4--,exp4 #ae1 ,to find whether we can make a magnet with two ,n poles4--,exp4 #af1 ,to study the bar magnet with two ,n poles4--,discussion2 ,consequent ,poles4--,exp4 #ag1 ,to study consequent poles4 ,exp4 #ah1 ,to study the theory of magnetism4--,theory of ,magnetism2 ,magnetic ,saturation4--,exp4 #ai1 ,to find whether soft iron will permanently retain magnetism4--,retentivity or ,coercive ,force2 ,residual ,magnetism4--,exp4 #bj1 ,to test the retentivity of soft steel4--,discussion4--,exp4 #ba1 ,to test the retentivity of hard steel4--,exp4 #bb1 ,to test the effect of heat upon a magnet4--,discussion4--,exp4 #bc1 ,to test the effect of breaking a magnet4--,discussion4 ,,chapter ,,iii4 ,induced ,magnetism #bj ,exp4 #bd1 ,to find whether we can magnetize a piece of iron without touching it with a magnet4--,temporary ,magnetism2 ,induced ,magnetism4--,exp4 #be1 ,to find whether a piece of steel can be permanently magnetized by induction4--,exp4 #bf1 ,to study the inductive action of a magnet upon a piece of soft iron4--,polarization2 ,pole ,pieces4--,exps4 #bg-cj1 ,to study pole pieces4 ,,chapter ,,iv4 ,the ,magnetic ,field #bc ,exp4 #ca1 ,to study the space around the magnet1 in which pieces of iron become temporary magnets by induction4--,discussion2 ,the ,magnetic ,field4--,exp4 #cb1 ,to study the magnetic field of a bar magnet4--,magnetic ,figures2 ,lines of ,magnetic ,force4--,exps4 #cc-cg1 ,to study the magnetic fields of various combinations of bar magnets4--,exps4 #ch-ci1 ,to study the lifting power of combinations of bar magnets4--,discussion2 ,compound ,magnets4--,exps4 #dj-db1 ,to study the magnetic field of the horseshoe magnet4--,discussion2 ,resistance to ,lines of ,force4--,exp4 #dc1 ,to show that lines of force are on all sides of a magnet4--,discussion4--,exp4 #dd1 ,to study a horseshoe magnet with movable poles4--,discussion2 ,advantages of ,horseshoe ,magnets4 ,,chapter ,v4 ,terrestrial ,magnetism #ca ,the ,magnetism of the ,earth4--,declination4--,exp4 #de1 ,to study the lines of force above and below a bar magnet placed horizontally4--,the ,dip or ,inclination of the ,magnetic ,needle4--,exp4 #df1 ,to study the dip or inclination of the magnetic needle due to the action of the earth4--,discussion2 ,balancing ,magnetic ,needles4--,exps4 #dg-dh1 ,to study the inductive influence of the earth4--,discussion4--,natural ,magnets4--,exp4 #di1 ,to test the effect of twisting a wire held north and south in the earth's magnetic field4--,exp4 #ej1 ,to test for magnetism in bars of iron1 tools1 etc4 ,,part ,,ii4--,,static ,,electricity4 ,,chapter ,,vi4 ,electrification #ci ,some ,varieties of ,electricity4--,exp4 #ea-eb1 ,to study electrification by friction4--,discussion4--,electrified and ,neutral bodies4--,force2 ,resistance2 ,work2 ,potential ,energy2 ,electrification4--,heat and ,electrification4--,exps4 #ec-ed1 ,to study electrical attraction4--,discussion4--,exp4 #ee1 ,to study mutual attractions4--,mutual ,attractions4--,exps4 #ef-eh1 ,to study electrical repulsions4--,the ,carbon ,electroscope4--,discussion of ,experiments #ef1 #eg1 #eh4--;,exp4 #ei1 ,to study the electrification of glass4--,questions4--,exp4 #fj1 ,to compare the electrification produced by ebonite and flannel with that produced by glass and silk4--,discussion4--,laws4 ,,chapter ,,vii4 ,insulators and ,conductors #dg ,exps4 #fa-fc1 ,to study insulators4--,conductors4--,exp4 #fd1 ,to study conduction4--,discussion4--,exp4 #fe1 ,to study conduction4--,telegraph line using static electricity4--,discussion4--,relation between conductors and insulators4--,electrics and ,non-electrics4--,exp4 #ff1 ,to study the effect of moisture upon an insulator4--,discussion4--,exp4 #fg1 ,to test the effects of moisture upon bodies to be electrified4 ,,chapter ,,viii4 ,charging and ,discharging ,conductors #eb ,the ,electrophorus4--,exp4 #fh1 ,to learn how to use the electrophorus4--,exp4 #fi1 ,to study charging by conduction4--,exp4 #gj1 ,to study potential2 ,electromotive force4--,pressure2 ,potential2 ,electromotive force2 ,current1 ,spark4--,theories about ,electrifications4--,exp4 #ga1 ,to study some methods of discharging an electrified body4--,disruptive1 ,conductive and ,convective ,discharges4--,exp4 #gb1 ,to study intermittent or step-by-step discharges4--,discussion4--,exp4 #gc1 ,to ascertain the location of the charge upon an electrified conductor4--,discussion4--,hollow and ,solid ,conductors4--,exp4 #gd1 ,to study the effect of points upon a charged conductor4--,electric ,density4--,electric ,wind4 ,,chapter ,,ix4 ,induced ,electrification #fj ,electric ,fields2 ,lines of ,force4--,exp4 #ge1 ,to study electric induction4--,electric ,polarization2 ,theory of ,induction4--,exp4 #gf1 ,to learn how to charge a body by induction4--,free and ,bound ,electrifications4--,exp4 #gg1 ,to show that a neutral body is polarized before it is attracted by a charged one4--,polarization ,precedes ,attraction4--,exp4 #gh1 ,to find whether electric induction will act through an insulator4--,dielectrics4--,exp4 #gi1 ,to find whether a polarized conductor can act inductively upon another conductor4--,successive ,induction4--,inductive ,capacity4--,exp4 #hj1 ,to study the action of the electrophorus4--,discussion4--,details of action4--,exp4 #ha1 ,to see1 hear1 and feel the results of inductive influence and polarization4--,discussion4 ,,chapter ,x4 ,condensation of ,electrification #fh ,exp4 #hb1 ,to find whether a large surface will hold more electrification than a small one4--,electrical ,capacity4--,exp4 #hc1 ,to find whether the capacity of a given conductor can be increased without increasing its size4--,condensation2 ,condensers4--,the ,leyden ,jar4--,fulminating ,panes4--,induction ,coil ,condensers4--,submarine ,cables4--,exp4 #hd1 ,to study the condensation of electrification4--,discussion4--,exp4 #he1 ,to study the action of the condenser4--,discussion4--,exp4 #hf1 ,to study the effect of electrical discharges upon the human body4--,shocks2 ,dischargers4--,exps4 #hg-hh1 ,to show the strong attraction between opposite electrifications in the condenser4--,discussion4--,exp4 #hi1 ,to show how the condenser may be slowly discharged4--,the ,electric ,chime4--,exp4 #ij1 ,to ascertain the location of a charge in a condenser4--,discussion4--,exp4 #ia1 ,to find whether any electrification remains in the condenser after it has once been discharged4--,residual ,charge4--,exp4 #ib1 ,to study successive condensation2 the chime cascade4--,discussion4 ,,chapter ,,xi4 ,electroscopes #gg ,electroscopes4--,our leaf electroscope4--,exp4 #ic1 ,to study the leaf electroscope2 charging by conduction4--,discussion4--,exp4 #ie1 ,to learn some uses of the electroscope4--,discussion4--,the ,proof-plane4 ,,chapter ,,xii4 ,miscellaneous ,experiments #ha ,exp4 #if1 ,to show that friction always produces two kinds of electrification4--,discussion4--,exp4 #ig1 ,to show successive sparks4--,exp4 #ih1 ,to show to the eye the strong attraction between a charged and a neutral body4--,exp4 #ii1 ,to feel the strong attraction between a charged and a neutral body4--,exp4 #ajj1 ,the human body a frictional electric machine4--,static ,electric ,machines4 ,,chapter ,,xiii4 ,atmospheric ,electricity #hd ,atmospheric ,electricity4--,lightning4--,thunder4--, lightning ,rods4--,causes of ,atmospheric ,electricity4--,st4 ,elmo's ,fire4--,aurora ,borealis4 ,,part ,,iii4--,,current ,,electricity4 ,,chapter ,,xiv4 ,,construction ,,and ,,use ,,of ,,apparatus #hi ,exp4 #aja1 ,to study the effect of the electric current upon the magnetic needle4--,electrical ,connections4--,current ,detectors4--,exp4 #ajb1 ,to study the construction and use of a simple key4--,exp4 #ajc1 ,to study the construction and use of a simple current reverser4--,exp4 #ajd1 ,to study the simple current detector4--,exp4 #aje1 ,to study the construction and use of the simple galvanoscope4--,discussion2 ,true ,readings4--,exp4 #ajf1 ,to study the construction and use of a simple astatic needle4--,astatic ,needles4--,exp4 #ajg1 ,to study the construction and use of a simple astatic galvanoscope4--,astatic ,galvanoscopes4 ,,chapter ,,xv4 ,,galvanic ,,cells ,,and ,,batteries #ajb ,exp4 #ajh1 ,to study the effect of dilute sulphuric acid upon carbon and various metals4--,to amalgamate4--,dilute sulphuric acid4--,discussion4--,exp4 #aji1 ,to study the effect of dilute sulphuric acid upon various combinations of metals4--,discussion4--,exp4 #aaj1 ,to study the construction of a simple ,voltaic or ,galvanic cell4--,the ,electric ,current4--,source of the ,electrification4--,the ,electric ,circuit2 ,open and ,closed ,circuits4--,plates or ,elements4--,direction of ,current4--,poles or ,electrodes4--,chemical ,action in the ,simple ,galvanic ,cell4--,action in ,cell ,using ,impure ,zinc2 ,action ,using ,pure ,zinc4--,exp4 #aaa1 ,to see what is meant by local currents in the cell4--,local ,action2 ,local ,currents4--,reasons for ,amalgamating ,zinc ,plates4--,exp4 #aab1 ,to study the single-fluid ,galvanic ,cell4--,the ,simple ,cell4--,polarization of ,cells4--,effects of ,polarization4--,remedies for ,polarization2 ,depolarizers4--,exp4 #aac1 ,to study the two-fluid ,galvanic ,cell4--,setting ,up the ,two-,fluid ,cell4--,care of ,two-,fluid ,cell4--,copper ,sulphate ,solution4--,chemical ,action in the ,two-,fluid ,cell4--,various ,galvanic ,cells2 ,open and ,closed ,circuit ,cells4--,the ,leclanch ,cell--,dry ,cells4--,the ,bichromate of ,potash ,cell4--,the ,daniell ,cell4--,the ,gravity ,cell4 ,,chapter ,,xvi4 ,,the ,,electric ,,circuit #aae ,exp4 #aad1 ,to see what is meant by divided circuits and shunts4--,divided ,circuits2 ,shunts4--,exp4 #aae1 ,to see what is meant by short circuits4 ,,chapter ,,xvii4 ,,electromotive ,,force #aag ,electromotive ,force4--,unit of ,e4 ,m4 ,f42 ,the ,volt4--,exp4 #aaf1 ,to see whether the ,e4 ,m4 ,f4 of a cell depends upon the materials used in its construction4--,discussion4--,electromot ive ,series4--,exp4 #aag1 ,to see whether the ,e4 ,m4 ,f4 of a cell depends upon its size4--,discussion4 ,,chapter ,,xviii4 ,,electrical ,,resistance #abj ,resistance4--,exp4 #aah1 ,to study the general effect of resistance upon a current4--,external ,resistance2 ,internal ,resistance2 ,unit of ,resistance2 ,the ,ohm4--,resistance ,coils2 ,resistance ,boxes4--,simple ,resistance ,coil4--,exp4 #aai1 ,to test the power of various substances to conduct galvanic electricity4--,conductors and ,nonconductors4--,exp4 #abj1 ,to find the effect of sulphuric acid upon the conductivity of water4--,internal ,resistance4--,exp4 #aba1 ,to find what effect the length of a wire has upon its electrical resistance4--,discussion4--,exp4 #abb1 ,to find what effect the size 7area of cross-section7 of a wire has upon its electrical resistance4--,discussion4--,exp4 #abc1 ,to compare the resistance of a divided circuit with the resistance of one of its branches4 ,discussion4--,exp4 #abd1 ,to study the effect of decreasing the resistance in one branch of a divided circuit4--,current in ,divided ,circuits4 ,,chapter ,,xix4 ,,measurement ,,of ,,resistance #acj ,exp4 #abe1 ,to study the construction and use of a simple ,wheatstone's ,bridge4--,the ,simple ,bridge4--,equipotential ,points4--,example4--,exp4 #abf1 ,to measure the resistance of a wire by means of ,wheatstone's ,bridge2 the bridge method4--,allowances for ,connections4--,exps4 #abg-acg1 ,to measure the resistances of various wires1 coils1 etc41 by the bridge method4--,table4--,exp4 #ach1 ,to study the effect of heat upon the resistance of metals4--,effect of ,heat upon ,resistance4--,exp4 #aci1 ,to measure the resistance of a wire by the method of substitution4--,simple ,rheostat4--,exp4 #adj1 ,to measure the ,e4 ,m4 ,f4 of a cell by comparison with the two-fluid cell4--,exp4 #ada1 ,to measure the internal resistance of a cell by the method of opposition4 ,,chapter ,,xx4 ,,current ,,strength #adb ,strength of ,current4--,unit of ,current ,strength2 ,the ,ampere4--,measurement of ,current ,strength4--,the ,tangent ,galvanometer4--,the ,ammeter4--,the ,voltameter4--,unit of ,quantity2 ,the ,coulomb4--,electrical ,horse-power2 ,the ,watt4--,ohm's ,law4--,internal ,resistance and ,current ,strength4--,exp4 #adb1 ,having a cell with large plates1 to find how the strength of the current is affected by changes in the position of the plates1 the external resistance being small4--,exp4 #adc1 ,same as ,exp4 #adb1 but with small plates4--,exp4 #add1 ,to find whether the changes in current strength1 due to changes in internal resistance1 are as great when the external resistance is large1 as they are when the external resistance is small4--,discussion1 with examples4--,arrangement of ,cells and ,current ,strength4--,cells in ,series4--,cells ,abreast4--,exp4 #ade1 ,to find the best way to join two similar cells when the external resistance is small4--,exp4 #adf1 ,to find the best way to join two similar cells when the external resistance is large4--,best ,arrangement of ,cells4 ,,chapter ,,xxi4 ,,chemical ,,effects ,,of ,,the ,,electric ,,current #aea ,chemical ,action and ,electricity4--,electrolysis4--,exp4 #adg1 ,to study the electrolysis of water4--,composition of ,water4--,electromotive ,force of ,polarization4--,exp4 #adh1 ,to coat iron with copper4--,exp4 #adi1 ,to study the electrolysis of a solution of copper sulphate4--,electroplating4--,exp4 #aej1 ,to study the chemistry of electroplating4--,discussion4--,electrot yping4--,voltameters4--,exp4 #aea1 ,to study the construction and action of a simple storage cell4--,secondary or ,storage ,cells4 ,,chapter ,,xxii4 ,,electromagnetism #aeh ,electromagnetism4--,exp4 #aeb1 ,to study the lines of force about a straight wire carrying a current4--,ampere's ,rule4--,lines of ,force ,about ,parallel ,wires4--,exp4 #aec1 ,to study the lines of force about a coil of wire like that upon the galvanoscope4--,exp4 #aed1 ,to study the magnetic field about a small coil of wire4--,coils4--,polarity of ,coils4--,exp4 #aee1 ,to test the attracting and sucking power of a magnetized coil or helix4--,exp4 #aef1 ,to find whether a piece of steel can be permanently magnetized by an electric current4--,exp4 #aeg1 ,to study the effect of a piece of iron placed inside of a magnetized coil of wire4 ,,chapter ,,xxiii4 ,,electromagnets #afe ,electromagnets4--,cores of ,electromagnets4--,exps4 #aeh-afc1 ,to study straight electromagnets2 ,lifting power2 ,residual magnetism of core2 ,magnetic tick2 ,magnetic figures2 ,magnetic field4--,horseshoe ,electromagnets4--,use of ,yoke4--,experimental ,magnets4--,method of ,joining ,coils4--,exps4 #afd-agc1 ,to study horseshoe electromagnets2 ,to test the poles2 ,to study the inductive action of one core upon the other2 ,magnetic figures2 ,permanent ,magnetic ,figures2 ,lifting power2 ,residual magnetism when magnetic circuit is closed4--,closed ,magnetic ,circuits4 ,,chapter ,,xxiv4 ,,thermoelectricity #age ,exp4 #agd1 ,to find whether electricity can be produced by heat4--,home-made ,thermopile4--,thermoelectricity4--,pelt ier ,effect4--,thermopiles4 ,,chapter ,,xxv4 ,,induced ,,currents #agh ,electromagnetic ,induction4--,exp4 #age1 ,to find whether a current can be generated with a bar magnet and a hollow coil of wire4--,discussion4--,induced ,currents and ,work4--,exp4 #agf1 ,to find whether a current can be generated with a bar magnet and a coil of wire having an iron core4--,exp4 #agg1 ,to find whether a current can be generated with a horseshoe magnet and a coil of wire having an iron core4--,induced ,currents and ,lines of ,force4--,exp4 #agh1 ,to find whether a current can be generated with an electromagnet and a hollow coil of wire4--,exp4 #agi1 ,to find whether a current can be generated with an electromagnet and a coil of wire having an iron core4--,discussion of ,exps4 #agh-agi4--;,exp4 #ahj1 ,to study the effect of starting or stopping a current near a coil of wire or other closed circuit4--,exp4 #aha1 ,to study the effect of starting or stopping a current in a coil placed inside of another coil4--,discussion of ,exps4 #ahj-aha4--;,direction of ,induced ,current4--,laws of ,induction4--,primary and ,secondary ,currents4--,exp4 #ahb1 ,to see what is meant by alternating currents4--,direct and ,alternating ,currents4--,self-induction2 ,extra ,currents4 ,,chapter ,,xxvi4 ,,the ,,production ,,of ,,motion ,,by ,,currents #ahg ,currents and ,motion4--,exp4 #ahc1 ,motion produced with a hollow coil and a piece of iron4--,exp4 #ahd1 ,motion with hollow coil and bar magnet4--,exp4 #ahe1 ,motion with electromagnet and piece of iron4--,exp4 #ahf1 ,motion with electromagnet and bar magnet4--,exp4 #ahg1 ,motion with electromagnet and horseshoe magnet4--,exp4 #ahh1 ,motion with two electromagnets4--,discussion of ,exps4 #ahc-ahh4--;,exp4 #ahi1 ,rotary motion with a hollow coil of wire and a permanent magnet4--,exp4 #aij1 ,rotary motion with an electromagnet and a permanent magnet4--,discussion of ,exps4 #ahi-aij4 ,,chapter ,,xxvii4 ,,applications ,,of ,,electricity #aib ,things ,electricity ,can ,do4--,exp4 #aia1 ,to study the action of a simple telegraph sounder4--,discussion4--,telegraph ,line2 ,connections4--,operation of ,line4--,exp4 #aib1 ,to study the action of the relay on telegraph lines4--,the ,relay4--,exp4 #aic1 ,to study the action of a two-pole telegraph instrument4--,exp4 #aid1 ,to study the action of a simple single needle telegraph instrument4--,exp4 #aie1 ,to study the action of a simple automatic contact breaker1 or current interrupter4--,automatic ,current ,interrupters4--,exp4 #aif1 ,to study the action of a simple electric bell1 or a buzzer4--,electric ,bells and ,buzzers4--,exp4 #aig1 ,to study the action of a simple telegraph recorder4--,exp4 #aih1 ,to study the action of a simple annunciator4--,discussion4--,exp4 #aii1 ,to study the shocking effects of the extra current4 ,induction ,coils4--,action of ,induction ,coils4--,transformers4--,the ,dynamo4--,the ,electric ,motor4--,exp4 #bjj1 ,to study the action of the telephone4--,the ,telephone4--,the ,bell1 or ,magneto-transmitter4--,the ,receiver4--,the ,carbon ,transmitter4--,induction ,coils in ,telephone ,work4--,electric ,lighting and ,heating4--,arc ,lamps4--,the ,incandescent ,lamp4 ,,chapter ,,xxviii4 ,,wire ,,tables #bjh ,,apparatus ,,list #baj ,,index #bae ,,magnetism ,a ,few ,dont's for ,young ,students4 ,don't fail to make at least a part of your own apparatus2 there is a great deal of satisfaction and pleasure in home-made apparatus4 ,don't experiment in all parts of the house1 if working at home4 ,fit up a small room for your den1 and carry the key4 ,don't begin an experiment before you really know what you are trying to do4 ,read the directions carefully1 then begin4 ,don't rush through an experiment to see what happens at the end of it4 ,see what happens at each step1 and notice every little thing that seems unusual4 ,don't try to do all parts of an experiment at the same time4 ,understand one part1 then proceed4 ,don't fail to ask yourself questions1 and form an opinion about the results of an experiment before you read what the author has to say about it4 ,don't fail to keep a note-book4 ,keep all the data and arithmetical work for future reference4 ,don't leave the apparatus around after you have finished the day's work4 ,,part ,i4--,,magnetism4 ,,chapter ,i4 ,,iron ,,and ,,steel4 #a4 ,introduction4 ,we should know something about iron and steel at the start1 because we are to use them in nearly every experiment4 ,the success with some of the experiments will depend largely upon the quality of the iron and steel used4 ,when we buy a piece of iron from the blacksmith1 we get more than iron for our money4 ,hidden in this iron are other substances 7carbon1 phosphorus1 silicon1 etc471 which are called impurities by the chemist4 ,if all the impurities were taken out of the iron1 however1 we should have nothing but a powder left2 this the chemist would call chemically pure iron1 but it would be of no value whatever to the blacksmith or mechanic4 ,the impurities in iron and steel are just what are needed to hold the particles of iron together1 and to make them valuable4 ,by regulating the amount of carbon1 phosphorus1 etc41 manufacturers can make different grades and qualities of iron or steel4 ,when carbon is united with the pure iron1 we get what is commonly called iron4 #b4 ,kinds of ,iron and ,steel4 ,cast iron is the most impure form of iron4 ,stoves1 large kettles1 flatirons1 etc41 are made of cast iron4 ,wrought iron is the purest form of commercial iron4 ,it usually comes in bars or rods4 ,blacksmiths hammer these into shapes to use on wagons1 machinery1 etc4 ,steel contains more carbon than wrought iron1 and less than cast iron4 ,soft steel is very much like wrought iron in appearance1 and it is used like wrought iron4 ,hard steel has more carbon in it than soft steel4 ,tools1 needles1 etc41 are made of this4 ,,experiment #a4 ,to study steel4 ,apparatus4 ,a steel sewing-needle 7,no4 #a74;,a ,footnote ,a3 ,,note4 ,each piece of apparatus used in the following experiments has a number4 ,see ,apparatus list at the back of this book for details4 ,the numbers given under ,apparatus1 in each experiment1 refer to this list4 #c4 ,directions4 7,a7 ,bend a sewing-needle until it breaks4 ,is the steel brittle8 7,b7 ,if you have a file1 test the hardness of the needle4 #d4 ,discussion4 ,needle steel is usually of good quality4 ,it will be very useful in many experiments4 ,do you know how to make the needle softer8 ,,experiment #b4 ,to find whether a piece of hard steel can be made softer4 ,illustration3 ,fig4 #a4 ,apparatus4 ,fig4 #a4 ,a needle2 a cork1 ,ck 7,no4 #b72 lighted candle 7,no4 #c74 ,the bottom of the candle should be warmed and stuck to a pasteboard base4 #e4 ,directions4 7,a7 ,stick the point of the needle into ,ck1 ,fig4 #a1 then hold the needle in the flame until it is red-hot4 7,the upper part of the flame is the hottest47 7,b7 ,allow the needle to cool in the air4 7,c7 ,test the brittleness of the steel by bending it4 ,test its hardness with a file 7,exp4 #a74 #f4 ,annealing4 ,this process of softening steel by first heating it and then allowing it to cool slowly1 is called annealing4 ,all pieces of iron and steel are1 of course1 hard2 but you have learned that some pieces are much harder than others4 ,,experiment #c4 ,to find whether a piece of annealed steel can be hardened4 ,apparatus4 ,the needle just annealed and bent2 cork1 etc41 of ,exp4 #b2 a glass of cold water4 #g4 ,directions4 7,a7 ,heat the bent portion of the needle in the candle flame 7,exp4 #b7 until it is red-hot1 then immediately plunge the needle into the water4 7,b7 ,test its brittleness and hardness1 as in ,exp4 #b4 #h4 ,hardening2 ,tempering4 ,good steel is a very valuable material2 the same piece may be made hard or soft at will4 ,by sudden cooling1 the steel becomes very hard4 ,this process is called hardening1 but it makes the steel too brittle for many purposes4 ,by tempering is meant the letting down of the steel from the very hard state to any desired degree of hardness4 ,this may be done by suddenly cooling the steel when at the right temperature1 it not being hot enough to produce extreme hardness4 7,the approximate temperature of hot steel can be told by the colors which form on a clean surface4 ,these are due to oxides which form as the steel gradually rises in temperature47 ,,experiment #d4 ,to test the hardening properties of soft iron4 ,apparatus4 ,a piece of soft iron wire about #c in4 7#g4e cm47 long 7,no4 #d72 the candle1 water1 etc41 of ,exp4 #c4 #i4 ,directions4 7,a7 ,test the wire by bending and filing4 7,b7 ,heat the wire in the candle flame as you did the needle 7,fig4 #a71 then cool it suddenly with the water4 ,study the results4 #aj4 ,discussion4 ,soft iron contains much less carbon than steel4 ,the hardening quality which steel has is due to the proper amount of carbon in it4 ,if you have performed the experiments so far1 you will be much more able to understand later ones1 and you will see why we are obliged to use soft iron for some parts of electrical apparatus1 and hard steel for other parts4 ,,chapter ,,ii4 ,,magnets4 #aa4 ,kinds of ,magnets4 ,among the varieties of magnets which we shall discuss1 are the natural1 artificial1 temporary1 permanent1 bar1 horseshoe1 compound1 and electro-magnet4 ,illustration3 ,fig4 #b4 ,the ,horseshoe ,magnet1 ,h ,m 7,fig4 #b71 is the most popular form of small magnets4 ,the red paint has nothing to do with the magnetism4 ,the piece1 ,a1 is called its armature1 and is made of soft iron1 while the magnet itself should be made of the best steel1 properly hardened4 ,the armature should always be in place when the magnet is not in use1 and care should be taken to thoroughly clean the ends of the magnet before replacing the armature4 ,the horseshoe magnet is artificial1 and it is called a permanent magnet1 because it retains its strength for a long time1 if properly cared for4 ,,experiment #e4 ,to study the horseshoe magnet4 ,apparatus4 ,fig4 #b4 ,the horseshoe magnet1 ,h ,m 7,no4 #af74 #ab4 ,directions4 7,a7 ,remove the armature1 ,a1 from the magnet1 then move ,a about upon ,h ,m to see 7#a7 if the curved part of ,h ,m has any attraction for ,a1 and 7#b7 to see if there is any attraction for ,a at points between the curve and the extreme ends of ,h ,m4 #ac4 ,poles2 ,equator4 ,the ends of a magnet are called its poles4 ,the end marked with a line1 or an ,n1 should be the north pole4 ,the unmarked end is the south pole4 ,n and ,s are abbreviations for north and south4 ,the central part1 at which there seems to be no magnetism1 is called the neutral point or equator4 ,,experiment #f4 ,to ascertain the nature of substances attracted by a magnet4 ,apparatus4 ,the horseshoe magnet1 ,h ,m 7,fig4 #b72 silver1 copper1 and nickel coins2 iron filings 7,no4 #ag71 nails1 tacks1 pins1 needles2 pieces of brass1 lead1 copper1 tin1 etc4 7,ordinary tin is really sheet iron covered with tin47 ,use the various battery plates for the different metals4 #ad4 ,directions4 7,a7 ,try the effect of ,h ,m upon the above substances1 and upon any other substances thought of4 #ae4 ,magnetic ,bodies2 ,diamagnetic ,bodies4 ,substances which are attracted by a magnet are said to be magnetic4 ,a piece of soft iron wire is magnetic1 although not a magnet4 ,very strong magnets show that nickel1 oxygen1 and a few other substances not containing iron1 are also magnetic4 ,some elements are actually repelled by a powerful magnet2 these are called diamagnetic bodies4 ,it is thought that all bodies are more or less affected by a magnet4 #af4 ,practical ,uses of ,magnets4 ,many practical uses are made of magnets1 such as the automatic picking out of small pieces of iron from grain before it is ground into flour1 and the separation of iron from other metals1 etc4 ,the most important uses of magnets are in the compass and in connection with the electric current1 as in machines like dynamos and motors4 7,see experiments with electro-magnets47 ,,experiment #g4 ,to study the action of magnetism through various substances4 ,apparatus4 ,horseshoe magnet1 ,h ,m2 a sheet of stiff paper2 pieces of sheet glass1 iron1 zinc1 copper1 lead1 thin wood1 etc42 sewing-needle4 7,a tin box may be used for the iron1 and battery plates for the other metals47 #ag4 ,directions4 7,a7 ,place the needle upon the paper and move ,h ,m about immediately under it4 7,b7 ,in place of the paper1 try wood1 glass1 etc4 7,c7 ,invent an experiment to show that magnetism will act through your hand4 7,d7 ,invent an experiment to show that magnetism will act through water4 #ah4 ,magnetic ,transparency2 ,magnetic ,screens4 ,substances1 like paper1 are said to be transparent to magnetism4 ,iron does not allow magnetism to pass through it as readily as paper and glass2 in fact1 thick iron may act as a magnetic screen4 ,,experiment #h4 ,to find whether a magnet can give magnetism to a piece of steel4 #ai4 ,note4 ,you have seen that the horseshoe magnet can lift nails1 iron filings1 etc42 you have used this lifting power to show that the magnet was really a magnet1 and not merely an ordinary piece of iron painted red4 ,can we give some of its magnetism to another piece of steel8 ,can we pass the magnetism along from one piece of steel to another8 ,apparatus4 ,the horseshoe magnet1 ,h ,m2 two sewing-needles that have never been near a magnet2 iron filings4 #bj4 ,directions4 7,a7 ,test the needles for magnetism with the iron filings1 and be sure that they are not magnetized4 7,b7 ,remove the armature1 ,a1 from ,h ,m1 then touch the point of one of the needles to one pole of ,h ,m4 7,c7 ,lay ,h ,m aside1 and test the point of the needle for magnetism4 7,d7 ,if you find that the needle is magnetized1 rub its point upon the point of the other needle2 then test the point of the second needle for magnetism4 #ba4 ,discussion2 ,bar ,magnets4 ,a piece of good steel will attract iron after merely touching a magnet4 ,to thoroughly magnetize it1 however1 a mere touch is not sufficient4 ,there are several ways of making magnets1 depending upon the size1 shape1 and strength desired4 ,for these experiments1 the student needs only a good horseshoe magnet1 or1 better still1 the electro-magnets described later2 with these any number of small magnets may be made4 ,straight magnets are called bar magnets4 ,,experiment #i4 ,to make small magnets4 ,apparatus4 ,fig4 #c4 ,the horseshoe magnet1 ,h ,m2 sewing-needles2 iron filings4 7,see ,apparatus ,book1 ,pg4 #adj1 for various kinds of steel suitable for small magnets47 #bb4 ,directions4 7,a7 ,hold ,h ,m 7,fig4 #c7 in the left hand1 its poles being uppermost4 ,grasp the point of the needle with the right hand1 and place its point upon the ,n or marked pole of ,h ,m4 7,b7 ,pull the needle along in the direction of its length 7see the arrow71 continuing the motion until its head is at least an inch from the pole4 7,c7 ,raise the needle at least an inch above ,h ,m1 lower it to its former position 7,fig4 #c71 and repeat the operation #c or #d times4 ,do not slide the needle back and forth upon the pole1 and be careful not to let it accidentally touch the ,s pole of ,h ,m4 7,d7 ,test the needle for magnetism with iron filings1 and save it for the next experiment4 ,illustration3 ,fig4 #c4 ,illustration3 ,fig4 #d4 ,,experiment #aj4 ,to find whether a freely-swinging bar magnet tends to point in any particular direction4 ,apparatus4 ,fig4 #d4 ,a magnetized sewing-needle 7,exp4 #i72 the flat cork1 ,ck 7,no4 #b72 a dish of water4 7,you can use a tumbler1 but a larger dish is better47 #bc4 ,note4 ,an oily sewing-needle may be floated without the cork by carefully lowering it to the surface of the water4 ,all magnets1 pieces of iron and steel1 knives1 etc41 should be removed from the table when trying such experiments4 ,why8 #bd4 ,directions4 7,a7 ,place the little bar magnet 7the needle7 upon the floating cork1 turn it in various positions1 and note the result4 #be4 ,north-seeking ,poles2 ,south-seeking ,poles2 ,pointing ,power4 ,it should be noted that the point swings to the north1 provided the needle is magnetized as directed in ,exp4 #i4 ,this is called the north1 or north-seeking pole4 ,the ,n-seeking pole is sometimes called the marked pole4 ,for convenience1 we shall hereafter speak of the ,n-seeking pole as the ,n pole1 and of the ,s-seeking pole as the ,s pole4 ,we shall hereafter speak of the tendency which a bar magnet has to point ,n and ,s1 as its pointing power4 ,an unmagnetized needle has no pointing power4 #bf4 ,the ,magnetic ,needle2 ,the ,compass4 ,a small bar magnet1 supported upon a pivot1 or suspended so that it may freely turn1 is called a magnetic needle4 ,when balanced upon a pivot having under it a graduated circle marked ,n1 ,e1 ,s1 ,w1 etc41 it is called a compass4 ,these have been used for centuries4 7,see ,apparatus ,book for ,home-made ,magnetic ,needles47 ,,experiment #aa4 ,to study the action of magnets upon each other4 ,apparatus4 ,two magnetized sewing-needles 7magnetized as in ,exp4 #i72 the cork1 etc41 of ,exp4 #aj4 #bg4 ,directions4 7,a7 ,float each little bar magnet 7needles7 separately to locate the ,n poles4 7,b7 ,leave one magnet upon the cork1 and with the hand bring the ,n pole of the other magnet immediately over the ,n pole of the floating one4 ,note the result4 7,c7 ,try the effect of two ,s poles upon each other4 7,d7 ,what is the result when a ,n pole of one is brought near a ,s pole of the other8 ,,experiment #ab4 ,to study the action of a magnet upon soft iron4 ,apparatus4 ,a magnetized sewing-needle2 cork1 etc41 of ,exp4 #aj2 a piece of soft iron wire1 #c in4 long2 iron filings4 #bh4 ,directions4 7,a7 ,test the wire for magnetism with filings4 ,be sure that it is not magnetized4 ,if it shows any magnetism1 twist it thoroughly before using4 7,exp4 #ai47 7,b7 ,float the magnetized needle 7,exp4 #aj71 then bring the end of the wire near one pole of the needle and then near the other pole4 7,c7 ,place the wire upon the cork1 hold the needle in the hand and experiment4 #bi4 ,laws of ,attraction and ,repulsion4 ,from experiments #aa and #ab are derived these laws3 7#a7 ,like poles repel each other2 7#b7 ,unlike poles attract each other2 7#c7 ,either pole attracts and is attracted by unmagnetized iron or steel4 ,the attraction between a magnet and a piece of iron or steel is mutual4 ,attraction1 alone1 simply indicates that at least one of the bodies is magnetized2 repulsion proves that both are magnetized4 ,,experiment #ac4 ,to learn how to produce a desired pole at a given end of a piece of steel4 ,apparatus4 ,same as in ,exp4 #i4 #cj4 ,directions4 7,a7 ,magnetize a sewing-needle 7,exp4 #i7 by rubbing it upon the ,n pole of ,h ,m from point to head4 ,float it and locate its ,n pole4 7,b7 ,take another needle that has not been magnetized1 and rub it on the same pole 7,n7 from head to point4 ,locate its ,n pole4 7,c7 ,magnetize another needle by rubbing it from point to head upon the ,s pole of ,h ,m2 locate its ,n pole4 ,can you now determine1 beforehand1 how the poles of the needle magnet will be arranged8 #ca4 ,rule for ,poles4 ,the end of a piece of steel which last touches a ,n pole of a magnet1 for example1 becomes a ,s pole4 #cb4 ,our ,compass 7,no4 #ah74 ,while the floating magnetic needle described in ,exp4 #aj1 and shown in ,fig4 #d1 does very well1 it will be found more convenient to use a compass whenever poles of pieces of steel are to be tested4 ,fig4 #e shows merely the cover of the box which serves as a base for the magnetic needle furnished4 ,we shall hereafter speak of this apparatus as our compass1 ,o ,c4 7,see ,apparatus ,book1 ,chap4 ,,vii1 for various forms of home-made magnetic needles and compasses47 #cc4 ,review2 ,magnetic ,problems4 ,to be sure that you understand and remember what was learned in ,exp4 #aa1 do these problems3 #a4 ,using the ,s pole of the horseshoe magnet1 magnetize a needle so that its head will become a ,n pole4 ,test with floating cork1 as in ,exp4 #aa4 #b4 ,using the ,n pole of the horseshoe magnet1 magnetize a needle so that its head shall be a ,s pole4 ,test4 #c4 ,magnetize two needles1 one on the ,n and one on the ,s pole of the horseshoe magnet1 in such a way that the two points will repel each other4 ,test4 ,if the student cannot do these little problems at once1 and test the results satisfactorily to himself1 he should study the previous experiments again before proceeding4 ,illustration3 ,fig4 #e4 ,illustration3 ,fig4 #f4 ,,experiment #ad4 ,to find whether the poles of a magnet can be reversed4 ,apparatus4 ,fig4 #f4 ,the horseshoe magnet1 ,h ,m2 a thin wire nail1 ,w ,n1 #b in4 7#e cm47 long2 a piece of stiff paper1 cut as shown1 to hold ,w ,n2 thread with which to suspend the paper2 compass1 ,o ,c 7,no4 #ah74 #cd4 ,directions4 7,a7 ,magnetize ,w ,n so that its point shall be a ,s pole4 ,test with ,o ,c to make sure that you are right4 7,b7 ,swing ,w ,n in the paper 7,fig4 #f71 then slowly bring the ,s pole of ,h ,m near its point4 ,note result4 7,c7 ,quickly bring the ,s pole of ,h ,m near the point4 ,is ,w ,n still repelled8 ,has its ,s pole been reversed8 #ce4 ,discussion2 ,reversal of ,poles4 ,the poles of weak magnets may be easily reversed4 ,this often occurs when the apparatus is mixed together4 ,it is always best1 before beginning an experiment1 to remagnetize the pieces of steel which have already served as magnets4 ,the same may be shown by magnetizing a needle1 rubbing it first in one direction1 and then in another upon the magnet1 testing1 in each case1 the poles produced4 ,,experiment #ae4 ,to find whether we can make a magnet with two ,n poles4 ,apparatus4 ,the horseshoe magnet1 ,h ,m2 an unmagnetized sewing-needle2 compass1 ,o ,c 7,no4 #ah74 #cf4 ,note4 ,you have already learned that the polarity of a weak magnet can be changed 7,exp4 #ad74 ,can you think of any method by which two ,n poles can be made in one piece of steel8 #cg4 ,directions4 7,a7 ,place the needle upon ,h ,m1 as in ,fig4 #g4 7,b7 ,keeping the part1 ,c1 in contact with the ,n pole of ,h ,m1 and using the ,n pole of ,h ,m as a pivot1 turn the needle end for end so that its head will be in contact with the ,s pole of ,h ,m4 7,c7 ,pull the needle straight from ,h ,m1 being careful not to slide it in either direction4 7,d7 ,test the polarity of the ends with ,o ,c 7,fig4 #e71 and save it for the next experiment4 ,illustration3 ,fig4 #g4 ,illustration3 ,fig4 #h4 ,,experiment #af4 ,to study the bar magnet with two ,n poles4 ,apparatus4 ,the strange magnet just made 7,exp4 #ae72 iron filings2 compass1 ,o ,c 7,no4 #ah74 #ch4 ,directions4 7,a7 ,sprinkle filings over the whole length of the needle and then raise it 7,fig4 #h74 7,b7 ,break the needle at its center1 and test1 with ,o ,c1 the two new ends produced at that point4 ,remember that repulsion is the test for polarity4 #ci4 ,discussion2 ,consequent ,poles4 ,iron filings cling to a magnet where poles are located4 ,in this case1 two small magnets were made in one piece of steel2 they had a common ,s pole at the center4 ,the pointing power 7 #be7 of such a magnet is very slight2 would it have any pointing power if we could make the end poles of equal strength8 ,intermediate poles1 like those in the needle just discussed1 are called consequent poles4 ,practical uses are made of consequent poles in the construction of motors and dynamos4 ,,experiment #ag4 ,to study consequent poles4 ,apparatus4 ,an unmagnetized sewing-needle2 horseshoe magnet1 ,h ,m 7,no4 #af72 iron filings 7,no4 #ag72 compass 7,no4 #ah74 #dj4 ,directions4 7,a7 ,let w1 x1 y1 and z stand for four places along the body of the needle1 w being at its point and z at its head4 7,b7 ,touch w with the ,n pole of ,h ,m1 x with the ,s pole1 y with the ,n pole1 and z with the ,s pole4 ,do not slide ,h ,m along on the needle1 just touch the needle as directed4 7,c7 ,cover the needle with filings1 then lift it4 ,,experiment #ah4 ,to study the theory of magnetism4 ,apparatus4 ,a thin bar magnet1 ,b ,m 7,no4 #ba72 iron filings2 a sheet of paper4 ,fig4 #i shows simply the edge of ,b ,m and the paper4 ,b ,m should be magnetized as directed in ,exp4 #i4 ,illustration3 ,fig4 #i4 #da4 ,directions4 7,a7 ,sprinkle some iron filings upon a sheet of paper4 7,b7 ,bring one pole of ,b ,m in contact with the filings 7,fig4 #i71 and lightly sweep it through them several times1 always in the same direction4 ,are the filings simply pushed about8 7,c7 ,do the same with a stick1 and compare the result with that produced with ,b ,m4 #db4 ,theory of ,magnetism2 ,magnetic ,saturation4 ,this bringing into line the particles of iron indicates that each particle became a magnet4 ,this experiment should aid in understanding what is thought to take place when steel is magnetized4 ,the pile of filings represents the body to be magnetized1 and each little filing stands for a particle of that body4 ,a bar of steel is composed of extremely small particles1 called molecules4 ,they are very close together and do not move from place to place as easily as the pieces of filings4 ,a magnet1 however1 when properly rubbed upon the steel1 seems to have power to make the molecules point in the same direction4 ,this produces an effect upon the whole bar4 ,each molecule of the steel is supposed to be a magnet4 ,when these little magnets pull together1 the whole bar becomes a strong magnet4 ,when a magnet is jarred1 and the little magnetized molecules are mixed again1 they pull in all sorts of directions upon each other4 ,this lessens the attraction for outside bodies4 ,steel is said to be saturated1 when it contains as much magnetism as possible4 ,a piece of steel becomes slightly longer when magnetized4 ,it is thought1 by many1 that there is a current of electricity around each molecule1 making a little magnet of it4 7,see electro-magnets47 ,,experiment #ai4 ,to find whether soft iron will permanently retain magnetism4 ,apparatus4 ,a piece of soft iron wire1 #c or #d in4 7#g4e to #aj cm47 long 7,no4 #d72 the horseshoe magnet1 ,h ,m2 iron filings2 flat cork1 ,f ,c 7,no4 #b71 and the dish of water used in ,exp4 #aj 7,fig4 #d74 #dc4 ,directions4 7,a7 ,magnetize the wire 7,exp4 #i74 ,notice that the wire clings strongly to ,h ,m4 7,b7 ,test the lifting power of the little wire magnet by seeing about how many iron filings its poles will raise4 7,c7 ,test the pointing power 7 #be7 of the wire by floating it on ,f ,c 7,fig4 #d74 7,d7 ,holding one end of the wire in the hand1 thoroughly jar it by striking the other end several times against a hard surface4 7,e7 ,test the lifting and pointing powers1 as in ,b and ,c4 #dd4 ,retentivity or ,coercive ,force2 ,residual ,magnetism4 ,soft iron loses most of its magnetism when simply removed beyond the action of a magnet4 ,we say that it does not retain magnetism2 that is1 it has very little retentivity or coercive force4 ,this is an important fact1 the action of many electric machines and instruments depending upon it4 ,a slight amount of magnetism remains1 however1 in the softest iron1 after removing it from a magnet4 ,this is called residual magnetism4 ,a piece of iron may show poles1 when tested with the compass1 although it may have almost no pointing power4 ,,experiment #bj4 ,to test the retentivity of soft steel4 ,apparatus4 ,a wire nail1 ,w ,n 7,no4 #ai72 horseshoe magnet1 ,h ,m2 iron filings2 flat cork1 ,f ,c2 the dish of water 7,exp4 #aj1 ,fig4 #d74 #de4 ,directions4 7,a7 ,with ,h ,m magnetize the nail2 this is made of soft steel4 7,b7 ,test the lifting and pointing powers of ,w ,n 7,exp4 #ai74 7,c7 ,strike ,w ,n several times with a hammer to jar it4 7,d7 ,again test its lifting and pointing powers4 #df4 ,discussion4 ,soft steel has a greater retentivity than soft iron4 ,it contains less carbon than cast or tool steel1 and is called mild steel or machinery steel4 ,you do not want soft steel for permanent magnets4 ,,experiment #ba4 ,to test the retentivity of hard steel4 ,apparatus4 ,a hard steel sewing-needle 7,no4 #a72 other articles used in ,exp4 #bj4 #dg4 ,directions4 7,a7 ,magnetize the needle with ,h ,m4 7,b7 ,test its lifting and pointing powers 7,exp4 #ai74 7,c7 ,hammer the needle and test again as in 7,b74 ,,experiment #bb4 ,to test the effect of heat upon a magnet4 ,apparatus4 ,a magnetized sewing-needle2 the candle1 cork1 etc41 of ,exp4 #b4 7,see ,fig4 #a47 #dh4 ,directions4 7,a7 ,test the needle for magnetism4 7,b7 ,stick the needle into the cork 7,fig4 #a71 and heat it until it is red-hot4 7,c7 ,test the needle again for magnetism4 7,d7 ,see if you can again magnetize the needle4 #di4 ,discussion4 ,heating a body is supposed to thoroughly stir up its molecules4 ,jarring or twisting a magnet tends to weaken it4 7,see ,exp4 #ai47 ,the molecules of steel do not move about or change their relative positions as readily as those of soft iron4 ,when the molecules of hard steel are once arranged1 by magnetizing them1 for example1 they strongly resist any outside influences which tend to mix them up again4 ,a magnet does not attract a piece of red-hot iron4 ,the particles of the hot iron are supposed to vibrate too rapidly to be brought into line2 that is1 the iron cannot become polarized by induction4 7,see ,exp4 #bd47 ,,experiment #bc4 ,to test the effect of breaking a magnet4 ,apparatus4 ,a magnetized sewing-needle2 iron filings2 compass1 ,o ,c 7,no4 #ah74 ,illustration3 ,fig4 #aj4 #ej4 ,directions4 7,a7 ,break the little bar magnet 7needle71 and test the two new ends produced for magnetism1 with the iron filings4 7,fig4 #aj74 7,b7 ,touch the two new poles together to see whether they are like or unlike4 7,c7 ,test the nature of the poles with ,o ,c 7,fig4 #e7 7,d7 ,break one of the halves and test its parts4 #ea4 ,discussion4 ,the above results agree with the theory that each molecule is a magnet 7,exp4 #ah74 ,no matter into how many pieces a magnet is broken1 each part becomes a magnet4 7,fig4 #aj74 ,this shows that those molecules near the equator of the magnet really have magnetism4 ,their energy1 however1 is all used upon the adjoining molecules2 hence no external bodies are attracted at that point4 ,,chapter ,,iii4 ,,induced ,,magnetism4 ,illustration3 ,fig4 #aa4 ,,experiment #bd4 ,to find whether we can magnetize a piece of iron without touching it with a magnet4 ,apparatus4 ,horseshoe magnet1 ,h ,m2 iron filings1 ,i ,f 7,fig4 #aa74 #eb4 ,directions4 7,a7 ,hold the armature of the magnet in a vertical position 7,fig4 #aa71 its lower end being directly in a little pile of iron filings4 7,b7 ,bring the ,n pole of ,h ,m near the upper end of ,a1 but do not let them touch each other4 7,c7 ,keeping ,a and the pole of ,h ,m the same distance apart1 lift them4 ,do any filings cling to ,a8 7,d7 ,without moving or jarring ,a1 take ,h ,m away from it and note result upon the filings4 #ec4 ,temporary ,magnetism2 ,induced ,magnetism4 ,the armature1 ,a1 was induced to become a magnet without even touching ,h ,m4 ,its magnetism was temporary1 however1 as the filings dropped as soon as the inductive action of ,h ,m was removed4 ,a small amount of residual magnetism 7#dd7 remained in ,a4 ,soft iron is exceedingly valuable1 because it has very little retentivity 7#dd71 and because it can be easily magnetized by induction4 ,the armature was made of soft iron4 ,it had induced magnetism4 ,it was a temporary magnet4 ,,experiment #be4 ,to find whether a piece of steel can be permanently magnetized by induction4 ,apparatus4 ,an unmagnetized sewing-needle2 horseshoe magnet1 ,h ,m2 iron filings2 sheet of stiff paper4 #ed4 ,directions4 7,a7 ,test the needle for magnetism4 7,b7 ,place the unmagnetized needle upon the paper1 then move ,h ,m about immediately under it1 so that the needle will be attracted4 7,c7 ,test the needle again for permanent magnetism4 ,illustration3 ,fig4 #ab4 ,,experiment #bf4 ,to study the inductive action of a magnet upon a piece of soft iron4 ,apparatus4 ,horseshoe magnet1 ,h ,m2 iron filings1 ,i ,f2 a piece of soft iron wire about an inch long1 ,i ,w 7,fig4 #ab71 placed upon the ,n pole of ,h ,m2 compass1 ,o ,c 7,no4 #ah71 7 #cb74 #ee ,directions4 7,a7 ,test the lower end of ,i ,w for magnetism with ,i ,f4 7,b7 ,leaving ,i ,w upon the ,n pole of ,h ,m1 test the pole at the lower end of ,i ,w with ,o ,c1 to determine whether it is ,n or ,s4 7,c7 ,jar ,i ,w 7,exp4 #ai71 then place it upon the ,s pole of ,h ,m1 and again test the polarity of the lower end4 #ef4 ,polarization2 ,pole ,pieces4 ,the wire1 ,i ,w 7,fig4 #ab71 was acted upon by induction 7,exp4 #bd7 and behaved like a magnet4 ,poles were produced in it1 so we say that the wire was polarized4 ,pieces of iron1 placed upon the poles of a magnet1 are called pole pieces4 ,it should be noted that the lower end of the wire has a pole like the pole of ,h ,m1 to which it is attached4 ,,experiments #bg-cj4 ,to study pole pieces4 ,apparatus for ,experiments #bg-cj4 ,horseshoe magnet1 ,h ,m2 soft iron wires2 iron filings1 ,i ,f4 #eg4 ,directions4 7,a7 ,suspend two wires1 each about an inch long 7,fig4 #ac7 from one pole of ,h ,m4 ,do their lower ends attract or repel each other8 ,illustration3 ,fig4 #ac4 ,illustration3 ,fig4 #ad4 ,,experiment #bh4 #eh4 ,directions4 7,a7 ,place the two wires just used so that one shall cling to the ,n pole of ,h ,m1 and the other to the ,s pole of ,h ,m 7,fig4 #ad74 7,b7 ,bring the lower ends of the wires near each other4 ,do they attract or repel each other8 ,,experiment #bi4 #ei4 ,directions4 7,a7 ,bend a #b-;inch iron wire1 as in ,fig4 #ae1 and place it upon the poles of ,h ,m4 7,b7 ,see if its central part1 marked ,x1 will strongly attract filings4 ,illustration3 ,fig4 #ae4 ,illustration3 ,fig4 #af4 ,,experiment #cj4 #fj4 ,directions4 7,a7 ,bend the wire just used a little more1 and place its ends upon one pole of ,h ,m 7,fig4 #af74 7,b7 ,see if the iron filings and small wires will cling to its central part4 ,,chapter ,,iv4 ,,the ,,magnetic ,,field4 ,,experiment #ca4 ,to study the space around a magnet1 in which pieces of iron become temporary magnets by induction4 ,apparatus4 ,a bar magnet1 ,b ,m 7,no4 #ba72 a compass 7,no4 #ah72 a sheet of stiff paper about #a ft4 7#cj cm47 square1 with a center line1 ,c ,l1 drawn parallel to one of its sides 7,fig4 #af-a_/b71 and with another line1 ,e ,w1 drawn perpendicular to ,c ,l4 7,see ,apparatus ,book1 ,chap4 ,,vi41 for various ways of making home-made permanent magnets47 #fa4 ,directions4 7,a7 ,lay the paper upon the table1 and place the compass over the center of the line1 ,c ,l1 previously drawn4 7,b7 ,place the eye directly over the compass-needle1 then turn the paper until the line is ,n and ,s2 that is1 until the line is parallel to the length of the needle4 ,pin the paper to the table to hold its center line ,n and ,s4 7,c7 ,place ,b ,m upon the paper1 as shown 7,fig4 #af-a_/b71 its ,n pole to the north1 and its center at the cross line1 ,e ,w4 ,illustration3 ,fig4 #af-a_/b4 7,d7 ,slowly move the compass entirely around and near ,b ,m1 and note the various positions taken by the needle4 ,note especially the way in which its ,n pole points4 ,this is to get a general idea of the action of the needle4 7,e7 ,place the compass in the position marked #a1 which is on ,e ,w1 about #a in4 from the line1 ,c ,l4 ,press the wooden support down firmly upon the paper to show1 by the dent made in the paper by the pin-head1 the exact place on the paper that is under the center of the compass-needle4 ,before removing the compass from this position1 look down upon it again1 and make a dot on the paper with a pencil directly under each end of the needle4 ,remove the compass1 and draw a line through the dent and the two dots just made4 ,this will show a plan of the exact position of the needle4 7,f7 ,repeat this for the various points marked #b1 #d1 #f in4 from ,c ,l1 always marking on the plan the position of the ,n pole of the needle4 ,do the same with the other points marked on ,fig4 #af-a_/b by dots1 and study the resulting diagram4 #fb4 ,discussion2 ,the ,magnetic ,field4 ,the compass-needle was decidedly affected all around ,b ,m 7,fig4 #ag71 showing that induction can take place in a considerable space around a magnet2 this space is called the magnetic field of the magnet4 ,let us consider one position taken by the compass-needle in the field of ,b ,m 7,fig4 #ag71 as1 for example1 the one in which the needle has been made black4 ,the ,s pole of the black needle is attracted by the ,n pole of ,b ,m1 and is repelled by the ,s pole of ,b ,m4 ,the ,n pole of the compass-needle is attracted by the ,s pole of ,b ,m1 and is repelled by ,b ,m's ,n pole4 ,the position which it takes1 therefore1 is due to the action of these #d forces1 together with its tendency to point ,n and ,s4 ,illustration3 ,fig4 #ag4 ,every magnet has a certain magnetic field1 with its lines of force passing through the surrounding air in certain definite positions4 ,as soon1 however1 as a piece of iron or another magnet is brought within the field1 the original position of the lines of force is changed4 ,this has to be considered in the construction of electrical machinery4 ,,experiment #cb4 ,to study the magnetic field of a bar magnet4 ,apparatus4 ,a sheet of stiff paper2 iron filings1 ,i ,f2 bar magnet1 ,b ,m 7,no4 #ba72 a sifter for the filings 7,no4 #bd72 7,see ,apparatus ,book1 #dh1 #di1 #ej1 for home-made sifters47 #fc4 ,directions4 7,a7 ,place ,b ,m upon the table1 and lay the paper over it4 7,b7 ,with the sifter sprinkle some filings upon the paper directly over ,b ,m1 then tap the paper gently1 to assist the particles to take final positions4 ,study the results4 #fd4 ,magnetic ,figures2 ,lines of ,magnetic ,force4 ,the filings clearly indicated the extent and nature of the magnetic field of ,b ,m4 ,you should notice how the filings radiate from the poles1 and how they form curves from one pole to the other4 ,they make upon the paper a magnetic figure4 ,each particle of the filings becomes a little magnet1 by induction 7,exp4 #bd71 and takes a position which depends upon attractions and repulsions1 as discussed in ,exp4 #ca4 ,magnetism seems to reach out in lines from the poles of a magnet4 ,the position and direction of some of the lines are shown by the lines of filings4 ,they are very distinct near the poles1 and are considered1 for convenience1 to start from the ,n pole of a magnet1 where they separate4 ,they then pass through the air on all sides of the magnet1 and finally enter it again at the ,s pole4 ,these lines are called lines of force or lines of magnetic induction4 ,the poles must not be considered mere points at the ends of a magnet4 ,as shown by magnetic figures1 the lines of magnetic induction flow from a considerable portion of the magnet's ends4 ,,experiments #cc-cg4 ,to study the magnetic fields of various combinations of bar magnets4 ,apparatus for ,exps4 #cc-cg4 ,two bar magnets1 ,b ,m 7,nos4 #ba1 #bb72 an iron ring1 ,i ,r 7,no4 #bc72 iron filings1 ,i ,f2 a sheet of stiff paper2 the sifter 7,no4 #bd74 #fe4 ,note4 ,the student will find it very helpful to make the magnetic figures of the combinations given4 ,thoroughly magnetize the bar magnets upon an electro-magnet1 or upon a strong horseshoe magnet1 and mark their ,n poles in some way4 ,the ,n poles may be marked by sticking a small piece of paper to them4 #ff4 ,directions4 7,a7 ,arrange the two magnets1 ,b ,m1 as in ,fig4 #ah1 with their unlike poles about an inch apart4 7,the dotted circle indicates the iron ring to be used in the next experiment4 ,about a quarter1 only1 of the magnets are shown47 7,b7 ,place the paper over the magnets1 and sift filings upon it immediately over the unlike poles4 ,note particularly the lines of filings between ,n and ,s4 7,c7 ,make a sketch of the result4 7,see experiments with electromagnets1 and the illustrations of magnetic figures with them47 ,,experiment #cd4 #fg4 ,directions4 7,a7 ,leaving the opposite poles an inch apart1 as in ,exp4 #cc1 place the iron ring1 ,i ,r 7,no4 #bc71 between them 7,fig4 #ah1 dotted circles74 7,b7 ,place the paper over it all1 and sprinkle filings upon it to get the magnetic figure4 7,c7 ,make a sketch of the resulting figure1 and compare it with the figure made in ,exp4 #cc4 ,why do the lines of force appear indistinct in the center of the ring and around it8 7,see #gd47 ,illustration3 ,fig4 #ah4 ,illustration3 ,fig4 #ai4 ,,experiment #ce4 #fh4 ,directions4 7,a7 ,arrange the two bar magnets1 as in ,exp4 #cc1 but with their two ,n poles an inch apart4 7,b7 ,make the magnetic figure of the combination4 ,do the lines of force flow from one ,n pole directly to the ,n pole of the other8 ,do the particles of filings reaching out from one ,b ,m attract or repel those from the other ,b ,m8 ,,experiment #cf4 #fi4 ,directions4 7,a7 ,place the two bar magnets side by side1 so that their unlike poles shall be arranged as in ,fig4 #ai4 7,b7 ,make the magnetic figure4 ,,experiment #cg4 #gj4 ,directions4 7,a7 ,turn one ,b ,m end for end1 so that their like poles shall be near each other1 but otherwise arranged as in ,fig4 #ai4 7,b7 ,make and study the magnetic figure4 ,,experiments #ch-ci4 ,to study the lifting power of combinations of bar magnets4 ,apparatus for ,exps4 #ch-ci4 ,two bar magnets1 ,b ,m 7,no4 #ba1 #bb71 of about equal strength2 iron filings1 ,i ,f4 #ga4 ,directions4 7,a7 ,find out about how many filings you can lift with the ,n pole of one magnet4 7,b7 ,place the two magnets together 7,fig4 #bj71 their like poles being in contact2 then see whether the two ,n poles will lift more or less filings than one pole4 ,illustration3 ,fig4 #bj4 ,,experiment #ci4 #gb4 ,directions4 7,a7 ,remove all filings from the two magnets just used1 and hold them tightly together 7,fig4 #bj71 with their unlike poles in contact4 7,b7 ,compare the amount of filings you can lift at one end of this combination with that lifted in ,exp4 #ch 7,a7 and 7,b74 #gc4 ,discussion2 ,compound ,magnets4 ,many lines of force pass into the air from two like poles4 ,such a combination is called a compound magnet4 ,a piece of thin steel can be magnetized more strongly in proportion to its weight than a thick piece1 because the magnetism does not seem to penetrate beyond a certain distance into the steel4 ,thin steel may be magnetized practically through and through4 ,a thick magnet has but a crust of magnetized molecules2 in fact1 a thick magnet may be greatly weakened by eating the outside crust away with acid4 ,by riveting several thin bar or horseshoe magnets together1 thick permanent magnets of considerable strength are made4 #gd4 ,lines of force1 in passing from the ,n to the ,s pole of a magnet1 meet a resistance in the air1 which does not carry or conduct them as easily as iron or steel4 ,in the arrangement of ,exp4 #ci the lines of force are not obliged to push their way through the air1 as each magnet serves as a return conductor for the lines of force of the other4 ,either magnet may be considered an armature for the other4 ,to show in another way that few lines of force pass into the air1 the student may lay the above combination upon the table and make a magnetic figure4 7,see ,apparatus ,book1 p4 #ch1 for method of making home-made compound magnets47 ,in the case where a ring was placed between the poles of two bar magnets 7,exp4 #cd71 the lines of force from the ,n pole jumped across the first air-space4 ,they then disappeared in the body of the ring1 until they were obliged to jump across the second air-space1 to get to the ,s pole4 ,the weakness of the field in the central space was clearly shown by the filings4 ,there were no stray lines of force passing through the air1 because it was easier for them to go through the iron ring4 ,this will be discussed again under ,dynamos and ,motors4 7,see also #gh47 ,,experiments #dj-db4 ,to study the magnetic field of the horseshoe magnet4 ,apparatus for ,exps4 #dj-db4 ,horseshoe magnet1 ,h ,m2 iron filings1 ,i ,f2 sheet of stiff paper4 #ge4 ,directions4 7,a7 ,place ,h ,m1 with its armature removed1 flat upon the table1 and cover it with the paper2 then make the magnetic figure4 7,exp4 #cb47 7,b7 ,compare the number of well-defined curves at the poles with the number at the equator4 ,,experiment #da4 #gf4 ,directions4 7,a7 ,make the magnetic figure of ,h ,m with its armature in place4 7,b7 ,is the attraction for outside bodies increased or decreased by placing the armature on ,h ,m8 ,,experiment #db4 #gg4 ,directions4 7,a7 ,lay ,h ,m flat upon the table1 and place one or two matches between its poles and the armature2 cover with paper as before1 and make the magnetic figure4 ,do lines of force still pass through the armature8 #gh4 ,discussion2 ,resistance to lines of ,force4 ,it is evident1 from the last #c experiments1 that lines of force will pass through iron whenever possible1 on their way from the ,n to the ,s pole of a magnet4 ,when the armature of a horseshoe magnet is in place1 most of the lines of magnetic induction crowd together and pass through it rather than push their way through the air4 ,air is not a good conductor of lines of force2 and the magnet has to do work to overcome the resistance of the air1 when the armature is removed1 in order to complete the magnetic circuit4 ,this work causes a magnet to become gradually weaker4 ,the soft iron armature is an excellent conductor of lines of force2 it completes the magnetic circuit so perfectly that very little work is left for the magnet to do4 ,,experiment #dc4 ,to show that lines of force are on all sides of a magnet4 ,apparatus4 ,our compass1 ,o ,c 7,no4 #ah72 horseshoe magnet1 ,h ,m2 glass tumbler1 ,g ,t2 sheet of stiff paper2 iron filings1 ,i ,f4 ,arrange as in ,fig4 #ba4 ,h ,m may be supported in a vertical position by placing paper1 or a handkerchief1 under it4 ,the poles should just touch the stiff paper placed over the tumbler4 ,illustration3 ,fig4 #ba4 #gi4 ,directions4 7,a7 ,sprinkle iron filings upon the paper1 and study the resulting magnetic figure4 7,b7 ,place ,o ,c upon the paper in different positions4 ,does the magnetic needle always come to rest about parallel to the lines of filings8 #hj4 ,discussion4 ,the student should keep in mind the fact that the filings in the magnetic figure show the approximate extent and form of the magnetic field simply in one plane4 ,if the paper were held in some other position near the magnet 7in a tilted position1 for example17 the lines of filings would not be the same as those produced in ,exp4 #dj-db4 ,the lines of force come out of every side of the ,n pole4 ,when a magnetic needle is placed in any magnetic field1 its ,n pole points in the direction in which the lines of force are passing2 that is1 it points towards the ,s pole of the magnet producing the field4 ,,experiment #dd4 ,to study a horseshoe magnet with movable poles4 ,apparatus4 ,a narrow strip of spring steel1 ,s ,s 7,no4 #be72 iron filings1 ,i ,f4 #ha4 ,directions4 7,a7 ,magnetize the spring steel1 ,s ,s4 7,b7 ,bend ,s ,s until its poles are about #a_/d in4 apart1 then using it as a horseshoe magnet1 and keeping its poles the same distance apart1 see about how many filings you can lift4 7,c7 ,clean the poles of ,s ,s1 press them tightly together1 then again test its lifting power with filings4 ,illustration3 ,fig4 #bb4 #hb4 ,discussion2 ,advantages of ,horseshoe ,magnets4 ,when the opposite poles of the flexible magnet are pressed together1 the lines of force do not have to pass through the air2 there is very little attraction for outside bodies4 ,the same effect is produced with the armature 7,exp4 #da74 ,a horseshoe magnet has a strong attraction for its armature1 because it has a double power to induce and to attract4 ,suppose the ,n pole of a bar magnet1 ,b ,m 7,fig4 #bb71 be placed near one end of a piece of iron1 as1 for example1 the armature1 ,a4 ,a will become a temporary magnet by induction 7,exp4 #bd74 ,the ,s pole of ,a1 polarized by induction1 will be attracted by ,b ,m1 while its ,n pole will be repelled by ,b ,m2 so1 you see1 that a bar magnet does not pull to advantage4 ,,chapter ,v4 ,,terrestrial ,,magnetism4 #hc4 ,the ,magnetism of the ,earth4 ,the student must have guessed1 before this1 that the earth acts like a magnet4 ,it causes the magnetic needle to take a certain position at every place upon its surface1 and this position depends upon the earth's attractions and repulsions for it4 ,the earth has lines of force which flow from its ,n magnetic pole1 and these lines1 before they can get to the earth's ,s magnetic pole1 must spread out through the air on all sides of the earth4 ,as the magnetic needle points to the earth's ,n magnetic pole 7which is more than #a1jjj miles from its real ,n pole71 it is evident that the compass-needle does not show the true north for all places upon the earth's surface4 ,in fact1 the ,n pole of the needle may point ,e1 ,w1 or even ,s4 ,this effect would be seen by carrying a compass around the earth's ,n magnetic pole4 ,illustration3 ,fig4 #bc4 #hd4 ,declination4 ,for convenience1 we shall represent the true ,n and ,s1 at the place where you are experimenting1 by the full line1 ,n ,s1 in ,fig4 #bc4 ,the dotted line shows the direction taken by the compass-needle4 ,the angle1 ,a1 between them1 is called the angle of variation or the declination4 ,this angle is not the same for all places2 and1 in fact1 it changes slowly at any given place2 so it becomes necessary to construct magnetic maps for the use of mariners and others4 ,,experiment #de4 ,to study the lines of force above and below a bar magnet placed horizontally4 ,apparatus4 ,a bar magnet1 ,b ,m 7,no4 #ba72 compass1 ,o ,c 7,no4 #ah74 #he4 ,directions4 7,a7 ,lay ,b ,m upon the table and place ,o ,c upon its center4 ,note the position of the compass-needle4 7,b7 ,slide ,o ,c along from one end of ,b ,m to the other1 and study the effect upon its needle4 ,do lines of force curve over ,b ,m as well as around its sides1 as shown in ,exp4 #ca8 7,c7 ,place ,o ,c upon the table4 ,hold ,b ,m horizontally above ,o ,c1 and move ,o ,c back and forth under ,b ,m4 ,does the needle remain horizontal1 or does it show that lines of force pass under ,b ,m on their way from its ,n to its ,s pole8 ,illustration3 ,fig4 #bd4 #hf4 ,the ,dip or ,inclination of the ,magnetic ,needle4 ,the needle is said to dip when it takes positions like those in ,fig4 #bd4 ,compass-needles should be horizontal1 when properly balanced1 and entirely free from all effects other than those of the earth4 ,the excessive dip shown 7,fig4 #bd7 is due1 of course1 to the efforts of the magnetic needle to place itself in the direction in which the lines of force of ,b ,m pass4 ,,experiment #df4 ,to study the dip or inclination of the magnetic needle1 due to the action of the earth4 ,apparatus4 ,fig4 #be4 ,our compass1 ,o ,c 7,no4 #ah72 horseshoe magnet1 ,h ,m 7,no4 #af72 piece of paper4 #hg4 ,directions4 7,a7 ,place ,o ,c upon the table1 and mark upon a piece of paper the height of the ,n pole of its needle above the table4 7,fig4 #be47 ,the paper should be held in a vertical position1 and near the pole4 ,illustration3 ,fig4 #be4 7,b7 ,with ,h ,m reverse the poles of the compass-needle 7,exp4 #ac71 so that its former ,n pole shall become a ,s pole4 7,c7 ,place the needle upon its pivot again1 and mark upon the paper1 as before1 the height of its new ,n pole above the table4 ,does the needle remain horizontal8 7,d7 ,remagnetize the needle1 and reverse its poles so that it will again balance4 ,illustration3 ,fig4 #bf4 #hh4 ,discussion2 ,balancing ,magnetic ,needles4 ,if a piece of unmagnetized steel be balanced and then magnetized1 it will no longer remain horizontal2 it will dip4 ,try this4 ,compass-needles are balanced after they are magnetized4 ,can you now see why the needle did not remain horizontal after its poles were changed8 ,a piece of steel first balanced and then magnetized1 has to have its ,s pole slightly weighted1 as suggested by the line at ,s 7,fig4 #bf x71 to make it horizontal4 ,the magnetic needle does not tend to dip at the earth's equator1 because the lines of force of the earth are nearly horizontal at the equator4 ,as we pass toward the north or south on the earth1 the lines of force slant more and more as they come from or enter the earth's magnetic poles4 ,what position would the needle take if we should hold it directly over the earth's ,n magnetic pole8 ,fig4 #bd shows what the needle does when held near the poles of a bar magnet4 ,,experiments #dg-dh4 ,to study the inductive influence of the earth4 ,apparatus for ,exps4 #dg-dh4 ,compass1 ,o ,c1 7,no4 #ah72 an iron stove poker1 or other rod of iron2 a hammer4 7,the iron and hammer are not furnished47 #hi4 ,note4 ,you have seen 7,exp4 #bd71 that iron becomes magnetized by induction when placed near a magnet4 ,as the earth acts like a huge magnet1 having poles1 lines of force1 etc41 will it magnetize pieces of iron which are in the air or upon its surface8 #ij4 ,directions4 7,a7 ,test the poker for poles with ,o ,c1 remembering that repulsion is necessary to prove that it is polarized4 ,if the poker has very weak poles1 proceed2 but if it shows some strength1 hold it in an east and west direction1 and hit it several sharp blows on the end with the hammer4 ,test for polarity again4 7,b7 ,with one hand hold the poker in the ,n and ,s line1 give it a dip toward the north1 and strike it several times with the hammer to thoroughly stir up its molecules4 7,c7 ,test again for poles with ,o ,c1 and note especially whether the lower end 7of the poker7 became a ,n or a ,s pole4 ,,experiment #dh4 #ia4 ,directions4 7,a7 ,turn the poker end for end 7,see ,exp4 #dg72 repeat the striking1 and test again the pole produced at the lower and north end of it4 7,b7 ,now hold the poker horizontally in the east and west line1 and pound it4 7,c7 ,test for poles4 ,has this strengthened or weakened the poker magnet8 #ib4 ,discussion4 ,dipping the poker places it nearly in the same direction as that taken by the earth's lines of force4 ,the magnetic influence of the earth acts to advantage upon the poker1 by induction1 only when the poker is properly held4 ,it no doubt occurs to the student that the end of a magnetic needle which points to the north is really opposite in nature to the north magnetic pole of the earth4 ,the ,n pole of a needle1 then1 must be in reality a ,s pole to be attracted by the earth's ,n pole4 ,it has been agreed1 for convenience1 to call the ,n-seeking pole of a magnet its ,n pole4 #ic4 ,natural ,magnets4 ,nearly all pieces of iron become more or less magnetized by the inductive action of the earth's magnetism4 ,your poker was slightly magnetized at the start1 perhaps1 from standing in a dipping position4 ,induction takes place along lines of force4 ,in northern latitudes the earth's lines of force have a dip to the north4 ,you should now see why the greatest effect was produced upon the poker when it1 also1 was made to dip4 ,parts of machinery1 steel frames of bridges and buildings1 tools in the shop1 and even certain iron ores1 become polarized by this inductive action4 ,these might all be called natural magnets4 ,magnetic iron ore1 called lodestone1 is referred to1 however1 when speaking of natural magnets4 ,lodestone was used thousands of years ago to indicate ,n and ,s1 and it was discovered1 later1 that it could impart its power to pieces of steel when the two were rubbed together4 ,,experiment #di4 ,to test the effect of twisting a wire held north and south in the earth's magnetic field4 ,apparatus4 ,compass1 ,o ,c 7,no4 #ah72 a piece of soft iron wire1 #f in4 7#ae cm47 long 7,no4 #ae74 ,bend up about an inch of the wire at each end so that it may be firmly held when twisting it4 ,note4 ,you have seen that we can pound magnetism into or out of a piece of iron at will4 ,can we twist it into a wire and out again without the use of magnets8 #id4 ,directions4 7,a7 ,test the wire for poles with ,o ,c4 7,b7 ,hold the wire in a ,n and ,s direction1 dipping it at the same time1 as directed in ,exp4 #dg for the poker1 and twist it back and forth4 7,c7 ,test again for poles with ,o ,c4 ,as the poles of the wire may be very weak1 bring them slowly toward the compass-needle 7see ,exp4 #ad71 and note the first motions produced upon the needle4 7,d7 ,hold the wire horizontally east and west1 twist and test again4 ,has its magnetism become weaker or stronger than before8 ,,experiment #ej4 ,to test for magnetism in bars of iron1 tools1 etc4 ,apparatus4 ,steel drills2 files2 chisels2 bars or rods of iron that have been standing in an upright position2 stove-lid lifters2 stove pokers1 etc41 etc42 a compass4 #ie4 ,directions4 7,a7 ,with the compass test the ends of the above for magnetism1 and note which ends are ,s4 ,notes4 ,,static ,,electricity ,,part ,,ii4--,,static ,,electricity ,,chapter ,,vi4 ,,electrification4 #ajj4 ,some ,varieties of ,electricity4 ,static electricity does not seem to flow in currents as readily as some other varieties2 its tendency is to stand still1 hence the name1 static4 ,the simplest way to produce it is by friction4 ,thermo electricity is produced by changes in temperature4 ,when certain combinations of metals become hotter or colder1 a current is produced4 ,voltaic or ,galvanic electricity is produced by chemical action4 ,batteries give this variety4 ,induced electricity is produced by other currents1 and by combinations of magnets and moving coils of wire1 as in the dynamo4 ,this is1 by far1 the most important variety of electricity1 and the dynamo is the most important producer of it4 ,each of the above varieties of electricity will be studied experimentally with simple apparatus4 ,,experiments #ea-eb4 ,to study electrification by friction4 ,apparatus4 ,ebonite sheet1 ,e ,s 7,no4 #bf72 flannel cloth1 ,f ,c 7,no4 #cj74 ,see what is said in preface about static electricity4 #aja4 ,directions4 7,a7 ,examine ,e ,s4 ,note that its surface is not smooth1 like that of ordinary hard-rubber combs4 ,can you think of any reason for this8 7,b7 ,hold its flat surface near your face1 then near the back of your hand4 ,do you feel anything unusual8 7,c7 ,lay ,e ,s upon a flat board1 or uncovered wooden table1 and slide it about4 ,can you easily pick it up8 7,d7 ,place ,e ,s flat upon the table again2 keep it from sliding about with your left hand1 and rub it vigorously for a minute with ,f ,c4 ,does ,e ,s act exactly as it did before in 7,b7 and 7,c78 7,e7 ,repeat the experiment in a dark room4 7,f7 ,thoroughly electrify ,e ,s1 and see if it will cling to the wall strongly enough to support its own weight4 #ajb4 ,discussion2 ,electrified and ,neutral ,bodies4 ,the ebonite sheet became electrified or charged2 and as the electrification was produced by friction1 we may say that the action of the ebonite indicated the presence of frictional electricity4 ,no one can tell just why the ebonite acted so queerly1 but we can learn a great deal by experimenting4 ,bodies which are not charged are said to be neutral4 ,the table1 chairs1 earth1 etc41 are neutral4 ,we may consider that a neutral body has been discharged4 #ajc4 ,force2 ,resistance2 ,work2 ,potential ,energy2 ,electrification4 ,it takes force to raise water into a tank placed on the roof4 ,in raising the water1 work has to be done1 and we have to do the work2 but when we once have the water in the tank we have accomplished something4 ,the water has potential energy2 that is1 on account of its high position1 we can make it do some work by simply turning a stop-cock so that the water can run out and turn a water-wheel1 for example4 ,it takes force to vigorously rub a piece of ebonite with a flannel cloth1 for resistance has to be overcome2 that is1 work has to be done4 ,several things are accomplished by this work2 heat is produced1 for we can feel that the ebonite gets warm2 we can hear sounds and see sparks4 ,the simple muscular exertion on our part has been changed to heat1 light1 and sound4 ,the most wonderful part of it all1 however1 is that we have electrified or charged the ebonite4 ,we did the work at first1 and now the ebonite has the power to do something1 as you will soon see4 ,electrification is1 then1 a sort of potential energy4 #ajd4 ,heat and ,electrification4 ,we say that heat passes to or from a body to make it hot or cold4 ,heat produces the sensation of warmth1 but heat isn't warmth4 ,we can force a cold body to become hot2 in other words1 we can get it into a hot condition in various ways1 such as rubbing it1 hammering it1 or by placing it near or in contact with another hot body4 ,electrification is1 also1 a condition or state into which we can force a body2 but electrification isn't electricity4 ,we know whether a body is hot or cold by its effects upon us1 upon thermometers1 and upon other bodies4 ,we can tell1 also1 whether a body is electrified or not by the way it acts1 and1 in certain cases1 by the sound1 heat1 and light which accompany the electrification4 ,do not get the idea that an electrified body is covered with a layer of electricity just as a board is covered with a layer of paint4 ,illustration3 ,fig4 #bh4 ,,experiment #eb4 #aje4 ,directions4 ,repeat ,exp4 #ea1 but in place of the ebonite1 use hot tissue-paper1 hot brown paper1 hot newspaper1 or a hot silk handkerchief4 ,rub your hand vigorously over them4 ,do these become charged8 ,,experiments #ec-ed4 ,to study electrical attractions4 ,apparatus4 ,the ebonite sheet1 ,e ,s 7,no4 #bf72 flannel cloth1 ,f ,c 7,no4 #cj72 small pieces of dry tissue-paper1 ,t ,p 7,no4 #ca72 thread 7,no4 #cb74 #ajf4 ,directions4 7,a7 ,thoroughly electrify ,e ,s as before1 then lift and hold it in the air4 7,fig4 #bh47 7,b7 ,see what the paper and thread will do when held loosely near ,e ,s4 #ajg4 ,discussion4 ,exp4 #ec shows that an electrified body attracts neutral ones4 ,this much was known about electricity over #b1jjj years ago4 ,they didn't have ebonite then1 but some of the educated men of ,greece knew that amber would attract light bodies after being rubbed4 ,the ,greek word for amber is elektron1 and from this has been made the word electricity4 ,,experiment #ed4 #ajh4 ,directions4 ,charge a sheet of hot paper by friction2 lift it1 by its opposite ends1 and lower it over small pieces of tissue-paper placed on the table4 ,what happens to the little pieces8 ,,experiment #ee4 ,to study mutual attractions4 ,apparatus4 ,the support and its attachments 7,see #aji72 support wire1 ,s ,w 7,no4 #cf72 silk thread1 ,s ,t 7,no4 #cc71 or a rubber band1 ,r ,b 7,no4 #de72 ebonite rod1 ,e ,r 7,no4 #bh72 flannel cloth1 ,f ,c 7,no4 #cj72 wire swing1 ,w ,s 7,no4 #cg74 ,tie one end of ,s ,t to ,w ,s1 ,fig4 #bi2 tie the other end of ,s ,t to ,s ,w2 adjust ,w ,s by bending1 if necessary1 so that it will securely hold ,e ,r4 ,it will be found convenient to use a rubber band instead of ,s ,t2 if you do1 let ,w ,s straddle one end of ,r ,b 7,fig4 #cc71 and hang the other end of ,r ,b upon ,s ,w4 #aji4 ,the support consists of a support base 7,s ,b1 ,fig4 #ef71 a support rod 7,s ,r1 ,fig4 #ef71 and a support wire 7,s ,w1 ,fig4 #bi74 ,there is a small hole in one end of ,s ,r to receive the wire1 ,s ,w1 and a large hole in the other end to take the short ebonite which holds the insulating table 7,fig4 #cb74 ,a little paper should be wound around the lower end of ,s ,r1 so that it will stand solidly in the spool which forms a part of the base4 #aaj4 ,directions4 7,a7 ,electrify ,e ,r with ,f ,c1 and place ,e ,r in the swing1 ,w ,s 7,fig4 #bi74 ,illustration3 ,fig4 #bi4 7,b7 ,bring your finger near one side of the rubbed end of ,e ,r1 then near the unrubbed end1 and compare the results4 #aaa4 ,mutual ,attractions4 ,a neutral body1 like the hand1 for example1 attracts electrified ones4 ,from ,exp4 #ec1 #ed1 #ee1 it is seen that the attraction between a neutral and an electrified body is mutual2 each attracts the other4 ,,experiment #ef4 ,to study electrical repulsions4 ,apparatus4 ,same as for ,exp4 #ee2 ebonite sheet1 ,e ,s 7,no4 #bf74 #aab4 ,directions4 7,a7 ,charge ,e ,r1 and place it in ,w ,s1 ,fig4 #bi4 7,b7 ,charge ,e ,s1 and bring it slowly near one side of the charged end of ,e ,r4 ,,experiment #eg4 ,to study electrical repulsions4 ,apparatus4 ,a sheet of tissue-paper1 ,t ,p 7,no4 #ca72 shears or a knife4 ,cut ,t ,p1 as in ,fig4 #cj4 ,each leg should be about #a_/d in4 wide and #c or #d in4 long4 #aac4 ,directions4 7,a7 ,heat the paper1 then place it flat upon the table and electrify it by rubbing it with your hand4 ,you must rub away from the uncut part1 or you will break the legs4 7,b7 ,raise ,t ,p1 holding it by the uncut part4 ,note the action of legs1 and make a sketch of them4 ,illustration3 ,fig4 #cj4 ,illustration3 ,fig4 #ca4 ,,experiment #eh4 ,to study electrical repulsions4 ,apparatus4 ,ebonite rod1 ,e ,r 7,no4 #bh72 a carbon electroscope1 ,c ,e1 ,fig4 #ca 7see #aad72 the support complete 7see #aji72 small piece of damp tissue-paper4 #aad4 ,the ,carbon ,electroscope4 ,light an ordinary match1 and let it burn until it is charred through and through4 ,the black substance remaining is carbon4 ,this is very light2 it has1 also1 another important property which you will soon understand4 ,tie a small piece of the carbon to one end of a dry silk thread1 and fasten the other end of the thread to the support wire1 ,s ,w1 which is fastened to the support 7,fig4 #ca74 ,we shall call this piece of apparatus the carbon e-lec-tro-scope4 7,see ,electroscopes1 ,chapter ,,xviii41 ,apparatus ,book47 #aae4 ,directions4 7,a7 ,electrify ,e ,r1 then hold it near the carbon of the electroscope4 7,b7 ,bring the charged rod near little pieces of damp tissue-paper4 #aaf4 ,discussion of ,experiments #ef1 #eg1 #eh4 ,in #ef the two pieces of ebonite were made of the same material1 and both were rubbed with flannel4 ,they must have been similarly electrified4 ,in #eg1 different parts of the same piece of paper were similarly electrified4 ,in #eh1 the little piece of carbon took some of the electrification from the charged rod1 just as it would take molasses from your finger should your sticky finger touch it4 ,the electrification on the carbon must have been of the same kind as that on the rod4 ,the carbon was charged by contact4 ,we learn1 then1 that two bodies repel each other when they have the same kind of electrification4 ,do two charged bodies always repel each other8 ,is it possible that there are different kinds of electrifications8 ,,experiment #ei4 ,to study the electrification of glass4 ,apparatus4 ,the sheet of glass1 ,g 7,no4 #ch71 heated 7a hot bottle or lamp chimney will do72 a piece of silk large enough to rub ,g4 7,a silk handkerchief is just the thing1 but in case you have no silk1 use the flannel cloth1 ,f ,c1 ,no4 #cj47 #aag4 ,directions4 7,a7 ,vigorously rub the hot glass with the silk 7or flannel71 also heated4 7,b7 ,test ,g for electrification by means of little pieces of tissue-paper and the carbon electroscope1 ,exp4 #eh4 #aah4 ,questions4 ,will two pieces of electrified glass repel each other8 ,arrange an experiment to show whether you are right or not4 ,is the charge on the glass exactly like that on the ebonite8 ,do you know how to find out8 ,,experiment #fj4 ,to compare the electrification produced by ebonite and flannel with that produced by glass and silk4 ,apparatus4 ,the support 7see #aji72 wire swing1 ,w ,s 7,no4 #cg72 ebonite rod1 etc41 of ,exp4 #ee 7,fig4 #bi72 the glass1 ,g1 and silk of ,exp4 #ei4 #aai4 ,directions4 7,a7 ,electrify ,e ,r1 and place it in ,w ,s1 ,fig4 #bi4 7,b7 ,bring the uncharged glass near ,e ,r1 noting the action of ,e ,r4 7,c7 ,heat and electrify ,g2 bring it near ,e ,r1 and carefully note whether the attraction between them is stronger or weaker than before1 or whether they repel each other4 #abj4 ,discussion4 ,we know that the glass was electrified1 because it lifted tissue-paper2 hence1 its charge was not of the same kind as that on the ebonite4 ,had the electrifications been exactly alike1 we should have had a repulsion 7,exps4 #ef1 #eg1 #eh74 ,the exact difference between these two kinds of electrifications is not known4 ,it has been agreed1 for convenience1 to call that produced by glass and silk a positive electrification4 ,with ebonite and flannel a negative electrification is produced4 ,the sign is generally written for the word positive1 and - for negative4 ,these signs indicate kind1 and not more or less1 as in arithmetic4 #aba4 ,laws4 ,we have learned from the experiments these facts1 which are called laws3 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 attracts1 and is attracted by a neutral body4 ,,chapter ,,vii4 ,,insulators ,,and ,,conductors4 ,,experiment #fa4 ,to study insulators4 ,apparatus4 ,ebonite rod1 ,e ,r 7,no4 #bh72 flannel cloth1 ,f ,c 7,no4 #cj72 tissue-paper1 ,t ,p 7,no4 #ca74 #abb4 ,directions4 7,a7 ,holding one end of ,e ,r in the hand1 charge the other end by rubbing it with ,f ,c4 7,b7 ,with bits of the ,t ,p test each end of ,e ,r for a charge1 and compare the results4 ,,experiment #fb4 ,to study insulators4 ,apparatus4 ,the ebonite sheet1 ,e ,s 7,no4 #bf72 flannel cloth1 ,f ,c 7,no4 #cj74 #abc4 ,directions4 7,a7 ,thoroughly electrify ,e ,s 7,exp4 #ea1 ,d71 then lift and hold it in the air1 as in ,fig4 #bh4 7,b7 ,by moving your rounded knuckle about near the surface of ,e ,s1 see if you can get more than one spark from it4 ,,experiment #fc4 ,to study insulators4 ,apparatus4 ,a hard-rubber comb 7not furnished72 flannel cloth1 ,f ,c 7,no4 #cj72 dull pointed nail 7,no4 #ai74 #abd4 ,directions4 7,a7 ,electrify the comb with ,f ,c4 7,b7 ,move the nail along near the teeth of the comb1 and listen carefully4 #abe4 ,discussion of ,experiments #fa1 #fb1 #fc2 ,insulators4 ,in #fa the electrification remained at one end of the rod4 ,in #fb and #fc the sparks showed that all parts of the ebonite were not discharged at the same time4 ,a substance1 like ebonite1 which will not allow electrification to pass from one part of it to another1 is called an insulator4 ,silk and glass are also insulators4 ,do you now see why a silk thread was used to make the carbon electroscope8 ,why do they fasten telegraph wires to glass insulators8 #abf4 ,conductors4 ,it has already been stated that water in an elevated tank has potential energy4 ,we can allow the water to flow through a conducting pipe to another tank a little lower than the first1 and it will still retain much of the potential energy1 but not all4 ,can we conduct from one place to another this peculiar state of things1 this queer form of potential energy which we call electrification8 ,it is clear1 from the last experiments1 that in order to do it we need something besides ebonite1 which really acts like a closed stop-cock to the flow of electrification4 ,to keep electrification in one place we need an insulator2 to get it from one place to another we need a conductor4 ,insulators are as important as conductors4 ,you saw that sparks went to the finger from the ebonite1 so we call the finger a conductor4 ,you have learned that attractions and repulsions show the presence of electrification4 ,can we have our charged body in one place and get attractions or repulsions at some other place8 ,illustration3 ,fig4 #cb4 ,,experiment #fd4 ,to study conduction4 ,apparatus4 ,fig4 #cb2 the support 7see #aji72 a bent hairpin1 ,h ,p 7,no4 #ci72 ebonite sheet1 ,e ,s2 flannel cloth1 ,f ,c2 tin disk1 ,b ,f ,b 7,no4 #dj71 which is the bottom of the flat-box1 ,f ,b2 the insulating table1 ,i ,t 7see #abg74 #abg4 ,the ,insulating ,table consists of a tin box 7exactly like that used for the electrophorus cover71 and an ebonite rod about #a-c_/d in4 long4 ,see #aci for full details about fitting the rod into the box1 etc4 ,the lower end of the short rod fits into the large hole in one end of the support rod1 ,s ,r4 ,arrange as in ,fig4 #cb4 ,b ,f ,b should swing about very easily4 #abh4 ,directions4 7,a7 ,charge ,e ,s1 then rub it upon ,i ,t1 as shown1 noting the action of ,b ,f ,b4 #abi4 ,discussion4 ,ebonite being an insulator 7 #abe71 we say that ,i ,t1 ,h ,p and ,b ,f ,b were insulated4 ,you can see that the electrification must have passed through ,i ,t and ,h ,p to get to the disk1 ,b ,f ,b4 ,h ,p was the conductor1 allowing the disk1 also1 to become charged4 ,the wood1 ,s ,r1 is a conductor1 and1 as it was not insulated from the earth1 ,s ,r was neutral4 ,account for the attraction4 7,see #aba47 ,illustration3 ,fig4 #cc4 ,,experiment #fe4 ,to study conduction4 ,apparatus4 ,a copper wire1 ,c ,w 7,no4 #dd72 insulating rubber band1 ,r ,b 7,no4 #de1 ,fig4 #cc72 wire swing1 ,w ,s 7,no4 #cg72 the other half of the flat box1 ,t ,f ,b 7,no4 #da72 apparatus of ,exp4 #fi4 #acj4 ,telegraph ,line4 ,to have our telegraph line using frictional electricity complete1 we must have3 7#a7 ,some way of generating or making the electricity2 7#b7 ,some means of getting it or its effects to the other end of the line2 7#c7 ,some way of showing that it has been taken there4 ,the charged ,e ,s will be the source of the electrification4 ,new ,york will represent the end at which we send the message1 so at ,n4 ,y4 we must have a sending instrument4 ,see ,fig4 #cc1 which explains itself4 ,r ,b or a silk thread must be used to insulate the sender4 ,around one leg of ,w ,s is twisted one bare end of the conductor1 ,c ,w4 ,boston will represent the end of the line at which the message is received1 and there we need a receiving instrument4 ,this is similar to the apparatus described in ,exp4 #fi1 ,fig4 #cg4 ,in addition to this1 tie the middle of a moist cotton thread that is #f in4 long1 to ,b ,c 7,fig4 #cg71 and let its two free ends lie over the top and reach down against the bottom of the tin2 that is1 on the left-hand side4 ,fig4 #db will give you an idea in regard to the looks of the thread2 at first1 however1 it should be close to the bottom of the tin4 ,twist the other bare end of the copper wire around ,b ,c4 ,when the line is properly constructed and ready for use1 both instruments and ,c ,w are entirely insulated4 ,do not let any part of ,c ,w touch the table or your clothing4 #aca4 ,directions4 7,a7 ,touch the insulated sending instrument with the charged ebonite sheet1 and watch for any motion in the receiving instrument4 ,note4 ,better results will be obtained by using the charged electrophorus cover as the source of electrification1 instead of ,e ,s4 7,exp4 #fh47 #acb4 ,discussion4 ,the action here was like that in the previous experiment1 the difference being that a longer conductor was used4 ,electrification is always looking for some place to get to the earth1 just as water will run from a roof to the ground4 ,you will understand more about it a little later4 ,in our apparatus just described1 the only way that the earth could be reached was through the wooden rod ,s ,r4 ,do not get the idea that real messages are sent in any such way1 or that electricity flows through a wire as water flows through a pipe4 #acc4 ,relation between ,conductors and ,insulators4 ,the above terms are merely relative4 ,static electricity is easily conducted by dry wood1 while ,galvanic electricity is practically insulated by it4 ,a substance may be an insulator for currents of low potential1 while at the same time it will conduct high potential currents4 7,see ,potential #add47 #acd4 ,electrics and ,non-electrics4 ,bodies like glass1 sealing-wax1 amber1 etc41 were called electrics by the first students of electricity1 because it was upon these substances that they could easily produce electrification4 ,they called iron and other metals non-electrics1 because they could detect no electrification after rubbing them4 ,can you explain why they did not detect any electrification on metals8 ,can you devise an experiment to prove that metals may be charged8 ,do you see any relation between a non-electric and a conductor8 ,,experiment #ff4 ,to study the effect of moisture upon an insulator4 ,apparatus4 ,same as for ,exp4 #fe1 with the exception of the copper wire2 this is to be replaced by a dry silk thread about #b feet 7#fj cm47 long 7,no4 #cc74 #ace4 ,directions4 7,a7 ,see if a charge can be sent through the thread1 in the same manner as it was through the copper4 ,is dry silk a conductor8 7,b7 ,thoroughly wet the thread1 being careful not to wet the rubber band insulator 7,fig4 #cc72 see if wet silk is a conductor4 #acf4 ,discussion4 ,dry silk is an insulator1 while wet silk is a good conductor of static electricity4 ,it is the water1 however1 which really does the conducting4 ,even small amounts of moisture on glass1 or other insulators1 will allow the charge to escape4 ,glass collects much moisture from the air4 ,do you now see why it is necessary1 to get good results1 to have the paper1 glass1 etc41 hot before electrifying them8 ,,experiment #fg4 ,to test the effects of moisture upon bodies to be electrified4 ,apparatus4 ,two pieces of newspaper1 each about #d in4 7#aj cm47 square4 #acg4 ,directions4 7,a7 ,heat one piece to make it thoroughly dry1 and leave the other cold4 7,b7 ,stroke each1 say #aj times1 with your hand1 pressing them upon the table2 then place them upon the wall at the same time1 being careful not to let them touch your clothing4 ,see which will cling to the wall the longer4 ,,chapter ,,viii4 ,,charging ,,and ,,discharging ,,conductors4 #ach4 ,the ,electrophorus4 ,while the ebonite sheet alone1 or a good hard-rubber comb1 may be used for many experiments in frictional electricity1 the sparks produced are small1 and the ebonite has to be electrified as often as it is discharged4 ,to obtain real good sparks1 and to avoid this continual rubbing1 the student should be provided with an e-lec-troph'-o-rus4 ,this is1 really1 a simple1 cheap1 and efficient frictional electric machine4 ,an electrophorus consists of #b insulators and #a conductor--that is1 of #c parts3 7#a7 insulating handle1 7#b7 cover1 and 7#c7 a plate or base of insulating material4 ,illustration3 ,fig4 #cd4 #aci4 ,our ,electrophorus is shown in ,fig4 #cd4 ,for the insulating handle use the ebonite rod1 ,e ,r 7,no4 #bh72 for the plate1 use the ebonite sheet1 ,e ,s 7,no4 #bf74 ,the electrophorus cover1 ,e ,c 7,no4 #db71 furnished1 is a tin box with a fancy top4 ,a hole has been punched in the center of its top1 and into the hole has been riveted a short tube1 so that the handle1 ,e ,r1 can be firmly held4 ,the hole has been made a little larger than ,e ,r for convenience4 ,to make ,e ,r fit tightly in the hole1 so that you can lift ,e ,c1 wrap a small piece of paper around the end of ,e ,r before pushing it into the hole4 ,you can easily find out how much paper to use to make a good fit4 ,with a knife cut away all loose points of paper that stick out of the hole around ,e ,r2 this is important4 ,the top and bottom of ,e ,c should be pressed firmly together4 ,first learn how to use the electrophorus4 ,with the large amount of electrification produced we can then find out how it works4 ,,experiment #fh4 ,to learn how to use the electrophorus4 ,apparatus4 ,shown in ,figs4 #cd1 #ce4 ,do not fail to read #aci4 #adj4 ,directions4 7,a7 ,place ,e ,s upon a flat1 uncovered1 wooden table1 and rub it vigorously for a minute with the warm flannel1 ,f ,c1 to thoroughly charge it4 ,do not let ,e ,s slide about1 and do not lift it from the table4 7,b7 ,with the right hand grasp ,e ,r at its extreme end1 and place ,e ,c upon ,e ,s4 7,c7 ,touch ,e ,c for an instant with a finger of your left hand 7,fig4 #ce74 7,d7 ,remove your finger entirely from ,e ,c1 then lift ,e ,c by its insulating handle1 ,e ,r1 at the same time holding ,e ,s down to the table1 if it tries to follow ,e ,c4 ,illustration3 ,fig4 #ce4 ,illustration3 ,fig4 #cf4 7,e7 ,bring your left hand near ,e ,c 7,fig4 #cf74 ,you should get a good spark from ,e ,c4 7,f7 ,it is not necessary to immediately rub ,e ,s again4 ,you have discharged ,e ,c by taking a spark from it4 ,to recharge it1 simply place it upon ,e ,s again2 let it remain there while you count #e2 touch it as before1 and then lift by ,e ,r4 #ada4 ,extra ,notes4 ,you may repeat the above operation many times4 ,as soon as the sparks begin to get small1 electrify ,e ,s again4 ,the charge on ,e ,c is 1 although that on ,e ,s is -4 ,you will understand1 later1 why this is so4 ,if you do not get a good spark from the electrophorus1 read the directions again4 ,the ebonite must be well electrified2 the cover must be lifted by the end of its handle2 you must touch the cover and withdraw your finger from it before lifting4 ,you must allow the cover to remain upon the ebonite #c or #d seconds each time4 ,the board1 or table1 upon which ,e ,s rests1 must be flat1 and not warped1 so that ,e ,c will fit down perfectly upon ,e ,s4 ,,experiment #fi4 ,to study charging by conduction4 ,apparatus4 ,fig4 #cg4 ,to one end of a silk thread1 ,s ,t1 is tied a little bent clamp1 ,b ,c 7,no4 #df72 the other end of ,s ,t is tied to the support wire1 ,s ,w 7,no4 #cf72 the bottom of the flat box1 ,b ,f ,b 7,no4 #dj71 is supported by ,b ,c1 and thus insulated from the table and earth2 the electrophorus 7,exp4 #fh7 is also necessary4 #adb4 ,directions4 7,a7 ,charge ,e ,c 7,exp4 #fh71 and bring it near ,b ,f ,b 7,fig4 #cg74 ,note the spark4 7,b7 ,repeat 7,a7 twice1 noting the relative sizes of the sparks4 ,does ,b ,f ,b continue to be attracted by ,e ,c8 7,c7 ,bring your knuckle slowly towards the charged disk1 ,b ,f ,b4 ,illustration3 ,fig4 #cg4 ,illustration3 ,fig4 #ch4 ,,experiment #gj4 ,to study potential2 electro-motive force4 ,apparatus4 ,the insulating table1 ,i ,t1 ,fig4 #ch4 7,for details see ,exp4 #fd2 the electrophorus ,exp4 #fh74 #adc4 ,directions4 7,a7 ,pass a spark from the thoroughly charged ,e ,c 7,exp4 #fh7 to ,i ,t4 7,b7 ,recharge ,e ,c1 and see how many times ,i ,t will take good sparks from it1 and note the relative sizes of the sparks4 7,c7 ,as soon as ,i ,t refuses to take more sparks from ,e ,c1 touch ,e ,c to see if it is completely discharged4 7,d7 ,touch ,i ,t4 #add4 ,pressure2 ,potential2 ,electro-motive ,force4 ,water runs down hill4 ,it always tries to run from a high place to a lower one4 ,electrification acts very much like water in this respect4 ,we say that water has a pressure1 or a head of so many feet4 ,in speaking of a charge1 we say that it has a potential1 or an electro-motive force4 ,water may have a high or low pressure1 and a charge may have a high or low potential4 ,the greater the pressure of water1 the harder it tries to break away and get somewhere2 the greater the potential of a charge1 the farther it will jump to your hand4 #add;a4 ,current2 ,spark4 ,electrification will easily pass from a place of high potential to one of low potential through a conductor1 and when it passes we say we have an electric current1 or a current of electricity4 ,water has no desire to flow on a dead level1 and the electric current does not care to flow between two places of equal potential4 ,the potential of the earth and of all neutral bodies is zero2 that is1 they have no charge1 no potential2 so it is very easy for a charge to escape into the earth4 ,dry air is a pretty good insulator1 but when the attraction between a charged and a neutral body gets great enough1 the spark rips right through the air4 ,benjamin ,franklin proved by experiment that lightning is caused by the electrification in the clouds and air4 7,see ,atmospheric ,electricity47 #ade4 ,theories about ,electrifications4 ,the ,one-,fluid ,theory suggests that neutral bodies have a certain amount of electrification1 and that they have a certain potential called zero potential4 ,if the potential of a body becomes greater than that of the earth1 the body is said to be positively electrified2 if the potential of the body is less than that of the earth1 it is said to be negatively electrified4 ,if we fill a bottle with sea water1 we have a great deal of water when we compare it with the bottle1 but a very little water when we compare it with the sea4 ,the earth is so large that small amounts of electrification taken from it or added to it do not affect its potential to any extent4 #adf4 ,the ,two-,fluid ,theory suggests that there are two absolutely different kinds of electrification1 one called positive 771 and the other negative 7-74 ,when these two are equal in quantity1 the body is said to be neutral4 ,if the body contains more than -1 the body is said to be charged positively4 ,it is evident then1 if the two-fluid theory be accepted1 that no matter how strongly a body is charged positively there must be in it some negative electrification2 that is1 we may charge a neutral body by adding electrification to it1 or by taking - electrification from it4 ,there must always be1 then1 some and - electrifications in a body4 ,these theories do not require much consideration by the student of elementary electricity4 ,the best thing he can do is to learn what electricity can do1 and how it can be used4 ,illustration3 ,fig4 #ci4 ,,experiment #ga4 ,to study some methods of discharging an electrified body4 ,apparatus4 ,the electrophorus 7,exp4 #fh72 an ordinary pin 7,fig4 #ci74 #adg4 ,note4 ,you have seen sparks pass from ,e ,c to your rounded knuckle1 and to other conductors4 ,in all of these cases the discharge was sudden1 one spark doing the work4 ,can we slowly discharge ,e ,c1 or discharge it without sounds8 #adh4 ,directions4 7,a7 ,thoroughly charge ,e ,c1 and test it with your knuckle to be sure that it is working properly4 7,b7 ,charge ,e ,c again2 hold the pin in your left hand 7,fig4 #ci71 and slowly bring its head toward ,e ,c2 listen for sparks4 7,c7 ,recharge ,e ,c1 and bring the point of the pin slowly toward it4 ,touch ,e ,c to see whether it has been discharged or not4 #adi4 ,disruptive1 ,conductive1 and ,convective ,discharges4 ,sudden discharges1 accompanied by bright sparks1 are said to be disruptive4 ,when the electrification is continuously carried away by a conductor1 there is a conductive discharge4 ,there is a convective discharge when the electrification escapes from points into the air4 7,see #aee47 ,the nature of the discharge depends upon the potential of the charge1 upon the nature of the charged conductor1 and upon the nature of the surrounding air and objects4 ,convective discharges are often silent1 as in ,exp4 #ga 7,c74 ,in this case1 electrification passed from the earth through the pin-point to the cover to neutralize it4 7,see ,induced ,electricity47 ,illustration3 ,fig4 #dj4 ,,experiment #gb4 ,to study intermittent or step-by-step discharges4 ,apparatus4 ,electrophorus 7,exp4 #fh72 carbon electroscope 7 #aad71 7,exp4 #eh74 #aej4 ,directions4 7,a7 ,charge ,e ,c1 then hold your hand on one side of the carbon 7,fig4 #dj71 and hold ,e ,c upon the opposite side4 ,what should the carbon do8 #aea4 ,discussion4 ,the carbon and ,e ,c were insulated1 while the hand was grounded--that is1 it was connected with the earth4 ,carbon is a good conductor2 it may be quickly charged and discharged4 ,,experiment #gc4 ,to ascertain the location of the charge upon an electrified conductor4 ,apparatus4 ,the electrophorus 7,exp4 #fh72 the insulating table1 ,i ,t 7,exp4 #fd72 the tin box1 ,t ,b 7,no4 #dg71 ,fig4 #da2 a piece of moist cotton thread1 ,c ,t1 #e or #f in4 long1 bent double1 and hung over the edge of the open box1 ,t ,b4 ,one-half of ,c ,t should be inside of ,t ,b1 which1 in turn1 should stand on ,i ,t4 ,illustration3 ,fig4 #da4 #aeb4 ,directions4 7,a7 ,charge ,e ,c2 pass a spark to ,t ,b1 and note the action of both parts of ,c ,t4 #aec4 ,hollow and ,solid ,conductors4 ,the moist thread1 being a conductor1 became charged as well as the box4 ,the electrification seemed to be entirely on the outside of ,t ,b4 ,a hollow conductor will hold as large a charge as a solid one having the same amount of surface4 ,this refers to charges of static electricity1 not to currents4 ,an electric current passes through the whole substance of a conductor4 ,,experiment #gd4 ,to study the effect of points upon a charged conductor4 ,apparatus4 ,the electrophorus 7,fig4 #cd72 a pin1 bent slightly to keep it from rolling4 #aed4 ,directions4 7,a7 ,charge ,e ,c2 test its charge with your knuckle4 ,be sure that you get a good spark4 7,b7 ,charge ,e ,c again1 and hold it by its insulating handle1 ,e ,r1 long enough to count #aj before discharging it with your knuckle4 ,be sure that it holds its charge during this time4 7,c7 ,while ,e ,c is upon ,e ,s 7,fig4 #cd71 lay the bent pin upon ,e ,c1 so that its point will project into the air4 ,the point should stick out about #a_/d in4 from the edge of ,e ,c4 7,d7 ,touch ,e ,c2 raise it by ,e ,r2 count #aj as before2 then test with your knuckle to see if ,e ,c is still charged4 #aee4 ,electric ,density2 ,electric ,wind4 ,a charge resides upon the outside of a conductor 7,exp4 #gc71 and it continually tries to escape4 ,it seems to pile up at points and corners1 and we say that it is denser at such places than at well-rounded parts of a charged conductor4 ,all points and sharp places should be removed from a conductor1 if it is desired to keep a charge for any length of time4 ,electrification may escape from a point so rapidly that currents are produced in the surrounding air4 ,as the particles of air become charged1 they repel each other4 ,the movement of the air particles may be so great that a lighted candle will be affected when placed near the point4 ,this current of air is called electric wind4 ,electrification easily passes from points1 and the electrophorus may be easily and silently discharged by holding a pointed pin near it 7,exp4 #ga1 ,c74 ,thorns1 leaves with sharp edges1 etc41 have a great effect upon atmospheric electricity4 ,they allow a silent escape of electrification from the earth to neutralize that in the clouds which is opposite in nature4 7,see ,atmospheric ,electricity47 ,,chapter ,,ix4 ,,induced ,,electrification4 #aef4 ,electric ,field2 ,lines of ,force4 ,in our study of magnetism you learned that a magnet can act through the air1 and induce a piece of iron to become a magnet4 ,you saw how the iron filings arranged themselves around the magnet1 showing that the lines of force reached out from the poles in a very peculiar manner4 ,there is an electric field all around a charged conductor1 just as there is a magnetic field about a magnet4 ,the lines of force in the electric field pass from the positively charged body to the negatively charged one1 or to some neutral one1 which1 you will soon see1 is practically the same thing4 ,when the positively charged electrophorus cover is held above the negatively charged ebonite sheet1 a very strong electric field exists between them4 #aeg4 ,note4 ,you have seen that we can charge an insulated conductor by touching it with the charged cover1 or by allowing a spark to pass to the conductor4 ,what effect1 if any1 has a charged body upon an insulated conductor before they touch each other1 and before any spark passes to the conductor8 ,illustration3 ,fig4 #db4 ,,experiment #ge4 ,to study electric induction4 ,apparatus4 ,fig4 #db4 ,the insulating table1 ,i ,t 7for details see ,exp4 #fd72 tin box1 ,t ,b 7,no4 #dg1 ,fig4 #db72 moist cotton thread1 ,c ,t2 the electrophorus 7,exp4 #fh72 tie ,c ,t around one end of the closed ,t ,b1 and leave the ends of ,c ,t long enough to hang down over the end4 ,place a match on each side of ,t ,b to keep it from rolling4 #aeh4 ,directions4 ,part #a4--7;,a7 ,pass a spark from the charged ,e ,c to ,t ,b1 and note the action of the thread1 which will be our electroscope4 ,remove ,e ,c4 7,b7 ,touch the charged ,t ,b with the finger1 watching ,c ,t4 ,part #b4 7,c7 ,bring the re-charged ,e ,c near the neutral ,t ,b1 and parallel to its end surface2 but keep them at least an inch apart1 so that a spark cannot pass4 ,watch ,c ,t4 7,d7 ,withdraw ,e ,c1 and try to explain the action of ,c ,t4 #aei4 ,electric ,polarization2 ,theory of ,induction4 ,this experiment should remind the student of ,exp4 #bd1 in magnetism1 in which a piece of soft iron was magnetized by the inductive action of a magnet4 ,the soft iron was in a magnetic field2 it became polarized4 ,is it possible that the box1 ,t ,b1 was polarized1 being in the electric field of ,e ,c8 ,we know1 by the action of ,c ,t 7,fig4 #db71 that the top end of ,t ,b was charged while ,e ,c was in place4 ,the charge was not conducted4 ,you know1 from previous experiments1 that and - electrifications rush together whenever possible4 ,why can we not suppose that a neutral body1 like the box at the start1 contains an equal amount of both kinds1 and that these different electrifications have already rushed together8 ,if you imagine a small army of positive soldiers struggling1 man to man1 with the same number of equally strong negative soldiers1 you can readily see that one-half of them can hold the other half from running away4 ,a body remains neutral1 then1 according to this idea1 as long as it has an equal quantity of the two opposite kinds of electrification4 7,see ,theories1 #ade1 #adf47 ,as soon as the positively charged ,e ,c was brought near ,t ,b1 it destroyed the neutrality of ,t ,b1 by pulling at its - electrification1 and by pushing back its electrification to the top end and into ,c ,t4 ,we say that the charged ,e ,c produced a separation of the combined electrifications of ,t ,b by induction1 and not by contact4 ,as soon as the inductive action of ,e ,c was removed1 ,t ,b became neutral again4 ,illustration3 ,figs4 #dc-dd4 #afj4 ,note4 ,figs4 #dc and #dd may aid the student4 ,in ,fig4 #dc1 ,t ,b is supposed to be neutral4 ,the double sign means that the and - electrifications are united2 and1 as there are an equal number of both kinds1 none are left free to tell the tale4 ,fig4 #dd shows what happens when the ,e ,c is near4 ,what would happen if we could cut into ,t ,b at the middle with an insulated knife while it is polarized by ,e ,c8 ,,experiment #gf4 ,to learn how to charge a body by induction4 ,apparatus4 ,fig4 #db1 same as in ,exp4 #ge4 #afa4 ,directions4 7,a7 ,bring the charged ,e ,c within an inch of the bottom of ,t ,b1 and as soon as ,c ,t is repelled1 showing that ,t ,b is polarized 7,exp4 #ge71 touch ,t ,b with your finger2 then remove your finger while you still hold ,e ,c in place4 7,b7 ,withdraw ,e ,c and its inductive action4 ,explain the motions of ,c ,t during the experiment4 ,is it still repelled by ,t ,b after ,e ,c is removed8 #afb4 ,free and ,bound ,electrifications4 ,as explained in ,exp4 #ge1 and as shown in ,fig4 #dd1 ,t ,b became polarized4 ,the - electrification was drawn towards ,e ,c2 it was held or bound there as long as ,e ,c was near4 ,the was actually repelled by ,e ,c1 and it was free to escape through your arm as soon as ,t ,b was touched1 leaving the top end of ,t ,b neutral4 ,as soon as ,e ,c was removed1 the - electrification1 no longer held by ,e ,c1 spread all over ,t ,b and on to ,c ,t4 ,t ,b was charged by induction4 ,it was charged negatively by driving out electrification4 ,,experiment #gg4 ,to show that a neutral body is polarized before it is attracted by a charged one4 ,apparatus4 ,the electrophorus 7,exp4 #fh72 dry tissue-paper1 ,t ,p4 ,cut out #b pieces of ,t ,p1 each about #a_/d inch square4 #afc4 ,directions4 7,a7 ,place the bits of dry ,t ,p upon a board or table1 and convince yourself that they are attracted equally by the charged ,e ,c4 7,b7 ,slightly moisten one piece of ,t ,p only4 ,see if one is attracted by ,e ,c more readily than the other4 #afd4 ,polarization ,precedes ,attraction4 ,dry tissue-paper is not a good conductor2 you have seen 7,exp4 #eb7 that it can be electrified1 which indicates that it is at least a partial insulator4 ,insulators are not easily polarized4 7,why87 ,even if the pieces of ,t ,p were polarized1 the opposite electrifications were so near each other that the attraction of ,e ,c for the - was nearly overcome by the repulsion for the 2 the result being that ,t ,p was not strongly attracted by ,e ,c until the had a chance to escape4 ,the moist tissue-paper allowed its to escape more quickly than the dry piece4 ,a conductor is attracted by a charged body more strongly than an insulator1 because the latter is not easily polarized4 ,a neutral body1 then1 is really no longer neutral when it is in the electric field4 ,polarization precedes attraction4 ,,experiment #gh4 ,to find whether electric induction will act through an insulator4 ,apparatus4 ,small bits of carbon 7,exp4 #eh72 bits of moist tissue-paper1 ,t ,p2 one-half of the flat box1 ,t ,f ,b 7,no4 #da72 sheet of glass1 ,g 7,no4 #ch72 electrophorus 7,exp4 #fh74 ,place the carbon and ,t ,p into ,t ,f ,b 7,fig4 #de71 and cover with the glass4 #afe4 ,directions4 7,a7 ,charge the electrophorus cover1 ,e ,c 7,exp4 #fh71 move it about a little above the glass1 and see if the carbon1 etc41 are attracted4 #aff4 ,dielectrics4 ,the carbon must have been polarized and attracted through the glass4 ,you saw1 ,exp4 #g1 that the lines of magnetic force could penetrate and act through paper1 glass1 etc42 it is now evident that the electric field is not easily fenced in1 even by an insulator4 ,substances1 like the glass1 which allow this inductive influence to act through them1 are called dielectrics4 ,illustration3 ,fig4 #de4 ,illustration3 ,fig4 #df4 ,,experiment #gi4 ,to find whether a polarized conductor can act inductively upon another conductor4 ,apparatus4 ,fig4 #df4 ,insulating table1 ,i ,t 7for details see ,exp4 #fd72 ebonite sheet1 ,e ,s 7,no4 #bg72 flat box complete ,f ,b 7,nos4 #dj1 #da72 sheet of glass1 ,g 7,no4 #ch72 small piece of slightly moist tissue-paper1 ,t ,p2 charged electrophorus cover1 ,e ,c4 ,arrange as shown4 #afg4 ,directions4 7,a7 ,hold ,e ,c1 charged1 near and under ,i ,t1 then bring your finger1 ,f1 near ,t ,p4 ,explain the action of ,t ,p4 #afh4 ,successive ,induction4 ,the inductive influence of ,e ,c first polarized ,i ,t2 this acted through the dielectric1 ,e ,s1 and polarized ,f ,b1 which1 in turn1 polarized ,t ,p through the second dielectric1 ,g4 ,this induction after induction is called successive induction4 #afi4 ,inductive ,capacity4 ,dielectrics are insulators4 ,two substances may be equally good insulators1 that is1 they may equally well resist the spread of electrification over their surfaces1 or the flow of the electric current through them1 while one may be1 nevertheless1 a better dielectric than the other4 ,the better the dielectric1 the easier it is for the electric field to polarize a conductor placed beyond the dielectric4 ,a good dielectric is said to have a high inductive power or capacity4 ,glass is about #c times as good a dielectric as dry air2 and as the latter 7under certain conditions7 is taken as the standard1 or as unity1 we may say that the specific inductive capacity of glass is about #c4 ,,experiment #hj4 ,to study the action of the electrophorus4 ,apparatus4 ,the electrophorus 7,exp4 #fh72 small bits of moist tissue-paper1 ,t ,p4 #agj4 ,directions4 7,a7 ,thoroughly electrify ,e ,s1 ,fig4 #cd1 and place ,e ,c upon it by its handle1 ,e ,r4 7,b7 ,touch ,e ,c1 as directed in ,exp4 #fh1 and listen for a small spark which should pass from ,e ,c to your finger4 7,c7 ,again1 place a little piece of ,t ,p upon ,e ,c before lowering it upon ,e ,s4 ,do not touch ,e ,c1 but bring your finger near ,t ,p4 ,what does ,t ,p do8 ,now1 touch ,e ,c and see1 when you bring your finger near it1 if ,t ,p acts as it did before4 7,d7 ,again1 place several pieces of ,t ,p upon ,e ,c 7,e ,s being thoroughly charged72 touch ,e ,c1 then lift it by its handle4 ,note action of ,t ,p1 which should be slightly moist4 #aga4 ,discussion4 ,the electrification upon the ebonite is negative 7,exp4 #fj74 ,although ,e ,s and ,e ,c 7,fig4 #cd7 seem quite smooth1 there are many little hills1 valleys1 and air-spaces between them1 which keep them from touching each other perfectly4 ,the ebonite has the electric field at the start1 and it really acts across these minute air-spaces by induction 7,exp4 #ge71 and polarizes ,e ,c4 ,the air-spaces form the dielectric 7,exp4 #gh74 ,the - electrification of ,e ,c being repelled by the - of ,e ,s1 it is driven to the top of ,e ,c1 while the is drawn to the bottom4 ,this is kept from rushing to the - of ,e ,s by the air dielectric1 and because ,e ,s is a non-conductor4 ,by touching ,e ,c the free - escapes to the earth1 leaving ,e ,c positively charged when it is lifted4 ,illustration3 ,fig4 #dg4 ,illustration3 ,fig4 #dh4 ,illustration3 ,fig4 #di4 ,illustration3 ,fig4 #ej4 ,illustration3 ,fig4 #ea4 #agb4 ,details of ,action4 ,the different steps in the action of the electrophorus are shown graphically in ,figs4 #dg to #ea4 ,fig4 #dg shows ,e ,s negatively charged4 ,e ,c is neutral at first1 ,fig4 #dh2 that is1 it is supposed to contain both and -1 as shown by the double sign 7 #afj74 ,fig4 #di shows that ,e ,c has been polarized by the inductive action of ,e ,s4 ,the repelled - escapes to the finger 7this escaping is what gave the small spark to the finger and charged the ,t ,p in the last experiment71 leaving the top uncharged1 while the is bound 7,fig4 #ej74 ,as soon as ,e ,c is lifted 7,fig4 #ea7 the spreads all over ,e ,c1 which is then charged4 ,the 1 upon going to the top1 charged the pieces of ,t ,p 7,exp4 #hj1 ,d71 causing them to be repelled4 ,the charge of - upon ,e ,s has not been removed1 so the operation may be repeated many times before ,e ,s must be again electrified4 ,the - electrification on the ebonite acts inductively through ,e ,s1 drawing up electrification from the earth4 ,to make this action easier a sole1 or metal conductor1 is often placed under the ebonite4 ,,experiment #ha4 ,to see1 hear1 and feel the results of inductive influence and polarization4 ,apparatus4 ,ebonite sheet1 ,e ,s 7,no4 #bf72 insulating table1 ,i ,t2 flannel cloth1 ,f ,c4 #agc4 ,directions4 7,a7 ,thoroughly charge ,e ,s with ,f ,c4 ,with the right hand bring ,e ,s near and parallel to the top surface of ,i ,t1 but do not let them touch each other4 7,b7 ,remove ,e ,s1 then touch ,i ,t to see if it is charged4 7,c7 ,repeat 7,a71 and while you hold ,e ,s about #a_/b inch from ,i ,t1 their flat surfaces being parallel1 touch ,i ,t4 ,watch for any sparks1 and note any peculiar actions of ,e ,s4 7,d7 ,remove your finger from ,i ,t1 then withdraw ,e ,s2 finally touch ,i ,t with your knuckle4 #agd4 ,discussion4 ,this apparatus is really the electrophorus upside down4 ,it shows very clearly 7#a7 the escape of the - electrification from ,i ,t1 by the spark2 7#b7 that the attraction between ,i ,t and ,e ,s is much greater than before1 when this - is removed2 and 7#c7 it shows the different steps of the inducing and charging process1 as described in ,exp4 #ge1 and as shown in ,figs4 #dc and #dd4 ,,chapter ,x4 ,,condensation ,,of ,,electrification4 ,,experiment #hb4 ,to find whether a large surface will hold more electrification than a small one4 ,apparatus4 ,the insulating table 7for details1 see ,exp4 #fd72 a large tin basin or pan 7not furnished72 the electrophorus 7,exp4 #fh74 #age4 ,directions4 7,a7 ,test the electrophorus and be sure that it is working properly4 7,b7 ,as in ,exp4 #gj1 see how many good sparks ,i ,t will take from ,e ,c 7which should be recharged at each trial7 before the potential of ,i ,t is raised so that it equals the potential of ,e ,c4 7,c7 ,carefully set the basin or pan upon ,i ,t1 then count the number of good sparks you can pass to it from ,e ,c 7recharged at each trial74 ,compare the number of sparks necessary to raise the potential of the large surface until it equals that of ,e ,c1 with the number found in part 7,b74 #agf4 ,electrical ,capacity4 ,it takes more heat to raise the temperature of a gallon of ice-water to the boiling point1 than it takes for a quart of ice-water4 ,you have just seen that a large insulated surface will take more sparks from a charged body than a small one1 before its potential is raised to that of the small one1 and to that of the charging body4 ,we say that a large surface has a greater capacity than a small one1 the shape and other conditions being the same4 ,,experiment #hc4 ,to find whether the capacity of a given conductor can be increased without increasing its size4 ,apparatus4 ,fig4 #eb4 ,insulating table4 ,i ,t 7,exp4 #fd72 the extra ebonite sheet1 ,e ,s 7,no4 #bg72 the complete flat box1 ,f ,b 7,no4 #dj1 #da72 the charged electrophorus cover1 ,e ,c 7,exp4 #fh74 ,arrange1 as shown1 ,i ,t being insulated from the earth by ,e ,s4 ,f ,b should rest upon a wooden table or other large conductor4 #agg4 ,directions4 7,a7 ,see how many good sparks ,i ,t will take from ,e ,c4 ,re-charge ,e ,c at each count1 and note the relative sizes of the sparks4 7,b7 ,discharge ,i ,t by touching it with your knuckle4 ,illustration3 ,fig4 #eb4 #agh4 ,condensation2 ,condensers4 ,as ,i ,t easily held more sparks than it would take before 7,exp4 #gj71 we say that its capacity has been increased4 ,its potential didn't increase1 because that could not get greater than the potential of ,e ,c1 the charging body4 ,to describe this state of affairs1 we say that the electrification was denser than before1 and that it was condensed4 ,the capacity of ,i ,t was greatly increased by the presence of another conductor1 ,f ,b1 insulated from ,i ,t1 but grounded4 ,such a combination1 #b conductors1 with a dielectric between them1 is called a condenser4 ,a condenser can hold much more electrification at a certain potential than an equal amount of surface can hold when not properly arranged4 ,we might call a condenser a storage battery for static electricity4 ,the capacity of a condenser depends1 among other things1 upon the area of the conducting surfaces1 and upon the thickness and nature of the dielectric4 ,among the various forms of condensers may be mentioned the ,leyden jar1 and the fulminating pane4 #agi4 ,the ,leyden ,jar consists of a wide-mouthed glass jar1 with tin-foil pasted upon the inside and outside to within #b or #c inches of the top4 ,the inner coat or conductor is connected to a knob or ball at the top by means of a chain4 ,to charge the jar1 the outer coat is connected with the earth by holding it in the hand1 or by resting it upon a table while the electrification is passed to the knob4 ,a ,leyden ,battery consists of #b or more connected jars1 the object being to increase the area of the surface4 ,the jar is discharged by touching one end of a discharger 7 #ahh7 to the outer coat1 and swinging its other end over to the knob1 when a bright spark will pass between the knob and discharger4 7,see ,exp4 #hf47 #ahj4 ,fulminating ,panes1 or ,franklin's ,plates1 are practically the same as a ,leyden ,jar4 ,the tin-foil1 however1 is pasted upon the opposite sides of a pane of glass1 a margin of about an inch being left all around4 ,one side of the pane is charged1 and takes the place of the inside coat of the jar4 ,the other side is grounded4 ,the pane is discharged by connecting the two sheets of foil4 #aha4 ,induction ,coil ,condensers consist of sheets of tin-foil separated by sheets of paraffined paper1 which act as the dielectric4 7,see ,induction ,coils47 #ahb4 ,submarine ,cables1 with the surrounding water1 act like condensers1 the result being that the condensing effect slows up the electric current and retards the signals4 ,these make a condenser of enormous capacity4 ,the wires inside form one conductor1 and the water the other1 while the insulation around the wires forms the dielectric4 ,,experiment #hd4 ,to study the condensation of electrification4 ,apparatus4 ,same as in last experiment1 but arrange so that ,f ,b and ,i ,t shall be near each other at one side2 that is1 so that the edge of ,e ,s shall be even with the edges of the two tins4 #ahc4 ,directions4 7,a7 ,pass good sparks to ,i ,t from the charged ,e ,c until something happens4 ,watch the side where ,i ,t and ,f ,b are near each other4 #ahd4 ,discussion4 ,we may say that the electrification was condensed1 in this experiment1 until the charge became so great that the condenser suddenly discharged itself4 ,condensers may be made in many ways1 but they all consist of #b conductors1 with a dielectric between them4 ,one conductor is insulated1 and receives the charge2 the other conductor is grounded4 ,illustration3 ,fig4 #ec4 ,,experiment #he4 ,to study the action of the condenser4 ,apparatus4 ,fig4 #ec4 ,the insulating table1 ,i ,t2 ebonite sheet1 ,e ,s 7,no4 #bg72 flat box1 ,f ,b1 complete 7,nos4 #dj1 #da72 the electrophorus 7,exp4 #fh74 ,note that this is really the same apparatus as that just used2 both conductors of this condenser1 however1 are insulated and reversed in position4 #ahe4 ,directions4 7,a7 ,see that your electrophorus works properly1 then find out how many good sparks you can pass from ,e ,c to ,f ,b1 recharging ,e ,c each time4 ,note the relative sizes of the sparks1 and compare the result with the number taken by the condenser in the last experiment4 7,b7 ,when ,f ,b seems to be fully charged1 touch ,i ,t with your knuckle4 7,from your study of induction what should be the result87 7,c7 ,now see if ,f ,b will again take good sparks from the charged ,e ,c4 ,pass sparks to ,f ,b until it seems fully charged4 7,d7 ,again touch ,i ,t1 then repeat 7,a7 and 7,b7 several times1 until a bright spark passes from ,f ,b over the edge of ,e ,s to ,i ,t4 #ahf4 ,discussion4 ,the action of the condenser1 as clearly shown1 depends upon induction4 ,you should now be able to explain and show by diagram the different steps4 ,e ,c was positively charged 7,exp4 #hj74 ,this also charged ,f ,b positively by contact4 ,f ,b acted inductively through the dielectric1 ,e ,s1 drawing up some of the - in ,i ,t1 and repelling some of the 4 ,as ,i ,t was insulated1 this free electrification could not escape4 ,before we touched ,i ,t1 its and - electrifications1 although partially separated1 were struggling against this inductive action2 and1 on account of their strong attraction for each other1 our efforts to charge the condenser were retarded4 ,upon touching ,i ,t the free escaped to the earth4 7,this was the cause of the spark47 ,this left some - electrification bound on the underside of ,e ,s1 and some bound on the upperside of ,e ,s4 ,the capacity of ,f ,b was increased by this process1 as the already put into it was very much occupied by the attractions of the induced - just under ,e ,s4 ,as more was given to ,f ,b1 more - was drawn up under ,e ,s and more was pushed out of ,i ,t4 ,this action went on until the two conductors were strongly and oppositely charged4 ,this action goes on continuously when the lower conductor is grounded4 ,the spark between the tins was due to the rushing together of the and - electrifications2 it showed that there was a momentary current of electricity4 ,,experiment #hf4 ,to study the effect of electrical discharges upon the human body4 ,apparatus4 ,the condenser 7,fig4 #eb71 with ,e ,s centrally placed so that the apparatus cannot discharge itself2 the hairpin discharger1 ,h ,p ,d 7,no4 #dh72 the electrophorus4 #ahg4 ,directions4 7,a7 ,charge the condenser 7,exp4 #hc7 with #aj good sparks from ,e ,c1 then touch ,i ,t 7,fig4 #eb74 7,b7 ,recharge the condenser with #aj sparks1 then touch ,f ,b4 ,discharge it by again touching ,i ,t as in 7,a74 7,c7 ,recharge with #aj sparks2 then place your thumb against ,f ,b1 and quickly swing the first finger of the same hand over to ,i ,t1 and get a slight shock4 7,d7 ,recharge with as many sparks as you think you can stand4 7,e7 ,instead of using your hand to discharge the condenser1 try the bent hairpin4 ,keeping one end against ,f ,b1 swing the other end over near ,i ,t4 #ahh4 ,shocks2 ,dischargers4 ,the two conductors being oppositely charged in the condenser 7,exp4 #he71 it is only necessary to place some conductor between them to allow the charges to rush together4 ,any conductor so used is called a discharger4 ,the hand carried the whole current which caused the shock4 ,when ,i ,t was touched first1 the current was obliged to pass through your body1 through the floor1 and up the table-legs into ,f ,b4 ,always touch the grounded conductor first with the discharger1 so that you will get a good spark and not a shock4 ,,experiments #hg-hh4 ,to show the strong attraction between the opposite electrifications in the condenser4 ,apparatus4 ,flat box1 ,f ,b 7,nos4 #dj1 #da72 sheet of glass1 ,g 7,no4 #ch72 electrophorus 7,exp4 #fh74 ,the two parts of ,f ,b are used for the conductors of the condenser 7,fig4 #ed7 for the sake of lightness4 ,the bottoms should be next to the glass1 which is used for the dielectric on account of its stiffness4 ,the lower tin should rest upon the table4 ,the glass should be perfectly clean and dry 7hot74 #ahi4 ,directions4 7,a7 ,charge the condenser with #ae or #bj good sparks from ,e ,c4 7,b7 ,lift the condenser by one corner of ,g 7,fig4 #ed71 being careful not to discharge it4 ,explain why the lower conductor follows the glass4 ,illustration3 ,fig4 #ed4 ,,experiment #hh4 #aij4 ,directions4 7,a7 ,charge and lift the condenser as just explained 7,exp4 #hg74 ,fig4 #ed4 7,b7 ,with your right hand touch the upper tin alone1 then the lower tin alone4 7,c7 ,touch both tins at the same time1 and note the action of the lower one4 #aia4 ,discussion4 ,this clearly shows how strongly the two electrifications are bound in the condenser4 ,each refuses to escape to the earth1 but they instantly rush together at the first opportunity4 ,the dielectric may be shattered in a very heavily-charged condenser by this strong attraction4 ,illustration3 ,fig4 #ee4 ,,experiment #hi4 ,to show how the condenser maybe slowly discharged4 ,apparatus4 ,fig4 #ee4 ,the condenser 7,exp4 #hc72 the carbon electroscope with support 7,exp4 #eh72 the electrophorus 7,exp4 #fh74 #aib4 ,directions4 7,a7 ,charge the condenser by means of the electrophorus2 then hang the carbon so that it can swing between the upper conductor and ,e ,c placed as shown4 #aic4 ,the ,electric ,chime4 ,the charging and discharging of the carbon being rapid1 it acts like a chime as it taps against the tins4 ,,experiment #ij4 ,to ascertain the location of the charge in the condenser4 ,apparatus4 ,the condenser1 consisting of flat box1 ,f ,b 7,nos4 #dj1 #da72 ebonite sheet1 ,e ,s 7,no4 #bg72 insulating table1 ,i ,t 7,exp4 #fd72 7when charging1 arrange as in ,fig4 #eb472 the electrophorus2 hairpin discharger1 ,h ,p ,d 7,no4 #dh74 #aid4 ,directions4 7,a7 ,charge the condenser with #ae or #bj good sparks from ,e ,c4 7,b7 ,lift ,i ,t away from ,e ,s by its insulating handle1 and set it upon the table4 7,it may be necessary to hold ,e ,s down47 7,c7 ,lift ,e ,s directly up and away from ,f ,b4 7,lift by #b corners2 do not scrape ,e ,s along on ,f ,b2 do not allow ,e ,s to touch your clothing47 7,d7 ,replace ,e ,s and then ,i ,t by its handle quickly1 making the condenser complete again4 7,e7 ,with ,h ,p ,d see if the condenser still holds a charge4 ,touch ,f ,b first 7,exp4 #hf74 #aie4 ,discussion4 ,as the conductors were completely discharged1 being left for a few moments upon the table1 it is evident that the opposite electrifications must reside in and upon the dielectric4 ,the conductors allow an even and rapid discharge from all parts of the dielectric at the same time4 ,the dielectric is considerably strained when a condenser is heavily charged4 ,this strain1 caused by the attraction of the opposite electrifications1 may be great enough to break or puncture the dielectric4 ,,experiment #ia4 ,to find whether any electrification remains in the condenser after it has once been discharged4 ,apparatus4 ,the condenser 7,fig4 #eb72 the electrophorus 7,exp4 #fh72 hairpin discharger1 ,h ,p ,d4 #aif4 ,directions4 7,a7 ,thoroughly charge the condenser4 7,b7 ,discharge it with ,h ,p ,d1 being sure to touch ,f ,b first1 and to touch ,i ,t for an instant while ,h ,p ,d is against ,f ,b4 7,c7 ,after a few moments use ,h ,p ,d again1 and see if you get a slight spark4 #aig4 ,residual ,charge4 ,the two electrifications on the opposite sides of the dielectric have such an attraction for each other1 when the condenser is charged1 that they seem to penetrate1 or soak into1 the dielectric4 ,these do not completely soak out again at the discharge4 ,the small amount left is called a residual charge4 ,illustration3 ,fig4 #ef4 ,,experiment #ib4 ,to study successive condensation2 the chime cascade4 ,apparatus4 ,fig4 #ef4 ,this really consists of two condensers1 joined by a wire4 ,the upper condenser consists of ,t ,f ,b 7,no4 #da71 ,e ,s 7,no4 #bg71 and the insulating table1 ,i ,t4 7,see ,exp4 #fd47 ,the lower condenser consists of the cover of the tin box1 ,c ,t ,b 7,no4 #dg71 the sheet of glass ,g 7,no4 #ch71 and ,b ,f ,b 7,no4 #dj74 ,the tin box1 ,t ,b 7,no4 #dg71 is placed under this to raise it1 simply4 ,a wire or hairpin1 ,h ,p1 is hung upon the edge of ,t ,f ,b1 its lower end being inside of ,c ,t ,b and not quite touching it4 ,this acts like a pendulum1 which is to swing to ,c ,t ,b at the proper time4 ,the source of electrification is ,e ,c4 ,note4 ,you have learned that in charging the condenser with the positively charged ,e ,c1 electrification is driven from ,f ,b into the earth4 ,can we use this to charge a second condenser8 #aih4 ,directions4 7,a7 ,pass #ae or #bj good sparks from ,e ,c to the under side of ,i ,t 7,fig4 #ef71 noting the action of ,h ,p4 7,b7 ,hold ,e ,c in the hand1 and1 with its insulating handle1 poke ,h ,p away from the condensers4 ,do not discharge them4 7,c7 ,with ,h ,p ,d test the lower condenser for a charge1 touching ,t ,b first4 7,d7 ,with ,h ,p ,d touch ,t ,f ,b first 7why871 and discharge the upper condenser4 #aii4 ,discussion4 ,a long row of condensers may be charged in this way4 ,there is no advantage in it1 as the electrification is merely divided between them4 ,how can two condensers be joined to get the advantages of a large surface8 ,,chapter ,,xi4 ,,electroscopes4 #bjj4 ,electroscopes are instruments to show the presence1 relative amount1 or kind of electrification on a body4 7,see ,apparatus ,book1 ,chap4 ,,xviii1 for ,home-,made ,electroscopes47 ,the carbon electroscope has been described 7,exp4 #eh74 ,the pith-ball electroscope is made by using pith from elder1 corn-stalk1 or milk-weed1 in place of the carbon4 ,the gold-leaf electroscope is a very delicate instrument4 ,the gold-leaf is supported1 as suggested in ,fig4 #eg1 at the lower end of a wire conductor which sticks through and hangs from the cork of a glass jar or flask4 ,to the top end of the wire is soldered a ball or disk4 ,the glass jar insulates the gold-leaf1 and keeps it dry and free from dust4 ,illustration3 ,fig4 #eg4 #bja4 ,our ,leaf ,electroscope 7,fig4 #eg7 is made with aluminum-leaf4 ,gold-leaf is too delicate for unskilful handling1 and aluminum will do for all ordinary experiments4 ,to cut it into any desired shape1 place it between two sheets of paper1 then cut through paper and all4 #bjb4 ,construction4 ,bend one leg of a hairpin1 ,h ,p1 as in ,fig4 #eg1 and slide it onto ,i ,t4 ,hang a wire1 ,w1 or another hair pin straightened1 then bent1 from the horizontal leg of ,h ,p4 ,this is to support the leaves1 ,l1 which are made from a strip of aluminum-leaf about #d in4 long and #c_/d in4 wide4 ,moisten the under side of the horizontal part of ,w with paste or mucilage2 press it upon the middle of the strip laid flat upon the table1 and then lift ,w4 ,the leaves should cling to ,w4 ,each leaf should be1 then1 #b in4 long4 ,they should hang close together when not in use4 ,a large chimney1 or fruit-jar1 may be used to surround the leaves1 and to keep currents of air from them4 ,the leaves should not touch the side of the jar when spread4 ,,experiment #ic4 ,to study the leaf electroscope2 charging by conduction4 ,apparatus4 ,the leaf electroscope 7,fig4 #eg1 #bja1 #bjb72 ebonite rod1 ,e ,r 7,no4 #bh72 flannel cloth1 ,f ,c 7,no4 #cj74 #bjc4 ,directions4 7,a7 ,thoroughly charge ,e ,r1 then scrape it along upon ,i ,t1 noting the action of the leaves1 ,l4 7,b7 ,see if the leaves will remain spread for some time4 7,c7 ,touch ,i ,t to discharge it1 and note the action of ,l4 #bjd4 ,discussion4 ,no explanation should be necessary for this4 ,are the leaves charged alike8 ,as they were charged by contact1 is the electrification on them or -8 ,,experiment #id4 ,to charge the leaf electroscope by induction4 ,apparatus4 ,our electroscope 7,fig4 #eg1 #bjb72 ebonite sheet1 ,e ,s 7,no4 #bg72 flannel cloth1 ,f ,c 7,no4 #cj74 #bje4 ,directions4 7,a7 ,charge ,e ,s with ,f ,c1 then hold ,e ,s above ,i ,t 7,fig4 #eg71 their surfaces being kept parallel and about #b or #c inches apart4 ,watch the leaves4 7,b7 ,withdraw ,e ,s4 ,do the leaves remain spread8 7,c7 ,repeat 7,a71 and before removing ,e ,s1 touch ,i ,t4 7,d7 ,remove your finger from ,i ,t1 then withdraw ,e ,s4 ,do the leaves now remain spread8 #bjf4 ,discussion4 ,the permanent divergence of ,l was due to a charge given by induction4 7,exp4 #gf47 ,as ,e ,s was -1 what was the kind of a charge in ,l8 ,did any electrification go to the electroscope from ,e ,s8 ,in 7,c7 what became of the charge in ,l8 ,explain why the leaves again diverged in 7,d74 ,the electroscope was charged with electrification by taking - out of it4 ,,experiment #ie4 ,to learn some uses of the electroscope4 ,apparatus4 ,our electroscope 7,fig4 #eg1 #bjb72 ebonite rod1 ,e ,r 7,no4 #bh72 ebonite sheet1 ,e ,s 7,no4 #bg72 glass1 ,g 7,no4 #ch72 flannel cloth1 ,f ,c 7,no4 #cj74 #bjg4 ,directions4 7,a7 ,with the charged ,e ,r charge the electroscope negatively by conduction 7,exp4 #ic74 ,note the amount of permanent divergence of the leaves4 7,b7 ,electrify the glass1 which will be 1 7or use the ,e ,c71 and slowly lower it over ,i ,t1 noting the effect upon ,l4 ,raise and lower ,g or ,e ,c several times4 ,does ,g1 which has an opposite charge to the electroscope1 make ,l diverge more or less8 7,c7 ,discharge the electroscope and recharge as in 7,a74 7,d7 ,slowly lower the charged ,e ,s over ,i ,t4 7,e7 ,slowly lower the palm of your hand over ,i ,t4 ,note4 ,if the ,g is brought too near the -ly charged electroscope1 ,l will first collapse and then instantly diverge again with a charge by contact4 ,the first motions should be observed4 #bjh4 ,discussion4 ,as a neutral body causes a slight collapse of the leaves1 as well as a body charged positively 7when the charge in the leaves is -71 an increase of divergence is really the only sure test to tell how a body is charged4 ,the - leaves collapse when a body is brought near ,i ,t1 because the - in them is drawn up towards the body4 ,the leaves diverge more when a - body is brought near1 because the - in ,i ,t is repelled into them4 #bji4 ,the ,proof-plane4 ,since charges of static electricity reside upon the outside of conductors1 it is an easy matter to take samples of the electrification4 ,this may be done with a little instrument called a carrier1 or proof-plane4 ,it consists of a small conductor with an insulating handle4 ,a ring or coin may be used for the conductor1 and a silk thread for the handle4 ,by touching the carrier to any charged body1 it1 also1 becomes charged2 and the nature of the charge may be determined by the use of a previously charged leaf electroscope 7,exp4 #ie74 ,a delicate gold-leaf electroscope would be ruined by coming in contact with a heavily charged body4 ,the carrier allows a small sample to be tested4 ,,chapter ,,xii4 ,,miscellaneous ,,experiments4 ,illustration3 ,fig4 #eh4 ,,experiment #if4 ,to show that friction always produces two kinds of electrifications4 ,apparatus4 ,fig4 #eh4 ,the carbon electroscope 7,exp4 #eh72 flannel cloth1 ,f ,c1 doubled twice to make #d thicknesses 7see ,fig4 #eh72 ebonite sheet1 ,e ,s 7,no4 #bf72 ebonite rod1 ,e ,r 7,no4 #bh72 charged electrophorus cover1 ,e ,c4 #baj4 ,directions4 7,a7 ,vigorously rub ,e ,s with ,f ,c 7folded as in ,fig4 #eh74 ,see if you can discover any attraction between them4 7,b7 ,rub ,e ,s again1 but do not lift ,f ,c from it with the hand alone4 ,slip ,e ,r under the top fold in ,f ,c 7,fig4 #eh71 and lift ,f ,c straight up from ,e ,s4 ,do not let ,f ,c touch the table or your hand4 7,c7 ,see if ,f ,c is charged1 using #b or #c different tests4 7,d7 ,charge the electroscope with ,f ,c until the carbon is strongly repelled4 7,e7 ,bring the positively charged ,e ,c slowly near the carbon1 and note the result4 7,f7 ,slowly bring the negatively charged ,e ,s near the carbon that has been charged by contact with ,f ,c4 #baa4 ,discussion4 ,this experiment showed that while the ebonite was negatively charged1 the flannel was positively charged4 ,one kind of electrification is never produced without the other4 ,it can also be shown that the two kinds are equal in amount4 ,,experiment #ig4 ,to show successive sparks4 ,apparatus4 ,fig4 #ei4 ,the electrophorus 7,exp4 #fh72 the extra ebonite sheet1 ,e ,s 7,no4 #bg72 three coins 7marked ,a1 ,b1 ,c1 in ,fig4 #ei74 ,the coins should nearly touch each other1 and rest upon ,e ,s4 ,a part1 only1 of the electrophorus cover is shown4 #bab4 ,directions4 7,a7 ,thoroughly charge the electrophorus cover4 7,b7 ,place your finger upon the coin marked ,a1 to ground it1 then quickly touch the coin ,c with the charged cover1 at the same time watching for sparks between the coins4 ,if you cannot see the sparks1 darken the room a little1 and look at the center coin1 ,b1 while doing the experiment4 ,illustration3 ,fig4 #ei4 ,illustration3 ,fig4 #fj4 ,,experiment #ih4 ,to show to the eye the strong attraction between a charged and a neutral body4 ,apparatus4 ,the flat box1 ,f ,b 7,nos4 #dj1 #da72 the electrophorus 7see ,exp4 #fh74 #bac4 ,directions4 7,a7 ,stand ,f ,b upon its edge upon a level table1 then bring the charged electrophorus cover near it4 7,b7 ,instead of the above1 use light hoops made of paper1 eggshells1 feathers1 sawdust1 etc4 ,,experiment #ii4 ,to feel the strong attraction between a charged and a neutral body4 ,apparatus4 ,fig4 #fj4 ,the flat box ,f ,b 7,nos4 #dj1 #da72 the electrophorus 7,exp4 #fh74 #bad4 ,directions4 7,a7 ,hold ,f ,b in the left hand1 as shown1 then slowly bring near it the charged cover1 at the same time looking between them so that you can keep them the same distance apart all the way round4 7,b7 ,bring them near enough to allow a spark to pass from ,e ,c to ,f ,b4 ,,experiment #ajj4 ,the human body a frictional electric machine4 ,apparatus4 ,yourself2 a carpet2 a room with dry air1 easily had on a cold winter's day4 #bae4 ,directions4 7,a7 ,scrape your feet along upon the carpet1 then quickly touch your finger to some conductor1 as1 for example1 a friend's nose4 7,b7 ,it is possible to light the gas by the above process4 ,have a friend turn on the gas just before you bring your finger to the jet1 and be sure that the spark from your finger passes through the gas on its way to the conductor1 the jet4 7,c7 ,bring your finger quickly near a small piece of tissue paper after you have scraped your feet along to charge your body4 #baf4 ,static ,electric ,machines are used to produce large quantities of static electricity4 ,in the early forms1 the electrification was produced by friction4 ,modern machines depend upon the principle of induction4 ,the electrophorus 7,exp4 #fh7 is really a very simple form of induction machine4 ,the potential of these machines is very great1 as the spark may jump many inches4 ,thousands of ,galvanic cells would be needed to make a spark an inch long4 ,when the spark passes through the air it meets with an extremely high resistance1 as air practically insulates ordinary electricity4 ,this high resistance in the circuit reduces the strength of the current4 ,while the potential is very high1 the strength of the current is very low4 7,see ,ohm's ,law47 ,,chapter ,,xiii4 ,,atmospheric ,,electricity4 #bag4 ,atmospheric ,electricity4 ,the air is generally electrified1 even in clear weather4 ,its charge is usually 4 ,clouds are sometimes 1 and sometimes -4 ,the cause of atmospheric electricity is not thoroughly understood4 ,it is thought1 by some1 to be due to the friction of the particles of vapor upon each other4 ,it is also thought that the evaporation of sea water1 and the friction of winds1 produce it4 #bah4 ,lightning4 ,benjamin ,franklin1 in #ageb1 proved by his famous kite experiment that atmospheric and frictional electricities were of the same nature4 ,by means of a kite1 the string being wet by the rain1 he succeeded1 during a thunder-storm1 in drawing sparks1 charging condensers1 etc4 ,lightning may be produced by the passage of electricity between clouds1 or between the cloud and the earth1 which1 with the intervening air1 have the effect of a condenser4 ,if one cloud is charged1 it acts inductively upon another1 producing in it the opposite kind of electrification4 ,when the attraction between the two electrifications becomes great enough1 it overcomes the resistance of the air1 and lightning is produced4 ,the flash is practically instantaneous4 ,the direction taken seems to depend upon the conditions of the surrounding air4 ,it has generally a zigzag motion1 and is then called chain lightning4 ,the air in the path of the electricity becomes intensely heated2 it is this effect1 and not the electricity which we see4 ,in hot weather flashes are often seen which light up 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 potential of the lightning spark is beyond all calculation4 ,the spark jumps through miles of air1 which is1 really1 an insulator4 ,this spark represents billions and billions of volts4 #bai4 ,thunder is caused by the violent disturbances produced in the atmosphere by lightning4 ,the nature of the sound depends1 among other things1 upon the distance of the observer from the discharge1 and upon the length and shape of the path taken4 ,clouds1 hills1 and other objects produce echoes1 which also modify the original sound4 ,it takes nearly five seconds for the sound to travel one mile4 #bbj4 ,lightning-,rods1 when well constructed1 often prevent violent discharges of atmospheric electricity4 ,they have pointed prongs at the top1 which allow the negative of the earth 7which is being attracted by the cloud when it is positively charged7 to pass quietly into the air above2 this neutralizes the cloud4 ,in case of a discharge1 the rods aid in conducting the electricity to the earth4 #bba4 ,causes of ,atmospheric ,electricity4 ,there are several theories about this4 ,some think that it is due to the rotation of the earth1 different parts being acted upon differently by the heat of the sun4 ,some claim that the evaporation of the water in the ocean produces it1 while others say that the electrification is produced in the clouds by the friction of their particles upon each other4 ,the matter has not been settled4 #bbb4 ,st4 ,elmo's ,fire ,electrification from the earth is often drawn up through the masts of ships to neutralize that in the clouds 7see #bbj71 and1 as it escapes from the points of the masts1 light is produced4 ,this may be clearly shown by repeating ,exp4 #ga in the dark2 the head of the pin 7,fig4 #ci7 will represent the end of a mast1 and the charged electrophorus cover will be the charged cloud4 #bbc4 ,aurora ,borealis1 also called ,northern ,lights1 are luminous effects often seen in the north4 ,they often occur at the same time with magnetic storms1 at which times 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 magnetism1 caused by the action of the sun4 ,,current ,,electricity4 ,,part ,,iii4--,,current ,,electricity4 ,,chapter ,,xiv4 ,,construction ,,and ,,use ,,of ,,apparatus4 ,note4--,before taking up the study of cells and the electric current1 let us perform a few experiments in order to understand the construction and use of some of the apparatus needed for such study4 ,a dry cell will be used as the source of the electricity for these first experiments1 because it is convenient4 ,you will understand its action later4 ,use this cell only as directed2 improper use of it might spoil it4 ,illustration3 ,fig4 #fa4 ,,experiment #aja4 ,to study the effect of the electric current upon the magnetic needle4 ,apparatus4 ,a compass 7,no4 #ah72 a dry cell1 ,d ,c 7,no4 #ea72 wires with spring connectors attached 7 #bbf7 for making connections4 ,fig4 #ff shows a plan or top view of the arrangement4 ,any other form of cell will do in place of ,d ,c4 #bbf4 ,electrical ,connections4 ,one must constantly join wires1 connect wires with apparatus1 or connect one piece of apparatus to another1 to make the proper electrical connections4 ,a very simple method of connections has been used in all the apparatus described in these experiments4 ,a little arrangement which we shall call a spring connector1 ,s ,c1 7,fig4 #fa71 gives us a means of quickly making connections2 that is1 it does away with expensive binding-posts4 ,it is made of brass1 nickel plated1 and may be used anywhere without affecting the magnetic needle4 ,six or eight wires1 about ,no4 #bd gauge1 each about #a-a_/b ft4 long1 should be prepared with a connector at each end4 ,you may use wire furnished 7,no4 #ec74 ,scrape the insulation from the ends of the wires for about #a-a_/b inches1 then twist the bare ends around the connectors as shown in ,fig4 #fa4 ,the wire should pass around tightly at least #d or #e times and then be twisted a little1 as shown1 to help tighten it4 ,do not put it on so poorly or in such quantity that the part1 ,b1 will spread4 #bbg4 ,fig4 #fb shows how the connector should be slipped upon a thin piece of metal1 ,m1 like that on the galvanoscope1 for example4 ,the wire1 ,w1 from the apparatus itself is permanently fastened under the head of the screw1 ,s1 while the wire from any other apparatus is one of those kept on hand as above mentioned and connected with ,s ,c4 ,illustration3 ,fig4 #fb4 ,illustration3 ,fig4 #fc4 ,illustration3 ,fig4 #fd4 #bbh4 ,fig4 #fc shows how several wires may be quickly joined1 electrically1 by slipping the connectors at their ends upon a thin metal plate1 ,m ,p1 which may be a piece of tin1 zinc1 copper1 etc4 ,m ,p should not be too thick4 ,in case the connectors become too much spread to pinch the plate1 squeeze the part1 ,a1 a little more together4 #bbi4 ,fig4 #fd shows the method of connecting with the special form of binding-post used1 for example1 upon the resistance coil1 ,r ,c4 ,the end1 ,c1 of ,s ,c1 is pressed down into the tube1 ,t1 until you feel1 by moving it1 that it springs firmly against the sides of the tube4 ,in case you wish ,s ,c to fit very tightly in ,t1 one of the legs may be slightly bent outwards4 ,illustration3 ,fig4 #fe4 #bcj4 ,the connector may be used in still another way2 that is1 by pushing the part1 ,a1 into the hole of an ordinary binding-post1 7,fig4 #fe71 and using it just the same as a thick wire4 #bca4 ,directions4 7,a7 ,stand the compass and ,d ,c near each other 7,fig4 #ff74 ,attach one end of an insulated copper wire1 ,c ,w1 to the binding-post1 ,c1 which is on the carbon plate of the cell4 ,do not join the other end to the other binding-post1 ,zn1 of the zinc plate4 7,b7 ,with the left hand hold ,c ,w above and near the compass-needle1 and in the ,n and ,s line1 so that it will extend over the entire length of the needle4 7,c7 ,take the free end of ,c ,w in the right hand and touch binding-post1 ,zn1 for an instant only1 watching the needle4 ,repeat4 #bcb4 ,current ,detectors4 ,we know that a magnet can act1 by induction1 through the air upon a piece of iron or upon another magnet4 ,the deflection of the needle in this experiment shows that there must be a magnetic field around a wire carrying a current4 ,this fact is of the greatest possible importance4 ,the simple magnetic needle1 when used as above1 becomes a detector of electricity4 ,illustration3 ,fig4 #ff4 ,illustration3 ,fig4 #fg4 ,,experiment #ajb4 ,to study the construction and use of a simple key4 ,apparatus4 ,a key1 ,k 7,no4 #ee7 7 #bcc72 a dry cell1 ,d ,c1 7,no4 #ea72 a compass1 ,o ,c 7,no4 #ah74 ,arrange as shown in ,fig4 #fg1 which is a top view or plan4 ,connect the pieces of apparatus with wires and spring connectors 7 #bbf74 ,binding-post1 ,c1 is joined to ,i 7in7 of the key2 ,o 7out7 of key is joined to binding-post1 ,zn1 the wire1 ,c ,w1 passing directly over and near ,o ,c1 which is to be used as a detector4 ,the current cannot pass until the lever1 ,l1 is pressed4 ,a metal plate1 ,m ,p1 is used to connect two short wires 7 #bbh7 in case ,c ,w is not long enough4 ,illustration3 ,fig4 #fh4 #bcc4 ,a key is merely a piece of apparatus by which the circuit can be conveniently and rapidly opened and closed at the will of the operator2 that is1 by it the electricity can be quickly turned on or off4 ,fig4 #fh shows a simple form of key4 ,to the base1 ,b1 are fastened two metal pieces or straps1 the upper one1 ,l1 being the lever or key proper4 ,the front end of ,l is raised above ,o1 so that the two do not touch each other unless ,l is firmly pressed down4 ,a screw1 ,s1 keeps ,l from springing too far above ,o4 ,for convenience we shall suppose that the wire leading to the key joins it at ,i 7in72 the wire from the key is joined to ,o 7out71 by means of connectors 7 #bbf74 ,the key may be put into any circuit by first cutting a wire and then joining the ends to ,i and ,o4 ,spring connectors make the best connections with this form of key4 7,for ,home-,made ,keys see ,apparatus ,book47 #bcd4 ,directions4 7,a7 ,the magnetic needle being directly under the wire1 press ,l down for an instant only and note the action of the needle4 7,b7 ,press ,l again1 hold it down for #c seconds1 not over that1 and watch the needle4 ,discussion4 ,the key allows us to easily regulate the length of time during which the current passes4 ,this experiment shows1 also1 that the magnetic field about the wire disappears as soon as the current ceases to pass4 ,illustration3 ,fig4 #fi4 ,,experiment #ajc4 ,to study the construction and use of a simple current reverser4 ,apparatus4 ,a dry cell1 ,d ,c 7,no4 #ea72 a compass1 ,o ,c 7,no4 #ah72 a current reverser1 ,c ,r 7,no4 #eg7 7,see #bce72 an insulated copper wire1 ,c ,w1 #b or #c feet long1 with spring connectors joined to its ends 7 #bbf74 ,arrange as in ,fig4 #gj4 ,the wire1 ,c ,w1 leading from ,x should be held by the left hand so that it will be just above 7or below7 and parallel to the magnetic needle4 ,the current cannot pass through ,c ,w until one of the straps or levers on ,c ,r is pressed4 7,see ,apparatus ,book for ,home-,made ,reversers47 #bce4 ,the ,current ,reverser4 7,no4 #eg47 ,to the wooden base 7,fig4 #fi7 are fastened four metal straps1 each turned up at the end so that spring connectors 7 #bbg7 can be slipped on to make electric connections with other pieces of apparatus4 ,suppose that at ,c and ,z connections are made with the carbon and zinc of the cell1 by means of wires and spring connectors 7 #bbf74 ,the current comes from the cell to ,c4 ,as the two straps1 #b and #c1 press firmly up against strap #d1 and do not touch #a1 it is evident that no current can pass from #a to #b or to #c until they are pressed down upon #a4 ,two wires are joined by spring connectors to #b and #c at their turned up ends1 ,x and ,y1 and these wires lead to any desired instrument4 ,illustration3 ,fig4 #gj4 #bcf4 ,directions4 7,a7 ,press down lever #b 7,fig4 #gj71 for an instant only1 at the same time noting carefully in which direction the ,n pole of the needle is deflected4 7,b7 ,after allowing lever #b to spring up again1 and after the needle comes to rest1 press down lever #c for an instant1 watching the needle4 ,is the ,n pole of the needle deflected in the same direction as it was in 7,a78 #bcg4 ,discussion4 ,the reverser gives us a quick and easy means of reversing the current which is to pass through any desired instrument1 first in one direction and then in the opposite direction4 ,suppose 7,fig4 #fi7 that the current enters ,c ,r at ,c1 as it does when ,c is joined to the carbon of the cell2 the current can go no farther until one lever is lowered4 ,if lever #b 7,fig4 #fi7 be now pressed down1 as in part 7,a71 the current will pass along #b1 which does not now touch #d1 out through ,x to a coil of wire or any instrument1 and back to the reverser by the wire joined to ,y4 ,it will then pass from #c onto #d1 to ,z1 and back to the ,cell2 that is1 the current enters ,c ,w at ,x4 ,when lever #c is pressed1 the current still entering ,c ,r at ,c1 the electricity will pass onto #c and out at ,y1 and back through ,x1 #d and ,z to the cell4 ,the current1 then1 can be made to pass out of ,x or ,y at will by pressing the proper lever4 ,this experiment also teaches something about currents1 but these will be discussed later4 ,illustration3 ,fig4 #ga4 ,,experiment #ajd4 ,to study the simple current detector4 ,apparatus4 ,the compass 7,no4 #ah72 dry cell1 ,d ,c 7,no4 #ea72 current reverser1 ,c ,r 7,no4 #eg72 copper wire1 ,c ,w1 a few feet long1 with spring connectors on its ends4 7,see ,apparatus ,book1 ,chapter ,,xiii1 for ,home-,made ,detectors47 #bch4 ,directions4 7,a7 ,join the ends of the wire to ,x and ,y of the reverser1 ,c ,r1 as in the last experiment4 ,coil up ,c ,w so that you can hold the coil with your left hand1 as shown in ,fig4 #ga1 the magnetic needle being inside of it and parallel to it4 7,b7 ,press lever #b of the reverser for an instant only4 ,is the needle deflected more or less than it was when the wire simply passed over or under it once8 7,c7 ,reverse the current through ,c ,w by pressing lever #c1 and note the result4 7,d7 ,get clearly in mind which way the ,n pole of the needle is deflected when the current enters ,c ,w at ,x1 also when it enters at ,y4 #bci4 ,discussion4 ,the current passed over the needle in one direction1 and under it in the opposite direction2 that is1 the part of the wire above helps that below4 ,each turn of the wire increases the strength of the magnetic field about the coil1 and helps to deflect the needle4 ,in this way1 by increasing the number of turns1 detectors may be made that will show the presence of very weak currents4 ,the magnetic fields about wires and coils will be studied in a later chapter4 ,illustration3 ,fig4 #gb4 ,,experiment #aje4 ,to study the construction and use of the simple galvanoscope4 ,apparatus4 ,the galvanoscope1 ,g ,v1 complete 7,no4 #eh71 described in #bdj-bdf2 dry cell1 ,d ,c 7,no4 #ea72 current reverser1 ,c ,r 7,no4 #eg7 7 #bce72 wires1 with spring connectors1 to join the different pieces of apparatus 7#bbf74 7,see ,apparatus ,book1 ,chapter ,,xiii1 for ,home-,made ,galvanoscopes47 #bdj4 ,the ,galvanoscope 7,fig4 #gb7 is more than a mere detector of electricity4 ,with it we shall be able to study1 more fully1 cells1 currents1 etc41 etc4 ,we must first understand its construction4 #bda4 ,the ,coil-support1 ,c ,s1 is fastened to the cross-piece1 ,c ,p1 on which are the #c binding-posts or coil-ends1 ,l1 ,m and ,r 7left1 middle1 right74 ,the legs1 ,g ,l1 are screwed to ,c ,p in such a way that ,c ,p is held a little above the table3 this allows ,c ,s to be tipped to the front or rear to adjust it vertically4 ,on account of the peculiar arrangement of the legs1 the galvanoscope can be made to stand firmly1 even upon uneven surfaces4 ,the screws holding ,g ,l should not be put in far enough to tear the threads in the wood1 ,c ,p4 #bdb4 ,the ,galvanoscope ,coils1 ,g ,c1 are two in number1 both being fastened to the coil-support1 ,c ,s4 ,the first coil has five turns of wire1 its ends being fastened to ,l and ,m2 the other coil has ten turns1 with ends at ,m and ,r4 ,the current can1 at will1 be made to pass through #e1 #aj or #ae turns of wire by making the proper connections4 ,suppose that we have two wires direct from a cell1 or from the current reverser1 with spring connectors on them so that we can slip them onto ,l1 ,m or ,r1 which stand for left1 middle or right4 ,when the wires are joined to ,l and ,m the current can pass through but #e turns2 when joined to ,m and ,r it will go through #aj turns2 and when to ,l and ,r it will pass through the entire #ae turns4 ,when the current enters the galvanoscope at ,l and passes out at ,m or ,r1 it will pass through the turns of wire from left to right1 at the top2 that is1 it will pass in a clockwise direction4 #bdc4 ,the ,compass-needle1 furnished with ,o ,c 7,no4 #ah71 will do also for this galvanoscope4 ,it should be placed upon the pin-point after fixing on the pointers 7 #bdf74 ,the length of the needle should be parallel to the plane of the coil when no current passes2 that is1 the coil and coil-support should be in the ,n and ,s line4 ,the needle can be centered in regard to right and left1 and in regard to up and down1 by properly adjusting the position of the pin-point support1 ,p ,p ,s2 this is held firmly to ,c ,s by two spring-connectors4 ,by removing ,s ,c1 the support1 ,p ,p ,s1 may be raised or lowered4 #bdd4 ,to place the coil in the ,n and ,s line1 simply swing the galvanoscope bodily around1 at the same time looking down upon the needle1 until the length of the needle becomes parallel to the coil-support4 ,when once carefully adjusted ,n and ,s1 a line may be drawn upon the table as a guide for its position in future experiments4 ,the coil should stand in a vertical plane1 and this straight up and down position can be easily adjusted4 ,to place the coil in the ,e and ,w line1 turn it until the pointers are at the #ij 7#ij degree7 marks1--the #j 7zero degree7 marks remaining1 of course1 as described above4 #bde4 ,the ,degree-,card1 ,g ,d ,c 7,fig4 #gb7 has a dot at its center1 to show where to make a pin-hole for the pin that supports the compass-needle4 ,with this you can tell how many degrees the needle is deflected when the current passes4 ,this card1 ,g ,d ,c1 should be pressed down over the pin-point4 ,the zero points of ,g ,d ,c should be ,n and ,s1 also1 when the coil is in that position2 that is1 they should be in the plane of the coil4 ,the pointers on the needle 7 #bdf7 will then be at ,o1 when the needle is at rest1 no current passing through the coils4 7,see ,apparatus ,book #bgb for ,home-,made ,degree-,card47 ,g ,d ,c may be held permanently in position after it is adjusted1 by sticking a short pin through it into ,p ,p ,s4 ,do not let this pin interfere1 however1 with the swinging of the needle4 ,illustration3 ,fig4 #gc4 #bdf4 ,pointers 7,fig4 #gc7 should be fastened to the needle1 in order to make the readings of degrees accurate4 ,fasten to the compass-needle a piece of ,no4 #cj insulated copper wire1 as shown4 ,it may be cut to the proper length after it is wound around the needle4 ,see that the wire does not touch the pin when needle is in place2 balance needle by cutting a little from the heavier end of wire with shears2 bend the ends of wire so that they are at opposite sides of the degree-card1 both pointing at ,o1 for example4 ,the needle must swing freely1 be nicely balanced1 and the wire must not touch pin or degree-card4 ,illustration3 ,fig4 #gd4 #bdg4 ,directions4 7,a7 ,arrange as in ,fig4 #gd1 the coil being ,n and ,s 7 #bdd74 ,join the ends of the wires1 #b and #c1 with the #e-turn coil of ,g ,v as shown4 ,wire1 #b1 is connected to ,l 7,fig4 #gb74 ,press lever #b of ,c ,r 7,fig4 #fi7 for an instant1 watching the compass-needle and noting how many degrees it swings the first time4 ,get thoroughly in mind the direction in which the ,n pole of the needle is deflected when the current passes around ,g ,c in a clockwise direction4 ,there must be no magnets1 iron1 or pieces of steel within #c feet of ,a ,g4 7,b7 ,press lever1 #c1 for an instant1 watching the needle4 ,the current will now pass in an anti-clockwise direction4 ,is the needle deflected about the same number of degrees as in 7,a78 7,c7 ,change the ends of the wires1 #b and #c1 to the #aj-turn coil 7 #bdb7 and repeat 7,a7 and 7,b74 7,d7 ,change #b and #c to ,l and ,r 7,fig4 #gb71 thus allowing the current to pass around #ae turns2 then repeat 7,a7 and 7,b74 #bdh4 ,discussion2 ,true ,readings4 ,is not possible to get the magnetic needle1 ,m1 exactly in the center of ,g ,c2 the pointers will not exactly be in the axis of ,m2 the coils will not be exactly ,n and ,s3 hence1 if you pass a certain current through the coil and the pointer reads #bj degrees1 you will find1 if you reverse the current1 that the pointer may read #bd degrees on the other side of the zero mark4 ,to get the true reading1 average the two1 in this case the average being #bb degrees4 ,the galvanoscope gives us an instrument with which we can study1 more fully1 cells1 currents1 etc4 #bdi4 ,note of ,caution4 ,it has already been stated that the compass-needle should be in the center of the coil 7 #bdc71 and that the coil should be in the ,n and ,s line 7 #bdd74 ,in addition to the above1 see that there are no magnets near ,g ,v1 when using it2 tap ,g ,v occasionally to be sure that the needle swings freely1 hold the eye directly over the pointers when reading degrees2 the pointers should be at zero when no current passes through ,g ,v2 be sure that the electrical connections are good4 ,there are several sources of error in taking readings1 and in all the quantitative experiments given4 ,the author takes it for granted that such errors will be looked out for by the teacher4 ,illustration3 ,fig4 #ge4 ,,experiment #ajf4 ,to study the construction and use of a simple astatic needle4 ,apparatus4 ,two unmagnetized sewing-needles 7,no4 #a72 horseshoe magnet1 ,h ,m 7,no4 #af72 piece of stiff paper doubled and cut as in ,fig4 #ge2 a pin-point on which to support the paper4 ,the pin may be stuck through a cork1 or that of ,o ,c 7,no4 #ah7 may be used4 #bej4 ,directions4 7,a7 ,draw each needle across the ,n pole of ,h ,m five times from point to head 7,exp4 #i74 ,this should make them of nearly equal strength1 both points being ,n poles4 7,b7 ,stick the needles through the paper as shown1 the ,n poles being at the same end of the paper4 ,balance the paper upon the pin-point4 ,has this combination a strong or weak pointing-power8 7,c7 ,turn one of the needles end for end4 ,again test the pointing-power4 #bea4 ,discussion2 ,astatic ,needles4 ,by arranging the needles so that their poles oppose each other1 the pointing-power becomes almost nothing4 ,this sort of a needle is needed in some experiments in electricity4 ,their magnetic fields are still retained4 ,the combination is called an astatic needle2 it is used to detect very feeble currents4 ,the more nearly equal the magnets are in strength1 the better4 ,they are usually arranged with one above the other 7,fig4 #gf74 ,illustration3 ,fig4 #gf4 ,illustration3 ,fig4 #gg4 ,,experiment #ajg4 ,to study the construction and use of a simple astatic galvanoscope4 ,apparatus4 ,an astatic galvanoscope1 ,a ,g 7,no4 #ei7 7 #beb-bed72 dry cell1 ,d ,c 7,no4 #ea72 current reverser1 ,c ,r 7,no4 #eg7 7 #bce72 wires for connections 7 #bbf74 ,arrange as shown in ,fig4 #hj1 which is a top view4 ,the wires from ,c ,r are connected to the binding-posts of ,a ,g at the back1 the spring connectors being slipped into them 7 #bbi74 #beb4 ,construction of the ,astatic ,galvanoscope4 ,when not to be used for a long time1 or for shipping1 the legs1 ,a 7,fig4 #gg7 may be removed1 and the whole packed inside of the box1 ,b4 ,the ,coil1 ,c1 has a resistance of about #e ohms1 and is fastened to the coil-support1 ,c ,s4 ,the ends of the coil are permanently fastened to the binding-posts1 ,l and ,r 7left and right74 ,the ends are so arranged that when the current enters at ,l it will pass around the coil in a clockwise direction4 #bec4 ,the ,astatic ,needle 7,exp4 #ajf7 is supported by a small thread1 ,t1 which is tied to the thread-wire1 ,t ,w4 ,this ,t ,w springs into an eyelet1 ,e1 which1 in turn1 rests in a hole made in the end of ,b4 ,e should turn easily in the hole1 but it should not wabble4 ,fig4 #gh shows a sectional view of the coil and needle4 ,the wire1 ,w1 should be bent1 as shown1 so that the magnets can be as near the center-line of ,c as possible4 ,fig4 #gi shows a front view of the needle4 ,as a matter of convenience it will be best to arrange the poles of the needles1 as shown1 to agree with the descriptions of the experiments4 ,to keep the needle from being affected by air currents1 the glass plate 7,no4 #ch7 may be placed in front of the box1 ,b4 ,stand it upon the legs1 ,a1 and tie a string around it1 and ,b1 to hold it in place4 ,illustration3 ,fig4 #gh4 ,illustration3 ,fig4 #gi4 #bed4 ,adjusting the ,needle4 ,as ,t is tied to ,t ,w1 the needle may be swung completely around by turning ,t ,w4 ,this should be done until the length of the needle is parallel to the turns of ,c4 ,the up and down position of the needle should be fixed as nearly as possible when fastening ,t to ,t ,w1 the exact place being finally fixed by raising or lowering ,t ,w through ,e4 ,the spring in ,t ,w should hold it firmly in ,e after adjustment4 ,the wire1 ,w1 joining the needle-magnets should not touch the coil4 ,it may be made to just swing free from ,c by tilting the box forward or backward a little4 ,the construction of the legs1 etc41 makes it possible to tilt the box1 and to make it stand firmly upon an irregular surface4 ,illustration3 ,fig4 #hj4 #bee4 ,directions4 7,a7 ,see that there are no magnets within #c feet of ,a ,g4 ,test the astatic needle1 after you have it properly suspended1 to convince yourself that it does not try to swing around in a ,n and ,s line4 ,in case the needle-magnets have been in contact with other magnets1 or are not equally magnetized1 remagnetize them as directed in ,exp4 #ajf4 ,they must remain in any position given them by turning ,t ,w4 ,finally1 bring them parallel to the turns of the coil4 7,see #bed47 ,arrange as in ,fig4 #hj4 7,b7 ,press lever #b of ,c ,r 7 #bce7 for an instant only4 ,this allows the current to enter ,a ,g at ,l4 ,repeat several times until you thoroughly fix in your mind the direction in which the right-hand end of the needle is deflected4 ,does the needle jump suddenly when the current passes8 7,c7 ,press lever #c for an instant only4 ,study the result4 #bef4 ,astatic ,galvanoscopes4 ,it is evident that in the ordinary current detector 7,exp4 #ajd71 the pointing power of the needle has to be overcome by the magnetic field about the coil1 before the needle can be forced from its ,n and ,s line4 ,very weak currents will not visibly move the needle in ordinary detectors4 ,to make a sensitive instrument we must have strong fields about both the needle and coil1 and we must1 at the same time1 decrease the pointing power of the needle4 ,both of these things are accomplished by using an astatic needle in connection with a coil containing considerable wire4 ,the uses of the astatic galvanoscope will be studied more fully in later experiments4 ,,chapter ,,xv4 ,,galvanic ,,cells ,,and ,,batteries4 ,,experiment #ajh4 ,to study the effect of dilute sulphuric acid upon carbon and various metals4 ,apparatus4 ,a piece each of copper and iron wire #d in41 7#aj cm47 long2 two narrow strips of sheet zinc 7,no4 #fj71 one being amalgamated 7 #beg72 a carbon rod 7,no4 #fd72 a tumbler 7,no4 #fe71 partly filled with dilute sulphuric acid1 7 #beh72 mercury 7,no4 #eb74 #beg4 ,to amalgamate one of the above zinc strips is to coat it with mercury4 ,remove all jewelry from the hands before proceeding4 ,wash the zinc with water1 and with a cloth remove all dirt from its surface4 ,amalgamated zinc is very brittle1 so lay it flat upon a piece of board or upon a plate1 after dipping it for an instant in the dilute acid4 ,place a small drop or two of mercury upon the strip1 and rub the mercury about upon both sides of the zinc with a cloth made wet with the dilute acid4 ,mercury clings strongly to zinc or tin1 so you may use a narrow piece of either as a spoon to carry a small drop from the supply to the zinc4 ,tap it upon the zinc to dislodge the drops4 ,do not get on too much mercury1 just enough to coat it1 or1 at least1 that part of it that will be under the acid4 ,be careful not to break the thin zinc when amalgamating it1 as it gets very brittle4 ,it should look bright4 7,see ,apparatus ,book #cb1 #cc47 ,note4 ,should any mercury get upon copper plates it may be removed by heating them in a flame4 #beh4 ,dilute sulphuric acid1 for these experiments1 should be made by mixing #a part1 by volume1 of concentrated acid1 with #bj parts of water4 ,do not let the acid get upon clothes or carpets4 ,do not add water to acid4 ,mix by slowly adding the acid to the water in a glass or earthen dish1 stirring at the same time4 ,mix over a sink or out of doors4 7,for fuller details see ,app4 ,book2 #ba1 #bb1 #bc1 #bd1 #be47 ,to save time1 make at least a quart of the mixture1 bottle1 and label it for use4 #bei4 ,directions4 7,a7 ,bend over one end of each of the wires and metal strips1 and hang them upon the edge of the tumbler 7,fig4 #ha71 so that their lower ends shall be in the acid4 ,do not let them touch each other4 ,stand the carbon rod in the acid4 ,if there is no visible action upon any of the above substances1 add a few drops of concentrated acid to the tumbler4 ,note carefully what takes place in the tumbler1 and state which of the substances are dissolved1 which simply made brighter1 and which not acted upon at all4 #bfj4 ,discussion4 ,the bubbles of gas that arise from the zinc when it dissolves are hydrogen1 and they indicate that a vigorous chemical action is going on in the tumbler1 and that the zinc is being eaten away4 ,illustration3 ,fig4 #ha4 ,illustration3 ,fig4 #hb4 ,,experiment #aji4 ,to study the effect of dilute sulphuric acid upon various combinations of metals4 ,apparatus4 ,the same as in the last experiment4 ,a small piece of amalgamated zinc1 however1 will be better than the whole strip4 #bfa4 ,directions4 7,a7 ,twist one end of the clean copper wire around the small piece of amalgamated zinc 7,fig4 #hb74 ,hold one end of the wire in the hand and dip the combination into the acid4 ,what takes place8 ,watch the surface of the copper1 remembering that each1 alone1 was not acted upon by the acid 7,exp4 #ajh74 7,b7 ,use the clean iron wire in place of the copper wire1 and repeat 7,a74 ,watch the surface of the iron4 7,c7 ,with a string or thread tie a small piece of well amalgamated zinc to the carbon rod 7,fig4 #hb71 then dip the combination into the acid4 ,watch the surface of the carbon4 #bfb4 ,discussion4 ,while amalgamated zinc is not rapidly dissolved by dilute sulphuric acid1 a vigorous action of some kind takes place when it is in contact with another metal or with carbon in the acid4 ,the bubbles of hydrogen that are liberated do not seem to come from the zinc2 they appear to grow1 in the fluid1 directly at the surface of the copper1 iron1 or other metal used with the zinc4 ,this shows that something besides the mere dissolving of a metal takes place4 ,can we arrange our apparatus so that we can get some useful results from this action8 ,,experiment #aaj4 ,to study the construction of a simple ,voltaic or ,galvanic cell4 ,apparatus4 ,a narrow strip of zinc 7,no4 #fj71 amalgamated as directed in #beg4 7,an amalgamated zinc rod 7,no4 #gd7 may be used in place of the strip72 a narrow strip of sheet copper 7,no4 #fg72 the tumbler of dilute acid of ,exp4 #ajh2 a flexible copper wire about #b feet long1 with spring connectors 7,no4 #ed7 attached to its ends4 7,see ,electrical ,connections1 #bbf47 ,illustration3 ,fig4 #hc4 #bfc4 ,directions4 7,a7 ,holding the amalgamated zinc strip in one hand and the copper strip in the other 7,fig4 #hc71 dip them into the acid1 but do not let them touch each other4 ,note any chemical action4 7,b7 ,touch the copper and zinc together1 below the surface of the acid4 ,watch the copper4 7,c7 ,separate the lower ends of the strips1 then touch them together above the acid4 ,anything still happen to the copper8 7,d7 ,slip one spring connector with the attached wire upon the zinc strip1 then stand the strips in the tumbler1 so that they can not touch each other4 ,now touch the copper strip with the free end of the wire1 at the same time watching the copper4 7,e7 ,raise the wire from ,cu1 touch it to ,cu again1 and repeat several times until you are sure that something takes place every time the wire touches ,cu4 #bfd4 ,the ,electric ,current4 ,something must happen in or through the wire1 and it can only happen when the two metals are joined in some way4 ,this peculiar1 invisible action in the wire is called the electric current1 and such an arrangement is called a ,galvanic cell4 #bfe4 ,source of the ,electrification4 ,when two different metals are placed in acid they are electrified unequally by chemical action4 ,each has a higher potential than the acid1 but their potentials are not the same4 ,this electrification tends to pass from the place of higher to the place of lower potential1 and the conducting wire allows this transfer to take place4 ,as the difference of potential is kept up by the continued chemical action1 the current is continuous1 and not simply instantaneous1 as in discharges of frictional electricity4 ,as heat is produced by the burning of coal1 so electrification is produced by the chemical burning of zinc4 ,chemical energy is the source of electrification in the ,galvanic cell1 just as muscular energy was the source of the electrification in the experiments with frictional electricity4 #bff4 ,the ,electric ,circuit2 ,open and ,closed ,circuits4 ,the simple ,galvanic cell just used1 together with the wire which joined the metal strips1 is called an electric circuit4 ,if the current should pass through a telegraph instrument1 for example1 on its way from one strip to the other1 the telegraph instrument would also be in the circuit4 ,when the wire is cut or removed from one metal strip1 the circuit is said to be open--that is1 we have an open circuit4 ,when the current passes1 the circuit is closed4 ,we also say make and break the circuit1 and that the circuit has been broken4 #bfg4 ,plates or ,elements4 ,the copper and zinc strips are called the plates or elements of the cell4 ,the zinc1 ,zn1 ,fig4 #hd1 is dissolved by the acid1 and is called the positive plate 7 plate74 ,the copper1 ,cu1 is the negative plate 7- plate74 ,the copper is also called the cathode1 and the zinc the anode4 #bfh4 ,direction of ,current4 ,it has been agreed1 for convenience1 that in the cell the current passes from the zinc through the liquid to the copper1 where the hydrogen bubbles are deposited4 ,it then passes through the wire1 or other conductor furnished1 back to the zinc1 through the liquid to ,cu again1 and so on around and around thousands of times per second4 ,the current really starts at the surface of the zinc1 where the chemical action is4 ,when carbon and zinc are used1 the action and direction of the current are the same1 carbon being the - plate4 ,illustration3 ,fig4 #hd4 #bfi4 ,poles or ,electrodes4 ,if the wire were cut1 the electricity coming from the plate would be stopped at the end of the wire marked 1 ,fig4 #hd1 after passing through the acid and up ,cu4 ,this end of the wire is called the pole or electrode 7positive74 ,the end of the wire joined to ,zn is called the - pole or electrode2 that is1 the electrode is the end of the wire attached to the - plate4 ,the tops of ,cu and ,zn may be considered electrodes4 ,the top of ,cu is the pole of the cell1 while ,cu is the - plate4 #bgj4 ,chemical ,action in the ,simple ,galvanic ,cell4 ,the chemical formula of sulphuric acid is ,h#b,,so#d 7read ,h1 #b1 ,s1 ,o1 #d74 ,this means that it is a compound of hydrogen 7,h71 sulphur 7,s71 and oxygen 7,o74 ,the ,h#b,,so#d stands for molecule of acid1 and the small figures show that the molecule is made up of #b atoms of hydrogen 7,h#b71 one of sulphur 7,s71 and #d of oxygen 7,o#d74 ,the atoms are held together by chemical attraction or affinity4 ,there is a stronger chemical affinity between zinc 7,zn7 and ,,so#d than between ,h#b and ,,so#d2 so1 as soon as the ,zn gets a chance1 as it does in the cell1 it drives out the ,h#b1 and it takes its place in the molecule4 ,this chemical reaction may be shown by the following chemical equation3 ,zn ,h#b,,so#d ,zn,s,o#d ,h#b4 ,zinc and sulphuric acid produce zinc sulphate and hydrogen4 ,the zinc sulphate produced weakens the effect of the acid2 in fact1 the acid has to be renewed occasionally1 as it is changed to the sulphate which remains in solution4 #bga4 ,action in ,cell ,using ,impure ,zinc4 ,the above action takes place in the cell when impure zinc is used1 even when no current passes1 heat being produced by the reaction instead of useful electricity4 7,see ,local ,currents47 ,action in ,cell ,using ,pure ,zinc4 ,when pure zinc 7or impure zinc that has been properly amalgamated7 is used in the cell1 it dissolves1 or is eaten away1 only when the current passes4 ,it should be noted that the bubbles of hydrogen do not even then appear at the zinc2 they are not seen throughout the body of the liquid4 ,there seems to be an unseen transfer of hydrogen from the zinc1 through the liquid1 to the copper 7or other - plate used71 and it appears there in the shape of bubbles4 ,the larger the quantity of pure zinc dissolved1 the stronger the current1 and the larger the amount of hydrogen produced4 ,as the zinc dissolves it parts with its latent energy1 and this energy forces the electric current through the circuit4 ,while the hydrogen of the decomposed acid makes its way towards the - plate1 the ,,so#d part of it travels towards the ,zn plate1 where the ,,znso#d is formed4 7,see #bgj47 ,,experiment #aaa4 ,to see what is meant by local currents in the cell4 ,apparatus4 ,tumbler of dilute sulphuric acid4 7 #beh72 strip of unamalgamated zinc2 crystal of copper sulphate 7blue vitriol7 7,no4 #hf72 a galvanized iron nail 7,no4 #fi71 this being iron covered with zinc4 #bgb4 ,directions4 7,a7 ,hold the nail in the acid for a few seconds1 and note result4 7,b7 ,rub the copper sulphate upon the zinc simply in one spot1 then place the zinc in the acid1 noting the result at the spot4 #bgc4 ,local action2 ,local ,currents4 ,ordinary commercial zinc contains such impurities as carbon1 iron1 lead1 etc41 in small quantities4 ,it was seen1 ,exp4 #aji1 that when different metals were in contact with the zinc1 the zinc was rapidly dissolved by the acid4 ,the impurities in the zinc act like the copper plate in the simple cell1 thus producing local currents in the zinc1 which rapidly destroy it without doing any good4 ,these currents pass from zinc to impurities1 and back to the zinc1 without going out into the main wire4 ,this local action takes place even when the main circuit is open4 #bgd4 ,reasons for ,amalgamating ,zinc ,plates4 ,pure zinc is not affected by dilute sulphuric acid1 but it is too expensive to use in cells2 so amalgamated zinc is used instead1 because it is cheaper1 and acts the same as pure zinc4 ,the impurities are removed from the surface of the zinc1 as the zinc alone is dissolved by the mercury4 ,there is1 then1 a liquid layer of pure zinc with mercury upon the surface of the amalgamated plate4 ,this is not acted upon by the acid when the circuit is open4 ,a stronger and more regular current is produced with amalgamated zinc than with the impure unamalgamated zinc4 ,,experiment #aab4 ,to study the single-fluid ,galvanic cell4 ,apparatus4 ,the galvanoscope ,g ,v 7,no4 #eh71 7,see #bdj1 etc472 the simple cell arranged as described in #bge1 the zinc being amalgamated4 #bge4 ,the ,simple ,cell should be arranged so that the plates will be held firmly in position4 ,the zinc1 ,zn 7,no4 #fj71 and copper1 ,cu 7,no4 #fg71 should be fastened to the wooden cross-piece1 ,w ,c ,p 7,no4 #gj71 as shown in ,fig4 #he4 ,care should be taken not to use longer screws than those provided for 7,no4 #gb74 ,if the screws touch each other they will short circuit the cell4 ,partly fill the tumbler 7,no4 #fe7 with dilute sulphuric acid 7 #beh71 join wires with connectors to the plates4 ,the free ends of the wires are then ready to join to apparatus4 ,the ends of wires may be fastened under the screw-heads instead of using connectors on the plates4 ,do not put the plates into the acid until you read the directions4 #bgf4 ,directions4 7,a7 ,arrange as in ,fig4 #hf4 ,place the coil of ,g ,v1 ,n and ,s 7 #bdd74 ,before putting the plates in the acid join them to the #ae-turn coil of ,g ,v 7 #bdb74 ,the compass-needle should point to zero4 ,see that the needle swings freely4 7,b7 ,place the plates in the acid1 and quickly bring the needle to rest with the aid of the hand1 so that you can take the reading at once before the hydrogen bubbles entirely cover the copper plate4 ,watch the action of the needle for a few minutes4 ,make a note of the reading1 in degrees1 at the beginning of the experiment and at the end of five minutes4 7,see ,note47 ,illustration3 ,fig4 #he4 ,illustration3 ,fig4 #hf4 ,note4 ,if no change takes place in the position of the needle1 the change beginning inside of #aj seconds after the plates are let down into the acid1 withdraw the plates1 then clean and thoroughly dry the copper to remove all traces of hydrogen4 ,this may be done by heating the copper over a gas flame4 ,let the copper remain in the air #ae minutes1 then try again4 ,in taking the first reading you must work quickly4 ,catch the needle during its first swing4 ,if you allow it to swing back and forth until it comes to rest1 your first reading will not be what it should be4 7,c7 ,after the needle has remained in one position1 without change1 for #b or #c minutes1 take hold of the wooden cross-piece1 move the plates back and forth in the acid to dislodge the hydrogen bubbles1 and note carefully the action of the needle4 ,does the current seem stronger when the plates are moved8 ,can you get the needle back to the first reading8 7,d7 ,remove the plates from the acid1 dry and clean the copper1 let them stand in the air for #ae minutes1 then take another quick reading and compare it with the first4 #bgh4 ,polarization of ,cells4 ,the acid gets a little weaker1 of course1 as it is decomposed by the zinc 7 #bgj71 but the chief cause of the weakening of the current is hydrogen1 which forms a filmy coating upon the copper plate4 ,this coating even seems to soak into the copper1 and it takes some time for it to be thoroughly removed4 ,the zinc plate is kept comparatively free from hydrogen by amalgamation4 #bgi4 ,effects of ,polarization4 ,the hydrogen bubbles weaken the current in at least two ways4 ,in the first place1 hydrogen is not a conductor of electricity2 so it holds the current back1 as any other resistance would4 ,secondly1 acid acts upon hydrogen as it would upon another metal4 ,when the copper plate becomes well covered with hydrogen1 the acid cannot touch it2 so we really have a hydrogen plate in the cell4 ,hydrogen acts very much like zinc in the acid2 we say that it is more electro-positive than copper4 ,the result is1 then1 that a new current starts up1 and as this is towards the zinc1 in the acid1 it partially destroys or neutralizes the main zinc-to-copper current4 ,practical use is made of the principles of polarization 7see ,secondary ,batteries74 #bhj4 ,remedies for ,polarization2 ,depolarizers4 ,any scheme by which the hydrogen may be destroyed and kept from the inactive1 or negative plate1 will prevent polarization4 ,mechanical means have been employed to brush away the hydrogen by keeping up a constant circulation of the liquid4 ,chemical action is another means by which the hydrogen may be side-tracked before it gets to the - plate in single-fluid cells4 ,substances like nitric acid and bichromate of potash1 called depolarizers1 contain large quantities of oxygen1 and1 during the chemical changes that take place1 this oxygen unites with the hydrogen4 ,these substances are used in zinc-carbon cells4 7,see #bhf1 etc4 for various forms of cells47 ,there is another form of cell1 the two-fluid type1 in which electro-chemical means are employed1 and in which a metal is deposited upon the - plate instead of hydrogen4 ,the - plate is usually copper1 copper being deposited upon it4 ,,experiment #aac4 ,to study the two-fluid ,galvanic cell4 ,apparatus4 ,the glass tumbler1 ,g ,t1 7,no4 #fe72 porous cup1 ,p ,c1 7,no4 #gc72 the strip of zinc 7,no4 #fj71 well amalgamated 7 #beg71 or the amalgamated zinc rod 7,no4 #gd72 piece of sheet copper 7,no4 #ge71 bent so that it will surround ,p ,c2 copper wires1 ,c ,w1 with connectors2 a saturated solution of copper sulphate1 commonly called blue vitriol or blue stone 7,see #bhc72 dilute sulphuric acid 7,see #beh74 ,with the above1 set up the two-fluid cell 7,see #bha74 ,the galvanoscope1 ,g ,v1 complete1 is also needed1 and if quantitative work is to be done1 a pair of scales weighing to #j4a gram is necessary4 7,see ,app4 ,book1 ,chapter ,i1 for ,home-,made ,two-,fluid ,cells47 ,illustration3 ,fig4 #hg4 #bha4 ,setting ,up the ,two-,fluid ,cell4 ,fig4 #hg4 ,stand the amalgamated zinc rod1 ,zn1 in ,p ,c1 then place ,p ,c in the tumbler1 ,g ,t2 put in the copper plate as shown4 ,pour diluted acid 7 #beh7 into ,p ,c until it stands about #b-a_/b in4 deep2 then at once pour the copper solution 7 #bhc7 into ,g ,t1 on the outside of ,p ,c1 until it stands at the same height as the acid in ,p ,c4 ,as soon as the liquids have soaked into ,p ,c the cell will be ready for use2 but it is better to connect it with the galvanoscope at once and note the increase of current during the first few minutes while the liquids soak through ,p ,c4 ,a crystal of copper sulphate should be put outside of ,p ,c to keep the solution full strength4 ,this is a form of the well-known ,daniell cell4 ,fig4 #hg shows a form of home-made two-fluid cell as described in ,apparatus ,book4 ,if you have the one furnished1 use the rod instead of sheet zinc1 and use connectors on the plates4 #bhb4 ,care of ,two-,fluid ,cell4 ,this experimental cell should be taken apart when not in use4 ,it should not be left in open circuit1 even for half an hour4 ,even after the plates are removed1 copper may be deposited upon ,p ,c in case there are any metallic impurities on it4 ,remove the plates and ,p ,c1 and thoroughly wash them4 ,the copper solution should be put into a bottle to prevent evaporation2 the dilute acid may be thrown away to be replaced by fresh acid for the next experiment4 #bhc4 ,copper ,sulphate ,solution is made by adding the blue crystals to water until no more will dissolve--that is1 the solution should be saturated1 extra crystals always being left in the stock bottle4 ,an ounce of the crystals to half a tumbler of water will be about right1 but a pint or so should be made at a time and be kept bottled to save time4 #bhd4 ,directions4 7,a7 ,in case you have access to a pair of scales that weigh to within #j4a gram1 carefully weigh both copper and zinc before proceeding4 ,they should be washed and dried with a cloth4 ,see that there are no drops of mercury upon the zinc that may fall off during the experiment4 7,b7 ,replace the plates in the cell1 and connect them with the #ae-turn coil of ,g ,v1 placed ,n and ,s4 ,allow the circuit to remain closed for half an hour1 and record the position of the needle every #e minutes4 7,c7 ,again wash1 dry with a cloth without rubbing1 and weigh both the zinc and copper4 ,compare the new weights with those found in 7,a74 #bhe4 ,chemical ,action in the ,two-,fluid ,cell4 ,in this form of cell the hydrogen is not allowed to collect upon the copper plate4 ,the action inside of ,p ,c is like that explained in #bgj1 hydrogen being set free4 ,as soon as this hydrogen 7,h#b7 comes in contact with the copper sulphate 7,cu,s,o#d71 and it begins to do this in the walls of ,p ,c1 a new chemical reaction takes place4 ,hydrogen has a stronger attraction for ,,so#d than ,cu has1 so it unites with the ,,so#d1 forming ,h#b,,so#d 7sulphuric acid71 and this at the same time throws out the ,cu bodily4 ,this ,cu is then free1 instead of hydrogen1 to be deposited upon the copper plate4 ,the current is constant1 as there is no polarization4 #bhf4 ,various ,galvanic ,cells2 ,open and ,closed ,circuit ,cells4 ,there is no one form of cell that is best for all kinds of work4 ,if momentary currents only are wanted1 such as for bells1 telephones1 etc41 in which the cell has plenty of time to rest1 open circuit cells are used4 ,these cells polarize1 however1 when the circuit has to be closed for any length of time4 ,this form of cell is always ready for use1 and may not need attention for months at a time4 ,the most common forms of the open circuit cells are the ,leclanch 7 #bhg7 and dry cell 7 #bhh74 ,open circuit cells polarize quickly1 because the depolarizer 7 #bhj7 is slow in destroying the hydrogen4 ,when a strong current is needed for a considerable time1 such as for telegraph lines1 motors1 etc41 a closed circuit cell is necessary4 ,the depolarization must be rapid and constant4 ,the bichromate 7 #bhi7 and the ,daniell cell 7 #bij7 are very common forms of closed circuit cells4 7,see1 also1 ,storage ,cells47 #bhg4 ,the ,leclanch ,cell is an open circuit cell in which carbon and zinc are the plates4 ,the carbon is surrounded with dioxide of manganese1 a depolarizer2 the two are either packed together in a porous cup1 or the latter is compressed into blocks1 which are fastened to the carbon4 ,the porous cup stands in a jar containing a solution of sal ammoniac 7ammonium chloride71 which acts as the exciting fluid1 and in which stands a zinc rod4 ,the zinc is not acted upon when the circuit is open4 ,the hydrogen given off by the decomposition of the ammonium chloride is destroyed by the oxygen contained in the manganese dioxide4 ,the ,e4 ,m4 ,f4 is nearly #a4e volts4 #bhh4 ,dry ,cells are for open circuit work4 ,sheet zinc forms at the same time the active plate and the outside cylinder or case4 ,a carbon plate acts as the inactive or - plate4 ,the exciting fluid is kept from spilling by its being absorbed by one of the various substances used for that purpose4 #bhi4 ,the ,bichromate of ,potash ,cell is a very common one for laboratory use4 ,it gives a strong current1 and although a single fluid cell1 it does not readily polarize4 ,zinc and carbon plates are used4 ,in the sulphuric acid1 which is the exciting fluid1 is dissolved bichromate of potash4 ,this cell is used for running small motors1 induction coils1 etc4 ,it has1 with fresh solutions1 an ,e4 ,m4 ,f4 of about #b volts4 7,see ,apparatus ,book1 ,chapter ,i41 for ,home-,made ,batteries47 #bij4 ,the ,daniell ,cell1 of which the two-fluid cell used in ,exp4 #aab is a form1 is noted for its constant current4 ,the ,e4 ,m4 ,f4 is a little over #a volt1 and it should be kept working through a resistance when not in regular use2 it should not be left in open circuit4 ,the porous cup keeps the two fluids from mixing1 but it does not stop the current4 #bia4 ,the ,gravity ,cell is a form of the above4 ,as one of the fluids is heavier than the other1 no porous cup is needed4 ,gravity1 together with the action of the current1 tends to keep the fluids separated4 ,a copper plate is placed in the bottom of the jar1 and upon this is put the copper sulphate solution4 ,the zinc plate is supported by the top of the jar and rests in a solution of zinc sulphate1 which is lighter than the blue solution below4 ,an insulated wire extends from the copper through the liquids4 ,this cell is used for telegraph and similar work4 7,see ,apparatus ,book for ,home-,made ,gravity ,cell1 its ,regulation1 etc47 ,,chapter ,,xvi4 ,,the ,,electric ,,circuit4 ,,experiment #aad4 ,to see what is meant by divided circuits or shunts4 ,apparatus4 ,the galvanoscope1 ,g ,v 7,no4 #eh72 astatic galvanoscope1 ,a ,g 7,no4 #ei72 two-fluid cell1 #b-;,f ,c 7see #bha72 #f wires with connectors2 small thin pieces of tin or other metal1 ,m ,p1 for rapidly making connections 7 #bbf74 ,arrange as in ,fig4 #hh4 ,the wires1 #a and #d1 from #b-;,f ,c1 lead to the metal plates ,m ,p-,a and ,m ,p-,b1 for convenience4 ,the wires1 #b and #c1 from ,g ,v1 are also connected with these plates4 ,the wires1 #e and #f 7dotted lines71 lead from ,a ,g1 to be used as directed in part 7,b7 of the experiment4 ,see that ,g ,v is properly placed4 ,see that ,a ,g is adjusted4 ,illustration3 ,fig4 #hh4 #bib4 ,directions4 7,a7 ,without ,a ,g in place1 take the reading of ,g ,v4 ,the current now passes from ,cu through #a1 ,m ,p-,b1 #b1 ,g ,v1 #c1 ,m ,p-,a1 #d to ,zn4 7,b7 ,connect wires #e and #f to the plates1 as shown by the dotted lines4 ,again take reading of ,g ,v1 and compare it with the first reading4 ,does some of the current pass through ,a ,g8 #bic4 ,divided ,circuits2 ,shunts4 ,the current divides at ,m ,p-,b into two parts2 one part may be called a shunt of the other4 ,the circuit is said to be divided2 it has two branches4 ,if the two ends of a wire be fastened to another as in ,fig4 #aja1 the circuit is also divided4 ,when two or more conductors lead side by side from one point to another1 they are called parallel circuits2 that is1 the conductors are joined in parallel4 ,as strong currents would injure delicate galvanometers1 a small part only of the current may be allowed to pass through the galvanometer by using a shunt4 ,fig4 #hi shows such an arrangement1 in which most of the current passes through the shunt1 ,s4 ,there are many practical uses of shunts4 ,illustration3 ,fig4 #hi4 ,,experiment #aae4 ,to see what is meant by short circuits4 ,apparatus4 ,about the same as in ,exp4 #aad1 ,fig4 #hh4 ,the astatic galvanoscope is not needed2 in place of it provide a short piece of metal1 such as a battery-plate1 or even a jack-knife4 ,arrange as in ,fig4 #hh1 but without ,a ,g4 #bid4 ,directions4 7,a7 ,with the current passing as described in ,exp4 #aad 7,a71 take the reading of ,g ,v4 7,b7 ,lay the ends of the metal1 or other thick conductor1 upon ,m ,p-,a and ,m ,p-,b4 ,compare the new reading of ,g ,v with that in part 7,a74 7,c7 ,remove the conductor used to short circuit ,g ,v1 take the reading in degrees1 then touch ,m ,p-,a to ,m ,p-,b2 watch ,g ,v4 #bie4 ,short ,circuits are very apt to occur unless care is taken4 ,do not allow uninsulated wires to touch each other4 ,as shown by the above experiment1 practically the whole of the current may be side-tracked by a shunt of low resistance4 ,a galvanic cell is short-circuited by connecting the plates directly by a wire or other conductor4 ,,chapter ,,xvii4 ,,electromotive ,,force4 #bif4 ,electromotive ,force4 ,it has been stated that a galvanic cell has the power to charge one of its plates positively and the other negatively2 this power is called electromotive force1 and1 for short1 ,e4 ,m4 ,f4 is written4 ,the ,e4 ,m4 ,f4 of a cell depends upon the kinds of plates used and their condition1 the chemicals used in the exciting fluids1 etc4 ,the greater the ,e4 ,m4 ,f4 of a cell the greater its power to force the current through wires1 etc4 ,the ,e4 ,m4 ,f4 of a cell does not depend upon the size of its plates1 as will be seen by later experiments4 #big4 ,unit of ,e4 ,m4 ,f42 ,the ,volt4 ,a certain amount of ,e4 ,m4 ,f4 has been taken as the standard1 and1 in honor of ,volta1 it has been called the volt4 ,the ,e4 ,m4 ,f4 of the two-fluid cell used in ,exp4 #aac is not far from #a volt4 ,if a certain cell has the power to keep up twice the difference of potential between its terminals that the ,daniell cell has1 we say that it has an ,e4 ,m4 ,f4 of about #b volts4 ,voltmeters are instruments to measure ,e4 ,m4 ,f4 ,,experiment #aaf4 ,to see if the ,e4 ,m4 ,f4 of a cell depends upon the materials used in its construction4 ,apparatus4 ,tumbler two-thirds full of dilute sulphuric acid 7#beh72 strips of zinc1 ,zn 7,no4 #fj72 copper strips1 ,cu 7,no4 #fg72 iron strip1 ,i 7,no4 #gf72 lead strip1 ,l 7,no4 #gg72 carbon rod 7,no4 #fd72 the galvanoscope1 ,g ,v 7,no4 #eh72 #b wires with connectors 7 #bbf71 so that the plates can be changed quickly2 the wooden cross-piece1 ,w ,c ,p 7,no4 #gj74 ,arrange as in ,fig4 #ij4 ,the metal strips are all of the same size2 they may be held with the hand firmly against ,w ,c ,p1 in order to have them the same distance apart in each trial4 ,they should be lowered to the bottom of the tumbler in each case1 in order to have them acted upon by the same amount of acid4 ,place ,g ,v properly4 ,illustration3 ,fig4 #ij4 #bih4 ,directions4 7,a7 ,with ,zn and ,cu connected to ,g ,v as shown 7,fig4 #ij71 take the reading in degrees1 and note in which direction 7east or west7 the ,n end of the needle is deflected4 ,tabulate results1 as shown in ,fig4 #ia1 filling in each column of your table made out on paper4 7,b7 ,in like manner try the following combinations in the order given1 in each case connecting the first-mentioned plate with the left-hand binding-post1 ,l1 of ,g ,v4 ,for 7,b7 use zinc-iron4 7,c7 ,use zinc-lead2 7,d7 iron-copper2 7,e7 iron-lead2 7,f7 lead-copper2 7,g7 copper-carbon4 ,illustration3 ---------------------------------------- ------------------ ,,part ,,plates4 ,,liquid4 ,,deflection4 ,,current ,,in ,,cell ,,from ---------------------------------------- ----------------- 7,a7 ,,zinc4 ,,copper4 ,,dil4 ,,sulp4 #fe ,,west4 ,,cu ,,to ,,zn ,,acid4 7,b7 7,c7 ,fig4 #ia4 #bii4 ,note4 ,some of the combinations produce but slight currents4 ,in case ,g ,v is not delicate enough to show clearly which way the current passes1 use the astatic galvanoscope in its place for such combinations4 #cjj4 ,discussion4 ,exp4 #aaf clearly showed that different combinations of metals in the acid have different powers of pushing electricity through the galvanoscope4 ,although some of the pairs of metals furnished so weak a current that it was necessary to use the astatic galvanoscope to study the current1 all produced some current1 and from the results can be formed an electromotive series 7 #cja74 ,the strength of acid1 condition of plates1 etc41 affect the ,e4 ,m4 ,f4 of a cell4 #cja4 ,electromotive ,series4 ,all metals are not acted upon to the same degree by dilute acid4 ,from the results of ,exp4 #aaf it is seen1 part 7,b71 that iron is electronegative to zinc2 that is1 the current in the cell flows from zinc to iron4 ,part 7,d7 showed that iron is electropositive to copper1 as the current flowed from iron to copper in the cell4 ,it is possible to arrange the metals in a series1 one below the other1 in such a way that any one will be electronegative to those above it and electropositive to those below it2 that is1 the list should have the most electropositive metal at the top1 and the one least acted upon by the acid at the bottom4 ,make such a list from your results4 ,the farther the metals used are apart in the list1 the greater will be the ,e4 ,m4 ,f4 of the cell4 ,good carbon is acted upon the least of all1 so zinc and carbon are better than zinc and copper4 ,,experiment #aag4 ,to see whether the electromotive force of a cell depends upon its size4 ,apparatus4 ,galvanoscope2 two glass tumblers2 dilute acid2 two wooden cross-pieces2 two copper and two zinc strips1 the same size as those used for ,exp4 #aab4 7,see #bge74 ,these materials will form two simple cells like ,fig4 #he4 ,have about #c in4 of acid in one tumbler1 and but #a in4 in the other4 ,the plates of one cell will then be about #b-a_/b in4 in acid1 and those of the other cell only #a_/b in4 in acid4 ,this gives us the same effect as a large and a small cell4 #cjb4 ,directions4 7,a7 ,join the large and small cells with ,g ,v so that their currents will oppose each other4 ,to do this1 join the two zinc plates by means of a wire and connectors4 ,with two other wires connect the two copper plates with the galvanoscope binding-posts1 and watch for any indication of current4 ,does one cell oppose the other8 #cjc4 ,discussion4 ,the ,e4 ,m4 ,f4 of a cell1 then1 does not depend upon the size of its plates4 ,the small piece of zinc--that is1 the one in but little acid--had the same potential as the large piece2 they must have had1 as they were joined4 ,the large cell will give a stronger current1 under certain conditions1 than the small one2 but this depends upon other things than ,e4 ,m4 ,f4 7,see experiments under ,current ,strength47 ,a zinc-copper cell1 like the one just used 7,exp4 #aag71 has the same voltage as one of the same kind would have1 even though it were made as large as a barrel4 ,,chapter ,,xviii4 ,,electrical ,,resistance4 #cje4 ,resistance4 ,it is harder for a horse to draw a wagon through deep sand than over a smooth pavement4 ,we may say that the sand holds the horse back--that is1 it offers a resistance4 ,the electric current does not pass through all sorts of substances with the same ease1 and when it succeeds in pushing its way through a circuit of considerable resistance1 we cannot expect it to arrive at the end of its journey without being weaker than when it started4 ,do we expect this of a man or horse8 ,we shall soon see that there is a definite relation between resistance and the strength of the current at the end of its journey4 ,,experiment #aah4 ,to study the general effect of resistance upon a current4 ,apparatus4 ,galvanoscope1 ,g ,v 7,no4 #eh72 resistance coil1 ,r ,c 7,no4 #gi7 7 #caj72 two-fluid cell1 #b-;,f ,c 7 #bha72 #d wires with connectors 7 #bbf74 ,arrange as in ,fig4 #ib4 ,the current passes as shown by the arrow1 and the circuit may be opened and closed at the metal plate1 ,m ,p1 or by using a key in its place4 ,properly place ,g ,v4 #cjf4 ,directions4 7,a7 ,take the reading of ,g ,v in degrees1 the current passing through the entire length of ,r ,c4 7,see #caj47 7,b7 ,change the end of wire #d from binding-post ,r to ,m1 on ,r ,c1 so that the current will pass through one-half only of ,r ,c4 ,note the reading of ,g ,v4 7,c7 ,remove ,r ,c entirely and connect wires #c and #d by means of a metal plate4 ,compare the readings of 7,a71 7,b7 and 7,c74 ,what do they show8 ,illustration3 ,fig4 #ib4 #cjg4 ,external ,resistance2 ,internal ,resistance4 ,when we consider a circuit like that shown in ,fig4 #ib we see that it is composed of two parts1 and that we have two kinds of resistances4 ,the wires1 instruments1 etc41 make up what is called the external resistance of the circuit2 that is1 the part that is external to the cell4 ,the liquids in the cell offer a resistance to the current2 this is called internal resistance4 7,see #cad47 ,the strength of the current depends upon the relation between these two resistances1 as will be seen by future experiments1 as well as upon the ,e4 ,m4 ,f4 of the cell4 ,as liquids are not as good conductors as metals1 the internal resistance of cells may be quite high4 #cjh4 ,unit of ,resistance2 ,the ,ohm4 ,whenever anything is to be measured1 a standard1 or unit1 is necessary4 ,the unit of resistance is called the ohm1 in honor of ,ohm1 who made careful investigations upon this subject4 ,a column of mercury having a length of a little over #c feet has been taken as a unit4 7,the column taken is #ajf4c cm4 with a weight of #ad4deba grams2 it has a cross-section of about #a sq4 mm41 at a temperature of #j;,c47 ,mercury is a liquid1 and has no grain to affect the resistance4 ,for the use of students1 #i ft4 #i in4 of ,no4 #cj copper wire1 or #ci ft4 #a in4 of ,no4 #bd copper wire will make a fairly good ohm4 ,we might1 of course1 take any other length as our standard2 the above1 however1 will give results that are approximately correct4 7,see wire tables at the end of this book47 #cji4 ,resistance ,coils2 ,resistance ,boxes4 ,coils of wire1 having carefully-measured resistances1 are called resistance coils4 ,the wire for any coil is doubled at the center before it is wound into coils or upon spools 7,fig4 #ic7 to avoid the magnetic effect4 ,the ends of the coils are attached to binding-posts1 or to brass blocks1 in regular instruments1 so that one or more coils can be used at a time2 that is1 so that they may be handled in a manner similar to that in which the different coils on the galvanoscope are used4 ,if we have #d coils of #a1 #b1 #b1 and #e ohms resistance1 we shall be able to use any number of ohms from #a to #aj by making the proper connections4 7,see ,apparatus ,book1 chapter ,,xvii1 for ,home-made ,resistance ,coils47 ,for protection and convenience1 coils are usually placed in a box1 the whole being called a resistance box4 ,the ends of the coils are joined to brass blocks1 placed near each other on the top of the box1 and between which may be pressed plugs when it is desired to short circuit the coils4 ,by removing a plug1 the coil1 whose ends are joined to the blocks touching it1 is brought into the circuit4 ,illustration3 ,fig4 #ic4 ,illustration3 ,fig4 #id4 #caj4 ,simple ,resistance ,coil4 ,fig4 #id shows a simple form of coil1 ,r ,c 7,no4 #gi74 ,the total resistance is #b ohms1 ,l 7left7 and ,r 7right7 being binding-posts to which the ends of the coil1 ,c1 are joined4 ,m 7middle7 connects with the middle of the wire1 at which point the wire is doubled4 ,the coil is fastened to a stiff pasteboard base1 ,b4 ,connections4 ,when #b ohms resistance are wanted1 let the current enter at ,l and leave at ,r 7or the reverse74 ,when #a ohm is wanted1 let the current leave or enter at ,m1 the other wire being joined to ,l or to ,r4 ,connections should be made with spring connectors4 ,see #bbi4 ,,experiment #aai4 ,to test the power of various substances to conduct galvanic electricity4 ,apparatus4 ,galvanoscope1 ,g ,v 7,no4 #eh72 dry cell1 ,d ,c1 or two-fluid cell1 #b-;,f ,c2 pieces of different metals2 wood1 dry and damp2 tumbler of pure water2 rubber2 ebonite2 silk2 glass1 etc41 etc4 ,arrange as in ,fig4 #ib1 leaving out ,r ,c1 and instead of having ,m ,p between wires #a and #b1 use their free ends to press firmly upon the ends of the substance to be tested2 that is1 the body under test should take the place of ,m ,p in the ,fig4 ,g ,v will show a deflection1 of course1 when the particular thing under test is a conductor4 #caa4 ,directions4 7,a7 ,make tests with the above substances1 and with any others at hand1 and note which are conductors and which are not4 #cab4 ,conductors and ,nonconductors4 ,it is evident1 from the experiments1 that bodies which conduct static electricity do not necessarily conduct galvanic electricity4 ,the greater the ,e4 ,m4 ,f4 of a current1 the greater its power to overcome resistance4 ,some bodies1 like dry wood1 that readily conduct the high potential static electricity1 make fairly good insulators for the low potential galvanic currents4 ,for convenience1 substances may be divided into good conductors1 partial conductors1 and insulators1 or nonconductors4 ,good ,conductors4 ,metals1 charcoal1 graphite1 acids1 etc4 ,partial ,conductors4 ,dry wood1 paper1 cotton1 etc4 ,insulators4 ,oils1 porcelain1 silk1 resin1 shellac1 ebonite1 paraffine1 glass1 dry air4 ,illustration3 ,fig4 #ie4 ,,experiment #abj4 ,to find the effect of sulphuric acid upon the conductivity of water4 ,apparatus4 ,galvanoscope1 ,g ,v2 cell2 #b-;,f ,c2 connecting wires2 saucer or tumbler1 ,s2 a little sulphuric acid4 ,arrange as in ,fig4 #ie4 #cac4 ,directions4 7,a7 ,put a little pure water in ,s1 and see if enough current can pass through it to deflect the needle of ,g ,v4 ,the ends of the wires1 #a and #b1 should be gradually moved toward each other1 the needle being watched4 7,b7 ,put #d or #e drops of concentrated acid into the water2 stir it1 then repeat the test4 ,what effect has the acid8 #cad4 ,internal ,resistance4 ,as found in ,exp4 #abj1 pure water is not a good conductor of galvanic electricity4 ,the acid in the simple cell1 and in other single-fluid cells1 acts upon the zinc and at the same time makes it possible for the current to pass1 as it reduces the internal resistance4 ,as seen later1 this resistance in cells is greatly diminished by bringing the plates near each other1 and by increasing the surface of the plates that are in contact with the acid4 ,the larger the plates the less the internal resistance1 other things remaining the same4 ,the internal resistance of a battery can be changed by connecting the cells differently4 7,see ,chap4 on ,arrangement of ,cells47 ,illustration3 ,fig4 #if4 ,,experiment #aba4 ,to find what effect the length of a wire has upon its electrical resistance4 ,apparatus4 ,a ,no4 #cj ,german-silver wire1 ,g-,s ,w1 a little over two meters long1 un-insulated 7,no4 #ha72 the two-fluid cell1 #b-;,f ,c 7,exp4 #aac72 galvanoscope1 ,g ,v 7,no4 #eh72 plate binding-posts1 ,x1 ,y and ,z 7,no4 #hc-hd-he72 copper washers 7,no4 #hg74 ,arrange as in ,fig4 #if1 so that the current will flow1 at first1 as shown by the arrow4 ,the metal plates1 ,m ,p #a and ,m ,p #b1 are used so that the connections may be changed without disturbing ,g ,v4 ,the binding-posts may be fastened directly to the top of the table2 but it will be more convenient to permanently fix them to a board1 ,b1 as shown1 so that the same arrangement can be used for future experiments4 ,the binding-posts1 ,x and ,y1 should be about #a_/h in4 apart1 just far enough so that their edges do not touch each other4 ,the binding-post1 ,z1 should be fastened to ,b with its inside end #a meter7#ajj centimeters1 cm47 from the ends of ,x and ,y4 ,marks should be made upon ,b1 #aj centimeters apart1 as indicated by the cross lines4 ,this distance may be taken from the scale on the rule 7,no4 #hh74 ,fasten one end of the ,no4 #cj wire1 ,g-,s ,w1 to ,x4 ,to do this twist its end around the screw1 ,s1 between ,x and the copper washer1 then turn the screw in with a screw-driver until it firmly holds ,x to the board4 ,pass the wire around the screw in ,z1 and bring its free end to the other binding-post1 ,y1 to be fastened 7,fig4 #if74 ,two meters of wire then form a path for the current from ,x to ,y4 ,have the board wide enough so that another set of binding-posts can be put by the side of ,y4 ,it will be best to permanently leave the ,no4 #cj wire upon the board1 and to fasten the ,no4 #bh wire 7next experiment7 to another set of binding-posts1 placed in the same manner as those in ,fig4 #if4 ,make holes in the wood with an awl before forcing in the screws4 #cae4 ,note4 ,this experiment is usually done with a reverser in the circuit1 first taking readings with the current passing in one direction1 and then in the opposite direction4 ,considerable time will be saved by taking all the readings for one direction of the current at a time1 simply using different lengths of ,german-silver wire1 and allowing the current to flow constantly during each part4 ,this obviates all danger of poor contacts in the reverser1 etc42 it saves the trouble of handling the reverser1 and much of the time needed for the needle to come to rest4 ,illustration3 ---------------------------------------- -------------- ,,length ,,of ,,circ41 ,,cm4#bjj #ahj #afj #adjabjajj #hj #fjbjj ,o ---------------------------------------- -------------- ,,deflection2 ,,west #bf #bh #cj #bffg ---------------------------------------- -------------- ,,deflection2 ,,east #be #bg #cj #befg ---------------------------------------- -------------- ,,average #be4ebg4e #cj #be4efg ---------------------------------------- -------------- ,fig4 #ig4 #caf4 ,directions4 7,a7 ,with the circuit arranged as in ,fig4 #if1 and with ,g ,v properly placed1 take the reading of ,g ,v1 the current passing through #bjj cm4 of ,no4 #cj ,g-,s ,w4 ,record your results in a diagram made like ,fig4 #ig4 ,the row of figures across the top shows the length of the circuit4 ,the table is started with results from one experiment4 ,your results will probably be different from these4 7,b7 ,get the deflection with the current passing through #ahj cm4 of wire4 ,to do this press a piece of copper 7,o1 ,fig4 #if7 upon the wire at the mark #aj cm4 from ,z1 another thin piece of metal1 ,u1 having been slipped under the wire4 ,this will allow the current to pass across from one wire to the other4 ,record the deflection in the col4 marked #ahj4 7,c7 ,record the deflections for the lengths1 #afj cm41 #adj1 #abj1 #ajj1 #hj1 and #fj2 then repeat 7,a7 to be sure that the cell has been working uniformly4 ,this deflection should agree with that in 7,a74 7,d7 ,change the direction of the current through ,g ,v2 to do this1 change wire1 #a1 from ,m ,p #b to ,m ,p #a1 and wire #e to ,m ,p #b4 ,this must be done without disturbing ,g ,v4 7,e7 ,repeat 7,a71 7,b71 and 7,c71 and record the deflections for the different lengths4 7,f7 ,get the average deflections4 7,g7 ,take1 for future use1 the deflection produced without ,g-,s ,w being in the circuit4 ,swing the end of wire1 #c1 that is joined to ,y1 around to ,m ,p #b4 ,the current will then pass simply through ,g ,v4 ,record deflection in col4 marked ,o4 ,note4 ,it is best to do the next experiment at once with the same cell1 so that the results of the two experiments can be compared4 ,in case this is impossible1 get your cell to produce the same deflection when you use it again1 as shown in col4 ,o1 ,fig4 #ig4 ,you can regulate the deflection of the needle of ,g ,v by varying the strength and quantity of the acid in ,p ,c4 #cag4 ,discussion4 ,the resistance of a wire evidently depends 7,exp4 #aba7 upon its length4 ,the exact relation between resistance and length cannot be seen from these results1 however1 which are used in the next experiment4 ,it will be shown later that in a wire1 other things remaining the same1 the resistance varies directly as its length4 ,,experiment #abb4 ,to find what effect the size 7area of cross-section7 of a wire has upon its electrical resistance4 ,apparatus4 ,same as in last experiment1 with one change1 however4 ,replace the ,no4 #cj ,g-silver wire with a ,no4 #bh ,g-silver wire 7,no4 #hb71 or1 what is better still1 fasten it to another set of binding-posts on the board and leave the ,no4 #cj for future use4 ,the two should be stretched side by side for constant use4 #cah4 ,directions4 7,a7 ,see that your cell is in the same condition as for ,exp4 #aba2 that is1 it should produce the same deflection of the needle of ,g ,v as before1 when the two1 only1 are in the circuit4 7,see ,exp4 #aba1 ,g47 ,the deflection may be changed by changing the strength and quantity of the dilute acid and copper solution4 7,b7 ,find the average deflection of the needle with the #b meters of ,no4 #bh ,g-s wire in the circuit1 arranged as in ,fig4 #if4 7,c7 ,compare this average deflection with the results obtained in ,exp4 #aba1 in order to find what length of the ,no4 #cj wire has the same resistance as #b meters of ,no4 #bh wire4 ,to find how many times greater one length is than another1 we divide the larger length by the smaller2 hence1 to find the relation between the two lengths of wire that gave the same deflection1--lengths of equal resistance1--we divide the #bjj centimeters 7the length of the ,no4 #bh7 by the length of ,no4 #cj found as directed4 7,d7 ,from the wire tables it will be found that the area of cross-section of ,no4 #bh wire is about #a4ei times that of ,no4 #cj wire4 ,how does this quotient1 or ratio1 compare with that found in part 7,c78 ,what is the relation between the area of cross-section of a wire and its resistance8 7,see #cai1 also ,exp4 #acf47 #cai4 ,discussion4 ,if we find that a certain wire1 ,x1 which is #egf feet long1 has the same resistance as a shorter one1 ,y1 #cfj feet long1 we see 7#egf divided by #cfj7 that the ratio of their lengths is #a4f4 ,this means that the longer one1 ,x1 is #a4f times as good a conductor as ,y2 or1 in other words1 that the resistance of ,y is #a4f times that of ,x4 ,it is easier for water to flow through a large pipe than it is through a small one4 ,the same general principle is true of electricity4 ,a large wire offers less resistance to the current than a small one of the same material4 ,if one wire is twice the size of another of equal length1 it will be twice as good a conductor as the other2 that is1 it will have one-half the resistance of the smaller1 provided they are of the same material4 7,see ,laws47 ,,experiment #abc4 ,to compare the resistance of a divided circuit with the resistance of one of its branches4 ,apparatus4 ,same as in last experiment4 ,arrange as in ,fig4 #ih4 #cbj4 ,directions4 7,a7 ,note the deflection of the needle when the current passes through #a meter of ,g-s wire1 as shown4 ,this will be considered as one branch of the divided circuit4 7,b7 ,still allowing the current to pass as in part 7,a71 press a piece of copper firmly across the binding-posts ,x and ,y1 to electrically connect them1 and note the reading of the needle4 ,in this case the current divides at ,z through the two branches4 ,what is learned from the results of 7,a7 and 7,b78 7,c7 ,see if you can show the same results with apparatus arranged as in ,fig4 #ii4 ,illustration3 ,fig4 #ih4 ,illustration3 ,fig4 #ii4 #cba4 ,discussion4 ,two wires placed side by side as in 7,b71 ,exp4 #abc1 really form a conductor having twice the size 7area of cross section7 of one of the branches4 ,the more paths a current has in going from one place to another1 the less the resistance4 7,see ,exp4 #ace47 ,the wires are said to be in parallel or in multiple arc4 ,illustration3 ,fig4 #ajj4 ,illustration3 ,fig4 #aja4 ,,experiment #abd4 ,to study the effect of decreasing the resistance in one branch of a divided circuit4 ,apparatus4 ,galvanoscope1 ,g ,v 7,no4 #eh72 resistance coil1 ,r ,c 7,no4 #gi72 two-fluid cell1 #b-;,f ,c 7 #bha71 or a dry cell2 #f connecting wires2 metal plates1 ,m ,p4 ,arrange as in ,fig4 #ajj1 so that the current divides into two branches at ,m ,p #a4 ,the branches unite at ,m ,p #b4 #cbb4 ,directions4 7,a7 ,take the reading of ,g ,v with #b ohms resistance in the lower branch2 that is1 with the whole of ,r ,c in circuit4 7,b7 ,take the reading of ,g ,v with one ohm in circuit2 that is1 with the end of wire1 #e1 connected to ,m instead of to ,r4 7,c7 ,cut out ,r ,c from the lower branch by replacing it with a metal plate1 thus joining wires #c and #e4 ,compare the results from 7,a71 7,b71 and 7,c71 and explain4 #cbc4 ,current in ,divided ,circuits4 ,let us consider a circuit like that shown in ,fig4 #aja4 ,if the points1 ,c and ,z1 were at the same potential1 no current would pass from ,c to ,z4 ,as the current does pass1 ,z must be at a lower potential than ,c2 there is a fall of potential from ,c to ,z4 ,if the branch1 ,a ,b1 has the same resistance as ,r ,x1 the same amount of current will pass through each4 ,exp4 #abd has shown that when the branches have unequal resistances1 most of the current passes through the one of small resistance4 ,if ,r ,x has a greater resistance than ,a ,b1 most of the current will pass through ,a ,b4 ,,chapter ,,xix4 ,,measurement ,,of ,,resistance4 ,illustration3 ,fig4 #ajb4 ,,experiment #abe4 ,to study the construction and use of a simple ,wheatstone's ,bridge4 ,apparatus4 ,fig4 #ajb4 ,a ,wheatstone's bridge1 ,w ,b 7,no4 #hj71 7 #cbd72 astatic galvanoscope1 ,a ,g 7,no4 #ei72 dry cell1 ,d ,c 7,no4 #ea72 key1 ,k 7,no4 #ee72 #g wires with spring connectors1 two of which1 ,r and ,x1 are equal in length2 metal plate1 ,m ,p1 for connecting wires4 ,arrange as in ,fig4 #ajb4 ,the carbon of ,d ,c is joined to ,k1 and this to the point1 ,c1 of the bridge4 ,the zinc of ,d ,c connects with the point ,z on ,w ,b4 ,the ,a ,g is placed between the branches for clearness4 ,wire #c is joined to the left-hand binding-post of ,a ,g1 and wire #d joins ,m ,p with the right-hand one4 ,when the end of wire #c does not touch ,g-s ,w1 it is evident that as soon as ,k is pressed1 the current divides at ,c on its way to ,z1 where the branches unite again4 ,k is used so that ,d ,c will not be polarized by steady use4 ,illustration3 ,fig4 #ajc4 #cbd4 ,the ,simple ,wheatstone's ,bridge 7,fig4 #ajc7 consists of a wooden base1 ,w1 at the ends of which are fastened two aluminum conductors1 #a and #c4 ,at one side of ,w is fastened another conductor1 #b4 ,in ,fig4 #ajd are side views of the conductors4 ,these are used merely for convenience in making connections1 and take the place of the metal plates used in previous experiments4 ,a ,german-silver wire1 ,g-s ,w1 is stretched between #a and #c1 and under this is a scale1 ,s1 divided into #ajj small parts1 these being tenths of the larger divisions4 ,the ends of ,g-s ,w are held between eyelets1 as shown at ,e1 ,fig4 #ajd4 ,illustration3 ,fig4 #ajd4 ,reading the ,scale4 ,the value of part ,a can be read directly from the scale1 using the lower row of figures4 ,the point marked ,p1 for example1 would be read #c4g 7three and seven-tenths large divisions72 ,b would be #f4c1 found by subtracting #c4g from #aj4 ,the sum of ,a and ,b must always equal #aj4 ,the #f4c may also be read directly by using the upper row of figures for the whole numbers1 counting the tenths to the left4 ,try to divide the smallest divisions into halves1 at least2 that is1 if ,a #c4ge1 ,b #f4be4 ,take the readings carefully4 #cbe4 ,directions4 7,a7 ,touch the free end of wire1 #c1 to the point1 ,c1 which has a higher potential than ,m ,p4 ,press down ,k for an instant only4 ,some current should pass through ,a ,g1 as a shunt4 ,should it pass from ,c to ,m ,p or the reverse8 ,note in which direction the right-hand end of the astatic needle is deflected4 7,b7 ,swing the end of #c around and touch it to the point1 ,z1 which has a lower potential than ,m ,p4 ,press ,k for an instant1 watch the needle1 and compare with the results in 7,a74 7,c7 ,move the free end of #c along on ,g-s ,w1 touching ,k at intervals1 until a point is found at which the needle of ,a ,g is not deflected4 ,how does the potential of this point compare with that of ,m ,p8 #cbf4 ,discussion2 ,equipotential ,points4 ,since one end of the ,g-s ,w has a higher1 and its other end has a lower potential than ,m ,p1 there must be1 somewhere on it1 a point at which the potential is the same as at ,m ,p4 ,this place is quickly found by sliding the free end of wire1 #c1 along1 pressing ,k occasionally1 until ,a ,g shows that no current tends to pass through it in either direction1 when the current passes from ,c to ,z through the two branches of the divided circuit4 ,this point and ,m ,p are called equipotential points4 ,if the resistance of the part1 ,x1 be increased1 it should be evident that the part of the bridge-wire1 ,b1 should be also increased to find a point having the same potential as ,m ,p2 that is1 the end of #c should be moved towards ,c4 ,we have1 in the bridge-wire1 a simple means of varying the resistance of its parts1 ,a and ,b4 #cbg4 ,use of ,wheatstone's ,bridge4 ,it will be found1 upon trial1 if we put a resistance of #b ohms in place of ,r1 ,fig4 #ajb1 and #b ohms in place of ,x1 that the free end of wire #c will have to be at the center of the bridge-wire in order to get a balance2 that is1 to find the place where ,a ,g is not affected4 ,no matter what the resistance of ,r and ,x are1 provided they are equal1 this will be true4 ,the value of both ,a and ,b1 on the scale1 will be #e whole spaces1 no tenths4 ,from this we see that ,a3 ,b33 ,r3 ,x1 which reads ,a is to ,b as ,r is to ,x2 this means that ,a ,x ,b ,r4 ,supplying the values of the letters1 we have #e #b #e #b4 ,if we did not know the value of ,x1 that is1 if we were measuring the resistance of a coil of wire1 using a #b-ohm coil as the standard1 or ,r1 we could find the value of ,x1 knowing the other #c parts of the proportion4 #e ,x #e #b1 which means that #e times the value of ,x is #aj2 hence the value of ,x is #aj #e #b ohms4 ,suppose that we have ,r #b ohms1 which is the standard resistance coil 7,no4 #gi71 and are trying to find the resistance of a coil1 ,x4 ,we slide the end of wire1 #c1 along on the bridge-wire until the correct place is found4 7,see ,exp4 #abe1 #abf1 for details47 ,take the values of ,a and ,b 7 #cbd71 supply them in the equation given1 and work out the value of ,x4 #cbh4 ,,example4 ,r #b ohms2 ,a #c4g2 ,b #f4c2 to find the value of ,x in ohms4 ,a3 ,b33 ,r3 ,x1 which means that ,a ,x ,b ,r1 or #c4g ,x #f4c #b4 ,x must equal1 then 7#f4c #b7 #c4g #c4dje ohms4 ,note4 ,in practice it is most convenient to make connections as shown in ,fig4 #aje when measuring resistances 7,exp4 #abf74 ,the arrangement given in ,fig4 #ajb is simply for explanation4 ,it will be seen that the smaller ,a is1 compared with ,b1 the larger the unknown resistance compared with your standard4 ,illustration3 ,fig4 #aje4 ,,experiment #abf4 ,to measure the resistance of a wire by means of ,wheatstone's ,bridge2 the bridge method4 ,apparatus4 ,same as in ,exp4 #abe2 the two-ohm resistance coil1 ,r ,c 7,no4 #gi72 a coil of wire1 ,x1 as1 for example1 the #ae-turn coil on the galvanoscope1 ,g ,v 7,no4 #eh74 ,arrange as in ,fig4 #aje4 ,you will observe that the central conductor of the bridge 7#b1 ,fig4 #ajd7 takes the place of ,m ,p in previous explanations4 ,we still have the same kind of a divided circuit as explained in ,exp4 #abe1 ,a ,g being connected with points of equal potential4 ,it will be found convenient to have ,d ,c at the right1 and ,a ,g facing you at the left1 the key being in front4 7,see ,exp4 #ajg in regard to adjusting ,a ,g47 ,notice that you have a standard resistance 7#b ohms7 in place of ,r1 ,fig4 #ajb1 and an unknown resistance 7galvanoscope coil7 in place of ,x4 7,see #ccj47 #cbi4 ,directions4 7,a7 ,touch the free end of wire1 #c1 to the left-hand side of the bridge-wire1 press the key for an instant1 only1 and note the direction taken by the right-hand end of the needle4 ,move the end of wire1 #c1 to the right-hand side of the bridge-wire1 touch key1 watching needle4 ,does the needle move more or less than before8 ,in the same or opposite direction8 ,if the deflections are opposite1 the point that has the same potential as binding-post1 #b1 must be between the two points touched4 7,b7 ,be sure that all connections are good4 ,find the point on ,g-s ,w1 at which there is no deflection1 as directed in ,exp4 #abe 7,c74 ,note the readings on the scale1 as explained in #cbd4 7,c7 ,make the proper calculation1 #cbg1 #cbh1 and find the resistance of the coil of ,g ,v1 the resistances of the wires joining ,r ,c and ,g ,v to the bridge being neglected4 7,d7 ,make proper allowances for the resistances of the wires just mentioned 7see #ccj71 and compare them with the results found in part 7,c74 #ccj4 ,allowances for connections4 ,it should be remembered that the wires joining ,r ,c and ,g ,v to the bridge also have some resistance4 ,such connections1 in regular instruments1 are made by heavy copper straps or by thick1 short wires1 so that their resistances can be neglected4 ,in case you use the ordinary ,no4 #bd copper wire1 as directed1 the resistances of the pieces can be measured by means of the bridge1 or you can calculate their resistances from the wire tables4 ,the resistances should be allowed for4 ,it is evident that your standard resistance is #b ohms plus the resistance of the connecting wires1 and that the resistance of the coil1 ,x1 is found by deducting the resistance of its connecting wires from that found from the proportion previously used4 ,example4 ,we see from the table that the resistance of about #ci ft4 #a in4 of ,no4 #bd1 ,b and ,s copper wire is #a ohm4 ,this equals #dfi in4 ,if #dfi in4 have a ,r 7resistance7 of #a ohm1 #a in4 will have a ,r of one-#dfith of an ohm2 that is #a divided by #dfi1 which equals a little over 4#jjb ohm4 ,for every inch of ,no4 #bd wire used1 then1 for connections1 we may allow 4#jjb ohm4 ,this will be near enough for our purposes4 ,suppose that each connection is #ah in4 long1 the regular wires with connectors being used4 ,the ,r of the #cf in4 joined to ,r ,c will then be #cf times 4#jjb 4#jgb ohm4 ,our standard ,r must then be considered as #b4jgb ohm4 ,if we substitute this in the example1 as stated in #cbh1 we have #c4g ,x #f4c #b4jgb4 ,x must equal 7#f4c #b4jgb7_/c4g #c4ebh ohm1 which includes the unknown resistance and #cf in4 of connections1 the ,r of which is 4#jjb ohm2 #c4ebh - 4#jgb #c4def1 the resistance of ,x alone4 ,compare this with the answer to example1 #cbh4 ,make allowances according to length of connectors used4 ,note4--,carefully keep all the results of these experiments in a note book for future reference4 ,be sure that connections are good4 ,,experiments #abg-acg4 ,to measure the resistances of various wires1 coils1 etc41 by the bridge method4 ,apparatus4 ,the coils of wire1 etc41 as stated in the ,directions of each experiment4 ,the details of each piece of apparatus may be found by referring1 from the numbers given1 to the ,apparatus ,list1 and to descriptions in the paragraphs mentioned4 ,also all the apparatus of ,exp4 #abf4 ,note4 ,make proper allowances for connections 7 #ccj7 in all experiments in measuring resistances4 ,,experiment #abg4 #cca4 ,directions4 7,a7 ,as explained in ,exp4 #abf1 measure the resistance of the #aj-turn coil of ,g ,v1 allowing for connections 7 #ccj74 ,read the bridge-scale carefully4 7,b7 ,use one-half of the #b-ohm coil as standard and repeat4 ,,experiment #abh4 #ccb4 ,directions4 7,a7 ,measure the resistance of the #e-turn coil of ,g ,v 7see ,exp4 #abf1 etc471 using #b ohms as standard4 7,b7 ,use #a ohm as standard1 repeat1 and compare results4 7,c7 ,add the resistances of the #e and #aj-turn coils1 and compare the sum with the resistance of the #ae-turn coil1 as found in ,exp4 #abf1 ,d4 ,the difference should be but a few hundredths of an ohm4 ,,experiment #abi4 #ccc4 ,directions4 7,a7 ,measure the resistance of the coil of ,no4 #bd copper wire 7,no4 #hi74 ,this coil is used for later experiments4 ,spring connectors are fastened to the ends of this coil1 allowing it to be directly connected to the conductor on the bridge1 so no allowance should be made for its connecting wires4 7,see ,exp4 #abf for details47 ,mark the resistance upon the coil for future use4 7,see ,note47 ,note4 ,the student will be surprised1 perhaps1 to find that different results are obtained for the resistance of a given wire in case he uses different standard resistances in the various tests2 that is1 he will probably get a different result in ,exp4 #abg 7,a7 from the result of ,exp4 #abg 7,b74 ,the difference here1 however1 may not be large4 ,the best results are obtained by making the standard resistance as nearly equal as possible to the resistance to be measured1 so that a balance can be found when the end of wire #c 7,fig4 #aje7 is near the center of the bridge-wire4 ,if ,r1 ,fig4 #aje1 is much larger or smaller than ,x1 the point desired on ,g-s ,w will be near one of its ends1 and large errors thereby produced4 ,the approximate resistance of ,x can be found by trial1 then more or less resistance can be used for ,r to suit4 ,the student should make several coils as explained in ,apparatus ,book1 ,chapter ,,xvii4 ,the resistance of the different coils furnished should be measured and marked4 ,these can be used to vary the value of ,r4 ,,experiment #acj4 #ccd4 ,directions4 7,a7 ,measure the resistance of the coil of ,no4 #be copper wire 7,no4 #ij74 7,see ,exp4 #abf for details and the ,note1 ,exp4 #abi47 ,,experiment #aca4 #cce4 ,directions4 7,a7 ,measure the combined resistance of the two coils used in ,exps4 #abi and #acj1 when they are joined in series2 that is1 when one end of one coil is joined to one end of the other by means of a metal plate1 the free ends being connected to the bridge 7,exp4 #abf74 ,the current has to travel through the entire length of both coils4 7,b7 ,compare this result with the sum of their separate resistances found in ,exps4 #abi and #acj4 7,see ,exp4 #abi1 ,note47 ,,experiment #acb4 #ccf4 ,directions4 7,a7 ,measure the resistance of the two coils 7,exp4 #aca7 when they are joined in parallel4 7,see #bic47 ,they may be joined in parallel by connecting them both to the bridge at the same time1 one end of each being slipped onto #b 7,fig4 #ajc71 the other end of each being joined to #c4 ,in this way the current has two paths1 side-by-side1 to get from #b to #c4 7,see ,exp4 #abi1 ,note47 7,b7 ,compare this resistance with that of ,exp4 #aca4 ,,experiment #acc4 #ccg4 ,directions4 7,a7 ,measure the resistance of #a meter of ,no4 #bh ,german-silver wire4 ,use the wire as arranged on a board1 ,exp4 #abb 7,figs4 #if and #ih71 making the connections with the bridge from binding-posts1 ,x and ,z4 7,see ,exp4 #abi1 ,note47 ,the wires connecting the bridge with the ends of the ,g-s wire will each have to be about #b ft4 long4 ,in making deductions 7 #ccj7 figure according to the length used4 7,b7 ,divide the total resistance by #ajj to get the resistance of #a cm4 of the wire1 and carefully mark off the board into cm4 ,this will give #ajj parts between ,x and ,z4 ,,experiment #acd4 #cch4 ,directions4 7,a7 ,using the ,no4 #bh ,g-s wire on the board1 as arranged for ,exp4 #abb1 measure the resistance of the #b meters in series1 the connections being made with the bridge from ,x and ,y1 ,fig4 #ih4 7,b7 ,compare the result with that of ,exp4 #acc4 ,what is the relation between the length of a wire and its resistance8 ,see ,summary of ,laws4 7,see ,exp4 #abi1 ,note47 ,,experiment #ace4 #cci4 ,directions4 7,a7 ,measure the resistance of the above two meters of ,no4 #bh ,g-s wire when joined in parallel4 7 #bic47 ,the binding-posts1 ,x and ,y1 can be joined by a short wire with connectors on its ends1 or by clamping a thin strip across by means of spring connectors4 ,use the #b-ohm coil as the standard1 and make proper allowances4 7 #ccj47 7,b7 ,from the results of ,exps4 #acb and #ace what can be said about the resistances of parallel circuits as compared with the resistances of the separate branches8 ,,experiment #acf4 #cdj4 ,directions4 7,a7 ,arrange the #b meters of ,no4 #cj ,g-s wire on the table or board1 again 7,exp4 #aba1 ,fig4 #if74 7,b7 ,measure the resistance of one meter4 ,find the value of ,x approximately1 and use a resistance for ,r that will suit4 7,see ,exp4 #abi1 ,note47 7,c7 ,divide the result by #ajj to get the resistance of #a cm4 of the wire4 7,d7 ,compare the resistance of one meter of ,no4 #bh ,g-s wire1 found in ,exp4 #acc1 with the resistance of #a meter of ,no4 #cj ,g-s wire4 ,what is the relation1 then1 between the size 7area of cross-section7 of a wire and its resistance8 7,see the results of ,exp4 #abb1 and #cai1 also ,summary of ,laws47 ,,experiment #acg4 #cda4 ,directions4 7,a7 ,measure the resistance of #b meters of ,no4 #cj copper wire1 arranged on a board as in ,fig4 #if4 7,see ,exp4 #abi1 ,note47 ,get the resistance of #a meter4 7,b7 ,compare the conductivities of copper and ,german silver by studying the results of ,exps4 #acf and #acg4 ,which has the greater resistance8 ,to find out how many times greater one resistance is than the other1 divide the larger by the smaller4 ,,experiment #ach4 ,to study the effect of heat upon the resistance of metals4 ,apparatus4 ,same as for ,exp4 #abf2 the coil of ,no4 #bd wire 7,no4 #hi72 a lamp or other source of heat4 ,arrange as in ,fig4 #aje4 #cdb4 ,directions4 7,a7 ,measure the resistance of the coil as before1 ,exp4 #abi4 ,the result should nearly agree with that of ,exp4 #abi1 provided connections1 etc41 are the same4 7,b7 ,remove the coil from the bridge1 hold it about a foot above a lamp or stove1 to warm it thoroughly1 but do not heat it enough to injure the covering4 ,it will take a minute or so to warm it so that the heat will get to the inside also4 7,c7 ,replace the coil1 measure its resistance1 and compare the result with its resistance when cold4 ,does heat increase or decrease the resistance of a copper wire8 #cdc4 ,effect of ,heat upon ,resistance4 ,although there was but the fraction of an ohm difference in the resistances of the hot and cold coil1 it was evident that changes of temperature affect the conducting power of copper4 ,this is true of all metals2 but ,german silver and other alloys are much less affected than pure metals1 so they are used in making standard resistance coils4 ,the resistance of liquids that can be decomposed by the electric current decreases as the temperature rises4 ,carbon acts like the liquids1 while the resistance of metals increases as their temperature rises4 ,,experiment #aci4 ,to measure the resistance of a wire by the method of substitution4 ,apparatus4 ,the coil of ,no4 #bd wire 7,no4 #hi71 the resistance of which has been measured1 but which will be considered an unknown resistance1 ,x2 ,g ,v1 #b-;,f ,c1 ,m ,p1 connecting wires1 etc41 previously used2 rheostat 7 #cdd74 ,arrange as in ,fig4 #ajf first1 then as in ,fig4 #ajg4 #cdd4 ,simple ,rheostat4 ,the ,no4 #bh and ,no4 #cj ,g-s wires stretched upon the board 7,fig4 #if71 make a convenient form of rheostat4 ,the resistance per cm4 being known from the results of ,exp4 #acc and #acf1 the resistance for any number of cm4 is easily found4 ,the #aj-;cm4 divisions should be divided into centimeters4 ,these spaces may be marked off from the rule 7,no4 #hh74 ,illustration3 ,fig4 #ajf4 #cde4 ,directions4 7,a7 ,be sure that #b-;,f ,c gives a constant current1 shown by the uniform deflection at ,g ,v1 when arranged as in ,fig4 #ajf4 ,do not use a cell that quickly polarizes4 ,the coil1 ,x1 forms a part of the circuit2 it is joined to wires1 #a and #b1 by means of metal plates1 so that it may be quickly removed without disturbing either ,g ,v or #b-;,f ,c4 ,carefully read the deflection at ,g ,v4 7,b7 ,remove ,x from the circuit1 and join the free end of wire1 #b1 to binding-post1 ,x1 and the free end of wire1 #a1 to a small piece of sheet copper1 which can be firmly pressed upon the ,g-s wire to make a contact4 ,move this along on the ,g-s wire until the deflection produced equals that of part 7,a71 remembering that the longer the ,g-s wire in the circuit the less the deflection4 ,make two or three trials1 as one or two cm4 difference in length make but a little difference in the deflection4 ,note the number of cm4 of ,g-s wire used1 the resistance of which must equal that of the coil1 ,x4 7,c7 ,find the resistance of ,x by multiplying the length just found by the resistance of each cm41 and compare the result with the value found by using the bridge method directly4 ,illustration3 ,fig4 #ajg4 ,,experiment #adj4 ,to measure the ,e4 ,m4 ,f4 of a cell by comparison with the two-fluid cell4 ,apparatus4 ,rheostat 7 #cdd72 the two-fluid cell1 #b-;,f ,c 7,exp4 #aac71 the ,e4 ,m4 ,f4 of which may be taken as #a volt2 dry cell1 ,d ,c2 galvanoscope1 ,g ,v4 ,arrange first as in ,fig4 #ajg4 #cdf4 ,directions4 7,a7 ,be sure that #b-;,f ,c gives a constant current4 ,take the reading of ,g ,v without the rheostat in the circuit2 that is1 with wires1 #b and #a1 joined directly4 ,the deflection should be #ej or #fj degrees at least1 and be constant4 7,b7 ,attach a small piece of copper to the end of #a1 and firmly rub it along upon the ,g-s wire1 thus introducing resistance into the circuit1 until the deflection is1 say1 #fj 7#ej or #ee degrees will do74 ,note the length of ,g-s wire used and call it 7,b74 7,c7 ,gradually add more resistance by moving the end of #a along until the deflection is #ej1 #aj degrees less than before4 7,if the original was #ej make the new #dj74 ,call the number of cm4 of wire used 7,c74 7,d7 ,replace #b-;,f ,c with the dry cell ,d ,c4 ,add resistance1 as before1 until ,g ,v indicates a deflection of #fj1 being careful not to keep the circuit closed long enough to partially polarize ,d ,c4 ,make #b or #c trials1 allowing ,d ,c to rest a few minutes between each4 ,call the number of cm4 of ,g-s wire used 7,d74 7,e7 ,again add more resistance1 as in 7,c71 until the deflection is reduced to #ej4 ,call the length used 7,e74 #cdg4 ,calculation4 ,it is known that resistances that are able to reduce the strength of the currents equally are proportional to the electromotive forces2 that is1 the electromotive forces of the two cells are to each other as the two resistances necessary to produce equal changes in the deflections1 which1 of course1 indicate equal changes in the strength of the currents4 ,since the resistances used in the two cases are directly proportional to the lengths used1 we have3 ,length 7,c-,b73 ,length 7,e-,d733 ,e4 ,m4 ,f4 of #b-;,f ,c3 ,e4 ,m4 ,f4 of ,d ,c4 ,substitute the values found and find the ,e4 ,m4 ,f4 of ,d ,c4 ,,experiment #ada4 ,to measure the internal resistance of a cell by the method of opposition4 ,apparatus4 ,all the apparatus of ,exp4 #abf4 ,two simple cells 7 #bge71 the plates of which should be of the same size1 the same distance apart1 and immersed in acid to the same extent in both4 ,the acid in both should be of the same strength4 #cdh4 ,directions4 7,a7 ,connect the two cells in opposition1 so that no current will be generated by them1 and so that the two can be treated as a dead resistance4 ,do this by joining the two zinc plates by a wire with connectors1 and use wires to connect the copper plates to the bridge like any other unknown resistance4 7,b7 ,measure the resistance of the two by the regular bridge method1 allowing for wires used for connections4 ,one-half of the resistance found will give the internal resistance of one cell4 7,see ,note47 ,note4--,the standard resistance will have to be arranged to suit each particular case to make the calculations even approximately correct4 7,see ,exp4 #abi1 ,note47 ,the standard resistance may be increased by adding the various coils and rheostat wires1 their values being known4 #cdi4 ,summary of ,laws of ,resistance4 #a4 ,the resistance of a wire is directly proportional to its length1 provided its cross-section1 material1 etc41 are uniform4 ,,example4 ,if #ci4a ft4 of ,no4 #bd copper wire has a resistance of #a ohm1 #gh4b ft4 will have a resistance of #b ohms1 because #gh4b is twice #ci4a2 #gj4ch ft4 will have a resistance of #a4h ohms1 as 7#gj4ch #ci4a #a4h7 it is #a4h times #ci4a4 #b4 ,the resistance of a wire is inversely proportional to its area of cross-section4 ,the areas of cross-section of round wires vary as the squares of their diameters2 so the resistance of a wire is also inversely proportional to the square of its diameter1 other things being equal4 ,,example4 ,a ,no4 #cj wire has a diameter of about 4#ja inch1 while the diameter of a ,no4 #bd wire is about 4#jb in42 that is1 the ,no4 #bd has twice the diam4 that the ,no4 #cj has4 ,the area of cross-section of the ,no4 #bd1 however1 is four times that of the ,no4 #cj1 so its resistance is but #a_/d that of the ,no4 #cj1 the lengths1 etc41 being the same4 7,see ,wire ,tables47 #c4 ,the resistance of a wire depends upon its material1 as well as upon its length1 size1 etc4 #d4 ,the resistance of a wire depends upon its temperature4 7,see ,elementary ,electrical ,examples47 ,,chapter ,,xx4 ,,current ,,strength4 #cej4 ,strength of ,current4 ,the water in a certain tank may be under great pressure1 but if it is obliged to pass through long tubes before it can turn a water-wheel1 for example1 it is evident that the work done will depend not only upon the pressure in the tank1 but upon the resistance to be overcome before the water gets to the wheel4 ,the work that the water can do depends upon its rate of flow1 and may be used to measure the strength of the current4 ,the strength of a current of electricity is measured also by the work that it can do1 and it depends upon its rate of flow at the point measured4 ,the strength may be determined from its magnetic1 heating1 or chemical effects4 #cea4 ,unit of ,current ,strength2 ,the ,ampere4 ,a current having the strength of #a ampere1 when passed through a solution of silver nitrate under proper conditions1 will deposit #j4jjaaah gramme of silver in one second2 if passed through a solution of copper sulphate1 copper plates being used for the electrodes1 in the solution1 #j4jjjcbgg gramme of copper will be deposited in one second4 7,see ,chemical ,effects of the ,current47 ,the thousandth of an ampere is called the milliampere4 ,the strength of a current is proportional to the amount of chemical work that it can do per second4 7,see #ceg47 #ceb4 ,measurement of ,current ,strength4 ,the galvanoscope previously described simply shows the presence of a current1 or whether one current is larger or smaller than another4 ,when the degree-card is used to get the relative deflections1 the instrument may be called a galvanometer4 ,the ,tangent ,galvanometer is made on the same general idea as our galvanoscope1 the diameter of the coil being twenty times1 or more1 the length of the needle4 ,in these the strengths of the two currents compared are proportional to the tangents of the angles of deflection produced4 7,see ,elementary ,electrical ,examples47 ,there are several varieties of galvanometers1 each designed for its special work4 ,they are often calibrated or standardized so that the amperes of current passing through them can be read off directly from the scale4 #cec4 ,the ,ammeter is really a galvanometer from which may be read directly the strength of a current4 ,the coil has a low resistance so that it will not greatly reduce the strength of the current to be tested4 ,the ,voltameter measures the strength of a current by chemical means4 #ced4 ,unit of ,quantity2 ,the ,coulomb4 ,a current having a strength of #a ampere will do more chemical work by flowing one hour than it can do in #a second4 ,in speaking of the quantity of electricity we introduce the element of time4 ,the unit of quantity is called the coulomb1 just as a cubic foot of water may be taken as a unit of quantity for water4 ,a coulomb is the quantity of electricity given1 in one second1 by a current having a strength of #a ampere4 ,coulombs are found by multiplying amperes by seconds2 thus1 a current of #e amperes will give #bj coulombs in #d seconds4 #cee4 ,electrical ,horse-power2 ,the ,watt4 ,the electric current has power to do work1 and we speak of the horse-power of an electric motor in the same way as for a steam-engine4 ,a current with the strength of #a ampere and an ,e4 ,m4 ,f4 of #a volt has a unit of power called the watt4 #gdf watts make an electrical horse-power4 ,watts amperes volts4 ,watts #gdf the number of horse-power4 7,see ,transformers1 also ,elementary ,electrical ,examples47 #cef4 ,ohm's ,law4 ,it was first shown by ,ohm that the strength of a current is equal to its ,e4 ,m4 ,f4 divided by the resistance in the circuit2 that is1 ,strength of current 7amperes7 ,e4 ,m4 ,f4 7volts74 _/ resistance 7ohms74 ,if we let ,c stand for the strength in amperes1 ,e for the ,e4 ,m4 ,f4 in volts1 and ,r for the resistance in ohms1 we have the short formula1 easily remembered1 ,c ,e_/,r #ceg4 ,an ,ampere would be produced by a current of #a volt pushing its way through a resistance of #a ohm4 ,knowing any two of the three1 ,c1 ,e1 or1 ,r1 the other may be found4 ,the resistance1 ,r1 it must be remembered1 is the total resistance in the circuit1 and is composed of the total internal and external resistances4 7,see ,elementary ,electrical ,examples47 #ceh4 ,internal ,resistance and ,current ,strength4 ,it is evident that the internal resistance of a cell varies with the position and size of the plates4 ,we shall now study the effects of these changes upon the strength of the current4 ,illustration3 ,fig4 #ajh4 ,,experiment #adb4 ,having a cell with ,,large ,,plates1 to find how the strength of the current is affected by changes in the position of the plates1 the external resistance being small4 ,apparatus4 ,galvanoscope1 ,g ,v2 materials for simple cell 7,exp4 #aaj72 connecting wires4 ,arrange as in figure #ajh1 omitting the wooden cross-piece4 #cei4 ,directions4 7,a7 ,connect the wires with the #e-turn coil of ,g ,v1 which has but little resistance4 ,have the tumbler nearly full of dilute acid to get the effect of large plates2 that is1 the current has a large liquid conductor to pass through in the cell1 and the internal resistance will be small4 ,g ,v should be properly placed ,n and ,s4 7,b7 ,place the copper and zinc plates as far apart as possible in the acid1 and press them against the bottom of the tumbler4 ,note the reading of ,g ,v4 ,it is not necessary to take readings with reversed current4 7,c7 ,still pressing them against the bottom of the glass1 to keep the same amount of surface under acid1 slowly bring them near each other and watch the needle4 7,d7 ,hold the plates about an inch apart1 and against the bottom1 and note the reading of ,g ,v4 ,slowly raise the plates1 keeping them the same distance apart until they are out of the acid4 ,watch the action of the needle4 ,make a note of your readings in degrees and write your conclusions4 ,does a change in internal resistance affect the strength of the current8 ,,experiment #adc4 ,having a cell with ,,small ,,plates to find how the strength of the current is affected by changes in the position of the plates1 the external resistance being small4 ,apparatus4 ,same as in ,exp4 #adb1 the acid1 however1 being but #a in4 deep in the tumbler2 that is1 we have the effect of a cell with small plates1 each being about #a in4 by #a_/b in4 #cfj4 ,directions4 7,a7 ,repeat 7,b7 and 7,c7 of ,exp4 #adb1 recording the reading of ,g ,v in each case4 7,b7 ,compare the results with those of ,exp4 #adb1 remembering that the internal resistance is larger than before4 ,is the current as strong with small plates as with large plates when the external resistance is small8 ,when the external resistance is small 7the #e-turn coil1 for example71 should the cell have a high or low internal resistance to produce the greatest effect upon the needle8 ,illustration3 ,fig4 #aji4 ,,experiment #add4 ,to find whether the changes in current strength1 due to changes in internal resistance1 are as great when the external resistance is large1 as they are when the external resistance is small4 ,apparatus4 ,same as for ,exp4 #adb1 #adc1 also the rheostat containing the two meters of ,g-s wire 7,exp4 #aba74 #cfa4 ,directions4 7,a7 ,arrange as in ,fig4 #aji1 the external resistance being #b meters of ,no4 #cj ,g-s wire in series with ,g ,v4 ,the #b-;,f ,c in the ,fig4 is replaced1 however1 by the simple cell as in ,exp4 #adc4 7,b7 ,find the effect upon the strength of the current of moving the plates about when but #a in4 of acid is in the tumbler4 7,c7 ,nearly fill the tumbler with acid and repeat 7,b71 taking readings with plates near each other and as far apart as possible4 ,lift them nearly out of the acid and take the reading4 7,d7 ,still increase the external resistance of the circuit by adding coils of wire or the meter of ,no4 #bh ,g-s wire and repeat4 ,is the strength of the current greatly affected by slight changes in the internal resistance when the external resistance is large8 #cfb4 ,discussion4 ,we shall study1 by means of figures1 how changes in internal resistance affect the strength of the current4 ,let ,r stand for the total external resistance of a circuit1 and r for the total internal resistance of the cell or cells2 ohm's law1 then1 will be expressed by ,c ,e _/ 7,r r7 ,,example4 ,let us take a circuit 7,a7 when the external resistance1 ,r1 is small1 and 7,b7 when ,r is large compared with r1 ,e being taken as #a volt in both cases4 7,a7 ,let ,r #a1 and r #b2 substituting these values in the formula above1 we have3 ,c #a _/ 7#a #b7 #a _/ #c 4#cc ampere4 ,now let the internal resistance1 r1 be slightly increased from #b to #c ohms2 the value of ,c then becomes #a_/d ampere1 as ,r r #d4 ,the change in ,c1 then1 is the difference between #a_/c and #a_/d2 and this expressed in decimals becomes 4#cc - 4#be 4#jh ampere4 7,b7 ,let ,r #bjj ohms1 and r #b ohms as in 7,a74 ,substituting these values we have1 ,c #a _/ 7#bjj #b7 #a _/ #bjb 4#jjdie ampere4 ,increasing r from #b to #c1 as before1 etc41 we find that ,c #a divided by #bjc 4#jjdib ampere4 ,the above shows clearly 7,a7 that the value of ,c is changed considerably by changes in r when ,r is small1 and 7,b7 that changes in r produce very slight changes in ,c when ,r is large4 ,review your results of ,exps4 #adb-add4 7,see ,elementary ,electrical ,examples47 #cfc4 ,arrangement of ,cells and ,current ,strength4 ,we have seen that internal resistance affects current strength4 ,in joining cells1 then1 attention must be given to the internal resistance as well as to the ,e4 ,m4 ,f4 of the combination4 #cfd4 ,cells in ,series4 ,it has been shown by careful experiments that the ,e4 ,m4 ,f4 of two cells joined in series 7,fig4 #aaj7 is equal to the sum of the ,e4 ,m4 ,f4 of each4 ,ten cells1 joined in series1 have ten times the ,e4 ,m4 ,f4 of one cell1 provided they have the same ,e4 ,m4 ,f4 ,as the ,zn of one is joined to the ,cu of the other1 the current is obliged to pass through one solution after the other2 that is1 the internal resistance of the two in series is equal to the sum of their internal resistances4 ,ten cells1 joined in series1 have ten times the internal resistance of one cell1 provided they have equal internal resistances4 ,illustration3 ,fig4 #aaj4 ,illustration3 ,fig4 #aaa4 #cfe4 ,cells ,abreast4 ,when the positive plates are joined together and the negative plates are also joined together 7,fig4 #aaa71 the cells are said to be abreast1 in parallel1 or in multiple arc4 ,it has been shown that two cells of equal strength1 joined abreast1 have the same ,e4 ,m4 ,f4 as one cell4 ,the two ,cu plates1 being joined1 must have the same potential2 all the ,zn plates have the same potential1 so the difference of potential at the terminals of the combination is the same as that at the terminals of a single cell4 ,in two cells abreast 7,fig4 #aaa7 the current has two liquid paths1 side by side1 to get from ,cu to ,zn2 this makes the internal resistance one-half that of one cell1 provided their internal resistances are equal4 ,ten cells1 of equal internal resistance1 when joined abreast1 have one-tenth the internal resistance of one cell4 ,,experiment #ade4 ,to find the best way to join two similar cells when the external resistance is small4 ,apparatus4 ,two simple cells using dilute sulphuric acid1 with copper and zinc elements1 as in ,exp4 #aab2 galvanoscope1 ,g ,v2 connecting wires1 etc4 ,have the zincs well amalgamated4 ,remove them from the acid as soon as readings are taken4 #cff4 ,directions4 7,a7 ,partly fill the tumblers with the acid4 ,join the cells in series 7,fig4 #aaj71 then connect wire #a 7,fig4 #aaj7 with the left-hand binding-post of ,g ,v1 and wire #b with the middle one1 thus putting the #e-turn coil into the circuit4 ,take the reading of ,g ,v4 7,b7 ,join the cells in multiple arc 7,fig4 #aaa71 connecting them as in 7,a7 with ,g ,v4 ,write down the reading1 and compare it with that found in 7,a74 7,c7 ,take the reading with but #a cell joined to ,g ,v4 ,,experiment #adf4 ,to find the best way to join two similar cells when the external resistance is large4 ,apparatus4 ,same as for ,exp4 #ade1 also the rheostat containing #b metres of ,no4 #bh or #cj ,g-s wire4 ,arrange the ,g-s wire in series with the #ae-turn coil of ,g ,v1 as shown in ,fig4 #aji1 two simple cells being used1 however1 instead of #b-;,f ,c as shown4 #cfg4 ,directions4 7,a7 ,take the reading of ,g ,v when the two cells are in series 7,exp4 #ade71 the external resistance being the #ae-turn coil and ,g-s wire4 7,b7 ,join the cells in parallel and take the reading1 using the same external resistance as in 7,a74 7,c7 ,increase the external resistance by adding coils of wire or #b metres of ,no4 #bh ,g-s wire and repeat 7,a7 and 7,b74 ,what does the experiment show8 7,d7 ,take the reading with #a cell and large external resistance4 #cfh4 ,best ,arrangement of ,cells4 ,it will be seen by experiments that with a given number of cells the strongest current is produced when they are arranged so that the internal resistance of the battery nearly equals the external resistance of the circuit4 ,when the external resistance is small1 the internal resistance may be kept down by joining the cells in parallel2 and1 although the ,e4 ,m4 ,f4 is also kept small1 the value of ,c will be larger than it would be with a larger internal resistance and a larger ,e4 ,m4 ,f4 ,when the external resistance is large1 the internal resistance can be made large by joining the cells in series4 ,the advantage comes1 however1 from having a large value of ,e4 ,a large resistance can not hold back a current of large ,e4 ,m4 ,f4 ,by joining the cells in series the value of ,e is made large1 and the value of ,c becomes large even though there is an increased internal resistance4 7,see ,elementary ,electrical ,examples47 ,,chapter ,,xxi4 ,,chemical ,,effects ,,of ,,the ,,electric ,,current4 #cfi4 ,chemical ,action and ,electricity4 ,we have learned that the electric current is produced1 in the cell1 by chemical action4 ,there is a definite relation between the chemical action and the current produced4 ,we are now to study the changing of electrical energy back1 again1 to chemical energy4 ,illustration3 ,fig4 #aab4 #cgj4 ,electrolysis is the name given to the process of decomposing chemical compounds by passing the electric current through them4 ,the compound decomposed is the electrolyte4 ,fig4 #aab shows a tumbler of liquid 7electrolyte7 through which the current is to pass in the direction of the arrow4 ,two carbon plates1 ,a and ,c1 are in the liquid1 and are joined to the source of electricity4 ,the current enters at ,a 7anode7 and leaves at ,c 7cathode74 ,illustration3 ,fig4 #aac4 ,,experiment #adg4 ,to study the electrolysis of water4 ,apparatus4 ,the two simple cells 7 #bge7 joined in series 7 #cfd71 although two ,daniell or two dry cells will be better4 ,a tumbler of water containing a few drops of sulphuric acid to make the water a conductor4 ,two pieces of sheet copper will serve as the electrodes4 ,the galvanoscope may also be put into the circuit as in ,fig4 #aac4 #cga4 ,directions4 7,a7 ,allow the current to pass1 and note 7#a7 whether gas is set free at both electrodes1 ,a and ,c1 and 7#b7 at which the quantity of gas is the greater4 ,if very little gas is produced use more cells4 7,b7 ,remove ,a and ,c from the liquid1 to remove the gas1 then watch the action of the needle of ,g ,v as the water is again decomposed4 #cgb4 ,composition of ,water4 ,the two gases liberated in ,exp4 #adg were hydrogen 7,h7 and oxygen 7,o74 ,the chemical formula for water is ,h#b,o1 which means that it is composed of two parts1 by volume1 of ,h and one part of ,o4 ,with proper apparatus these gases may be collected1 tested1 and the amounts measured4 #cgc4 ,electromotive ,force of ,polarization4 ,we know that ,h and ,o have a strong chemical attraction1 or affinity1 for each other4 ,in order1 then1 for the current to decompose water1 this attraction between the gases must be overcome2 and as soon as the current ceases1 these gases try to rush together again to form water4 ,this sets up an electromotive force of almost #a4e volts2 in fact1 a current is produced if the ,h and ,o be allowed to form water again 7,see ,storage ,cells74 ,to decompose water the current must have an ,e4 ,m4 ,f4 of over #a4e volts to overcome this ,e4 ,m4 ,f4 of polarization4 ,it was seen in the study of simple cells that the current became rapidly weaker as hydrogen was deposited upon the copper plate1 on account of this opposing electromotive force4 ,in decomposing other compounds1 the anode is made of the metal which is to be deposited at the cathode4 ,if copper is to be deposited from a solution of copper sulphate the anode should be a copper plate2 this keeps the solution at same strength1 and avoids the opposing ,e4 ,m4 ,f4 of polarization2 that is1 a very weak current will do the work 7,see ,exp4 #adi71 because the electrodes are of the same metal4 ,,experiment #adh4 ,to coat iron with copper4 ,apparatus4 ,iron nail1 solution of copper sulphate 7 #bhc74 #cgd4 ,directions4 7,a7 ,clean the nail with sandpaper1 then hold it in the copper solution for a few seconds4 ,machinists often cover iron or steel tools with a thin coating of copper in this way4 ,illustration3 ,fig4 #aad4 ,,experiment #adi4 ,to study the electrolysis of a solution of copper sulphate4 ,apparatus4 ,galvanoscope1 ,g ,v2 two-fluid cell1 #b-;,f ,c2 a tumbler1 ,t1 containing about an inch of copper sulphate solution 7 #bhc72 a wooden cross-piece to which is fastened a copper strip2 carbon rod1 ,c2 wire #b is held to ,c by a rubber band4 ,arrange as in ,fig4 #aad1 so that ,cu will be the anode 7 #cgj71 the current passing as shown by arrow4 ,a dry cell may be used for short experiments instead of the #b-;,f ,c4 #cge4 ,directions4 7,a7 ,the carbon being clean1 allow the current to pass1 ,c and ,cu being kept about #a_/b in4 apart4 ,watch the surface of ,c1 and note the beautiful color of the deposited copper4 ,save the coated rod for the next experiment4 ,has the ,cu plate been acted upon8 #cgf4 ,electroplating is the name given to the process of coating substances with metal with the aid of the electric current4 ,the copper sulphate1 ,cu,s,o#d1 is broken up into ,cu and ,,so#d by the current4 ,the ,cu goes to the cathode1 and the ,,so#d attacks the anode1 gradually dissolving it if it be copper2 that is1 the metal part of ,cu,s,o#d is carried in the direction of the current4 ,most metals are coated with copper before they are silver or gold plated4 ,a solution of silver is used for silver plating1 silver being used as the anode4 ,,experiment #aej4 ,to study the chemistry of electroplating4 ,apparatus4 ,same as in last experiment1 but use two carbon rods for the electrodes4 ,arrange as in ,fig4 #aad1 with the ,cu replaced by another carbon4 ,two simple cells 7 #bge7 are also needed4 #cgg4 ,directions4 7,a7 ,allow the current to pass as before4 ,is copper still deposited8 ,does anything occur now at the surface of the anode8 ,is the copper deposited as rapidly as before8 7,b7 ,try the effect of the two simple cells joined in series1 ,instead of the two-fluid cell4 7,c7 ,after a fair coating of copper has been deposited upon the carbon cathode1 reverse the direction of the current through the copper solution2 that is1 use the coated rod for the anode4 ,allow the current to pass until a change takes place in the anode4 #cgh4 ,discussion4 ,ions are the names given to the parts into which an electrolyte is decomposed by the electric current4 ,in the case of ,cu,s,o#d1 the ions are ,cu and ,,so#d1 which is called an acid radical4 ,this ,,so#d can not dissolve carbon or platinum1 so these are used when water is to be electrolyzed4 ,where copper is used as the anode for copper plating1 the ,,so#d attacks it1 forming ,cu,s,o#d again1 and this keeps the solution strong4 ,if carbon were used instead1 the ,,so#d would take ,h#b from the water around the anode and ,h#b,,so#d 7sulphuric acid7 would be formed1 the oxygen of the water being set free at the anode4 ,the amount of ,cu dissolved from the copper anode equals nearly the amount deposited upon the cathode4 ,exp4 #aej shows that the metal is carried in the direction of the current4 ,as hydrogen is produced at the cathode it is chemically considered a metal4 #cgi4 ,electrotyping consists in making a copy in metal1 of a woodcut1 page of type1 etc4 ,a mould or impression of the type is first made in wax1 or other suitable material 7the pages of this book1 for example1 as set up by the printer74 ,these moulds are1 of course1 the reverse of the type4 ,they are coated with graphite to make them conduct electricity1 and hung as the cathode1 in a bath of copper sulphate4 ,after a thin coat of copper has been deposited by an electric current1 the wax is removed and the thin copper backed with soft metal4 ,the metal surface next to the wax will be just like the type1 only made of copper4 ,these plates or electrotypes can be printed from1 the original type being used to set up another page4 7,see ,things a ,boy ,should ,know ,about ,electricity47 #chj4 ,voltameters are cells used to measure the strength of an electric current4 ,in the ,water ,voltameter the hydrogen and oxygen produced are measured4 ,the ,h acts like a metal and goes to the cathode1 two parts of ,h being formed to one of ,o4 ,copper ,voltameter4 ,this cell measures the amount of copper deposited in a given time by a current4 ,the copper cathode is weighed before and after the current flows4 ,the weight of ,cu deposited is then divided by the number of seconds during which the current passed1 and this result1 in turn1 by 4#jjjcbh1 which will give the average strength of the current in amperes4 7,see #cea47 ,other forms of voltameters are also used4 ,in all voltameters the quantity of metal deposited is proportional to the time that the current flows1 and to its strength4 ,illustration3 ,fig4 #aae4 ,,experiment #aea4 ,to study the construction and action of a simple storage cell4 ,apparatus4 ,two lead plates1 ,l ,p1 7,nos4 #gg1 #gh7 fastened to a wooden cross-piece 7 #bge74 ,the spring-connectors should not be forced upon the thick lead4 ,fasten one end of the wire under the screw-head4 ,a tumbler two-thirds full of dilute sulphuric acid 7 #beh72 the astatic galvanoscope1 ,a ,g2 wires to form connections2 the two simple cells joined in series4 ,arrange as in ,fig4 #aae4 ,one ,l ,p is joined to binding-post1 ,l1 of ,a ,g by the wire marked #a2 wire #b connects the other ,l ,p to the copper ,cu4 ,wire #c joins the zinc to any thin metal plate1 ,m ,p1 which is used for convenience1 so that the spring connectors can be quickly slipped on or off4 ,wire #d joins ,m ,p with binding-post ,r of ,a ,g4 #cha4 ,directions4 7,a7 ,get clearly in mind the direction in which the right-hand end of the astatic needle is deflected when the current passes1 remembering that it passes into ,a ,g at ,l and leaves at ,r4 ,allow the current to flow for #aj or #ae minutes through the circuit1 at the same time watching the needle to see whether the strength of the current remains constant4 7,b7 ,remove the connector from ,cu1 swing it over into the position of the dotted line 7,fig4 #aae71 slip the connector upon ,m ,p and watch the needle4 ,this cuts the cells out of the circuit2 but1 if you desire1 also remove wire #c from ,m ,p4 ,does the storage cell1 ,s ,c1 produce any current8 ,does it pass through ,a ,g in the same direction as that which came directly from the two cells8 7,c7 ,try the dry cell in place of the two simple cells4 ,try #b other cells in series if you have them4 #chb4 ,secondary or ,storage ,cells must be charged by a current before they can give out a current4 ,electricity is not really stored4 ,chemical changes are produced in the storage cell by the charging current1 as in the voltameter or electroplating bath2 and it is1 then1 potential chemical energy that is stored4 ,when the new compounds are allowed to go back to their original condition by joining the electrodes of the charged cell a current is produced4 ,in other words1 an electric current produces chemical changes in the cell by electrolysis1 and these new compounds have an ,e4 ,m4 ,f4 of polarization because they are constantly willing and anxious to get back to their old state4 ,the plates are lead and are usually coated with compounds of lead4 ,hydrogen and oxygen are given out at the electrodes4 ,the current from a dynamo is used to charge secondary batteries4 7,see ,things a ,boy ,should ,know ,about ,electricity47 ,,chapter ,,xxii4 ,,electromagnetism4 #chc4 ,electromagnetism is the name given to magnetism that is developed by electricity4 ,you have already seen that if a magnetic needle be placed in the magnetic field of a magnet1 its ,n pole will point in the direction in which the lines of force pass on their way from the ,n to the ,s pole of the magnet4 ,you have also seen that in the galvanoscope1 etc41 a coil of wire acts like a magnet when a current passes through it4 ,can we not1 then1 use the needle to study the lines of force about wires and coils8 ,illustration3 ,fig4 #aaf4 ,illustration3 ,fig4 #aag4 ,,experiment #aeb4 ,to study the lines of magnetic force about a straight wire carrying a current4 ,apparatus4 ,the compass1 ,o ,c2 key1 ,k2 dry cell1 ,d ,c4 ,arrange as in ,fig4 #aaf4 #chd4 ,directions4 7,a7 ,arrange the wire so that the current will flow through it from ,n to ,s over the compass-needle as soon as the circuit is closed 7,fig4 #aag1 ,a74 ,press ,k for an instant only1 and note the direction in which the ,n pole is deflected4 ,repeat two or three times until you get clearly in mind the direction taken by the needle4 ,sketch the result in your note-book1 and compare with ,fig4 #aah1 ,a4 ,the arrow shows the direction of the current4 7,b7 ,let the current pass for an instant from ,n to ,s and under the needle1 as shown in ,fig4 #aag1 ,b4 ,sketch result4 7,c7 ,let the current pass for an instant from ,s to ,n above the needle 7,fig4 #aag1 ,c74 ,sketch result4 7,d7 ,let it pass from ,s to ,n under the needle 7,fig4 #aag1 ,d74 ,sketch result4 7,e7 ,let it pass through the wire from east to west 7,fig4 #aag1 ,f7 above the needle1 then under it1 and note result4 ,compare the results with those indicated in ,fig4 #aah4 ,illustration3 ,fig4 #aah4 ,illustration3 ,fig4 #aai4 #che4 ,lines of ,force ,about a ,wire4 ,when a current passes through a wire1 the needle1 over or under it1 tends to take a position at right angles to the wire4 ,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 wire2 that is1 to the ,e and ,w line1 because the earth is at the same time pulling its ,n pole towards the ,n4 ,if the needle had no pointing power1 and at the same time retained its magnetic field1 it would point exactly at right angles to the wire as soon as the current passed4 ,if you look along the wire1 ,fig4 #aai1 from the point1 ,c1 towards the positions1 ,a and ,b1 you will see 7,a7 that under the wire the lines of force pass to the left1 and that above the wire 7,b7 they pass towards the right4 ,this is because the ,n pole points in the directions mentioned4 7,see ,fig4 #aah47 ,looking along the wire from ,z towards position1 ,d and ,c1 you will see just the opposite to the above1 as the current comes towards you4 ,rule4--,when the current goes from you1 the lines of force pass around the wire in a clockwise direction1 and when the current comes toward you they pass around it in an anti-clockwise direction4 #chf4 ,ampere's ,rule may be used to remember what has been learned in ,exp4 #aeb4 ,if you imagine yourself swimming in the wire with the current1 always facing the needle1 the ,n-seeking pole of the needle will always be deflected towards your left hand4 ,when the needle is above the wire you must imagine that you swim upon your back1 in order to face the needle4 ,another ,rule4--,hold the right hand with the thumb extended and with the fingers pointing in the direction of the current1 the palm being towards the needle and on the opposite side of the wire from the needle4 ,the ,n-seeking pole will then be deflected in the direction in which the thumb points4 #chg4 ,if a wire carrying a strong current be dipped in iron filings1 the magnetic field about the wire acts by induction upon the particles of filings1 making magnets of them4 ,these cling to each other simply because they are little magnets4 #chh4 ,lines of ,force about ,parallel ,wires4 ,when a current passes in the same direction in two parallel wires the lines of force pass around the wires in the same direction in both1 and the magnetic fields attract each other4 ,when the currents flow in opposite directions the magnetic fields repel each other4 ,,experiment #aec4 ,to study the lines of force about a coil of wire like that upon the galvanoscope4 ,apparatus4 ,galvanoscope1 ,g ,v2 dry cell2 key2 compass4 ,arrange as in ,fig4 #aaf1 using ,g ,v instead of the compass shown4 ,the coil of ,g ,v should be placed in the ,e and ,w line4 ,the current can pass only when the key is pressed4 ,connect the wires with ,g ,v1 so that the current will pass through the #ae-turn coil from ,w to ,e on top of the coil2 that is1 so that the current will have a clockwise motion4 ,fig4 #abj represents a front view of the coil4 ,illustration3 ,fig4 #abj4 ,illustration3 ,fig4 #aba4 #chi4 ,directions4 7,a7 ,hold the compass in the various places marked with a dot 7,fig4 #abj7 and note the directions taken by its ,n pole4 ,make a circle similar to the one shown to represent the coil1 and sketch upon it the way in which the lines of force pass around it according to your observations4 7,b7 ,make a diagram like ,fig4 #aba1 which represents a cross-section of the coil through the center4 ,imagine that you have removed the top half of the coil and that you are looking down upon the ends of the wire of the lower half4 ,draw curved arrows about the coil at ,w and ,e to show which way the lines of force are passing4 ,compare your results with those in ,fig4 #aai1 remembering that at ,e1 ,fig4 #aba1 the current is going away from you4 7,c7 ,move ,o ,c back and forth on the center-line that runs ,n and ,s through the coil1 and note the positions of the compass-needle4 ,does the coil seem to have poles8 7,d7 ,reverse the current through the coil and repeat your observations4 ,,experiment #aed4 ,to study the magnetic field about a small coil of wire4 ,apparatus4 ,a coil of wire 7,no4 #hi71 described in #cij2 current reverser1 ,c ,r 7,no4 #eg72 dry cell2 connecting wires1 etc4 #cij4 ,coils of wire for some of the following experiments should be wound upon wooden spools that have been turned down thin1 so that the wire will be as near the central hole as possible4 ,they should be wound with a winder4 7,see ,apparatus ,book1 ,chapter ,x47 ,for convenience we shall call the starting end of the coil1 that is1 the end that comes from the wire that is near the center1 the inside end1 ,i ,e4 ,the end of the last layer of the coil we shall call the outside end1 ,o ,e4 ,these letters should be noted in the diagrams4 ,see ,apparatus ,list for details of the special coils used in these experiments4 ,illustration3 ,fig4 #abb4 #cia4 ,directions4 7,a7 ,arrange as in ,fig4 #abb1 so that the axis of the coil will lie in the ,e and ,w line4 ,place ,o ,c about #b in4 from the ,e end of the coil4 ,press one lever of ,c ,r so that the current will pass around the coil for an instant in a clockwise direction2 that is1 so that it will enter the coil at ,o ,e4 ,note the action of the needle4 ,if the needle is not affected move it nearer the coil and press the lever again4 ,get clearly in mind the connections1 the direction in which the ,n end of the needle is deflected1 etc4 ,is the ,e end of the coil a ,n or a ,s pole8 7,b7 ,reverse the current through the coil4 ,what effect has it upon the polarity of the ,e end of the coil8 7,c7 ,place ,o ,c at the west end of the coil and repeat 7,a7 and 7,b74 7,d7 ,place ,o ,c in various positions about the coil and note the action of the needle when the current passes4 ,does this coil act like a magnet1 having poles1 magnetic field1 etc48 ,illustration3 ,fig4 #abc4 #cib4 ,polarity of ,coils4 ,it is evident from ,exps4 #aec and #aed that a coiled conductor has poles1 magnetic field1 etc41 when a current passes1 and that it strongly resembles a magnet1 even though no iron enters into its construction4 ,we may say that the coil becomes magnetized by the electric current4 ,fig4 #abc shows a right handed coil or helix of wire1 the current passing as shown by the small arrows4 ,the left-hand end is a ,s pole because the current passes around it in a clockwise direction4 ,when you face the right-hand end of the coil the current is seen to pass around it in an anti-clockwise direction2 this produces a ,n pole4 ,as the ,n pole of the magnetic needle is attracted toward the ,s pole of the coil1 it is clear that the lines of force pass through the inside of the coil as shown by the large arrows4 ,they then curve through the air and return to the ,s pole as with magnets4 ,,experiment #aee4 ,to test the attracting and sucking power of a magnetized coil or helix4 ,apparatus4 ,the coil1 battery1 etc41 used in ,exp4 #aed1 ,fig4 #abb2 a sewing-needle4 ,illustration3 ,fig4 #abd4 #cic4 ,directions4 7,a7 ,arrange the coil1 etc41 as described in ,exp4 #aed4 ,the coil need not lie in the ,e and ,w line1 however1 and a key may be used instead of the current reverser4 7,b7 ,magnetize the needle so that its point will be a ,n pole4 7,c7 ,tie a thread about the center of the magnetized needle1 hold the thread in the hand so that the ,s pole of the needle will swing freely at the hole at the right-hand end of the coil 7,fig4 #abd74 ,if the current passes as directed1 the right-hand end of the coil will be a ,n pole4 ,what happens to the needle when the key is pressed for an instant4 7,d7 ,change the needle to the left end of the coil and repeat4 7,e7 ,try a nail1 pen1 iron1 etc41 instead of the needle4 ,,experiment #aef4 ,to find whether a piece of steel can be permanently magnetized by an electric current4 ,apparatus4 ,same as for last experiment2 an unmagnetized sewing-needle2 the compass4 #cid4 ,directions4 7,a7 ,be sure that the needle is not magnetized4 ,it should attract both ends of the compass-needle4 ,how can any magnetism in the needle be removed8 7,b7 ,place the needle inside of the coil with its point to the east2 that is1 with its point at the ,n pole of the coil1 and its head at the ,s pole4 ,close the circuit for an instant4 ,test the needle again for poles4 ,is the point a ,n or a ,s pole8 7,c7 ,turn the needle end for end in the coil1 and see whether its polarity can be reversed4 7,d7 ,experiment with iron wire1 nails1 steel pens1 spring steel1 etc4 ,illustration3 ,fig4 #abe4 ,,experiment #aeg4 ,to study the effect of a piece of iron placed inside of a magnetized coil of wire4 ,apparatus4 ,same as in ,exp4 #aed2 a short rod or iron core1 ,i ,c1 of soft iron 7,no4 #ib7 that will fit inside of the coil4 ,this combination is called an electromagnet4 #cie4 ,directions4 7,a7 ,arrange first as for ,exp4 #aed1 ,fig4 #abb1 with the coil in the ,e and ,w line1 no core being used1 and place ,o ,c about #f in4 from the right-hand end of the coil4 7,b7 ,press the lever for an instant to see whether the field of the coil is strong enough to move the compass-needle at that distance4 ,move ,o ,c a little nearer or farther from the coil until the needle just moves1 when the circuit is closed4 7,c7 ,place ,i ,c inside of the coil 7,fig4 #abe71 and repeat 7,b7 to see whether the magnetic field of the coil is stronger or weaker than before4 7,d7 ,study the location of the poles4 ,can they be reversed8 ,,chapter ,,xxiii4 ,,electromagnets4 #cif4 ,electromagnets are important to the student of electricity4 ,they form the principal part of nearly every electrical instrument4 ,you have seen that a wire has a magnetic field about it the instant a current passes through it4 ,a coil1 or helix of wire1 has a stronger field than a straight wire carrying the same current1 because each turn1 or convolution1 adds its field to the fields of the other turns4 ,by having a core of soft iron instead of air1 wood1 or other non-magnetic material1 the strength of the magnet is greatly increased4 ,the central core may be permanently fixed in the coil1 or it may be removable4 7,see ,apparatus ,book1 ,chapter ,,ix1 for ,home-made ,electromagnets47 #cig4 ,cores of ,electromagnets4 ,a strong magnet has more lines of force passing from its ,n pole through the air to its ,s pole than a weak magnet4 ,by increasing the number of lines of force we increase the strength of a magnet4 ,it has been seen1 in experiments with permanent magnets1 that lines of force do not pass as readily through air as through soft iron1 and that lines of force will go out of their way to pass through iron4 ,it was learned in ,exp4 #aed that inside of a helix 7,fig4 #abc7 the lines of force pass from the ,s to the ,n pole2 they then spread out through the air and pass back on all sides of the coil to its ,s pole1 as in the case of permanent magnets4 ,the air around and inside of a helix offers a great resistance to the lines of force1 and tends to weaken the magnetic field4 ,when part of the circuit consists of an iron core1 which is a splendid conductor of lines of force1 the magnetic field is greatly increased in strength4 ,,experiments #aeh-afc4 ,to study straight electromagnets4 ,apparatus4 ,a good dry cell or other source of a fairly strong current2 coil with soft iron core2 key2 wires with connectors1 etc42 small nails2 iron-filings2 compass2 large wire nail2 tin box 7,no4 #id7 to act as a base for the electromagnets4 ,,experiment #aeh4 ,lifting power4 #cih4 ,directions4 7,a7 ,join the cell1 key1 and coil1 as explained in ,exp4 #aed1 so that the current will pass only when the key is pressed4 ,place the core inside of the coil 7,fig4 #abe74 ,two good cells in series can be used to advantage4 7,b7 ,hold the coil in a vertical position near small nails1 iron filings1 tin boxes1 etc42 then press the key and raise coil2 carry the clinging iron to another place1 break the circuit at the key1 and explain the result4 ,why do nails cling more strongly to the core than filings after the circuit is broken8 ,,experiment #aei4 ,residual magnetism of core4 #cii4 ,directions4 7,a7 ,after the current has passed through the coil with the core in place1 remove the core and test it for magnetism with the compass4 ,will the small end of the core attract both poles of the compass-needle1 or is it slightly magnetized8 7,b7 ,if there is any residual magnetism1 strike the core with a hammer and test again4 7,c7 ,use a soft steel wire nail for the core1 and repeat 7,a7 and 7,b74 ,why does soft iron make a better core than steel for electromagnets8 ,which should be the more easily magnetized8 ,,experiment #afj4 ,magnetic tick4 #djj4 ,directions4 7,a7 ,join the electromagnet with the cell and key as before 7,exp4 #aed74 ,hold one end of the core firmly against the top of a tin box which should stand upon the table and which should act as a sounding-board4 ,the flat boxes used in the experiments on static electricity are good for this1 or use the tin box1 ,no4 #id1 for a base4 ,rapidly open and close the circuit by means of the key and listen for any clicks made by the core4 7,b7 ,listen for this sound in telegraph sounders1 electric bells1 etc41 if you have them4 ,the armature should be held1 of course1 so that slight sounds can be heard4 #dja4 ,discussion4 ,a bar of iron becomes slightly longer when it is magnetized1 the particles of iron being made to point in the same direction4 ,as soon as the current ceases to flow through the coil the particles of the soft core nearly all resume their mixed positions4 ,the click heard is supposed to be due to the changes in the molecules of iron4 ,the core becomes gradually warmer when it is rapidly magnetized and demagnetized by a strong current4 ,illustration3 ,fig4 #abf4 ,,experiment #afa4 ,magnetic figures4 #djb4 ,directions4 7,a7 ,arrange as in ,fig4 #abf4 ,the key should be used in case a dry cell acts as the source of the current4 ,two good cells joined in series can be used to advantage4 ,lay the coil flat upon the table and place on it a piece of stiff1 smooth paper1 or a sheet of glass4 7,b7 ,sprinkle a few iron filings upon the glass1 which may be held in place by books4 ,gently tap the glass with a pencil while you close the circuit at the key4 ,do the filings arrange themselves as in the case of permanent magnets8 ,make a sketch of the field1 remembering that you have both ,n and ,s poles1 and compare it with previous results4 ,illustration3 ,fig4 #abg4 ,,experiment #afb4 ,magnetic figures4 #djc4 ,directions4 7,a7 ,arrange as in ,fig4 #abf1 but stand the coil on end1 using the base as directed in #djg1 to hold it firmly in position4 ,join the ends1 ,o ,e and ,i ,e1 to the key as before4 ,fig4 #abg shows a top view of the coil and base4 7,b7 ,with books1 etc41 fix a piece of stiff1 smooth paper1 or glass just over the top of the core1 and proceed as in ,exp4 #afa to study the field4 ,see #dag for making permanent pictures of magnetic fields4 ,,experiment #afc4 ,magnetic field4 #djd4 ,directions4 7,a7 ,use same arrangement as for ,exp4 #afb1 except filings and glass1 which are replaced by the compass4 7,b7 ,hold the compass about #b in4 from the top pole of the electromagnet1 close the circuit for a second or two and note action of needle4 ,is the top ,n or ,s1 when the current enters the coil at ,o ,e8 ,compare result with #cib4 7,c7 ,move the compass quickly about the pole1 the circuit being closed1 and note action of needle4 ,compare result with directions taken by particles of iron filings in ,exp4 #afc4 7,d7 ,reverse the direction of the current through the coil and test the nature of the pole at the top4 ,illustration3 ,fig4 #abh4 ,illustration3 ,fig4 #abi4 #dje4 ,horseshoe ,electromagnets4 ,fig4 #abh shows a simple form of electromagnet with two coils which have a bent piece of iron as a core for both4 ,the coils have to be wound on by hand in this form4 ,as this is troublesome1 the coils are generally wound on two separate cores which are joined by a yoke 7 #djf71 which takes the place of the curved part in ,fig4 #abh4 ,the separate coils can be quickly made with a winder and joined to suit4 7,see ,apparatus ,book1 ,chapter ,,ix1 for ,home-made ,electromagnets47 ,fig4 #abi shows a top view of a home-made experimental horseshoe electromagnet4 ,the coils are joined by an iron strap1 called the yoke1 which is screwed to a wooden base4 ,a strip of iron placed above the magnets to be attracted by them1 when the current passes1 is called the armature4 7,see ,telegraph ,sounders47 #djf4 ,use of ,yoke4 ,it has been explained 7 #hb7 why horseshoe magnets are1 in general1 better than straight ones4 ,the same is true of electromagnets2 there are two poles to attract1 and two to induce4 ,the lines of force pass through the yoke on their way from one core to the other1 and this reduces the resistance to them4 ,the strength of the horseshoe magnet would be greatly reduced if the lines of force were obliged to pass through two air spaces instead of one2 in fact1 if there were no yoke we should have simply two straight magnets4 ,the yoke should be made of soft iron4 ,illustration3 ,fig4 #acj4 ,illustration3 ,fig4 #aca4 #djg4 ,experimental ,magnets are quickly joined to a tin base 7,no4 #id71 which has #c holes punched in1 through which screws can be put to hold the cores in place4 ,fig4 #abg shows plan of tin4 ,fig4 #acj shows how removable cores are fastened to the base1 the coils being on the spools1 and ,fig4 #aca shows how home-made coils on bolts can be used4 ,the coils on bolts should be wound as directed in ,apparatus ,book1 ,chapter ,x4 ,the tin base also serves as the yoke4 ,removable ,cores4 ,fig4 #acj4 ,these are of soft iron 7,no4 #ib1 #ic74 ,in one end of each is a hole for the screws1 ,s4 ,part of the tin has been cut away in the ,fig4 ,the copper washer1 ,c ,w1 should be used4 7,see #djh47 ,connectors are fastened to the ends of the coils 7 #bbf-bcj74 ,bolt ,cores4 ,fig4 #aca4 ,after winding on the coils1 as directed in ,apparatus ,book1 remove the nut and put on an extra washer1 ,e ,w1 so that the ends of the coils will not be pressed against the tin1 but come out between the two washers4 ,push the screw-end of the bolt through holes 7about #b in4 apart7 punched in the tin1 then put on the nut1 as shown4 ,do not force the nut on too far1--just far enough to hold the cores in place4 ,the ends of the wires are not shown in ,figs4 #acj1 #aca4 ,connectors are fastened to them 7 #djh74 ,illustration3 ,fig4 #acb4 #djh4 ,method of ,joining ,coils4 ,to produce the best results the poles of the horseshoe electromagnet should be unlike4 ,as the coils are wound alike1 their ends must be joined in such a manner that the current will pass around them in opposite directions2 that is1 if the current enters one coil at the outside end1 ,o ,e1 it must enter the other coil at the inside end1 ,i ,e4 ,fig4 #acb shows a plan of the connections1 spring connectors being fastened to the coil-ends1 to allow rapid and easy changes in the arrangement4 ,l1 ,m1 and ,r are pieces of metal fastened to a strip of wood 7,no4 #ie71 used to make connections from cells or other apparatus4 ,they are turned up at each end as in ,fig4 #ajd1 #c4 ,care should be taken not to get short circuits by allowing two wires to touch the tin base4 ,by changing the ends of the coils upon ,l1 ,m1 and ,r 7left1 middle1 and right71 and by changing the direction in which the current enters the combination connecting plates 7,no4 #ie71 it is evident that the nature of the poles can be regulated to suit4 ,,experiments #afd-agc4 ,to study horseshoe electromagnets4 ,apparatus4 ,coils of wire with cores and yoke like those explained in this chapter4 ,coils fastened to tin base or yoke with wires leading from them to the combination connecting plates 7,no4 #ie1 ,fig4 #acb71 are very handy4 ,cells2 iron filings2 compass2 iron strip 7,no4 #gf74 ,,experiment #afd4 ,to test the poles4 #dji4 ,directions4 7,a7 ,arrange as in ,fig4 #abf1 but use the experimental magnets and combination connections 7,fig4 #acb7 in place of the single coil shown in ,fig4 #abf4 ,join ,o of the key with ,l1 and ,zn of the cell with ,r of ,fig4 #acb4 ,when the key is pressed the current will enter the magnets from ,l and leave at ,r4 7,b7 ,with the compass test the polarity of the cores as in ,exp4 #afc1 ,b1 ,c4 ,make a sketch of the arrangement1 and note which pole is ,n and which ,s4 7,c7 ,see which way the current must pass around each coil1 by the way it is wound1 and compare the results of 7,b7 with ,exp4 #aed1 ,fig4 #abc4 ,,experiment #afe4 ,to test the poles4 #daj4 ,directions4 7,a7 ,arrange as in ,exp4 #afd1 but reverse the direction of the current through the coils4 ,do this by joining ,o of the key 7,fig4 #abf7 with ,r of ,fig4 #acb1 and ,zn of the cell with ,l4 7,b7 ,repeat 7,b7 and 7,c7 of ,exp4 #afd and study results4 ,illustration3 ,fig4 #acc4 ,,experiment #aff4 ,to test the poles4 #daa4 ,directions4 7,a7 ,arrange all connections as in ,exp4 #afd1 then reverse the positions of ,o ,e and ,i ,e of coil ,a2 that is1 join ,o ,e to ,m1 and ,i ,e to ,l1 ,fig4 #acb4 ,this will make unlike ends come together at ,m2 in other words1 when the current enters at ,l and leaves at ,r it will pass around both coils in the same direction4 7,b7 ,study the nature of the poles1 as in ,exps4 #afd1 #afe1 and note results4 ,note4--,fig4 #acc shows simply the two cores of a horseshoe electromagnet with arrows to indicate in which direction the current is passing in each coil to produce ,n and ,s poles4 ,,experiment #afg4 ,to study the inductive action of one core upon the other4 #dab4 ,directions4 7,a7 ,arrange as for ,exp4 #afd1 but join the wire from ,zn of the cell to ,m 7,fig4 #acb74 ,in this way coil ,b will be cut out of the circuit4 ,place the coils in the ,e and ,w line4 7,b7 ,find about how far the residual magnetism of the core of ,b can act upon the compass-needle1 holding the compass on the side away from coil ,a1 no current passing4 7,c7 ,press the key for an instant1 and note whether the magnetism of coil ,b has been made stronger or weaker4 ,explain the action of core ,a on core ,b4 ,,experiment #afh4 ,magnetic figures4 #dac4 ,directions4 7,a7 ,arrange as in ,exp4 #afd4 ,with books1 etc41 fix a piece of smooth1 stiff paper1 or a sheet of glass1 just above the poles of the electromagnets4 7,b7 ,sprinkle iron filings upon the glass1 and gently tap it while the circuit is closed at the key for a few seconds4 ,make a sketch of the magnetic figure produced4 ,do the lines of force from the opposite poles attract or repel each other8 ,see #dag for making permanent figures4 7,see ,things a ,boy ,should ,know ,about ,electricity for drawings of magnetic figures47 ,note4--,if possible1 use two or three good cells in series for making magnetic figures1 as a fairly strong field is best4 ,,experiment #afi4 ,magnetic figures4 #dad4 ,directions4 7,a7 ,arrange apparatus as for ,exp4 #afe1 and make the magnetic figure for this combination1 as directed in ,exp4 #afh4 ,sketch and study the results4 ,,experiment #agj4 ,magnetic figures4 #dae4 ,directions4 7,a7 ,arrange the apparatus and connections as in ,exp4 #aff1 and make the magnetic figure of this combination as directed in ,exp4 #afh4 ,in this case the poles are alike4 ,sketch and study the results4 ,,experiment #aga4 ,magnetic figures4 #daf4 ,directions4 7,a7 ,arrange apparatus and connections as in ,exp4 #afg1 and make the magnetic figure of the combination as directed in ,exp4 #afh4 ,compare the figure produced with that of ,exp4 #afh4 ,in this case the current passes through but one coil4 #dag4 ,permanent ,magnetic ,figures can be made in several ways for future study and comparison4 7,a7 ,paraffine paper figures4 ,make paraffine paper as directed in ,apparatus ,book1 page #ace4 ,for this purpose smooth1 stiff1 white paper is best1 so that the filings will show plainly1 and but a thin coating of paraffine should be given4 ,place the magnets upon the table1 lay over them a piece of unparaffined paper1 and fix the paraffine paper directly over this4 ,this is necessary1 as the coated paper sticks when heated4 ,for electromagnets it will be necessary to support the edges of the paper with books1 etc4 ,sprinkle on the filings and tap the paper to make them arrange themselves while the circuit is closed4 ,after the lines of force show plainly1 the current need not be used again1 provided the paper be kept perfectly still4 ,pass the flame of a ,bunsen burner over the paper to melt the coating4 ,this will1 no doubt1 make the two pieces of paper stick together1 and permanently fix the particles of filings in place4 ,do not heat the paper too much--just enough to melt the paraffine4 ,if you have no gas1 hold a fire-shovel1 containing hot coals1 over the paper4 ,as soon as the paraffine cools1 the figures will stand considerable handling4 ,blue print figures are very pretty1 and last indefinitely4 ,get some blue-print paper at a photographer's1 who will give you directions about developing it with water4 ,keep this in the dark1 and take out but one sheet at a time for experiments4 ,to make the figures1 take your apparatus near a window where bright sunlight comes in4 ,pull down the curtain so that you have but a dim light when you make the magnetic figure1 as directed before4 ,after the lines of force show plainly1 raise the curtain1 and let the bright sunlight shine on it for #e or #f minutes1 or until the surface of the paper has a rich1 bronze color4 ,the paper cannot be acted upon by the light under the particles of filings4 ,quickly shake the filings from the paper1 and wash it in #c changes of water to develop it1 then pin the paper up to dry4 ,,experiment #agb4 ,lifting power4 #dah4 ,directions4 7,a7 ,arrange the apparatus as in ,exp4 #afd4 ,hold an iron strip 7,no4 #gf71 a screw-driver1 or other iron bar directly over and near the poles of the experimental electromagnet4 ,close the circuit at the key1 then lift the magnets by the armature1 as the iron strip may be called1 the circuit being kept closed for a few seconds4 ,if your cell is good there should be no trouble in lifting the magnets by the armature4 ,open the circuit1 and see whether the magnets drop4 7,b7 ,hold the magnets upside down directly over nails1 tin boxes1 iron filings1 or other pieces of iron4 ,close the circuit1 move the attracted iron to another place on the table1 and open the circuit4 ,can this principle be used for practical purposes8 ,note4--,some experiments illustrating practical uses of electromagnets will be given in a future chapter4 ,,experiment #agc4 ,residual magnetism when magnetic circuit is closed4 #dai4 ,directions4 7,a7 ,arrange as in ,exp4 #afd4 ,you have already seen that each core retains some magnetism after the circuit is closed4 ,place the iron strip firmly across the poles1 close the circuit for an instant1 open the circuit1 then see whether the armature still clings to the cores with some strength4 ,the armature should fit well upon the cores for this experiment4 7,b7 ,again press the armature upon the cores1 no current being used2 then lift it as in 7,a74 ,compare the attraction with that found in 7,a74 #dbj4 ,closed ,magnetic ,circuits4 ,it was seen in the study of the permanent horseshoe magnet1 that the armature clung strongly to the magnet4 ,the armature closed the magnetic circuit1 the lines of force having almost no resistance4 ,in the case of electromagnets the magnetic circuit becomes closed when the armature touches both poles at the same time4 ,the armature clings strongly to the poles even after the current ceases to flow4 ,as soon as the magnetic circuit is broken1 however1 but little residual magnetism remains4 ,the armatures of electromagnets are usually arranged so that they can not quite touch the cores1 to avoid this sticking4 ,,chapter ,,xxiv4 ,,thermoelectricity4 ,illustration3 ,fig4 #acd4 ,,experiment #agd4 ,to find whether electricity can be produced by heat4 ,apparatus4 ,the home-made thermopile described in #dba2 astatic galvanoscope2 connecting wires2 candle or alcohol lamp4 #dba4 ,home-made ,thermopile4 7,fig4 #acd47 ,for this you need #c hairpins1 copper wire1 a piece of wood about #c in4 long and #a in4 square on the ends1 #b pieces of tin1 and some small nails4 ,straighten the hairpins and scrape the coating off with sandpaper or a file4 ,scrape the insulation from #d pieces of copper wire1 each about #h in4 long4 ,twist the ends of the copper wire about the ends of the hairpins 7,fig4 #acd71 and then fasten the hairpins to the block4 ,they may be held firmly by small nails which should be driven partly into the block and bent over4 ,the hairpins at the right-hand side of the ,fig4 are shown to be near but not touching each other4 ,this allows all to be heated at the same time4 ,the tin binding-posts may be nailed or screwed to the block1 and if the bare copper wires #a and #d be placed under ,x and ,y before they are screwed down they will be electrically connected4 ,the ends of #a and #d may be held under the screw-heads4 ,the block may be supported upon other blocks to raise it to the proper height1 which will depend upon the length of the candle4 ,illustration3 ,fig4 #ace4 ,a thermopile in the form of a circle with several pairs of metals1 can easily be made by fastening the hairpins to a piece of cardboard 7,fig4 #ace7 with a hole at the center4 ,this may be supported by blocks1 the heat being applied under the center4 #dbb4 ,directions4 7,a7 ,arrange the apparatus as in ,fig4 #acd4 ,see that the astatic needle is properly adjusted1 no magnets being near it4 7,b7 ,heat the joints as shown1 and watch the needle4 ,can a current be produced by heat8 7,c7 ,remove the connector on wire #f from ,y to ,m1 thus cutting one pair out of the circuit4 ,heat the joints again and compare the strength of the current with that produced in 7,b74 7,d7 ,see whether much current is produced by one pair4 ,from results obtained do you see any relation between the strength of the current and the number of pairs8 #dbc4 ,thermoelectricity is produced by heating the junction between two metals4 ,different pairs of metals produce different results4 ,antimony and bismuth are often used4 ,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 the bismuth to antimony across the joint4 ,by cooling the junction below the temperature of the rest of the circuit a current will be produced in the opposite direction4 ,thermoelectric currents have a low potential4 ,the energy of the current is kept up by the heat absorbed4 #dbd4 ,peltier ,effect4 ,the action noted in #dbc can be reversed2 that is1 if a current from a battery be sent through the metals1 the parts at the junction become slightly warmer or cooler than before1 depending upon the direction of the current4 ,this is known as the ,peltier ,effect1 the heat not being due to the resistance to the current4 #dbe4 ,thermopiles4 ,as the ,e4 ,m4 ,f4 of the current produced by a single pair of metals is small1 several pairs are usually joined in series in such a way that the different currents help each other and flow in the same direction4 ,such combinations1 usually made of antimony and bismuth1 are called thermoelectric piles1 or simply thermopiles4 ,they are useful in detecting very small differences in temperature4 ,the heat of a match1 or the cold of a piece of ice1 will produce a current even at some distance1 the thermopile being connected with a sensitive short-coil astatic galvanometer4 7,see ,things a ,boy ,should ,know ,about ,electricity47 ,,chapter ,,xxv4 ,,induced ,,currents4 #dbf4 ,electromagnetic ,induction4 ,you have seen1 by experiments1 that a magnet has the power to induce another piece of iron or steel to become a magnet4 ,you have also seen1 in the study of static electricity1 that an electrified body has the power to act through space upon another conductor4 ,a body may be polarized and charged with static electricity by induction4 ,several questions now come up4 ,can a current of electricity in a conductor induce a current in another conductor not in any way connected with the first8 ,can current electricity produce effects through space8 ,is there an electromagnetic induction8 ,it has been seen that a current-carrying wire has a magnetic field1 and that magnetic fields can act through space4 ,it is evident1 then1 that a conductor will be surrounded and cut by lines of force when it is placed in a magnetic field1 or near a wire or coil through which a current passes4 ,let us study this by experiments4 ,,experiments #age-ahb4 ,to study induced currents4 ,apparatus4 ,the two coils of wire 7,nos4 #hi1 #ij72 two short1 soft iron cores 7,nos4 #ib1 #ic72 long iron core 7,no4 #if72 bar magnet 7,no4 #ig72 astatic galvanoscope 7,no4 #ei72 dry cell 7,no4 #ea72 key 7,no4 #ee72 horseshoe magnet2 connecting wires with spring connectors 7,no4 #ed7 on the ends 7 #bbf-bcj72 coil of wire 7,no4 #ih7 wound on an iron core2 compass4 ,illustration3 ,fig4 #acf4 ,,experiment #age4 ,to find whether a current can be generated with a bar magnet and a hollowed coil of wire4 #dbg4 ,directions4 7,a7 ,arrange as in ,fig4 #acf4 ,the coil 7,no4 #ij7 of fine wire is joined to ,a ,g 7,no4 #ei7 as shown4 ,small pieces of tin or copper1 #a and #b1 are used to make connections between the coil ends and wires1 #c and #d1 which are attached to the galvanoscope4 ,it is best to use the wires1 #c and #d1 so that the coil will be #b feet at least1 from ,a ,g2 otherwise the needle of ,a ,g might be affected by the magnet1 ,m 7,no4 #ig74 7,b7 ,get clearly in mind in which direction the right-hand end of the needle is deflected when a current enters ,a ,g at ,l1 the left-hand binding-post4 ,if you have forgotten the results of previous experiments1 use the cell for an instant1 touching the wire from the carbon to ,l and that from the zinc to ,r4 ,if any currents come from the coil1 later1 you should be able to tell in which direction they flow1 the coil and ,a ,g forming a closed circuit4 7,c7 ,hold the magnet1 ,m1 as shown1 and quickly push it into the coil until it has the place of a core1 at the same time watching the needle4 ,if a current is produced1 in which direction does it flow from the coil8 ,does the needle remain deflected8 ,is the current constant or temporary8 7,d7 ,after the magnet1 ,m1 has been placed in the coil1 as in 7,c71 and the needle has come to rest1 quickly pull ,m from the coil1 watching the needle4 ,if a current is produced1 does it pass from the coil in the same direction as before1 in 7,c78 7,e7 ,turn ,m end for end1 repeat 7,c7 and 7,d71 and study the results4 ,are lines of force made to cut the turns of the coil8 7,f7 ,repeat 7,c7 and 7,d71 moving ,m slowly4 #dbh4 ,discussion4 ,an induced current1 produced as in the above experiment1 is a momentary one4 ,no current passes when the magnet and coil are still2 at least one of them has to be in motion4 ,when the magnet is inserted1 the induced current is said to be an inverse one1 as it passes in a direction opposite to that which would be necessary to give the magnet its poles1 it being considered a core magnetized by the current4 ,a direct current is produced when the magnet is withdrawn from the coil4 ,rapid movements produce stronger currents than slow ones4 7,see #dci47 #dbi4 ,induced ,currents and ,work4 ,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 ,when the coil is pushed on to the magnet1 or when it is moved through a magnetic field1 force is also required4 ,we have1 in this simple experiment1 the key to the action of the dynamo and other important electrical machines4 ,these will be discussed later4 ,,experiment #agf4 ,to find whether a current can be generated with a bar magnet and a coil of wire having an iron core4 #dcj4 ,directions4 7,a7 ,arrange as in ,exp4 #age1 ,fig4 #acf1 and1 in addition1 place an iron core 7,no4 #ib7 inside of the coil 7,no4 #ij74 7,b7 ,hold the bar magnet 7,no4 #ig7 as in ,fig4 #acf1 and quickly lower it until it touches the core1 at the same time watching the needle4 ,study results1 direction of current1 etc41 as before4 7,c7 ,suddenly withdraw ,m from the core4 ,is the current produced in the same direction as that from 7,b78 7,d7 ,turn ,m end for end and repeat 7,b7 and 7,c74 7,e7 ,repeat 7,c7 and 7,d71 moving magnet slowly4 ,how does the strength of the current compare with that of ,exp4 #age8 ,are lines of force made to cut the turns of the coil8 ,illustration3 ,fig4 #acg4 ,,experiment #agg4 ,to find whether a current can be generated with a horseshoe magnet and a coil of wire having an iron core4 #dca4 ,directions4 7,a7 ,arrange the apparatus as in ,exp4 #agf1 but use the horseshoe magnet1 ,h ,m1 instead of the bar magnet4 ,fig4 #acg shows the coil 7,no4 #ij7 with one pole of ,h ,m held over the core4 7,b7 ,study the effect of quickly lowering and raising first one pole and then the other over the core1 as with the bar magnet4 ,get clearly in mind the direction in which the induced current flows in each case4 #dcb4 ,induced ,currents and ,lines of ,force4 ,in the experiments just given1 it should be remembered that the permanent magnets are sending out thousands of lines of force from their ,n poles1 and receiving them again at their ,s poles4 ,as the magnet is pushed into the coil 7,exp4 #age71 the lines of force not only cut through the turns of the coil1 but the number of lines of force that cut the coil at any instant varies rapidly as the magnet is moved4 ,motion is necessary1 with this arrangement1 to make a change in the number of cutting lines of force4 ,the current passes only while the magnet moves2 and the direction of the current at any moment depends upon whether the number of lines of force is increasing or decreasing at that moment4 7,see #dch1 #dci47 ,illustration3 ,fig4 #ach4 ,,experiment #agh4 ,to find whether a current can be generated with an electromagnet and a hollow coil of wire4 #dcc4 ,directions4 7,a7 ,the hollow coil 7,no4 #ij7 should be joined to the astatic galvanoscope1 as shown in ,fig4 #acf4 ,instead of the bar magnet in ,fig4 #acf1 an electromagnet is to be used1 and this should be joined in series with a cell and key1 as shown in ,fig4 #ach4 ,the current from the cell will pass only when ,k is pressed4 7,b7 ,note from the winding which way the current must pass around the coil when the circuit is closed at ,k1 and determine whether the lower end of the long iron core1 ,l ,i ,c 7,no4 #if7 should be ,n or ,s4 ,with the compass test the poles of the core to be sure you are right4 7,c7 ,quickly lower the end of ,l ,i ,c into the hollow coil 7,h1 ,fig4 #acf71 the circuit being kept closed long enough to allow the needle to partially come to rest again4 ,withdraw ,l ,i ,c before you open the circuit4 ,explain action of needle4 7,d7 ,reverse the direction of the current through the electromagnet1 by changing the connections1 and repeat 7,c74 ,does any induced current pass through ,a ,g when the core is held still in the coil ,h1 even though a current passes through coil ,e8 ,illustration3 ,fig4 #aci4 ,,experiment #agi4 ,to find whether a current can be generated with an electromagnet and a coil of wire having an iron core4 #dcd4 ,directions4 7,a7 ,fig4 #aci shows simply the arrangement of coils4 ,coil ,h 7,no4 #ij7 with core1 is joined to the galvanoscope as in ,fig4 #acf4 ,coil ,e1 with short core1 should be joined to key and cell as shown in ,fig4 #ach4 7,b7 ,keeping in mind the polarity of the lower end of core ,e1 quickly lower it to the core of ,h1 the circuit being kept closed for a few seconds4 ,does the needle remain deflected after the motion ceases8 7,c7 ,quickly raise ,e1 the circuit being still closed1 then open the circuit4 ,compare the directions taken by the induced currents in 7,b7 and 7,c74 #dce4 ,discussion of ,exps4 #agh1 #agi4 ,this motion in straight lines is not suitable for producing currents strong enough for commercial purposes4 ,in order to produce currents of considerable strength1 the coils of wire have to be pushed past magnets with great speed4 ,special machines 7see ,dynamos7 are constructed in which the coils are wound so 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 #adj4 ,,experiment #ahj4 ,to study the effect of starting or stopping a current near a coil of wire or other closed circuit4 #dcf4 ,directions4 7,a7 ,arrange as in ,fig4 #adj4 ,place the two coils1 ,h and ,e1 on the same core1 ,l ,i ,c4 ,connect ,e with the key and cell as before 7,fig4 #ach74 ,connect ,h with the astatic galvanoscope1 ,a ,g1 as in ,fig4 #acf4 ,keep the coils #b or #c feet from ,a ,g1 so that the needle will not be affected by them4 7,b7 ,close the circuit at the key1 watching the needle1 then as soon as the needle regains its former position1 open the circuit again4 ,compare the direction of the induced current in ,h with that of the current in ,e1 7#a7 when the main circuit is closed1 and 7#b7 when it is opened4 ,is any current induced in ,h by a steady current in ,e8 7,see ,transformers47 ,illustration3 ,fig4 #ada4 ,,experiment #aha4 ,to study the effect of starting or stopping a current in a coil placed inside of another coil4 #dcg4 ,directions4 7,a7 ,arrange as in ,fig4 #ada4 ,join coil ,h with the astatic galvanoscope1 ,a ,g4 ,place the small coil ,p 7,no4 #ih7 with core1 inside of ,h1 and connect the ends of ,p with the key and cell1 as shown4 7,b7 ,close the circuit at ,k2 watch the needle1 and as soon as it regains its position1 open the circuit again4 ,compare the direction of the induced current in ,h with that of the inducing current in ,p1 7#a7 when the inducing circuit is closed1 and 7#b7 when it is broken4 7,see ,induction ,coils47 #dch4 ,discussion of ,exps4 #ahj1 #aha4 ,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 ,we may consider that when the inducing circuit is closed1 the lines of force shoot out through the turns of the outside coil4 ,upon opening the circuit the lines of force cease to exist2 that is1 we may imagine them drawn in again4 ,illustration3 ,fig4 #adb4 #dci4 ,direction of ,induced ,current4 ,fig4 #adb shows the magnet on its way into the coil2 the number of lines of force is increasing in the coil1 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 a current from a cell were passed through the coil in the direction of this indirect current1 the lower end of a bar of iron would become a ,s pole4 7,see #dbh47 #ddj4 ,laws of ,induction4 7#a7 ,an increase in the number of lines of force that pass through a closed circuit produces an indirect induced current2 while a decrease produces a direct one4 7,see #dbh47 7#b7 ,the ,e4 ,m4 ,f4 of the induced current is equal to the rate of increase or decrease in the number of lines of force that pass through the circuit4 7#c7 ,a constant current produces no induced current1 provided there is no motion4 7#d7 ,closing a circuit produces an indirect current4 7#e7 ,opening a circuit produces a direct current4 7#f7 ,lenz's ,law4 ,induced currents have a direction that tends to stop the motion that produces them4 #dda4 ,primary and ,secondary ,currents4 ,in the preceding experiments in induction1 it must be kept in mind that the current from the cell did not pass through the galvanoscope4 ,there were two entirely separate circuits1 in no way connected4 ,the primary current comes from the cell1 while the secondary current is an induced one4 ,illustration3 ,fig4 #adc4 ,,experiment #ahb4 ,to see what is meant by alternating currents4 #ddb4 ,directions4 7,a7 ,arrange as in ,fig4 #adc4 ,connect coil ,h with ,a ,g1 as before4 ,place one pole of ,h ,m against the end of the core ,i ,c1 hold ,h with one hand1 and with the other quickly push the other pole of ,h ,m onto the core4 ,this should produce a momentary current through ,a ,g1 first in one direction1 and then in the other4 ,let the needle come to rest4 7,b7 ,move ,h ,m back and forth upon the end of ,i ,c1 changing its polarity rapidly4 ,a minute's practice will enable you to slide the core from one pole of ,h ,m to the other and back again rapidly--#c complete vibrations per second being about right4 ,the needle should be parallel to the coil of ,a ,g1 and if properly done1 the needle will be made to vibrate back and forth slightly at each change in the polarity of ,i ,c4 #ddc4 ,direct and ,alternating ,currents4 ,a current that flows steadily in one direction is said to be a direct current4 ,a cell gives a direct current when the circuit is closed4 ,when the current passes in one direction for an instant1 and then reverses immediately and flows in the opposite direction1 it is said to alternate4 ,the induced current which flowed through the galvanoscope in ,exp4 #ahb was an alternating one4 ,currents of this class have great practical uses4 #ddd4 ,self-,induction2 ,extra ,currents4 ,it has been shown that a magnetized coil can act through space and induce a current in a neighboring coil4 ,the lines of force which reach out from an electromagnet will generate a current in any conductor which happens to be in the field1 or which is moved across the lines4 ,it is evident1 then1 since the lines of force from each turn of a coil cut all the other turns of the same coil1 that each turn acts as a conductor placed in the field of every other turn4 ,the instant a current begins to flow through a coil1 there is an inverse current of self-induction started in the coil1 which opposes the current in the cell4 ,when the circuit is broken1 this extra current1 as it is also called1 is a direct one and adds its strength to that of the current from the cell2 as this takes place at the instant the circuit is broken1 a bright spark is seen at the key1 and this shows that the ,e4 ,m4 ,f4 of this extra current is high4 ,practical uses are made of it4 ,,chapter ,,xxvi4 ,,the ,,production ,,of ,,motion ,,by ,,currents4 #dde4 ,currents and ,motion4 ,we have seen1 in the experiments on induced currents1 that a current of electricity can be generated by properly moving magnets near coils of wire4 7,see ,dynamo-electric ,machines47 ,can we reverse this process8 ,can motion be produced by the electric current8 ,,experiments #ahc-aij4 ,to study the production of motion by means of the electric current4 ,apparatus4 ,the support1 including base1 rod1 and support wire1 ,s ,w 7,fig4 #add47 ,coils of wire 7,no4 #hi1 #ij72 iron cores for coils2 cell2 key2 connecting wires2 compass2 current reverser2 bar magnet2 horseshoe magnet4 ,illustration3 ,fig4 #add4 ,,experiment #ahc4 ,motion produced with a hollow coil and a piece of iron4 #ddf4 ,directions4 7,a7 ,arrange as in ,fig4 #add4 ,coil ,h 7,no4 #ij7 is to be used as a pendulum1 and can be supported by fastening a string to it1 the upper end of which should be tied to ,s ,w4 ,connect the ends of ,h with ,k and ,d ,c4 ,there will be a slight magnetic field about ,h as soon as the circuit is closed4 7,b7 ,hold ,i ,c near the end of the coil4 ,close the circuit for an instant4 ,is there any motion produced in ,h8 ,while the motion will be slight1 there should be enough to be noticed if the cell is strong4 7,c7 ,swing the suspended coil back and forth like a pendulum for a minute1 until you get in mind the rapidity of its vibrations4 ,stop it1 then repeat 7,b71 closing and opening the circuit at regular intervals1 so that the little impulses given by the attraction for ,i ,c will gradually cause ,h to vibrate4 ,the wires leading from ,h should not drag upon the table4 ,,experiment #ahd4 ,motion with hollow coil and bar magnet4 #ddg4 ,directions4 7,a7 ,substitute the bar magnet ,m 7,no4 #ig7 for the iron of ,exp4 #ahc 7,fig4 #add74 ,get clearly in mind the polarity of the coil from the way the current flows through it1 then test it with the compass to find whether you are right4 7,b7 ,hold the ,n pole of ,m near the left-hand end of the coil1 close the circuit for an instant and study results4 7,c7 ,reverse the magnet and repeat 7,b74 ,compare the results with those of ,exp4 #ahc4 ,try to make the coil vibrate4 ,,experiment #ahe4 ,motion with electromagnet and piece of iron4 #ddh4 ,directions4 7,a7 ,arrange as described in ,exp4 #ahc1 ,fig4 #add4 ,place a short core inside of the coil and repeat4 7,see #ddf for directions47 ,why is the motion produced much larger than that given by a hollow coil8 7,b7 ,the coil can gradually be made to swing through quite a little space by closing and opening the circuit regularly 7 #ddf1 ,c74 ,could any use be made of such a motion1 if it were on a large scale8 ,could it be made to run a machine8 ,illustration3 ,fig4 #ade4 ,,experiment #ahf4 ,motion with electromagnet and bar magnet4 #ddi4 ,directions4 7,a7 ,arrange as in ,fig4 #ade1 the coil being suspended and connected as in ,exp4 #ahc 7,fig4 #add74 7,b7 ,study the effect of closing the circuit when the ,n pole of ,m is held near the core of ,h4 ,reverse ,m1 and repeat4 ,illustration3 ,fig4 #adf4 ,,experiment #ahg4 ,motion with electromagnet and horseshoe magnet4 #dej4 ,directions4 7,a7 ,arrange as in ,fig4 #adf4 ,the ends of ,h 7,no4 #hi7 are joined to ,x and ,y of the current reverser ,c ,r 7,no4 #eg74 ,it is evident1 then1 that the direction of the current through ,h can be easily and rapidly reversed by ,c ,r4 7,see ,exp4 #ajc47 ,either pole of the horseshoe magnet ,h ,m will attract ,i ,c when it is not magnetized4 7,b7 ,place the end of ,i ,c near the ,n pole of ,h ,m so that it will be attracted to it4 ,you have learned that like poles repel each other1 so press the lever of ,c ,r that will produce a ,n pole at the left-hand end of ,i ,c4 ,the core ,i ,c should be repelled by the ,n pole of ,h ,m and be instantly attracted by its ,s pole4 7,c7 ,rapidly reverse the current and make ,i ,c jump back and forth from one pole to the other4 ,the results of this experiment should be remembered1 as they will aid in understanding motors4 ,a core #a_/d in4 in diameter can be placed in between the poles and be made to vibrate rapidly as the current is reversed4 ,illustration3 ,fig4 #adg4 ,,experiment #ahh4 ,motion with two electromagnets4 #dea4 ,directions4 7,a7 ,arrange as in ,fig4 #adg4 ,join the two coils1 ,h and ,e1 in parallel4 ,connect their two outside ends ,o ,e to a metal plate ,a1 and their inside ends ,i ,e to ,b4 ,join wires #a and #f to ,k1 ,d ,c1 ,a and ,b1 as shown4 ,when the circuit is closed at ,k1 the current will pass along wire #a and divide at ,a1 entering ,e and ,h at the same time by wires #b and #d and returning through #c and #e to ,b1 and thence to ,d ,c4 7,b7 ,close the circuit for an instant with wires arranged as in ,fig4 #adg4 ,do the electromagnets attract or repel each other8 ,study out the direction in which the current passes around the coils1 and see whether they should attract or repel4 7,c7 ,change wire #d to ,b1 and wire #e to ,a4 ,the polarity of ,h1 only1 will be changed when this circuit is closed4 ,press the key for an instant and study the results4 #deb4 ,discussion of ,exps4 #ahc-ahh4 ,from the results it is evident that motion can be produced with the aid of the electric current in many different ways4 ,it can be produced at the ends of wires which simply reach across the room1 or which reach miles from the source of the current4 ,to get practical results for commercial purposes we require a proper source of current1 proper conductors1 and proper apparatus to convert the motions into useful work4 ,the motions given to the parts of the apparatus in the previous experiments are not suitable for commercial purposes1 as they are in straight lines4 ,a rotary motion is needed to do good work2 and when this is applied to a shaft1 belts can be used to run all sorts of machinery4 7,see ,electric ,motors47 ,illustration3 ,fig4 #adh4 ,,experiment #ahi4 ,rotary motion with a hollow coil of wire and a permanent magnet4 #dec4 ,directions4 7,a7 ,arrange as in ,fig4 #adh4 ,a key can be used instead of the reverser4 ,the coil of the galvanoscope1 ,g ,v1 has a magnetic field about it when the circuit is closed4 ,the needle has a permanent field4 7,b7 ,close the circuit for an instant1 let the needle swing back past the zero mark1 close the circuit again1 etc41 until the added impulses give the needle a complete turn4 7,c7 ,keep the needle turning on its axis by opening and closing the circuit at the proper time4 ,with a little practice you can make it turn rapidly4 7,d7 ,reverse the motion of the needle4 7,see #dee47 ,illustration3 ,fig4 #adi4 ,,experiment #aij4 ,rotary motion with an electromagnet and a permanent magnet4 #ded4 ,directions4 7,a7 ,arrange as in ,fig4 #adi4 ,place the compass a short distance from the end of the core of the coil ,h 7,no4 #hi74 ,close the circuit1 and as soon as the needle gets part way around open it again1 closing it at the proper time to give the needle a new impulse4 ,the speed can be regulated1 somewhat1 by changing its distance from the core4 ,a key may be used in place of a reverser4 7,b7 ,reverse the direction of rotation4 #dee4 ,discussion of ,exps4 #ahi-aij4 ,we have1 in these experiments1 the key to the action of electric motors4 ,by properly opening and closing the circuit1 the rotary motion can be kept up as long as current is supplied4 ,if a small pulley were attached to the top of the compass-needle in ,exp4 #aij1 a tiny belt could be attached1 and we should have a machine that could do1 perhaps1 a fly-power of work4 7,see ,electric ,motors47 ,,chapter ,,xxvii4 ,,applications ,,of ,,electricity4 #def4 ,things ,electricity ,can ,do4 ,among the almost countless things that electricity can do are the following3 ,it signals without wires4 ,it drills rock1 coal1 and teeth4 ,it cures diseases and kills criminals4 ,it protects1 heats1 and ventilates houses4 ,it photographs the bones of the human body4 ,it rings church bells and plays church organs4 ,it lights streets1 cars1 boats1 mines1 houses1 etc4 ,it pumps water1 cooks food1 and fans you while eating4 ,it runs all sorts of machinery1 elevators1 cars1 boats1 and wagons4 ,it sends messages with the telegraph1 telephone1 and search-light4 ,it cuts cloth1 irons clothes1 washes dishes1 blackens boots1 welds metals1 prints books1 etc41 etc4 ,as this book deals almost exclusively with experiments1 to be performed with simple1 home-made apparatus1 space cannot be given for a discussion of the many instruments and machines which make electricity a practical every-day thing4 7,see ,things ,a ,boy ,should ,know ,about ,electricity47 ,the principles upon which a few important instruments depend1 however1 will be given4 ,illustration3 ,fig4 #aej4 ,,experiment #aia4 ,to study the action of a simple telegraph sounder4 #deg4 ,directions4 7,a7 ,arrange as in ,fig4 #aej4 ,the electromagnet is supported upon its base1 as directed in #djg4 ,coil ,h1 ,k1 and ,d ,c are joined in series4 ,the iron strip1 ,i1 can be held by the left hand1 while ,k is worked with the right4 7,b7 ,press the key1 closing the circuit for different lengths of time1 and note that the armature1 ,i1 responds exactly to the motions at ,k4 #deh4 ,discussion4 ,the downward click makes a distinct sound1 and in regular instruments the armature is allowed to make an upward click1 also4 ,the time between the two clicks can be short or long to represent dots or dashes1 which1 together with spaces1 represent letters4 7,for telegraph alphabet1 and complete directions for making and connecting a home-made telegraph line1 see ,apparatus ,book47 ,illustration3 ,fig4 #aea4 #dei4 ,telegraph ,line2 ,connections4 ,fig4 #aea 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 sounders ,s and s1 and the keys1 ,k and k1 are shown by a top view1 or plan4 ,the broad black lines of ,s and s represent the armatures1 which are directly over the electromagnets4 ,the keys have switches1 ,e and e4 ,the two stations1 ,r and ,l1 may be near each other 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 a wire1 ,r ,w1 or through the earth2 but for short lines a return wire is best4 #dfj4 ,operation of ,line4 ,suppose ,r 7right7 and ,l 7left7 have a line4 ,fig4 #aea 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 ,b through ,k1 ,s1 ,l ,w1 s1 k1 b1 ,r ,w and back to ,b4 ,this makes the armatures of ,s and s come down with a click at the same time4 7,see ,exp4 #aia47 ,as soon as the key is raised1 the armatures raise1 making the up-click4 7,see #deh47 ,as soon as ,r has finished1 he closes his switch1 ,e4 ,l then opens e 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 are used for such lines4 ,on large lines the current from a dynamo is used4 ,illustration3 ,fig4 #aeb4 ,,experiment #aib4 ,to study the action and use of the relay on telegraph lines4 #dfa4 ,directions4 7,a7 ,arrange as in ,fig4 #aeb4 ,place ,k and ,d ,c at one end of the table to represent the sending station4 ,at the other end of the table place ,e1 which is the electromagnet of the relay1 and ,h1 the electromagnet of the sounder4 ,connect the ends of ,e with ,k and ,d ,c1 ,l ,w being the line wire1 and ,r ,w the return4 ,in practice1 the return is through the earth4 ,the relay armature1 ,r ,a1 should vibrate towards ,e every time ,k is pressed4 ,c is a piece of copper against which ,r ,a presses each time it is attracted by ,e1 and this closes what is called the local circuit4 ,connect the poles of another battery1 ,l ,b1 with ,c and ,h1 and the other end of coil ,h with ,r ,a4 ,the sounder armature1 ,s ,a1 should be arranged as in ,exp4 #aia4 ,small springs are shown on the two armatures1 and these keep them away from the cores when the circuits are open4 7,b7 ,fasten the parts to a board1 and study the connections and action of this home-made outfit4 #dfb4 ,the ,relay replaces the sounder in the line wire circuit1 and its coils are usually wound with many turns of fine wire1 so that a feeble current will move its nicely adjusted armature4 ,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 ,the current passes back from the relay to the sending station through the earth4 ,the relay armature acts as an automatic key to open and close the local circuit1 which includes also a battery and sounder4 ,the line current does not enter the sounder4 7,see ,things ,a ,boy ,should ,know ,about ,electricity47 ,illustration3 ,fig4 #aec4 ,,experiment #aic4 ,to study the action of a two-pole telegraph instrument4 #dfc4 ,directions4 7,a7 ,arrange as in ,fig4 #aec4 ,connect the two coils to the connecting plates1 as described in #djh4 ,join a strip of copper ,cu with wire #b leading from ,d ,c1 and join the zinc of ,d ,c to ,m4 ,the ends of wires #a and #c should be near ,cu but they must not touch it4 ,if ,cu be slightly curved so that its ends are raised above the table1 the ends of wires #a and #c may be put directly under the ends of ,cu2 each half of ,cu can then be used as a key4 ,two armatures1 ,a and ,b1 should be held as shown4 ,d ,c can be placed at one side1 of course1 its terminals being joined to ,m and ,cu4 7,b7 ,press first one end and then the other of ,cu1 so that the current will pass through ,h or ,e at will4 7,c7 ,paste pieces of paper to the armatures1 the left one being marked with a dot1 and the other with a dash4 ,the one who sends the message can make dots or dashes at the instrument by pressing the proper key4 ,this form of instrument can be easily made by boys1 and the messages are more easily read by the eye than by the ear1 as in regular sounders4 ,illustration3 ,fig4 #aed4 ,,experiment #aid4 ,to study the action of a simple single needle telegraph instrument4 #dfd4 ,directions4 7,a7 ,arrange as in ,fig4 #aed4 ,stick a pin on each side of the ,n pole of the galvanoscope-needle through the degree-card1 so that the needle can make but part of a turn when the circuit is closed4 7,b7 ,touch one lever of the reverser ,c ,r1 then the other1 to see whether connections are right4 ,the needle should be forced against one pin and then against the other4 ,if motions to the left represent dots1 and those to the right dashes1 combinations of dots and dashes can be used for letters as in the sounder 7,exp4 #aia74 7,c7 ,arrange the apparatus shown in ,fig4 #abb so that messages can be sent4 ,illustration3 ,fig4 #aee4 ,,experiment #aie4 ,to study the action of a simple automatic contact breaker1 or current interrupter4 #dfe4 ,directions4 7,a7 ,arrange as in ,fig4 #aee4 ,slip a spring connector attached to wire #a upon the iron strip ,i1 a short distance from its end4 ,hold the left-hand end of ,i firmly in one hand1 and with the other hold the connector on wire #b just above that on #a4 ,the right-hand end of ,i should be just above the core of ,h4 7,b7 ,allow the current to pass through the circuit by touching the two connectors together gently4 ,does the armature make one click1 as in the telegraph sounder1 or does it vibrate rapidly8 7,c7 ,try the connectors in various positions on ,i4 #dff4 ,automatic ,current ,interrupters are used on bells1 buzzers1 induction coils1 etc4 ,the principle upon which they work is shown in the above experiment 7,fig4 #aee74 ,the current1 as it comes from the carbon of ,d ,c1 is obliged to stop when it reaches ,i1 unless the two connectors touch4 ,as soon as the current passes1 ,i is pulled down and away from the upper connector1 and this breaks the circuit4 ,i1 being held firmly in the hand1 immediately springs back to its former position1 closing the circuit4 ,the rapidity of the vibrations depends somewhat upon the position of the connectors upon ,i4 ,in regular instruments1 a platinum point is used where the circuit is broken2 this stands the constant sparking at that point4 ,illustration3 ,fig4 #aef4 ,,experiment #aif4 ,to study the action of a simple electric bell1 or a buzzer4 #dfg4 ,directions4 7,a7 ,fig4 #aef shows the circuit explained in ,exp4 #aie1 with a key or push-button put in1 so that the circuit can be closed at a distance from the vibrating armature4 7,b7 ,have a friend work the key while you hold ,i and wires #a and #b as directed in ,exp4 #aie4 ,the circuit must not be broken at two places1 of course1 so begin by holding the two connectors together4 ,the armature should vibrate rapidly each time ,k is pressed4 #dfh4 ,electric ,bells and ,buzzers are very nearly alike in construction2 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 ,by placing a bell near the end of the vibrating armature 7,fig4 #aef71 so that the bell would be struck by it at each vibration1 we should have an electric bell4 ,by making the wires #a and #c long1 the bell or buzzer can be worked at a distance4 7,see ,apparatus ,book1 ,chapter ,,xv1 for ,home-made ,bells and ,buzzers47 ,illustration3 ,fig4 #aeg4 ,,experiment #aig4 ,to study the action of a simple telegraph recorder4 #dfi4 ,directions4 7,a7 ,cut from a tin box1 or can1 a piece of tin about #d in4 long and #a-a_/b in4 wide4 ,bend this double to make two thicknesses4 ,this will serve as an armature ,i 7,fig4 #aeg74 ,nail to one end of ,i a small spool1 ,s1 and into this put a short length of lead-pencil1 ,p1 which may be held firmly in ,s by wrapping a little paper around it4 ,connect the ends of coil ,h to a key and cell as in ,fig4 #aef4 7,b7 ,hold or fasten ,i in place1 and have a friend make dots and dashes at the key1 while you draw a piece of paper past the end of ,p4 ,a little adjusting will be necessary to get the pencil to write only while the circuit is closed4 ,in regular machines all the parts are automatic4 ,illustration3 ,fig4 #aeh4 ,,experiment #aih4 ,to study the action of a simple annunciator4 #dgj4 ,directions4 7,a7 ,arrange as in ,fig4 #aeh4 ,fasten the two electromagnets1 ,h and ,e1 to a board or a piece of stiff cardboard4 ,they may be held in place by passing strings over them and through the board1 tying on the other side4 ,the ends of coils ,h and ,e should be joined to pieces of tin1 ,a1 ,b1 ,c1 by means of connectors4 ,k and ,k are keys or push-buttons1 which in real instruments are in different rooms4 ,two steel pens may be swung on pins a short distance from the ends of the cores1 so that their lower ends will be attracted to the cores the instant the current passes through them4 ,the residual magnetism should hold them against the cores until removed4 ,hairpins1 nails1 or needles can be used instead of pens4 7,b7 ,press first one ,k and then the other to see whether your connections are correct4 #dga4 ,annunciators4 ,there are many forms of annunciators in use to indicate1 in a hotel for example1 a certain room when a bell rings at the office4 ,if a bell be included in the circuit between ,d ,c and ,a in ,fig4 #aeh1 it will ring each time a key is pushed4 ,this will call attention to the fact that some one has rung1 and the annunciator will show the location of the special call4 ,large instruments are made with hundreds of electromagnets1 each one answering to a special room4 ,the instrument should be set1 of course1 after each call4 ,a nail or screw wound with insulated wire can be used for the electromagnets of a home-made annunciator4 ,,experiment #aii4 ,to study the shocking effects of the extra current4 #dgb4 ,directions4 7,a7 ,use the two electromagnets joined to the connecting plates 7,fig4 #acb71 to generate a self-induced or extra current4 ,connect ,r of ,fig4 #acb with the zinc of a dry cell1 and between ,l and the carbon of the cell place a key2 in other words1 join the electromagnets1 cell1 and key in series4 ,two good cells in series can be used to advantage4 7,b7 ,wet the ends of two fingers of the left hand1 press one upon ,l and the other on ,r1 thus making a shunt with your hand4 ,with the right hand work the key rapidly4 ,if the current is strong enough you should feel a slight shock in the fingers each time the circuit is broken4 ,the extra current 7 #ddd7 causes the shock as it shoots through the fingers4 7,c7 ,if you have electric bells or telegraph sounders use them for this experiment4 #dgc4 ,induction ,coils are instruments for producing induced currents of high ,e4 ,m4 ,f4 ,the apparatus shown in ,fig4 #ada forms a simple induction coil4 ,the primary coil is made of coarser wire and has less turns of wire than the secondary coil4 ,the current in the primary circuit is usually interrupted by an automatic interrupter 7,exp4 #aie71 thus producing an alternating current in the secondary coil1 the voltage of which depends upon the relative number of turns in the two coils4 ,induction coils are used in telephone work1 for medical purposes1 for ,x-ray work1 etc41 etc4 7,for ,home-made ,induction ,coils see ,apparatus ,book1 ,chapter ,,xi47 ,illustration3 ,fig4 #aei4 #dgd4 ,action of ,induction ,coils4 ,fig4 #aei shows a top view of one of the home-made induction coils described1 in full1 in the ,apparatus ,book4 ,wires #e and #f are the ends of the primary coil1 while wires #g and #h are the terminals of the secondary coil4 ,the battery wires should be joined to binding-posts ,w and ,x1 and the handles to ,y and ,z4 ,fig4 #afj shows the details of the automatic interrupter which is placed in the primary circuit4 ,illustration3 ,fig4 #afj4 ,if the current 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 ,s ,i1 as ,a is no longer attracted2 the circuit being closed1 the operation is rapidly repeated4 7,for commercial forms and uses of induction coils see ,things ,a ,boy ,should ,know ,about ,electricity47 #dge4 ,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 the same core2 in fact1 an induction coil may be considered a transformer4 ,if the secondary coil has #ajj times as many turns of wire as the primary1 a current with an ,e4 ,m4 ,f4 of #ajj volts can be taken from the secondary coil1 when the ,e4 ,m4 ,f4 of the current passing through the primary is #a volt2 but the strength 7amperes7 of the secondary current will be but one-hundredth that of the primary current4 ,by using the coil of fine wire as the primary1 the ,e4 ,m4 ,f4 of the current that comes from the other coil will be but one-hundredth that in the fine coil4 ,it will have #ajj times its strength1 however4 ,continuous currents from cells or dynamos must be interrupted1 as in induction coils1 to be transformed from one ,e4 ,m4 ,f4 to another4 ,transformers are now largely used in lighting and power circuits1 etc4 7,see ,things ,a ,boy ,should ,know ,about ,electricity47 #dgf4 ,the ,dynamo4 ,we saw in the ,exps4 of ,chapter ,,xxv4 that currents of electricity can be generated in a coil of wire 7closed circuit7 by rapidly moving it through the field of a magnet4 ,as shown by the experiments1 this can be accomplished in many ways4 ,the dynamo is a machine for doing this on a large scale1 the coils being given a rotary motion in a very strong magnetic field2 and as the number of lines of force that cut the coil is constantly changing1 there is a current in the coil as long as power is applied1 and this current is led from the machine by proper devices4 ,the dynamo is a machine for converting mechanical energy into an electric current1 through electromagnetic induction4 ,if a loop of wire 7,fig4 #afa7 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 ,such a current inside of the machine would be of no value2 it must be led out to external conductors4 ,some sort of sliding contact is necessary to connect a revolving conductor with a stationary one4 ,illustration3 ,fig4 #afa4 ,illustration3 ,fig4 #afb4 ,fig4 #afb shows the ends of a coil joined to two rings1 ,x1 ,y1 which are insulated from each other1 and which rotate with the coil4 ,two stationary pieces of carbon1 ,a1 ,b1 called brushes1 press against the rings1 and to these are joined wires 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 #afc4 ,in ,fig4 #afc the ends of the coil are joined to the two halves of a cylinder4 ,these halves1 ,x and ,y1 are insulated from each other and from the axis4 ,the current flows from ,x onto the brush ,a1 through some external circuit where it does work1 and thence back through brush ,b onto ,y4 ,by the time that ,y gets around to ,a the direction of the current in the loop has reversed1 so that it passes towards ,y2 but it still enters the outside circuit through ,a 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 ,in regular machines there are many loops of wire and several segments to the commutator4 ,the rotating coils are wound upon an iron core1 so that the lines of force1 in passing from one pole to the other1 will meet with as little resistance as possible4 ,the coils1 core1 and commutator1 taken together1 are called the armature4 ,the magnets which furnish the field are called the field-magnets4 ,these are electromagnets1 the current from the dynamo1 or a part of it1 being used to excite them4 ,there are many forms of dynamos1 and many ways of winding the armature and field-magnets1 but space will not permit a discussion of them here4 7,see ,things a ,boy ,should ,know ,about ,electricity47 #dgg4 ,the ,electric ,motor4 ,experiments have shown that motion can be produced by the electric current in many ways4 ,the galvanoscope may be considered a tiny motor4 ,an electric motor is a machine for transforming electric energy into mechanical power4 ,while the electric motor is similar in construction to the dynamo1 it is opposite to it in action4 ,motors receive current and produce motion4 ,the motion is a rotary one1 the power being applied to other machines by means of belts or gears4 ,illustration3 ,fig4 #afd4 ,,experiment #bjj4 ,to study the action of the telephone4 #dgh4 ,directions4 7,a7 ,join the ends of coil ,h 7,fig4 #afd7 to the astatic galvanoscope4 ,move magnet ,m back and forth in front of the soft iron core1 while ,h is held in position4 ,watch the needle4 ,imagine that vibrations in the air caused by the voice are strong enough to give ,m a slight motion to and fro1 and you can see how a current would be sent through the galvanoscope by speaking against ,m4 #dgi4 ,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 the sound out again is called the receiver4 ,sound itself does not pass over the line4 ,although the same apparatus may be used for both transmitter and receiver1 they are generally different in construction4 ,illustration3 ,fig4 #afe4 #dhj4 ,the ,bell or ,magneto-transmitter generates its own current1 and is1 strictly speaking1 a dynamo that is run by the voice4 ,you have seen1 by experiments1 that a current can be generated in a coil of wire by moving a magnet back and forth in front of its soft iron core4 ,in the telephone this process is reversed1 soft iron in the shape of a thin disc 7,d1 ,fig4 #afe7 being made to vibrate by the voice immediately in front of a coil having a permanent magnet1 ,m1 for a core4 ,the soft iron diaphragm is fixed near1 but it does not touch the magnet4 ,the coil consists of many turns of fine insulated wire4 ,the current generated is an alternating one and exceedingly feeble2 in fact1 it can not be detected by a galvanoscope4 #dha4 ,the ,receiver has the same construction as the bell transmitter1 and receives the currents from the line4 ,as the diaphragm is always attracted by the magnet1 it is under a constant strain4 ,this strain is increased when a current passes through the coil in a direction that adds strength to the magnet1 and decreased when the current weakens the magnet4 ,when the current through the coil is always in the same direction1 but varies in strength1 the diaphragm will vibrate on account of the varying pull upon it4 ,illustration3 ,fig4 #aff4 ,when the current through the coil is an alternating one1 the same result is obtained1 as the magnet gets weaker and stronger many times per minute4 ,fig4 #aff shows two bell instruments joined1 either being used as the transmitter and the other as the receiver4 #dhb4 ,the ,carbon ,transmitter does not in itself generate a current like the magneto-transmitter2 it merely produces changes in the strength of a current that flows through it1 and that comes from some outside source4 ,in ,fig4 #afg1 ,x and ,y are two carbon buttons1 ,x being attached to the diaphragm1 ,d4 ,button ,y presses gently against ,x4 ,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 circuit1 in which also is the receiver1 ,r4 ,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 ,illustration3 ,fig4 #afg4 #dhc4 ,induction ,coils in ,telephone ,work4 ,as the resistance of telephone lines is large1 a current with a fairly high ,e4 ,m4 ,f4 is desired4 ,while the current from one or two cells is sufficient to work the transmitter1 it is not strong enough to force its way over a long line4 ,to get around this difficulty an induction coil is used to transform the battery current1 that flows through the transmitter and primary coil1 into a current with a high ,e4 ,m4 ,f4 that can go into the main line and force its way to a distant receiver4 ,the battery current in the primary coil is undulating1 but always in the same direction1 the magnetic field around the core getting weaker and stronger4 ,this causes an alternating current in the secondary coil and main line4 ,illustration3 ,fig4 #afh4 ,fig4 #afh shows the two coils1 ,p1 ,s1 of the induction coil4 ,the primary1 ,p1 is joined in series with a cell and transmitter4 ,the secondary coil1 ,s1 is joined to the 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 ,there are many forms of transmitters4 7,see ,things a ,boy ,should ,know ,about ,electricity47 #dhd4 ,electric ,lighting and ,heating4 ,whenever resistance is offered to the electric current1 heat is produced4 ,by proper appliances1 the heat of resistance can be applied just where it is needed1 and many commercial processes depend upon electricity for their success4 ,dynamos are used to generate currents for lighting and heating purposes4 ,there are two great systems of lighting1 the one by arc lamps and the other by incandescent lamps4 7,see ,things a ,boy ,should ,know ,about ,electricity47 #dhe4 ,arc ,lamps produce a light when a current passes from one carbon rod to the other across an air-space4 ,as the current starts through the lamp1 the ends of the carbons touch1 and the imperfect contact causes resistance enough to heat the ends red-hot4 ,they are then automatically separated1 and the current passes from one to the other1 causing the arc4 ,the resistance of the air-space is reduced by the intensely heated vapor and flying particles of carbon4 #dhf4 ,the ,incandescent ,lamp consists of a glass bulb1 in which is a vacuum1 and the light is caused by the passage of a current through a thin fibre of vegetable carbon1 enclosed in the vacuum4 ,the fibre would burn instantly if allowed to come in contact with the air4 ,the fibres have a high resistance1 and are easily heated to incandescence4 ,,chapter ,,xxviii4 ,,wire ,,tables4 ,copper ,wire ,tables are very convenient1 and a necessity when working electrical examples4 ,the tables here given are taken from a dealer's catalogue1 and will be found sufficiently accurate for ordinary work4 ,explanation of ,tables4 ,in the first column are given the sizes of wires by numbers4 ,the ,b ,s or ,american gauge is used4 ,in the table below is given a comparison between the ,b ,s and the ,birmingham gauges4 ,the second column gives the diameters of wires4 ,the diameter of ,no4 #cf wire is #e thousandths of an inch2 the diameter of ,no4 #bd wire is a little over #bj thousandths or #b hundredths of an inch4 ,the third column contains what is called circular mils1 a mil being a thousandth of an inch4 ,the figures in this column are obtained by squaring those in the second2 thus1 for ,no4 #cf wire1 #e #e #be4 ,this column is useful when working examples where the squares of the diameters are wanted4 ,the rest of the table explains itself4 ,the table at the bottom gives a comparison between the fractional and decimal parts of an inch4 ,space can not be given here for a series of examples showing the many uses of this table4 7,see ,elementary ,electrical ,examples47 ,,copper ,,wire ,,tables4 7,based on the ,b4 ,a4 ,unit47 ,gauge ,,diam- ,sectional,capac- ,,ohms ,,eter4 ,,area ity4 ---------------------------------------- --------------------- ,b4,s4 ,in ,in ,in ,amp- ,per ,per ,per ,no4 #ajjjths,circular eres4 #a1jjj ,mile4 ,pound4 ,mils4 feet4 ---------------------------------------- --------------------- #jjjj4dfj #baafjj4 #cab4 4#jdijf 4#beijc 4#jjjjgg #jjj4djifd #afghje4 #bfb4 4#jfahf 4#cbffd 4#jjjab #jj4cfdh #accjgi4 #bbj4 4#jghja 4#daahg 4#jjjai #j4cbdhf #ajeecd4 #ahe4 4#jihca 4#eaiji 4#jjjca #a4bhic #hcfid4 #aef4 4#abdjd 4#fedij 4#jjjdi #b4begfc #ffcgc4 #aca4 4#aefdj 4#hbeh 4#jjjgh #c4bbidb #ebfcd4 #aaj4 4#aigbc #a4jdad 4#jjabe #d4bjdca #dagdc4 #ib4c 4#bdhfi #a4cac 4#jjaih #e4ahaid #ccajb4 #gg4f 4#cacfa #a4fee 4#jjcad #f4afbjb #bfbea4 #fe4b 4#ciedf #b4jhh 4#jjdii #g4addbh #bjhag4 #ed4h 4#dihga #b4fcc 4#jjgib #h4abhdi #afeaj4 #df4a 4#febi #c4c 4#jabe #i4aaddc #acjid4 #ch4g 4#ghib #d4a 4#jaig #aj4ajahi #ajchb4 #cb4e 4#hdda #d4d 4#jbgj #aa4jijgdb #hbcd4 #bg4c #a4bed #f4d 4#jeja #ab4jhjhjh #fecj4 #bc4 #a4ehj #h4c 4#jgi #ac4jgaifa #eagh4 #ai4c #a4iie #aj4d 4#abg #ad4jfdjhd #dajg4 #af4b #b4ejd #ac4b 4#bjj #ae4jegjfh #cbeg4 #ac4f #c4agb #af4g 4#cbj #af4jejhb #behc4 #aa4e #d4jja #bc4 4#eab #ag4jdebeg #bjdh4 #i4f #e4jd #bf4 4#haa #ah4jdjcjc #afbd4 #h4a #f4cf #cc4 #a4bi #ai4jcehi #abhh4 4444 #h4be #dc4 #b4aa #bj4jcaifa #ajba4 4444 #aj4ab #ec4 #c4bg #ba4jbhdfb #haj4 4444 #ab4gf #fh4 #e4bj #bb4jbecdg #fdb4 4444 #af4be #he4 #h4ce #bc4jbbega #eji4 4444 #bj4cj #ajh4 #ac4c #bd4jbja #djd4 4444 #be4fj #ace4 #bj4i #be4jagi #cbj4 4444 #cb4b #agj4 #cc4b #bf4jaeid #bed4 4444 #dj4g #bad4 #eb4i #bg4jadaie #bja4 4444 #ea4c #bgj4 #hd4b #bh4jabfda #aei4h 4444 #fd4h #cdc4 #acd4 #bi4jaabeg #abf4g 4444 #ha4f #dhb4 #bac4 #cj4jajjbe #ajj4e 4444 #ajc4 #ech4 #cch4 #ca4jjhibh #gi4g 4444 #acj4 #fhe4 #eci4 #cb4jjgie #fc4 4444 #afd4 #hfe4 #hef4 #cc4jjgjh #ej4a 4444 #bjf4 #ajcc4 #aceg4 #cd4jjfcjd #ci4gd 4444 #bfj4 #achi4 #baff4 #ce4jjefad #ca4e 4444 #cbh4 #ahbj4 #ceba4 #cf4jje #be4 4444 #dad4 #bbjj4 #edfi4 #cg4jjddec #ai4h 4444 #ebc4 #bgfe4 #hgdb4 #ch4jjcife #ae4gb 4444 #ffj4 #cdhf4 #acggb4 #ci4jjceca #ab4dg 4444 #hcb4 #dcie4 #bahif4 #dj4jjcadd #i4hh 4444 #ajdi #eedb4 #cdhbc4 ---------------------------------------- --------------------- ,gauge ,,feet4 ,,pounds4 ---------------------------------------- ---------- ,b4,s4 ,per ,per ,per ,per ,no4 ,pound4 ,ohm4 #a1jjj feet4 ,ohm4 ---------------------------------------- ---------- #jjjj #a4efabbbjdig4g #fdj4ea #abihg4 #jjj #a4ifhg #afbee4bg #ejg4ie #hccc4 #jj #b4dhbd #abhia4cg #djb4hc #ebfc4 #j #c4acjc #ajbbc4jh #cai4de #cbbe4 #a #c4idgad #hajg4di #bec4cd #bjda4 #b #d4iggbb #fdbi4eh #bjj4ia #abhb4 #c #f4bgfe #ejih4fa #aei4cb #hjj4 #d #g4iada #djdc4f #abf4ce #eje4 #e #i4igihc #cbjf4fa #ajj4bj #cah4 #f #ab4ehdg #bedb4hi #gi4dfb #bjj4 #g #ae4hfif #bjae4ea #fc4jac #abf4 #h #bj4jjig #aeii4c #di4igf #hj4 #i #be4bbi #abfh4dd #ci4fcf #ej4 #aj #ca4hbab #ajee4ff #ca4dbf #cg4 #aa #dj4abjb #gig4fdi #bd4ibd #bj4 #ab #ej4eijf #fcb4eee #ai4gff #ab4fe #ac #fc4gidh #eja4fc #ae4fgd #g4hg #ad #hj4ddae #cig4hbb #ab4dce #e4jj #ae #aja4dcfe #cae4dhb #i4hei #c4ab #af #abg4ab #bej4ahd #g4hai #a4ie #ag #afa4bi #aih4dji #f4aii #a4bc #ah #bjc4cgd #aeg4ce #d4iaf 4#gge #ai #bef4dfh #abd4ggg #c4hii 4#dgc #bj #cbc4cii #ih4iecc #c4jid 4#cje #ba #djg4hae #gh4dgc #b4deb 4#aib #bb #ead4aic #fb4bcf #a4ide 4#aai #bc #fdh4deb #di4cejd #a4edb 4#jge #bd #hag4fhh #ci4acfe #a4bbc 4#jdg #be #ajca4jch #ca4jcha 4#ifii 4#jcj #bf #acjj4ahj #bd4faca 4#gfib 4#jahg #bg #afci4di #ai4eaia 4#fjii 4#jaah #bh #bjfg4cfd #ae4dgic 4#dhcg 4#jjgd #bi #bfjf4iei #ab4bhed 4#chce 4#jjdg #cj #cbhg4jhd #i4gcee 4#cjjb 4#jjbi #ca #ddad4di #g4gbadc 4#bdac 4#jjah #cb #ebbf4iae #f4abbdc 4#aiac 4#jjaa #cc #feij4da #d4heege 4#aeag 4#jjjgf #cd #hcab4h #c4hdiff 4#abjd 4#jjjdf #ceajdha4gg #c4jecje 4#jief 4#jjjbh #cfacbad4af #b4dbag 4#jgeg 4#jjjah #cgaffei4ig #a4ibjhf 4#jfjjc 4#jjjaa #chbajac4be #a4ebbib 4#jdgeh 4#jjjjg #cibfdif4bcg #a4bjggg 4#jcgee 4#jjjjd #djccdbj4fc #j4igihd 4#jbiib 4#jjjjbi ---------------------------------------- ---------- ,comparative ,table of the ,fractional and ,decimal ,parts of an ,inch4 ----------------- #a_/fd 4#jaefbe #a_/cb 4#jcabej #c_/fd 4#jdfhge #a_/af 4#jfbejj #e_/fd 4#jghabe #c_/cb 4#jicgej #g_/fd 4#ajicge #a_/h 4#abejjj #i_/fd 4#adjfbe #e_/cb 4#aefbej #aa_/fd 4#agahge #c_/af 4#ahgejj #ac_/fd 4#bjcabe #g_/cb 4#bahgej #ae_/fd 4#bcdcge #a_/d 4#bejjjj #ag_/fd 4#bfefbe #i_/cb 4#bhabej #ai_/fd 4#bifhge #e_/af 4#cabejj #ba_/fd 4#cbhabe #aa_/cb 4#cdcgej #bc_/fd 4#ceicge #c_/h 4#cgejjj #be_/fd 4#cijfbe #ac_/cb 4#djfbej #bg_/fd 4#dbahge #g_/af 4#dcgejj #bi_/fd 4#decabe #ae_/cb 4#dfhgej #ca_/fd 4#dhdcge #a_/b 4#ejjjjj ----------------- ,comparative ,table of ,b4 and ,s4 and ,b4 ,w4 ,gauges in ,decimal ,parts of an ,inch4 --------------------------------------- ,birmingham ,american ,no4 of ,wire ,gauge4 7,b4 and ,s47 ,wire ,gauge4 ,wire ,gauge4 --------------------------------------- #jjjj 4#df 4#ded #jjj 4#djifd 4#dbe #jj 4#cfdh 4#ch #j 4#cbdhf 4#cd #a 4#bhic 4#c #b 4#begfc 4#bhd #c 4#bbidb 4#bei #d 4#bjdca 4#bch #e 4#ahaid 4#bb #f 4#afbjb 4#bjc #g 4#addbh 4#ah #h 4#abhdi 4#afe #i 4#aaddc 4#adh #aj 4#ajahi 4#acd #aa 4#jijgdb 4#ab #ab 4#jhjhjh 4#aji #ac 4#jgaifa 4#jie #ad 4#jfdjhd 4#jhc #ae 4#jegjfh 4#jgb #af 4#jejhb 4#jfe #ag 4#jdebeg 4#jeh #ah 4#jdjcjc 4#jdi #ai 4#jcehi 4#jdb #bj 4#jcaifa 4#jce #ba 4#jbhdfh 4#jcb #bb 4#jbecdg 4#jbh #bc 4#jbbega 4#jbe #bd 4#jbja 4#jbb #be 4#jagi 4#jb #bf 4#jaeid 4#jah #bg 4#jadaie 4#jaf #bh 4#jabfda 4#jad #bi 4#jaabeg 4#jac #cj 4#jajjbe 4#jab #ca 4#jjhibh 4#ja #cb 4#jjgie 4#jji #cc 4#jjgjh 4#jjh #cd 4#jjfcjd 4#jjg #ce 4#jjefad 4#jje #cf 4#jje 4#jjd #cg 4#jjddec #ch 4#jjcife #ci 4#jjceca #dj 4#jjcaad --------------------------------------- ,,list ,,of ,,apparatus ,,for ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment4 ,the #ajj pieces of apparatus in the following list are referred to1 by number1 in the experiments contained in ,the ,study of ,elementary ,electricity and ,magnetism by ,experiment4 ,this list is furnished to give those who wish to make their own apparatus an idea of the approximate size1 etc41 of the various articles used4 ,the author is preparing a price catalogue of the articles included in this list1 and of odds and ends needed in the construction of simple1 home-made apparatus4 ,no4 #a4 ,a package of #be steel sewing-needles4 ,to be suitable for experiments in magnetism1 these should be of good1 hard steel1 and not too thick4 ,no4 #b4 ,a flat cork1 about #a in4 in diameter and #c_/h in4 thick4 ,no4 #c4 ,a candle for annealing steel4 ,no4 #d-ae4 ,one dozen assorted annealed iron wires1 from #a in4 to #f in4 in length4 ,the iron should be very soft4 ,no4 #af4 ,one ,english horseshoe magnet1 #b-a_/b in4 long1 best quality4 ,no4 #ag4 ,a small box of iron filings from soft iron4 ,no4 #ah4 ,a compass 7,fig4 #e74 ,the needle swings very freely2 it is enclosed in a wooden pill box1 the cover of which forms the support4 ,no4 #ai1 #bj4 ,two soft steel wire nails1 #b in4 long4 ,no4 #ba1 #bb4 ,two pieces of spring steel1 about #c in4 long and #c_/h in4 wide1 to be magnetized by the student and used as bar magnets4 ,no4 #bc4 ,an iron ring1 or washer1 about #g_/h in4 in diameter4 ,no4 #bd4 ,a sifter for iron filings4 ,this consists of a pasteboard pill box3 ,prick holes through the bottom with a pin4 ,no4 #be4 ,a thin1 flexible piece of spring steel1 about #c in4 long and #a_/h in4 wide4 ,no4 #bf1 #bg4 ,two ebonite sheets 7,e ,s1 ,fig4 #cd71 each #d in4 square4 ,these are made with a special surface4 ,they are very much better than the ordinary smooth ebonite4 ,no4 #bh4 ,one ebonite rod 7,e ,r1 ,fig4 #cd71 #c-a_/b in4 long1 with special surface4 ,no4 #bi4 ,one ebonite rod1 #a-c_/d in4 long1 with special surface1 used to support the insulating table1 ,no4 #dc 7,i ,t1 ,fig4 #cb74 ,no4 #cj4 ,one piece of flannel cloth1 #g in4 square4 ,no4 #ca4 ,six sheets of tissue-paper1 each #d in4 square4 ,no4 #cb4 ,a few feet of white cotton thread4 ,no4 #cc4 ,a few feet of black silk thread4 ,no4 #cd4 ,one support base 7,s ,b1 ,fig4 #ef74 ,this is of thin wood1 about #c-c_/d in4 by #f-a_/b in41 to one end of which is fastened a spool for holding the support rod 7,no4 #ce74 ,no4 #ce4 ,one support rod 7,s ,r1 ,fig4 #ef71 #g in4 long and #e_/af in4 in diameter4 ,this rod has a hole in each end4 ,the small hole is for holding the support wire 7,no4 #cf72 the large hole is for the ebonite rod 7,no4 #bi74 ,no4 #cf4 ,one support wire 7,s ,w1 ,fig4 #add74 ,no4 #cg4 ,one wire swing 7,w ,s1 ,fig4 #bi74 ,no4 #ch4 ,one sheet of glass1 #d in4 square4 ,no4 #ci4 ,one bent hairpin 7,h ,p1 ,fig4 #cb74 ,no4 #dj4 ,bottom of flat box 7,b ,f ,b1 ,fig4 #cb71 #c-e_/h in4 in diameter4 ,no4 #da4 ,top of flat box 7,t ,f ,b1 ,fig4 #cc74 ,no4 #db4 ,one electrophorus cover 7,e ,c1 ,fig4 #cd71 #c-e_/h in4 in diameter4 ,this has rounded edges1 and a small tube is riveted into the top of it to hold the insulating handle1 ,e ,r4 ,no4 #dc4 ,one insulating table 7,i ,t1 ,fig4 #cb74 ,this is made the same as ,no4 #db1 and is supported by ,no4 #bi4 ,no4 #dd4 ,one insulated copper wire1 #b-a_/b feet long4 ,no4 #de4 ,one rubber band 7,r ,b1 ,fig4 #cc74 ,no4 #df4 ,six bent wire clamps 7,b ,c1 ,fig4 #cg74 ,no4 #dg4 ,one tin box conductor 7,t ,b1 ,fig4 #db74 ,this cylindrical conductor is about the size of an ordinary baking powder box4 ,no4 #dh4 ,one hairpin discharger for the condenser4 ,no4 #di4 ,two sheets of aluminum-leaf for the leaf electroscope 7,fig4 #eg7 and other experiments4 ,no4 #ej4 ,one bent wire 7,h ,p1 ,fig4 #eg7 used in connection with the leaf electroscope4 ,no4 #ea4 ,a dry cell1 ordinary size about #g in4 high and #b-a_/b in4 in diameter4 ,no4 #eb4 ,enough mercury to amalgamate battery zincs4 ,a wooden pill box containing about half a thimbleful will do4 ,no4 #ec4 ,a coil containing #be feet of ,no4 #bd insulated copper wire for connections4 ,no4 #ed4 ,one dozen spring connectors 7,fig4 #fa7 for making connections4 ,these are made of brass1 nickel plated1 and do not affect the compass-needle4 ,no4 #ee4 ,a telegraph key 7,fig4 #fh7 without switch4 ,the metal straps are made of aluminum2 they are #a_/b in4 wide1 and are fastened to a neat wooden base4 ,no4 #ef4 ,three metal plates1 each about #b in4 by #c_/d in41 on which spring connectors 7,no4 #ed7 are to be pushed in order to join two wires4 ,no4 #eg4 ,a current reverser 7,fig4 #fi74 ,the straps are made of aluminum and are fastened to a neat wooden base4 ,no4 #eh4 ,a galvanoscope 7,fig4 #gb7 including a degree-card 7,no4 #ii74 ,the cardboard coil-support1 ,c ,s1 is #e #f-a_/d in41 and the hole in it is #c-c_/h in4 in diameter4 ,the coil is #d-a_/d in4 in diameter1 made of ,no4 #bd insulated copper wire4 ,no4 #ei4 ,an astatic galvanoscope 7,fig4 #gg74 ,the whole may be taken apart and mailed in the containing box1 ,b1 which is #d-c_/h #c-a_/h #a in4 ,the coil is made of ,no4 #ca wire1 and has a resistance of about #e ohms4 ,spring connectors are used to join a wire to the apparatus by pushing the connectors into the tubular binding-posts1 ,l and ,r4 ,no4 #fj-fc4 ,four strips of sheet zinc1 #d in4 by #a_/b in41 not amalgamated4 ,no4 #fd4 ,a carbon rod1 #d in4 long 7,fig4 #ha74 ,no4 #fe1 #ff4 ,two glass tumblers 7,fig4 #ha74 ,no4 #fg1 #fh4 ,two strips of sheet copper1 #d in4 by #a_/b in4 7,fig4 #he74 ,no4 #fi4 ,one galvanized iron nail4 ,no4 #gj1 #ga4 ,two wooden cross-pieces 7,fig4 #he74 ,no4 #gb4 ,one dozen brass screws1 #e_/h in4 long1 size ,no4 #e1 with round heads4 ,no4 #gc4 ,a porous cup 7,p ,c1 ,fig4 #hg7 that will stand inside of the tumblers 7,no4 #fe74 ,no4 #gd4 ,a zinc rod1 about #c_/h in4 in diameter1 like those used in ,leclanch cells4 ,no4 #ge4 ,a sheet copper plate for the two-fluid cell 7,c1 ,fig4 #hg74 ,this is #b in4 wide2 it nearly surrounds the porous cup1 and is supported upon the edge of the tumbler by a narrow strip1 ,a1 with which connections are made by spring connectors 7,no4 #ed74 ,no4 #gf4 ,one strip of sheet iron1 #d in4 by #a_/b in4 ,no4 #gg1 #gh4 ,two strips of sheet lead1 #d in4 by #a_/b in4 ,no4 #gi4 ,a resistance coil 7,fig4 #id74 ,the coil is made of ,no4 #bd insulated copper wire2 it has a resistance of #b ohms 7nearly7 and is fastened to a cardboard base4 ,it is so arranged that either one or two ohms can be used at will4 ,no4 #hj4 ,a ,wheatstone's bridge 7,fig4 #ajc71 including a scale 7,no4 #ajj74 ,the aluminum straps1 #a1 #b1 #c1 are fastened to a neat wooden base1 #aj in4 long by #b in4 wide4 ,a ,no4 #bh ,german-silver wire is used for the bridge4 ,no4 #ha4 ,a piece of ,no4 #cj uncovered ,german-silver wire1 #b4a meters long1 used for resistance 7,fig4 #if74 ,no4 #hb4 ,a piece of ,no4 #bh uncovered ,german-silver wire1 #b4a meters long4 ,no4 #hc-he4 ,three plate binding-posts1 consisting of bent straps of sheet aluminum 7,x1 ,y1 ,z1 ,fig4 #if74 ,no4 #hf4 ,two ounces of copper sulphate1 commonly called bluestone4 ,the crystals may be kept in a large wooden pill box4 ,no4 #hg4 ,one dozen copper washers4 ,no4 #hh4 ,one combination rule1 #a ft4 long1 marked with ,english and metric systems4 ,no4 #hi4 ,a hollow coil of ,no4 #bd insulated copper wire 7,fig4 #acj74 ,the spool1 on which the wire is wound1 has a hole for a five-sixteenths inch core4 ,it is turned down thin1 so that the wire is near the core4 ,the coil is about #a-a_/h in4 long and #a in4 in diameter4 ,spring connectors are joined to the ends of the coil4 ,no4 #ij4 ,a hollow coil of ,no4 #be insulated copper wire1 similar to ,no4 #hi1 with spring connectors attached to its ends4 ,no4 #ia4 ,carbon rod for electroplating4 ,no4 #ib1 #ic4 ,two soft iron cores1 with screws 7,i ,c1 ,fig4 #acj74 ,these cores are #e_/af in4 in diameter1 and have a threaded hole in one end for fastening them to ,no4 #id4 ,no4 #id4 ,a tin box with three holes punched in its top 7,fig4 #acb74 ,this serves as a base1 as well as a yoke1 for the two electromagnets1 ,a1 ,b1 shown in plan4 ,no4 #ie4 ,combination connecting plates 7,fig4 #acb74 ,three aluminum straps are fastened to a wooden base4 ,they are turned up at their ends so that spring connectors can be easily pushed upon them4 ,no4 #if4 ,one long iron core 7,l ,i ,c1 ,fig4 #adj74 ,this is of soft iron1 #e_/af in4 in diameter1 and long enough to pass through both coils 7,no4 #hi1 #ij74 ,no4 #ig4 ,bar magnet1 about #d in4 long and #e_/af in4 in diameter4 ,no4 #ih4 ,coil of insulated wire wound on a soft iron core1 to act as a primary coil for induction experiments4 ,this coil fits inside of the hollow coils 7,nos4 #hi1 #ij74 ,no4 #ii4 ,a printed degree-card for the galvanoscope 7,no4 #eh74 ,this is printed on stiff cardboard1 about #c in4 in diameter4 ,no4 #ajj4 ,a printed scale for the ,wheatstone's bridge 7,no4 #hj74 ,this is printed on stiff paper4 ,the scale is #h in4 long1 and is divided into #aj large divisions1 each of which is subdivided into #aj parts1 thus making #ajj parts in all4 ,,index4 ,numbers refer to paragraphs4 ,see ,table of ,contents for the various experiments4 ,abreast1 arrangement of cells1 #cfe4 ,accumulators4 7,see storage cells47 ,action1 local1 #bgc4 ,air1 as insulator1 #add1 a4 ,alternating currents1 #ddc4 ,amalgamating1 #beg1 #bgd4 ,amber1 #ajg4 ,ammeter1 #cec4 ,ampere1 the1 #cea1 #ceg4 ,ampere's rule1 #chf4 ,annealing1 #f4 ,annunciators1 #dga4 ,anode1 #cgc1 #cgh4 ,applications of electricity1 ,chap4 ,,xxvii4 ,arc lamp1 #dhe4 ,arrangement1 of cells1 #cfc to #cfh4 ,armature1 the1 #aa1 #gh1 #dgf4 ,astatic needles1 #bea1 #bec1 #bed2 galvanoscope1 #beb1 #bef4 ,atmospheric electricity1 ,chap4 ,,xiii41 #bag2 causes of1 #bba4 ,attraction1 mutual1 #aaa2 and repulsion1 laws of magnetic1 #bi2 electric1 laws of1 #aba4 ,aurora borealis1 #bbc4 ,batteries1 ,chap4 ,,xv42 storage1 #chb4 ,bell1 electric1 #dfh4 ,bell telephone1 #dhj4 ,bichromate cell1 #bhi4 ,bound electrification1 #afb1 #aia4 ,breaking a magnet1 #ea4 ,bridge1 ,wheatstone's1 #cbd to #ccj4 ,brushes1 #dgf4 ,buzzers1 electric1 #dfh4 ,cable1 submarine1 as condenser1 #ahb4 ,capacity1 inductive1 #afi2 electrical1 #agf1 #agh4 ,carbon1 transmitter1 #dhb2 electroscope1 #aad4 ,cathode1 #cgc4 ,cell1 galvanic1 ,chap4 ,,xv42 arrangement of1 #cfc1 #cfd1 #cfe1 #cfh2 chemical action in1 #bgj1 #bga2 direction of current in1 #bfh2 local action in1 #bgc2 open and closed circuit1 #bhf2 polarization of1 #bgh2 poles of1 #bfi2 simple1 #bge2 secondary1 #chb2 single-fluid1 #bge2 two-fluid1 #bha1 #bhe2 various galvanic1 #bhf to #bia4 ,charge1 in condenser1 #aie2 residual of condensers1 #aig4 ,charging conductors1 ,chap4 ,,viii4 ,chemical action1 #cfi4 ,chemical effects of current1 ,chap4 ,,xxi4 ,circuit1 electric1 #bff2 divided1 #bic2 short1 #bie4 ,coercive force1 #dd1 #df4 ,coils1 #cij2 induction1 #dgc1 #dgd2 method of joining1 #djh2 polarity of1 #cib2 resistance1 #cji2 simple resistance1 #caj4 ,commutator1 #dgf4 ,compass1 #bf2 our1 #cb2 needle1 #bdc1 #bdi4 ,compound magnets1 #gc4 ,condensation of electrification1 ,chap4 ,x41 #agh4 ,condensers1 #agh2 action of1 #ahf1 #aia2 induction coil1 #aha2 submarine cables1 #ahb4 ,conductive discharge1 #adi1 #ahd4 ,conductors1 #abf1 #abi1 #acc2 hollow and solid1 #aec2 and insulators1 relation between1 #acc2 and non-conductors1 #cab4 ,connections1 electrical1 #bbf to #bcj4 ,contact breaker1 ,exp4 #aie2 #dff4 ,convective discharge1 #adi4 ,copper sulphate solution1 #bhc4 ,cores1 of electromagnets1 #cig4 ,coulomb1 the1 #ced4 ,current electricity1 ,part ,,iii4 ,current1 #add1 a1 #bfd2 detectors1 #bcb1 #bci2 direction of in cell1 #bfh2 direct and alternating1 #ddc2 extra1 #ddd2 interrupters1 #dff2 primary and secondary1 #dda2 measurement of1 #ceb2 reverser1 #bce1 #bcg2 strength of1 ,chap4 ,,xx41 #cej1 #ceh1 #cfb to #cfe2 unit of1 #cea4 ,daniell cell1 #bij4 ,declination1 #hd4 ,depolarizers1 #bhj1 #bhb4 ,detectors1 current1 #bcb1 #bci4 ,diamagnetic bodies1 #ae4 ,dielectric1 #ahd1 #aia1 #aie4 ,dielectrics1 #aff4 ,dip1 #hf4 ,direct currents1 #dbh1 #ddc4 ,dischargers1 #ahh4 ,discharges1 kinds of1 #adi4 ,divided circuits1 #bic1 #cbc4 ,dry cells1 #bhh4 ,dynamo1 #dce1 #dgf4 ,earth's magnetism1 #hc1 #ib1 #ic4 ,electric1 bells1 #dfh2 chime1 #aic2 circuit1 #bff1 ,chap4 ,,xvi42 current1 #add1 a1 #bfd2 density1 #aee2 field1 #aef2 horse-power1 #cee2 lighting1 #dhd2 machines1 static1 #baf2 motor1 #dgg2 polarization1 #aei2 resistance1 ,chap4 ,,xviii42 wind1 #aee4 ,electricity1 static1 ,part ,,ii42 ,current1 ,part ,,iii42 ,applications of1 ,chap4 ,,xxvii41 #def2 kinds of1 #ajj2 derivation of name1 #ajg2 ,atmospheric1 ,chap4 ,,xiii41 #bag4 ,electrification1 ,chap4 ,,vi41 #ajc1 #aaf1 #acb1 #acd2 and heat1 #ajd2 condensation of1 ,chap4 ,x42 escape of1 #aee2 free and bound1 #afb2 induced1 ,chap4 ,,ix42 kinds of1 #abj2 of earth1 #bbb2 source of in cells1 #bfe2 theories about1 #ade2 two kinds of1 #abj1 #baa4 ,electrics and non-electrics1 #acd4 ,electrified bodies1 #ajb1 #ajg4 ,electrodes1 #bfi4 ,electromagnetism1 ,chap4 ,,xxii41 #chc4 ,electromagnets1 ,chap4 ,,xxiii41 #cif2 cores of1 #cig2 horseshoe1 #dje4 ,electromotive force1 #add1 ,chap4 ,,xvii41 #bif1 #cjj1 #cjc2 measurement of1 ,exp4 #adj2 of polarization1 #cgc1 #chb2 series1 #cja2 unit of1 #big4 ,electrophorus1 #ach2 action of1 #aga1 #agb2 our1 #aci4 ,electrolysis1 #cgj4 ,electrolyte1 #cgj4 ,electroplating1 #cgf1 #cgh4 ,electroscope1 action of1 #bjf1 #bjh2 carbon1 #aad2 pith-ball1 #bjj2 our leaf1 #bja1 #bjb4 ,electroscopes1 ,chap4 ,,xi4 ,electrotyping1 #cgi4 ,equator of magnet1 #ac4 ,equipotential points1 #cbf4 ,external resistance1 #cjg1 #cfh4 ,extra current1 #ddd2 ,exp4 #aii4 ,field1 electric1 #aef2 magnetic1 ,chap4 ,,iv41 #fb1 #hj2 magnets1 #dgf4 ,figures1 magnetic1 #fd2 permanent1 #dag4 ,force1 #ajc2 lines of magnetic1 #fd1 #gc1 #hj1 #aef2 lines of electric1 #aef2 lines of about a wire1 #che4 ,franklin1 ,benjamin1 #bah4 ,free electrification1 #afb4 ,frictional electricity1 ,part ,,ii4 ,fulminating panes1 #ahj4 ,galvanic cells1 ,chap4 ,,xv41 #bfe2 chemical action in1 #bgj2 various kinds of1 #bhf to #bia4 ,galvanoscope1 #bdj to #bdi4 ,glass1 as insulator1 #acf4 ,gold-leaf electroscope1 #bjj1 #bji4 ,gravity cell1 #bia4 ,hardening steel1 #h1 #aj4 ,heat1 effect on resistance1 #cdc2 effect on magnet1 #di4 ,horse-power1 electric1 #cee4 ,horseshoe magnet1 #aa2 advantages of1 #hb2 electromagnets1 #dje4 ,hydrogen1 #bfj1 #bfb1 #bga1 #bgh1 #bgi1 #cgc4 ,inclination of needle1 #hf4 ,induced currents1 ,chap4 ,,xxv42 and work1 #dbi2 and lines of force1 #dcb1 #dce1 #dch2 direction of1 #dci4 ,induced magnetism1 ,chap4 ,,iii4 ,induction coils1 #dgc2 action of1 #dgd2 condensers of1 #aha2 with telephone1 #dhc4 ,induction1 electromagnetic1 #dbf2 laws of1 #ddj2 static1 theory of1 #aei2 successive1 #afh4 ,inductive capacity1 #afi4 ,insulators1 ,chap4 ,,vii41 #abe4 ,internal resistance1 #cjg1 #cad1 #ceh1 #cfb1 #cfh4 ,iron and steel1 ,chap4 ,i4 ,iron1 hardening properties of1 ,exp4 #d2 impurities of1 #a2 kinds of1 #b2 soft1 #aj4 ,jar1 ,leyden1 #agi4 ,key1 #bcc1 #bcd4 ,lamp1 arc1 #dhe2 incandescent1 #dhf4 ,laws1 of electrification1 #aba2 of induction1 #ddj2 of magnetism1 #bi2 of resistance1 #cdi4 ,leclanch cell1 #bhg4 ,leyden jar1 #agi4 ,lighting1 #dhd1 #dhe1 #dhf4 ,lightning1 #add1 a2 #bah2 rods1 #bbj4 ,lines of force1 about a wire1 #che1 #chh2 electric1 #aef2 and induced currents1 #dcb1 #dch2 magnetic1 #fd1 #gc1 #gd1 #hj1 #aef2 resistance to1 #gh1 #cig4 ,local action1 #bgc4 ,local currents1 #bgc4 ,lodestone1 #ic4 ,magnetic1 bodies1 #ae2 circuits1 closed1 #dbj2 field1 #fb1 #hj2 figures1 permanent1 #dag2 figures1 #fd1 ,exp4 #afa1 #afb1 ,exps4 #afh to #aga2 force1 lines of1 #fd1 #hj1 #aef2 induction of the earth1 #ib2 needle1 #bf2 needles1 balancing of1 #hh2 needle1 dip of1 #hf2 problems1 #cc2 saturation1 #db2 screens1 #ah2 tick1 ,exp4 #afj2 transparency1 #ah4 ,magnetism1 ,part ,i42 induced1 ,chap4 ,,iii41 #ec2 residual1 #dd1 #ec2 temporary1 #ec2 terrestrial1 ,chap4 ,v42 theory of1 #db2 of earth1 #hc2 laws of1 #bi4 ,magnets1 bar1 #ba2 compound1 #gc2 effect of breaking1 #ea2 equator of1 #ac1 #ea2 experimental1 #djg2 kinds of1 #aa2 natural1 #ic2 poles of1 #ac1 #be2 practical uses of1 #af4 ,mercury1 #bgd4 ,motion1 production of1 ,chap4 ,,xxvi41 #dde1 #deb1 #dee4 ,motors1 electric1 #dgg4 ,mutual attractions1 #aaa4 ,natural magnets1 #ic4 ,needle1 astatic1 #bea1 #bec1 #bed2 magnetic1 #bf1 #cb4 ,negative electrification1 #abj4 ,neutral bodies1 #ajb4 ,non-conductors1 #cab4 ,non-electrics1 #acd4 ,north-seeking poles1 #be4 ,ohm1 the1 #cjh4 ,ohm's law1 #cef4 ,one-fluid theory1 #ade4 ,open and closed circuits1 #bff2 cells1 #bhf4 ,oxygen1 #cgb1 #cgc1 #chb4 ,peltier effect1 #dbd4 ,pith-ball electroscope1 #bjj4 ,plates or elements1 #bfg4 ,polarization of cells1 #bgh2 effects of1 #bgi2 electric1 #aei1 #afd2 electromotive force of1 #cgc2 magnetic1 #ef2 remedies for1 #bhj4 ,poles1 #ac1 #be1 #fd1 #ib2 consequent1 #ci2 of coils1 #cib2 of electrodes1 #bfi2 reversal of1 #ce2 rule for1 #ca4 ,pole pieces1 #ef4 ,positive electrification1 #abj4 ,potential1 #acc1add2 energy1 #ajc4 ,primary current1 #dda4 ,proof-plane1 #bji4 ,quantity1 unit of1 #ced4 ,recorder1 ,exp4 #aig4 ,relay1 telegraph1 #dfb4 ,repulsion1 laws of electrostatic1 #aba2 laws of magnetic1 #bi4 ,residual1 charge in condenser1 #aig2 magnetism1 #dd2 magnetism of core1 ,exp4 #aei4 ,resistance1 coils1 #cji2 effect of heat on1 #cdc2 electrical1 ,chap4 ,,xviii41 #cje1 #cai1 #cba2 external and internal1 #cjg1 #cfb1 #cfh2 internal1 #cad1 #ceh2 laws of1 #cdi2 to lines of force1 #gh2 measurement of1 ,chap4 ,,xix42 unit of1 #cjh4 ,retentivity1 #dd1 #df4 ,reverser1 current1 #bce1 #bcg4 ,rheostat1 simple1 #cdd4 ,saturation1 magnetic1 #db4 ,secondary cells1 #chb2 current1 #dda4 ,self-induction1 #ddd4 ,series arrangement of cells1 #cfd4 ,shocks1 #ahh4 ,short circuits1 #bie4 ,shunts1 #bic4 ,silk1 as insulator1 #acf4 ,single-fluid cell1 #bge4 ,single needle telegraph1 ,exp4 #aid4 ,sounder1 telegraph1 #deh4 ,spark1 #add1 a4 ,static electricity1 ,part ,,ii4 ,static electric machines1 #baf4 ,steel1 ,chap4 ,i42 kinds of1 #b2 magnetism of1 #db1 #df1 #di4 ,st4 ,elmo's fire1 #bbb4 ,storage cells1 #chb4 ,successive1 induction1 #afh2 condensation1 #aii4 ,sulphuric acid1 #beh1 #bfb1 #cad4 ,tangent galvanometer1 #ceb4 ,telegraph1 line1 #dei1 #dfj2 relay1 #dfb2 single needle instrument1 ,exp4 #aid2 sounder1 #deh2 static1 #acj4 ,telephone1 the1 #dgi2 ,bell1 #dhj2 carbon transmitter1 #dhb2 with induction coils1 #dhc2 receiver1 #dha4 ,tempering steel1 #h4 ,temporary magnetism1 #ec4 ,terrestrial magnetism1 ,chap4 ,v4 ,thermoelectricity1 ,chap4 ,,xxiv41 #dbc4 ,thermopile1 #dbe2 home-made1 #dba4 ,thunder1 #bai4 ,transformers1 #dge4 ,transmitters1 #dhj1 #dhb4 ,two-fluid cell1 #bhj1 #bha2 care of1 #bhb2 chemical action in1 #bhe4 ,two-fluid theory of electrification1 #adf4 ,unit of1 current strength1 #cea2 ,e4 ,m4 ,f41 #big2 of power1 #cee2 quantity1 #ced2 resistance1 #cjh4 ,variation1 angle of1 #hd4 ,varieties of electricity1 #ajj4 ,volt1 the1 #big4 ,voltameters1 #big1 #cec1 #chj4 ,water1 composition of1 #cgb4 ,watt1 the1 #cee4 ,wheatstone's bridge1 #cbd to #ccj4 ,wind1 electric1 #aee4 ,wire tables1 ,chap4 ,,xxviii4 ,yoke1 use of1 #djf4 ,zero1 potential1 #add1 a4 ,zinc1 chemical action with1 #bga2 with commercial1 #bgc4 ,zinc plates1 reasons for amalgamating1 #bgd4 ,notes4 ,notes4 ,,electrical ,,books ,,electrical ,,apparatus ,,games ,,puzzles ,,educational ,,amusements ,illustration ,,thomas ,m4 ,,st4 ,,john1 ,met4 ,e4 ,a ,word to ,parents ,about ,games and ,educational ,amusements4 ,systematic play is as important as systematic work4 ,the best games and home amusements are as valuable to a child as school-studies2 in fact1 they bring out and stimulate qualities in a child1 which no school-study can4 ,fascinating home amusements are as necessary as school-books4 ,boys and girls like to be busy4 ,their amusements should be entered into as heartily1 chosen as carefully1 and purchased as willingly as school-books4 ,games4--,,jingo and ,,hustle-,,ball are good games4 ,they are interesting and full of action4 ,they arouse a child's common-sense4 ,they cultivate an ability to think rapidly1 judge correctly1 and decide quickly4 ,they educate the eye and hand at the same time4 ,they are very simple1 and may be played at once4 ,educational ,amusements4--,there is a peculiar fascination about ,electricity and ,magnetism1 which makes these subjects appeal to every boy and girl4 ,there is nothing better than science studies1 to teach children to observe and to see what they look at2 besides1 it is fun to experiment4 ,fun ,with ,electricity and ,fun ,with ,magnetism are educational amusements4 ,they contain fascinating experiments and are systematically arranged4 ,juvenile ,work in ,electricity4 ,from ,the ,electrical ,engineer1 ,may #ai1 #ahih4 ,the position that ,young ,america is now taking in the electric and magnetic field is very clearly shown at the ,electrical ,show now being held at ,madison ,square ,garden1 by an exhibit of simple experimental apparatus made by young boys from the ,browning ,school1 of this city4 ,the models shown cover every variety of apparatus that is dear to the heart of a boy1 and yet1 along the whole line from push-buttons to motors1 one is struck by the extreme simplicity of design and the ingenious uses made of old tin tomato cans1 cracker boxes1 bolts1 screws1 wire1 and the wood that a boy can get from a soap box4 ,the apparatus in this exhibit was made by boys #ac1 #ad and #ae years of age1 from designs made by ,mr4 ,thomas ,m4 ,st4 ,john1 of the ,browning ,school4 ,it clearly shows that good1 practical apparatus can be made from cheap materials by an average boy4 ,the whole exhibit is wired and in working order1 and it attracts the attention of a large number of parents and boys who hover around to see1 in operation1 the telegraph instruments1 buzzers1 shocking coils1 current detectors1 motors1 etc4 ,mr4 ,st4 ,john deserves the thanks of every boy who wants to build his own electrical apparatus for amusement or for experimental purposes1 as he has made the designs extremely simple1 and has kept constantly in mind the fact that the average boy has but a limited supply of pocket money1 and an equally limited supply of tools4 ,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 ,magnets4--,,vii4 ,magnetic ,needles and ,compasses4--,,viii4 ,yokes and ,armatures4--,,ix4 ,electro-,magnets4--,x4 ,wire-,winding ,apparatus4--,,xi4 ,induction ,coils and ,their ,attachments4--,,xii4 ,contact ,breakers and ,current ,interrupters4--,,xiii4 ,current ,detectors and ,galvanometers4--,,xiv4 ,telegraph ,keys and ,sounders4--,,xv4 ,electric ,bells and ,buzzers4--,,xvi4 ,commutators and ,current ,reversers4--,,xvii4 ,resistance ,coils4--,,xviii4 ,apparatus for ,static ,electricity4--,,xix4 ,electric ,motors4--,,xx4 ,odds and ,ends4--,,xxi4 ,tools and ,materials4 ,the author of this book is a teacher and writer of great ingenuity1 and we imagine that the effect of such a book as this falling into ,juvenile hands must be highly stimulating and beneficial4 ,it is full of explicit details and instructions in regard to a great variety of apparatus1 and the materials required are all within the compass of very modest pocket-money4 ,moreover1 it is systematic and entirely without rhetorical frills1 so that the student can go right along without being diverted from good helpful work that will lead him to build useful apparatus and make him understand what he is about4 ,the drawings are plain and excellent4 ,we heartily commend the book4--,electrical ,engineer4 ,those who visited the electrical exhibition last ,may cannot have failed to notice on the south gallery a very interesting exhibit1 consisting1 as it did1 of electrical apparatus made by boys4 ,the various devices there shown1 comprising electro-magnets1 telegraph keys and sounders1 resistance coils1 etc41 were turned out by boys following the instructions given in the book with the above title1 which is unquestionably one of the most practical little works yet written that treat of similar subjects1 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 made4 ,in his book ,mr4 ,st4 ,john has given directions in simple language for making and using these devices1 and has illustrated these directions with admirable diagrams and cuts4 ,the little volume is unique1 and will prove exceedingly helpful to those of our young readers who are fortunate enough to possess themselves of a copy4 ,for schools where a course of elementary science is taught1 no better text-book in the first-steps in electricity is obtainable4--,the ,great ,round ,world4 ,exhibit of ,experimental ,electrical ,apparatus ,,at ,,the ,,electrical ,,show1 ,,madison ,,square ,,garden1 ,,new ,,york4 ,while only #dj pieces of simple apparatus were shown in this exhibit1 it gave visitors something of an idea of what young boys can do if given proper designs4 ,illustration3 ,,how ,,two ,,boys ,,made ,,their ,,own ,,electrical ,,apparatus ,gives ,proper ,designs--,designs for over #aej ,things4 ,,just ,,published4 ,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-a_/b 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 ,fun ,with ,magnetism4 ,,book ,,and ,,complete ,,outfit ,,for ,,sixty-,,one ,,experiments ,,in ,,magnetism4444 ,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 ,a ,few ,off-,hand ,statements that have been made about ,fun ,with ,magnetism and ,fun ,with ,electricity in letters of inquiry to the author4 7,these statements were absolutely unsolicited47 ,my little boy has your ',fun ,with ,magnetism' and enjoys it so much that if the ',fun ,with ,electricity' is ready ,i would like to have it for him4 ,please let me know1 etc4 ,i have had much fun with ',fun ,with ,magnetism4' ,my boy has ',fun ,with ,magnetism' and has enjoyed it very much and would like the other4 ,will you1 etc4 ,please let me know when ',fun ,with ,electricity' is upon the market1 for if it is as good as this1 ,i shall certainly want it4 ,i have just received ',fun ,with ,magnetism' and am delighted with it4 ,please send me #ab sets1 etc4 ,i have ',fun ,with ,magnetism' and ',fun ,with ,electricity' and have enjoyed them very much4 ,please send1 etc4 ,i am much pleased with ',fun ,with ,electricity' and would like to have1 etc4 ',fun ,with ,electricity' is fine and ,i have had lots of fun with it4 ,please send1 etc4 ,having experimented with both of your apparatus ',fun ,with ,magnetism' and ',fun ,with ,electricity1' and having found them both amusing and instructive1 ,i wish to ask1 etc4 ,i have purchased your outfits ',fun ,with ,electricity' and ',fun ,with ,magnetism1' and though they are designed for amusement1 ,i find them a great help in my studies4 ,will you please1 etc4 ,i have one of your outfits of ',fun ,with ,electricity1' and ,i enjoy it very much1 some of the experiments being very astonishing4 ,will you please1 etc4 ,i have enjoyed ',fun ,with ,magnetism' and ',fun ,with ,electricity' very much4 ,my little boy has your book ',fun ,with ,electricity1' which has given him much amusement4 ,he would like to have1 etc4 ,i am very much pleased with both outfits4 ,i am very much in favor of such things for boys2 it keeps them occupied with something that is both amusing and instructive4 ,send me1 etc4 ,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 #g-a_/b inches1 and has #ch illustrations1 #ee pages1 good paper and clear type4 ,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 ,puzzles4 ,,book1 ,,key1 ,,and ,,complete ,,outfit ,,for ,,four ,,hundred ,,puzzles4444 ,the ,,book measures #e #g-a_/b 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 #h ,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 ,things ,a ,boy ,should ,know ,about ,electricity4 7,in ,preparation47 ,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 ,the following are ,some of the ,things ,electricity ,can ,do3 ,it signals without wires4 ,it drills rock1 coal1 and teeth4 ,it cures diseases and kills criminals4 ,it protects1 heats1 and ventilates houses4 ,it photographs the bones of the human body4 ,it rings church bells and plays church organs4 ,it lights streets1 cars1 boats1 mines1 houses1 etc4 ,it pumps water1 cooks food1 and fans you while eating4 ,it runs all sorts of machinery1 elevators1 cars1 boats1 and wagons4 ,it sends messages with the telegraph1 telephone1 telautograph1 and search-light4 ,it cuts cloth1 irons clothes1 washes dishes1 blackens boots1 welds metals1 prints books1 etc41 etc4 ,everyone ,should ,know ,about ,electricity4 ,things ,a ,boy ,should ,know ,about ,electricity will interest you4 ,we shall be glad to send you complete information as soon as it is ready4 ,send us your address now4 ,dewey ,flag ,poles ,,are ,,little ,,models ,,of ,,real ,,flag ,,poles4444 ,illustration ,they are appropriate for any occasion1 and suitable for any kind of decoration4 ,they should stand on tables1 mantels1 pianos1 etc42 in fact1 there is no better ornament for general use4 ,they should be in every home and in every school-room in the ,united ,states4 ,no toy fort complete without a ,dewey ,flag ,pole4 ,the children can fasten them on the windowsill and watch them flutter by the hour4 ,they hoist like big flags1 at half-mast1 etc4 ,invaluable for store-window decoration4 ,illustration ,,prices ,,small ,,size3 height #ah inches1 fitted with ,united ,states or ,cuban ,silk ,flag 7#df in47 post-paid1 #cj;c4 ,,large ,,size3 height #bd inches1 fitted with ,united ,states ,silk ,flag 7#g #aj in471 post-paid1 #dj;c4 ,,large ,,size3 fitted with ,cuban or ,british ,silk ,flag 7#hab in471 post-paid1 #ej;c4 ,,dewey ,,flag ,,poles are beautifully made of hard wood1 and fitted with best ,silk ,flags4 ,,games4 ,hustle,ball4 ,a quick1 sharp1 decisive game that is thoroughly ,american4 ,played by means of ,magic ,wands1 and ,polished ,balls of ,steel4 ,needed3 ,a quick eye and a nimble hand4--,shakespeare4 ,the ,rule3 ,just keep cool--and hustle4 ,four ,games with ,one ,outfit3 ,hustle ,ball1 ,leap-,frog1 ,cross-,country ,race1 ,magnetic ,potato-,race4 ,the game-board is new and original1 as well as the methods of playing4 ,the game is put up in a strong box having a beautifully lithographed cover1 and measures #h #ae-a_/b inches4 ,with the game-board are furnished1 magic wands1 polished steel balls1 an extra strength horseshoe magnet1 and a complete set of illustrated rules and directions for playing4 ,unlike all other games4 ,any one can play ,hustle-,ball4 ,just the thing for progressive parties4 ,hustle-,ball games are intensely exciting4 ,no waiting for some one to play4 ,you win or lose a point in a few seconds4 ,by handicapping the best players1 all games are made equally interesting and exciting4 ,a game for ,grandparents1 as well as for ,grandchildren4 ,a ,brand-,new ,idea in ,games4 ,illustration ,illustration ',a ,,hustle ,,from ,,the ,,word ,,go4' ,this ,exciting ,game will be sent1 ,charges ,prepaid1 by mail or express1 upon receipt of #fe ,cents4 ,address ,,thomas ,m4 ,,st4 ,,john1 #djg ,west #east ,street1 ,new ,york ,city4 ,,jingo ,,the ,,great ,,war ,,game ,social ,exciting ,interesting ,simple4 ,a ,thorough ,war ,game3--,infantry ,against ,infantry1 ,cavalry ,against ,cavalry1 ,etc4 ,jingo is really a great war contest between ,england and ,america4 ,upon the game-board are #ad beautiful war scenes1 each lithographed in #h colors4 ,american and ,english flags1 coats of arms1 cannon1 torpedoes1 etc41 aid in making this game artistic1 handsome and attractive4 ,the following companies1 ships1 etc41 are shown3--,american1 #abth ,u4 ,s4 ,infantry1--#fth ,u4 ,s4 ,cavalry1--#b;d ,u4 ,s4 ,light ,artillery1--,u4 ,s4 ,mortar ,battery1--,u4 ,s4 ,monitor ,miantonomoh1--,u4 ,s4 ,ram ,katahdin1--,u4 ,s4 ,battleship ,indiana1--,u4 ,s4 ,torpedo ,boat ,cushing1--,u4 ,s ,dynamite ,cruiser ,vesuvius4 ,english1 #cjth ,east ,lancashire1--#ast ,royal ,dragoons1--,royal ,horse ,artillery1--,royal ,artillery1--,h4 ,m4 ,s4 ,thunderer1--,h4 ,m4 ,s4 ,seagull1--,h4 ,m4 ,s4 ,nile1--,h4 ,m4 ,s4 ,australia1--,h4 ,m4 ,s4 ,dart4 ,the game board is over #af inches square when opened4 ,jingo is made and finished in a manner which makes it the most beautiful1 artistic1 and practical game ever published4 ,just what every boy likes4 ,a good idea well carried out4 ,the ,game-board is a work of art4 ,any child can play ,jingo at once4 ,it is the handsomest game on the market4 ,,jingo ,,junior is the ,greatest ,game ever ,invented for ,little ,folks4 ,it is played upon the ,jingo board with the extra ammunition furnished4 ,these ,two ,great ,games make a most complete and beautiful outfit for home amusement4 ,,jingo ,,and ,,jingo ,,junior4 ,two ,fascinating and ,entirely ,different ,games1 ,played with ,one ,outfit1 and ,complete in ,one ,box4 ,illustration ,,this ,,handsome ,,outfit for playing the ,,two ,,great ,,war ,,games will be sent ,,charges ,,prepaid upon receipt of #a4jj4 ,address ,,thomas ,m4 ,,st4 ,,john1 #djg ,west #east ,street1 ,new ,york ,city4 ,transcriber's ,notes ,in the text version1 ,italic text is denoted by underscores and bold text by equal signs4 ,obvious punctuation errors have been repaired4 ,the book contains some inconsistent hyphenation which has been left as printed4 p4 xi4 7,,toc7 constructiou changed to construction p4 xiv4 7,,toc7 ,the ,prodution of ,motion changed to ,the ,production of ,motion p4 #bg4 para4 #gc4 thick permament magnets changed to thick permanent magnets p4 #ii4 para #bec4 wabble may be a typo for wobble but has been left on the off chance that this could be what was intended4 p4 #aah4 ,fig #ia4 ,the final column has been scored through but appears to read ,,cu to ,,zn p4 #aca4 para4 #cbd1 #cbe4 ,german-silver ,wire1 ,g-s ,w used here but previously ,g ,s ,w used4 p4 #afd4 para #cie4 circuit in closed changed to circuit is closed p4 #aff4 para #cih4 core inside of the c l changed to core inside of the coil after checking original scans4 p4 #afi-agj4 ,it appears that a word has been omitted across the page break4 ,the copper washer1 ,c ,w1 be used4 has been changed to ,the copper washer1 ,c ,w1 should be used44 7,alternative words are possible67 p4 #baa4 ,no4 #ce4 #e-af in4 changed to #e_/af in4 p4 #bac4 ,no4 #ib1 #ic4 #e-af in4 changed to #e_/af in4 p4 #bad4 ,no4 #if4 and ,no4 #ig4 #e-af in4 changed to #e_/af in4 p4 #baf4 ,entry for ,coulomb moved from end of ,c to above ,current4