99 99 99 99 99 ,transcriber's ,note3 ,the original publication has been replicated faithfully except as shown in the ,,transcriber',s ,,amendments at the end of the text4 ,this etext presumes a mono-spaced font on the user's device1 such as ,courier ,new4 ,words in italics are indicated like this4 ,text emphasized with bold characters or other treatment is shown like this4 ,superscripts are indicated like this3 ,sta ,maria4 ,subscripts are indicated like this3 ,h#b,o4 ,footnotes are located near the end of the work4 99 99 99 99 99 ,illustration ,illustration ,,the ,,thought ,,is ,,in ,,the ,,question ,,the ,,information ,,is ,,in ,,the ,,answer ,,hawkins ,,electrical ,,guide ,,number ,,one ,,questions ,,answers ,,illustrations ,a ,,progressive ,,course ,,of ,,study ,,for ,,engineers1 ,,electricians1 ,,students ,,and ,,those ,,desiring ,,to ,,acquire ,a ,,working ,,knowledge ,,of ,,electricity ,,and ,,its ,,applications ,a ,,practical ,,treatise by ,,hawkins ,,and ,,staff ,,theo4 ,,audel ,,co4 #gb ,,fifth ,,ave4 ,,new ,,york4 ,,copyrighted1 #aiad1 ,,by ,,theo4 ,,audel ,,co41 ,,new ,,york4 ,printed in the ,united ,states4 ,,preface ,the word 8guide0 is defined as3 ,one who leads another in any path or direction2 a person who shows or points out the way1 especially by accompanying or going before2 more particularly1 one who shows strangers or tourists about2 a conductor2 leader1 as 8let us follow our guide40 ,this book1 or 8,guide10 is so called because it leads or points out the way to the acquirement of a theoretical and practical knowledge of ,electricity4 ,there are several guides1 each covering in detail a certain phase of the broad subject of ,electricity and leading the reader progressively1 and in such a way1 that he easily grasps1 not only the simple fundamental facts1 but the more complex problems1 encountered in the study of ,electricity4 ,this is accomplished by the aid of a very large number of illustrations1 together with specific explanations1 worded in concise and simple language4 ,the ,guides are written partly in the question and answer form1 as this style of presentation has met with hearty approval1 not only from those of limited education1 but also from the better informed4 ,where recourse is had to the question and answer form1 the special aim of the author has been to give short and direct answers1 in such plain language as to preclude a misconception of the meaning4 ,with this in view1 the answer gives simply the information sought by the question4 ,the answer is limited to one paragraph so that the reader may concentrate upon the fact or facts demanded by the question4 ,any enlargement of the answer or specific explanations of items contained therein1 are presented in separate paragraphs printed1 in smaller type4 ,with this plan of separating the answer1 as it were1 from items of secondary importance1 and making it short and simple1 its content is more forcibly impressed upon the mind of the reader4 ,in a text book1 it is necessary to illustrate and explain the various species of commercial apparatus met with in practice1 and in this connection the ,publishers desire to call attention to the manner in which the author has treated what may be classed as the 8descriptive matter40 ,contrary to the usual custom of giving descriptions of commercial machines in the main text1 where they would occupy considerable space1 to the exclusion of the more important matter1 all such descriptions are placed in small type directly under the illustrations1 leaving space for an adequate presentation of the underlying principles1 theories1 and for the large amount of practical information that is essential to obtain a general knowledge of ,electricity and its numerous applications4 ,credit is largely due to ,frank ,d4 ,graham1 ,b4,s41 ,m4,s4 7,princeton ,university71 and ,m4,e4 7,stevens ,institute71 practical engineer1 for the authorship of the ,guides1 and for original sketches illustrating electrical principles and construction4 ,,table ,,of ,,contents ,,guide ,,no4 #a4 ,,introductory ,,chapter ,,signs ,,and ,,symbols ,,electricity #a to #d ,nature and source--kinds of electricity3 static1 current1 dynamic1 radiated1 positive1 negative1 atmospheric1 frictional1 resinous1 vitreous4 ,,static ,,electricity #e to #bf ,electrical attraction and repulsion--the charge--distribution of the charge--free and bound electricity--conductors and insulators--electroscopes--gold leaf electroscope--electric screens--electrification by induction--nature of the induced charge--the electrophorus--condensers2 ,leyden jar--electric machines--action of ,toepler-,holtz machine--,wimshurst machines4 ,,the ,,electric ,,current #bg to #cd ,volt--ampere--ohm--,ohm's law--production of the electric current--current strength--voltage drop in an electric current4 ,,primary ,,cells #ce to #fg ,the word 8battery0--action of cell--chemical changes2 polarization--effects of polarization--methods of depolarization-- depolarizers--depolarizer bag--,volta's contact law--contact series of metals--laws of chemical action in cell-- requirements of a good cell--single and two fluid cells-- the ,leclanche cell--,fuller bichromate cell--the ,edison cell--,grenet bichromate cell--,daniell cell--directions for making a ,daniell cell--gravity cells--,daniell gravity cell--so-called 8dry0 cells--points relating to dry cells-- care of cells--cleanliness--separating the elements--creeping-- amalgamated zinc--battery connections4 ,,conductors ,,and ,,insulators #fh to #gd ,the so-called 8non-conductors0--table of conductors and insulators--mode of transmission--effect of heat--heating effect of the current--insulators--impregnating compounds-- water as a conductor4 ,,resistance ,,and ,,conductivity #ge to #hb ,standard of resistance--conductivity of metals and liquids--effect of heat--laws of electrical resistance-- conductivity--specific conductivity--divided circuits4 ,,electrical ,,and ,,mechanical ,,energy #hc to #ib ,definitions3 energy1 matter1 molecule1 work1 foot-pound1 volt-coulomb1 ampere-hour1 power1 horse power1 watt1 kilowatt1 watt-hour--mechanical equivalent of heat--,british thermal unit--electrical horse power--the farad4 ,,effects ,,of ,,the ,,current #ic to #ajd ,thermal effect--use of heat from the current--magnetic effect--chemical effect--electrolysis--electro-chemical series--electric osmose--electric distillation--muscular contractions--electroplating--electrotyp ing4 ,,magnetism #aje to #abd ,two kinds of magnetism--nature of each--poles--magnetic field--magnetic force--magnetic circuit--magnetic flux--the ,maxwell--the ,gauss--magnetic effect of the current--corkscrew rule--solenoids--permeability--magnetic saturation--magnetomotive force--reluctance--analogy between electric and magnetic circuits--hystereses--residual magnetism4 ,,electromagnetic ,,induction #abe to #acf ,faraday's discovery--,faraday's machine--,faraday's principle-- line of force--induction of current--laws of electromagnetic induction--rules for direction of induced current--,fleming's rule--,ampere's rule--the palm rule--self-induction4 ,,induction ,,coils #acg to #aed ,self-induction--mutual induction--primary induction coils-- secondary induction coils--plain secondary induction coils--secondary induction coils with vibrator and condenser2 cycle of action--magnetic vibrators--vibrator adjustment-- table of induction coil dimensions--table of sparking distances in air--points relating to induction coils--wiring diagram4 ,,the ,,dynamo #aee to #afj ,operation--essential parts--field magnets--armature-- construction of dynamos--parts2 bed plate1 field magnets1 armature1 commutator1 brushes4 ,,the ,,dynamo3 ,,basic ,,principles #afa to #agj ,definitions--essential parts--elementary alternator-- operation--direction of induced current--application of ,fleming's rule--cycle of operation--the sine curve2 its construction and application4 ,,the ,,dynamo3 ,,current ,,commutation #aga to #ahj ,how the current is produced--how direct current is obtained-- the commutator--inductors--8continuous current0--action of four coil elementary dynamo--conditions for steadiness of the current4 ,,classes ,,of ,,dynamo #aha to #aih ,classification--bipolar and multi-polar dynamos--difference between dynamo and magneto--self-exciting dynamo--the series dynamo--regulation of series dynamo2 difficulties experienced-- the shunt dynamo--adaptation--operation--character istic-- regulation--the compound dynamo--service intended for-- regulation--over compounding--usual degree of over compounding-- short shunt--long shunt--voltage of short and long shunt machines --separately excited dynamos--,dobrowolski three wire dynamo4 ,,field ,,magnets #aii to #bbj ,object--essential parts--classes of field magnet--multi-polar field magnets--construction--choice of materials--design--pole pieces--eddy current--laminated fields--construction to reduce reluctance of the magnetic circuit--magnetizing coils--methods of winding--coil ends--insulation--attachment of coils--coil connections--heating--ventilation4 ,,introductory ,,chapter ,the subject matter of this work relates to one of the secrets of creation which appears to have been intended at the very beginning to be 8sought out40 ,this idea is expressed in a certain saying copied three or four thousand years ago by the men of ,hezekiah1 ,king of ,judah3 from ,solomon's proverbs3 8,it is the glory of ,god to conceal a thing3 ,but the glory of ,kings 7i4e41 wise men71 to search out a matter40 ,in all that may be said hereafter through the work1 it is admitted that the results recorded are the determinations of experiments performed by an incredible number of searchers extending through many ages4 ,these inquiries have been pursued with a generous rivalry which has permitted discovery to be added to discovery1 until the sum total has been wrought into such exactness that it has been thoughtlessly stated that there is nothing more1 save its application4 ,it may be well1 however1 to state a few fundamental facts relating to electricity3 #a1 ,electricity and magnetism are one and the same thing2 #b1 what is really known about it has come as a discovery and not as an invention4 ,thus1 we say the intrepid explorer discovered the pole1 not that he invented it4 ,so with electricity it has been a subject of discovery while its many applications to useful purposes have been veritable inventions2 #c1 the earth itself is a magnet4 ,this last is shown by the fact that the earth affects a magnet just as one magnet affects another4 ,magnets are bodies1 either natural or artificial1 which have the property of attracting iron1 and the power1 when freely suspended1 of taking a direction toward the poles of the earth4 ,the natural magnet is sometimes called the loadstone4 ,this word is said to be derived from loedan1 a ,saxon word which signifies to guide4 ,it is an oxide of iron of a peculiar character1 found occasionally in beds of iron ore4 ,though commonly met with in irregular masses only a few inches in diameter1 however1 loadstones of larger sizes are sometimes found4 ,by means of simple experiments it may be ascertained that the magnet has the following general properties1 viz3 #a1 power of attraction2 #b1 power of repulsion2 #c1 power of communicating magnetism to iron or steel2 #d1 polarity1 or the power of taking a direction toward the poles of the earth2 #e1 power of inclining itself toward a point below the horizon4 ,speaking generally we may say1 that magnetism is a department of electrical science which treats of the properties and effects of the magnet4 ,the same terms are also used to denote the unknown cause of magnetic phenomena1 as when we speak of magnetism as excited1 imparted1 and so on4 ,lightning and the ,northern ,lights are displays of electricity on a grand scale4 ,electricity is a term derived from the ,greek word for amber1 that being the substance in which a property of the agent now denominated electricity was first observed4 ,the ancient ,greek philosophers were acquainted with the fact that amber1 when rubbed1 acquired the property of attracting light bodies2 hence the effect was denominated electrical and in later times1 the term electricity has been used to denote the unknown cause of electrical phenomena1 and broadly the science which treats of electrical phenomena and their causes4 ,electricity1 whatever it may prove to be1 is not matter nor is it energy2 it is however a means or medium of transmitting energy4 ,if electricity is to transmit or convey energy along a wire1 this energy must be imparted to the electricity from some external source1 that is to say1 before electricity can perform any work it must be set in motion1 against more or less resistance4 ,this involves that pressure must be applied1 and to obtain this pressure1 energy must be expended from some external source4 ,accordingly1 in electrical engineering1 the first principle to be grasped is that of energy4 ,without the expenditure of energy no useful work can be accomplished4 ,energy may be defined as the capacity for performing work4 ,although electricity is not energy1 electricity under pressure is a form of energy spoken of as electrical energy4 ,in an expenditure of energy in this form1 the electricity acts simply as a transmission agent or medium to transmit the energy imparted to it in causing it to flow4 ,in a similar manner1 steam acts as a transmission agent or medium to transmit the heat energy of the coal to the steam engine1 where it is converted into mechanical energy4 ,as just stated1 electricity under pressure is a form of energy1 and its generation is simply a transformation of energy from one form into another4 ,usually1 mechanical energy is converted into electrical energy1 and a dynamo is employed for effecting the transformation4 ,in transforming the mechanical energy of waterfalls into electric energy1 this natural power of water due to its weight and motion is first converted into rotary motion by a turbine or water wheel1 and then converted into electric energy by a dynamo1 or an alternator4 ,all dynamos are but machines for converting into electric energy the energy which is given to them by some prime mover1 as a steam engine1 a gas engine1 by hydraulic or even by wind power4 ,all electric motors are merely machines for reconverting the electric energy which they receive by means of the conducting wires or mains1 into mechanical energy4 ,all electric lamps are contrivances for converting into luminous energy a percentage of the electric energy that is supplied through the mains4 ,potential and ,kinetic ,energy4--,potential energy is the capacity for performing work which a body possesses by virtue of its position4 ,kinetic energy is the capacity for performing work which a body possesses by virtue of its motion4 ,it must be evident that position or motion given to a body enables it to perform work4 ,in the first instance1 for example1 a heavy weight at the top of a high tower possesses potential energy4 ,a ten pound weight supported one foot above a plane has ten foot pounds of potential energy4 ,the flywheel of a steam engine in motion is an example of a body possessing kinetic energy4 ,some of this kinetic energy which was stored up in the fly wheel during the working stroke is expended in moving the engine over the 8dead center10 and any other point where no torque is produced by the pressure on the piston4 ,chemical ,energy can be converted into electric energy to a limited extent by means of the electric battery1 but the cost of this energy is so high that it is commercially feasible only where small quantities are required1 and the cost of production is secondary to the convenience of generation1 as for signalling purposes1 the operation of bells and annunciators1 etc4 ,the chemical energy of coal and other fuels cannot be directly converted into electric energy4 ,for power producing purposes1 the chemical energy of a fuel is first converted into heat by combustion1 and the heat thus obtained converted into mechanical energy by some form of heat engine1 and the mechanical energy subsequently transformed into electric energy in an electric generator4 ,energy cannot be created or destroyed4 ,this is the law known as the conservation of energy which has been built up by ,helmholtz1 ,thomson1 ,joule and others4 ,it teaches further1 that energy can be transmitted from one body to another or transformed in its manifestations4 ,energy may be dissipated1 that is1 converted into a form from which it cannot be recovered1 as is the case with the great percentage of heat escaping from the exhaust nozzle of a locomotive or in the circulating water of a steamship1 but the total amount of energy in the universe1 it is argued1 remains constant and invariable4 ,following this law comes the doctrine of the conservation of electricity as announced by ,lippman1 being undoubtedly the outcome of the ideas of ,maxwell and of ,faraday as to the nature of electricity4 ,according to their doctrine1 electricity cannot be created or destroyed1 although its distribution may be altered4 ,lippman states that every charge of electricity has an opposite and equal charge somewhere in the universe more or less distributed2 that is1 the sum of positive charges is always equal to the sum of negative charges4 ,in altering the distribution of electricity1 we may cause more to appear at one place and less at another1 or may change it from the condition of rest to that of motion1 or may cause it to spin round in whirlpools or vortices1 which themselves can attract or repel other vortices4 ,according to this view all our electrical machines and batteries are merely instruments for altering the distribution of electricity by moving some of it from one place to another1 or for causing electricity1 when accumulated or heaped1 together in one place1 to do work in returning to its former distribution4 ,electrical engineering has developed largely and widely within a very short time and its many applications has created so great a demand for various kinds of electrical apparatus1 that their manufacture forms one of the leading industries4 ,electricity is very valuable as a medium for the transmission of energy1 especially to long distances2 it is also used to great advantage in lighting1 being free from the disagreeable properties of gas or oil4 ,again1 electricity finds various applications1 in extracting gold from the ore1 pumping and ventilation of mines1 traction1 telephone1 telegraph1 electroplating1 therapeutics1 etc4 ,these few1 of its many applications will perhaps serve to indicate the far reaching interest and importance of electricity1 and possibly help to kindle in the student something of the eagerness in his work and enthusiasm without which he will fail to do justice either to his calling or to himself4 ,,signs ,,and ,,symbols ,the following signs1 symbols and abbreviations are almost universally employed in descriptive and technical works on electrical subjects4 ,although1 in the arrangement of the ,guides1 the direct current and alternating current matter has been kept separate1 it is perhaps advisable in the case of signs and symbols1 to combine those relating to the alternating current with the direct current and other symbols1 making a single table1 rather than have them scattered throughout the work4 #a4 ,fundamental4 l1 ,length4 cm4 centimeter2 in41 or inch1 ft4 or foot4 ,m1 ,mass4 gr4 mass of #a gramme kg4 #a kilogramme4 ,t1 t1 ,time1 s second4 #b4 ,derived ,geometric4 ,s1 s1 ,surface4 ,e1 ,volume4 1 1 ,angle4 #c4 ,derived ,mechanical4 v1 ,velocity4 1 ,angular velocity4 r1 ,momentum4 a1 ,acceleration4 g1 ,acceleration due to gravity #cb4b feet per second4 ,f1 f1 ,force4 ,w1 ,work4 ,p1 ,power4 1 ,dyne4 1 ,ergs1 ft4 lb41 ,foot pound4 ,h4,p41 h4p4 ,horse power4 ,i4,h4,p41 ,indicated horse power4 ,b4,h4,p41 ,brake horse power4 ,e4,h4,p41 ,electrical horse power4 ,j1 ,joule's equivalent4 p1 ,pressure4 ,k1 ,moment of inertia4 #d4 ,derived ,electrostatic4 e1 ,pressure difference4 i1 ,current4 r1 ,resistance4 q1 ,quantity4 c1 ,capacity4 sc1 ,specific inductive capacity4 #e4 ,derived ,magnetic4 m1 ,strength of pole4 ,script ,j1 ,intensity of magnetization4 ,script ,m1 ,magnetic moment4 ,script ,h1 ,horizontal intensity of earth's magnetism4 ,script ,h1 ,field intensity4 1 ,magnetic flux4 ,script ,b1 ,magnetic flux density or magnetic induction4 ,script ,h1 ,magnetizing force4 ,script ,f1 ,magnetomotive force4 ,script ,r1 ,reluctance1 magnetic resistance4 1 ,magnetic permeability4 1 ,magnetic susceptibility4 1 ,reluctivity 7specific magnetic resistance74 #f4 ,derived ,electromagnetic4 ,r1 ,resistance1 ohm4 ,o1 do1 megohm4 ,e1 ,volt1 pressure4 ,eim ,impressed pressure4 ,ea1 ,eo ,active pressure2 ohmic drop4 ,ev ,virtual pressure4 ,emax ,maximum pressure4 ,eav ,average pressure4 ,eef ,effective pressure4 ,ei ,inductance pressure4 ,ec ,capacity pressure4 ,u1 ,difference of pressure1 volt4 ,i1 ,intensity of current1 ampere4 ,iim ,impressed current4 ,ia ,active current4 ,iv ,virtual current4 ,imax ,maximum current4 ,iav ,average current4 ,ief ,effective current4 ,q1 ,quantity of electricity1 ampere-hour2 coulomb4 ,c1 ,capacity1 farad4 ,w1 ,electric energy1 watt-hour2 ,joule4 ,p1 ,electric power1 watt2 kilowatt4 p1 ,resistivity 7specific resistance7 ohm centimeter4 ,g1 ,conductance1 mho4 1 ,conductivity 7specific conductivity74 ,y1 ,admittance1 mho4 ,z1 ,impedance1 ohm4 ,x1 ,reactance1 ohm4 ,xi ,inductance reactance4 ,xc ,capacity reactance4 ,b1 ,susceptance1 mho4 ,l1 ,inductance 7coefficient of ,induction71 henry4 v1 ,ratio of electromagnetic to electrostatic unit of quantity #cajaj centimeters per second approximately4 #g4 ,symbols in general use4 ,d1 ,diameter4 r1 ,radius4 t1 ,temperature4 1 ,deflection of galvanometer needle4 ,n1 n1 ,number of anything4 1 ,circumference diameter #c4adaeib4 1 #b;f #f4bhca frequency1 in alternating current4 1 f1 ,frequency1 periodicity1 cycles per second4 1 ,phase angle4 ,g1 ,galvanometer4 ,s1 ,shunt4 ,n1 n1 ,north pole of a magnet4 ,s1 s1 ,south pole of a magnet4 ,a4,c4 ,alternating current4 ,d4,c4 ,direct current4 ,p4,d4 ,pressure difference4 ,p4,f4 ,power factor4 ,c4,g4,s4 ,centimeter1 ,gramme1 ,second system4 ,b4,s4 ,brown ,sharpe wire gauge4 ,b4,w4,g4 ,birmingham wire gauge4 ,r4p4m4 ,revolutions per minute4 ,c4,p4 ,candle power4 --o--1 ,incandescent lamp4 --,x--1 ,arc lamp4 ,symbol3 ,condenser ,,or ,symbol3 ,condenser ,condenser4 ,symbol3 ,battery of cells ,battery of cells4 ,symbol3 ,dynamo ,dynamo1 or direct current motor4 ,symbol3 ,alternator ,alternator1 or alternating current motor4 ,symbol3 ,converter ,converter4 ,symbol3 ,static transformer ,static transformer4 ,symbol3 ,inductive resistance ,inductive resistance4 ,symbol3 ,non-inductive resistance ,non-inductive resistance4 ,,chapter ,i ,,electricity ,nature and ,source of ,electricity4--,what is electricity8 ,this is a question that is frequently asked1 but has not yet been satisfactorily answered4 ,it is a force1 subject to control under well known laws4 ,while the nature and source of electricity still remain a mystery1 many things about it have become known1 thus1 it is positively assured that electricity never manifests itself except when there is some mechanical disturbance in ordinary matter4 ,the true nature of electricity has not yet been discovered4 ,many think it a quality inherent in nearly all the substances1 and accompanied by a peculiar movement or arrangement of the molecules4 ,some assume that the phenomena of electricity are due to a peculiar state of strain or tension in the ether which is present everywhere1 even in and between the atoms of the most solid bodies4 ,if the latter theory be the true one1 and if the atmosphere of the earth be surrounded by the same ether1 it may be possible to establish these assumptions as facts4 ,the most modern supposition regarding this matter1 by ,maxwell1 is that light itself is founded on electricity1 and that light waves are merely electromagnetic waves4 ,the theory 8that electricity is related to1 or identical with1 the luminiferous ether10 has been accepted by the most prominent scientists4 ,but while electricity is still a mystery1 much is known about the laws governing its phenomena4 ,man has mastered this mighty force and made it his powerful servant2 he can produce it and use it4 ,electricity1 it is also conceded1 is without weight1 and1 while it is without doubt1 one and the same1 it is for convenience sometimes classified according to its motion1 as3 #a4 ,static electricity1 or electricity at rest2 #b4 ,current electricity1 or electricity in motion2 #c4 ,magnetism1 or electricity in rotation2 #d4 ,electricity in vibration 7radiation74 ,other useful divisions are3 #a4 ,positive2 #b4 ,negative electricity2 #c4 ,static2 #d4 ,dynamic electricity4 ,static ,electricity4--,this is a term employed to define electricity produced by friction4 ,it is properly employed in the sense of a static charge which shows itself by the attraction or repulsion between charged bodies4 ,when static electricity is discharged1 it causes more or less of a current1 which shows itself by the passage of sparks or a brush discharge2 by a peculiar prickling sensation2 by a peculiar smell due to its chemical effects2 by heating the air or other substances in its path2 and sometimes in other ways4#a ,current ,electricity4--,this may be defined as the quantity of electricity which passes through a conductor in a given time--or1 electricity in the act of being discharged1 or electricity in motion4 ,an electric current manifests itself by heating the wire or conductor2 by causing a magnetic field around the conductor and by causing chemical changes in a liquid through which it may pass4 ,dynamic ,electricity4--,this term is used to define current electricity to distinguish it from static electricity4 ,radiated ,electricity4--,electricity in vibration4 ,where the current oscillates or vibrates back and forth with extreme rapidity1 it takes the form of waves which are similar to waves of light4 ,positive electricity4--,this term expresses the condition of the point of an electrified body having the higher energy from which it flows to a lower level4 ,the sign which denotes this phase of electric excitement is 2 all electricity is either positive or negative4 ,negative ,electricity4--,this is the reverse condition to the above and is expressed by the sign or symbol -4 ,these two terms are used in the same sense as hot and cold4 ,atmospheric ,electricity is the free electricity of the air which is almost always present in the atmosphere4 ,its exact cause is unknown4 ,the phenomena of atmospheric electricity are of two kinds2 there are the well known manifestations of thunderstorms2 and there are the phenomena of continual slight electrification in the air1 best observed when the weather is fine2 the ,aurora constitutes a third branch of the subject4 ,illustration3 ,,fig4 #a4--,the electric eel4 ,there are several species inhabiting the water1 and which have the power of producing electric discharges by certain portions of their organism4 ,the best known of these are the ,torpedo1 the ,gymnotus1 and the ,silurus1 found in the ,nile and the ,tiger4 ,the ,electric ,ray1 of which there are three species inhabiting the ,mediterranean and ,atlantic is provided with an electric organ on the back of its head1 as shown in the illustration4 ,this organ consists of lamin composed of polygonal cells to the number of #hjj or #ajjj1 or more1 supplied with four large bundles of nerve fibres2 the under surface of the fish is -1 the upper 4 ,in the ,surinam eel1 the electric organ goes the whole length of the body along both sides4 ,it is able to give a very severe shock1 and is a formidable antagonist when it has attained its full length of #e or #f feet4 ,frictional ,electricity is that produced by the friction of one substance against another4 ,resinous ,electricity4--,the kind of electricity produced upon a resinous substances such as sealing wax1 resin1 shellac1 rubber or amber when rubbed with wool or fur4 ,resinous electricity is negative electricity4 ,vitreous ,electricity4--,a term applied to the positive electricity developed in a glass rod by rubbing it with silk4 ,this electric charge will attract to itself bits of pith or paper which have been repelled from a rod of sealing wax or other resinous substance which had been rubbed with wool or fur4 ,,chapter ,,ii ,,static ,,electricity ,static electricity may be defined simply as electricity at rest2 the term properly applies to an isolated charge of electricity produced by friction4 ,the presence of static electricity manifests itself by attraction or repulsion4 ,electrical ,attraction and ,repulsion4--,when a glass rod1 or a stick of sealing wax or shellac is held in the hand and rubbed with a piece of flannel or cat skin1 the parts will be found to have the property of attracting bodies1 such as pieces of silk1 wool1 feathers1 gold leaf1 etc42 they are then said to be electrified4 ,in order to ascertain whether bodies are electrified or not1 instruments called electroscopes are used4 ,there are two opposite kinds of electrification3 #a4 ,positive2 #b4 ,negative4 ,franklin called the electricity excited upon glass by rubbing it with silk positive electricity1 and that produced on resinous bodies by friction with wool or fur1 negative electricity4 ,the electricity developed on a body by friction depends on the rubber as well as the body rubbed4 ,thus glass becomes negatively electrified when rubbed with catskin1 but positively electrified when rubbed with silk4 ,illustration3 ,,figs4 #b and #c4--,pith ball pendulum or electroscope2 the figures illustrate also electrical attraction and repulsion4 ,the nature of the electricity set free by friction depends on the degree of polish1 the direction of the friction1 and the temperature4 ,if two glass discs of different degrees of polish be rubbed against each other1 that which is most polished is positively1 and that which is least polished is negatively electrified4 ,if two silk ribbons of the same kind be rubbed across each other1 that which is transversely rubbed is negatively and the other positively electrified4 ,if two bodies of the same substance1 of the same polish1 but of different temperatures1 be rubbed together1 that which is most heated is negatively electrified4 ,generally speaking1 the particles which are most readily displaced are negatively electrified4 ,in the following list1 which is mainly due to ,faraday1 the substances are arranged in such order that each becomes positively electrified when rubbed with any of the bodies following1 but negatively when rubbed with any of those which precede it3 #a4 ,catskin4 #b4 ,flannel4 #c4 ,ivory4 #d4 ,rock crystal4 #e4 ,glass4 #f4 ,cotton4 #g4 ,silk4 #h4 ,the hand4 #i4 ,wood4 #aj4 ,metals4 #aa4 ,caoutchouc4 #ab4 ,sealing wax4 #ac4 ,resin4 #ad4 ,sulphur4 #ae4 ,gutta-percha4 #af4 ,gun cotton4 ,the ,charge4--,the quantity of electrification of either kind produced by friction or other means upon the surface of a body is spoken of as a charge1 and a body when electrified is said to be charged4 ,it is clear that there may be charges of different values as well as of either kind4 ,when the charge of electricity is removed from a charged body it is said to be discharged4 ,good conductors of electricity are instantaneously discharged if touched by the hand or by any conductor in contact with the ground1 the charge thus finding a means of escaping to earth4 ,a body that is not a good conductor may be readily discharged by passing it rapidly through the flame of a lamp or candle2 for the flame instantly carries off the electricity and dissipates it in the air4 ,distribution of the ,charge4--,when an insulated sphere of conducting material is charged with electricity1 the latter passes to the surface of the sphere1 and forms there an extremely thin layer4 ,the distribution of the charge then1 depends on the extent of the surface and not on the mass4 ,boit proved that the charge resides on the surface by the following experiment3 ,a copper ball was electrified and insulated4 ,two hollow hemispheres of copper of a larger size1 provided with glass handles1 were then placed near the sphere1 as in fig4 #d4 ,so long as they did not touch the sphere1 the charge remained on the latter1 but if the hemispheres touched the inner sphere1 the whole of the electricity passed to the exterior1 and when the hemispheres were separated and removed the inner globe was found to be completely discharged4 ,the distribution of a charge over an insulated sphere of conducting material is uniform1 provided the sphere is remote from all other conductors and electrified bodies4 ,illustration3 ,,fig4 #d4--;,boit's experiment which proved that the charge resides on the surface4 ,figs4 #e to #h show1 by the dotted lines1 the distribution of a charge for bodies of various shapes4 ,fig4 #f shows that for elongated bodies1 the charge collects at the ends4 ,the effects of points is illustrated in fig4 #i2 when a charged body is provided with a point as here shown1 the current accumulates at the point to such a high degree of density that it passes off into the air1 and if a lighted candle be held in front of the point1 the flame will be visibly blown aside4 ,fig4 #aj shows an electric windmill or experimental device for illustrating the escape of electricity from points4 ,it consists of a vane of several pointed wires bent at the tips in the same direction1 radiating from a center which rests upon a pivot4 ,when mounted upon the conductor of an electrostatic machine1 the vane rotates in a direction opposite that of the points4 ,the movement of the vane is due to the repulsion of the electrified air particles near the points and the electricity on the points themselves4 ,the motion of the air is called electric wind4 ,this device is also called electric flyer1 and electric whirl4 ,illustration3 ,,figs4 #e to #h4--;,illustrating the distribution of the charge on conductors of various shapes4 8,free0 and 8,bound0 ,electricity4--,these terms may be defined as follows3 ,the expression free electricity relates to the ordinary state of electricity upon a charged conductor1 not in the presence of a charge of the opposite kind4 ,a free charge will flow away to the earth if a conducting path be provided4 ,a charge of electricity upon a conductor is said to be bound1 when it is attracted by the presence of a neighboring charge of the opposite kind4 ,conductors and ,insulators4--,the term conductors is applied to those bodies which readily allow electricity to flow through them1 in distinction from insulators or so-called non-conductors1 which practically allow no flow of electricity4 ,strictly speaking1 there is no substance which will prevent the passage of electricity1 hence1 the term non-conductors1 though extensively used1 is not correct4 ,illustration3 ,,fig4 #i4--;,experiment to illustrate the effect of pointed conductors4 ,illustration3 ,,fig4 #aj4--;,electric windmill which operates by the reaction due to the escape of the electric charge from the points4 ,electroscopes4--,these are instruments for detecting whether a body be electrified or not1 and indicating also whether the electrification be positive or negative4 ,the earliest electroscope devised consisted of a stiff straw balanced lightly upon a sharp point2 a thin strip of brass or wood1 or even a goose quill1 balanced upon a sewing needle will serve equally well4 ,another form of electroscope is the pith ball pendulum1 shown in figs4 #b and #c4 ,when an electrified body is held near the electroscope it is attracted or repelled thus indicating the presence and nature of the charge4 ,gold ,leaf ,electroscope4--,this form of electroscope1 which is very sensitive1 was invented by ,bennet4 ,its operation depends on the fact that like charges repel each other4 ,illustration3 ,,fig4 #aa4--;,gold leaf electroscope2 it consists of two strips of gold foil suspended from a brass rod within a glass jar4 ,used to detect the presence and sign of an electric charge4 ,the gold leaf electroscope as shown in fig4 #aa1 is conveniently made by suspending the two narrow strips of gold leaf within a wide mouthed glass jar1 which both serves to protect them from draughts of air and to support them from contact with the ground4 ,a piece of varnished glass tube is pushed through the cork1 which should be varnished with shellac or with paraffin wax4 ,through this passes a stiff brass wire1 the lower end of which is bent at a right angle to receive the two strips of gold leaf1 while the upper end is attached to a flat plate of metal1 or may be furnished with a brass knob4 ,when kept dry and free from dust it will indicate excessively small quantities of electricity4 ,a rubbed glass rod1 even while two or three feet from the instrument1 will cause the leaves to repel one another4 ,if the knob be brushed with only a small camel's hair brush1 the slight friction produces a perceptible effect4 ,with this instrument all kinds of friction can be shown to produce electrification4 ,the gold leaf electroscope can be further used to indicate the kind of electricity on an excited body4 ,thus1 if a piece of brown paper be rubbed with a piece of india rubber1 the nature of the charge is determined as follows3 ,illustration3 ,,fig4 #ab4--;,distribution of electrification on a charged hollow sphere4 ,if an insulated conductor d be inserted through the opening in the sphere and brought in contact with the interior surface and afterwards carefully removed1 it will be found1 by testing with the gold leaf electroscope1 that it has received no charge4 ,if touched to the outside1 however1 the conductor will receive part of the charge4 ,first charge the gold leaves of the electroscope by touching the knob with a glass rod rubbed on silk4 ,the leaves diverge1 being electrified with positive electrification4 ,when they are thus charged the approach of a body which is positively electrified will cause them to diverge still more widely2 while1 on the approach of one negatively electrified1 they will tend to close together4 ,if now the brown paper be brought near the electroscope1 the leaves will be seen to diverge more1 proving the electrification of the paper to be of the same kind as that with which the electroscope is charged4 ,the gold leaf electroscope will also indicate roughly the amount of electricity on a body placed in contact with it1 for the gold leaves open out more widely when the quantity of electricity thus imparted to them is greater4 ,illustration3 ,,figs4 #ac and #ad4--;,electrification produced by rubbing dissimilar bodies together and then separating them4 ,if the insulated glass and leather discs ,a and ,b be rubbed together1 but not separated1 no signs of electrification can be detected2 but if the discs be drawn apart a little distance the space between them is found to be an electric field1 and as they separate farther and farther1 electric forces will be found to exist in more and more of the surrounding space1 the electrification being indicated by 8lines of force40 ,it should be noted that work has to be done in separating the charged discs to overcome the attraction which tends to hold them together4 ,the stress indicated by the lines of force consists of a tension or pull in the direction of their length and a pressure or thrust at right angles to that direction4 ,electric ,screens4--,that the charge on the outside of a conductor always distributes itself in such a way that there is no electric force within the conductor was first proved experimentally by ,faraday4 ,he covered a large box with tin foil and went inside with the most delicate electroscopes obtainable4 ,faraday found that the outside of the box could be charged so strongly that long sparks would fly from it without any electrical effects being observable anywhere inside the box4 ,to repeat the experiment in modified form1 let an electroscope be placed beneath a bird cage or wire netting1 as in fig4 #ae4 ,let charged rods or other powerfully charged bodies be brought near the electroscope outside the cage4 ,the leaves will be found to remain undisturbed4 ,illustration3 ,,fig4 #ae4--,the electric screen4 ,a screen of wire gauze surrounding a delicate electrical instrument will protect it from external electrostatic induction4 ,electrification by ,induction4--,an insulated conductor1 charged with either kind of electricity1 acts on bodies in a neutral state placed near it in a manner analogous to that of the action of a magnet on soft iron2 that is1 it decomposes the neutral electricity1 attracting the opposite and repelling the like kind of electricity4 ,the action thus exerted is said to take place by influence or induction4 ,the phenomenon of electrification by induction may be demonstrated by the following experiment3 ,in fig4 #af1 let the ebonite rod be electrified by friction and slowly brought toward the knob of the gold leaf electroscope4 ,the leaves will be seen to diverge1 even though the rod does not approach to within a foot of the electroscope4 ,illustration3 ,,fig4 #af4--;,experiment to illustrate electrostatic induction4 ,the leaves will diverge1 even though the charged ebonite rod does not approach to within a foot of the electroscope4 ,this experiment shows that the mere influence which an electric charge exerts upon a conductor placed in its vicinity is able to produce electrification in that conductor4 ,this method of producing electrification is called electrostatic induction4 ,as soon as the charged rod is removed the leaves will collapse1 indicating that this form of electrification is only a temporary phenomenon which is due simply to the presence of the charged body in the neighborhood4 ,nature of the ,induced ,charge4--,this is shown by the experiment illustrated in fig4 #ag4 ,let a metal ball ,a be charged by rubbing it with a charged rod1 and let it then be brought near an insulated metal cylinder ,b which is provided with pith balls on strips of paper ,c1 ,d1 ,e1 as shown4 ,the divergence of ,c and ,e will show that the ends of ,b have received electrical charges because of the presence of ,a1 while the failure of ,d to diverge will show that the middle of ,b is uncharged4 ,further1 the rod which charged ,a will be found to repel ,c but to attract ,e4 ,illustration3 ,,fig4 #ag4--;,experiment illustrating the nature of an induced charge4 ,the apparatus consists of a metal ball and cylinder1 both mounted on insulated stands1 pith balls being placed on the cylinder at points ,c1 ,d1 and ,e4 ,from these experiments1 the conclusion is that when a conductor is brought near a charged body1 the end away from the inducing charge is electrified with the same kind of electricity as that on the inducing body1 while the end toward the inducing body receives electricity of opposite sign4 ,the ,electrophorus4--,this is a simple and ingenious instrument1 invented by ,volta in #agge for the purpose of procuring1 by the principle of induction1 an unlimited number of charges of electricity from one single charge4 ,it consists of two parts1 as shown in fig4 #ai1 a round cake of resinous material ,b1 cast in a metal dish or 8sole0 about one foot in diameter1 and a round disc ,a1 of slightly smaller diameter made of metal or of wood covered with tinfoil1 and provided with a glass handle4 ,shellac1 or sealing wax1 or a mixture of resin shellac and ,venice turpentine1 may be used to make the cake4 ,illustration3 ,,figs4 #ah and #ai4--,the electrophorus and method of using4 ,charge ,b2 place ,a in contact with ,b1 and touch ,a 7fig4 #ah74 ,the disc is now charged by induction and will yield a spark when touched by the hand1 as in fig4 #ai4 ,to use the electrophorus1 the resinous cake ,b must be first beaten or rubbed with fur or a woolen cloth1 the disc ,a is then placed on the cake1 touched with the finger and then lifted by the handle4 ,the disc will now be found to be charged and will yield a spark when touched with the hand1 as in fig4 #ai4 ,the 8cover0 may be replaced1 touched1 and once more removed1 and will thus yield any number of sparks1 the original charge on the resinous plate meanwhile remaining practically as strong as before4 ,the theory of the electrophorus is very simple1 provided the student has clearly grasped the principle of induction4 ,illustration3 ,,figs4 #bj to #bc4--;,illustrating 8how the electrophorus works40 ,when the resinous cake is first beaten with the cat's skin its surface is negatively electrified1 as indicated in fig4 #bj4 ,again1 when the metal disc is placed down upon it1 it rests really only on three or four points of the surface1 and may be regarded as an insulated conductor in the presence of an electrified body4 ,the negative electrification of the cake therefore acts inductively on the metallic disc or 8cover10 attracting a positive charge to its under side1 and repelling a negative charge to its upper surface1 as shown in fig4 #ba4 ,if1 now1 the cover be touched for an instant with the finger1 the negative charge of the upper surface 7which is upon the upper surface being repelled by the negative charge on the cake7 will be neutralized by electricity flowing in from the earth through the hand and body of the experimenter4 ,the attracted positive charge will1 however remain being bound as it were by its attraction towards the negative charge on the cake4 ,illustration3 ,,fig4 #bd4--,lines of force of a charged sphere and a conductor under induction4 ,the negative electrification on the end a of the cylinder indicates that a certain number of lines end there1 while the positive electrification on the end b similarly indicates that an equal number of lines set out from that end4 ,it is one of the fundamental properties of a conductor that it yields instantly to the smallest electric force1 and that no electric force can be permanently maintained within the substance of a conductor in which no current is passing4 ,there can1 therefore1 be no electrostatic strain and no lines of force within the material of a conductor where the electric field has become steady4 ,hence the lines starting from b are entirely distinct from those ending at a4 ,the two sets are equal in number because no charge has been given to the cylinder1 either positive or negative1 and therefore the sum of all the positive electrifications 7or lines starting from b7 must be equal to the sum of all the negative electrifications 7or the lines ending at a74 ,in all nine lines have been drawn at each end of the cylinder1 leaving the thirteen lines emanating from the sphere which do not run on to the cylinder4 ,if the cylinder be withdrawn to a distance from ,k1 it 7the cylinder7 will be found to show no signs of electrification4 ,fig4 #bb shows the result after the cover has been touched4 ,if1 finally1 the cover be lifted by its handle1 the remaining positive charge will no longer be 8bound0 on the lower surface by attraction1 but will distribute itself on both sides of the cover1 and may be used to give a spark4 ,it is clear that no part of the original charge has been consumed in the process1 which may be repeated as often as desired4 ,as a matter of fact1 the charge on the cake slowly dissipates--especially if the air be damp4 ,hence it is needful sometimes to renew the original charge by again beating the cake with the cat's skin4 ,illustration3 ,,fig4 #be4--;,faraday's ice-pail experiment4 ,an ice-pail ,p connected with the gold leaves of an electroscope ,c1 is placed on an insulating stand ,s4 ,a charged conductor ,k1 carried by a silk thread1 is lowered into the pail1 and finally touches it at the bottom4 ,while it is being lowered the leaves of the electroscope diverge farther and farther1 until ,k is well within the pail1 after which they diverge no more1 even when ,k touches the pail or is afterwards withdrawn by the insulating thread4 ,after withdrawal1 ,k is found to be completely discharged4 ,the labor of touching the cover with the finger at each operation may be saved by having a pin of brass or a strip of tinfoil projecting from the metallic 8sole0 on to the top of the cake1 so that it touches the plate each time1 and thus neutralizes the negative charge by allowing electricity to flow in from the earth4 ,illustration3 ,,figs4 #bf to #bi4--;,explanation of ,faraday's ice pail experiment4 ,for simplicity the electroscope1 insulating stand and silk thread have been omitted4 ,only the three principal conductors ,k1 ,p1 and the earth ,e are shown4 ,in fig4 #bf the ball ,k is sufficiently close to ,p to act inductively on it2 six lines are shown as falling on ,p1 and the other six as passing to ,e by different paths4 ,corresponding to the six lines falling on ,p from ,k1 six others pass to ,e from the lower surfaces4 ,in fig4 #bg where ,k is just entering the pail1 two lines only pass from ,k to ,e through the dielectric2 the remaining ten fall on ,p1 and ten others starting from the distant parts of ,p pass to ,e4 ,in fig4 #bh1 ,k is so far within ,p that none of its lines can reach ,e through the dielectric2 they all fall on ,p and from the outside of ,p an equal number start and pass through the dielectric to ,e4 ,it is evident that in this position ,k can be moved about within ,p1 without affecting the outside distribution in the slightest1 and that even when ,k touches ,p as shown in fig4 #bi1 and when1 therefore1 all lines between them disappear1 the lines in the dielectric outside remain just as they are in fig4 #bh4 ,k is now completely discharged1 since lines no longer emanate from it1 hence it can be removed by the silk cord without disturbing the electrification of ,p4 ,if ,k be again charged and introduced into ,p it will be again discharged1 for the fact that ,p is already charged will have no effect on the final result1 provided when ,k touches ,p it is well under cover4 ,since the electricity thus yielded by the electrophorus is not obtained at the expense of any part of the original charge1 it is a matter of some interest to inquire whence is the source from which the energy of this apparently unlimited supply is drawn2 for it cannot be called into existence without the expenditure of some other form of energy4 ,the fact is1 more work is done in lifting the cover when it is charged with the positive electricity than when it is not charged2 for when charged1 there is the force of the electric attraction to be overcome as well as the force of gravity2 this excess force is the real origin of the energy stored up in the separate charges4 ,illustration3 ,,figs4 #cj and #ca4--,the ,leyden jar and discharger4 ,its discovery is attributed to the attempt of ,musschenbrock and his pupil ,cuneus to collect the supposed electric 8fluid0 in a bottle half filled with water4 ,the bottle was held in the hand and was provided with a nail to lead the 8fluid0 down through the cork to the water from the electric machine4 ,the invention of the ,leyden jar is also claimed by ,kleist1 ,bishop of ,pomerania4 ,condensers2 ,leyden ,jar4--,a condenser is an apparatus for condensing a large quantity of electricity on a comparatively small surface4 ,the form may vary considerably1 but in all cases it consists essentially of two insulated conductors1 separated by an insulator and the working depends on the action of induction4 ,a form of condenser generally used in making experiments on static electricity is the ,leyden jar1 so named from the town of ,leyden where it was invented4 ,it consists of a glass jar coated inside and out to a certain height with tinfoil1 having a brass rod terminating in a knob passed through a wooden stopper1 and connected to the inner coat by a loose chain1 as shown in fig4 #cj4 ,the jar may be charged by repeatedly touching the knob with the charged plate of the electrophorus or by connecting the inner coating to one knob of an electrical machine and the outer coating to the other knob4 ,the discharge of a condenser is effected by connecting the plates having an opposite charge4 ,this may be done by use of a wire or a discharger1 as shown in fig4 #ca2 the connection is made between the outer coat and the knob4 ,when the knob of the discharger is sufficiently close to the knob of the jar1 a bright spark will be observed between the knobs4 ,this discharge occurs whenever the difference of potential between the coats is great enough to overcome the resistance of the air between the knobs4 ,let a charged jar be placed on a glass plate so as to insulate the outer coat4 ,let the knob be touched with the finger4 ,no appreciable discharge will be noticed4 ,let the outer coat be in turn touched with the finger4 ,again no appreciable discharge will appear4 ,but if the inner and outer coatings be connected with the discharger1 a powerful spark will pass4 ,electric ,machines4--,various machines have been devised for producing electric charges such as have been described4 ,the ordinary 8static0 or electric machine1 is nothing but a continuously acting electrophorus4 ,fig4 #cb represents the so-called ,toepler-,holtz machine4 ,upon the back of the stationary plate ,e1 are pasted paper sectors1 beneath which are strips of tinfoil ,,ab and ,,cd called inductors4 ,in front of ,e is a revolving glass plate carrying discs l1 m1 n1 o1 p and q1 called carriers4 ,to the inductors ,,ab and ,,cd are fastened metal arms t and u1 which bring ,b and ,c into electrical contact with the discs l1 m1 n1 o1 p and q1 when these discs pass beneath the tinsel brushes carried by t and u4 ,a stationary metallic rod rs carries at its ends stationary brushes as well as sharp pointed metallic combs4 ,the two knobs ,r and ,s have their capacity increased by the ,leyden jars ,l and ,l4 ,illustration3 ,,fig4 #cb4--,the ,toepler-,holtz electric machine4 ,illustration3 ,,fig4 #cc4--,principle of ,toepler-,holtz electric machine4 ,action of the ,toepler-,holtz ,machine4--,the action of the machine described above is best understood from the diagram of fig4 #cc4 ,suppose that a small charge is originally placed on the inductor ,,cd4 ,induction takes place in the metallic system consisting of the discs l and o and the rod rs1 l becoming negatively charged and o positively charged4 ,as the plate carrying l1 m1 n1 o1 p1 q rotates in the direction of the arrow the negative charge on l is carried over to the position m1 where a part of it passes over to the inductor ,,ab1 thus charging it negatively4 ,when l reaches the position n the remainder of its charge1 being repelled by the negative electricity which is now on ,,ab1 passes over into the ,leyden jar ,l4 ,when l reaches the position o it again becomes charged by induction1 this time positively1 and more strongly than at first1 since now the negative charge on ,,ab1 as well as the positive charge on ,,cd1 is acting inductively upon the rod rs4 ,when l reaches the position u1 a part of its now strong positive charge passes to ,,cd1 thus increasing the positive charge upon this inductor4 ,in the position v the remainder of the positive charge on l passes over to ,l4 ,this completes the cycle for l4 ,thus as the rotation continues ,,ab and ,,cd acquire stronger and stronger charges1 the inductive action upon rs becomes more and more intense1 and positive and negative charges are continuously imparted to ,l and ,l until a discharge takes place between the knobs ,r and ,s4 ,there is usually sufficient charge on one of the inductors to start the machine1 but in damp weather it will often be found necessary to apply a charge to one of the inductors by means of the ebonite or glass rod before the machine will work4 ,the ,wimshurst ,machine4--,the essential parts of an ordinary ,wimshurst machine1 as shown in fig4 #cd1 are two insulating plates or drums4 ,on each plate are fixed a large number of strips of conducting material1 which are equal in size and are equally spaced--radially if on a plate1 and circumferentially if on a drum4 ,the plates1 or drums1 are made to rotate in opposite directions4 ,the capacity of the inductors therefore varies from a maximum when each strip on one plate is facing a strip on the other1 to a minimum when the conducting strips on each plate are facing blank or insulating portions of the other plate4 ,there are three pairs of contact brushes1 the members of two of the pairs being at opposite ends of diametrical conducting rods placed at right angles to one another2 the third pair are insulated from one another and form the principal collectors1 the one giving positive and the other negative electricity4 ,the plates are revolving in opposite directions2 thus if there be a charge on one of the conducting segments of one plate and an opposite charge on one of the conducting segments on the other plate near it1 their potential will be raised as the rotation of the plates separates them4#b ,illustration3 ,,fig4 #cd4--,the ,wimshurst ,electric ,machine4 ,,chapter ,,iii ,,the ,,electric ,,current ,the ordinary statement that an electric current is flowing along a wire is only a conventional way of expressing the fact that the wire and the space around the wire are in a different state from that in which they are when no electric current is said to be flowing4 ,in order to make laymen understand the action of this so called current1 it is generally compared with the flow of water4 ,in comparing hydraulics and electricity1 it must be borne in mind1 however1 that there is really no such thing as an 8electric fluid10 and that water in pipes has mass and weight1 while electricity has none4 ,it should be noted1 however1 that electricity is conveniently spoken of as having weight in explaining some of the ways in which it manifests itself4 ,all electrical machines and batteries are merely instruments for moving electricity from one place to another1 or for causing electricity1 when accumulated in one place1 to do work in returning to its former level of distribution4 ,the head or pressure in a standpipe is what causes water to move through the pipes which offer resistance to the flow4 ,similarly1 the conductors1 along which the electric current is said to flow1 offer more or less resistance to the flow1 depending on the material4 ,copper wire is generally used as it offers little resistance4 ,the current must have pressure to overcome the resistance of the conductor and flow along its surface4 ,this pressure is called voltage caused by what is known as difference of potential between the source and terminal4 ,illustration3 ,,fig4 #ce4--;,analogy of the flow of water to the electric current4 ,the water in the reservoirs ,a and ,b stands at different heights4 ,as long as this difference of level is maintained1 water from ,b will flow through the pipe ,r to ,a4 ,if by means of a pump ,p the level in ,b be kept constant1 flow through ,r will also be maintained4 ,here1 by means of the work expended on the pump1 the level in the reservoir is kept constant2 and in the corresponding case of the electric current1 by the conversion of chemical energy a constant difference of potential is maintained4 ,the pressure under which a current flows is measured in volts and the quantity that passes in amperes4 ,the resistance with which the current meets in flowing along a conductor is measured in ohms4 ,ques4 ,what is a volt8 ,ans4 ,a volt is that electromotive force 7,e4 ,m4 ,f47 which produces a current of one ampere against a resistance of one ohm4 ,ques4 ,what is an ampere8 ,ans4 ,an ampere is the current produced by an ,e4 ,m4 ,f4 of one volt in a circuit having a resistance of one ohm4 ,it is that quantity of electricity which will deposit 4#jjejhd grain of copper per second4 ,ques4 ,what is an ohm8 ,ans4 ,an ohm is equal to the resistance offered to an unvarying electric current by a column of mercury at #cb ,fahr41 #ad4deba grams in mass1 of a constant cross sectional area1 and of the length of #ajf4c centimeters4 ,ohm's ,law4--,in a given circuit1 the amount of current in amperes is equal to the ,e4 ,m4 ,f4 in volts divided by the resistance in ohms2 that is3 current pressure _/ resistance volts _/ ohms expressed as a formula3 ,i ,e_/,r 7#a7 in which ,i current strength in amperes2 ,e electromotive force in volts2 ,r resistance in ohms4 ,from 7#a7 is derived the following3 ,e ,,ir 7#b7 ,r ,e_/,i 7#c7 ,from 7#a7 it is seen that the flow of the current is proportional to the voltage and inversely proportional to the resistance2 the latter depends upon the material1 length and diameter of the conductor4 ,since the current will always flow along the path of least resistance2 it must be so guarded that there will be no leakage4 ,hence1 to prevent leakage1 wires are insulated1 that is1 covered by wrapping them with cotton or silk thread or other insulating material4 ,if the insulation be not effective1 the current may leak1 and so return to the source without doing its work4 ,this is known as a short circuit4 ,the conductor which receives the current from the source is called the lead1 and the one by which it flows back1 the return4 ,when wires are used for both lead and return1 it is called a metallic circuit3 when the ground is used for the return1 it is called a ground circuit4 ,an electric current is said to be3 #a4 ,direct1 when it is of unvarying direction2 #b4 ,alternating1 when it flows rapidly to and fro in opposite directions2 #c4 ,primary1 when it comes directly from the source2 #d4 ,secondary1 when the voltage and amperage of a primary current have been changed by an induction coil2 #e4 ,low tension1 when its voltage is low2 #f4 ,high tension1 when its voltage is high4 ,a high tension current is capable of forcing its way against considerable resistance1 whereas1 a low tension current must have its path made easy4 ,production of the ,electric ,current4--,to produce a steady flow of water in a pipe two conditions are necessary4 ,there must first be available a hydraulic pressure1 or1 as it is technically called1 a 8head0 of water produced by a pump1 or a difference of level or otherwise4 ,in addition to the pressure there must also be a suitable path or channel provided for the water to flow through1 or there will be no flow1 however great the 8head10 until something breaks down under the strain4 ,in the case just cited1 although there is full pressure in the water in the pipe1 there is no current of water as long as the tap remains closed4 ,the opening of the tap completes the necessary path 7the greater part of which was already in existence7 and the water flows4 ,illustration3 ,,fig4 #cf4--;,hydraulic analogy of the electric current4 ,if1 say #aj gallons of water flow in every second into a system of vessels and pipes of any shape1 whether simple or more complicated as shown in the figure1 and #aj gallons flow out again per second1 it is evident that through every cross section of any vessel or pipe of the system #aj gallons of water pass every second4 ,this follows from the fact that water is an uncompressible liquid and must be practically of the same density throughout the system4 ,the water moves slowly where the section is large and quickly where it is small1 and thus the quantity of water that flows through any part of the system is independent of the cross section of that part4 ,the same condition holds good for the electric current2 if in a closed circuit a constant current circulates1 the same amount of electricity will pass every cross section per second4 ,hence the following law3 ,the magnitude of a constant current in any circuit is equal in all parts of the circuit4 ,for the production of a steady electric current two very similar conditions are necessary4 ,there must be a steadily maintained electric pressure1 known under different aspects as 8electromotive force10 8potential difference10 or 8voltage40 ,this alone1 however1 is not sufficient4 ,in addition1 a suitable conducting path is necessary4 ,any break in this path occupied by unsuitable material acts like the closed tap in the analogous case above mentioned1 and it is only when all such breaks have been properly bridged by suitable material1 that is1 by conductors1 that the effects which denote the flow of the current will begin to be manifested4 ,the necessary electromotive force or voltage required to cause the current to flow may be obtained3 #a4 ,chemically2 #b4 ,mechanically2 #c4 ,thermally4 ,in the first method1 two dissimilar metals such as copper and zinc called elements1 are immersed in an exciting fluid or electrolyte4 ,illustration3 ,,fig4 #cg4--,volta's 8,crown of ,cups40 ,the metallic elements ,c and ,z each consisted of two metals1 the plate ,c being of copper and the plate ,z of zinc4 ,they were placed1 as shown1 in the glass vessels1 which contained salt water and ordinary water or lye4 ,into each vessel1 except the two end ones1 the copper end of one arc and the zinc end of the next were introduced1 the series1 however long1 ending with copper dipping into the terminal vessel at one end and zinc into that at the other4 ,the arrangement is almost exactly that of a modern one-fluid primary battery4 ,when the elements are connected at their terminals by a wire or conductor a chemical action takes place1 producing a current which flows from the copper to the zinc4 ,this device is called a cell1 and the combination of two or more of them connected so as to form a unit is known as a battery4 ,the word battery is frequently used incorrectly for a single cell4 ,that terminal of the element from which the current flows is called the plus or positive pole1 and the terminal of the other element the negative pole4 ,cells are said to be primary or secondary according as they generate a current of themselves1 or first require to be charged from an external source1 storing up a current supply which is afterwards yielded in the reverse direction to that of the charging current4 ,an electric current is generated mechanically by a dynamo4 ,in either case no electricity is produced1 but part of the supply already existing is simply set in motion by creating an electric pressure4 ,an electric current1 according to the third method1 is generated directly from heat energy1 as will be later explained2 the current thus obtained is very feeble4 ,illustration3 ,,fig4 #ch4--;,hydrostatic analogy of fall of potential in an electrical circuit4 ,illustration3 ,,fig4 #ci4--,showing method of connecting voltmeter to find potential difference between any two points as m and n on an electrical circuit4 ,strength of ,current4--,it is important that the reader have a clear conception of this term1 which is so often used4 ,the exact definition of the strength of a current is as follows3 ,the strength of a current is the quantity of electricity which flows past any point of the circuit in one second4 ,example4--,if1 during #aj seconds1 #be coulombs of electricity flow through a circuit1 then the average strength of the current during that time is #b-a_/b coulombs per second1 or #b-a_/b amperes4 ,voltage ,drop in an ,electric ,circuit4--,a difference of potential exists between any two points on a conductor through which a current is flowing on account of the resistance offered to the current by the conductor4 ,for instance1 in the electrical circuit shown in fig4 #ci1 the potential at the point a is higher than that at m1 that at m higher than that at n1 etc41 just as in the water circuit1 shown in fig4 #ch1 the hydrostatic pressure at a is greater than that at m1 that at m greater than that at n1 etc4 ,the fall in the water pressure between m and n 7fig4 #ch7 is measured by the water head n's4 ,in order to measure the fall in electrical potential between m and n1 7fig4 #ci71 the terminals of a volt meter are placed in contact with these points as shown4 ,its reading will give the difference of potential between m and n1 in volts1 provided that its own current carrying capacity is so small that it does not appreciably lower the potential difference between the points m and n by being touched across them2 that is1 provided the current which flows through it is negligible in comparison with that which flows through the conductor which already joins the points m and n4 ,,chapter ,,iv ,,primary ,,cells ,the word 8battery0 is a much abused word1 being often used incorrectly for 8cell10 as in fig4 #dj4 ,hence1 careful distinction should be made between the two terms4 ,a battery consists of two or more cells joined together so as to form a single unit4 ,there are numerous forms of primary cell2 they may be classified as follows3 #a4 ,according to the service for which they are designed2 #b4 ,according to the chemical features4 ,with respect to the first method cells are classified as3 #a4 ,open circuit cells2 ,used for intermittent work1 where the cell is in service for short periods of time1 such as in electric bells1 signaling work1 and electric gas lighting4 ,if kept in continuous service for any length of time the cell soon polarizes or 8runs down10 but will recuperate after remaining on open circuit for some little time4 #b4 ,closed circuit cells4 ,this type of cell is adapted to furnishing current continuously1 as in telegraphy1 etc4 ,with respect to the second method1 cells are classified as3 #a4 ,one fluid2 #b4 ,two fluid2 ,ques4 ,describe a primary cell4 ,ans4 ,a primary cell consists of a vessel containing a liquid in which two dissimilar metal plates are immersed4 ,in one fluid cells both metal plates are immersed in the same solution4 ,in two fluid cells each metal plate is immersed in a separate solution1 one of which is contained in a porous cup which is immersed in the other liquid4 ,ques4 ,what name is given to the metal plates8 ,ans4 ,they are called elements4 ,ques4 ,what is the fluid called8 ,ans4 ,the electrolyte or exciting fluid4 ,the term 8electropoion0 is a trade name for the electrolyte employed in the ,fuller cell4 ,action of a ,primary ,cell4--,the fundamental fact on which the electro-chemical generation of current depends is1 that if a plate of metal be placed in a liquid there is a difference of electrical condition produced between them of such sort that the metal either takes a lower or higher electrical potential than the liquid1 according to the nature of the metal and the liquid4 ,if two different metals be placed in one electrolytic liquid1 then there is a difference of state produced between them1 so that1 if joined by wire outside the liquid1 a current of electricity will traverse the wire4 ,this current proceeds in the liquid from the metal which is most acted upon chemically to that which is least acted upon4 ,referring to fig4 #da1 the construction and action of a simple primary cell may be briefly described as follows3 ,place in a glass jar some water having a little sulphuric or other acid added to it4 ,place in it separately two clean strips1 one of zinc1 ,z1 and one of copper1 ,c4 ,this cell is capable of supplying a continuous flow of electricity through a wire whose ends are brought into connection with the two strips4 ,when the current flows1 the zinc strip is observed to waste away1 its consumption in fact furnishing the energy or electromotive force required to drive the current through the cell and the connecting wire4 ,the cell may therefore be regarded as a kind of chemical furnace in which the fuel is the zinc4 ,illustration3 ,,fig4 #dj4--,simple primary cell4 ,it consists of two dissimilar metal plates 7such as copper and zinc which are called the elements71 immersed in the electrolyte or exciting fluid contained in the glass jar4 ,ques4 ,how are the positive and negative elements of a primary cell distinguished8 ,ans4 ,the plate attacked by the electrolyte is the negative element1 and the one unattacked the positive element4 ,chemical ,changes2 ,polarization4--,the chemical changes which take place in a simple cell1 consisting of zinc and copper elements in an electrolyte of dilute sulphuric acid1 may be briefly described as follows3 ,when the two elements are connected and the current commences to flow1 the sulphuric acid acts on the surface of the zinc plate and forms sulphate of zinc4 ,the formation of this new substance necessitates the liberation of some of the hydrogen contained in the sulphuric acid1 and it will be found that bubbles of free hydrogen gas speedily appear on the surface of the negative element1 that is1 on the copper plate4 ,while the zinc is being dissolved to form zinc sulphate1 hydrogen gas is liberated from the sulphuric acid4 ,illustration3 ,,fig4 #da4--,simple primary cell with circuit closed1 showing direction of the current4 ,some bubbles of the gas rise to the surface of the electrolyte and so escape into the air1 but much of it clings to the surface of the copper element which thus gradually becomes covered with a thin film of hydrogen4 ,partly on account of the decreased area of copper plate in contact with the electrolyte1 and partly because the hydrogen tends to produce a current in the opposite direction1 the useful electrical output becomes considerably diminished and the cell is said to be polarized4 ,this state of affairs may be rectified by stirring up the electrolyte1 or by shaking the cell1 so as to assist the hydrogen bubbles to detach themselves from the surface of the copper plate and make their way to the atmosphere through the electrolyte4 ,this1 however1 is only a temporary remedy1 as the polarized condition will soon be reached again1 and a further agitation of the cell will be necessary4 ,hence1 a simple cell of this kind is not desirable for practical work1 and it must be modified to adapt it to constant use4 ,when the sulphuric acid in a cell acts in the zinc element and produces sulphate of zinc1 a certain amount of work is done which is manifested partly in the form of useful electric energy1 and partly as heat which warms the electrolyte and which is thereby lost for all practical purposes4 ,ques4 ,if the zinc and copper electrodes of a simple cell be not connected externally what changes take place within the cell8 ,ans4 ,the zinc plate immediately becomes strongly charged with negative electricity1 and the copper plate weakly so4 ,as long as the plates remain unconnected1 and the zinc is pure1 no further action takes place4 ,ques4 ,if the electrodes be connected externally what happens8 ,ans4 ,if the plates be connected by a wire outside the electrolyte1 the tendency which dissimilar electrical charges have to neutralize one another causes a flow of negative electricity through the wire from zinc to copper1 and a positive flow in the opposite direction4 ,the 8static0 charge being thus disposed of1 a fresh charge is given to the plates by the action of the acid1 which commences to dissolve the zinc4 ,as long as the wire connects the copper and zinc plates1 the acid will continue its action on the zinc until either acid or zinc is exhausted4 ,the reader may ask3 how can there be a positive flow when both plates are negatively electrified8 ,an analogy is the best way to make this point clear3 ,imagine two equal vessels1 from each of which the air has been partially exhausted1 but from one 7,a7 #aj times as much air has been taken as from the other 7,b74 ,connect ,a and ,b by a tube4 ,now1 although both vessels have less than the atmospheric pressure1 that is1 both have 8negative0 pressures1 yet a current of air will flow from ,b to ,a until the pressures in each are equalized2 that is1 until both have equal 8negative charges0 of air4 ,there is a second important effect of the acid solution or electrolyte in a cell4 ,if pure sulphuric acid were used1 the first action or production of an electrical charge on the zinc plate would be the same1 but when the plates were joined by the wire the current would soon cease4 ,the reason for this lies in the fact that the sulphate of zinc1 which is the compound produced by the acid plus the zinc1 being insoluble in pure undiluted sulphuric acid1 remains on the surface of the zinc plate4 ,the coating of sulphate of zinc thus formed also operates as a protective agent1 and no further electrical charge can be induced until it is removed4 ,the addition of water to the acid has the effect of allowing the sulphate of zinc to dissolve1 and the zinc plate is left free for further action4 ,ques4 ,what governs the rate of current flow of a primary cell8 ,ans4 ,the size of the elements and their proximity4 ,effects of ,polarization4--,the film of hydrogen bubbles affects the strength of the current of the cell in two ways3 #a4 ,it weakens the current by the increased resistance which it offers to the flow1 for bubbles of gas are bad conductors2 #b4 ,it weakens the current by setting up an opposing electromotive force4 ,hydrogen is almost as oxidizable a substance as zinc1 especially when freshly deposited 7in the 8nascent0 state71 and is electro-positive2 hence1 the hydrogen itself produces a difference of potential1 which would tend to start a current in the opposite direction to the true zinc-to-copper current4 ,it is therefore an important matter to abolish this polarization1 otherwise the currents furnished by batteries would not be constant4 ,methods of ,depolarizing4--,one of the chief aims in the arrangement of the numerous cells which have been devised is to avoid polarization4 ,the following are the methods usually employed3 #a4 ,chemical methods2 a4 ,oxidation of the hydrogen by potassium bichromate and by nitric acid4 b4 ,substitution of the hydrogen by some other substance which does not give a counter electromotive force of polarization2 for instance1 in the ,daniell cell by replacement of the copper in copper sulphate by the hydrogen1 the copper being deposited on the positive pole4 #b4 ,electro-chemical means2 ,it is possible by employing double cells1 to secure such action that some solid metal1 such as copper1 shall be liberated instead of hydrogen bubbles1 at the point where the current leaves the liquid4 ,this electro-chemical exchange obviates polarization4 #c4 ,mechanical methods4 a4 ,agitation of the liquid or of the positive electrode1 in order to prevent the accumulation of hydrogen thereon4 b4 ,corrugating or roughing the positive electrode1 as in the ,smee cell4 ,this causes the hydrogen gas to form in large bubbles which rise to the surface more rapidly than the small bubbles which form on a smooth electrode4 ,in the simplest form of cell1 as zinc1 copper1 and dilute sulphuric acid1 no attempt has been made to prevent the evil of polarization1 hence1 it will quickly polarize when the current is closed for any length of time1 and may be classified as an open circuit cell4 ,when polarization is remedied by chemical means1 the chemical added is one that has a strong affinity for hydrogen and will combine with it1 thus preventing the covering of the negative plate with the hydrogen gas4 ,illustration3 ,,figs4 #db and #dc4--;,carbon cell and carbon cylinder4 ,carbon possesses a natural power to prevent a limited amount of polarization by absorbing the hydrogen gas coming from the zinc rod2 hence it is used in various shapes for open circuit cells1 which gives rise to as many different names1 such as ,samson1 ,hercules1 ,law1 ,national1 ,standard1 etc4 ,in all these types of cell1 sal-ammoniac and zinc are used1 and by corrugating the carbon1 fluting it1 or making concentric cylinders1 special merits are obtained in each case4 ,the carbon element is usually made in the form of a porous cup1 filled with oxide of manganese to prevent polarization1 and then sealed4 ,the zinc rod is inserted through a porcelain insulator4 ,about #d to #f ounces of sal-ammoniac are generally used for cells of ordinary size4 ,the salt is placed in the jar1 water poured in until it is about two-thirds full1 and then stirred till all the salt is dissolved4 ,when the carbon cylinder is inserted1 the solution should be within #a-a_/b inches of the top of the jar4 ,the electromotive force is from #a4j to #a4d volts for the different forms of carbon cell4 ,ques4 ,what is a depolarizer8 ,ans4 ,a substance employed in some types of cell to combine with the hydrogen which would otherwise be set free at the positive electrode and cause polarization4 ,the chemical used for this purpose may be either in a solid or liquid form1 which gives rise to several types of cell1 such as cells with a single fluid1 containing both the acid and the depolarizer1 cells with a single exciting fluid and a solid depolarizer1 and cells with two separate fluids4 ,in the two fluid cell1 the zinc is immersed in the liquid 7frequently dilute sulphuric acid7 to be decomposed by the action upon it1 and the negative plate is surrounded by the liquid depolarizer1 which will be decomposed by the hydrogen gas it arrests1 thereby preventing polarization4 ,in open circuit cells polarization does not have much opportunity to occur1 since the circuit is closed for such a short period of time2 hence1 these cells are always ready to deliver a strong current when used intermittently4 ,in closed circuit cells polarization is prevented by chemical action1 so that the current will be constant and steady till the energy of the chemicals is expended4 ,ques4 ,what is a depolarizer bag8 ,ans4 ,a cylinder of hemp or other fabric used in place of a porous pot in some forms of ,leclanche cell1 and also as a support for the depolarizing mass in some forms of dry cell where the electrolyte is of a thin gelatinous nature4 ,volta's ,contact ,law4--,when metals differing from each other are brought into contact1 different results are obtained1 both as to the kind of electrification as well as the difference of potentials4 ,volta found that iron1 when in contact with zinc1 becomes negatively electrified2 the same takes place1 but somewhat weaker1 when iron is touched with lead or tin4 ,when1 however1 iron is touched by copper or silver1 it becomes positively electrified4 ,volta1 ,seebeck1 ,pfaff1 and others have investigated the behavior of many metals and alloys when in contact with each other4 ,the following lists are so arranged that those metals first in each list become positively electrified when touched by any taking rank after them3 ,,contact ,,series ,,of ,,metals ,according to ,volta4 ,according to ,pfaff4 zinc zinc lead cadmium tin tin iron lead copper tungsten silver iron gold bismuth graphite antimony - manganese ore copper silver gold uranium tellurium platinum - palladium ,volta laid down a law regarding the position of the metals in his table which may be stated as follows3 ,the difference of potential between any two metals is equal to the sum of the differences of potentials of all the intermediate members of the series4 ,hence1 it is immaterial for the total effect whether the first and the last are brought into contact directly1 or whether the contact is brought about by means of all or any of the intermediate metals4 ,volta's law further asserts that when any number of metals are brought into contact with each other1 but so that the chain closes with the metal with which it was begun1 the total difference must be zero4 ,laws of ,chemical ,action in the ,cell4--,there are two simple laws of chemical action in the cell3 #a4 ,the amount of chemical action in a cell is proportional to the quantity of electricity that passes through it4 ,one coulomb of electricity in passing through the cell liberates 4#jjjjajceb of a gramme of hydrogen1 and causes 4#jjjfccdd of a gramme of zinc to dissolve in the acid4 #b4 ,the amount of chemical action is equal in each cell of a battery connected in series4 ,requirements of a ,good ,cell4--,the several conditions which should be fulfilled by a good cell are as follows3 #a4 ,its electromotive force should be high and constant2 #b4 ,its internal resistance should be small2 #c4 ,it should be perfectly quiescent when the circuit is open2 #d4 ,it should give a constant current1 and therefore must be free from polarization1 and not liable to rapid exhaustion2 #e4 ,it should be easily cared for1 and if possible1 should not emit corrosive fumes2 #f4 ,it should be cheap and of durable materials4 ,single and ,two ,fluid ,cells4--,the distinction between a single and a two fluid cell has already been given4 ,the single fluid cell of ,volta with its zinc and copper plates represents the simplest form of primary cell4 ,in the two fluid cell1 the positive 7zinc7 plate is immersed in the exciting liquid 7usually dilute sulphuric acid7 and is decomposed by the action upon it1 while the negative plate is placed in the liquid depolarizer which is decomposed by the hydrogen arrested by it1 thus preventing polarization4 ,in some forms of cell1 the two liquids are separated by a porous partition of unglazed earthenware1 which1 while it prevents the liquids mixing except very slowly1 does not prevent the passage of hydrogen and electricity4 ,illustration3 ,,figs4 #dd and #de4--,leclanche cell and porous cup4 ,this very common form of cell is an example of the single fluid type1 with a solid depolarizer surrounding the negative element2 the latter is generally carbon1 the positive element being zinc4 ,the liquid used is a strong solution of ammonium chloride1 commonly known as sal-ammoniac1 and which resembles table salt4 ,in the porous cup type of cell1 a carbon slab is placed in the porous cup1 and is surrounded by a mixture of small pieces of carbon and manganese dioxide1 the top being covered by means of pitch1 leaving one or two small holes for air and gas to pass through4 ,the depolarizer will take care of a limited amount of the hydrogen produced when the cell is on closed circuit1 but if the circuit be closed for any length of time polarization occurs4 ,the cell is thus of the open circuit class1 and will furnish a good current where it is required only intermittently4 ,zinc is dissolved only when the cell is being used4 ,this type of cell1 or its modification1 is used for gas lighting and bell work4 ,the cell requires very little attention4 ,water must be added as the solution evaporates1 and the zinc rod replenished when necessary4 ,the electromotive force is about #a4dh volts and the internal resistance about #d ohms4 ,complete depolarization is usually obtained also in single fluid cells1 having in addition a depolarizing solid body1 such as oxide of manganese1 oxide of copper1 or peroxide of lead1 in contact with the carbon pole4 ,such cells really do not belong to the single fluid cells1 and are considered in the two fluid class4 ,a few examples of single and double fluid primary cells will now be described4 ,the ,leclanche ,cell4--,this cell was invented by ,leclanche1 a ,french electrician1 and was the first cell in which sal-ammoniac was used4 ,this form of cell1 as shown in fig4 #de1 is in general use for electric bells1 its great recommendation being that1 once charged1 it retains its power without attention for considerable time4 ,two jars are employed in its construction2 the outer one is of glass1 contains a zinc rod1 and is charged with a solution of ammonium chloride1 called sal-ammoniac4 ,the inner jar is of porous earthenware1 containing a carbon plate1 and is filled with a mixture of manganese peroxide and broken gas carbon4 ,when the carbon plate and the zinc rod are connected1 a steady current of electricity is set up1 the chemical action which takes place being as follows3 the zinc becomes oxidized by the oxygen from the manganese peroxide1 and is subsequently converted into zinc chloride by the action of the sal-ammoniac4 ,after the battery has been in continuous use for some hours1 the manganese becomes exhausted of oxygen1 and the force of the electrical current is greatly diminished2 but if the battery be allowed to rest for a short time1 the manganese obtains a fresh supply of oxygen from the atmosphere1 and is again fit for use4 ,after about #ah months work1 the glass cell will probably require recharging with sal-ammoniac1 and the zinc rod may also need renewing2 but should the porous cell get out of order1 it is better to get a new one than to attempt to recharge it4 ,the directions for setting up a ,leclanche cell are as follows3 #a4 ,place in the glass jar six ounces of sal-ammoniac1 and pour in water until the jar is one-third full1 then stir thoroughly4 #b4 ,place the porous cup in the solution1 and if necessary add water until it rises to within #a-a_/b inches of the top of the porous cup4 #c4 ,put the zinc rod in place and set the cell away 7not connected up71 for about #ab hours1 so as to allow the liquid to thoroughly soak into the porous cup4 ,this will lower the level of the liquid to about one-third the height of the jar4 ,the cell will then be ready for use4 ,as the level of the liquid is lowered by evaporation1 it should be maintained at the stated height by adding water4 ,the ,leclanche cell is adapted to open circuit work1 being extensively used for ringing electric bells4 ,the objections to the ,leclanche cell are3 #a4 ,rapid polarization2 #b4 ,high internal resistance due to porous pot2 #c4 ,restricted space for electrolyte causing rapid lowering of level of liquid by evaporation2 #d4 ,eating away of the zinc rod at the surface of the liquid1 rendering the rod useless before the lower part is consumed4 ,fuller ,bichromate ,cell4--,in the bichromate cells or the chromic acid cells1 bichromate of soda1 or bichromate of potassium1 is used for the depolarizer1 water and sulphuric acid being added for attacking the zinc4 ,the ,fuller cell is of the two fluid type4 ,a pyramidal block of zinc at the end of a metallic rod covered with gutta-percha is placed in the bottom of a porous cup containing an ounce of mercury4 ,the cup is then filled with a very dilute solution of sulphuric acid or water and placed in a jar of glass or earthenware containing the bichromate solution and the carbon plate4 ,the diffusion of the acid through the porous cup is sufficiently rapid to attack the zinc1 which being well amalgamated1 prevents local action2 while the hydrogen passes through the porous cup and combines with the oxygen in the bichromate of potassium4 ,this type of cell has an electromotive force of #b4ad volts1 and is suited to open circuit1 or semi-closed circuit work4 ,the directions for setting up a ,fuller cell are as follows3 #a4 ,to make the 8electropoion0 fluid1 mix together one gallon of sulphuric acid and three gallons of water1 and in a separate vessel1 dissolve six pounds of bichromate of potash in two gallons of boiling water2 then thoroughly mix together the two solutions4 #b4 ,immerse the zinc in a solution of dilute sulphuric acid1 and then in a bath of mercury1 and rub it with a brush or cloth so as to reach all parts of the surface4 #c4 ,pour into the porous cell one ounce 7a tablespoonful7 of mercury1 and fill the porous cell with water up to within two inches of the top4 #d4 ,place the porous cell and the carbon plate in the glass jar1 as in fig4 #df1 and fill glass jar to within about three inches of the top with a mixture of three parts of electropoion fluid to two parts of water4 ,illustration3 ,,figs4 #df and #dg4--,the telephone standard and compound forms of the ,fuller cell4 ,the type shown in fig4 #df is especially adapted to long distance telephoning1 and that shown in fig4 #dg to incandescent lamps1 motors1 nickel and other electroplating4 ,the ,fuller cell is a double fluid variety and has the advantage over the ,grenet type1 in that the zinc is always kept well amalgamated and does not require removal from the solution4 ,the ,fuller cell is suitable for open and semi-closed circuit work2 its electromotive force is about #b4ad volts4 #e4 ,the zinc should be lifted out occasionally and the sulphate washed off4 #f4 ,the supply of mercury in the porous cell should be maintained1 so as to have the zinc always well amalgamated4 #g4 ,to renew1 clean all deposits from carbon plate and zinc1 and set up with fresh solution4 ,the ,edison ,cell4--,this is a single fluid cell with a solid depolarizer1 as shown in fig4 #dh1 and is well adapted for use on closed circuits4 ,illustration3 ,,fig4 #dh4--;,edison cell1 type ,r ,r4 ,the electrolyte used is caustic soda1 the positive element zinc1 and the negative element copper oxide4 ,the ,edison cell is suitable for large stationary gas engine ignition1 railroad crossing signals1 electroplating1 fire alarms1 telephone circuits1 etc4 ,the positive element is zinc1 and the negative element black oxide of copper4 ,the exciting fluid is a solution of caustic potash4 ,the black oxide of copper plates are suspended from the cover of the jar by a light framework of copper1 one end of which forms the positive pole of the battery4 ,a zinc plate is suspended on each side of the copper oxide element and kept from coming in contact with the latter by means of vulcanite buttons4 ,when the cell is in action1 the water is decomposed1 and the oxygen thus liberated combines with the zinc and forms oxide of zinc1 which combines with the potash to form a double salt of zinc and potash4 ,the last combination dissolves as rapidly as it is formed4 ,the hydrogen liberated by the decomposition of the water reduces the copper oxide to pure metallic copper4 ,it is highly important that the copper oxide plates be completely submerged in the solution of caustic potash1 and that heavy paraffin oil be poured on top of the solution to the depth of about #a_/d of an inch to exclude the air4 ,if oil be not used1 the formation of creeping salts will reduce the life of the battery fully two-thirds4 ,the battery has a low electromotive force1 about #j4g of a volt1 but as the internal resistance is also very low1 quite a large current can be drawn from the cell4 ,the ,bunsen ,cell1 shown in figs4 #di and #ej1 is a two fluid cell constructed with zinc and carbon electrodes4 ,the negative plate is carbon1 the positive plate amalgamated zinc4 ,the excitant is a dilute solution of sulphuric acid4 ,the top part of the carbon is sometimes impregnated with paraffin 7to keep the acid from creeping up74 ,the force of the ,bunsen cell increases after setting up for about an hour1 and the full effect is not attained until the acid soaks through the porous cell4 ,carbons are not affected and last any length of time4 ,the zinc is slowly consumed through the mercury coating4 ,grenet ,bichromate ,cell4--,in this cell1 as shown in figs4 #di and #ej1 the positive element is zinc and the negative element carbon4 ,the electrolyte is a solution of bichromate of potash in a mixture of sulphuric acid and water4 ,illustration3 ,,figs4 #di and #ej4--;,american and ,french forms of ,grenet cell4 ,the elements are zinc and carbon4 ,in the ,grenet cell1 a zinc plate is suspended by a rod between two carbon plates1 so that it does not touch them1 and when the cell is not in use the zinc is withdrawn from the solution by raising and fastening the rod by means of a set screw1 as the acid attacks the zinc when the cell is on open circuit4 ,this cell has an electromotive force of over #b volts at first1 and gives a strong current for a short time1 but the liquid soon becomes exhausted1 as will be noted by the change in the color of the solution from an orange to a dark red1 and must be replenished4 ,the zinc should be kept well amalgamated and out of the solution except when in use4 ,it is a good type of cell for experimental work4 ,to make the electrolyte take #c ounces of finely powdered bichromate of potash and #a pint of boiling water2 stir with a glass rod and after it is cool1 add slowly1 stirring all the time1 #c ounces of sulphuric acid4 ,the electrolyte may also be prepared as follows3 take #d ounces of bichromate of soda1 #a-a_/d pints of boiling water1 and #c ounces of sulphuric acid4 ,the cell consists of a glass bottle containing the electrolyte and fitted with a lid from which the elements are supported4 ,there is a zinc plate in the center and a carbon plate on each side4 ,the two carbon plates are connected to the same terminal1 thus forming a large negative surface1 and the zinc plate to a terminal on the top of the brass rod to which it is attached4 ,this rod slides through a hole in the lid so that the zinc plate can be lifted out of the electrolyte when the cell is not at work1 thus preventing wasteful consumption of zinc and of the electrolyte4 ,bichromate cells give a strong current1 the electromotive force of a single cell being #b volts4 ,illustration3 ,,fig4 #ea4--,the ,bunsen cell4 ,this is a two fluid cell and has a bar of carbon immersed in strong nitric acid contained in a porous cup4 ,this cup is then placed in another vessel1 containing dilute sulphuric acid1 and immersed in the same liquid1 is a hollow cylindrical plate of zinc1 which nearly surrounds the porous cup4 ,the hydrogen1 starting at the zinc1 traverses by composition and recomposition1 the sulphuric acid2 it then passes through the porous partition1 and enters into chemical action with the nitric acid1 so that none of it reaches the carbon4 ,water is produced by this action1 which in time dilutes the acid1 and orange colored poisonous fumes of nitric oxide rise from the battery4 ,if the nitric acid first be saturated with nitrate of ammonia1 the acid will last longer and the fumes be prevented4 ,strong sulphuric acid cannot be used in any battery2 one part of sulphuric acid is generally added to #ab parts by weight1 or #bj by volume1 of water4 ,grove used a strip of platinum instead of carbon in his cell4 ,a solution of bichromate of potassium is frequently substituted for the nitric acid in the porous cup1 thereby avoiding disagreeable fumes4 ,bunsen's and ,grove's cells produce powerful and constant currents1 and are well adapted for experiments1 but they require frequent attention1 and are expensive1 so that they are little used for work of long duration4 ,the electromotive force of these cells is from #a4ge to #i4ea volts4 ,daniell ,cell4--,this is one of the best known and most widely used forms of primary cell4 ,it is a double fluid cell1 composed of an inner porous vessel containing an electrolyte of either dilute sulphuric acid or dilute zinc sulphate solution1 and an outer vessel containing a saturated solution of copper sulphate4 ,a zinc rod is placed in the inner electrolyte1 and a thin plate of sheet copper in the outer electrolyte4 ,sometimes this arrangement of the elements is modified1 the outer vessel being made of copper and serving as the copper plate4 ,this would then contain the copper sulphate solution1 while the zinc sulphate and the zinc rod would be contained in the porous pot as before4 ,the chemical reactions which take place in a ,daniell cell are as follows3 ,the zinc dissolves in the dilute acid1 thus producing zinc sulphate1 and liberating hydrogen gas4 ,the free hydrogen passes through the walls of the porous pot1 but when it reaches the copper sulphate solution it displaces some of the copper therefrom1 and combines with this solution1 forming sulphuric acid4 ,the copper1 which is thus set free1 is deposited on the surface of the copper plate4 ,in this way polarization is avoided1 and a practically constant current is obtained4 ,when the zinc sulphate solution is employed in place of dilute acid1 a similar series of chemical reactions occur1 except that the zinc is liberated instead of hydrogen4 ,daniell cells are used especially for electroplating1 electrotyping and telegraphic work4 ,the electromotive force of a single cell is #a4jgi volts4 ,directions for ,making a ,daniell ,cell4--,the simple ,daniell cell shown in fig4 #eb may be easily made as follows3 ,the outer vessel ,a1 consists of a glass jar 7an ordinary glass jam jar will do7 containing a solution of sulphuric acid 7#a part in #ab to #bj parts of water71 and a zinc rod ,b4 ,inside the jar is placed a porous pot ,c containing a strip of thin sheet copper ,d1 and a saturated solution of sulphate of copper 7also called 8blue stone0 and 8blue vitrol074 ,the zinc is preferably of the ,leclanche form1 which will be found to be cleaner1 more durable1 and cheaper than a zinc sheet4 ,the porous pot should be dipped in melted paraffin wax1 both top and bottom1 to prevent the solution mingling too freely and 8creeping40 ,a few crystals of copper sulphate are placed in the pot as shown4 ,illustration3 ,,fig4 #eb4--,simple ,daniell cell for closed circuit work4 ,to maintain a constant current for an indefinite time1 it is only necessary to maintain the supply of copper crystals and zinc4 ,the cell as shown in the figure is easily made by following the direction given in the accompanying text4 ,in mixing the sulphuric acid and water1 the acid should be added to the water--never the reverse4 ,zinc sulphate is sometimes used instead1 as it reduces the wasteful consumption of the zinc1 but it should be pure4 ,with care the cell will last for weeks4 ,when it weakens or 8runs down10 an addition of sulphuric acid to the outer jar and a few more crystals placed in the porous pot will put the cell in good condition4 ,illustration3 ,,fig4 #ec4--;,daniell gravity cell1 8crowfoot0 pattern4 ,this is a two fluid cell in which gravity instead of a porous cup is depended upon to keep the liquids separate4 ,the two solutions consist of copper sulphate and dilute sulphuric acid1 the elements being made of zinc and copper4 ,gravity ,cells4--,in a two liquid cell1 instead of employing a porous cell to keep the two liquids separate1 it is possible1 where one of the liquids is heavier than the other1 to arrange that the heavier liquid shall form a stratum at the bottom of the cell1 the lighter floating upon it4 ,such arrangements are called gravity cells2 but the separation is never perfect1 the heavy liquid slowly diffusing upwards4 ,daniell ,gravity ,cell4--,in this cell1 shown in fig4 #ec1 the same elements are used as in the ordinary ,daniell cell1 but the porous pot is dispensed with1 the two solutions being separated by the action of gravity as explained in the preceding paragraph4 ,illustration3 ,,fig4 #ed4--,partz acid gravity cell4 ,in this form of cell1 the electrolyte which surrounds the zinc is either magnesium sulphate or common salt4 ,the depolarizer is a bichromate solution which surrounds the perforated carbon plate located in the bottom of the jar4 ,a vertical carbon rod fits snugly into the tapered hole in the carbon plate1 and extends through the cover forming the positive pole4 ,the depolarizer1 being heavier than the electrolyte1 remains at the bottom of the jar1 and the two liquids are thus kept separate4 ,this depolarizer is placed on the market in the form of crystals1 known as sulpho-chromic salt1 made by the action of sulphuric acid upon chromic acid4 ,when dissolved1 its action is similar to that of the chromic acid solution4 ,after the cell has been set up with everything else in place1 the crystals are introduced into the solution1 near the bottom of the jar1 through the vertical glass tube shown1 and slowly dissolve and diffuse over the surface of the carbon plate4 ,when the cell current weakens a few tablespoonfuls of the salt introduced through the tube will restore the current to its normal value4 ,the cell should remain undisturbed to prevent the solution from mixing4 ,its electromotive force is from #a4i to #b volts1 and the #f in4 #h in4 size has an internal resistance of about 4#e ohm4 ,since the depolarizer is quite effective1 the cell may be used on open or closed circuit work4 ,the copper sulphate solution1 being the heavier of the two1 rests at the bottom of the battery jar1 while the dilute sulphuric acid remains at the top4 ,to suit this arrangement the copper and zinc elements are located as shown1 the copper elements being at the bottom1 and the zinc element1 shaped like a crow's foot 7hence the name 8crowfoot cell07 is suspended at the top4 ,the absence of the porous pot decreases the internal resistance1 but the electromotive force is the same as in the ordinary type of ,daniell cell4 ,illustration3 ,,fig4 #ee4--,wheelock cell2 the elements are carbon and zinc4 ,to set up1 place the grid in the bottom of the jar and fill its two troughs each about half full of mercury4 ,place the porous cell in position on the grid so that it sits perfectly upright1 resting in the recess of the latter4 ,the zincs stand with lower ends resting in mercury in the troughs of the grid4 ,into the porous cell1 to a height of only two-thirds full1 pour solution consisting of equal parts water and sulphuric acid1 by measure4 ,add to this #a_/b pound nitrate soda1 #a ounce chromic acid4 ,this solution may be made up in the above proportion and kept in covered receptacle in any desired quantity1 ready for use4 ,in the outer jar for #f #h size1 #b-a_/b pints of water1 and #a_/b gill sulphuric acid1 #a part sulphuric acid to #bj parts water1 or as much sulphuric acid as it will take without boiling4 ,when a charge becomes exhausted it may be renewed by adding sulphuric acid and salts in the proportions given above1 after drawing out with syringe enough of the old solutions to make room for the additions1 but the best action is obtained with entirely new solutions4 ,zincs must be kept thoroughly amalgamated by keeping a good supply of mercury in the troughs4 ,when a current is produced by a ,daniell cell3 #a4 ,copper is deposited on the copper plate2 #b4 ,copper sulphate is consumed2 #c4 ,the sulphuric acid remains unchanged in quantity2 #d4 ,zinc sulphate is formed2 #e4 ,zinc is consumed4 ,if1 however1 the copper sulphate solution be too weak1 the water is decomposed instead of the copper sulphate1 and hydrogen is deposited on the copper plate4 ,this deposit of hydrogen lowers the voltage1 hence care should be taken to maintain an adequate supply of copper sulphate4 ,the voltage of a ,daniell cell varies from about #a4jg volt to #a4ad volt1 according to the density of the copper sulphate solution and the amount of zinc sulphate present in the dilute sulphuric acid4 8,dry0 ,cells4--,it is often necessary to use cells in places where there is considerable jarring or motion1 as for automobile or marine ignition4 ,the ordinary cell is not well adapted to this service on account of the liability of spilling the electrolyte1 hence1 the introduction of the so-called dry cell4 ,a dry cell is composed of two elements1 usually zinc and carbon1 and a liquid electrolyte4 ,a zinc cup closed at the bottom and open at the top forms the negative electrode2 this is lined with several layers of blotting paper or other absorbing material4 ,the positive electrode consists of a carbon rod placed in the center of the cup2 the space between is filled with carbon--ground coke and dioxide of manganese mixed with an absorbent material4 ,this filling is moistened with a liquid1 generally sal-ammoniac4 ,the top of the cell is closed with pitch to prevent leakage and evaporation4 ,a binding post for holding the wire connections is attached to each electrode and each cell is placed in a paper box to protect the zincs of adjacent cells from coming into contact with each other when finally connected together to form a battery4 ,points ,relating to ,dry ,cells4--,the following instructions on the care and operation of dry cells should be carefully noted and followed to get the best results3 ,illustration3 ,,figs4 #ef and #eg4--,round and rectangular types of the so-called 8dry0 cell4 #a4 ,in renewing dry cells 7or any other kind of cell71 a greater number should never be put in series than was originally required to do the work1 because the additional cells increase the voltage beyond that required1 which causes more current than is necessary to flow through the coil4 ,this increased current flow shortens the life of the battery4 #b4 ,in connecting dry cells in places where there is vibration1 heavy copper wire should not be used1 because vibration will cause it to break4 #c4 ,water should not be allowed to come in contact with the paper covers of the cells because they form the insulation1 hence1 when moist1 current will leak across from one cell to another1 resulting in running down the battery4 #d4 ,dry cells will deteriorate when not in use1 making it necessary to renew them about every sixty days4 ,the reason dry cells deteriorate is because the moisture evaporates4 ,freezing1 exposure to heat1 and vibration which loosens the sealing1 causes the evaporation4 #e4 ,weak cells can be strengthened somewhat by removing the paper jacket1 punching the metal cup full of small holes1 and then placing in a weak solution of sal-ammoniac1 allowing the cells to absorb all they will take up4 ,this is only to be recommended in cases of emergency when they are hard to get4 ,illustration3 ,,figs4 #eh to #fc4--,various zincs2 fig4 #eh ,fuller2 fig4 #ei ,daniell2 fig4 #fj ,leclanche square2 fig4 #fa ,leclanche round2 fig4 #fb ,sampson2 fig4 #fc1 bottle4 #f4 ,the average voltage of a dry cell when new is one and one-half volts1 while the amperage ranges from about twenty-five to fifty amperes according to size4 #g4 ,a dry cell when fresh should show from #bj to #be amperes when tested2 the date of manufacture should also be noted as fresh cells are most efficient4 #h4 ,dry cells should be tested with an ammeter1 care being taken to do it quickly as the ammeter being of a very low resistance short circuits the cell4 ,a volt meter is not used in testing because1 while the cells are not giving out current1 their voltage remains practically the same1 and a cell that is very weak will show nearly full voltage4 ,when no ammeter is at hand1 the battery current may be tested by disconnecting the end of one of the terminal wires and snapping it across the binding post of the other terminal2 the intensity of the spark produced will indicate the condition of the battery4 ,points ,relating to the ,care of ,cells4--,to get the best results from primary cells1 they should receive proper attention and be maintained in good condition4 ,the instructions here given should be carefully followed4 ,illustration3 ,,figs4 #fd to #ff3 ,various carbons2 fig4 #fa ,cylindrical form2 fig4 #fe ,calland star2 fig4 #ff1 wheel4 ,cleanliness4--,in the care of batteries1 cleanliness is essential in order to secure best results4 ,zincs and coppers should be thoroughly cleaned every time a cell is taken out of use4 ,the zinc1 after being thoroughly cleaned1 should be rubbed with a little mercury4 ,this prevents local action4 ,porous cups should be soaked in clean water four or five hours and then wiped dry4 ,the terminals of each cell should be thoroughly cleansed and scraped bright so as to get good contact of the connecting wires and thus avoid extra resistance in the circuit4 ,separating the ,elements4--,obviously the positive and negative elements of a cell must not be in contact within the exciting fluid2 they should be separated by a space of #c_/h to #a_/b inch4 ,in the case of cells without porous cups1 periodic attention must be given to ensure this condition being maintained4 ,illustration3 ,,figs4 #fg to #fi4--,various zincs3 fig4 #fg ,crowfoot2 fig4 #fh ,lockwood2 fig4 #fi fire alarm4 ,creeping4--,as evaporation of the electrolyte takes place in a cell1 it increases in strength1 and crystals are left on the sides of the jar previously wetted by the solution1 the action being very marked when the solution is a saturated one4 ,the space between these crystals and the side of the jar acts as a number of capillary tubes1 and draws up more liquid1 which itself evaporates and deposits crystals above the former ones4 ,so that finally the film of crystals passes over the edge of the jar and forms on the outside1 thus making a kind of syphon which draws off the liquid4 ,this action may1 to a great extent1 be prevented by warming the edges of the glass1 or stoneware1 jars1 and of the porous pots1 before the cells are made up1 and dipping them while warm into some paraffin wax melted in warm oil1 a precaution that should always be carried out when a dense solution of zinc sulphate is employed in the cell4 ,amalgamated ,zinc4--,to 8amalgamate0 a piece of zinc1 dip it into dilute sulphuric acid to clean its surface1 then rub a little mercury over it by means of a piece of rag tied on to the end of a stick1 and lastly1 leave the zinc standing for a short time in a dish to catch the surplus mercury as it drains off4 ,illustration3 ,,figs4 #gj and #ga4--,two forms of copper element3 fig4 #gj1 regular form for crowfoot cell2 fig4 #ga1 signal pan bottom copper4 ,the action of the amalgamated zinc is not well understood2 by some it is considered that amalgamating the zinc prevents local currents by the amalgam mechanically covering up the impurities on the surface of the zinc and preventing their coming into contact with the liquid4 ,by others it is thought that amalgamating the zinc protects it from local action by causing a film of hydrogen gas to adhere to it4 ,this theory is based on the fact that while no action takes place when amalgamated zinc is placed in dilute sulphuric acid at ordinary atmospheric pressure1 the creation of a vacuum above the liquid causes a rapid evolution of hydrogen1 which1 however1 stops on the readmission of the air4 ,amalgamating a zinc causes it to act as a somewhat more positive substance than before1 therefore the voltage of a cell containing amalgamated zinc is slightly higher than that of a cell constructed with unamalgamated zinc4 ,illustration3 ,,fig4 #gb4--;,diagram of a series battery connection3 four cells are shown connected by this method4 ,if the cell voltage be one and one-half volts1 the pressure between the 77 and 7-7 terminals of the battery is equal to the product of the voltage of a single cell multiplied by the number of cells4 ,for four cells it is equal to six volts4 ,the addition of a very small amount of zinc to mercury causes the mercury to act as if it were zinc alone1 arising perhaps from the amalgam having the effect of bringing the zinc to the surface4 ,battery ,connections4--,there are three methods of connecting cells to form a battery2 they may be connected3 #a4 ,in series2 #b4 ,in parallel2 #c4 ,in series multiple4 ,a series connection consists in joining the positive pole of one cell to the negative pole of the other1 as shown in fig4 #gb2 this adds the voltage of each cell4 ,thus1 connecting in series four cells of one and one-half volts each will give a total of six volts4 ,fig4 #gc illustrates a parallel or multiple connection2 this is made by connecting the positive terminal of one cell with the positive terminal of another cell and the negative terminal of the first cell with the negative terminal of the second cell4 ,illustration3 ,,fig4 #gc4--;,diagram of a multiple or parallel connection4 ,when connected in this manner the voltage of the battery is the same as that of a single cell1 but the current is equal to the amperage of a single cell multiplied by the number of cells4 ,thus with #a-a_/b volt #ae ampere dry cells1 the combination or battery connected as shown would give #d #ae #fj amperes at a pressure of #a-a_/b volts4 ,illustration3 ,,fig4 #gd4--;,diagram of a series multiple connection4 ,two sets of cells are connected in series and the two batteries thus formed1 connected in parallel4 ,the pressure equals the voltage of one cell1 multiplied by the number of cells in one battery1 and the amperage1 that of one cell multiplied by the number of batteries4 ,this form of connection is objectionable unless all the cells be of equal strength4 ,if old cells be placed on one side and new cells on the other1 current will flow 7as in fig4 #ge7 from the stronger through the weaker until the pressure of all the cells thus becomes equal4 ,this process therefore wastes some of the energy of the strong cells4 ,a paralleled or multiple connection adds the amperage of each cell2 that is1 the amperage of the battery will equal the sum of the amperage of each cell4 ,for instance1 four cells of twenty-five amperes each would give a total of one hundred amperes when connected in parallel4 ,a series multiple connection1 fig4 #gd1 consists of two series sets of cells connected in parallel4 ,in series multiple connections the voltage of each set of cells or battery must be equal1 or the batteries will be weakened1 hence each battery of a series multiple connection should contain the same number of cells4 ,the voltage of a series multiple connection is equal to the voltage of one cell multiplied by the number of cells in one battery1 and the amperage is equal to the amperage of one cell multiplied by the number of batteries4 ,illustration3 ,,fig4 #ge4--;,diagram to illustrate incorrect wiring4 ,the current pressure of the six cell battery being greater than that of the smaller unit1 current will flow from the former through the latter until the pressure of the six cells is equal to that of the four cells4 ,fig4 #ge shows an incorrect method of wiring in series multiple connection4 ,if the circuit be open1 the six cells1 on account of having more electromotive force than the four cells1 will overpower them and cause a current to flow in the direction indicated by the arrows until the pressure of the six cells has dropped to that of the four4 ,this will use up the energy of the six cells1 but will not weaken the four cell battery4 ,this action can be corrected by placing a two-way switch in the circuit at the junction of the two negative terminals so that only one battery can be used at a time4 ,,chapter ,v ,,conductors ,,and ,,insulators ,bodies differ from each other in a striking manner in the freedom with which the electric current moves upon them4 ,if the electric current be imparted to a certain portion of the surface of glass or wax1 it will be confined strictly to that portion of the surface which originally receives it1 by contact with the source of electricity2 but if it be in like manner imparted to a portion of the surface of a metallic body1 it will instantaneously diffuse itself uniformly over the entire extent of such metallic surface1 exactly as water would spread itself uniformly over a level surface on which it is poured4#c ,bodies in which the electric current moves freely are called conductors1 and those in which it does not move freely are called insulators4 ,there is1 however1 no substance so good a conductor as to be devoid of resistance1 and no substance of such high resistance as to be a non-conductor4 ,mention should be made here of the misuse of the word non-conductor2 the so-called 8non-conductors0 are properly termed insulators4 ,the bodies named in the following series possess conducting power in different degrees in the order in which they stand1 the most efficient conductor being first1 and the most efficient insulator being last in the list4 ,,table ,,of ,,conductors ,,and ,,insulators ,silver ,copper ,aluminum ,zinc ,brass 7according to composition7 ,platinum ,iron ,good conductors#d ,nickel 7metals and alloys7 ,tin ,lead ,german silver 7copper #b parts1 zinc #a1 nickel #a7 ,platinoid 7,german silver #di parts1 tungsten #a part7 ,antimony ,mercury ,bismuth4 ,charcoal and coke ,carbon ,plumbago ,acid solutions ,fair conductors ,sea water ,saline solutions ,metallic ores ,living vegetable substances ,moist earth4 ,water ,the body ,flame ,linen ,cotton ,partial conductors ,mahogany ,pine ,dry woods ,rosewood ,lignum ,vit ,teak ,marble4 ,slate ,oils ,porcelain ,dry leather ,dry paper ,wool ,silk ,sealing wax ,sulphur ,insulators1 or ,resin so-called ,gutta-percha non-conductors4 ,shellac ,ebonite ,mica ,jet ,amber ,paraffin wax ,glass 7varies with quality7 ,dry air4 ,illustration3 ,,figs4 #gf to #gh4--,various covered wires4 fig4 #gf1 single2 fig4 #gg1 duplex2 fig4 #gh1 automobile high tension cable4 ,the earth is a good conductor2 much difficulty is frequently experienced by the wires making contact with some substance that will conduct the electricity to the earth4 ,this is called 8grounding40 ,illustration3 ,,figs4 #gi to #ha4--,standard porcelain insulators4 ,fig4 #gi1 tube type2 figs4 #hj and #ha1 grooved insulators4 ,mode of ,transmission4--,the exact nature of electricity is not known1 yet the laws governing its action1 under various conditions are well understood1 just as the laws of gravitation are known1 although the constitution of gravity cannot be defined4 ,electricity1 though not a substance1 can be associated with matter1 and its transmission requires energy4 ,while it is neither a gas nor a liquid1 its behavior sometimes is similar to that of a fluid so that it is said to 8flow0 through a conductor4 ,this expression of flowing does not really mean that there is an actual movement in the wire1 similar to the flow of water in a pipe1 but is a convenient expression for the phenomena involved4 ,effect of ,heat4--,the conducting power of bodies is affected in different ways by their temperature4 ,in the metals it is diminished by elevation of temperature2 but in all other bodies1 and especially in liquids1 it is augmented4 ,some substances which are insulators in the solid state1 become conductors when fused4 ,sir ,h4 ,davy found that glass raised to a red heat became a conductor2 and that sealing wax1 pitch1 amber1 shellac1 sulphur1 and wax1 became conductors when liquefied by heat4 ,heating ,effect of the ,current4--,if a current of electricity pass over a conductor1 no change in the heat condition of the conductor will be observed as long as its transverse section is so considerable as to leave sufficient space for the free passage of the current4 ,but1 if this thickness be diminished1 or the quantity of electricity passing over it be augmented1 or1 in general1 if the ratio of the electricity to the magnitude of the space afforded to it be increased1 the conductor will be found to undergo an elevation of temperature1 which will be greater1 the greater the quantity of the electricity and the less the space supplied for its passage4 ,illustration3 ,,fig4 #hb4--,standard two wire porcelain cleat4 ,these heat effects are manifested in different degrees in different metals1 according to their varying conducting powers4 ,the poorest conductors1 such as platinum and iron1 suffer much greater changes of temperature by the same charge than the best conductors1 such as gold and copper4 ,the charge of electricity1 which only elevates the temperature of one conductor a small amount1 will sometimes render another incandescent1 and will vaporize a third4 ,insulators4--,the term insulator is used in two ways3 #a1 as in insulating substance or medium1 and #b1 as a specially formed piece of some insulating material1 such as glass1 porcelain1 etc4 ,no substance has the power of absolutely preventing the passage of electric currents between conductors but many have sufficient insulating power for practical purposes4 ,the properties to be desired in a good insulating material are3 #a4 ,permanence2 #b4 ,high power of resisting breakdown2 #c4 ,mechanical strength2 #d4 ,fairly high dielectric or insulation resistance2 #e4 ,special qualities for the use to which the material is to be put4 ,permanence is the most important quality1 and is the one least easily attained4 ,the power of resisting breakdown is a complex quality1 for it is not solely dependent on mere puncturing pressure1 but also on mechanical goodness1 and to a certain extent on the insulation resistance4 ,it cannot be easily determined by a simple laboratory test1 but must be found by experience of actual service conditions4 ,impregnating ,compounds4--,these are used for the treatment of fibrous materials4 ,they increase the insulating properties of the fibrous materials1 render them moisture proof and able to withstand the effect of heat with less rapid deterioration4 ,when wires or cables are to be used under water1 they must be made impervious1 and great care must be taken to prevent the water penetrating and thus injuring the insulation4 ,water as a ,conductor4--,water1 whether in the liquid or vaporous form1 is a conductor1 though of an order greatly inferior to the metals4 ,this fact is of great importance in electrical phenomena4 ,the atmosphere contains1 suspended in it1 always more or less aqueous vapor1 the presence of which impairs its insulating property4 ,the best insulators become less efficient if their surface be moist1 the electricity passing by the conducting power of the moisture4 ,this circumstance also shows why it is necessary to dry previously the bodies on which it is desired to develop electricity by friction4 ,,chapter ,,vi ,,resistance ,,and ,,conductivity ,resistance is that property of a substance that opposes the flow of an electric current through it4 ,the practical electrician has to measure electrical resistance1 electromotive forces1 and the capacities of condensers4 ,each of these several quantities is measured by comparison with ascertained standards1 the particular methods of comparison varying1 however1 to meet the circumstances of the case4 ,ohm's law states that the strength of a current due to an electromotive force falls off in proportion as the resistance in the circuit increases4 ,it is therefore possible to compare two resistances with one another by finding out in what proportion each will cause the current of a constant battery to fall off4#e ,silver is taken as the standard1 with the percentage of #ajj1 and the conductivity of all other metals is expressed in hundredths of the conductivity of silver4 ,conductivity of ,metals and ,liquids4--,the metals in general1 conduct well1 hence their resistance is small1 but metal wires must not be too thin or too long1 or they will resist too much1 and permit only a feeble current to pass through them4 ,the liquids in the battery do not conduct nearly so well as the metals1 and different liquids have different resistances4 ,pure water will hardly conduct at all1 unless the voltage be very high4 ,salt and saltpetre dissolved in water are good conductors1 and so are dilute acids1 though strong sulphuric acid is a bad conductor4 ,gases are bad conductors4 ,effect of ,heat4--,another very important fact concerning the resistance of conductors is that the resistance in general increases with the temperature4 ,while this fact is true regarding metals1 it does not apply to non-metals4 ,the resistance of different metals does not increase in the same proportion4 ,iron at #ajj degrees ,c1 has lost #ci per cent4 of the conducting power it possessed at zero1 while silver loses but #bc per cent4 ,laws of ,electrical ,resistance4--,resistances in a circuit may be of two kinds3 #a4 ,resistance of the conductors2 #b4 ,resistance due to imperfect contact4 ,the latter kind of resistance is affected by pressure1 for when the surfaces of two conductors are brought into more intimate contact the current passes more freely from one conductor to the other4 ,the following are the laws of the resistance of conductors3 #a4 ,the resistance of a conducting wire is proportional to its length4 ,if the resistance of a mile of telegraph wire be #ac ohms1 that of fifty miles will be #ej #ac #fej ohms4 #b4 ,the resistance of a conducting wire is inversely proportional to the area of its cross section1 and therefore in the usual round wires is inversely proportional to the square of its diameter4 ,ordinary telegraph wire is about #a_/fth of an inch thick2 a wire twice as thick would conduct four times as well1 having four times the area of cross section2 hence an equal length of it would have only #a_/dth the resistance4 #c4 ,the resistance of a conducting wire of given length and thickness depends upon the material of which it is made--that is1 upon the specific resistance of the material4 ,conductivity4--,this is the inverse of resistance4 ,the term expresses the capability of a substance to conduct the electric current4 ,if the symbol ,y represent the conductivity of a substance1 and ,i the current then3 ,i_/,y its resistance2 and if ,r represent the resistance of a substance1 then ,i_/,r its conductivity4 ,good conductors of heat are also good conductors of electricity4 ,specific ,conductivity4--,the figure which indicates the relation between one substance and another as to their capacity to conduct electricity is called specific or relative conductivity4 ,taking the specific conductivity of silver as #ajj1 that of pure copper is #if4 ,the specific resistance of a substance is the reverse of its relative conductivity4 ,the specific resistance of a metal is generally expressed in millionths of an ohm as the resistance of a centimeter cube of that metal between opposite sides4 ,the following table gives the data for a few metals3 ,specific ,resistance ,specific ,substance4 in ,microhms4 ,conductivity4 ,silver #a4fji #ajj4 ,copper #a4fdb #if4 ,gold #b4aed #gd4 ,iron 7soft7 #i4hbg #af4 ,lead #ai4hdg #h4 ,german ,silver #ba4dgj #g4e ,mercury 7liquid7 #if4adf #a4f ,the specific resistance of copper is therefore3 #a4fdb _/ #a1jjj1jjj ohms1 or #a4fdb microhms4#f ,divided ,circuits4--,if a circuit be divided1 as in fig4 #hc1 into two branches at ,a1 uniting again at ,b1 the current will also be divided1 part flowing through one branch and part through the other4 ,the relative strength of current in the two branches will be proportional to their conductivities4 ,this law will hold good for any number of branch resistances connected between ,a and ,b4 ,conductivity is1 as shown before1 the reciprocal of resistance4 ,,example--,if1 in fig #hc1 the resistance of ,r #aj ohms1 and ,r #bj ohms1 the current through ,r will be to the current through ,r as #a_/aj to #a_/bj2 or1 as #b3a1 or1 in other words1 #b_/c of the total current will pass through ,r and #a_/c through ,r4 ,the joint resistance of the two branches between ,a and ,b will be less than the resistance of either branch singly1 because the current has increased facilities for travel4 ,in fact1 the joint conductivity will be the sum of the two separate conductivities4 ,taking again the resistance of ,r #aj ohms and ,r #bj ohms1 the joint conductivity is #a_/aj #a_/bj #c_/bj and the joint resistance is equal to the reciprocal#g of #c_/bj or #f-b_/c ,illustration3 ,,fig4 #hc4--;,divided circuit with two conductors in parallel4 ,in most cases the resistance of the different branches will be alike4 ,this simplifies the calculations considerably4 ,take1 for instance1 two branches of #ajj ohms resistance each and find the joint resistance4 ,,solution3 #a_/ajj #a_/ajj #b_/ajj2 the reciprocal is #ajj_/b #ej ohms1 or1 in other words1 the joint resistance is one-half of the resistance of a single branch1 and each branch1 of course1 will carry one-half of the total current in amperes4 ,with three branches of equal resistance1 the joint resistance will be #a_/c2 with four branches #a_/d2 with #ajj branches #a_/ajj of the resistance of a single branch4 ,illustration3 ,,fig4 #hd4--;,hydraulic analogy for divided circuits4 ,in the system of pipes shown1 water flows from ,a ,b to ,c ,d through the six vertical pipes #a to #f1 the greatest amount going through the one which offers the least resistance4 ,if pipes #a to #f all have the same dimensions1 equal quantities of water will flow through them4 ,it follows that the resistance which the water encounters diminishes with the increase in the number of pipes between ,a ,b and ,c ,d4 ,the electrical circuit presents the same conditions3 the greater the number of parallel connections 7corresponding to the pipes #a to #f7 the less is the resistance encountered by the current4 ,if1 for instance1 the resistance of an incandescent lamp hot be #ahj ohms1 the joint resistance of #ajj such lamps connected in multiple is #ahj_/ajj #a4h ohms4 ,if the electromotive force of the system is to be1 say #aaj volts1 then1 according to ,ohm's law1 the current for #ajj lamps is3 #aaj_/a4h #fa4aa amperes4 giving for each lamp a current of #aaj_/ahj 4#fa ampere4 ,in the case of two branches only1 the following rule may be applied also3 ,multiply the two resistances and divide the product by their sum4 ,written as a formula3 ,joint resistance 7,r ,r7_/7,r ,r7 ,again1 assuming that ,r #aj ohms and ,r #bj ohms3 ,joint resistance 7#aj #bj7_/7aj #bj7 #bjj_/cj #f-b_/c ohms4 ,this rule cannot be employed for more than two branches at a time4 ,,example--,a current of #db amperes flows through three conductors in parallel of #e1 #aj and #bj ohms resistance respectively4 ,find the current in each conductor4 ,,solution3 ,joint ,conductance #a_/e #a_/aj #a_/bj #g_/bj4 ,supposing the current to be divided into #g parts1 #d of these parts would flow in the first conductor #b in the second and #a in the third4 ,the whole current is #db amperes4 #d_/g of #db #bd4 #b_/g of #db #ab4 #a_/g of #db #f4 ,current in first conductor #bd amperes4 8 8 second 8 #ab 8 ,ans4 8 8 third 8 #f 8 ,,chapter ,,vii ,,electrical ,,and ,,mechanical ,,energy ,the production of electricity is simply a transformation of energy from one form into another1 usually mechanical energy is changed into electrical energy and a dynamo is simply a device for effecting the transformation4 ,prof4 ,fessenden truly remarks there are two independent properties of matter--gravity and inertia--and these give two ways of defining force and energy4 ,it should always be remembered that electricity is something real1 although not easily defined4 ,and then1 too1 while it is not matter and not energy1 yet under proper conditions 7it having the power of doing work7 it is convenient to speak of its performances as electric energy4 ,the following questions and answers1 although few in number1 may present the subject with clearness4 ,ques4 ,what is energy8 ,ans4 ,energy is the capacity for doing work4 ,steam under pressure is an example1 a spring bent ready to be released is another form1 again1 water stored in an elevated tank has capacity for doing work4 ,these examples illustrate potential energy1 as distinguished from kinetic energy4 ,potential energy may be defined as energy due to position1 and kinetic energy1 as energy due to momentum4 ,ques4 ,what is matter8 ,ans4 ,matter is anything occupying space1 and which prevents other matter occupying the same space at the same time4 ,ques4 ,what name is given the smallest quantity of matter which can exist8 ,ans4 ,the atom4 ,an atom means that which cannot be cut1 scratched1 or changed in form and that cannot be affected by heat or cold or any known force2 although inconceivably small1 atoms possess a definite size and mass4 ,ques4 ,what is a molecule8 ,ans4 ,a molecule is composed of two or more atoms4 ,ques4 ,what is the behaviour of these minute bodies8 ,ans4 ,they are perpetually in motion1 vibrating with incredible velocities4 ,ques4 ,why at this point are definitions of energy and of matter most useful8 ,ans4 ,because1 as stated1 all electric action is an exhibition of energy1 and energy must act through matter as its medium4 ,ques4 ,what is the difference between electricity and magnetism8#h ,ans4 ,the ultimate nature of neither is known4 ,there are1 however1 some differences4 ,to sustain a current of electricity requires energy4 ,to sustain magnetism requires no energy4 ,a current of electricity is always accompanied by a magnetic field of peculiar form4 ,magnetism alone cannot produce electricity4 ,electricity can do work2 but magnetism cannot in the same sense--and alike with electricity1 neither can it exist without contact with matter4 ,ques4 ,how is energy transmitted from one part of a material substance to another8 ,ans4 ,gradually and successively4 ,it requires a medium and also time4 ,ques4 ,what is the principal use or function in mechanics of electricity8 ,ans4 ,it is purely that of transmission4 ,it corresponds to ropes1 shafts and fluids as a medium of conveying and translating power or work4 ,ques4 ,what is work8 ,ans4 ,work is the overcoming of resistance through a certain distance4 ,as a quantity of water moving from a higher to a lower level will do work1 so also will a quantity of electricity falling through a difference of potential4 ,ques4 ,how is work measured8 ,ans4 ,in foot pounds4 ,ques4 ,what is a foot pound8 ,ans4 ,the amount of work done in raising a weight of one pound one foot or the equivalent1 overcoming a pressure of one pound through a distance of one foot4 ,ques4 ,what is the electrical unit of work8 ,ans4 ,the volt-coulomb4 ,a volt-coulomb of work is performed when one ampere of current flows for one second in a circuit whose resistance is one ohm1 when the pressure is one volt4 ,the ,ampere-,hour4--,a gallon of water may be drawn from a hydrant in a minute1 or in an hour2 it is still one gallon4 ,so in electricity1 a given amount of the current1 say one coulomb1 may be obtained in a second or in an hour4 ,the ampere is the unit rate of flow4 ,what is called the electric current is simply the relation of any quantity of electricity passed to the time it is passing2 that is quantity in coulombs current in amperes time in seconds1 or simply coulomb ampere second4 ,again3 #aj coulombs #b amperes #e seconds #aj amperes #a second #a ampere #aj seconds1 etc4 ,one ampere-hour is simply another way of saying #c1fjj coulombs4 ,of course #c1fjj coulombs of electricity may be obtained in any desired time4 ,it all depends on the rate of flow or the current strength in amperes4 ,for instance1 #b amperes in #a_/b hour1 or #d amperes in #a_/d hour will also give one ampere-hour of #c1fjj coulombs4 ,it is well to keep the distinction between coulombs and amperes in mind1 as even in text books very lately published these units are confounded4 ,to illustrate further the difference between coulombs and amperes1 the following example is given4 ,it is sometimes estimated that the quantity of electricity in a flash of lightning is #a_/aj coulomb1 and the duration of the discharge #a_/bjjjj part of a second4 ,what is the current in amperes8 ,now since coulombs amperes seconds 7#a7 solving 7#a7 for the current1 amperes coulombs_/seconds 7#b7 substituting the given values in 7#b71 amperes 7#a_/aj7 _/ 7#a_/bjjjj7 #bjjj ,power4--,the term power means the rate at which work is done2 it is usually expressed as the number of foot pounds done in one minute1 that is power 7foot pounds7 _/ minutes ,power exerted for a certain time produces work4 ,ques4 ,what is the mechanical unit of power8 ,ans4 ,the horse power4 ,ques4 ,what is one horse power8 ,ans4 #cc1jjj foot pounds per minute4 ,the unit is due to ,james ,watt as being the power of a strong ,london draught horse to do work during a short interval and used by him to measure the power of his steam engines4 ,one horse power #cc1jjj ft4 lbs4 per minute #eej ft4 lbs4 per sec4 #a1ihj1jjj ft4 lbs4 per hour4 ,ques4 ,what is one horse power hour8 ,ans4 ,work done at the rate of one horse power for one hour4 ,ques4 ,what is the electrical unit of power8 ,ans4 ,the watt4 ,ques4 ,what is a watt8 ,ans4 ,it is the power due to a current of one ampere flowing at a pressure of one volt4 ,one watt one ampere one volt4 ,it is equal to one joule per second4 ,ques4 ,what is a kilowatt8 ,ans4 #a1jjj watts4 ,the ,watt-,hour4--,the elements which may be measured are1 however1 not only the volume of current1 the unit of which is the ampere1 and time1 the unit of which is the hour1 but also the pressure1 the unit of which is the volt4 ,it is evident that a perfect system of electrical measurement should take account of the total amount of energy consumed1 and should depend not only upon the volume of current1 but also upon the pressure at which the current is applied4 ,the basis of such a system if provided in a unit which is the product of the two units of current and pressure1 and which is termed a volt-ampere or watt4 ,the watt-hour represents the amount of work done by an electric current of one ampere strength flowing for one hour under a pressure of one volt4 ,,example--,an incandescent lamp taking one-half an ampere of current on a circuit having a pressure of #ajj volts1 or a lamp taking one ampere on a circuit having a pressure of #ej volts1 would each be consuming #ej watts of energy1 and this multiplied by the number of hours would give the total number of watt-hours for any definite time4 ,the watt1 then1 is an accurate and complete unit of measurement and is generally applicable to all forms of electrical consumption4 ,illustration3 ,,fig4 #he4--,tyndall's experiment illustrating the production of heat by friction4 ,a brass tube about #g inches in length and #c_/d of an inch in diameter1 is fixed on a small wheel4 ,by means of a cord passing round a much larger wheel1 this tube can be rotated with any desired velocity4 ,the tube is three parts full of water1 and is closed by a cork4 ,in making the experiment1 the tube is pressed between a wooden clamp1 while the wheel is rotated with some rapidity4 ,the water rapidly becomes heated by the friction1 and its temperature soon exceeds the boiling point4 ,the pressure caused by the formation of steam forces out the cork and projects it to a height of several yards4 ,a watt of electrical energy corresponds to #a_/gdf of a horse power of mechanical energy2 hence1 if a lamp or motor require energy equivalent to #a_/gdf of a horse power for one hour1 it might be said to take one watt-hour4 ,mechanical ,equivalent of ,heat4--,the eminent ,english physicist1 ,james ,prescott ,joule1 worked for more than forty years in establishing the relation between heat and mechanical work2 he stated the doctrine of the conservation of energy and discovered the law1 known as ,joule's law1 for determining the relation between the heat1 current pressure1 and time in an electric circuit4 ,ques4 ,what is heat8 ,ans4 ,a form of energy4 ,heat is produced in the agitation of the molecules of matter--the energy expended in agitating these molecules is transformed into heat4 ,illustration3 ,,fig4 #hf4--;,joules' experiment on the mechanical equivalent of heat1 in which he caused paddle-wheels to rotate in a vessel of water by means of falling weights ,w4 ,the amount of work done by gravity upon the weights in causing them to descend through any distance d was equal to their weight ,w times the distance4 ,if the weights descended slowly and uniformly1 this work was all expended in overcoming the resistance of the water to the motion of the paddle-wheels through it2 that is1 it was wasted in eddy currents in the water4 ,joule measured the rise in the temperature of the water and found that the mean of his three best trials gave #dbg gram meters as the amount of work required to develop enough heat to raise a gram of water one degree4 ,he then repeated the experiment1 substituting mercury for water1 and obtained #dbe gram meters as the work necessary to produce a calorie of heat4 ,the difference between these numbers is less than was to have been expected from the unavoidable errors in the observations4 ,he then devised an arrangement in which the heat was developed by the friction of iron on iron1 and again obtained #dbe4 ,this corresponds to #ggb foot pounds1 but later experiments show that the correct value is #ggh foot pounds4 ,ques4 ,how is heat measured8 ,ans4 ,in ,british thermal units 7,b4t4u474 ,ques4 ,what is the ,british thermal unit8 ,ans4 ,the quantity of heat required to raise the temperature of #a lb4 of pure water #a ,fahr41 at or near #ci4a ,f41 the temperature of maximum density4 ,ques4 ,what is the mechanical equivalent of heat8 ,ans4 ,the number of foot pounds of mechanical energy equivalent to one ,british thermal unit4 ,joule's experiments #ahdc-ej gave the figure #ggb ft4 lbs4 which is known as ,joule's equivalent4 ,later experiments gave higher figures1 and the present accepted value is #ggh ft4 lbs41 that is3 #a ,b4t4u4 #ggh ft4 lbs4 ,electrical ,horse ,power4--,it is desirable to establish the relation between watts and foot pounds in order to determine the capacity of an electric generator or motor in terms of horse power4 ,one watt is equivalent to one joule per second or #fj joules per minute4 ,one joule in turn1 is equivalent to 4#gcgd ft4 lbs41 hence #fj joules equal3 #fj 4#gcgd #dd4bdd ft4 lbs4 ,since one horse power #ccjjj ft4 lbs4 per minute1 the electrical equivalent of one horse power is #ccjjj #dd4bdd #gdf watts4 or1 #gdf _/ #ajjj 4#gdf kilowatts 7,k4,w47 ,again1 one kilowatt or #ajjj watts is equivalent to #ajjj #gdf #a4cd horse power4 ,the ,farad4--,the measure constructed to hold a gallon of water may be called the gallon measure4 ,the capacity of a condenser which would contain a charge of one coulomb under one volt pressure is the farad4 ,it may seem strange that there is a unit of quantity and another of capacity to hold that quantity1 when in the case of water the term 8gallon0 may suffice for the measure and the liquid it can hold4 ,electricity in this respect1 however1 corresponds to a compressible fluid or a gas4 ,a gallon measure may hold a gallon of gas or ten2 it depends entirely upon the pressure4 ,so a condenser of a certain size may hold any number of coulombs1 according to the electrical pressure4 ,the farad being inconveniently large for practical use1 one-millionth of a farad1 called a microfarad1 is generally adopted4 ,,chapter ,,viii ,,effects ,,of ,,the ,,current ,the term 8electric current10 in the present state of our knowledge1 should be regarded as denoting the existence of a state of things in which certain definite experimental effects are produced1 for some of which there certainly is no analogy exhibited in ordinary hydraulic currents4 ,the following are the most important of these effects3 #a4 ,thermal effect2 #b4 ,magnetic effect2 #c4 ,chemical effect4 ,it is rather to these effects than to any imaginary current flow in the conductor that the mind of the reader should be directed4 ,with this preliminary caution1 which should never be lost sight of1 the use of familiar words and expressions connected with the flow of water in pipes is justified in order to avoid roundabout and cumbrous phrases which1 though perhaps more nearly in accord with present knowledge of the facts1 would not tend to clearness or conciseness4 ,the three most important effects of the current just mentioned1 may be presented in more detail as follows3 #a4 ,the ,thermal effect3-- ,the conductor along which the current flows becomes heated4 ,the rise of temperature may be small or great according to circumstances1 but some heat is always produced4 #b4 ,the ,magnetic effect2 ,the space both outside and inside the substance of the conductor1 but more especially the former1 becomes a 8magnetic field0 in which delicately pivoted or suspended magnetic needles will take up definite positions and magnetic materials will become magnetized4 ,illustration3 ,,fig4 #hg4--,lenz's apparatus for measuring the heat given off by an electric current4 ,it consisted of a wide mouthed stoppered bottle fixed upside down1 with its stopper1 b in a wooden box2 the stopper was perforated so as to give passage to two thick platinum wires1 connected at one end with binding screws1 s1 while their free ends were provided with platinum cones by which the wires under investigation could be readily affixed2 the vessel contained alcohol1 the temperature of which was indicated by a thermometer fitted in a cork inserted in a hole made in the bottom of the vessel4 ,the current is passed through the platinum wires1 and its strength measured by means of a galvanometer interposed in the circuit4 ,by observing the increase of temperature in the thermometer in a given time and knowing the weight of the alcohol1 the mass of the wire1 the specific heat1 and the calorimetric values of the vessel1 and of the thermometer1 compared with alcohol1 the heating effect which is produced by the current in a given time can be calculated4 #c4 ,the ,chemical effect2-- ,if the conductor be a liquid which is a chemical compound of a certain class called electrolytes1 the liquid will be decomposed at the places where the current enters and leaves it4 ,thermal ,effect4--,if a quantity of electricity were set flowing in a closed circuit and the latter offered no resistance1 it would flow forever1 just as a wagon set rolling along a circular railway would never stop if there were no friction4 ,illustration3 ,,fig4 #hh4--,the ,seebeck effect3 ,if in a complete metallic circuit having junctions of dissimilar metals1 the junctions are at different temperatures1 then generally a steady current will flow in the circuit as long as the differences of the temperatures of the junction is maintained4 ,to demonstrate this1 a piece of copper ,k bent in the shape seen in the figure1 was placed on a block of bismuth ,a ,b1 carrying a pivoted magnetic needle ,n ,s2 as soon as the equality of temperatures was altered by either heating or cooling one of the junctions of the two metals1 the needle indicated a current which continued to flow as long as the difference of temperature was maintained at the junctions4 ,the movement of the needle indicated the direction in which the current flowed4 ,if1 for instance1 the north junction ,b were heated1 the ,n pole moved eastwards1 showing that at the heated junction the current flows from the bismuth to the copper1 at the cold junction from the copper to the bismuth4 ,when matter in motion is stopped by friction1 the energy of its motion is converted into heat by the friction thus causing the matter to come to rest4 ,similarly1 when electricity in motion1 that is1 an electric current is stopped by resistance1 the energy of its flow is transformed into heat by the resistance of the circuit4 ,if the terminals of a battery be joined by a short thick wire of low resistance1 most of the heat will be developed in the battery1 whereas1 if a thin wire of high resistance be used it will become hot1 while the battery itself will remain comparatively cool4 ,to investigate the development of heat by a current1 ,joule and ,lenz used instruments on the principle of fig4 #hg1 in which a thin wire joined to two stout conductors is enclosed within a glass vessel containing alcohol1 into which is placed a thermometer4 ,the resistance of the wire being known1 its relation to the other resistances can be calculated4 ,joule found that the number of heat units developed in a conductor is proportional to3 #a4 ,the resistance2 #b4 ,the square of the current strength2 #c4 ,the time that the current lasts4 ,joules' law may be stated as follows3 ,the heat generated in a conductor by an electric current is proportional to the resistance of the conductor1 the time during which the current flows1 and the square of the strength of the current4 ,the quantity of heat in calories may be calculated by use of the equation1 calories per second volts amperes 4#bd4 7#a7 ,the total number of calories ,h developed in t seconds will be given by ,h ,p4,d4 ,c t 4#bd4 7#b7 ,,example--,if a current of #aj amperes flows in a wire whose terminals are at a potential difference of #ab volts1 how much heat will be developed in #e minutes8 ,substituting in equation 7#b73 #aj #ab 7#fj #e7 4#bd #hfdj calories4 ,since by ,ohm's ,law potential difference ,i ,r substituting ,,ir for ,p4,d4 in 7#b7 ,h ,i#b ,r t 4#bd ,use of ,heat from ,electric ,current4--,in the transmission of electricity from place to place1 it is very desirable that none of the energy be expended in heating the conductor4 ,hence copper wires of the proper size must be used4 ,in wiring a building for electric lights1 the insurance rules require that the wires be of a certain size and that they be put up in a certain manner4 ,otherwise they will not insure a building against fire4 ,it is often desirable1 however1 to use the electric current for the purpose of producing heat4 ,the carbons of the arc and incandescent lamps are intensely heated that they may produce light4 ,coils of ,german silver wire or other high resistance wire are heated by the passage of a current through them4 ,in this manner the electric stove is made4 ,soldering coppers1 smoothing irons1 and baking ovens are heated in a similar manner4 ,magnetic ,effect4--,an electric current flowing in a wire causes it to be surrounded by a magnetic field1 which consists of lines of force encircling the wire4 ,the field is strongest near the wire and diminishes gradually in strength at increasing distances therefrom4 ,the presence of this magnetic field is shown by various experiments and the subject is fully explained in chapter ,,ix on magnetism4 ,chemical ,effect4--,pats van ,trostwyk 7#aghi7 pointed out that an electric discharge was capable of decomposing water2 to show this he used gold wires1 which he allowed to dip in water1 connecting one of them with the inner1 and another with the outer coating of a ,leyden jar1 and passing the discharge through the water4 ,the gas bubbles collected proved to consist of oxygen and hydrogen gas4 ,nicholson and ,carlisle 7#ahjj7 dipped a copper wire which was connected with one of the poles of a voltaic pile into a drop of water1 which happened to be on the plate connected with the other pole2 gas bubbles appeared1 and the drop of water became smaller and smaller4 ,this experiment was repeated in a somewhat different manner1 the brass wires from a pile being brought under a tube filled with water and closed at the top4 ,gas bubbles were produced by the wire in connection with the negative pole of the pile1 and the water was observed to diminish gradually4 ,at the positive wire1 on the contrary1 no gas came off1 but the metal lost its metallic lustre1 became dark1 and finally crumbled away4 ,the gas which had collected in the tube proved to be hydrogen2 while on examining the black mass it was found that the constituents of brass1 viz41 copper and zinc1 had become oxidized4 ,illustration3 ,,fig4 #hi4--;,an electrolytic cell4 ,the parts are3 ,a1 cell2 ,b1 electrolyte2 ,c1 positive electrode or cathode2 ,d1 negative electrode or cathode4#i ,electrolysis4--,electric analysis or more briefly electrolysis was the term applied by ,faraday to the process of decomposing a liquid by the passage of a current of electricity through it4 ,the vessel containing the liquid is known as an electrolytic cell4 ,in fig4 #hi1 ,a is the cell1 which may be of glass or of any other suitable material1 and ,b is the liquid which is to be electrolyzed4 ,current enters by the positive electrode ,c1 also known as the anode1 traverses the liquid1 and leaves by the negative electrode1 or cathode1 ,d4 ,illustration3 ,,fig4 #ij4--,modern apparatus for decomposing water by electrolysis4 ,platinum electrodes ,p and ,p are placed at the bottom of two upright tubes ,o and ,h1 and are connected to the terminals ,t and ,t by platinum wires1 which are fused through the glass of the tubes4 ,these tubes have glass stop cocks ,s and ,s at their upper ends1 and at their lower ends are connected by a short glass tube1 from the center of which rises the large central tube which expands with a bulb at its upper end1 which is open at the top4 ,the three tubes can be filled with acidulated water from the central tube1 the previously contained air being allowed to escape through the stop cocks1 which are afterwards closed4 ,if it be so filled1 and the terminal ,t be attached to the positive and ,t to the negative pole of a suitable battery1 bubbles of gas will be observed to rise from the plates ,p and ,p1 and finding their way to the top of the respective tubes1 will displace the liquid1 which will be driven into the open central tube4 ,the gas rising from the anode ,p is oxygen 7,o71 and that rising from the cathode ,p is hydrogen 7,h74 ,if the tubes are graduated1 the latter will be found to occupy about twice the volume of the former4 ,the proportion is theoretically #b to #a2 however1 on account of the different solubilities of the two gases in water1 oxygen being the more soluble of the two1 is deficient in quantity4 ,the passage of current through the water splits up its molecules into their constituent atoms of oxygen and hydrogen1 the former being given off in bubbles at the anode1 and the latter at the cathode4 ,when current is passed through a solution of copper sulphate between platinum electrodes1 the liquid is decomposed1 atoms of copper being deposited at the cathode1 bubbles of oxygen being given off at the anode1 and sulphuric acid being formed in the liquid1 which latter becomes more and more acid as the copper is withdrawn4 ,illustration3 ,,fig4 #ia4--;,grotthuss' theory of electrolysis4 ,grotthuss in 7#ahjf71 announced his theory that the molecules in an electrolyte have their individual electro-positive and electro-negative atoms charged positively and negatively respectively4 ,in an ordinary liquid1 for instance in water1 the molecules are arranged indifferently1 like row #a1 with their positive and negative ends pointing in all directions4 ,when the charged plates ,a and ,b connected to the and - poles of a battery are inserted in the water1 the molecules under the action of the laws of electrostatic action turn as shown in row #b1 so that all the hydrogen or shaded ends 77 are turned towards the 7-7 plate ,b and all the oxygen or unshaded ends 7-7 towards the 77 plate ,a4 ,all along the row the electrical forces are supposed to tear the molecules asunder1 depositing ,h on ,b and ,o on ,a4 ,the atoms in the middle of the liquid1 however1 recombine1 for the hydrogen atoms in their journey towards ,b meet the oxygen atoms travelling in the opposite direction1 and we get the state of affairs represented in row #c4 ,the next step is to rotate once more the atoms into the positions shown in row #b1 and so on4 ,in this way the theory accounts for the products only appearing at the electrodes and not in the body of the liquid4 ,if1 however1 the anode be of copper instead of platinum1 no sulphuric acid will be formed1 neither will oxygen be given off at the anode4 ,as copper is deposited at the cathode1 an equal quantity will be dissolved at the anode1 so that the original constitution of the liquid is maintained4 ,the atoms separated from each other by the electric current were called ions by ,faraday2 those going to the anode being anions1 and those going to the cathode being kathions4 ,anions are generally regarded as electro-negative1 because they move as if attracted to the positive electrode1 while kathions are regarded as electro-positive4 ,in order to explain the transfer of electricity and the transfer of matter through the electrolyte1 ,grotthuss put forward the hypothesis that when two metal plates at different potentials are placed in a cell1 the effect produced in the liquid is that the molecules of the liquid arrange themselves in innumerable chains1 as shown in fig4 #ia1 in which every molecule has its atoms pointing in a certain direction1 the electro-positive atom being attracted towards the cathode and the electro-negative towards the anode4 ,an interchange then takes place all along the line1 the free atoms appearing at the electrodes1 and every atom discharging a minute charge of electricity upon the electrode at which it is liberated4 ,electro-chemical ,series4--,this is an arrangement of the metals in a series in such a manner that the most electro-positive is at one end and the most electro-negative at the other4 ,the order of the metals varies with the electrolyte in which the metals are tested4 ,the following table shows such series for the most common metals1 in three different solutions3 ,sulphuric acid4 ,hydrochloric acid4 ,caustic potash4 ,zinc ,zinc ,zinc ,cadmium ,cadmium ,tin ,tin ,tin ,cadmium ,lead ,lead ,antimony ,iron ,iron ,lead ,nickel ,copper ,bismuth ,bismuth ,bismuth ,iron ,antimony ,nickel ,copper ,copper ,silver ,nickel ,silver ,antimony ,silver ,gold ,platinum ,faraday stated several laws of electrolysis1 as follows3 #a4 ,the quantity of an ion liberated in a given time is proportional to the quantity of electricity that has passed through the voltameter#aj in that time4 #b4 ,the quantity of an ion liberated in a voltameter is proportional to the electro-chemical equivalent of the ion4 #c4 ,the quantity of an ion liberated is equal to the electro-chemical equivalent of the ion multiplied by the total quantity of electricity that has passed4 ,electric ,osmose4--,porret observed that if a strong current be led into certain liquids as if to electrolyze them1 a porous partition being placed between the electrodes1 the current mechanically carries part of the liquid through the porous diaphragm1 so that the liquid is forced to a higher level on one side than on the other4 ,this phenomenon is known as electric osmose4 ,electric ,distillation4--,closely connected with the preceding phenomenon is that of the electric distillation of liquids4 ,it was noticed by ,beccaria that an electrified liquid evaporates more rapidly than one not electrified4 ,gernez has recently shown that in a bent closed tube1 containing two portions of liquid1 one of which is made highly and the other highly -1 the liquid passes over from to -4 ,this apparent distillation is not due to difference of temperature1 nor does it depend on the extent of surface exposed1 but is effected by a slow creeping of the liquid along the interior surface of the glass tubes4 ,bad conductors1 such as turpentine1 do not thus pass over4 ,illustration3 ,,fig4 #ib4--;,effect of the electric current on a frog's legs2 discovered in #afgh by ,galvani4 ,muscular ,contractions4--,it was discovered in #afgh that when a portion of muscle of a frog's leg1 hanging by a thread of nerve bound with a silver wire1 was held over a copper support so that both nerve and wire touched the copper1 the muscle immediately contracted4 ,more than a century later ,galvani's attention was drawn to the subject by his observation of spasmodic contractions in the legs of freshly killed frogs under the influence of the 8return shock0 experienced every time a neighboring electric machine was discharged4 ,the limbs of the frog1 prepared as directed by ,galvani1 are shown in fig4 #ib4 ,after the animal has been killed the hind limbs are detached and skinned2 the crural nerves and their attachments to the lumbar vertebrae remaining4 ,for some hours after death the limbs retain their contractile power4 ,the frog's limbs thus prepared form an excessively delicate galvanoscope4 ,electroplating4--,this is the process of depositing a layer or coating of a rarer metal upon the surface of a baser1 or of a metal upon any conducting surface1 by electrolysis4 ,the electric current used may be obtained from a battery or other source4 ,the battery has its positive plate connected to a rod extending across a trough or tank containing the plating bath4 ,suspended from the rod are anodes of gold1 silver1 or copper or whatever metal from which a deposit is desired4 ,the other plates of the battery or the negative elements1 are connected with another rod across the trough1 to which are suspended the articles to be plated4 ,electrotyping4--,this is the process by which1 type1 wood cuts1 etc41 are reproduced in copper by the process of electroplating4 ,a mould is first made of the set type in wax2 this mould is next coated with black lead to give it a metallic surface1 as the wax is an insulator2 the mould is then subjected to the process of electro deposition1 resulting in the formation of a film of copper on the prepared surface4 ,the copper shell is removed from the mould by applying hot water2 the shell is then backed up with electrotype metal to render it strong enough for use4 ,almost all the illustrations in this book1 for example1 are printed from electrotype copies1 and not from the original wood blocks1 which would not wear so well4 ,,chapter ,,ix ,,magnetism ,magnetism4--,the ancients applied the word 8magnet10 magnes lapes1 to certain hard black stones which possess the property of attracting small pieces of iron1 and as discovered later1 to have the still more remarkable property of pointing north and south when hung up by a string4 ,at this time the magnet received the name of lodestone or 8leading stone40 ,it is commonly1 though incorrectly1 spelled loadstone4 ,illustration3 ,,fig4 #ic4--,simple compass4 ,it consists of a magnetic needle resting on a steel pivot1 protected by a brass case covered with glass1 and a graduated circle marked with the letters ,n1 ,e1 ,s1 ,w1 to indicate the cardinal points2 a b is a lever which arrests the needle by pushing it against the glass when the button d is pressed4 ,ques4 ,describe two kinds of magnetism4 ,ans4 ,magnets have two opposite kinds of magnetism or magnetic poles1 which attract or repel each other in much the same way as would two opposite kinds of electrification4 ,ques4 ,what is the nature of each kind of magnetism8 ,ans4 ,one has a tendency to move toward the north and the other toward the south4 ,illustration3 ,,figs4 #id to #if4--,simple bar magnet and horse shoe magnet with keeper4 ,these are known as permanent magnets in distinction from electromagnets4 ,the horse shoe magnet will attract more than the bar magnet because both poles act together4 ,a piece of soft iron1 or keeper is placed across the ends of a horse shoe magnet to assist in preventing the loss of magnetism4 ,illustration3 ,,figs4 #ig and #ih4--;,horizontal magnetic needle1 and magnetic 8dip0 needle4 ,a magnetic needle consists of a small bar magnet1 supported upon a pivot or suspended so that it is free to turn in a horizontal or vertical plane4 ,the form of magnetic needle illustrated in fig4 #ig is arranged to show the magnetic meridian2 the needle moves upon a perpendicular axis or pivot ab4 ,in fig4 #ih1 the needle sn turns upon a horizontal axis ab4 ,this needle indicates the dip or inclination1 that is1 the angle which it makes with the horizontal plane1 due to the fact that in most places the lines of force are not horizontal4 ,in the northern hemisphere the ,n pole of the needle is depressed1 in the southern hemisphere the ,s pole is similarly affected4 ,when used1 the dip needle must be set so that the plane in which the needle swings contains the magnetic meridian1 as indicated by the horizontal needle4 ,ques4 ,where is the magnetism the strongest8 ,ans4 ,in two regions called the poles4 ,ques4 ,describe the distribution of magnetism in a long shaped magnet4 ,ans4 ,the strongest magnetism resides in the ends1 while all around the magnet half way between the poles there is no attraction at all4 ,illustration3 ,,fig4 #ii4--,magnetic poles4 ,if a bar magnet be plunged into iron filings and then lifted1 as illustrated in the figure1 a mass of filings will cling to the ends of the magnet but not to the middle4 ,the ends are called the poles of the magnet4 ,ques4 ,how are the poles designated8 ,ans4 ,they are called the north pole and the south pole4 ,ques4 ,what is the distinguishing feature of each8 ,ans4 ,the north pole points approximately to the earth's geographical north1 while the south pole of a magnet points approximately to the earth's geographical south4 ,the north pole is the positive 77 pole and the south pole is the negative4 ,the north and south poles were formerly called in ,france1 the austral and boreal poles respectively4 ,magnetic ,field4--,when a straight bar magnet is held under a piece of card board upon which iron filings are sprinkled1 the filings will arrange themselves in curved lines radiating from the poles4 ,if a horse shoe magnet be held at right angles to the plane of the card board1 the filings will arrange themselves in curved lines1 as shown in fig4 #ajh4 ,these lines are called magnetic lines of force or simply lines of force2 they show that the medium surrounding a magnet is in a state of stress1 the space so affected being called the magnetic field4 ,illustration3 ,,fig4 #ajj4--;,badly magnetized bar4 ,properly magnetized magnets have only two poles2 it is possible1 however1 by special or careless magnetization1 to produce magnets with more than two poles1 but no process will produce a magnet with a single pole4 ,if an abnormal magnet with more than two poles be dipped into iron filings1 the latter will adhere at places other than the two ends1 as shown in the illustration4 ,the polarities are alternately ,n and ,s2 that is1 the regions ,n1 ,b1 ,n1 have north polarity1 while ,a and ,c have south polarity4 ,these are known as consequent poles4 ,illustration3 ,,figs4 #aja to #ajg4--;,effect of breaking a magnet into several parts4 ,if a magnetized needle be broken1 each part will be found to be a complete magnet having a ,n and ,s pole4 ,the sub-division may be continued indefinitely1 but always with the same result as indicated in the figure4 ,this is evidence of the correctness of the molecular theory of magnetism1 which states that the molecules of a magnet are themselves minute magnets arranged in rows with their opposite poles in contact4 ,ques4 ,what is the extent and character of the magnetic field8 ,ans4 ,the influence of a magnet is supposed to extend in all directions indefinitely1 however1 the effect is very slight beyond a comparatively limited area4 ,illustration3 ,,fig4 #ajh4--,the region about a magnet in which its magnetic forces can be detected is called the magnetic field4 ,this can be represented graphically by placing a piece of cardboard over the magnet and sprinkling iron filings on the paper1 gently tapping at the same time4 ,each filing becomes a temporary magnet by induction1 and sets itself1 like the compass needle1 in the direction of the line of force of the magnetic field4 ,illustration3 ,,fig4 #aji4--,tracing lines of force with a suspended magnet4 ,if a small magnetic needle1 suspended by a thread1 be held near a magnet1 it will point in some fixed direction depending on the proximity of the poles of the magnet4 ,the direction taken by the magnet is called the direction of the force at the point1 and if the suspended needle be moved forward in the direction of the pole1 it will trace out a curved line which will be found to start from one of the poles1 and end at the other4 ,any number of such lines can be traced2 the space filled by these lines of force is called the magnetic field4 ,illustration3 ,,fig4 #aaj4--,magnetic action3 ,unlike poles of magnets attract each other4 ,illustration3 ,,fig4 #aaa4--,magnetic action3 ,like poles of magnets repel each other4 ,magnetic ,force4--,this is the force with which a magnet attracts or repels another magnet or any piece of iron or steel4 ,the force varies with the distance1 being greater when the magnet is nearer and less when the magnet is farther off4 ,the following are the laws relating to magnetic force3 #a4 ,like magnetic poles repel one another2 unlike magnetic poles attract one another4 #b4 ,the force exerted between two magnetic poles varies inversely as the square of the distance between them4 ,magnetic ,circuit4--,the path taken by magnetic lines of force is called a magnetic circuit2 the greater part of such a circuit is usually in magnetic material1 but there are often one or more air gaps included4 ,the total number of lines of force in the circuit is known as the magnetic flux4 ,ques4 ,how is magnetic flux measured8 ,ans4 ,by a unit called the maxwell4 ,named after ,james ,clerk ,maxwell the ,scottish physicist4 ,ques4 ,what is the maxwell8 ,ans4 ,the amount of magnetism passing through every square centimetre of a field of unit density4 ,ques4 ,what is the unit of field strength8 ,ans4 ,the gauss4 ,ques4 ,what is a gauss8 ,ans4 ,the intensity of field which acts on a unit pole with a force of one dyne4 ,it is equal to one line of force per square centimetre4 ,named after ,karl ,friedrich ,gauss1 the ,german mathematician4 ,the ,magnetic ,effect of the ,current4--,hans ,christian ,oerstead1 the ,danish scientist1 discovered in #ahai that a magnet tends to set itself at right angles to a wire carrying an electric current4 ,he also found that the way in which the needle turns1 whether to the right or left of its usual position1 depends3 #a1 upon the position of the wire that carries the current1 whether it be above or below the needle1 and #b1 on the direction in which the current flows through the wire4 ,illustration3 ,,fig4 #aab4--;,illustrating ,maxwell's 8corkscrew rule0 for relative directions of current and lines of force4 ,according to the rule3 the direction of the current and that of the resulting magnetic force are in the same relation to each other as is the forward travel and rotation of an ordinary corkscrew1 ,thus1 in the figure1 if a current flow through the wire ab in the direction from a to b1 the magnetic lines will encircle the wire in the direction of the curved arrow ro which shows the direction in which the corkscrew must be turned to advance in the direction of the arrow n4 ,to keep these movements in mind numerous rules have been suggested1 of which the following will be found convenient3 ,corkscrew ,rule4--,if the direction of travel of a right handed corkscrew represent the direction of the current in a straight conductor1 the direction of rotation of the corkscrew will represent the direction of the magnetic lines of force4 ,illustration3 ,,fig4 #aac4--;,experiment showing direction of lines of force in the magnetic field surrounding a conductor carrying an electric current4 ,a piece of copper wire is pierced through the center of a sheet of cardboard1 and carried vertically for two or three feet then bent around to the terminals of a battery or other source of current4 ,if iron filings be sprinkled over the card while the current is passing1 they will arrange themselves in circles around the wire1 thus indicating the form of the magnetic field surrounding the conductor4 ,compass needles may also be used to show the direction of the lines of force at any point4 ,illustration3 ,,fig4 #aad4--,right hand rule to determine the direction of magnetic field around a conductor carrying a current4 ,the thumb of the right hand is placed along the conductor1 pointing in the direction in which the current is flowing1 then1 if the fingers be partly closed1 as shown in the illustration1 the finger tips will point in the direction of the magnetic whirls4 ,ques4 ,what is the effect of a current flowing in a loop of wire8 ,ans4 ,if1 in figs4 #aaf and #aag1 the current flow in the direction indicated by the arrow1 the lines for magnetic force are found to surround the loop as shown2 all the lines leave on one side of the loop and return on the other2 accordingly1 a north pole is formed on one side1 and a south pole on the other4 ,illustration3 ,,fig4 #aae4--,right hand palm rule to determine the direction of the magnetic field around a conductor carrying a current3 ,place the palm of the outstretched right hand above and to the right side of the wire with the fingers pointing in the direction of the current1 and the thumb extended at right angles1 that is1 pointing downward4 ,the direction in which the thumb points will indicate the direction of the magnetic whirls4 ,illustration3 ,,fig4 #aaf4--,lines of force of a circular loop4 ,if a current flow through the loop in the direction indicated1 the lines of force both inside and outside the loop1 will cross the plane of the loop at right angles1 and all those which cross the loop on the inside will pass through the plane in one direction 7downwards in the figure71 while all on the outside will return through the plane in the opposite direction4 ,solenoids4--,a solenoid consists of a spiral of conducting wire wound cylindrically so that1 when an electric current passes through it1 its turns are nearly equivalent to a succession of parallel circular circuits1 and it acquires magnetic properties similar to those of a bar magnet4 ,illustration3 ,,fig4 #aag4--,lines of force of a circular loop4 ,if the loop pass through a piece of cardboard at right angles to its plane1 and the current flow as indicated1 the dotted lines on the cardboard will represent the direction of the lines of force in the plane of the cardboard4 ,the student should verify the lines of force as here given by applying the corkscrew rule4 ,ques4 ,what is the character of the lines of force of a solenoid in which a current is flowing8 ,ans4 ,the lines of force must be thought of as closed loops linked with the current4 ,the conductor conveying the current passes through all the loops of force1 and these are1 so to speak1 threaded or slung on the current-line of flow1 as in fig4 #aaf4 ,ques4 ,what is the distribution of the lines of force8 ,ans4 ,the lines of force form continuous closed curves running through the interior of the coil2 they issue from one end and enter into the other end of the coil1 as shown in fig4 #aag4 ,ques4 ,what are the properties of a solenoid8 ,ans4 ,a solenoid has north and south poles1 and in fact possesses all the properties of an ordinary permanent magnet1 with the important difference that the magnetism is entirely under control4 ,since a solenoid carrying a current attracts and repels by its extremities the poles of a magnet1 two such solenoids will attract and repel each other4 ,illustration3 ,,fig4 #aah4--,magnetic field of a solenoid4 ,this is best observed by cutting a piece of cardboard and fitting it around the solenoid1 as shown4 ,if iron filings be sprinkled on the cardboard and a current passed through the solenoid1 the character of the field is indicated4 ,with the current in the direction shown1 it will be found that wherever small compass needles are placed1 the direction in which their north poles turn is along arrows marked on the card4 ,the card only exhibits the field in one of the sectional planes of the coil1 but it is obvious that the field is the same for all sectional planes4 ,ques4 ,how does the magnetic strength of a solenoid vary8 ,ans4 ,it is proportional to the strength of the electric current passing through it4 ,ques4 ,on what1 besides the current strength1 does the magnetizing power of a solenoid depend8 ,ans4 ,the magnetic effect or the magnetizing power is proportional to the number of turns of wire composing the coil4 ,ques4 ,how may the magnetizing power of a solenoid be increased8 ,ans4 ,by inserting in the solenoid an iron core or round bar of soft iron4 ,illustration3 ,,fig4 #aai4--,right hand rule for polarity of a solenoid3 ,if the solenoid be grasped in the right hand1 so that the fingers point in the direction in which the current is flowing in the wires1 the thumb extended will point in the direction of the north pole4 ,ques4 ,describe the action of an iron core4 ,ans4 ,at first1 the presence of an iron core greatly increases the strength of the field2 after a time1 however1 as the strength of the current flowing in the exciting coils is increased1 the conductibility of the iron for the lines of force appears to decrease1 until a point is eventually reached when the presence of the iron core appears to have no effect in increasing the strength of the field4 ,permeability4--,permeability is a measure of the ease with which magnetism passes through any substance4 ,it is defined as3 the ratio between the number of lines of force per unit area passing through a magnetizable substance1 and the magnetizing force which produces them4 ,illustration3 ,,figs4 #abj and #aba4--;,illustrating the effect of introducing an iron core into a solenoid4 ,in the upper figure1 the air space or 8air core0 surrounded by the solenoid offers considerable resistance to the passage of magnetic lines1 allowing only a small number to pass through4 ,if a piece of iron be introduced1 as in the lower figure1 the number of lines will be greatly increased4 ,the number of lines ,b passing through a unit cross section of the iron core divided by the number of lines ,h1 passing through a unit cross section of the air core is called the permeability and designated by the ,greek letter 4 ,in other words1 it is the ratio of flux density to magnetizing force4 ,permeability is a measure of the ease with which magnetism passes through any substance4 ,the permeability of good soft wrought iron is sometimes #cjjj times that of air1 varying with the quality of the iron4 ,ques4 ,what is the effect of increasing the magnetization8 ,ans4 ,the magnetic permeability decreases as the magnetization increases4 ,ques4 ,what is magnetic saturation8 ,ans4 ,the state of a magnet which has reached the highest degree of magnetization4 ,illustration3 ,,fig4 #abb4--;,action of currents on solenoids4 ,to demonstrate this fact experimentally1 a solenoid is constructed as shown1 so that it can be suspended by two pivots in the cups a and c4 ,the solenoid is then movable about a vertical axis1 and if a rectilinear current ,,qp be passed beneath it1 which at the same time traverses the wires of the solenoid1 the latter is seen to turn and set at right angles to the lower current2 that is1 in such a position that its circuits are parallel to the fixed current2 moreover1 the current in the lower part of each of the circuits is in the same direction as in the rectilinear wire4 ,if1 instead of passing a rectilinear current below the solenoid1 it be passed vertically on the side1 an attraction or repulsion will take place1 according as the two currents in the vertical wire1 and in the nearest part of the solenoid1 are in the same or in contrary directions4 ,a magnet1 just after being magnetized1 will appear to have a higher degree of magnetism than it is able to retain permanently2 that is1 it will appear to be super-saturated1 since it will support a greater weight immediately after being magnetized than it will after its armature has been once removed4 ,for all practical purposes1 magnetic saturation may be defined as3 ,that point of magnetization where a very large increase in the magnetizing force does not produce any perceptible increase in the magnetization4 ,from tests it has been shown that permeability increases with the flux density up to a certain point and then decreases1 indicating that the iron is approaching a state of saturation4 ,magnetomotive ,force4--,this is a force similar to electromotive force1 that is1 magnetic pressure4 ,when a coil passes around a core several times1 its magnetizing power1 or magnetomotive force1 7m4m4f47 is proportional both to the strength of the current and to the number of turns in the coil4 ,the product of the current passing through the coil multiplied by the number of turns composing the coil is called the ampere turns4 ,it is known by experiment that one ampere turn produces #a4beff units of magnetic pressure1 hence3 magnetic pressure #a4beff turns amperes that is1 magnetomotive force 7m4m4f47 #a4beff n ,i4 ,the unit of magnetic pressure is the gilbert 7named after ,william ,gilbert1 the ,english physicist7 and is equal to #a #a4beff ampere turn 4#gieh ampere turn4 ,reluctance4--,the magnetic pressure 7magnetomotive force7 acting in a magnetic circuit encounters a certain opposition to the production of a magnetic field1 just as electromotive force in an electric circuit encounters opposition to the production of a current4 ,in the magnetic circuit this opposition is called the reluctance2 it is simply magnetic resistance and may be defined as3 the resistance offered to the magnetic flux by the substance magnetized1 being the ratio of the magnetomotive force to the magnetic flux4 ,the unit of reluctance or magnetic resistance is the oersted 7named after ,hans ,christian ,oersted1 the ,danish physicist7 and is defined as3 the reluctance offered by a cubic centimetre of vacuum4 ,illustration3 ,,fig4 #abc4--,mutual action of solenoids4 ,when two solenoids traversed by a current are allowed to act on each other1 one of them being held in the hand and the other being movable about a vertical axis1 as shown in the figure1 attraction and repulsion will take place just as in the case of two magnets 7see figs4 #aaj and #aaa74 ,analogy ,between ,electric and ,magnetic ,circuits4--,the total number of magnetic lines of force1 or magnetic flux1 produced in any magnetic circuit will depend on the magnetic pressure 7m4m4f47 acting on the circuit and the total reluctance of the circuit1 just as the current in the electrical circuit depends upon the electrical pressure and the resistance of the circuit4 ,to make this plain1 ,ohm's law states that electric current electromotive force _/ resistance or ,i ,e_/,r expressed in units amperes volts _/ ohms ,the resistance1 as already explained1 depends on the materials of which the circuit is composed1 and their geometrical shape and size4 ,similarly1 in the magnetic circuit1 the total number of magnetic lines produced by a given magnetizing solenoid depends on the magnetic pressure1 the material composing the circuit1 and its shape and size4 ,that is1 magnetic flux magnetomotive force _/ reluctance expressed in units1 the equation becomes3 maxwells gilberts _/ oersteds ,the gilbert is the unit of magnetomotive force1 equivalent to the magnetomotive force of 4#gieh ampere turn4 ,it should be noted that in the electric circuit resistance causes heat to be generated and therefore energy to be wasted1 but in the magnetic circuit reluctance does not involve any similar waste of energy4 ,ques4 ,upon what does the reluctance of a magnetic circuit depend8 ,ans4 ,the reluctance is directly proportional to the length of the circuit1 and inversely proportional to its cross sectional area4 ,the reluctance of a magnetic circuit is calculated according to the following equation3 reluctance length in centimetres _/ 7permeability cross section in square centimetres7 ,hysteresis4--,the term hysteresis has been given by ,ewing to the subject of lag of magnetic effects behind their causes4 ,hysteresis means to 8lag behind10 hence its application to denote the lagging of magnetism1 in a magnetic metal1 behind the magnetizing flux which produces it4 ,ques4 ,what is the cause of hysteresis8 ,ans4 ,it is due to the friction between the molecules of iron or other magnetic substance which requires an expenditure of energy to change their positions4 ,illustration3 ,,figs4 #abd and #abe4--;,experiment illustrating the molecular theory of magnetism4 ,coarse steel filings are placed inside a small glass tube and the contents magnetized4 ,it will be found that filings which at first had no definite arrangement will rearrange themselves under the influence of magnetic force1 and assume symmetrical positions1 each one lying in line with1 or parallel to its neighbor1 as shown in the lower figure4 ,ques4 ,when do the molecules change their positions8 ,ans4 ,both in the process of magnetization and demagnetization4 ,ques4 ,what becomes of the loss of energy due to hysteresis8 ,ans4 ,it is converted into heat in changing the positions of the molecules during magnetization and demagnetization4 ,ewing gives the value for the energy in ergs dissipated per cubic centimetre1 for a complete cycle of doubly reversed strong magnetization for a number of substances as follows3 ,substance ,energy dissipated 7ergs7 ,very soft annealed iron #i1cjj ,less 8 8 8 #af1cjj ,hard drawn steel wire #fj1jjj ,annealed 8 8 #gj1jjj ,same steel glass hard #gf1jjj ,piano steel wire annealed #id1jjj 8 8 8 normal temper #aaf1jjj 8 8 8 glass hard #aag1jjj ,approximately #bh foot pounds of energy are converted into heat in making a double reversal of strong magnetization in a cubic foot of iron4 ,residual ,magnetism4--,when a mass of iron has once been magnetized1 it becomes a difficult matter to entirely remove all traces when the magnetizing agent has been removed1 and1 as a general rule1 a small amount of magnetism is permanently retained by the iron4 ,this is known as residual magnetism1 and it varies in amount with the quality of the iron4 ,well annealed1 pure wrought iron1 as a rule1 possesses very little residual magnetism1 while1 on the other hand1 wrought iron1 which contains a large percentage of impurities1 or which has been subjected to some hardening process1 such as hammering1 rolling1 stamping1 etc41 and cast iron1 possess a very large amount of residual magnetism4 ,residual magnetism in iron is of great importance in the working of the self-exciting dynamo1 and is1 indeed1 the essential principle of this class of machine4 ,that is1 without residual magnetism in the field magnet core1 the dynamo when started would not generate any current unless it received an initial excitation from an external source4 ,,chapter ,x ,,electromagnetic ,,induction ,the word induction1 introduced by ,faraday1 has various meanings so far as it relates to electricity4 ,it signifies1 in general1 phenomena produced in bodies by the influence of other bodies1 having no necessary material connection with them4 ,a body charged with electricity causes or 8induces0 charges on neighboring bodies4 ,the process in this case is called electrostatic induction4 ,a magnet induces magnetism in neighboring masses of iron or other magnetic materials by the process of magnetic induction4 ,again1 a moving magnet induces electric currents in neighboring conductors by the process of electromagnetic induction4 ,faraday's ,discovery4--,all dynamos of whatever form1 are based upon the discovery made by ,faraday#aa in #ahca1 which may be stated as follows3 ,electric currents are generated in conductors by moving them in a magnetic field1 so as to cut magnetic lines of force4 ,ques4 ,what does the expression 8cut lines of force0 mean8 ,ans4 ,a conductor1 forming part of an electric circuit1 cuts lines of force when it moves across a magnetic field in such manner as to alter the number of magnetic lines of force which are embraced by the circuit4 ,it is important to clearly understand the meaning of this expression1 which will be later explained in more detail4 ,illustration3 ,,fig4 #abf4--;,faraday's dynamo which embodies his discovery in #ahca of electromagnetic induction1 the principle upon which all dynamos work1 as well as induction coils1 transformers1 and other electrical apparatus4 ,faraday's ,machine4--,after various experiments1 ,faraday made his 8new electrical machine0 as shown in fig4 #abf4 ,this piece of apparatus is preserved and was shown in perfect action by ,prof4 ,s4 ,p4 ,thompson in a lecture delivered ,april #aath1 #ahia1 after an interval of sixty years4 ,it consists of a horse shoe magnet and a copper disc attached to a shaft and supported so as to turn freely4 ,the magnet is so placed that its inter-polar lines of force traverse the disc from side to side4 ,there are two copper brushes1 one bears against the shaft1 and the other against the circumference of the disc4 ,a handle serves to rotate the disc in the magnetic field4 ,now1 if the north pole of the magnet be nearest the observer and the disc be rotated clockwise1 the current induced in the circuit will flow out at the brush which touches the circumference1 and return through the brush at the shaft4 ,faraday's ,principle4--,the principle deduced from ,faraday's experiment may be stated as follows3 ,when a conducting circuit is moved in a magnetic field so as to alter the number of lines of force passing through it1 a current is induced therein1 in a direction at right angles to the direction of the motion1 and at right angles also to the direction of the lines of force1 and to the right of the lines of force1 as viewed from the point from which the motion originated4 ,faraday's principle may be extended as follows to cover all cases of electromagnetic induction3 ,when a conducting circuit is moved in a magnetic field1 so as to alter the number of lines of force passing through it1 or when the strength of the field is varied so as to either increase or decrease the number of lines of force passing through the circuit1 a current is induced therein which lasts only during the interval of change in the number of lines of force embraced by the circuit4 ,ques4 ,explain just what happens when a current is induced by electromagnetic induction4 ,ans4 ,in order to induce an electromotive force by moving a conductor across a uniform magnetic field1 it is necessary that the conductor1 in its motion1 should so cut the magnetic lines as to alter the number of lines of force that pass through the circuit of which the moving conductor forms a part4 ,ques4 ,what is the proper name for a 8conductor0 which moves across the magnetic field8 ,ans4 ,an inductor1 because it is that part of the electric circuit in which induction takes place4 ,in the case of a dynamo1 an inductor may be either a copper wire or copper bar4 ,ques4 ,how may a conducting circuit be moved across a magnetic field without having a current induced therein8 ,ans4 ,if a conducting circuit--a wire ring or single coil1 for example--be moved in a uniform magnetic field1 as shown in fig4 #abg1 so that only the same number of lines of force pass through it1 no current will be generated1 for since the coil is moved by a motion of translation to another part of the field1 as many lines of force will be left behind as are gained in advancing from its first to its second position4 ,illustration3 ,,fig4 #abg4--;,electromagnetic induction3 ,in order to induce a current by electromagnetic induction1 a conductor must be so moved through a magnetic field that the number of lines of force passing through it 7that is1 embraced7 are altered4 ,if a coil be given a simple motion of translation in a uniform magnetic field as indicated in the figure1 no current will be induced because the number of lines of force passing through it are not changed1 that is1 during the movement as many lines are lost as are gained4 ,ques4 ,describe another movement by which no current will be induced4 ,ans4 ,if the coil be merely rotated on itself around a central axis1 that is1 like a fly wheel rotating around a shaft1 the number of lines of force passing through the coil will not be altered1 hence no current will be generated4 ,ques4 ,state the essential condition for current induction in a uniform field4 ,ans4 ,the coil in which a current is to be induced1 must be tilted in its motion across the uniform field1 or rotated around any axis in its plane as in fig4 #abh1 so as to alter the number of lines of force which pass through it4 ,illustration3 ,,fig4 #abh4--;,electromagnetic induction3 ,if a coil be given a motion of rotation from any point within its own plane so that it passes through a uniform magnetic field1 a current will be induced in the coil because the number of lines of force passing through it is altered4 ,ques4 ,in what direction will the current flow in the coil1 fig4 #abh8 ,ans4 ,the current induced in the coil will flow around it in a clockwise direction 7as observed by looking along the magnetic field in the direction in which the magnetic lines run7 if the effect of the movement be to diminish the number of lines of force that pass through the coil4 ,the current will flow in the opposite direction1 7counter-clockwise7 if the movement be such as to increase the number of intercepted lines of force4 ,ques4 ,if the magnetic field be not uniform1 as in fig4 #abi1 what will be the result8 ,ans4 ,the effect of moving the coil by a simple motion of translation from a dense region of the field to one less dense1 or vice versa1 will be to induce a current because in either case1 the number of lines of force passing through the coil is altered4#ab ,laws of ,electromagnetic ,induction4--,there are certain laws of electromagnetic induction which1 on account of the importance of the subject1 it is well to carefully consider4 ,the facts presented in the preceding paragraphs are embodied in the following fundamental laws3 ,illustration3 ,,fig4 #abi4--;,electromagnetic induction3 ,if a coil be given a simple motion of translation in a non-uniform or variable magnetic field1 a current will be induced in the coil1 whether the motion be from the dense to the less dense region of the field or the reverse1 because the number of lines of force passing through the coil is altered4 #a4 ,to induce a current in a circuit1 there must be a relative motion between the circuit and a magnetic field1 of such a kind as to alter the number of magnetic lines embraced in the circuit4 #b4 ,the electromotive force induced in a circuit is proportional to the rate of increase or decrease in the number of magnetic lines embraced by the circuit4 ,for instance1 if n equal the number of magnetic lines embraced by the circuit at the beginning of the movement1 and n the number embraced after a very short interval of time t1 then the average induced electromotive force 7n - n7_/t ,it would require the cutting of #ajj1jjj1jjj lines per second to produce an electromotive force equal to that of one ,daniell cell4 ,the unit of electromotive force1 called the volt1 is the electric pressure produced by cutting #ajj1jjj1jjj lines per second1 usually expressed #ajh4 ,illustration3 ,,fig4 #acj4--;,experiment illustrating ,lenz's law which states that in all cases of electromagnetic induction1 the direction of the induced current is such as to tend to stop the motion producing it4 ,in the experiment1 in order to produce the induced current1 energy must be expended in bringing the magnet to the coil and in taking it away1 which is in accordance with the law of conservation of energy4 #c4 ,by joining in series a number of conductors or coils moving in a magnetic field1 the electromotive forces in the separate parts are added together4 ,the reason for this is apparent by considering a coil of wire having several turns and moving in a magnetic field so as to cut magnetic lines4 ,during the movement1 the lines cut by the first turn are successively cut by all the other turns of the coil1 hence1 the total number of lines cut is equal to the number cut by a single turn multiplied by the number of turns4 ,the electromotive forces therefore of the separate turns are added4 ,,example--,if a coil of wire of #ej turns cut #ajj1jjj lines in #a_/ajj of a second1 what will be the induced voltage8 ,the number of lines cut per second per turn of the coil is #ajj1jjj #ajj #aj1jjj1jjj4 ,the total number of lines cut by the coil of #ej turns is #aj1jjj1jjj #ej #ejj1jjj1jjj4 which will induce a pressure of #ejj1jjj1jjj #ajh #e volts4 ,illustration3 ,,fig4 #aca4--;,experiment illustrating ,lenz's law4 ,if a copper ring be held in front of an ordinary electromagnet1 and the current circulating through the coil of the magnet be in such a direction as to magnetize the core as indicated by the letters ,s ,n1 then as the current increases in the coil more and more of the lines of force proceeding from ,n pass through the ring ,o ,o from left to right4 ,while the field is thus increasing currents will be induced in the copper ring in the direction indicated by the arrows1 such currents tending to set up a field that would pass through the ring from right to left1 and would therefore retard the growth of the field due to the electromagnet ,m4 #d4 ,a decrease in the number of magnetic lines which pass through a circuit induces a current around the circuit in the positive direction4 ,the term positive direction is understood to be the direction along which a free ,n pole would tend to move4 #e4 ,an increase in the number of magnetic lines which pass through a circuit induces a current in the negative direction around the circuit4 ,the reason for the change of direction of the current for decrease or increase in the number of lines cut1 as stated in the fourth and fifth laws1 will be seen by aid of the formula given under the second law1 viz3 electromotive force 7n - n7_/t 7#a7 but by ,ohm's law current electromotive force _/ resistance or1 ,i ,e_/,r 7#b7 ,substituting 7#a7 in 7#b7 current 77n - n7_/t7_/,r or 7n - n7_/7,rt7 7#c7 ,illustration3 ,,fig4 #acb4--;,fleming's rule for direction of induced current4 ,extend the thumb1 forefinger and middle finger of the right hand so that each will be at right angles to the other two4 ,place the hand in such position that the thumb will point in the direction in which the conductor moves1 the forefinger in the direction of the lines of force 7,n to ,s71 then will the middle finger point in the direction in which the induced current flows4 ,now in equation 7#c7 if there be a decrease in the number of lines cut n will be less than n hence the current will be positive 772 again1 if the lines increase n will be greater than n1 which will give a minus value1 that is1 the current will be negative or in a reverse direction4 #f4 ,the approach and recession of a conductor from a magnet pole will yield currents alternating in direction4 ,since the strength of the field depends on the proximity to the pole1 the approach and recession of a conductor involve an increase and decrease in the rate of cutting of magnetic lines1 hence a reversal of current4 #g4 ,the more rapid the motion1 the higher will be the induced electromotive force4 ,in other words1 the greater the number of lines cut per unit of time1 the higher will be the voltage4 ,illustration3 ,,fig4 #acc4--;,a rule for direction of induced current which1 in some cases1 is more conveniently applied than ,fleming's rule3 ,hold the thumb1 forefinger and remaining fingers of the right hand at right angles to each other2 place the hand in such position that the forefinger points in the direction of motion of the conductor1 the three fingers in the direction of the lines of force1 then will the thumb point in the direction of the induced current4 #h4 ,lenz's law4 ,the direction of the induced current is always such that its magnetic field opposes the motion which produces it4 ,this is illustrated in figs4 #acj and #aca4 ,rules for ,direction of ,induced ,current4--,there are a number of rules to quickly determine the direction of an induced current1 when the direction of the lines of force1 and motion of the conductor are known4 ,the first rule here given was devised by ,fleming and is very useful4 ,it is sometimes called the 8dynamo rule40 ,fleming's ,rule4--,if the forefinger of the right hand be pointed in the direction of the magnetic lines1 and the thumb 7at right angles to the forefinger7 be turned in the direction of the motion of the conductor1 then will the middle finger1 bent at right angles to both thumb and forefinger1 show the direction of the induced current4 ,the application of this rule is shown in fig4 #acb4 ,here the right hand is so placed at the north pole of a magnet1 that the forefinger points in the direction of the magnetic lines2 the thumb in the direction of motion of the conductor2 the middle finger pointed at right angles to the thumb and forefinger indicates the direction of the current induced in the conductor4 ,illustration3 ,,fig4 #acd4--,the palm rule for direction of induced current3 ,if the palm of the right hand be held against the direction of the lines of force1 the thumb in the direction of the motion1 then the fingers will point in the direction of the induced current4 ,ampere's ,rule4--,if a man could swim in a conductor with the current1 then the north seeking 77 pole of a magnetic needle placed directly ahead of him1 will be deflected to the left1 while the south seeking 7-7 pole will be urged to the right4 ,for certain particular cases in which a fixed magnet pole acts on a movable circuit1 the following converse to ,ampere's rule will be found useful3 ,if a man swim in the wire with the current1 and turn so as to look along the direction of the lines of force of the pole 7that is1 as the lines of force run1 from the pole if it be north seeking1 toward the pole if it be south seeking71 then he and the conducting wire with him will be urged toward his left4 ,the palm rule4--,if the palm of the right hand be held facing or against the lines of force1 and the thumb in the direction of the motion1 then will the fingers point in the direction of the induced current4 ,self-induction4--,this term signifies the property of an electric current by virtue of which it tends to resist any change of value4 ,self-induction is sometimes spoken of as electromagnetic inertia1 and is analogous to the mechanical inertia of matter4 ,it is on account of self-induction of the induced currents in the armature winding of a dynamo1 that sparks appear at the brushes when the latter are not properly adjusted1 hence the importance of clearly understanding the nature of this peculiar property of the current4 ,self-induction is fully explained in the chapter following4 ,,chapter ,,xi ,,induction ,,coils ,the induction coil has always been a popular piece of apparatus with those interested in electrical science2 the experiments which can be performed with its aid are very numerous4 ,it is of considerable importance1 especially in its application to such useful purposes as ,x ray work1 wireless telegraphy and ignition for gas engines4 ,the latter has caused manufacturers to give much attention to the development of the induction coil1 resulting in many refinements of design and construction4 ,induction coils may be divided into two general classes3 #a4 ,primary coils2 #b4 ,secondary coils4 ,the subject of electromagnetic induction has been fully explained in chapter ,x1 but it may be said1 with special reference to induction coils1 that the operation of the two classes just mentioned is respectively due to3 #a4 ,self-induction2 #b4 ,mutual induction4 ,self-induction4--,this is the property of an electric current by virtue of which it tends to resist any change in its rate of flow4 ,it is sometimes spoken of as electromagnetic inertia and is analogous to the mechanical inertia of matter4 ,self-induction is due to the action of the current upon itself during variations in strength4 ,it becomes especially marked in a coil of wire1 in which the adjacent turns act inductively upon each other upon the principle of mutual induction arising between two separate adjacent circuits4 ,self-induction manifests itself by giving 8momentum0 to the current so that it cannot be instantly stopped when the circuit is broken1 the result being a bright spark at the moment of breaking the circuit4 ,on account of this spark a primary induction coil is used in low tension or 8make and break0 ignition systems4 ,illustration3 ,,fig4 #ace4--;,diagram illustrating the action of mutual induction between two circuits2 the one including a source of electrical energy and a switch2 the other including a galvanometer1 but having no cell or other electrical source4 ,during the increase or decrease in the strength of the current as on closing or opening the key a current is induced in the secondary circuit in a direction opposite to that of the primary current as indicated by the arrows4 ,in a single circuit1 consisting of a straight wire and a parallel return wire there is little or no self-induction4 ,when a circuit containing a primary induction coil and a battery is closed there is no spark because at the instant of closing the circuit the current is at rest and on account of self-induction the current cannot at once rise to its full value4 ,mutual ,induction4--,this is a particular case of electromagnetic induction in which the magnetic field producing an electromotive force in a circuit is due to the current in a neighboring circuit4 ,the effect of mutual induction may be explained with the aid of fig4 #ace4 ,if1 as illustrated1 a circuit including a battery and a switch1 be placed near another circuit1 formed by connecting the two terminals of a galvanometer by a wire1 it will be found that whenever the first circuit1 #a1 is closed by the switch1 allowing a current to pass in a given direction1 a momentary current will be induced in the second circuit1 #b1 as shown by the galvanometer4 ,a similar result will follow on the opening of the battery circuit1 the difference being that the momentary induced current occurring at closure moves in a direction opposite to that in the battery circuit1 while the momentary current at opening moves in the same direction4 ,currents1 besides being induced in circuit #b at make or break of circuit #a1 are also induced when the current in #a is fluctuating in intensity4 ,the most marked results are observed when the make or break is sudden1 the action being strongest at the break of the current in #a4 ,the inductive effect of the current in the arrangement shown in fig4 #ace is very weak4 ,ques4 ,what name is given to circuit #a8 ,ans4 ,the primary circuit4 ,ques4 ,what name is given to circuit #b8 ,ans4 ,the secondary circuit4 ,ques4 ,what names are given respectively to the currents in circuits #a and #b8 ,ans4 ,the primary and secondary or induced currents4 ,primary ,induction ,coils4--,these represent the simplest form of coil1 and are used chiefly in low tension ignition to intensify the spark when a battery forms the current source4 ,a primary coil consists of a long iron core wound with a considerable length of low resistance insulated copper wire1 the length of the core and the number of turns of the insulated wire winding determining the efficiency4 ,the effect of the iron core is to increase the self-induction4 ,illustration3 ,,fig4 #acf4--,primary induction coil as used for low tension ignition4 ,coils of this type are made in a great variety of form and size4 ,ordinarily the winding consists of about six convolutions of ,no4 #ad copper wire4 ,the winding is usually covered and the ends capped with ebonite heads so that the core wires are not exposed4 ,the spark produced1 as previously explained1 is due to self-induction1 and it should be remembered that in the operation of the coil1 the spark occurs at the instant of breaking the circuit1 not at the instant of making4 ,secondary ,induction ,coils4--,the arrangement shown in fig4 #acg1 may be considered as a very simple or rudimentary form of secondary induction coil4 ,in the actual coil1 the primary and secondary circuits 7corresponding to #a and #b in fig4 #ace7 are made up of coils of insulated wire1 as shown in fig4 #adc1 the primary coil ,p1 being wound over a core ,c and the secondary coil ,s being wound over the primary4 ,the one property of such an arrangement that makes it of great value for most purposes is that the voltage of the induced currents may be increased or diminished to any extent depending on the relation between the number of turns in the primary and secondary winding4 ,this relation may be expressed in the following rule3 ,the voltage of the secondary current is 7approximately7 to the voltage of the primary current as the number of turns of the secondary winding is to the number of turns of the primary winding4 ,illustration3 ,,fig4 #acg4--,production of spark with plain coil4 ,connect the ends or leads of the secondary winding to fixed insulators and bend the ends so they are from one-sixteenth to one-eighth inch apart4 ,connect one end of the primary winding to an electric battery1 and with the other lead of the primary winding brush against the other terminal of the battery1 as indicated4 ,when the contact is broken there will be a spark both at the point of rupture in the primary circuit and at the gap4 ,an electric impulse is also induced in the secondary circuit when the primary circuit is closed and the current flowing in it gradually rises to its maximum value1 but this impulse is too feeble to cause a spark to jump across the gap4 ,only the impulse induced in the secondary during the dying out of the current in the primary is utilized4 ,for instance1 if the voltage of the primary current be #e volts1 the primary winding have #aj turns and the secondary #ajj turns1 then ,secondary voltage3 #e 33 #ajj 3 #aj from which ,secondary voltage #ej volts 7approximately7 ,the watts in each circuit are approximately the same2 hence3 if1 for instance1 the current strength in the primary circuit be #e amperes1 the watts in primary circuit are #e #e #be4 ,accordingly1 for the secondary circuit the current strength is3 #be watts _/ #ej volts #a_/b ampere 7approximately7 ,from this1 it is seen that where the voltage is raised in the secondary circuit1 the current flow is small as compared to that in the primary circuit2 therefore1 heavy wire is used in the primary winding and fine wire in the secondary1 as indicated in figs4 #acg and #adc4 ,for most purposes a very much higher secondary voltage is required than in the example just given4 ,illustration3 ,,fig4 #ach4--;,diagram of battery and coil connections for jump spark ignition as applied to a motor cycle4 ,coils are usually plainly labeled with the abbreviations3 8,bat410 8,pri410 8,sec410 indicating that the wires are to be connected to the battery1 the primary circuit or contact maker1 and the spark plug4 ,the battery and primary wires being for the low tension circuit are easily distinguished from the secondary wire by the small amount of insulation surrounding them4 ,secondary induction coils may be divided into three general classes3 #a4 ,plain coils2 #b4 ,vibrator coils2 #c4 ,condenser coils4 ,the plain coil gives but one spark when the primary circuit is made and broken1 while the vibrator coil gives a series of sparks following each other in rapid succession4 ,plain ,secondary ,induction ,coils4--,coils of this class are very simple and consist of3 #a4 ,core2 #b4 ,primary winding2 #c4 ,secondary winding4 ,the construction of a plain coil1 such as would be suitable for ignition service1 is about as follows3 ,the core is made of soft annealed iron wires 7,no4 #bj ,b and ,s gauge7 from one-half to three-quarters of an inch in diameter and about six inches long4 ,over this core is slipped a spool of insulating material 7hard rubber or composition71 on which is wound first the primary winding of the coil1 which consists of several layers of about ,no4 #ah ,b and ,s gauge silk insulated magnet wire4 ,after the primary winding has been wound over the insulated core1 and the ends have been properly brought out through the heads of the spool to be connected to binding posts thereon1 a layer of insulating material is applied over the primary wire1 and the secondary winding is then wound on4 ,the wire for the secondary winding consists of about ,no4 #cf ,b and ,s gauge silk covered magnet wire1 the amount used varying considerably1 depending on the desired voltage of the secondary current4 ,when all the wire has been wound on1 the ends are brought out to the binding posts1 the coil is soaked in shellac dissolved in alcohol and baked1 or in melted paraffin or a paraffin compound1 and allowed to cool4 ,it is then placed in either a cylindrical hard rubber shell or in a hard wood box4 ,the proportions of such coils vary greatly2 for motor cycle use they are made long and of small diameter 7#ajb-a_/b inches for instance71 while for some other purposes short and thick coils are found more convenient4 ,ques4 ,how may the coil just described be connected for demonstrating purposes8 ,ans4 ,connect the ends of the secondary winding to fixed insulators and bend the ends so they are about #a_/h inch or less apart4 ,connect one end of the primary winding to a battery and brush the other end of the primary winding against the other terminal of the battery as indicated in fig4 #acg4 ,ques4 ,what happens when the primary circuit is made8 ,ans4 ,an electric pressure is induced in the secondary circuit1 but of not enough intensity to cause a spark to jump across the air gap4 ,illustration3 ,,fig4 #aci4--;,a ,medical coil with armature and attachments consisting of electrodes1 foot place1 sponge1 induction coil etc4 ,a current of any degree of intensity may be obtained4 ,the currents furnished are3 #a1 primary1 #b1 secondary2 and #c1 primary and secondary combined4 ,ques4 ,what happens when the primary circuit is suddenly broken8 ,ans4 ,a spark is produced both at the point of break in the primary circuit and at the air gap in the secondary circuit4 ,ques4 ,why is a spark produced at the air gap at break and not at make of the primary current8 ,ans4 ,because when the current is flowing it cannot be stopped instantly on account of self-induction1 that is1 it acts as though it possessed weight4 ,if the reader has charge of a gas engine with a make and break ignition system1 he will often avoid vexatious delays in locating ignition troubles1 if he remember that one of the most important conditions for obtaining a good spark is that the break take place with great rapidity4 ,this1 of course1 involves that the ignition spring be adjusted to the proper tension4 ,illustration3 ,,fig4 #adj4--,rhumkorff induction coil4 ,a secondary coil with vibrator and condenser2 a type generally used in the laboratory4 ,the name ,rhumkorff was formerly very widely applied to induction coils for the reason that some of the earliest coils were constructed by ,rhumkorff4 ,secondary ,induction ,coils with ,vibrator and ,condenser4--,a plain secondary coil1 such as just described1 will only give feeble sparks for its size for the following reasons3 ,the inductive effect of the primary winding in the secondary depends as previously explained on the rate at which the current in the primary winding decreases or dies out4 ,if a strong inductive effect is to be produced in the secondary1 the current in the primary must stop suddenly4 ,this is prevented by self-induction in the primary winding1 which opposes any change in the current strength4 ,the direct result is that1 as the primary circuit is broken1 a spark appears at the break1 which means that the current continues to flow after the break has occurred1 dying down comparatively slowly1 hence1 the inductive effect on the secondary winding is small4 ,illustration3 ,,fig4 #ada4--;,conventional diagram of a condenser4 ,a condenser is a device designed to absorb or hold an electric charge in about the same manner as a vessel will hold a liquid4 ,every conductor of electricity forms a condenser and its capacity for holding a charge depends upon the extent of its surface4 ,a condenser is therefore made of conductive material formed into such shape as to present the maximum surface for a given amount of material4 ,the spark at the break in the primary circuit is even larger than that in the secondary circuit1 and as this primary spark serves no useful purpose1 but1 on the contrary1 quickly burns away the contact points1 such an arrangement is obviously defective4 ,the vibrator-condenser coil is designed to overcome this trouble and also to give a series of sparks following in rapid succession instead of one4 ,it should be noted that a series of sparks following each other with considerable rapidity may be obtained with a plain coil by placing a mechanical vibrator in the primary circuit1 as used on some motor cycle ignition circuits4 ,the object of the vibrator1 of a vibrator-condenser coil1 is to rapidly make and break the primary circuit during the time the primary circuit is closed externally4 ,it consists of a flat steel spring secured at one end1 with the other free to vibrate4 ,at a point about midway between its ends1 contact is made with the point of an adjusting screw1 from which it springs away and returns in vibrating4 ,the points of contact of blade and screw are tipped with platinum4 ,one wire of the primary circuit is connected to the blade and the other to the screw1 hence1 the circuit is made when the blade is in contact with the screw and broken when it springs away4 ,illustration3 ,,fig4 #adb4--;,construction of condenser for an induction coil4 ,the conducting material used is tinfoil1 of which a large number of sheets are prepared1 all cut to the same size4 ,these are placed1 one on top of the other1 like the pages of a book1 with a thin layer of insulating material between1 usually two sheets of paraffined paper4 ,numbering the successive sheets of tinfoil serially1 all sheets of even number are connected together and all sheets of odd number are connected together1 these connections forming the terminals of the condenser4 ,the condenser is then connected across the break in the primary circuit4 ,a condenser is used to absorb the self-induced current of the primary winding and thus prevent it opposing the rapid fall of the primary current4 ,every conductor of electricity forms a condenser and its capacity for absorbing a charge depends upon the extent of its surface4 ,hence1 a condenser is constructed of conductive material so arranged as to present the greatest surface for a given amount of material4 ,the usual form of condenser for induction coils as shown in figs4 #ada and #adb is composed of a number of layers of tin foil separated by paraffin paper1 each alternate layer being connected at the ends4 ,fig4 #adc is a diagram of a vibrator coil4 ,,cc represents the core composed of soft iron wires4 ,,pp is the primary winding and ,,ss the secondary4 ,there is no connection between these windings and they are carefully insulated4 ,y is the vibrator or trembler and ,d the center about which it vibrates4 ,w is a switch used for opening and closing the primary circuit2 ,b1 a battery of five cells4 ,the point of adjusting screw ,a rests against a platinum point ,r soldered upon the vibrator4 ,illustration3 ,,fig4 #adc4--;,diagram of a vibrator coil4 ,the parts are as follows3 ,a1 contact screw2 ,b battery2 ,c1 core2 ,d1 vibrator terminal2 ,g1 condenser2 ,p1 primary winding2 ,s1 secondary winding2 ,w1 switch2 ,y1 vibrator4 ,when the switch is closed1 the following cycle of actions take place3 #a1 the primary current flows and magnetizes core2 #b1 magnetized core attracts the vibrator and breaks primary circuit2 #c1 the magnetism vanishes1 including a momentary high tension current in the secondary winding2 #d1 magnetic attraction of the core having ceased1 vibrator spring renews contact2 #e1 primary circuit is again completed and the cycle begins anew4 ,if the switch ,w be closed1 the electric current generated by the battery ,b will flow through the primary winding4 ,this will cause the core ,,cc to become magnetized1 and the vibrator ,y will at once be drawn toward it4 ,this will break the connection at ,r4 ,the core1 being made of soft iron1 immediately upon the interruption of the current1 will again lose its magnetism1 and the vibrator will return to its original position4 ,this again closes the circuit1 after which the operation of opening and closing it is repeated with great rapidity so long as the switch ,w remains closed4 ,illustration3 ,,fig4 #add4--;,circuit diagram of a master vibrator coil4 ,b1 is the battery2 ,c1 the unit coils2 ,c#a1 ,c#b1 etc41 the condensers2 ,p1 the primary windings and ,s1 the secondary windings2 ,h#a1 ,h#b1 etc41 the spark plugs2 ,t1 the timer2 ,,mp1 the master primary2 ,v1 the vibrator2 ,w1 the common primary connection2 #a1 #b1 etc41 the stationary contacts of the timer4 ,the cycle of actions may be briefly stated as follows3 #a4 ,a primary current flows and magnetizes the core2 #b4 ,the magnetized core attracts the vibrator which breaks the primary circuit2 #c4 ,the core loses its magnetism and the vibrator springs back to its original position2 #d4 ,the vibrator1 by returning to its original position1 closes the primary circuit and the cycle begins again4 ,illustration3 ,,fig4 #ade4--,the ,splitdorf master vibrator coil4 ,as shown in the illustration the several unit coils are indicated by the figures #a1 #b1 #c1 and #d4 ,a fifth unit ,v at the left contains the master vibrator4 ,the primary wires ,p connect with the timer and the secondary wires ,s with the plugs4 ,b ,b shows the battery connections4 ,magnetic ,vibrators4--,many types of vibrator are used on induction coils1 the most important requirement being that the break occur with great rapidity4 ,in order to render the break as sudden as possible1 different expedients have been resorted to1 all tending to make the mechanism more complicated1 yet having sufficient merit in some cases to warrant their adoption4 ,in the plain vibrator1 the circuit is broken at the instant the spring begins to move1 hence1 the operation must be comparatively slow4 ,in order to render the break more abrupt some vibrators have two moving parts1 one of which is attracted by the magnetic core of the coil and moved a certain distance before the break is effected4 ,a vibrator of this type is shown in fig4 #adf and described under the illustration4 ,illustration3 ,,fig4 #adf4--;,a hammer vibrator4 ,when at rest1 the upward tension of the spring1 which carries the armature ,a1 holds the platinum points in contact and causes the upper spring ,c1 to leave shoulder of adjusting screw ,d1 and rest against the heavy brass plate above it4 ,when the iron core ,b1 attracts the armature ,a1 the downward tension on the upper spring1 ,c1 causes the latter to follow the armature down1 holding the platinum point in contact1 until the end of the upper spring ,c1 strikes the lower shoulder of the adjusting screw1 ,d1 which gives it a 8hammer break40 ,the adjusting screw is held firmly in position by a bronze spiral spring under shoulder ,d4 ,vibrator ,adjustment4--,when a vibrator coil is used1 the quality of the spark depends largely upon the proper adjustment of the vibrator4 ,the following general instructions for adjusting a plain vibrator should be carefully noted3 #a4 ,remove entirely the contact adjusting screw4 #b4 ,see that the surfaces of the contact points are flat1 clean and bright4 #c4 ,adjust the vibrator spring so that the hammer or piece of iron on the end of the vibrator spring stands normally about one-sixteenth of an inch from the end of the coil4 #d4 ,adjust the contact screw until it just touches the platinum contact on the vibrator spring--be sure that it touches1 but very lightly4 ,now start the engine2 if it miss at all1 tighten up1 or screw in the contact screw a trifle further--just a trifle at a time1 until the engine will run without missing explosions4 ,,table ,,of ,,induction ,,coil ,,dimensions4 ,length of spark #c_/h inch #a_/b inch #a inch #b inches ---------------------------------------- -------------------------------- ,size of bobbin #b-a_/h #b-a_/b #c #c_/h #d #b-c_/d ends #a-a_/d #e_/af #c_/h ---------------------------------------- -------------------------------- ,length of bobbin #d #e-a_/b #f-a_/b #f-a_/b ---------------------------------------- -------------------------------- ,length and #d-a_/d #f #e_/h #f-a_/b #c_/d ---- diameter of core #g_/af ---------------------------------------- -------------------------------- ,size of base #g-a_/d #i #e #b #ad-a_/b #ab #g-a_/b #c-a_/d #f #c-a_/d #a-a_/b #a-c_/d ---------------------------------------- -------------------------------- ,size of tinfoil #d #b #e-a_/b #f #d #f #f sheets #c-a_/d ---------------------------------------- -------------------------------- ,number of tinfoil #cf #dj #dj #fj sheets ---------------------------------------- -------------------------------- ,size of paper #e #c #f-a_/b #i #e ---- sheets #d-a_/d ---------------------------------------- -------------------------------- ,primary coil ,no4 #ah ,no4 #ah #b layers ,no4 #b layers #ad #af1 silk ,b4 ,w4 ,g4 silk covered4 covered4 ---------------------------------------- -------------------------------- ,secondary coil #c_/d lb4 #a lb4 #a-a_/d lbs4 #b-a_/b lbs4 ,no4 #dj ,no4 #dj ,no4 #ch ,no4 #cf ---------------------------------------- -------------------------------- ,,table ,,of ,,sparking ,,distances ,,in ,,air4#ac ,distance4 ,volts4 7,inches47 ------------------------- #ejjj 4#bbe #ajjjj 4#dg #bjjjj #a4jj #cjjjj #a4fbe #cejjj #b4jj #dejjj #b4ie #fjjjj #d4fe #gjjjj #d4he #hjjjj #g4a #ajjjjj #i4f #acjjjj #ab4ie #aejjjj #ae4jj ,points ,relating to ,ignition ,coils4--#a4 ,most ignition induction coils or 8spark coils0 as they are called1 have terminals marked 8battery10 8ground10 etc41 and to short circuit the timer for the purpose of testing the vibrator1 it is only necessary to bridge with a screw driver from the 8battery0 binding post to the 8ground0 binding post4 #b4 ,in adjusting the vibrator of an ignition coil1 the latter should not require over one-half ampere of current4 ,illustration3 ,,fig4 #adg to #afa4--,wiring diagrams showing connections of some standard spark coils4 ,key3 ,b1 to battery2 ,c1 to commutator or timer2 ,g1 to ground 7engine frame72 ,p1 to plugs2 ,s1 to switch4 #a1 #f terminal standard non-vibrator coil2 #b1 #c terminal standard vibrator coil2 #c and #d1 terminal standard vibrator coil2 #e1 standard double vibrator coil2 #f1 standard triple vibrator coil2 #g1 standard quadruple vibrator coil2 #h1 single dash coil2 #i1 single dash coil with switch2 #aj1 double dash coil2 #aa1 double dash coil with switch2 #ab1 triple dash coil2 #ac1 triple dash coil with switch2 #ad1 quadruple dash coil2 #ae1 sextuple dash coil4 #c4 ,a half turn of the adjusting screw on a coil will often increase the strength of the current four or five times the original amount1 hence1 the necessity of carefully adjusting the vibrator4 ,when the adjustment is not properly made it causes1 #a1 short life of the battery1 #b1 burned contact points1 and #c1 poor running of the engine4 #d4 ,in adjusting a multi-unit coil1 if any misfiring be noticed1 hold down one vibrator after another until the faulty one is located1 then screw in its contact screw very slightly4 #e4 ,the number of cells in the circuit should be proportioned to the design of the coil4 ,if the coil be described by the maker as a #d volt coil1 it should be worked by two cells of a storage battery or four dry cells4 ,the voltage of the latter will be somewhat higher1 but since their internal resistance is also greater1 the current delivery will be about the same4 ,most coils are made to operate on from #d to #f volts4 #f4 ,it is a mistake to use a higher voltage than that for which the coil is designed1 because it does not improve the spark and the contact points of the vibrator will be burned more rapidly1 moreover1 the life of the battery will be shortened4 ,,chapter ,,xii ,,the ,,dynamo ,the dynamo is a machine which converts mechanical energy into electrical energy by electromagnetic induction4 ,the word dynamo is used to designate a machine which produces direct current as distinguished from the alternator or machine generating an alternating current4 ,in a broader sense1 the word generator is used to denote any machine generating electric current by electromagnetic induction2 the term therefore includes both dynamos and alternators4 ,operation of a ,dynamo4--,a dynamo does not create electricity1 but generates or produces an induced electromotive force which causes a current of electricity to flow through a circuit of conductors in much the same way as a force pump causes a current of water to flow in pipes4 ,the electromotive force generated in the dynamo causes the current of electricity to pass from a lower to a higher potential in the machine1 and from the higher back to the lower potential in the external circuit2 that is1 the dynamo generates electrical pressure which overcomes the resistance or opposition to the current flow in the circuit4 ,the pump produces a mechanical pressure which1 for instance1 may be used to force water into an elevated reservoir against the back pressure due to its weight4 ,illustration3 ,,fig4 #afb4--;,holzer ,cabot type 8,m0 dynamo4 ,the design of the base is such that it allows the field ring or frame to drop down1 lowering the center of gravity1 which gives increased stability4 ,the pedestals are bolted directly to the base4 ,both front and rear pedestals are removable1 so that the armature may be taken out from either end without disturbing the brushes or connections4 ,the journals are provided with oil rings which keep the oil in continual circulation around the shaft by means of oil grooves in the journal4 ,the pole pieces are cylindrical in shape and are fitted with shoes which retain the field coils in place and assist commutation4 ,the field coils are former wound1 the insulation being reinforced with mica4 ,they are soaked in varnish and baked for #bd hours at #bbe ,fahr4 ,the armature is wound as desired1 series1 shunt or compound4 ,the armature core is of the drum type and is laminated1 the discs being held by end plates locked without through bolts4 ,the armature coils are formed of round1 ribbon or bar copper1 and are without joint except at the commutator2 they lie in troughs of insulating material1 the upper layers being insulated from the lower layers2 they are retained in place by maple wedges secured by binding wires1 soldered throughout their length4 ,the commutator segments are drop forged in the smaller1 and hard drawn in the larger sizes4 ,radial brushes are used4 ,the efficiency of this type machine is stated by the maker at from #hj to #ij1 according to size4 ,the point to be emphasized is that the dynamo does not create electricity 7nor the pump water7 but sets into motion something already existing by generating sufficient pressure to overcome the opposition to its movement4 ,illustration3 ,,fig4 #afc4--;,general ,electric #af ,,kw multi-polar dynamo designed to operate at moderate and slow speeds4 ,the outer structure of the machine consists of a magnet frame having feet in one casting4 ,adjustment is provided for moving the machine on its bed plate to tighten the belt4 ,the field coils are former wound and the series windings permit of any degree of compounding up to #aj by the use of suitable ,german silver shunts connected across the series field4 ,essential ,parts of a ,dynamo4--,the dynamo in its simplest form consists of two principal parts3 #a4 ,the field magnet2 #b4 ,the armature4 ,illustration3 ,,fig4 #afd4--;,general ,electric dynamo with end shield and armature removed showing construction4 ,the core of the armature consists of laminations keyed to spider with space blocks inserted at intervals to provide ventilating ducts for cooling the core and windings4 ,the armature is former wound--that is1 the inductors are bent to the proper shape on a form2 they are1 therefore1 interchangeable4 ,ques4 ,what is the object of the field magnet8 ,ans4 ,to provide a field of magnetic lines or lines of force to be cut by the armature inductors as they revolve in the field4 ,ques4 ,what is an armature8 ,ans4 ,a collection of inductors mounted on a shaft and arranged to rotate in a magnetic field with provision for collecting the currents induced in the inductors4 ,a simple loop or turn or wire may be considered as the simplest form of armature4 ,ques4 ,how do armatures and field magnets differ in dynamos and alternators8 ,ans4 ,a characteristic feature is that in the dynamo the field magnet is the stationary part and the armature the rotating part1 while in the alternator the reverse conditions usually obtain4 ,ques4 ,with respect to this feature1 what names are sometimes given to the armature and field magnet8 ,ans4 ,the stator and the rotor depending on which moves4 ,ques4 ,what is the real distinction between an armature and a field magnet8 ,ans4 ,the name field magnet is properly given to that part which1 whether stationary or revolving1 maintains its magnetism steady during operation2 the name armature is properly given to that part which1 whether revolving or fixed1 has its magnetism changed in a regularly repeated fashion when the machine is in motion4 ,construction of ,dynamos4--,in the make up of a dynamo1 as actually constructed1 there are five principal parts1 as follows3 #a4 ,bed plate2 #b4 ,field magnets2 #c4 ,armature2 #d4 ,commutator2 #e4 ,brushes4 ,,chapter ,,xiii ,,the ,,dynamo3 ,,basic ,,principles ,a dynamo is a machine for converting mechanical energy into electrical energy1 by means of electromagnetic induction1 the amount of electric energy thus obtained depending upon the mechanical energy originally supplied4 ,the word dynamo is properly applied to a machine which generates#ad direct current1 as distinguished from the alternator1 which generates alternating current4 ,ques4 ,define a dynamo with respect to its principle of operation4 ,ans4 ,a dynamo is a machine for filling and emptying conducting loops with magnetic flux1 and utilizing the electromotive force thus induced in them for the production of current in the external circuit4 ,the fitness of this definition is apparent1 having in mind the principles of electromagnetic induction4 ,ques4 ,what are the three essential parts of a dynamo8 ,ans4 ,the field magnet1 armature1 and commutator4 ,ques4 ,what is the object of the field magnet8 ,ans4 ,to provide a magnetic field1 through which the conducting loops arranged on a central hub and forming the armature are carried1 or the flux carried through them1 so that they are successively filled and emptied of magnetic lines4 ,ques4 ,what is a commutator8 ,ans4 ,a device for causing the alternating currents generated in the armature to flow in the same direction in the external circuit4 ,ques4 ,upon what does the voltage depend8 ,ans4 ,upon the rate at which each conducting loop is filled and emptied of lines of force and the number of such loops with their grouping or connection4 ,ques4 ,how is the operation of a dynamo best explained8 ,ans4 ,by considering first the action of the simplest form of current generator1 or elementary alternator4 ,ques4 ,describe an elementary alternator4 ,ans4 ,it consists1 as shown in fig4 #afe1 of a single rectangular loop of wire ,a ,b ,c ,d1 one end being attached to a ring ,f and the other to the shaft ,g1 and arranged so as to revolve around the axis ,x ,x1 which is located midway between the two poles of the magnet4 ,two metallic strips or brushes ,m and ,s connected with the external circuit1 bear on the ring ,f and shaft ,g1 respectively1 in order to 8collect0 the current generated in the armature when the machine is in operation4 ,the long1 straight1 horizontal arrows joining the two poles of the magnet1 represent the lines of force which make up the magnetic field between the poles4 ,the field is here assumed to be uniform1 as indicated by the equal spacing of the arrows4 ,ques4 ,what happens when the loop is rotated8 ,ans4 ,according to the law of electromagnetic induction1 when the loop is rotated around its horizontal axis in the direction indicated by the curved arrow1 an electromotive force will be induced in the loop1 the magnitude of which depends on the rate of change of the number of lines of force threading through1 or embraced by the loop4 ,illustration3 ,,fig4 #afe4--,simple elementary alternator4 ,its parts are a single conducting loop1 ,a ,b ,c ,d1 placed between the poles of a permanent magnet1 and having its ends connected with a ring1 ,f1 and shaft1 ,g1 upon which bear brushes ,m and ,s1 connected with the external circuit4 ,when the loop is rotated clockwise the induced current will flow in the direction indicated by the arrows during the first half of the revolution4 ,that is1 if the number of lines embraced by the loop be increased from1 say1 #j to #ajjj1 or decreased from #ajjj to #j1 in one second1 the electromotive force generated will be two times as great as if the increase or decrease were only #ejj lines per second4 ,ques4 ,upon what does the direction of the induced current depend8 ,ans4 ,upon the direction of the lines of force and direction of rotation of the loop4 ,ques4 ,how is ,fleming's rule applied to determine the direction of current8 ,ans4 ,in applying this rule1 the horizontal portion of the loop1 such as ,a ,b or ,c ,d 7fig4 #afe71 is to be considered as moving up or down2 that is1 the component of its motion at right angles to the lines of force is taken as the direction of motion4 ,when the loop is in the position ,a ,b ,c ,d1 such that its plane is vertical or perpendicular to the lines of force1 the maximum number of magnetic lines thread through it1 but when it is in a horizontal position1 ,a ,b ,c ,d1 so that its plane is parallel to the lines of force1 no lines pass through the loop4 ,during the rotation from position ,a ,b ,c ,d to ,a ,b ,c ,d1 the number of lines passing through the loop is reduced from the maximum to zero1 the reduction taking place with increasing rapidity as the loop approaches the horizontal position1 the electromotive force thus induced increasing in like proportion4 ,continuing the rotation from the horizontal position ,a ,b ,c ,d to the inverted vertical position ,a ,b ,c ,d 7fig4 #aff71 the number of lines passing through the loop is increased from zero to the maximum1 the increase taking place with decreasing rapidity as the loop approaches the inverted vertical position1 the electromotive force thus induced decreasing in like proportion4 ,ques4 ,how does the current flow during the first half of the revolution of the loop8 ,ans4 ,it flows in the direction ,a ,b ,c ,d 7fig4 #afe71 as is easily ascertained by aid of ,fleming's rule4 ,illustration3 ,,fig4 #aff4--,simple elementary alternator1 showing reversal of current when the loop has made one half revolution from the position of fig4 #afe4 ,it should be noted that ,a ,b1 for instance1 which has been moving downward during the first half of the revolution 7fig4 #afe71 moves upward during the second half 7fig4 #aff72 hence1 the current during the latter interval flows in the opposite direction4 ,ques4 ,what is the path of the current to the external circuit8 ,ans4 ,it flows out through brush ,m 7fig4 #afe7 and returns through brush ,s1 thus making ,m positive and ,s negative4 ,ques4 ,what occurs during the second half of the revolution8 ,ans4 ,the wire ,a ,b 7fig4 #aff71 which before was moving in a downward direction1 moves in an upward direction2 hence1 the current is reversed and flows around the loop in the direction ,a ,d ,c ,b 7fig4 #aff71 going out through brush ,s and returning through brush ,m4 ,this makes ,m negative and ,s positive4 ,illustration3 ,,fig4 #afg4--;,illustrating the increase and decrease in the rate magnetic lines are cut by a revolving loop4 ,the initial position of the loop is taken at right angles to the direction of the lines of force4 ,since the loop rotates at a constant speed1 it is evident that it does not cut the magnetic lines at uniform rate1 because the intercepted arcs #j-a1 #a-b1 etc41 are unequal4 ,these arcs1 rectified at the right by the horizontal lines #j-a1 #a-b1 etc41 show more clearly the increase and decrease in the rate at which the magnetic lines are cut4 ,ques4 ,what may be said of the electromotive force during the second half of the revolution8 ,ans4 ,it varies in a similar manner as in the first half of the revolution2 that is1 the magnetic lines are cut with increasing rapidity during the third quarter1 and with decreasing rapidity during the fourth quarter of the revolution1 which causes the electromotive force to increase and decrease during these intervals4 ,the cycle of events just described may be summed up as follows3 ,during the revolution of the loop3 #a4 ,from #j to #ij1 the electromotive force increases from #j to maximum2 #b4 ,from #ij to #ahj1 the electromotive force decreases from maximum to zero2 #c4 ,from #ahj to #bgj1 current reverses and the electromotive force increases from zero to maximum2 #d4 ,from #bgj to #cfj1 the electromotive force decreases from maximum to zero4 ,it was stated that1 during the revolution of the loop1 the magnetic lines were cut 8with increasing or decreasing rapidity10 causing the electromotive force to rise or fall4 ,the reason for this is illustrated in fig4 #afg4 ,the loop is here shown in a horizontal position at right angles to the direction of the magnetic field2 the latter1 as indicated by the even spacing of the vertical arrows representing the magnetic lines1 is assumed to be uniform4 ,the wire ,c ,d of the loop1 as it rotates at constant speed1 cuts the magnetic lines at the points #j1 #a1 #b1 #c1 etc41 but the distances #j-a1 #a-b1 #b-c1 etc41 between these points1 are unequal2 that is1 the wire ,c ,d travels farther in cutting the lines #j and #a1 than it does in cutting #a and #b1 and still less in cutting the lines #b and #c4 ,after cutting the line #d1 which passes through the axis of revolution1 the opposite conditions obtain4 ,if the arcs #j-a1 #a-b1 etc41 of the dotted circle1 which are intercepted by the magnetic lines and passed through by the wire1 be rectified and laid down under each other1 as lines #j-a1 #a-b1 etc41 the time of passage of the wire between successive magnetic lines will vary as the length1 since the speed is uniform4 ,thus the wire in passing from line #j to line #a1 takes much more time than in passing from #a to #b1 as indicated at the left of the figure by #j-a and #a-b1 and still less in passing from #b to #c2 that is1 the rate of cutting the lines increases as ,c ,d rotates from #j to #d and decreases from #d to #h4 ,since similar conditions prevail with respect to ,a ,b1 for its corresponding movement1 it is evident that the number of lines which thread through the loop are decreased with increasing rapidity as the loop rotates through the first quarter of a revolution1 and increased with decreasing rapidity during the second quarter of the revolution4 ,moreover1 it must be evident that the reverse conditions obtain for the third and fourth quarters of the revolution4 ,the ,sine ,curve4--,in the preceding paragraph it was shown that an alternating current is induced in the armature of either an alternator or dynamo2 that is1 the current3 #a1 begins with zero electromotive force1 #b1 rises to a maximum1 #c1 decreases again to zero1 #d1 increases to a maximum in the opposite direction1 and #e1 decreases to zero4 ,illustration3 ,,fig4 #afh4--;,application and construction of the sine curve4 ,the sine curve is a wave-like curve used to represent the changes in strength and direction of an alternating current4 ,an elementary alternator is shown at the left to illustrate the application of the sine curve to the alternating current cycle4 ,it consists of a loop of wire ,a ,b ,c ,d1 whose ends are attached to the ring ,f and shaft ,g1 being arranged to revolve in a uniform magnetic field indicated by the vertical arrows which represent magnetic lines at equidistances4 ,the alternating current induced in the loop is carried to the external circuit through the brushes ,m and ,s4 ,now1 as the loop rotates1 the induced electromotive force will vary in such a manner that its intensity at any point of the rotation is proportional to the sine of the angle corresponding to that point1 this is represented by the wave-like curve4 ,the mean value of the sine curve1 or average electromotive force developed during the revolution1 or period1 is equal to #b 1 or 4#fcg of that of the maximum ordinate1 that is1 average electromotive force 4#fcg amplitude4 ,the sine curve lies above the horizontal axis during the first half of the revolution and below it during the second half1 which indicates that the current flows in one direction for a half revolution and in the opposite direction during the remainder of the revolution4 ,a wave-like curve1 as shown in fig4 #afh1 is used to represent these several changes1 in which the horizontal distances represent time1 and the vertical distances1 the varying values of the electromotive force4 ,it is called the sine curve because a perpendicular at any point to its axis is proportional to the sine of the angle corresponding to that point4 ,ques4 ,describe the construction and application of the sine curve4 ,ans4 ,in fig4 #afh1 at the left1 is shown an elementary armature in the horizontal position1 but at right angles to the magnetic field4 ,the dotted circle indicates the circular path described by ,a ,b or ,c ,d during the revolution of the loop4 ,now1 as the loop rotates1 the induced electromotive force will vary in such a manner that its intensity at any point of the rotation is proportional to the sine of the angle corresponding to that point4 ,hence1 on the horizontal line which passes through the center of the dotted circle1 take any length1 as #jh1 and divide it into any number of parts representing fractions of a revolution1 as #j1 #ij1 #ahj1 etc4 ,erect perpendiculars at these points1 and from the corresponding points on the dotted circle project lines parallel to #jh2 the intersections with the perpendiculars give points on the sine curve4 ,thus the loop passes through #b at the #ij point of its revolution1 hence1 projecting over to the corresponding perpendicular gives #b #b1 a point whose elevation from the axis is proportional to the electromotive force at that point4 ,in like manner other points are obtained1 and the curved line through them will represent the variation in the electromotive force for all points of the revolution4 ,at #ij1 the electromotive force is at a maximum2 hence1 by using a pressure scale such that the length of the perpendicular #b #b for #ij will measure the maximum voltage the length of the perpendicular at any other point will represent the actual pressure at that point4 ,the curve lies above the horizontal axis during the first half of the revolution1 and below it during the second half1 which indicates that the current flows in one direction for a half revolution and in the opposite direction during the remainder of the revolution4 ,the application of the sine curve to represent the alternating cycle1 is further illustrated in figs4 #afi to #agc1 which show the position of the armature at each quarter of the revolution4 ,illustration3 ,,figs4 #afi to #agc4--,the sine curve with view of armature for each #ij of the revolution1 showing progressively the application of the sine curve to the alternating current cycle4 ,in fig4 #agi1 the loop ,a ,b ,c ,d is in the vertical position at the beginning of the revolution4 ,at this instant the electromotive force is zero1 hence the sine curve as shown begins at ,e1 the zero point--that is1 on the axis or line of no pressure4 ,as soon as the loop rotates out of the vertical plane1 the electromotive force rises and the current begins to flow in the direction indicated by the arrows1 going out to the external circuit through brush ,m1 and returning through brush ,s4 ,continuing the rotation1 the electromotive force increases in proportion to the sine of the angle made by the plane of the loop with the horizontal1 until the loop comes into the horizontal position illustrated in fig4 #agj4 ,this increase is indicated by the gradual rise of the sine curve from ,e to ,f4 ,the loop has now made one quarter of a revolution and the electromotive force reached its maximum value4 ,as the loop rotates past the horizontal position of fig4 #agj1 the electromotive force gradually decreases in intensity1 reaching the zero point at the end of the second quarter--that is1 when the loop has turned one half revolution4 ,this is indicated by the gradual fall of the curve from ,f to ,g4 ,when the loop turns out of the vertical position shown in fig4 #aga the current reverses1 because the movement of ,a ,b and ,c ,d is reversed2 at this instant the brush ,m becomes negative1 and ,s positive4 ,this reversal of current is indicated by the curve falling below the axis from ,g to ,i4 ,during the second half of the revolution1 figs4 #aga to #agc1 the changes that occur are the same as in the first half1 with the exception that the current is in the reverse direction2 these changes are as shown by the curve from ,g to ,i4 ,,chapter ,,xiv ,,the ,,dynamo3 ,,current ,,commutation ,how the ,dynamo ,produces ,direct ,current3 ,the ,commutator4--,the essential difference between an alternator and a dynamo is that the alternator delivers alternating current to the external circuit while the dynamo delivers direct current4 ,in both machines1 as before stated1 alternating currents are induced in the armature1 but the kind of current delivered to the external circuit depends on the manner in which the armature currents are collected4 ,in the case of an alternator1 the method is quite simple4 ,as previously explained1 each end of the loop is connected with an insulated collector ring carried by the shaft1 the current being collected by means of brushes which bear against the rings4 ,this principle1 rather than the actual construction1 is shown in the preceding illustrations4 ,its important point1 as distinguished from other methods of collecting the current1 is that each end of the loop is always in connection with the same brush4 ,ques4 ,how is direct current obtained in a dynamo8 ,ans4 ,a form of switch called the commutator is placed between the armature and the external circuit and so arranged that it will reverse the connections with the external circuit at the instant of each reversal of current in the armature4 ,ques4 ,how is a commutator constructed8 ,ans4 ,it consists of a series of copper bars or segments arranged side by side forming a cylinder1 and insulated from each other by sheets of mica or other insulating material4 ,illustration3 ,,figs4 #agd to #agh4--;,commutation of the current4 ,these figures show how a dynamo transforms alternating into the so-called direct current4 ,during the first half of the revolution the current flows in the direction ,a ,b1 out through segment ,f of the commutator and brush ,m1 returning through brush ,s and segment ,g1 figs4 #agd and #age4 ,at the beginning of the second half of the revolution1 fig4 #agf1 the current in the armature reverses and flows around the loop in the direction ,b ,a4 ,at this instant the brushes ,m and ,s pass the gaps between the commutator segments1 thus reversing contact with the segments1 and causing the current in the external circuit to remain in the same direction4 ,ques4 ,where is the commutator placed8 ,ans4 ,it is attached to the shaft at the front end of the armature4 ,ques4 ,what are inductors8 ,ans4 ,the insulated wires wound on the armature core1 and in which the electric current is induced4 ,ques4 ,how are the inductors connected to the commutator8 ,ans4 ,the ends of each conducting loop or coil must be connected with the commutator segments in a certain order to correspond with the type of winding4 ,ques4 ,explain in detail how direct current is obtained in a dynamo4 ,illustration3 ,,figs4 #agi to #aha4--;,elementary dynamo armatures4 ,fig4 #a1 single turn loop2 fig4 #b1 coil of two turns in series2 fig4 #c1 coil of two turns in parallel4 ,in operation the amplitude or maximum pressure induced with the two turn coil1 fig4 #ahj1 is double that of a single turn loop1 fig4 #agi4 ,in fig4 #ahj1 the pressure is double that induced in fig4 #aha1 while the amount of current generated with series turns1 fig4 #ahj1 is only half that generated with turns in parallel fig4 #aha4 ,ans4 ,it will be easily seen by the aid of a series of illustrations just how the alternating armature currents are transformed into direct current4 ,figs4 #agd to #agh show1 in several positions1 a single loop of wire with its ends joined to a commutator2 the latter has only two segments1 one for each end of the loop4 ,in fig4 #agd the loop is shown in the vertical position1 and it should be noted that the division between the two segments forming the commutator is in the same plane as the loop4 ,when the loop is in the vertical position1 as shown in fig4 #agd1 brush ,m is in contact with segment ,f1 and ,s with ,g4 ,as the armature rotates1 the current flows for one half revolution in the direction ,a ,b1 through segment ,f and out to the external circuit through brush ,m as shown in figs4 #agd and #age1 returning through brush ,s and segment ,g4 ,at the beginning of the second half of the revolution1 fig4 #agf1 the current in the loop reverses and flows in the opposite direction ,b ,a as indicated by the arrows4 ,at this instant1 however1 the brushes ,m and ,s pass out of contact with segments ,f and ,g1 and come into contact with ,g and ,f respectively2 that is1 ,m leaves ,f and contacts with ,g1 while ,s leaves ,g and contacts with ,f4 ,the effect of this is to reverse the connections with the external circuit at the instant the alternation or reversal of current in the armature takes place1 thus keeping the current in the external circuit in the same direction4 ,illustration3 ,,fig4 #ahb4--;,gramme ring armature with one coil1 and characteristic sine curve below4 ,with one coil as shown1 there are two pulsations of the current per revolution of the armature4 ,ques4 ,how is this indicated by the sine curve8 ,ans4 ,the sine curve1 instead of falling below the axis1 as in figs4 #afi to #agc1 again rises as in the first half of the period1 that is ,g,h,i is identical with ,e,f,g4 ,ques4 ,is the direct current indicated by the sine curve in figs4 #agd to #agh continuous8 ,ans4 ,no2 it is properly described as a pulsating current1 or one1 constant in direction1 but periodically varying in intensity so as to progress in a series of throbbings or pulsations instead of with uniform strength4 ,ques4 ,what is generally understood by the word 8continuous0 as applied to the current obtained from a dynamo8 ,ans4 ,it is usually accepted as meaning a steady or non-pulsating direct current2 one that has a uniform pressure and constant direction of flow as opposed to an alternating current4 ,ques4 ,is a continuous current ever obtained with a dynamo8 ,ans4 ,no4 ,illustration3 ,,fig4 #ahc4--;,gramme ring armature with two coils placed #ahj apart4 ,this arrangement gives double the pressure of the one coil armature1 fig4 #ahb4 ,it should be clearly understood at the outset that it is impossible to obtain a continuous current with a dynamo4 ,the so-called continuous current which it is said to produce is in reality a pulsating current1 but with pulsations so minute and following each other with such rapidity that the current is practically continuous1 and as such is generally called continuous4 ,ques4 ,how is the so-called continuous current produced by a dynamo8 ,ans4 ,in order to obtain a large number of small pulsations per revolution of the armature instead of two large pulsations1 as with the single loop armature1 the latter must be replaced by one having a great number of loops properly connected to commutator segments and so arranged that the successive loops begin the cycle progressively4 99 99 99 99 99 ,the difficulties encountered in connecting up numerous loops were overcome by ,gramme1 who1 in #ahga invented a 8ring0 armature4 ,his method consists in winding a ring with a continuous coil of wire1 connections being made at suitable intervals with the commutator4 ,illustration3 ,,fig4 #ahd4--;,four separate coils wound on ring to illustrate the action of a ,gramme ring armature4 ,if the ring be rotated the electromotive forces induced in adjacent coils will be equal and tend to produce currents in opposite directions2 hence1 if the inner ends be joined1 the junctions would be at a higher potential 7 or -7 than the loose ends4 ,with proper connections current may be collected at the junctions4 ,in order to understand the action of such an arrangement1 it will be well to first consider four separate coils wound on a ring as shown in fig4 #ahd4 ,these coils are all similar1 but at the moment occupy different magnetic positions on the ring4 ,the rotation being clockwise1 #a is about to enter the field adjacent to the north pole1 while #b is emerging from the field in the region of the south pole4 ,again1 #c is approaching the south pole and #d receding from the north pole4 ,ques4 ,describe in detail the action of the four coils wound around the ring as in fig4 #ahd4 ,ans4 ,according to the laws of electromagnetic induction1 pressures are set up at the ends of the coils such as tend to produce currents in the directions indicated by the arrows4 ,now1 assuming the electromotive forces in coils #a and #b to be equal1 if the adjacent ends be joined1 no flow of current will take place1 but the junction will be at a higher pressure than the loose ends of the coils and if a wire be attached to this junction1 and the necessary circuits completed1 a current will flow along the wire outward from the junction4 ,similarly1 if the adjacent ends of coils #c and #d be joined1 there will be no flow of current1 but the junction will be at a lower pressure than the loose ends1 and if a wire be attached to the junction and the necessary circuits completed1 current will flow from the junction around the coils4 ,illustration3 ,,fig4 #ahe4--;,gramme ring armature with four coils4 ,the electromotive force induced in coils ,a1 ,a reaches the zero point at the instant that of coils ,b1 ,b is at a maximum2 hence1 sine curve ,no4 #a1 beginning at zero1 and ,no4 #b1 at the maximum1 show the pressure changes for ,a1 ,a and ,b1 ,b1 respectively4 ,the summation of these curves gives the resultant curve ,no4 #c1 showing changes in pressure of current delivered to the external circuit4 ,ques4 ,what may be said with respect to the four coil ,gramme ring armature shown in fig4 #ahe8 ,ans4 ,according to the laws of electromagnetic induction1 with the north pole of the field at the left and clockwise rotation1 the induced currents flow upward on both sides of the ring1 hence1 the electromotive forces oppose each other at only two of the junctions1 namely3 at the one connected to brush ,m where the pressures on either side are both directed toward the junction and the other at the junction connected to brush ,s1 at which the pressures are both directed from the junction4 ,illustration3 ,,fig4 #ahf4--;,gramme ring armature with six coils4 ,the sine curves #a1 #b and #c1 represent the conditions due to coils ,,aa1 ,,bb and ,,cc1 respectively1 and #d1 the resultant pulsations4 ,it is evident1 then1 that the pressure at ,m is higher than at ,s2 that is1 ,m is positive and ,s negative2 consequently1 the current flows from ,m to the external circuit and returns through ,s4 ,ques4 ,in what other way may the four coils of the armature in fig4 #ahe be regarded8 ,ans4 ,they may be considered as two pairs ,a ,a and ,b ,b1 the action of either pair being identical with the two coil armature shown in fig4 #ahc2 this1 in turn1 produces the same effect as the one coil armature of fig4 #ahb1 with the exception that the amplitude of the current generated with two coils is twice as great as that with one coil of the same number of turns4 ,again considering the action of the four ring coil shown in fig4 #ahe1 and starting at the beginning of the revolution1 the variation of electromotive force induced in coils ,,aa is indicated by the dotted sine curve #a1 and of ,,bb by dotted curve #b4 ,it will be seen that #a begins at the axis or line of no pressure1 and #b at maximum pressure4 ,illustration3 ,,fig4 #ahg4--,the resultant curves of figs4 #ahc1 #ahe and #ahf are here shown for comparison to illustrate the approach to uniform pressure as the number of coils are increased4 ,it should be noted that the number of pulsations per cycle depends on the number of coils1 and that as the pulsations increase in number1 the variation in pressure decreases4 ,the two curves overlap each other1 and in order to determine the effect of this it is necessary to trace the resultant curve1 #c4 ,this is easily done1 as the resultant electromotive force induced at any point in the revolution of the armature is equal to the sum of the pressures induced in ,,aa and ,,bb4 ,thus1 at the beginning of the revolution the pressure induced in ,,aa is at zero point1 and in ,,bb at its maximum ,j1 hence1 the resultant curve begins at the point ,j4 ,again1 for any point in the revolution1 as ,n1 the height of the resultant curve is equal to ,,np ,,nt ,,nv4 ,for #de or #a_/h revolution1 the resultant curve reaches its amplitude1 which is equal to #b ,,rz ,,rw1 and at #ij it again reaches its minimum1 ,,xy4 ,ques4 ,state the conditions upon which the steadiness of the current depends4 ,ans4 ,it depends on the number of coils and the manner in which they are connected4 ,comparing curves #a and #c1 in fig4 #ahe1 it will be noted that with four coils the variation of pressure or amplitude of the pulsations is less than half that obtained with two2 moreover1 with four coils the number of pulsations per cycle is doubled4 ,in order to further observe the approach to continuous current obtained by increasing the number of coils1 the effect of a six coil armature is shown in fig4 #ahf1 the resultant curve being obtained in the same manner as just explained4 ,for comparison1 the curves for the three cases of two1 four1 and six coils are reproduced under each other in fig4 #ahg4 ,as the number of coils is further increased1 the amplitude of the pulsations decreases so that the resultant curve approaches nearer the form of a straight line4 ,in the actual dynamo there are a great many coils1 hence the amplitude of the pulsations is exceedingly small2 accordingly1 it is customary to speak of the current as 8continuous10 although as previously mentioned such is not the case4 ,,chapter ,,xv ,,classes ,,of ,,dynamo ,in order to adapt the dynamo to the varied conditions of service1 its design is modified in numerous ways1 giving rise to the different 8types40 ,these may be classified with respect to3 #a4 ,field magnets2 #b4 ,field excitation2 #c4 ,field winding4 ,the first division relates to the number of magnetic poles1 as unipolar1 bipolar1 and multi-polar dynamos2 also inter-polar dynamos4 ,under the second division are included the following3 #a4 ,self-exciting machines of which the magneto is the simplest4 ,its magnetic field is obtained from permanent magnets1 hence the electromotive force generated is comparatively small4 ,the more important type of self-exciting machine is provided with electromagnets in which the field of force is 8built up0 from the residual magnetism of the soft iron or steel cores of the field magnets of the dynamo itself4 ,nearly all commercial types of dynamo are of this class4 #b4 ,separately excited machines in which the field magnets are magnetized when the machine is in operation by current supplied from a separate source such as a battery or magneto generator4 ,with respect to the third division1 based on the field winding1 dynamos are classed as3 #a4 ,series wound2 #b4 ,shunt wound2 #c4 ,compound wound4 ,in addition to the foregoing there are further distinctions with respect to the mechanical features4 ,most dynamos have a revolving armature and stationary field magnets2 however1 in some cases1 both the armature and field magnets are stationary1 a revolving iron inductor being provided to intercept the magnetic lines intermittently which produces the same effect as is obtained in cutting the magnetic lines by a revolving armature4 ,ques4 ,what may be said of bipolar and multi-polar dynamos8 ,ans4 ,dynamos with bipolar field magnets were universally used prior to #ahij1 but since that time machines of this type are only made in very small sizes2 the multi-polar dynamo is the type now in general use4 ,ques4 ,state some of the features of the multi-polar dynamo4 ,ans4 ,in this class of machine1 the armature and field magnets are surrounded by a circular frame1 or ring yoke to which the field magnets are attached4 ,this ring arrangement has the advantages of strength1 simplicity1 symmetrical appearance1 and minimum magnetic leakage1 since the pole pieces have the least possible surface and the path of the magnetic flux is shorter4 ,ques4 ,what important advantage is gained by the use of multi-pole field magnets8 ,ans4 ,commercial voltages are obtained at moderate armature speed4 ,the difficulty experienced with bipolar machines is that1 with a dynamo of large output1 the speed at which its armature would have to rotate to generate commercial voltages would be excessive4 ,illustration3 ,,figs4 #ahh and #ahi4--;,circuit diagrams to illustrate the difference between a dynamo and a magneto4 ,the former has its field magnets ,f ,f magnetized by means of a small current flowing around a shunt circuit4 ,in a magneto the field magnets are permanently magnetized4 ,the strength of the magnet field of a magneto is constant while that of a dynamo varies with the output4 ,it is evident that with two or more magnetic fields1 secured by increasing the number of poles1 the armature inductors revolving between them cut more magnetic lines in one revolution than with a single field1 hence1 a given voltage is obtained with less speed of the armature than in the bipolar machine4 ,for instance1 if a bipolar dynamo be required to run at say #ijj revolutions per minute to generate #abe volts1 a four pole machine of equal output will require only #dej revolutions1 and one of eight poles only #bbe revolutions per minute4 ,ques4 ,what is a self-exciting dynamo8 ,ans4 ,a machine in which the initial excitation of the field is due to the residual magnetism retained by the cores4 ,ques4 ,what may be said of the field due to this residual magnetism8 ,ans4 ,it presents a very weak field1 and the voltage that could be generated by the armature revolving in such a field would be only about two to ten volts4 ,illustration3 ,,fig4 #aij4--,series wound dynamo1 used for series arc lighting1 and as a booster for increasing the pressure on a feeder carrying current furnished by some other generator4 ,the coils of the field magnet are in series with those of the armature and external circuit1 and consists of a few turns of heavy wire4 ,the characteristic of the series dynamo is to furnish current with increasing voltage as the load increases4 ,if overloaded1 the voltage will drop4 ,ques4 ,how then can commercial voltages such as #ajj or more volts be obtained with a self-exciting dynamo8 ,ans4 ,part or all of the current induced in the armature is passed through the windings of the field magnets1 thus strengthening the field4 ,the voltage1 therefore1 will 8build up10 increasing until the maximum has been reached4 ,the maximum voltage will depend upon the capacity of the field magnets as determined by the construction1 and upon the strength of current used to excite them4 ,ques4 ,how long does the process of 8building up0 require8 ,ans4 ,the time required to fully excite the field magnets is from ten to twenty seconds1 the rise in field strength being indicated on the voltmeter or by the gradual increase in the brilliancy of the pilot lamp4 ,ques4 ,name three important classes of dynamo4 ,ans4 ,series wound1 shunt wound1 and compound wound4 ,ques4 ,describe the winding of a series dynamo4 ,ans4 ,in this machine1 the field magnets are wound with a few turns of thick wire joined in series with the armature brushes as shown in fig4 #aij4 ,ques4 ,what is the effect of this arrangement8 ,ans4 ,all of the current generated by the machine passes through the coils of the field magnets to the external circuit4 ,the current in passing through the field magnets1 energizes them and strengthens the weak field due to the residual magnetism of the magnet cores1 resulting in the gradual building up of the field4 ,ques4 ,for what service is the series dynamo adapted8 ,ans4 ,it may be used for series arc lighting1 series incandescent lighting1 and as a booster for increasing the pressure on a feeder carrying current furnished by some other generator4 ,ques4 ,what is the effect of the series winding in the operation of the machine8 ,ans4 ,its characteristic is to furnish current at an increased voltage as the load increases4 ,if sufficient current be drawn to overload the machine1 the voltage will drop4 ,since the armature coils1 field magnets and external circuits are in series1 any increase in the resistance of the external circuit lessens the power of the machine to supply current1 because it diminishes the current in the coils of the field magnets and therefore diminishes the effective magnetism4 ,again1 a decrease in the resistance of the external circuit will increase the voltage because more current will flow through the field magnets4 ,accordingly1 when the external circuit has lamps in series 7as is common in an arc light circuit7 the switching on of an additional lamp both adds to the resistance of the circuit and diminishes the power of the machine to supply current4 ,when the lamps are in parallel1 the switching on of additional lamps not only diminishes the resistance of the circuit1 but causes the field magnets to be further excited by the increased current1 so that the greater the number of lamps put on1 the greater becomes the risk of inducing too much current4 ,the series dynamo has also the disadvantage of not starting action until a certain speed has been attained1 or unless the resistance of the external circuit be below a certain limit4 ,regulation of ,series ,dynamos4--,the series dynamo is ordinarily used for operating arc lamps connected in series4 ,the current generally consumed is about #aj amperes1 and it is necessary that it should remain at this strength to keep the lights burning steadily4 ,if it increase1 the lights will be too bright1 and if it decrease1 they will be too dim or flicker4 ,with all the lamps connected in series it is evident that the resistance of the circuit will vary widely as they are turned on or off1 the resistance increasing as the lamps are turned on1 and decreasing as they are turned off4 ,it is necessary1 therefore1 that some means of regulation be provided to enable the dynamo to increase or decrease the voltage in proportion to the load4 ,there are several methods of regulation1 as by3 #a4 ,variation of armature speed2 #b4 ,variation of position of brushes2 #c4 ,variation of field strength4 ,whatever method be used the necessary regulation should be accomplished by automatic devices1 as it would not be practical to station a man in constant attendance to regulate the voltage every time one or more lamps were thrown on or off4 ,ques4 ,when is the first method of regulation used8 ,ans4 ,it is only used in special cases1 as for constant load2 if the voltage be not just right to give the required current1 it may be adjusted by changing the speed of the engine4 ,ques4 ,what may be said of the second method8 ,ans4 ,in both the 8ring0 and 8drum0 types of armature1 rotating in a bipolar field1 there are two points situated at opposite extremities of a diameter of the commutator1 at one of which the potential is a maximum and at the other a minimum1 and it is at these points that the brushes must be placed in order to obtain the greatest difference of pressure1 the difference being less at other points4 ,hence1 by rocking the brushes around the commutator the pressure at the terminals of the machine may be varied and regulated as required4 ,ques4 ,what difficulty is experienced in rocking the brushes to regulate the voltage8 ,ans4 ,sparking takes place at the brushes when they are moved any considerable distance from the neutral position4 ,special dynamos have been designed to overcome this objectionable feature1 still this method of regulation is not extensively used4 ,ques4 ,what may be said of the third method of regulation8 ,ans4 ,the third method1 that of variation of field strength1 is the one in general use4 ,ques4 ,how is the field strength varied8 ,ans4 ,this may be done by the two path method1 or by the variable field coil method4 ,ques4 ,describe the two path method of field regulation4 ,ans4 ,an adjustable resistance or rheostat is connected in parallel with the field winding as shown in fig4 #aia4 ,this shunts more or less of the current from the field winding according to the amount of resistance made active by the lever1 ,l4 ,thus1 if the current in the armature and main circuit be #aj amperes and the resistance of the field winding #aj ohms1 a resistance of #dj ohms in parallel with the winding would cause the current to split in the ratio of #dj to #aj1 or #d to #a2 #b amperes would pass through the resistance and #h amperes through the field4 ,illustration3 ,,fig4 #aia4--,the two path method of regulating a series dynamo4 ,the ends of the series winding are connected by a shunt containing a rheostat4 ,the current induced in the armature1 divides and flows through the two paths thus offered1 the amount flowing through the shunt being regulated by the rheostat4 ,in this way the field strength is easily regulated4 ,illustration3 ,,fig4 #aib4--,regulation of series dynamo by variable field4 ,a multipoint switch is provided with connections to the field winding at various sections1 thus permitting more or less of the field winding to be cut out to regulate its strength4 ,ques4 ,describe the variable field coil method of field regulation4 ,ans4 ,this consists in dividing the field winding into a number of sections and throwing the sections in and out of circuit as shown in fig4 #aib4 ,since the strength of any magnet depends on the number of ampere turns in its field winding1 reducing or increasing the number of turns will respectively reduce or increase the field strength1 the current being kept constant4 ,ques4 ,what is the objection to this method8 ,ans4 ,this arrangement is undesirable for magnets of large size1 because of the tendency to flashing at the contacts of the regulating switch4 ,illustration3 ,,fig4 #aic4--,shunt wound dynamo for parallel circuit incandescent lighting1 and for mill and factory power4 ,the coils of the field magnet form a shunt to the main circuit2 they consist of many turns of fine wire and consequently absorb only a small fraction of the current induced in the armature4 ,the characteristic of the shunt dynamo is that it gives practically constant voltage for all loads within its range4 ,if overloaded the pressure will drop and the machine cease to generate current4 ,the ,shunt ,dynamo4--,the shunt wound dynamo differs from the series wound machine1 in that an independent circuit is used for exciting its field magnet4 ,this circuit is composed of a large number of turns of fine insulated copper wire1 which is wound round the field magnets and connected to the brushes1 so as to form a shunt or 8by pass0 to the brushes and external circuit1 as shown in fig4 #aic4 ,two paths are thus presented to the current as it leaves the armature1 between which it divides in the inverse ratio of the resistance4 ,one part of the current flows through the magnetizing coils1 and the other portion through the external circuit4 ,in all well designed shunt dynamos1 the resistance of the shunt circuit is always very great1 as compared with the resistance of the armature and external circuit1 the strength of the current flowing in the shunt coils being very small even in the largest machines4 ,ques4 ,for what service is the shunt dynamo adapted8 ,ans4 ,it is used for constant voltage circuits1 as in incandescent lighting4 ,ques4 ,in the operation of a shunt dynamo what is its characteristic feature8 ,ans4 ,the voltage at the dynamo remains practically unchanged1 and the current varies according to the load4 ,ques4 ,does the voltage remain constant for all loads8 ,ans4 ,there is a certain maximum load current that the shunt dynamo is capable of supplying at constant voltage2 beyond this1 the voltage will decrease1 the machine finally demagnetizing itself1 and ceasing to generate current4 ,ques4 ,why does the voltage not remain constant for all loads8 ,ans4 ,because there is a drop in the voltage in forcing the current through the armature windings which increases with the load4 ,ques4 ,what is the usual method of regulation for shunt dynamos8 ,ans4 ,the method of varying the current through the field coils by means of a rheostat inserted in series with the field winding as shown in fig4 #aid4 ,moving the lever ,l of the rheostat to the right increases the resistance in series with the field winding1 and this reduces the amount of current in that winding1 thus reducing the strength of the magnet and consequently the voltage at the brushes4 ,the contrary movement of the lever1 by cutting out the resistance1 produces the opposite effect4 ,the ,compound ,dynamo4--,this class of generator is designed to automatically give a better regulation of voltage on constant pressure circuits than is possible with a shunt machine4 ,it possesses the characteristics of both the series and shunt machines1 of which it is in fact a combination4 ,illustration3 ,,fig4 #aid4--,regulation of shunt dynamo by method of varying the field strength4 ,a rheostat is placed in series with the field coils1 and by varying the resistance1 more or less current will flow through the coils1 thus regulating the field strength4 ,the field magnets of the compound dynamo1 as shown in fig4 #aie1 are wound with two sets of coils1 one set being connected in series1 and the other set in parallel1 with the armature and external circuit4 ,the purpose of the series winding is to strengthen the magnets by the current supplied from the armature to the circuit1 and thus automatically sustain the pressure4 ,if the series winding were not present1 the pressure at the terminals would fall as the load increased4 ,this fall of pressure is counteracted by the excitation of the series winding1 which increases with the load and causes the pressure to rise4 ,the number of turns and relative current strengths of the series and shunt windings are so adjusted that the pressure at the terminals is maintained practically constant under varying loads4 ,with respect to the ratio between the number of turns of the two field windings1 the dynamo is spoken of as3 #a4 ,compound2 #b4 ,over compounded4 ,ques4 ,what is the difference between a compound and an over compounded dynamo8 ,ans4 ,in the first instance1 there are just enough turns in the series winding to maintain the voltage constant at the brushes for variable load4 ,if a greater number of turns be used in the series winding than is required for constant voltage at the brushes for all loads1 the voltage will rise as the load is increased1 and thus make up for the loss or drop in the transmission lines1 so that a constant voltage will be maintained at some distant point from the generator4 ,the machine is then said to be over compounded4 ,ques4 ,for what service is over compounding desirable8 ,ans4 ,for incandescent lighting where there is considerable length of transmission lines4 ,ques4 ,what is the usual degree of over compounding8 ,ans4 ,generally for a rise of voltage of from five to ten per cent4 ,in construction1 the field coils are wound with a greater number of turns than actually required1 the machine being accurately adjusted by a running load test after completion4 ,ques4 ,how is the degree of over compounding varied8 ,ans4 ,a rheostat is placed in shunt with the series winding so that the current passing through the winding may be regulated to control the voltage of the machine4 ,illustration3 ,,fig4 #aie4--;,compound wound dynamo1 used when better automatic regulation of voltage on constant pressure circuits is desired than is possible with the shunt machine4 ,the compound dynamo is a combination of the series and shunt types1 that is1 the field magnet is excited by both series and shunt windings4 ,with a proper selection of the number of turns in the series coils1 the voltage may be kept automatically constant for wide fluctuations in the load4 ,when the machine is over compounded its characteristic is to slightly increase the voltage with increase of load1 a desirable feature for long transmission lines in order to compensate for the line drop4 ,ques4 ,how are the ends of the shunt winding of a compound dynamo connected8 ,ans4 ,there are two methods of connection1 being known as the short shunt and the long shunt4 ,ques4 ,describe the short shunt4 ,ans4 ,in the short shunt1 the ends of the shunt winding are connected directly to the brushes as in fig4 #aif4 ,ques4 ,describe the long shunt4 ,ans4 ,in the long shunt1 one end of the shunt winding is connected to one of the brushes and the other end to the terminal connecting the series winding with the external circuit as in fig4 #aig4 ,ques4 ,which is the more desirable8 ,ans4 ,theoretically1 the long shunt is preferable as being the more efficient2 however1 in practice1 the gain is not very appreciable and the short shunt is generally used4 ,illustration3 ,,figs4 #aif and #aig4--,short and long shunt types of compound wound dynamos4 ,the distinction between the two is that the ends of the short shunt connect direct with the brush terminals1 while in the long shunt type1 fig4 #aig1 one end of the shunt connects with one brush terminal and the other with the terminal connecting the series winding with the external circuit4 ,r is the shunt field rheostat for regulating the current through the shunt4 ,ques4 ,what may be said regarding the voltage in short1 and long shunt machines8 ,ans4 ,in a short shunt machine1 the shunt winding is subjected to a higher voltage than with a long shunt4 ,the pressure applied through a shunt winding with a long shunt1 for any particular load1 is equal to the voltage at the brushes plus the drop in the series winding4 ,ques4 ,for what other service besides incandescent lighting are compound dynamos adapted8 ,ans4 ,they are employed in electric railway power stations where the load is very fluctuating4 ,ques4 ,what is the effect of a short circuit on a compound dynamo8 ,ans4 ,it overloads the machine1 since the excessive current flowing through the series field tends to keep the voltage at its normal value4 ,unless the line be automatically opened under such a condition either by a fuse or circuit breaker1 the machine and its driving engine may be damaged4 ,to avoid this danger fuses or automatic circuit breakers are employed4 ,ques4 ,mention another service for which the compound dynamo is used4 ,ans4 ,in some isolated plants1 as small country residences where it is frequently necessary to have a dynamo capable of charging a storage battery during the day1 and of furnishing current for lighting during a certain portion of the evening4 ,under such conditions the compound machine with slight modification is used1 the ordinary shunt dynamo not being capable of maintaining the necessary consistency of voltage1 without attention to the shunt regulator in driving the lamps direct1 the ordinary compound dynamo on the other hand1 being unsatisfactory for charging storage batteries4 ,ques4 ,how is the compound dynamo modified to adapt it to the dual service of lighting and battery charging8 ,ans4 ,it is furnished with alternative compound winding1 in which the series winding is provided with a switch1 which may be fixed either upon the machine itself or upon the switchboard4 ,this switch permits the series coils to be either short circuited in part or cut out of the circuit entirely while the machine is charging the storage battery1 being again cut into circuit when the machine is required to furnish current for the lamps4 ,illustration3 ,,fig4 #aih4--,separately excited dynamo4 ,current for field excitation is supplied by a second and smaller generator4 ,separately ,excited ,dynamos4--,in this class of machine the current required to excite the field magnets is obtained from some independent external source4 ,though used by ,faraday1 the separately excited dynamo did not come into favor until1 in #ahff1 ,wilde employed a small auxiliary magneto machine to furnish currents to excite the field magnets of a larger dynamo4 ,a separately excited dynamo is shown in fig4 #aih4 ,this method of field excitation is seldom used except for alternators2 it is1 however1 to be found occasionally in street railway power houses1 the shunt fields of all the dynamos being separately excited by one dynamo4 ,in common with the magneto1 the separately excited machine possesses the property that1 with the exception of armature reactions1 the magnetism in its field and therefore the total voltage of the machine is independent of variations in the load4 ,illustration3 ,,fig4 #aii4--;,diagram showing principle of ,dobrowolski three wire dynamo4 ,this type of machine is shown in more detail in fig4 #gie on page #gjh4 ,dobrowolski ,three ,wire ,dynamo4--,this type of dynamo was designed to operate a three wire system of distribution without a balancer4 ,the armature is provided with insulated slip rings connected to suitable points in the armature winding and 7by means of brushes7 with choking coils meeting at a common point1 to which the neutral wire of the system is connected1 the main terminals being connected with the outside wires4 ,the machine is capable of feeding unbalanced loads without serious disturbance of the pressure on either side of the system4 ,the principle of the ,dobrowolski three wire dynamo is illustrated in fig4 #aii4 ,the armature ,a is tapped at two points1 ,b and ,b1 and connected to slip rings ,c ,c4 ,a compensator or reactance coil ,d1 between the two halves of which there is minimum magnetic leakage1 is connected to ,c and ,c by brushes1 and has its middle point tapped and connected to the neutral wire ,e4 ,illustration3 ,,fig4 #bjj4--;,armature of ,westinghouse three wire dynamo4 ,collector rings are mounted at one end of the armature as shown1 and the leads to them with the armature winding are similar to those employed on the alternating current side of a rotary converter armature4 ,the connections from the armature to collector rings may be either single phase1 two phase1 or three phase4 ,the two phase connection with four collector rings and two balance coils is used in the ,westinghouse three wire dynamo4 ,it is clear1 from the symmetry of the arrangement1 that the center point of the coil must always be approximately midway in pressure between that of the brushes1 and hence any unbalanced current will return into the armature1 dividing equally between the two halves of the coil4 ,the arrangement forms a cheap and effective substitute for a balancer set1 but lacks the adjustable properties of the latter4 ,there are various modifications of the arrangement4 ,thus more than two slip rings may be used4 ,the compensator windings1 however1 should always be arranged so that the magnetizing effect of the neutral current is self-neutralized in the windings1 as otherwise saturation occurs causing a very heavy alternating magnetizing component4 ,,chapter ,,xvi ,,field ,,magnets ,the object of the field magnet is to produce an intense magnetic field within which the armature revolves4 ,it is constructed in various forms1 due in a large measure to considerations of economy1 and also to the special conditions under which the machine is required to work4 ,electromagnets are generally used in place of permanent magnets on account of3 #a1 the greater magnetic effect obtained1 and #b1 the ability to regulate the strength of the magnetic field by suitably adjusting the strength of the magnetizing current flowing through the magnet coils4 ,the field magnet1 in addition to furnishing the magnetic field1 has to do duty as a framework which often involves considerations other than those respecting maximum economy4 ,the ,make ,up of a ,field ,magnet4--,in construction1 the electromagnet1 used for creating a field in which the armature of a dynamo revolves1 consists of four parts3 #a4 ,yoke2 #b4 ,cores2 #c4 ,pole pieces2 #d4 ,coils4 ,these are shown assembled in figs4 #bja to #bjd4 ,ques4 ,what is the object of the yoke8 ,ans4 ,the yoke serves to connect the two 8limbs10 that is1 the cores and pole pieces1 and thus provide a continuous metallic circuit up to the faces of the pole pieces4 ,ques4 ,how is the yoke constructed8 ,ans4 ,it usually forms the frame of the dynamo as shown in figs4 #bje and #bjf4 ,illustration3 ,,fig4 #bja4--,salient pole1 bipolar field magnet with single coil wound around the yoke4 ,ques4 ,what may be said of the cores8 ,ans4 ,the cores1 which are usually of circular form1 carry the coils of insulated wire used to excite the magnets4 ,classes of ,field ,magnet4--,although numerous forms of field magnet have been devised1 they can be classed into two groups according to the type of pole1 as3 #a4 ,salient pole2 #b4 ,consequent pole4 ,the distinction between these two types of pole is shown in figs4 #bja to #bjc4 ,by inspection of the figures1 it will be seen that the term salient applies to poles produced when the pole pieces form the ends of the magnet1 as distinguished from consequent poles1 or those formed by coils wound on a continuous metal ring or equivalent4 ,in the salient pole bipolar magnet1 the winding may be either upon the limbs1 ,m ,m fig4 #bjb1 or upon the yoke1 ,y as shown in fig4 #bja4 ,the magnetic circuit of salient and consequent poles is indicated in the figures by the dotted lines4 ,illustration3 ,,fig4 #bjb4--,salient pole1 bipolar field magnet with two coils wound around the cores4 ,illustration3 ,,fig4 #bjc4--;,consequent pole1 bipolar field magnet with two coils on the cores4 ,this is known as the 8,manchester0 type in which the cores are connected at the ends by two yokes--so named from its original place of manufacture at ,manchester1 ,england4 ,multi-,polar ,field ,magnets4--,in the multi-polar machine1 the subdivision of the magnetic flux reduces the amount of material of both magnet and armature4 ,moreover1 there is less heating on account of the greater capability of dissipating the heat1 offered by the increased area of surface per unit of volume in each magnet pole and winding4 ,illustration3 ,,fig4 #bjd4--,modern dynamo with four consequent pole field magnets4 ,in this construction the ring shaped yoke also serves as a frame2 the circular form of yoke gives the least chance for magnetic leakage4 ,there may be four1 six1 eight1 or more poles1 arranged in alternate order around the armature4 ,fig4 #bjd shows a four pole field magnet having a common yoke or iron ring1 with four pole pieces projecting inwardly1 and over which the exciting coils are slipped4 ,in the larger machines the yoke is made in two parts bolted together as shown in fig4 #bjf1 so that the upper portion may be lifted off for examination of the armature4 ,ques4 ,can the number of poles in a multi-polar machine be advantageously increased to #af1 #cb1 or more8 ,ans4 ,a large number of poles is not advisable except in very large machines1 since it involves an increase in the expense of machine work1 fittings1 etc41 somewhat out of proportion to the reduction in cost of material and increase in efficiency4 ,ques4 ,what materials are generally used for field magnets8 ,ans4 ,wrought iron1 steel and copper4 ,there are a number of considerations which govern the selection of the materials to be used in a particular machine1 such as initial cost1 weight1 efficiency1 etc4 ,illustration3 ,,figs4 #bje and #bjf4--,solid and split construction of yoke for multi-polar dynamos4 ,in the latter type the yoke is in two halves joined along a horizontal diameter2 while the upper half may be conveniently removed to give access to the armature1 it has the disadvantage of the joint1 which1 no matter how well made1 will add to the reluctance of the magnetic circuit4 ,the figures also illustrate the circular and segmental forms of yoke construction4 ,ques4 ,in the construction of field magnets1 what governs the choice of materials8 ,ans4 ,for cores1 wrought iron is most desirable1 as requiring the smallest amount of material for a given flux4 ,there is a saving in copper due to using wrought iron for the core since1 on account of its small size1 the length of each turn of the magnetizing coil is reduced4 ,for heavy yokes1 where lightness is not essential1 but very often the reverse1 cast iron is used1 as its cross section can be made larger than that of the cores1 this increase in area serving to give strength and rigidity to the machine4 ,cast steel occupies a place intermediate between cast iron and wrought iron both in cost and magnetic properties4 ,illustration3 ,,figs4 #bjg to #bji4--,various sections of cast iron yoke4 ,in form1 these yokes may be either circular or segmental as shown in figs4 #bje and #bjf4 ,illustration3 ,,figs4 #baj to #bab4--,various sections of cast steel yoke4 ,the ribs shown in figs4 #baj and #baa are provided to secure stiffness4 ,ques4 ,name two forms of yoke in general use4 ,ans4 ,the solid1 and divided types as shown in figs4 #bje and #bjf4 ,ques4 ,what is the object of dividing a yoke8 ,ans4 ,to permit access to the armature1 where the construction does not admit of removal of the latter from the side4 ,ques4 ,how is the yoke usually divided8 ,ans4 ,across its horizontal diameter into an upper and lower half1 as shown in fig4 #bjf1 the lower half being seated on1 or more frequently cast in one piece with the bed plate4 ,ques4 ,what is the objection to dividing a yoke8 ,ans4 ,the joints introduced1 even if carefully faced and well bolted together1 add a little reluctance to the magnetic circuit4 ,illustration3 ,,figs4 #bac to #bae4--,some methods of attaching detachable cores4 ,the core seat is machined to receive the core1 it being necessary to secure good contact in order to avoid a large increase in the reluctance of the magnetic circuit4 ,ques4 ,how does this affect the poles adjacent to the points1 and what provision is made8 ,ans4 ,it weakens them1 and in order to overcome this1 the coils of these poles are given a few extra turns4 ,ques4 ,how is the reluctance of a yoke joint reduced8 ,ans4 ,by enlarging the area of contact2 the flange for the bolts furnishes the necessary increase4 ,ques4 ,what determines chiefly the cost of field magnets8 ,ans4 ,the material used in making the cores and their shape4 ,ques4 ,how does this affect the cost8 ,ans4 ,since considerable cross sectional area of core is required1 the problem confronting the designer is to design the core by judicious selection of material and shape1 that the required number of turns in the magnetizing coil is obtained with the shortest length of wire4 ,illustration3 ,,figs4 #baf to #bba4--;,comparison of field magnet core sections4 ,the shorter the perimeter or outside boundary of the core for a given cross sectional area1 the less will be the amount of copper required for the magnetizing coils4 ,all the above sections are of equal area1 and the figures marked on each represent relative values for the perimeters1 the circle for convenience being taken at #ajj4 ,ques4 ,what is the principal objection to the use of cast iron for core construction8 ,ans4 ,since its sectional area must be considerably more than wrought iron1 a much greater quantity of copper is required for the magnetizing coils4 ,copper is expensive1 while cast iron cores are less expensive than equivalent ones of wrought iron2 in this connection1 it is interesting to observe how different designers aim at true economy in construction4 ,steel is sometimes used in place of wrought iron1 and though less efficient magnetically1 it can be cast into the desired shape1 thus avoiding the somewhat expensive processes of forging and machining1 which are necessary in the case of wrought iron4 ,ques4 ,what form of core requires the least amount of copper for the magnetizing coils1 and why8 ,ans4 ,the cylindrical core1 because it has the shortest periphery or boundary for a given area enclosed4 ,illustration3 ,,figs4 #bbb to #bbe4--,several forms of pole piece4 ,where the extremities project as in figs4 #bbb and #bbc1 they are called horns4 ,the object of these is to reduce the reluctance of the air gap4 ,the width of 8fringe0 of the magnetic field is influenced by the shape of the pole piece2 the margin of fringe should be such that the flux density will vary from zero to a high value where the inductors enter4 ,figs4 #baf to #bba1 show a series of cross sections1 all of the same area4 ,the number marked on each section indicates the length of the boundary line1 that of the circle being taken for convenience as #ajj4 ,ques4 ,what are the pole pieces8 ,ans4 ,these are the end portions of the field magnets1 joined to1 or cast together with the core and placed adjacent to the armature4 ,the faces of the pole pieces are of circular shape1 thus forming the sides of the so-called armature chamber within which the armature rotates4 ,illustration3 ,,fig4 #bbf4--,unsymmetrical pole piece introduced by ,gravier to concentrate the magnetic field4 ,when the dynamo is working at small loads1 the flux in the gap is nearly uniform1 but at heavy loads1 the distortion due to the armature current forces the flux forward and saturates the forward horn1 thus preventing much change in its flux density1 on account of the saturation1 and the diminishing area4 ,lundell combined the unsymmetrical and slotted forms of pole piece as shown in fig4 #bcg4 ,ques4 ,why are the pole faces made larger than the coils8 ,ans4 ,in order to reduce the reluctance of the air gap between the face and the armature1 thus enabling fewer magnetizing coils to be used4 ,illustration3 ,,fig4 #bbg4--,pole piece with oblique slots2 a modification of ,lundell's form of pole piece as suggested by ,thompson4 ,in operation1 the neck of the casting becomes saturated and offers considerable reluctance1 which tends to prevent distortion of the magnetic field4 ,it is important that the field should be magnetically rigid1 that is1 not easily distorted4 ,this stiffness of field can be partially secured by judicious shaping of the pole pieces4 ,a few forms of pole piece are shown in figs4 #bbb to #bca4 ,if the projecting tips of the pole pieces1 or horns as they are called1 be widely separated1 as in fig4 #bbb1 they are not always good1 even though thin4 ,it is better that they should be extended as in fig4 #bbc so that they may be saturated by the leakage field or else cut off as in fig4 #bbd4 ,an extreme design1 suggested by ,dobrowolski1 as shown in fig4 #bbe1 surrounds the armature with iron4 ,illustration3 ,,fig4 #bbh4--,non-concentric pole faces2 one method of securing suitable magnetic 8fringe0 with fair magnetic rigidity of field4 ,illustration3 ,,figs4 #bbi to #bca4--,various shapes of pole piece for securing a gradual entrance of the armature inductors into the magnetic field4 ,another scheme1 proposed by ,gravier1 employed the unsymmetrical form shown in fig4 #bbf4 ,in this pole piece the forward horn is elongated4 ,the action due to this arrangement is such that when the machine is working at small loads1 the field in the gap is nearly uniform1 but at heavy loads with distorting reactions which have a tendency to drive the flux into the forward horn1 the small section of the latter causes it to become saturated1 thus reducing the distortion to a minimum4 ,eddy ,currents2 ,laminated ,fields4--,the field magnet cores and pole pieces1 as well as the armature of a dynamo are subject to eddy currents1 that is1 induced electric currents occurring when a solid metallic mass is rotated in a magnetic field4 ,these currents consume a large amount of energy and often occasion harmful rise in temperature4 ,this loss may be almost entirely avoided by laminating the pole piece1 or both pole piece and core2 in the latter case1 both form one part without any joint4 ,illustration3 ,,fig4 #bcb4--;,illustrating the alteration of magnetic field due to movement of mass of iron in the armature4 ,if the masses of iron in the armature are so disposed that as it rotates1 the distribution of the lines of force in the narrow field between the armature and the pole piece is being continually altered1 then1 even though the total amount of magnetism of the field magnet remain unchanged1 eddy currents will be set up in the pole piece and will heat it4 ,this is shown in the above figures1 which represent the effect of a projecting tooth1 such as that of a ,pacinotti ring1 in changing the distribution of magnetism in the pole piece4 ,illustration3 ,,fig4 #bcc4--;,eddy currents induced in pole pieces by movement of masses of iron4 ,these diagrams1 which correspond to those of fig4 #bcb1 show the eddy currents grouped in pairs of vortices4 ,the strongest current flows between the vortices and is situated just below the projecting tooth1 where the magnetism is most intense2 it moves onward following the tooth4 ,at ,c is shown what occurs during the final retreat of the tooth from the pole piece4 ,these eddy currents penetrate into the interior of the iron1 although to no great depth4 ,clearly the greatest amount of such eddy currents will be generated at that part of the pole piece where the magnetic perturbations are greatest and most sudden4 ,a glance at the figures shows that this should be at the forward horn of the pole piece4 ,however1 when a dynamo1 with horned pole pieces1 has been running for some time as a motor the forward horns are cool and the hindward horns hot4 ,illustration3 ,,fig4 #bcd4--;,fort ,wayne laminated pole piece before being cast welded into frame4 ,in the faces of solid pole pieces there exist minute electric currents called eddy currents which cause heating of the iron and increase the energy required to maintain a magnetic circuit in much the same manner as does reluctance4 ,this loss is reduced by dividing the magnetic circuit in the line of flux into numerous parallel paths separated by some material of relatively high resistance4 ,in construction1 the above core and pole piece is made up of sheets of annealed steel of two different widths assembled together to form proper size and shape4 ,the minute spacing between these laminations and the slight oxidizing on each surface is sufficient to reduce considerably the eddy currents4 ,by cast welding the pole piece into the frame1 a low reluctance is secured4 ,ques4 ,what is a laminated pole8 ,ans4 ,one built up of layers of iron sheets1 stamped from sheet metal and insulated1 as shown in fig4 #bcd4 ,ques4 ,what may be said of this construction8 ,ans4 ,it is a most approved method1 and one frequently employed in the construction of cores and pole pieces4 ,fig4 #bcd shows a combined core and pole piece made entirely of sheet iron punchings assembled and riveted together1 and fig4 #bce1 a core to be used with separate pole piece4 ,it should be noted that in both cases there is a longitudinal slot extending from the end into the core4 ,this was first suggested by ,lundell1 the object being to prevent1 as far as possible1 the distortion of the magnetic field due to armature reaction especially on heavy overloads4 ,illustration3 ,,fig4 #bce4--;,fort ,wayne laminated core without pole piece1 as used on large dynamos4 ,it is constructed of punchings from sheet iron1 and riveted under pressure4 ,the alternate end projections and grooved base insure good mechanical union of metal in cast welding to magnet frame4 ,reluctance between core and yoke is reduced to a minimum by cast welding4 ,the core is slotted parallel with the shaft to prevent1 as far as possible1 the distortion of the magnetic field1 especially on heavy overloads4 ,ques4 ,what mode of construction is adopted to reduce the reluctance of the magnetic circuit when laminated poles are used8 ,ans4 ,they are cast welded into the frame4 ,illustration3 ,,fig4 #bcf4--;,fort ,wayne one piece frame with cast welded combined cores and pole pieces4 ,in any electrical apparatus a magnetic circuit of low reluctance requires less energy to maintain a given flux than one having a comparatively high reluctance4 ,to reduce this to a minimum the pole pieces and cores are combined into one part and then cast welded into the yoke or frame4 ,thus the continuity of the magnetic circuit is practically unbroken save for the air gap4 ,the frame end of the core as shown in the illustrations has irregularities in the heights of the different sheets1 as well as grooved undercut surfaces1 in order to enable the molten metal of the frame to key well into the laminations of the core1 making a good joint1 both mechanically and electrically4 ,by this construction1 the continuity of the magnetic circuit is practically unbroken save for the air gap between the pole piece and armature4 ,fig4 #bcf shows a one piece frame of a six pole dynamo having cast welded into it1 combined cores and pole pieces4 ,ques4 ,what is the disadvantage of laminating a core8 ,ans4 ,it necessitates a nearly square or rectangular section1 which requires more copper for the winding than the cylindrical form4 ,illustration3 ,,fig4 #bcg4--,lundell type of combined core and pole piece2 a combination of ,gravier's unsymmetrical horns and longitudinal slot designed to prevent distortion of field4 ,the ,magnetizing ,coils4--,the object of the magnetizing coils1 is to provide1 under the various conditions of operation1 the number of ampere turns of excitation required to give the proper flux through the armature to produce the desired electromotive force4 ,with respect to the manner in which magnetizing coils are wound they are said to be3 #a4 ,spool wound2 #b4 ,former wound4 ,ques4 ,describe the methods of constructing spool wound coils4 ,ans4 ,the spool is made in various ways1 sometimes entirely of brass1 or of sheet iron with brass flanges1 or of very thin cast iron4 ,some builders use sheet metal with a flange of hardwood1 such as teak4 ,if a spool be simply put upon a lathe to be wound1 the inner end of the wire1 which must be properly secured1 should be brought out in such a way that it cannot possibly make a short circuit with any of the wires in the upper layers4 ,to avoid this difficulty1 the wire is sometimes wound on the spool in two separate halves1 the two inner ends of which are united1 so that both the working ends of the coil come to the outside as shown in fig4 #bch4 ,illustration3 ,,fig4 #bch4--,method of winding magnet spool so that the two ends of the coil will come to the outside4 ,this method has also been used for induction coils1 where it is desirable to keep the ends of the wire away from the core and primary coil4 ,ques4 ,describe the construction of former wound coils4 ,ans4 ,former wound coils are wound upon a block of wood having temporary flanges to hold the wire together during the winding4 ,such coils have pieces of strong tape inserted between the layers and lapped at intervals over the windings to bind them together4 ,coils are usually soaked with insulating varnish and stove dried4 ,ques4 ,what may be said with respect to the coil ends8 ,ans4 ,several methods of bringing out the ends of coils are shown in figs4 #bch to #bda4 ,in fig4 #bci copper strip1 laid in behind an end sheet of insulating material1 makes connection to the inner end1 as shown in the right side of the figure1 while another strip1 shown on the left side similarly inlaid1 serves as a mechanical and electrical attachment for the outer end of the winding4 ,illustration3 ,,fig4 #bci4--;,core and edge strip winding for shunt field coils of large multi-polar dynamo4 ,the winding consists of a copper strap ,s carefully insulated and placed edgewise on the core ,c in a single layer of winding4 ,with this arrangement1 the space occupied by insulation is reduced to a minimum1 and1 although the cooling surface is small1 each turn of the winding has one edge on the outer surface1 being ample for adequate cooling4 ,two other methods are shown in figs4 #bdj and #bda4 ,a simple device for securing the outer end is to fashion a terminal piece so that it can be laid upon the winding1 the last three or four turns of which are wound over its base1 and after winding1 are bared at the place and securely soldered4 ,ques4 ,how are the coils insulated8 ,ans4 ,the spools upon which the coils are wound are usually insulated with several layers of paper preparations2 a thickness of one-tenth of an inch made up of several superposed layers is generally sufficient4 ,varnished canvas is useful as an underlay1 and vulcanized fibre for lining the flanges4 ,it is important to protect the joint between the cylindrical part and the flanges4 ,a core paper may be laid upon every four layers of winding4 ,between series and shunt coils1 in compound wound machines there should be an insulation as efficient as that on the cores4 ,when the winding is completed1 two layers of pressed board or equivalent are laid over and bound with an external winding of hard rope or tape4 ,this protective external lagging covering the outer surface of the completed coils is not altogether a benefit for it tends to prevent dissipation of heat4 ,illustration3 ,,fig4 #bdj4--,one mode of bringing out the coil ends1 in which copper strip is laid in behind an end sheet of insulating material4 ,illustration3 ,,fig4 #bda4--;,another mode of bringing out the coil ends4 ,a narrow insulated strip of thin copper ,g1 leading to terminal ,h1 is connected with the end e of the coil before winding4 ,illustration3 ,,figs4 #bdb and #bdc4--,square and hexagonal order of 8bedding40 ,the term bedding is an expression used to indicate the relation between the cross sectional area of the winding when wound square1 as in fig4 #bdb1 and where wound in some other way1 as in fig4 #bdc4 ,in the square order of bedding1 the degree of bedding equals zero4 ,illustration3 ,,fig4 #bdd4--,method of securing coils in position when the pole pieces are simply extensions of the core without enlargement4 ,ques4 ,how are the coils attached8 ,ans4 ,where the pole pieces are simply extensions of the cores without enlargement1 the coils can be slipped over the ends1 but some kind of clamping device is necessary to hold them in place1 as for instance1 the method shown in fig4 #bdd4 ,in case the pole piece be made larger than the core and separate therefrom1 it is put into position after the coils are in place1 thus serving the double purpose of pole piece and clamp4 ,ques4 ,describe the coil connections4 ,ans4 ,coils are generally united in series so that the same magnetizing current may flow through all of them4 ,the coils should be so connected that they produce alternate north and south poles4 ,if all the coils be similarly wound with respect to the terminals1 and similarly placed2 that is1 so placed that the winding1 considered from the coil terminal nearest the pole face1 starts in all the coils in the same direction1 then the connections will come at the north end and at the south end of the spools4 ,illustration3 ,,fig4 #bde4--,western ,electric set of former wound field coils for four pole dynamo4 ,these coils are wound around a former or template1 and are then slipped over the cores before the latter are bolted to the yokes or frame4 ,heating4--,the heat generated in the magnetizing coils is dissipated in three ways2 by3 #a4 ,induction2 #b4 ,radiation2 #c4 ,convection4 ,in the first instance1 it passes through the copper and the insulation1 either to the external surface1 whence it passes off by radiation and convection into the air1 or to the magnet core and yoke1 which in turn conduct it away4 ,in large multi-polar machines the masses of metal in the pole cores and frame are more efficient in dissipating heat than the external surface of the coil4 ,illustration3 ,,fig4 #bdf4--;,fort ,wayne compound wound rectangular ventilated spool field coil4 ,the series and shunt coils are wound side by side1 ventilating passages being provided lengthwise through each coil and between the shunt and series coils as shown4 ,ventilation4--,sometimes provision is made for ventilation of the field magnet coils as shown in fig4 #bdf4 ,here the series and shunt coils are wound side by side1 ample ventilation being provided lengthwise through and between the coils4 ,,hawkins ,,practical ,,library ,,of ,,electricity ,,in ,,handy ,,pocket ,,form ,,price #a ,,each ,they are not only the best1 but the cheapest work published on ,electricity4 ,each number being complete in itself4 ,separate numbers sent postpaid to any address on receipt of price4 ,they are guaranteed in every way or your money will be returned4 ,complete catalog of series will be mailed free on request4 ,,electrical ,,guide1 ,,no4 #a ,containing the principles of ,elementary ,electricity1 ,magnetism1 ,induction1 ,experiments1 ,dynamos1 ,electric ,machinery4 ,,electrical ,,guide1 ,,no4 #b ,the construction of ,dynamos1 ,motors1 ,armatures1 ,armature ,windings1 ,installing of ,dynamos4 ,,electrical ,,guide1 ,,no4 #c ,electrical ,instruments1 ,testing1 ,practical ,management of ,dynamos and ,motors4 ,,electrical ,,guide1 ,,no4 #d ,distribution ,systems1 ,wiring1 ,wiring ,diagrams1 ,sign ,flashers1 ,storage ,batteries4 ,,electrical ,,guide1 ,,no4 #e ,principles of ,alternating ,currents and ,alternators4 ,,electrical ,,guide1 ,,no4 #f ,alternating ,current ,motors1 ,transformers1 ,converters1 ,rectifiers4 ,,electrical ,,guide1 ,,no4 #g ,alternating ,current ,systems1 ,circuit ,breakers1 ,measuring ,instruments4 ,,electrical ,,guide1 ,,no4 #h ,alternating ,current ,switch ,boards1 ,wiring1 ,power ,stations1 ,installation and ,operation4 ,,electrical ,,guide1 ,,no4 #i ,telephone1 ,telegraph1 ,wireless1 ,bells1 ,lighting1 ,railways4 ,,electrical ,,guide1 ,,no4 #aj ,modern ,practical ,applications of ,electricity and ,ready ,reference ,index of the #aj ,numbers4 ,theo4 ,audel ,co41 ,publishers #gb ,,fifth ,,avenue1 ,,new ,,york ,,footnotes3 #a ,,note4--,in #agdi1 ,benjamin ,franklin1 observing lightning to possess almost all the properties observable in electric sparks1 suggested that the electric action of points1 which was discovered by him1 might be tried on thunderclouds1 and so draw from them a charge of electricity4 ,he proposed1 therefore1 to fix a pointed iron rod to a high tower1 but shortly after succeeded in another way4 ,he sent up a kite during the passing of a storm1 and found the wetted string to conduct the electricity to the earth1 and to yield abundance of sparks4 ,these he drew from a key tied to the string1 a silk ribbon being interposed between his hand and the key for safety4 ,leyden jars could be charged1 and all other electrical effects produced1 by the sparks furnished from the clouds4 ,the proof of the identity was complete4 ,the kite experiment was repeated by ,romas1 who drew from a metallic string sparks #i feet long4 ,in #agec1 ,richmann1 of ,st4 ,petersburg1 who was experimenting with a similar apparatus1 was struck by a sudden discharge and killed4 #b ,,note4--,suppose that the conditions are as in the fig4 #cd1 that is1 the segment ,a#a is positive and the segment ,b#a negative4 ,now1 as ,a#a moves to the left and ,b#a to the right1 their potentials will rise on account of the work done in separating them against attraction4 ,when ,a#a comes opposite the segment ,b#b of the ,b plate1 which is now in contact with the brush ,y1 it will be at a high positive potential1 and will therefore cause a displacement of electricity along the conductor between ,y and ,y#a1 bringing a large negative charge on ,b#b and sending a positive charge to the segment touching ,y#a4 ,as ,a#a moves on1 it passes near the brush ,z and is partially discharged into the external circuit4 ,it then passes on until1 on touching the brush ,x1 it is put in connection with ,x1 and has a new charge1 this time negative1 driven into it by induction from ,b#b4 ,positive electricity1 then1 being carried by the conducting patches from right to left on the upper half of the ,a plate1 and negative from left to right on its lower half4 ,a similar process is taking place on the ,b plate1 but in this case the negative electricity is going from left to right above1 and the positive from right to left below4 ,on the whole1 therefore1 positive electricity is being supplied to the left hand main conductor ,z by both upper and lower plates1 and negative to ,z#a4 #c ,,note4--,the discovery of this property of matter is due to ,stephen ,gray1 who1 in #agbi1 found that a cork1 inserted into the end of a rubbed glass tube1 and even a rod of wood stuck into the cork1 possessed the power of attracting light bodies4 ,he found1 similarly1 that metallic wire and pack thread conducted electricity1 while silk did not4 ,gray even succeeded in transmitting a charge of electricity through a hempen thread over #gjj feet long1 suspended on silken loops4 ,a little later1 ,du ,fay succeeded in sending electricity to no less a distance than #a1bef feet through a moistened thread1 thus proving the conducting power of moisture4 ,from that time the classification of bodies into conductors and insulators has been observed4 #d ,,note4--,copper is pre-eminently the metal used for electric conduction1 being among the best conductors1 it is excelled by one or more of the other metals1 but no other approaches it in the average of all qualities4 #e ,,note4--,a current of electricity always flows in a conducting circuit when its ends are kept at different potentials1 in the same way that a current of water flows in a pipe when a certain pressure is supplied4 ,the same electrical pressure does not1 however1 always produce a current of electricity of the same strength1 nor does a certain pressure of water always produce a current of water of the same volume or quantity4 ,in both cases the strength or volume of the currents is dependent not only upon the pressure applied1 but also upon the resistance which the conducting circuit offers to the flow in the case of electricity1 and on the friction 7which may be expressed as resistance7 which the pipe offers to the flow in the case of water4 #f ,,note4--,the prefixes 8meg0 and 8micro0 denote million and millionth4 ,for example1 a megohm equals #a1jjj1jjj ohms1 a microhm equals #a_/a1jjj1jjj of an ohm4 #g ,,note4--,the reciprocal of a number is equal to #a the number2 for instance1 the reciprocal of #c_/bj #a #c_/bj #bj_/c #f-b_/c #h ,,note4--,a writer in the ,new ,science ,review undertakes to answer the question3 8,what is electricity80 ,in order to lead the reader up to the main question1 he first considers the natural forces1 gravitation and heat4 ,examples are given of how these forces are manifested and how energy is changed from one form to another4 ,every form of force1 the author says1 should be regarded as a different method in which energy makes itself known to the senses4 ,he calls particular attention to the important fact that the 8resistance of one kind or another is always the agent that acts to alter energy from one form to another10 and suggests that electricity is simply a form or manifestation that energy may assume under given conditions1 and generally is a mere transitory stage between the mechanical form and the heat form4 8,in most operations10 he continues1 8mechanical force passes to the heat form without passing through the electric form2 but whenever magnetism is brought into play as a resistance that must be overcome1 then mechanical power applied to overcome this resistance always becomes electricity1 if only momentarily in its passage from the mechanical to the heat form40 ,in conclusion1 he asks if the question3 8,what is electricity80 cannot be answered in a fairly satisfactory way by saying that it is simply a form that energy may assume while undergoing transformation from the mechanical or the chemical form to the heat form or the reverse4 #i ,,note4--,the cathode is the conductor by which current flows away as distinguished from the anode or conductor through which the current enters4 ,the terms usually apply to conductors leading the current through a liquid or gas1 as an electrolytic cell1 or vacuum tube4 #aj ,,note4--,the name voltameter was given by ,faraday to an electrolytic cell employed as a means of measuring an electric current by the amount of chemical decomposition the current effects in passing through the cell4 #aa ,,note4--,faraday's own description of his discovery is as follows3 8,two hundred and three feet of copper wire in one length were coiled round a large block of wood2 another two hundred and three feet of similar wire were introposed as a spiral between the turns of the first coil1 and metallic contact everywhere prevented by twine4 ,one of these helices was connected with a galvanometer1 and the other with a battery of one hundred pairs of plates1 four inches square1 with double coppers1 and well charged4 ,when the contact was made there was a sudden and very slight effect at the galvanometer1 and there was also a similar slight effect when the contact with the battery was broken40 #ab ,,note4--,in reality it would be impossible to have a magnetic field exactly like fig4 #abi1 for in the less dense part1 the magnetic lines would be of curved complex form4 #ac ,,note4--,these values are correct for effective sinusoidal voltages4 #ad ,,note4--,it should be understood that a dynamo does not generate electricity1 for if it were only the quantity of electricity that is desired1 it would be of no use1 as the earth may be regarded as a vast reservoir of electricity4 ,however1 electricity without pressure is incapable of doing work1 hence a dynamo1 or so-called 8generator10 is necessary to create an electromotive force by electromagnetic induction in order to cause the current to flow against the resistance of the circuit and do useful work4 99 99 99 99 99 ,,transcriber',s ,,amendments ,transcriber's ,note3 ,blank pages have been deleted4 ,some illustrations may have been moved4 ,notes at the bottom of pages in the text were converted to footnotes and footnote tags were added to the text itself4 ,the footnotes are now located prior to this section4 ,when the author's preference can be determined1 we have rendered consistent on a per-word-pair basis the hyphenation or spacing of such pairs when repeated in the same grammatical context4 ,the publisher's inadvertent omissions of important punctuation have been corrected4 ,duplicative front matter has been removed4 ,the following list indicates any additional changes4 ,the page number represents that of the original publication and applies in this etext except for footnotes and illustrations since they may have been moved4 ,,toc ,table of ,contents ,,toc ,added ,,introductory ,,chapter and ,,signs ,,and ,,symbols ,,toc between electric and neticmagnetic circuits ,,toc action of ,toepler-,holz,holtz machine #d species inhabiting the ,mediteranean,mediterranean #ad would fly from it without any elecricalelectrical #af pith balls on strips of paper ,c1 ,d1 ,e1 as shown4 #bh between the source and rerminalterminal4 #ci a certain anountamount of work #dc ,when metals differeingdiffering from each other #fa ,various zincs2 fig4 #eh ,fuller2 fig4 #ei ,daniel,daniell #fb ,various carbons2 fig4 #fa ,cylindrical fromform1 #fc fig4 #fh ,lockwood2 fig4 #fi fire alramalarm4 #ff ,a paralledparalleled or multiple connection #gj but no other aproachesapproachesit #ic ,with this prelimarypreliminary caution1 #if ,if a current of #aj amperes flowflows in a wire #ih as an electrotylicelectrolytic cell1 #ii rising from the kathodecathode ,p is hydrogen #ajj hydrogen atoms in their journey towards b,b meet #ajj at the electrodueselectrodes and not #acc ,,vi4#f4 ,the approach and recession of a conductor #adb #cb4 ,vibrator coils2 #adb #bc4 ,condenser coils4 #adc soaked in shellac dissolved in alchoolalcohol #aea the hammer or piece of of#bnd #8of' del iron #agj ,,fig4,,figs4 #afi to #agc4-- ,the sine curve #bji ,an extreme design1 suggested by ,dobrowolsky,dobrowolski1 99 99 99 99 99