By other methods other characteristic curves may be obtained, for whichthe titles under Curve may be consulted.114 STANDARD ELECTRICAL DICTIONARY.Characteristic, Drooping.A characteristic curve of a dynamo which indicates a fall in voltagewhen an excessive current is taken from the dynamo in question. It isshown strongly in some Brush machines, and is partly due to thearrangements for cutting out two of the coils as they approach theneutral line. It is an advantage, as it protects from overheating onshort circuit.Characteristic, External.In a dynamo the characteristic curve in which the relations of voltsbetween terminals to amperes in the outer circuit are plotted. (SeeCurve, External Characteristic.)Characteristic, Internal.A characteristic curve of a shunt dynamo, in which the relations ofvolts to amperes in the shunt circuit is plotted.Characteristics of Sound.Of interest, electrically, as affecting the telephone, they comprise:(1) Pitch, due to frequency of vibrations.(2) Intensity or loudness, due to amplitude of waves of sound.(3) Quality or timbre, the distinguishing characteristics of anyspecific sound due to overtones, discords, etc., by which the sound isrecognizable from others. The telephone is held by the U. S. courts tobe capable of reproducing the voice by means of the undulatory current.(See Current, Undulatory.)Charge.The quantity of electricity that is present on the surface of a body orconductor. If no electricity is supplied, and the conductor is connectedto the earth, it is quickly discharged. A charge is measured by theunits of quantity, such as the coulomb. The charge that a conductor canretain at a given rise of potential gives its capacity, expressible inunits of capacity, such as the farad. A charge implies the stretching orstraining between the surface of the charged body, and somecomplimentary charged surface or surfaces, near or far, of large orsmall area, of even or uneven distribution.Charge. v.(a) To introduce an electrostatic charge, as to charge a condenser.(b) To decompose the elements of a secondary battery, q. v., so as torender it capable of producing a current. Thus, a spent battery ischarged or recharged to enable it to do more work.Synonyms--Renovate--Revivify--Recharge.115 STANDARD ELECTRICAL DICTIONARY.Charge, Bound.A charge of electricity borne by the surface of a body so situated withreference to another oppositely charged body, that the charge isimperceptible to ordinary test, will not affect an electroscope norleave the surface if the latter is connected to the earth. To dischargesuch a body it must be connected to its complimentarily charged body.The bound charge was formerly called dissimulated or latent electricity.(See Charge, Free.)The charge or portion of a charge of a surface which is neutralizedinductively by a neighboring charge of opposite kind. The degree ofneutralization or of binding will depend on the distance of the twocharged surfaces from one another and on the electro-static nature ofthe medium intervening, which must of necessity be a dielectric. Acharge not so held or neutralized is termed a free charge. Thus asurface may be charged and by the approach of a surface less highlycharged may have part of its charge bound. Then if connected to earth.it will part with its unbound or free charge, but will retain the otheruntil the binding surface is removed, or until the electricity of suchsurface is itself bound, or discharged, or until connection is madebetween the two surfaces. Thus a body may have both a bound and a freecharge at the same time.Charge, Density of.The relative quantity of electricity upon a given surface. Thus acharged surface may have an evenly distributed charge or one of evendensity, or an unevenly distributed charge or one of uneven density. Ina thunderstorm the earth has a denser charge under the clouds thanelsewhere.Synonym--Electrical Density.Charge, Dissipation of.As every body known conducts electricity, it is impossible so toinsulate a surface that it will not lose its charge by leakage. Anabsolute vacuum might answer, and Crookes in a high vacuum has retaineda charge against dissipation for years. The gradual loss is termed asabove.Charge, Distribution of.The relation of densities of charge on different parts of a chargedbody. On a spherical conductor the charge is normally of evendistribution; on other conductors it is unevenly distributed, being ofgreatest density at points, edges, and parts of smallest radius ofcurvature. Even distribution can also be disturbed by local induction,due to the presence of oppositely charged bodies.116 STANDARD ELECTRICAL DICTIONARY.Charge, Free.The charge borne by an insulated body, independent of surroundingobjects. Theoretically it is an impossibility. A charge always has itscompliment somewhere in surrounding objects. As a matter of convenienceand convention, where the complimentary charge is so distributed thatits influence is not perceptible the charge is called a free charge. Ifconnected to earth the free charge will leave the body. If the body isconnected with an electroscope the free charge will affect the same.(See Charge, Bound.)Charge, Residual.When a Leyden jar or other condenser is discharged by the ordinarymethod, after a few minutes standing a second discharge of less amountcan be obtained from it. This is due to what is known as the residualcharge. It seems to be connected in some way with the mechanical ormolecular distortion of the dielectric. The jarring of the dielectricafter discharge favors the rapidity of the action, diminishing the timerequired for the appearance of the residual charge. The phenomenon, itwill be seen, is analogous to residual magnetism. This charge is thereciprocal of electric absorption and depends for its amount upon thenature of the dielectric. (See Absorption, Electric, and Capacity,Residual.)Synonym--Electric Residue.Chatterton's Compound.A cement used for cementing together layers or sheets of gutta percha,and for similar purposes in splicing telegraph cables. Its formula is:Stockholm Tar, 1 part.Resin, 1 part.Gutta Percha, 3 parts.All parts by weight.Chemical Change.When bodies unite in the ratio of their chemical equivalents, so as torepresent the satisfying of affinity or the setting free of thermal orother energy, which uniting is generally accompanied by sensible heatand often by light, as in the ignition of a match, burning of a candle,and, when the new compound exhibits new properties distinct from thoseof its components, a chemical combination is indicated. More definitelyit is a change of relation of the atoms. Another form of chemical changeis decomposition, the reverse of combination, and requiring or absorbingenergy and producing several bodies of properties distinct from those ofthe original compound. Thus in a voltaic battery chemical combinationand decomposition take place, with evolution of electric instead ofthermal energy.Chemical Equivalent.The quotient obtained by dividing the atomic weight, q. v., of anelement by its valency, q. v. Thus the atomic weight of oxygen is 16,its valency is 2. its chemical equivalent is 8. It is the weight of theelement corresponding to a unit weight of hydrogen, either as replacingit, or combining with it. In electro-chemical calculations the chemicalequivalent is often conveniently used to avoid the necessity of dividingby the valency when atomic weights are used. The latter is really thebetter practice. The atomic weights in the old system of chemicalnomenclature were chemical equivalents.117 STANDARD ELECTRICAL DICTIONARY.Chemical Recorder.A form of telegraphic recorder in which the characters, often of theMorse alphabet or some similar one, are inscribed on chemically preparedpaper by decomposition affecting the compound with which the paper ischarged. In the original chemical recorder of Bain, the instrument wassomewhat similar to the Morse recorder, except that the motionlessstylus, S, always pressing against the paper was incapable of making anymark, but being of iron, and the paper strip being impregnated withpotassium ferrocyanide, on the passage of a current a stain of Prussianblue was produced where the stylus touched the paper. The current passesfrom the line by way of the iron stylus, through the paper, and by wayof a brass surface, M, against which the paper is held and is pressed bythe stylus, to the earth. This recorder is extremely simple and has nopart to be moved by the current. The solution in which the paper isdipped contains a mixture of potassium ferrocyanide and ammoniumnitrate. The object of the latter is to keep the paper moist. In recentrecorders a solution of potassium iodide has been used, which gives abrown stain of free iodine, when the current passes. This staindisappears in a few days.Fig. 83. BAIN'S TELEGRAPH EMPLOYING CHEMICAL RECORDER.In the cut, R is the roll of paper, B is a tank of solution with roll,W1, for moistening the paper; M is the brass surface against which thestylus, S, presses the paper, P P; W, W are feed rollers; T is thetransmitting key, and zk the battery; Pl, Pl are earth plates. Theapparatus is shown duplicated for each end.118 STANDARD ELECTRICAL DICTIONARY.Chemistry.The science treating of atomic and molecular relations of the elementsand of chemical compounds of the same.Chimes, Electric.An apparatus employed to illustrate the principles of the electrostaticcharge, involving the ringing of bells by electrostatic attraction andrepulsion. It is used in connection with a frictional, or influenceelectric machine. Two bells are employed with a button or clappersuspended between them. One bell is connected to one of the primeconductors, q. v., of the machine. The other insulated therefrom isconnected to earth, or if an influence machine is used, to the otherprime conductor. The clappers are hung by a silk thread, so as to beentirely insulated. On working the machine the bells become oppositelyexcited. A clapper is attracted to one, then when charged is repelledand attracted to the other, it gives up its charge and becoming chargedwith similar electricity to that of the bell it touches, is repelled andattracted to the other, and this action is kept up as long as theexcitement continues, the bells ringing continuously.Fig. 84. ELECTRIC CHIMES.Chronograph, Electric.An apparatus for indicating electrically, and thereby measuring, thelapse of time. The periods measured may be exceedingly short, such asthe time a photographic shutter takes to close, the time required by aprojectile to go a certain distance, and similar periods.A drum rotated with even and known velocity may be marked by a styluspressed upon it by the action of an electro-magnet when a key istouched, or other disturbance. Then the space between two marks wouldgive the period elapsing between the two disturbances of the circuit. Asit is practically impossible to secure even rotation of a drum, it isnecessary to constantly measure its rate of rotation. This is effectedby causing a tuning-fork of known rate of vibration to be maintained invibration electrically. A fine point or bristle attached to one of itsarms, marks a sinuous line upon the smoked surface of the cylinder. Thisgives the basis for most accurately determining the smallest intervals.Each wave drawn by the fork corresponds to a known fraction of a second.For projectiles, the cutting of a wire opens a circuit, and the openingis recorded instead of the closing. By firing so as to cut two wires ata known distance apart the rate is obtained by the chronograph.Synonym--Chronoscope.119 STANDARD ELECTRICAL DICTIONARY.Chutaux's Solution.A solution for bichromate batteries. It is composed as follows:Water, 1,500 partsPotassium bichromate, 100 partsmercury bisulphate, 100 parts66° sulphuric acid, 50 parts.Circle, Galvanic or Voltaic.A term for the voltaic circuit; obsolete.Fig. 85. MAGIC CIRCLE.Circle, Magic.A form of electro-magnet. It is a thick circle of round iron and is usedin connection with a magnetizing coil, as shown, to illustrateelectro-magnetic attraction.120 STANDARD ELECTRICAL DICTIONARY.Circuit.A conducting path for electric currents properly forming a complete pathwith ends joined and including generally a generating device of somekind. Part of the conduction may be true and part electrolytic. (SeeElectrolytic Conduction.) The term has become extended, so that the termis often applied to any portion of a circuit conveniently considered byitself. The simplest example of a complete circuit would be a circularconductor. If rotated in the earth's field so as to cut its lines offorce a current would go through it, and it would be an electriccircuit. Another example is a galvanic battery with its ends connectedby a wire. Here the battery generates the current which, by electrolyticconduction, goes through the battery and by true conduction through thewire. For an example of a portion of a circuit spoken of as "a circuit"see Circuit, Astatic.Circuit, Astatic.A circuit so wound with reference to the direction of the currentspassing through it that the terrestrial or other lines of force have nodirective effect upon it, one member counteracting the other. It may beproduced by making the wire lie in two closed curves, A and B, eachenclosing an equal area, one of identical shape and disposition with theother, and with the current circulating in opposite directions in eachone. Thus each circuit represents a magnetizing turn of oppositepolarity and counteracting each other's directive tendency exhibited ina field of force with reference to an axis a c. Another form of astaticcircuit is shown in Fig. 86. The portions C, D, lying on opposite sidesof the axis of rotation a c, are oppositely acted on by the earth'sdirective force as regards the direction of their rotation.Figs. 86 and 87. ASTATIC CIRCUITS.Circuit, Branch.A circuit dividing into two or more parts in parallel with each other.121 STANDARD ELECTRICAL DICTIONARY.Circuit Breaker.Any apparatus for opening and closing a circuit is thus termed, but itis generally applied to automatic apparatus. A typical circuit breakeris the hammer and anvil of the induction coil. (See Induction Coil;Anvil.) Again a pendulum connected to one terminal of a circuit mayswing so as to carry a point on its lower end through a globule ofmercury as it swings, which globule is connected to the other terminal.A great many arrangements of this character have been devised.Synonym.--Contact Breaker.Circuit Breaker, Automatic.A circuit breaker worked by the apparatus to which it is attached, orotherwise automatically. (See Induction Coil; Anvil; Bell, Electric.)Circuit Breaker, File.A coarsely cut file, forms one terminal of an electric circuit, with astraight piece of copper or steel for the other terminal. The latterterminal drawn along the teeth makes and breaks the contact once forevery tooth. The movable piece should have an insulated handle.Circuit Breaker, Mercury.A circuit breaker which may be identical in principle, with theautomatic circuit breaker of an induction coil, but in which in place ofthe anvil, q. v., a mercury cup is used, into which the end of a wiredips and emerges as it is actuated by the impulses of the current. Eachdip makes the contact, which is broken as the wire springs back. Themercury should be covered with alcohol to protect it from oxidation.Circuit Breaker, Pendulum.A circuit breaker in which a pendulum in its swing makes and breaks acontact. It may be kept in motion by clockwork, or by an electro-magnet,attracting intermittently an armature attached to its rod, themagnet circuit being opened and closed by the pendulum or circuitbreaker itself. A mercury contact may be used with it.Fig. 88. PENDULUM CIRCUIT BREAKER.122 STANDARD ELECTRICAL DICTIONARY.Circuit Breaker, Tuning Fork.A circuit breaker in which a tuning fork makes and breaks the circuit.Each vibration of one of the prongs in one direction makes a contact,and the reverse vibration breaks a contact. The adjustment isnecessarily delicate, owing to the limited amplitude of the motion ofthe fork. The fork is kept in vibration sometimes by an electro-magnet,which is excited as the circuit is closed by the fork. One leg of thefork acts as the armature of the magnet, and is attracted according toits own natural period.Circuit Breaker, Wheel.A toothed wheel with a spring bearing against its teeth. One terminal ofa circuit connects with the wheel through its axle, the other connectswith the spring. When the wheel is turned the circuit is opened andclosed once for each tooth. The interstices between teeth on such awheel may be filled with insulating material, giving a cylindricalsurface for the contact spring to rub on.Fig. 89--TOOTHED WHEEL CIRCUIT BREAKER.Circuit, Closed.A circuit whose electric continuity is complete; to make an open circuitcomplete by closing a switch or otherwise is to close, complete, or makea circuit.Synonyms--Completed Circuit--Made Circuit.Circuit, Compound.A circuit characterized by compounding of generating or receivingdevices, as including several separate batteries, or several motors, orother receiving devices. It is sometimes used to indicate a circuithaving its battery arranged in series. It should be restricted to thefirst definition.123 STANDARD ELECTRICAL DICTIONARY.Circuit, Derived.A partial circuit connected to two points of another circuit, so as tobe in parallel with the portion thereof between such two points; a shuntcircuit.Synonyms--Shunt Circuit--Derivative Circuit--Parallel Circuit.Circuit, Electric, Active.A circuit through which a current passes. The circuit itself need onlybe a conducting ring, or endless wire. Generally it includes, as part ofthe circuit, a generator of electro-motive force, and through whichgenerator by conduction, ordinary or electrolytic, the same current goesthat passes through the rest of the circuit. One and the same currentpasses through all parts of a series circuit when such current isconstant.A current being produced by electro-motive force, and electromotiveforce disappearing in its production in an active circuit, there must besome source of energy which will maintain electromotive force againstthe drain made upon it by the current.The simplest conception of an active electric circuit is a ring orendless conductor swept through a field of force so as to cut lines offorce. A simple ring dropped over a magnet pole represents thesimplification of this process. In such a ring a current, exceedinglyslight, of course, will be produced. In this case there is no generatorin the circuit. An earth coil (see Coil, Earth,) represents such acircuit, with the addition, when experimented with, of a galvanometer inthe circuit.In practice, a circuit includes a generator such as a battery or dynamo,and by conductors is led through a continuous path. Electric lamps,electrolytic cells, motors and the like may be included in it.The term "circuit" is also applied to portions of a true circuit, as theinternal circuit, or external circuit. A certain amount of elasticity isallowed in its use. It by no means necessarily indicates a completethrough circuit.Circuit, Electrostatic.(a) A circuit through which an electrostatic or high tension dischargetakes place. It is virtually an electric circuit.(b) The term is applied also to the closed paths of electrostatic linesof force.Circuit, External.The portion of a circuit not included within the generator.Circuit, Grounded.A circuit, one of whose members, the return circuit, is represented bythe earth, so that the earth completes the circuit. In telegraphy eachend of the line is grounded or connected to an earth-plate, q. v., or tothe water or gas-pipes, and the current is assumed to go through theearth on its return. It really amounts to a discharging at one end, andcharging at the other end of the line. The resistance of the earth iszero, but the resistance of the grounding or connection with the earthmay be considerable.Synonyms--Ground Circuit--Earth Circuit--Single Wire Circuit.[Transcriber's note: The resistance of the earth is high enough thatlarge power system return currents may produce dangerous voltagegradients when a power line is shorted to the ground. Don't walk neardowned lines!]124 STANDARD ELECTRICAL DICTIONARY.Circuit Indicator.A pocket compass, decomposition apparatus, galvanometer or other devicefor indicating the condition of a wire, whether carrying a current ornot, and, if carrying one, its direction, and sometimes roughlyindicating its strength.Circuit, Internal.The portion of an electric circuit included within the generator.Circuit, Line.The portion of a circuit embracing the main line or conductor, as in atelegraph circuit the line carried on the poles; distinguished from thelocal circuit (see Circuit, Local,) in telegraphy.Circuit, Local.In telegraphy, a short circuit with local generator or battery included,contained within the limits of the office or station and operated by arelay, q. v. This was the original local circuit; the term is applicableto any similar arrangement in other systems. Referring to the cut, themain line circuit includes the main battery, E, Key, P, Relay, R, groundplates, G, G1. The relay magnet opens and closes the local circuit withits local battery, L, and sounder magnet, H, with its armature, B. Theminor parts, such as switches, are omitted.Fig. 90. LOCAL CIRCUIT OF TELEGRAPH SYSTEM.Circuit, Local Battery.A local circuit worked by and including a local battery in its course.125 STANDARD ELECTRICAL DICTIONARY.Circuit, Loop.A minor circuit introduced in series into another circuit by a cut-out,or other device, so as to become a portion of the main circuit.Circuit Loop Break.A supporter or bracket with two arms for carrying insulators. Its use isto enable a loop connection to be introduced into a line which is cut,so as to enable the connection of the ends of the loop to be made, oneto each end of the through wire, which ends are attached, one to each ofthe two insulators.Circuit, Main.The circuit including the main line and apparatus supplied by the mainbattery, as distinguished from the local circuit. (See Circuit, Local.)Circuit, Main Battery.The main circuit, including the main or principal battery in its course.Circuit, Metallic.A circuit in which the current outside the generator, or similar parts,is carried on a metallic conductor; a circuit without any groundcircuit. The including of a galvanic battery or electro plating bathwould not prevent the application of the term; its essential meaning isthe omission of the earth as the return circuit.Circuit, Negative Side of.The side of a circuit opposite to the positive side. (See Circuit,Positive Side of) It is defined as the half of a circuit leading to thepositive terminal of the generator.Circuit, Open.A circuit with its continuity broken, as by disconnecting a wire fromthe battery, or opening a switch; a broken circuit is its synonym. Toopen a switch or disconnect or cut the wire is termed opening orbreaking the circuit.Synonyms--Incomplete Circuit--Broken Circuit.Circuit, Positive Side of.This side is such that an observer standing girdled by the current withhis head in the positive side or region, would see the current passaround him from his right toward his left hand. It is also defined asthe half of the circuit leading to the negative terminal of thegenerator.Circuit, Recoil.The portion of a parallel circuit presenting an alternative path, q. v.,for a disruptive discharge.Circuit, Return.(a) The part of a circuit extending from the generator to the extremepoint in general, upon which no apparatus is placed. In telegraphsystems the ground generally forms the return circuit. The distinctionof return and working circuit cannot always be made.(b) It may also be defined as the portion of a circuit leading to thenegative terminal of the generator.126 STANDARD ELECTRICAL DICTIONARYCircuits, Forked.Circuits starting in different paths or directions from one and the samepoint.Circuit, Simple.A circuit containing a single generator, and single receiver of anykind, such as a motor or sounder, with a single connecting conductor. Itis also used to indicate arrangement in multiple arc, but not generally,or with approval.Circuits, Parallel.Two or more conductors starting from a common point and ending atanother common point are termed, parallel circuits, although really butparts of circuits. If of equal resistance their joint resistance isobtained by dividing the resistance of one by the number of parallelcircuits. If of unequal resistance r, r', r" , etc., the formula forjoint resistance, R, of two isR = ( r * r' ) / ( r + r' )This resistance may then be combined with a third one by the sameformula, and thus any number may be calculated.Synonym--Shunt Circuit.Circuit, Voltaic.Properly a circuit including a conductor and voltaic couple.It is also applied to the electric circuit, q. v., or to any circuitconsidered as a bearer of current electricity.Circular Units.Units of area, usually applied to cross sectional area of conductors, bywhose use area is expressed in terms of circle of unit diameter,usually a circular mil, which is the area of a circle of one-thousandthof an inch diameter, or a circular millimeter, which is the area of acircle of one millimeter diameter. Thus a wire one-quarter of an inchin diameter has an area of 250 circular mils; a bar one centimeter indiameter has an area of ten circular millimeters.[Transcriber's Note: Area is the diameter squared. A 1/4 inch wire has62500 circular mils of area. A one centimeter (10 millimeter) wire has100 circular millimeters of area. Actual area = circular mils * (PI/4).]Circumflux.The product of the total number of conductor turns on the armature of adynamo or motor, into the current carried thereby. For two pole machinesit is equal to twice the armature ampere-turns; for four pole machinesto four times such quantity, and so on.Clamp.The appliance for grasping and retaining the end of the rod that holds acarbon in the arc lamp.Clark's Compound.A cement used for the outside of the sheath of telegraph cables.Its formula is:Mineral Pitch, 65 parts.Silica, 30 parts.Tar, 5 parts.All parts by weight.127 STANDARD ELECTRICAL DICTIONARY.Cleats.A support; a short block of wood, grooved transversely, for holdingelectric wires against a wall. For the three wire system three groovesare used. The entire wiring of apartments is sometimes done by the"cleat system," using cleats instead of battens, q. v., or mouldings.The cleats are secured against the wall with the grooves facing it, andthe wires are introduced therein.Fig. 91. TWO WIRE CLEAT.Fig. 92. THREE WIRE CLEAT.Cleat, Crossing.A cleat with grooves or apertures to support wires which cross eachother. Two or three grooves are transverse, and on the under side, asabove; one groove is longitudinal and on the upper side.Cleavage, Electrification by.If a mass of mica is rapidly split in the dark a slight flash isperceived. Becquerel found that in such separation the two pieces cameaway oppositely charged with electricity. The splitting of mica is itscleavage.Clock, Controlled.In a system of electric clocks, the clocks whose movements arecontrolled by the current, regulated by the master or controlling clock.Synonym--Secondary Clock.Clock, Controlling.In a system of electric clocks the master clock which controls themovements of the others, by regulating the current.Synonym--Master Clock.Clock, Electric Annunciator.A clock operating any form of electric annunciator, as droppingshutters, ringing bells, and the like. It operates by the machineryclosing circuits as required at any desired hour or intervals.128 STANDARD ELECTRICAL DICTIONARY.Clock, Electrolytic.A clock worked by the electrolytic deposition and resolution of adeposit of metal upon a disc. It is the invention of Nikola Tesla. Ametallic disc is mounted on a transverse axis, so as to readily rotate.It is immersed in a vessel of copper sulphate. A current is passedthrough the bath, the terminals or electrodes being near to and facingthe opposite edges of the disc, so that the line connecting theelectrodes lies in the plane of the disc. If a current is passed throughthe solution by the electrodes, copper is deposited on one side of thedisc, and as it rotates under the influence of the weight thusaccumulated on one side, the same metal as it is brought to the otherside of the disc is redissolved. Thus a continuous rotation ismaintained. The cause of the deposition and solution is the position ofthe disc; one-half becomes negative and the other positive in theirmutual relations.Clock, Self-winding Electric.A clock which is wound periodically by an electric motor and battery.Clockwork, Feed.In arc-lamps the system of feeding the carbon or carbons by clockworkwhose movements are controlled by the resistance of the arc. This systemis employed in the Serrin, and in the Gramme regulators, among others.The carbons, if they approach, move clockwork. The movement of this isstopped or freed by an electro-magnet placed in shunt around the arcand carbons.Cloisons.Partitions or divisions; applied to the winding of electro-magnets andcoils where the winding is put on to the full depth, over singlesections of the core, one section at a time, until the whole core isfilled up.Closure.The closing or completion of a circuit by depressing a key or moving aswitch.Clutch.In arc lamps a device for the feed of the upper carbons. In its simplestform it is simply a plate or bar pierced with a hole through which thecarbon passes loosely. The action of the mechanism raises or lowers oneend of the plate or bar. As it rises it binds and clutches the carbon,and if the action continues it lifts it a little. When the same end islowered the carbon and clutch descend together until the opposite end ofthe clutch being prevented from further descent, the clutch approachesthe horizontal position and the rod drops bodily through the aperture.The cut shows the clutches of the Brush double carbon lamp. In practicethe lifting and releasing as regulated by an electro-magnet are so veryslight that practically an almost absolutely steady feed is secured. Asimilar clutch is used in the Weston lamp.129 STANDARD ELECTRICAL DICTIONARY.Clutch, Electro-magnetic.A clutch or appliance for connecting a shaft to a source of rotarymotion while the latter is in action. In one form a disc, in whose facea groove has been formed, which groove is filled with a coil of wire, isattached to the loose wheel, while the shaft carries a flat plate to actas armature. On turning on the current the flat plate is attached,adheres, and causes its wheel to partake of the motion of the shaft.Contact is made by brushes and collecting rings.In the cut, A A is the attracted disc; the brushes, B B, take current tothe collecting rings, C. The magnetizing coil is embedded in the body ofthe pulley, as shown.Fig. 93. CLUTCH OF BRUSH LAMP.Fig. 94. ELECTRO-MAGNETIC CLUTCH.130 STANDARD ELECTRICAL DICTIONARY.Coatings of a Condenser or Prime Conductor.The thin conducting coatings of tinfoil, gold leaf or other conductingsubstance, enabling the surface to receive and part with the electriccharge readily. Without such a coating the charge and discharge would bevery slow, and would operate by degrees only, as one part of anon-conducting surface might be densely charged and another part bequite devoid of sensible charge.Code, Cipher.A code of arbitrary words to designate prearranged or predeterminedwords, figures or sentences. The systems used in commerce have singlewords to represent whole sentences or a number of words of a sentence.This not only imparts a degree of secrecy, but makes the messages muchshorter. Codes are used a great deal in cable transmission.Code, Telegraphic.A telegraphic alphabet. (See Alphabets, Telegraphic.)Coefficient.In algebra, the numerical multiplier of a symbol, as in the expression"5x," 5 is the coefficient. In physics, generally a number expressingthe ratio or relation between quantities, one of which is often unity,as a standard or base of the set of coefficients. Thus the coefficientof expansion by heat of any substance is obtained by dividing its volumefor a given degree of temperature by its volume at the standardtemperature as 0º C., or 32º F. This gives a fraction by which if anyvolume of a substance, taken at 0º C., or at whatever may be taken asthe basic temperature, is multiplied, the expanded volume for the givenchange of temperature will be obtained as the product. A coefficientalways in some form implies the idea of a multiplier. Thus thecoefficient of an inch referred to a foot would be 1/12 or .833+,because any number of inches multiplied by that fraction would give thecorresponding number of feet.[Transcriber's note: 1/12 is 0.0833+]Coefficient, Economic.In machinery, electric generators, prime motors and similar structures,the number expressing the ratio between energy absorbed by the device,and useful, not necessarily available, work obtained from it. It isequal to work obtained divided by energy absorbed, and is necessarily afraction. If it exceeded unity the doctrine of the conservation ofenergy would not be true. The economic coefficient expresses theefficiency, q. v., of any machine, and of efficiencies there are severalkinds, to express any one of which the economic coefficient may be used.Thus, let W--energy absorbed, and w = work produced ; then w/W is theeconomic coefficient, and for each case would be expressed numerically.(See Efficiency, Commercial--Efficiency, Electrical--Efficiency ofConversion.)The distinction between useful and available work in a dynamo is asfollows: The useful work would include the work expended by the field,and the work taken from the armature by the belt or other mechanicalconnection. Only the latter would be the available work.131 STANDARD ELECTRICAL DICTIONARY.Coercive or Coercitive Force.The property of steel or hard iron, in virtue of which it slowly takesup or parts with magnetic force, is thus termed ("traditionally";Daniell). It seems to have to do with the positions of the molecules, asjarring a bar of steel facilitates its magnetization or accelerates itsparting, when not in a magnetic field, with its permanent or residualmagnetism. For this reason a permanent magnet should never be jarred,and permitting the armature to be suddenly attracted and to strikeagainst it with a jar injures its attracting power.Coercive force is defined also as the amount of negative magnetizingforce required to reduce remnant magnetism to zero.By some authorities the term is entirely rejected, as the phenomenondoes not seem directly a manifestation of force.Coil and Coil Plunger.A device resembling the coil and plunge, q. v., except that for theplunger of iron there is substituted a coil of wire of such diameter asto enter the axial aperture of the other, and wound or excited in thesame or in the opposite sense, according to whether attraction orrepulsion is desired.Coil and Plunger.A coil provided with a core which is free to enter or leave the centralaperture. When the coil is excited, the core is drawn into it. Variousforms of this device have been used in arc lamp regulators.Synonym--Sucking coil.Fig. 95. COIL AND COIL PLUNGER OF MENGIES ARC LAMP.Fig. 96. COIL AND PLUNGER EXPERIMENT.132 STANDARD ELECTRICAL DICTIONARY.Coil and Plunger, Differential.An arrangement of coil and plunger in which two plungers or one plungerare acted on by two coils, wound so as to act oppositely ordifferentially on the plunger or plungers. Thus one coil may be inparallel with the other, and the action on the plunger will then dependon the relative currents passing through the coils.Coil, Choking.A coil of high self-induction, used to resist the intensity of or"choke" alternating currents. Any coil of insulated wire wound aroundupon a laminated or divided iron core forms a choking coil. The ironcoil is usually so shaped as to afford a closed magnetic circuit.A converter or transformer acts as a choking coil as long as itssecondary is left open. In alternating current work special chokingcoils are used. Thus for theatrical work, a choking coil with a movableiron core is used to change the intensity of the lights. It is incircuit with the lamp leads. By thrusting in the core the self-inductionis increased and the current diminishes, lowering the lamps; bywithdrawing it the self-induction diminishes, and the current increases.Thus the lamps can be made to gradually vary in illuminating power likegas lights, when turned up or down.Synonyms--Kicking Coil--Reaction Coil.Fig. 97. DIFFERENTIAL COILS AND PLUNGERS.Fig. 98. BISECTED COILS.133 STANDARD ELECTRICAL DICTIONARY.Coils, Bisected.Resistance coils with connections at their centers, as shown in thediagram. They are used for comparing the resistances of two conductors.The connections are arranged as shown in the coil, each coil beingbisected. For the wires, movable knife-edge contacts are employed. Theprinciple of the Wheatstone bridge is used in the method andcalculations.Coil, Earth.A coil of wire mounted with commutator to be rotated so as to cut thelines of force of the earth's magnetic field, thereby generatingpotential difference. The axis of rotation may be horizontal, when thepotential will be due to the vertical component of the earth's field, orthe axis may be horizontal, when the potential will be due to thevertical component, or it may be set at an intermediate angle.Synonym--Delezenne's Circle.Fig. 99. DELEZENNE'S CIRCLE OR EARTH COIL.Coil, Electric.A coil of wire used to establish a magnetic field by passing a currentthrough it. The wire is either insulated, or so spaced that itsconvolutions do not touch.Coil, Flat.A coil whose windings all lie in one plane, making a sort of disc, or anincomplete or perforated disc.Coil, Induction.A coil in which by mutual induction the electromotive force of a portionof a circuit is made to produce higher or lower electro-motive force, inan adjoining circuit, or in a circuit, part of which adjoins theoriginal circuit, or adjoins part of it.An induction coil comprises three principal parts, the core, the primarycoil and the secondary coil. If it is to be operated by a steadycurrent, means must be provided for varying it or opening and closingthe primary circuit. A typical coil will be described.134 STANDARD ELECTRICAL DICTIONARY.The core is a mass of soft iron preferably divided to prevent extensiveFoucault currents. A cylindrical bundle of soft iron wires is generallyused. Upon this the primary coil of reasonably heavy wire, and of one ortwo layers in depth, is wrapped, all being carefully insulated withshellac and paper where necessary. The secondary coil is wrapped upon orover the primary. It consists of very fine wire; No. 30 to 36 is aboutthe ordinary range. A great many turns of this are made. In generalterms the electro-motive force developed by the secondary stands to thatof the primary terminals in the ratio of the windings. This is onlyapproximate.The greatest care is required in the insulating. The secondary issometimes wound in sections so as to keep those parts differing greatlyin potential far from each other. This prevents sparking, which woulddestroy the insulation.A make and break, often of the hammer and anvil type, is operated by thecoil. (See Circuit Breaker, Automatic.) As the current passes throughthe primary it magnetizes the core. This attracts a little hammer whichnormally resting on an anvil completes the circuit. The hammer asattracted is lifted from the anvil and breaks the circuit. The soft ironcore at once parts with its magnetism and the hammer falls upon theanvil again completing the circuit. This operation goes on rapidly, thecircuit being opened and closed in quick succession.Every closing of the primary circuit tends to produce a reverse currentin the secondary, and every opening of the primary circuit tends toproduce a direct current in the secondary. Both are of extremely shortduration, and the potential difference of the two terminals of thesecondary may be very high if there are many times more turns in thesecondary than in the primary.The extra currents interfere with the action of an induction coil. Toavoid their interference a condenser is used. This consists of twoseries of sheets of tin foil. Leaves of paper alternate with the sheetsof tin-foil, the whole being built up into a little book. Each sheet oftin-foil connects electrically with the sheet next but one to it. Thuseach leaf of a set is in connection with all others of the same set, butis insulated from the others. One set of leaves of tin-foil connectswith the hammer, the other with the anvil. In large coils there may be75 square feet of tin-foil in the condenser.The action of the condenser is to dispose of the direct extra current.When the primary circuit is opened this current passes into thecondenser, which at once discharges itself in the other directionthrough the coil. This demagnetizes the core, and the action intensifiesand shortens the induced current. The condenser prevents sparking, andin general improves the action of the coil.Many details enter into the construction of coils, and many variationsin their construction obtain. Thus a mercury cup into which a plungerdips often replaces the anvil and hammer.135 STANDARD ELECTRICAL DICTIONARY.The induction coil produces a rapid succession of sparks, which mayspring across an interval of forty inches. The secondary generally endsin special terminals or electrodes between which the sparking takesplace. A plate of glass, two inches in thickness, can be pierced bythem. In the great Spottiswoode coil there are 280 miles of wire in thesecondary, and the wire is about No. 36 A.W.G.Fig. 100. VERTICAL SECTION OF INDUCTION COIL.Fig. l01. PLAN OF INDUCTION COIL CONNECTIONS.Induction coils have quite extended use in electrical work. They areused in telephone transmitters, their primary being in circuit with themicrophone, and their secondary with the line and receiving telephone.In electric welding, and in the alternating current system they haveextended application. In all these cases they have no automatic circuitbreaker, the actuating current being of intermittent or alternatingtype.136 STANDARD ELECTRICAL DICTIONARY.In the cuts the general construction of an induction coil is shown. Inthe sectional elevation, Fig. 100, A, is the iron core; B is the primaryof coarse wire; C is a separating tube, which may be of pasteboard; D isthe secondary of fine wire; E, E are the binding posts connected to thesecondary; H, H are the heads or standards; K, K are the terminals ofthe primary; F is the vibrating contact spring; G, a standard carryingthe contact screw; J is the condenser with wires, L, M, leading to it.Referring to the plan, Fig. 101, H represents the primary coil; B and Aare two of the separate sheets of the condenser, each sheet withprojecting ears; G, G are the heads of the coil; the dark lines areconnections to the condenser. One set of sheets connects with theprimary coil at C, and also with the vibrating spring shown in plan andin the elevation at F. The other set of sheets connects with the post,carrying the contact screw. The other terminal of the primary runs to abinding post E. F, in the plan is a binding post in connection with thestandard and contact screw.Coil, Induction, Inverted.An induction coil arranged to have a lower electro-motive force in thesecondary than in the primary. This is effected by having more