Earth.(a) The earth is arbitrarily taken as of zero electrostatic potential.Surfaces in such condition that their potential is unchanged whenconnected to the earth are said to be of zero potential. All othersurfaces are discharged when connected to the earth, whose potential,for the purposes of man at least, never changes.(b) As a magnetic field of force the intensity of the earth's field isabout one-half a line of force per square centimeter.(c) The accidental grounding of a telegraph line is termed an earth, asa dead, total, partial, or intermittent earth, describing the extent andcharacter of the trouble.[Transcriber's note: Fallen power lines can produce voltage gradients onthe earth's surface that make walking in the area dangerous, as inhundreds of volts per foot. Lightning may be associated with substantialchanges in the static ground potential.]Earth, Dead.A fault, when a telegraph or other conductor is fully connected to earthor grounded at some intermediate point.Synonyms--Solid Earth--Total Earth.Earth, Partial.A fault, when a telegraph or other conductor is imperfectly connected toearth or grounded at some intermediate point.Earth Plate.A plate buried in the earth to receive the ends of telegraph lines orother circuits to give a ground, q. v. A copper plate is often used. Aconnection to a water or gas main gives an excellent ground, far betterthan any plate. When the plate oxidizes it is apt to introduceresistance.Earth Return.The grounding of a wire of a circuit at both ends gives the circuit anearth return.Earth, Swinging.A fault, when a telegraph or other conductor makes intermittentconnection with the earth. It is generally attributable to wind actionswinging the wire, whence the name.Ebonite.Hard vulcanized India rubber, black in color. Specific resistance inohms per cubic centimeter at 46º C. (115º F.): 34E15 (Ayrton); specificinductive capacity, (air = 1): 2.56 (Wüllner); 2.76 (Schiller); 3.15(Boltzmann). It is used in electrical apparatus for supporting memberssuch as pillars, and is an excellent material for frictional generationof potential. Its black color gives it its name, and is sometimes made apoint of distinction from Vulcanite, q. v.204 STANDARD ELECTRICAL DICTIONARY.Economic Coefficient.The coefficient of electric efficiency. (See Efficiency, Electric.)Edison Effect.A continuous discharge resulting in a true current which takes placebetween a terminal of an incandescent lamp filament and a plate placednear it. The lamp must be run at a definitely high voltage to obtain it.Ediswan.An abbreviation for Edison-Swan; the trade name of the incandescent lampused in Great Britain, and of other incandescent system apparatus.Fig. 142. GYMNOTUS ELECTRICUS.Eel, Electric (Gymnotus Electricus).An eel capable of effecting the discharge of very high potentialelectricity, giving painful or dangerous shocks. Its habitat is thefresh water, in South America. Faraday investigated it and estimated itsshock as equal to that from fifteen Leyden jars, each of 1.66 squarefeet of coating. (See Animal Electricity and Ray, Electric.)Effect, Counter-inductive.A counter-electro-motive force due to induction, and opposing a current.Efficiency.The relation of work done to energy absorbed. A theoretically perfectmachine would have the maximum efficiency in which the two qualitiesnamed would be equal to each other. Expressed by a coefficient, q. v.,the efficiency in such case would be equal to 1. If a machine producedbut half the work represented by the energy it absorbed, the restdisappearing in wasteful expenditure, in heating the bearings, inovercoming the resistance of the air and in other ways, its efficiencywould be expressed by the coefficient 1/2 or .5, or if one hundred wasthe basis, by fifty per centum. There are a number of kinds ofefficiencies of an electric generator which are given below.Efficiency, Commercial.Practical efficiency of a machine, obtained by dividing the availableoutput of work or energy of a machine by the energy absorbed by the samemachine. Thus in a dynamo part of the energy is usefully expended inexciting the field magnet, but this energy is not available for use inthe outer circuit, is not a part of the output, and is not part of thedividend.If M represents the energy absorbed, and W the useful or availableenergy, the coefficient of commercial efficiency is equal to W/M. M ismade up of available, unavailable and wasted (by Foucault currents,etc.,) energy. Calling available energy W, unavailable but utilizedenergy w, and wasted energy m, the expression for the coefficient ofcommercial efficiency becomesW / ( W + w + m )when M = W + w + mSynonym--Net efficiency.205 STANDARD ELECTRICAL DICTIONARY.Efficiency, Electrical.In a dynamo or generator the relation of total electric energy produced,both wasted and useful or available to the useful or availableelectrical energy. If we call W the useful electric and w the wastedelectric energy, the coefficient of electrical efficiency is equal toW / ( W + w )Synonyms--Intrinsic Efficiency--Economic Coefficient--Coefficient ofElectrical Efficiency.Efficiency of Conversion.In a dynamo or generator the relation of energy absorbed to totalelectric energy produced. Part of the electric energy is expended inproducing the field and in other ways. Thus a generator with highefficiency of conversion may be a very poor one, owing to theunavailable electric energy which it produces. The coefficient ofEfficiency of Conversion is obtained by dividing the total electricenergy produced by the energy absorbed in working the dynamo. If Mrepresents the energy absorbed, or work done in driving the dynamo orgenerator, W the useful electric, and w the wasted electrical energy,then the coefficient of efficiency of conversion is equal to(W + w ) / MIn the quantity M are included besides available (W) and unavailable (w)electric energy, the totally wasted energy due to Foucault currents,etc., calling the latter m, the above formula may be given( W+ w ) / (W + w + m )This coefficient may refer to the action of a converter, q. v., in thealternating system. Synonym--Gross Efficiency.Efficiency of Secondary Battery, Quantity.The coefficient obtained by dividing the ampere-hours obtainable from asecondary battery by the ampere hours required to charge it.Efficiency of Secondary Battery, Real.The coefficient obtained by dividing the energy obtainable from asecondary battery by the energy absorbed in charging it. The energy isconveniently taken in watt-hours and includes the consideration of thespurious voltage. (See Battery, Secondary.)206 STANDARD ELECTRICAL DICTIONARY.Efflorescence.The appearance of a dry salt upon the walls of a vessel containing asolution above the normal water-line from evaporation of a liquid. Itappears in battery jars and in battery carbons, in the latterinterfering with the electrical connections, and oxidizing or rustingthem. (See Creeping.)Effluvium, Electric.When a gas is made to occupy the position of dielectric between twooppositely electrified surfaces a peculiar strain or condition of thedielectric is produced, which promotes chemical change. The condition istermed electrical effluvium or the silent discharge. By an apparatusspecially constructed to utilize the condition large amounts of ozoneare produced.Synonym--Silent Discharge.Elastic Curve.A crude expression for a curve without projections or suddensinuosities; such a curve as can be obtained by bending an elastic stripof wood.Electrepeter.An obsolete name for a key, switch or pole changer of any kind.Elasticity, Electric.The phenomenon of the dielectric is described under this term. When apotential difference is established between two parts of the dielectric,a flow of electricity displacement current starts through thedielectric, which current is due to the electric stress, but isinstantly arrested by what has been termed the electric elasticity ofthe dielectric. This is expressed by( electric stress ) / ( electric strain )and in any substance is inversely proportional to the specific inductivecapacity.Electricity.It is impossible in the existing state of human knowledge to give asatisfactory definition of electricity. The views of various authoritiesare given here to afford a basis for arriving at the general consensusof electricians.We have as yet no conception of electricity apart from the electrifiedbody; we have no experience of its independent existence. (J. E. H.Gordon.)What is Electricity? We do not know, and for practical purposes it isnot necessary that we should know. (Sydney F. Walker.)Electricity … is one of those hidden and mysterious powers of naturewhich has thus become known to us through the medium of effects.(Weale's Dictionary of Terms.)This word Electricity is used to express more particularly the cause,which even today remains unknown, of the phenomena that we are about toexplain. (Amédée Guillemin.)207 STANDARD ELECTRICAL DICTIONARY.Electricity is a powerful physical agent which manifests itself mainlyby attractions and repulsions, but also by luminous and heating effects,by violent commotions, by chemical decompositions, and many otherphenomena. Unlike gravity, it is not inherent in bodies, but it isevoked in them by a variety of causes … (Ganot's Physics.)Electricity and magnetism are not forms of energy; neither are theyforms of matter. They may, perhaps, be provisionally defined asproperties or conditions of matter; but whether this matter be theordinary matter, or whether it be, on the other hand, thatall-pervading ether by which ordinary matter is surrounded, is a questionwhich has been under discussion, and which now may be fairly held to besettled in favor of the latter view. (Daniell's Physics.)The name used in connection with an extensive and important class ofphenomena, and usually denoting the unknown cause of the phenomena orthe science that treats of them. (Imperial Dictionary.)Electricity. . . is the imponderable physical agent, cause, force or themolecular movement, by which, under certain conditions, certainphenomena, chiefly those of attraction and repulsion, . . . areproduced. (John Angell.)It has been suggested that if anything can rightly be called"electricity," this must be the ether itself; and that all electricaland magnetic phenomena are simply due to changes, strains and motions inthe ether. Perhaps negative electrification. . .means an excess ofether, and positive electrification a defect of ether, as compared withthe normal density. (W. Larden.)Electricity is the name given to the supposed agent producing thedescribed condition (i. e. electrification) of bodies. (FleemingJenkin.)There are certain bodies which, when warm and dry, acquire by friction,the property of attracting feathers, filaments of silk or indeed anylight body towards them. This property is called Electricity, and bodieswhich possess it are said to be electrified. (Linnaeus Cumming.)What electricity is it is impossible to say, but for the present it isconvenient to look upon it as a kind of invisible something whichpervades all bodies. (W. Perren Maycock.)What is electricity? No one knows. It seems to be one manifestation ofthe energy which fills the universe and which appears in a variety ofother forms, such as heat, light, magnetism, chemical affinity,mechanical motion, etc. (Park Benjamin.)208 STANDARD ELECTRICAL DICTIONARY.The theory of electricity adopted throughout these lessons is, thatelectricity, whatever its true nature, is one, not two; that thisElectricity, whatever it may prove to be, is not matter, and is notenergy; that it resembles both matter and energy in one respect,however, in that it can neither be created nor destroyed. (Sylvanus P.Thomson.)In Physics a name denoting the cause of an important class of phenomenaof attraction and repulsion, chemical decomposition, etc., or,collectively, these phenomena themselves. (Century Dictionary.)A power in nature, often styled the electric fluid, exhibiting itself,when in disturbed equilibrium or in activity, by a circuit movement, thefact of direction in which involves polarity, or opposition ofproperties in opposite directions; also, by attraction for manysubstances, by a law involving attraction between substances of unlikepolarity, and repulsion between those of like; by exhibiting accumulatedpolar tension when the circuit is broken; and by producing heat, light,concussion, and often chemical changes when the circuit passes betweenthe poles, or through any imperfectly conducting substance or space. Itis evolved in any disturbance of molecular equilibrium, whether from achemical, physical, or mechanical cause. (Webster's Dictionary.)In point of fact electricity is not a fluid at all, and only in a few ofits attributes is it at all comparable to a fluid. Let us ratherconsider electricity to be a condition into which material substancesare thrown. . .(Slingo & Brooker.)[Transcriber's note: 2008 Dictionary: Phenomena arising from thebehavior of electrons and protons caused by the attraction of particleswith opposite charges and the repulsion of particles with the samecharge.]Electricity, Cal.The electricity produced in the secondary of a transformer by changes oftemperature in the core. This is in addition to the regularly inducedcurrent.Synonym--Acheson Effect.Electrics.Substances developing electrification by rubbing or friction; asGilbert, the originator of the term, applied it, it would indicatedielectrics. He did not know that, if insulated, any substance was oneof his "electrics." A piece of copper held by a glass handle becomeselectrified by friction.Electrification.The receiving or imparting an electric charge to a surface; a termusually applied to electrostatic phenomena.Electrization.A term in electro-therapeutics; the subjection of the human system toelectric treatment for curative, tonic or diagnostic purposes.Electro-biology.The science of electricity in its relation to the living organism,whether as electricity is developed by the organism, or as it affectsthe same when applied from an external source.209 STANDARD ELECTRICAL DICTIONARY.Electro-capillarity.The relations between surface tension, the potential difference and theelectrostatic capacity of fluids in contact. Although nominally incontact such surfaces are separated by about one-twenty-millionth of acentimeter (1/50000000 inch) ; thus a globule of mercury and water inwhich it is immersed constitute an electrostatic accumulator of definiteelectrostatic capacity. Again the mercury and water being in electricconnection differ in potential by contact (see Contact Theory). Adefinite surface tension is also established. Any change in one of thesefactors changes the other also. A current passed through the contactsurfaces will change the surface tension and hence the shape of themercury globule. Shaking the globule will change its shape and capacityand produce a current. Heating will do the same. (See Electrometer,Capillary; and Telephone, Capillary.) Mercury and water are named asliquids in which the phenomena are most conveniently observed. They areobservable in other parallel cases.Electro-chemical Equivalent.The quantity of an element or compound liberated from or brought intocombination, electrolytically, by one coulomb of electricity. Theelectro-chemical equivalent of hydrogen is found by experiment to be.0000105 gram. That of any other substance is found by multiplying thisweight by its chemical equivalent referred to hydrogen, which is itsatomic or molecular weight divided by its valency. Thus the atomicweight of oxygen is 16, its valency is 2, its equivalent is 16/2 = 8;its electro-chemical equivalent is equal to .0000105 X 8 = .000840 gram.Electro-chemical Series.An arrangement of the elements in the order of their relative electricalaffinities so that each element is electro-negative to all the elementsfollowing it, and electro-positive to the elements preceding it. Theusual series begins with oxygen as the most electro-negative and endswith potassium as the most electro-positive element. There is, ofcourse, no reason why other series of compound radicals, such assulphion (SO4), etc., should not also be constructed. For each liquidacting on substances a separate series of the substances acted on may beconstructed. Thus for dilute sulphuric acid the series beginning withthe negatively charged or most attacked one is zinc, amalgamated orpure, cadmium, iron, tin, lead, aluminum, nickel, antimony, bismuth,copper, silver, platinum. In other liquids the series is altogetherdifferent.Electro--chemistry.The branch of electricity or of chemistry treating of the relationsbetween electric and chemical force in different compounds andreactions. (See Electrolysis--Electrochemical series--Electro-chemicalEquivalent .)210 STANDARD ELECTRICAL DICTIONARY.Electro-culture.The application of electricity to the cultivation of plants. In onesystem wires are stretched or carried across the bed under the surface,and some are connected to one pole and others to the other pole of agalvanic battery of two or more elements. In some experiments improvedresults have thus been obtained.Another branch refers to the action of the electric arc light onvegetation. This has an effect on vegetation varying in results.Electrode.(a) The terminal of an open electric circuit.(b) The terminals of the metallic or solid conductors of an electriccircuit, immersed in an electrolytic solution.(c) The terminals between which a voltaic arc is formed, always inpractice made of carbon, are termed electrodes.(d) In electro-therapeutics many different electrodes are used whosenames are generally descriptive of their shape, character, or uses towhich they are to be applied. Such are aural electrodes for the ears,and many others.(e) The plates of a voltaic battery.Electrode, Indifferent.A term in electro-therapeutics. An electrode to which no therapeuticaction is attributed but which merely provides a second contact with thebody to complete the circuit through the same. The other electrode istermed the therapeutic electrode.Electrodes, Erb's Standards of.Proposed standard sizes for medical electrodes as follows:Name. Diameter.Fine Electrode, 1/2 centimeter .2 inchSmall " 2 " .8 "Medium " 7.5 " 3.0 "Large " 6X2 " 2.4 X .8 "Very large " 16x8 " 6.4 x 3.2 "Electrodes, Non-polarizable.In electro-therapeutics electrodes whose contact surface is virtuallyporous clay saturated with zinc chloride solution. The series terminatein amalgamated zinc ends, enclosed each in a glass tube, and closed withclay. Contact of metal with the tissues is thus avoided.Electrode, Therapeutic.A term in electro-therapeutics. An electrode applied to the body for thepurpose of inducing therapeutic action, or for giving the basis for anelectric diagnosis of the case. The other electrode is applied tocomplete the circuit only; it is termed the indifferent electrode.Electro-diagnosis.The study of the condition of a patient by the reactions which occur atthe terminals or kathode and anode of an electric circuit applied to theperson. The reactions are divided into kathodic and anodic reactions.211 STANDARD ELECTRICAL DICTIONARY.Electro-dynamic. adj.The opposite of electrostatic; a qualification of phenomena due tocurrent electricity.Synonym--Electro-kinetic.Electro-dynamic Attraction and Repulsion.The mutual attraction and repulsion exercised by currents of electricityupon each other. The theory of the cause is based upon stress of theluminiferous ether and upon the reaction of lines of force upon eachother. For a resumé of the theory see Induction, Electro-magnetic.Electro-dynamics.The laws of electricity in a state of motion; the inter-reaction ofelectric currents. It is distinguished from electro-magnetic inductionas the latter refers to the production of currents by induction. Thegeneral laws of electro-dynamics are stated under Induction,Electro-magnetic, q. v.Synonym--Electro-kinetics.Fig. 143. DIAGRAM OF CONNECTIONS OFSIEMENS' ELECTRO-DYNAMOMETER.212 STANDARD ELECTRICAL DICTIONARY.Electro-dynamometer, Siemens'.An apparatus for measuring currents by the reaction between two coils,one fixed and one movable, through which the current to be measuredpasses. It is one of the oldest commercial ammeters or currentmeasurers. It comprises a fixed coil of a number of convolutions and amovable coil often of only one convolution surrounding the other. Themovable coil is suspended by a filament or thread from a spiral spring.The spring is the controlling factor. Connection is established throughmercury cups so as to bring the two coils in series. In use the springand filament are adjusted by turning a milled head to which they areconnected until the coils are at right angles. Then the current isturned on and deflects the movable coil. The milled head is turned untilthe deflection is overcome. The angle through which the head is turnedis proportional to the square of the current. The movable coil must inits position at right angles to the fixed one lie at right angles to themagnetic meridian.Thus in the diagram, Fig. 143 A B C D is the fixed coil; E F G H is themovable coil; S is the spiral spring attached at K to the movable coil.The arrows show the course of the current as it goes through the coils.Electrolier.A fixture for supporting electric lamps; the analogue in electriclighting of the gasolier or gas chandelier. Often both are combined, thesame fixture being piped and carrying gas burners, as well as beingwired and carrying electric lamps.Electrolysis.The separation of a chemical compound into its constituent parts orelements by the action of the electric current. The compound may bedecomposed into its elements, as water into hydrogen and oxygen, or intoconstituent radicals, as sodium sulphate into sodium and sulphion, whichby secondary reactions at once give sodium hydrate and sulphuric acid.The decomposition proceeds subject to the laws of electrolysis. (SeeElectrolysis, Laws of.) For decomposition to be produced there is foreach compound a minimum electro-motive force or potential differencerequired. The current passes through the electrolyte or substanceundergoing decomposition entirely by Electrolytic Conduction, q. v. inaccordance with Grothüss' Hypothesis, q. v. The electrolyte thereforemust be susceptible of diffusion and must be a fluid.The general theory holds that under the influence of a potentialdifference between electrodes immersed in an electrolyte, the moleculestouching the electrodes are polarized, in the opposite sense for eachelectrode. If the potential difference is sufficient the molecules willgive up one of their binary constituents to the electrode, and the otherconstituent will decompose the adjoining molecule, and that one beingseparated into the same two constituents will decompose its neighbor,and so on through the mass until the other electrode is reached. Thisone separates definitely the second binary constituent from themolecules touching it.213 STANDARD ELECTRICAL DICTIONARY.Thus there is an exact balance preserved. Just as many molecules aredecomposed at one electrode as at the other, and the exact chain ofdecomposition runs through the mass. Each compound electrolyzed developsa binary or two-fold composition, and gives up one constituent to oneelectrode and the other to the other.Fig. 144. ACTION OF MOLECULES IN A SOLUTIONBEFORE AND DURING ELECTROLYSIS.The cut shows the assumed polarization of an electrolyte. The upper rowshows the molecules in irregular order before any potential differencehas been produced, in other words, before the circuit is closed. Thenext row shows the first effects of closing the circuit, and alsoindicates the polarization of the mass, when the potential difference isinsufficient for decomposition. The third row indicates thedecomposition of a chain of molecules, one constituent separating ateach pole.214 STANDARD ELECTRICAL DICTIONARY.Electrolysis, Laws of.The following are the principal laws, originally discovered byFaraday, and sometimes called Faraday's Laws of Electrolysis:1. Electrolysis cannot take place unless the electrolyte is a conductor.Conductor here means an electrolytic conductor, one that conducts by itsown molecules traveling, and being decomposed. (See Grothüss'Hypothesis.)II. The energy of the electrolytic action of the current is the samewherever exercised in different parts of the circuit.III. The same quantity of electricity--that is the same current for thesame period----- decomposes chemically equivalent quantities of thebodies it decomposes, or the weights of elements separated inelectrolytes by the same quantity of electricity (in coulombs or someequivalent unit) are to each other as their chemical equivalent.IV. The quantity of a body decomposed in a given time is proportional tothe strength of the current.To these may be added the following:V. A definite and fixed electro-motive force is required for thedecomposition of each compound, greater for some and less for others.Without sufficient electro-motive force expended on the molecule nodecomposition will take place. (See Current, Convective.)Electrolyte.A body susceptible of decomposition by the electric current, and capableof electrolytic conduction. It must be a fluid body and thereforecapable of diffusion, and composite in composition. An elemental bodycannot be an electrolyte.Electrolytic Analysis.Chemical analysis by electrolysis. The quantitative separation of anumber of metals can be very effectively executed. Thus, suppose that asolution of copper sulphate was to be analyzed. A measured portion ofthe solution would be introduced into a weighed platinum vessel. Thevessel would be connected to the zinc plate terminal of a battery. Fromthe other terminal of the battery a wire would be brought and wouldterminate in a plate of platinum. This would be immersed in the solutionin the vessel. As the current would pass the copper sulphate would bedecomposed and eventually all the copper would be deposited in a firmcoating on the platinum. The next operations would be to wash the metalwith distilled water, and eventually with alcohol, to dry and to weighthe dish with the adherent copper. On subtracting the weight of the dishalone from the weight of the dish and copper, the weight of the metalliccopper in the solution would be obtained.In similar ways many other determinations are effected. The processes ofanalysis include solution of the ores or other substances to be analyzedand their conversion into proper form for electrolysis. Copper as justdescribed can be precipitated from the solution of its sulphate. Foriron and many other metals solutions of their double alkaline oxalatesare especially available forms for analysis.The entire subject has been worked out in considerable detail byClassen, to whose works reference should be made for details ofprocesses.Electrolytic Convection.It is sometimes observed that a single cell of Daniell battery, forinstance, or other source of electric current establishing too low apotential difference for the decomposition of water seems to produce afeeble but continuous decomposition. This is very unsatisfactorilyaccounted for by the hydrogen as liberated combining with dissolvedoxygen. (Ganot.) The whole matter is obscure. (See Current, Convection.)215 STANDARD ELECTRICAL DICTIONARY.Electrolytic Conduction.Conduction by the travel of atoms or radicals from molecule to moleculeof a substance with eventual setting free at the electrodes of the atomsor radicals as elementary molecules or constituent radicals. A substanceto be capable of acting as an electrolytic conductor must be capable ofdiffusion, and must also have electrolytic conductivity. Such a body iscalled an electrolyte. (See Grothüss' Hypothesis--Electrolysis--Electrolysis, Laws of--Electro-chemical Equivalent.)Electro-magnet.A mass, in practice always of iron, around which an electric circuit iscarried, insulated from the iron. When a current is passed through thecircuit the iron presents the characteristics of a magnet. (SeeMagnetism, Ampére's Theory of--Solenoid--Lines of Force.) In generalterms the action of a circular current is to establish lines of forcethat run through the axis of the circuit approximately parallel thereto,and curving out of and over the circuit, return into themselves outsideof the circuit. If a mass of iron is inserted in the axis or elsewherenear such current, it multiplies within itself the lines of force, q. v.(See also Magnetic Permeability--Permeance--Magnetic Induction,Coefficient of Magnetic Susceptibility--Magnetization, Coefficient ofInduced.) These lines of force make it a magnet. On their direction,which again depends on the direction of the magnetizing current, dependsthe polarity of the iron. The strength of an electro-magnet, belowsaturation of the core (see Magnetic Saturation), is proportional nearlyto the ampere-turns, q. v. More turns for the same current or morecurrent for the same turns increase its strength.In the cut is shown the general relation of current, coils, core andline of force. Assume that the magnet is looked at endwise, the observerfacing one of the poles; then if the current goes around the core in thedirection opposite to that of the hands of a clock, such pole will bethe north pole. If the current is in the direction of the hands of aclock the pole facing the observer will be the south pole. The wholerelation is exactly that of the theoretical Ampérian currents, alreadyexplained. The direction and course of the lines of force created areshown in the cut.The shapes of electro-magnets vary greatly. The cuts show several formsof electro- magnets. A more usual form is the horseshoe or double limbmagnet, consisting generally of two straight cores, wound with wire andconnected and held parallel to each other by a bar across one end, whichbar is called the yoke.In winding such a magnet the wire coils must conform, as regardsdirection of the current in them to the rule for polarity already cited.If both poles are north or both are south poles, then the magnet cannotbe termed a horseshoe magnet, but is merely an anomalous magnet. In thefield magnets of dynamos the most varied types of electro-magnets havebeen used. Consequent poles are often produced in them by the directionof the windings and connections.To obtain the most powerful magnet the iron core should be as short andthick as possible in order to diminish the reluctance of the magneticcircuit. To obtain a greater range of action a long thin shape isbetter, although it involves waste of energy in its excitation.216 STANDARD ELECTRICAL DICTIONARY.Fig. 145 DIAGRAM OF AN ELECTRO-MAGNET SHOWING RELATION OFCURRENT AND WINDING TO ITS POLARITY AND LINES OF FORCE.Fig. 146. ANNULAR ELECTRO-MAGNETElectro-magnet, Annular.An electro-magnet consisting of a cylinder with a circular groove cut inits face, in which groove a coil of insulated wire is placed. On thepassage of a current the iron becomes polarized and attracts an armaturetowards or against its grooved face. The cut shows the construction ofan experimental one. It is in practice applied to brakes and clutches.In the cut of the electro-magnetic brake (see Brake, Electro-magnetic),C is the annular magnet receiving its current through the brushes, andpressed when braking action is required against the face of the movingwheel. The same arrangement, it can be seen, may apply to a clutch.217 STANDARD ELECTRICAL DICTIONARY.Fig. 147. BAR ELECTRO-MAGNET.Electro-magnet, Bar.A straight bar of iron surrounded with a magnetizing coil of wire. Barelectromagnets are not much used, the horseshoe type being by far themore usual.Electro-magnet, Club-foot.An electro-magnet, one of whose legs only is wound with wire, the otherbeing bare.Fig. 148. CLUB-FOOT ELECTRO-MAGNETS WITH HINGED ARMATURES.Electro-magnet, Hinged.An electro-magnet whose limbs are hinged at the yoke. On excitation by acurrent the poles tend to approach each other.Fig. 149. ELECTRO-MAGNET, HINGEDElectro-magnetic Attraction and Repulsion.The attraction and repulsion due to electromagnetic lines of force,which lines always tend to take as short a course as possible and alsoseek the medium of the highest permeance. This causes them toconcentrate in iron and steel or other paramagnetic substance and todraw them towards a magnet by shortening the lines of force connectingthe two. It is exactly the same attraction as that of the permanentmagnet for its armature, Ampére's theory bringing the latter under thesame title. In the case of two magnets like poles repel and unlikeattract. In the case of simple currents, those in the same directionattract and those in opposite directions repel each other. This refersto constant current reactions. Thus the attraction of unlike poles oftwo magnets is, by the Ampérian theory, the attraction of two sets ofcurrents of similar direction, as is evident from the diagram. Therepulsion of like poles is the repulsion of unlike currents and the sameapplies to solenoids, q. v. (See Magnetism and do. Ampére's Theoryof--Induction, Electro-dynamic--Electro-magnetic Induction.)218 STANDARD ELECTRICAL DICTIONARY.Electro-magnetic Control.Control of a magnet, iron armature, or magnetic needle in agalvanometer, ammeter, voltmeter or similar instrument by anelectro-magnetic field, the restitutive force being derived from anelectro-magnet. The restitutive force is the force tending to bring theindex to zero.Electro-magnetic Field of Force.A field of electro-magnetic lines of force, q. v., established throughthe agency of an electric current. A wire carrying a current issurrounded by circular concentric lines of force which have the axis ofthe wire as the locus of their centres. Electro-magnets produce lines offorce identical with those produced by permanent magnets. (See Field ofForce--Magnetic Field of Force--Controlling Field--Deflecting Field.)Electro-magnetic Induction.When two currents of unlike direction are brought towards each other,against their natural repulsive tendency work is done, and theconsequent energy takes the form of a temporary increase in bothcurrents. When withdrawn, in compliance with the natural tendency ofrepulsion, the currents are diminished in intensity, because energy isnot expended on the withdrawal, but the withdrawal is at the expense ofthe energy of the system. The variations thus temporarily produced inthe currents are examples of electro-magnetic induction. The currentshave only the duration in each case of the motion of the circuits. Onecircuit is considered as carrying the inducer current and is termed theprimary circuit and its current the primary current, the others aretermed the secondary circuit and current respectively. We may assume asecondary circuit in which there is no current. It is probable thatthere is always an infinitely small current at least, in every closedcircuit. Then an approach of the circuits will induce in the secondaryan instantaneous current in the reverse direction. On separating the twocircuits a temporary current in the same direction is produced in thesecondary.219 STANDARD ELECTRICAL DICTIONARY.A current is surrounded by lines of force. The approach of two circuits,one active, involves a change in the lines of force about the secondarycircuit. Lines of force and current are so intimately connected that achange in one compels a change in the other. Therefore the inducedcurrent in the secondary may be attributed to the change in the field offorce in which it lies, a field maintained by the primary circuit andcurrent. Any change in a field of force induces a current or change ofcurrent in any closed circuit in such field, lasting as long as thechange is taking place. The new current will be of such direction as tooppose the change. (See Lenz's Law.)The action as referred to lines of force may be figured as the cuttingof such lines by the secondary circuit, and such cutting may be broughtabout by moving the secondary in the field. (See Lines of Force--Fieldof Force.) The cutting of 1E8 lines of force per second by a closedcircuit induces an electro-motive force of one volt. (See Induction,Mutual, Coefficient of.)Electro-magnet, Iron Clad.A magnet whose coil and core are encased in a iron jacket, generallyconnected to one end of the core. This gives at one end two poles, onetubular, the other solid, and concentric with each other. It issometimes called a tubular magnet.Electro-magnet, One Coil.An electro-magnet excited by one coil. In some dynamos the field magnetsare of this construction, a single coil, situated about midway betweenthe poles, producing the excitation.Electro-magnetic Leakage.The leakage of lines of force in an electro-magnet; the same as magneticleakage. (See Magnetic Leakage.)Electro-magnetic Lines of Force.The lines of force produced in an electro-magnetic field. They areidentical with Magnetic Lines of Force, q. v. (See also Field ofForce-Line of Force.)Electro-magnetic Stress.The stress in an electro-magnetic field of force, showing itself in thepolarization of light passing through a transparent medium in such afield. (See Magnetic Rotary Polarization.)Electro-magnetic Theory of Light.This theory is due to J. Clark Maxwell, and the recent Hertz experimentshave gone far to prove it. It holds that the phenomena of light are dueto ether waves, identical in general factors with those produced byelectro-magnetic induction of alternating currents acting on the ether.In a non-conductor any disturbance sets an ether wave in motion owing toits restitutive force; electricity does not travel through such amedium, but can create ether waves in it. Therefore a non-conductor ofelectricity is permeable to waves of ether or should transmit light, orshould be transparent. A conductor on the other hand transmitselectrical disturbances because it has no restitutive force and cannotsupport an ether wave. Hence a conductor should not transmit light, orshould be opaque. With few exceptions dielectrics or non-conductors aretransparent, and conductors are opaque.220 STANDARD ELECTRICAL DICTIONARY.Again, the relation between the electrostatic and electro-magnet unitsof quantity is expressed by 1 : 30,000,000,000; the latter figure incentimeters gives approximately the velocity of light. Theelectro-magnetic unit depending on electricity in motion should havethis precise relation if an electro-magnetic disturbance was propagatedwith the velocity of light. If an electrically charged body were whirledaround a magnetic needle with the velocity of light, it should act inthe same way as a current circulating around it. This effect to someextent has been shown experimentally by Rowland.A consequence of these conclusions is (Maxwell) that the specificinductive capacity of a non-conductor or dielectric should be equal tothe square of its index of refraction for waves of infinite length. Thisis true for some substances--sulphur, turpentine, petroleum and benzole.In others the specific inductive capacity is too high, e. g., vegetableand animal oils, glass, Iceland spar, fluor spar, and quartz.Electro-magnetic Unit of Energy.A rate of transference of energy equal to ten meg-ergs per second.Electro-magnetism.The branch of electrical science treating of the magnetic relations of afield of force produced by a current, of the reactions ofelectro-magnetic lines of force, of the electromagnetic field of force,of the susceptibility, permeability, and reluctance of diamagnetic andparamagnetic substances, and of electro-magnets in general.Electro-magnet, Long Range.An electro-magnet so constructed with extended pole pieces or otherwise,as to attract its armature with reasonably constant force over aconsiderable distance. The coil and plunger, q. v., mechanismsillustrate one method of getting an extended range of action. When atrue electro-magnet is used, one with an iron core, only a very limitedrange is attainable at the best. (See Electro-magnet, Stopped Coil--do.Plunger.)Electro-magnet, Plunger.An electro-magnet with hollow coils, into which the armature enters as aplunger. To make it a true electro-magnet it must have either a yoke,incomplete core, or some polarized mass of iron.Electro-magnet, Polarized.An electro-magnet consisting of a polarized or permanently magnetizedcore wound with magnetizing coils, or with such coils on soft iron coresmounted on its ends. The coils may be wound and connected so as tocooperate with or work against the permanent magnet on which it ismounted. In Hughes' magnet shown in the cut it is mounted in opposition,so that an exceedingly feeble current will act to displace the armature,a, which is pulled away from the magnet by a spring, s.221 STANDARD ELECTRICAL DICTIONARY.Fig. 150 HUGHES' POLARIZED ELECTRO-MAGNETElectro-magnets, Interlocking.Electro-magnets so arranged that their armatures interlock. Thus twomagnets, A A and B B, may be placed with their armatures, M and N, atright angles and both normally pulled away from the poles. When thearmature M is attracted a catch on its end is retained by a hole in theend of the other armature N, and when the latter armature N is attractedby its magnet the armature M is released. In the mechanism shown in thecut the movements of the wheel R are controlled. Normally it is heldmotionless by the catch upon the bottom of the armature M, comingagainst the tooth projecting from its periphery. A momentary currentthrough the coils of the magnet A A releases it, by attracting M, whichis caught and retained by N, and leaves it free to rotate. A momentarycurrent through the coils of the magnet B B again releases M, whichdrops down and engages the tooth upon R and arrests its motion.Fig. 151. INTERLOCKING ELECTRO-MAGNETS.222 STANDARD ELECTRICAL DICTIONARY.Electro-magnet, Stopped Coil.An electro-magnet consisting of a tubular coil, in which a short fixedcore is contained, stopping up the aperture to a certain distance, whilethe armature is a plunger entering the aperture. This gives a longerrange of action than usual.Electro-magnet, Surgical.An electro-magnet, generally of straight or bar form, fitted withdifferent shaped pole pieces, used for the extraction of fragments ofiron or steel from the eyes. Some very curious cases of successfuloperations on the eyes of workmen, into whose eyes fragments of steel oriron had penetrated, are on record.Electro-medical Baths.A bath for the person provided with connections and electrodes forcausing a current of electricity of any desired type to pass through thebody of the bather. Like all electro-therapeutical treatment, it shouldbe administered under the direction of a physician only.Electro-metallurgy.(a) In the reduction of ores the electric current has been proposed butnever extensively used, except in the reduction of aluminum and itsalloys. (See Reduction of Ores, Electric.)(b) Electro-plating and deposition of metal from solutions is anotherbranch. (See Electroplating and Electrotyping.)(c) The concentration of iron ores by magnetic attraction may come underthis head. (See Magnetic Concentration of Ores.)Electrometer.An instrument for use in the measurement of potential difference, by theattraction or repulsion of statically charged bodies. They aredistinguished from galvanometers as the latter are really currentmeasurers, even if wound for use as voltmeters, depending for theiraction upon the action of the current circulating in their coils.Electrometer, Absolute.An electrometer designed to give directly the value of a charge inabsolute units. In one form a plate, a b, of conducting surface issupported or poised horizontally below a second larger plate C, also ofconducting surface. The poised plate is surrounded by a detached guardring--an annular or perforated plate, r g r' g'--exactly level and evenwith it as regards the upper surface. The inner plate is carried by adelicate balance. In use it is connected to one of the conductors andthe lower plate to earth or to the other. The attraction between them isdetermined by weighing. By calculation the results can be made absolute,as they depend on actual size of the plates and their distance, outsideof the potential difference of which of course nothing can be said. If Sis the area of the disc, d the distance of the plates, V-V1 thedifference of their potential, which is to be measured, and F the forcerequired to balance their attraction, we have:F = ( ( V - V1 )^2 * S ) / ( 8 * PI * d^2 )223 STANDARD ELECTRICAL DICTIONARY.If V = 0 this reduces toF = ( V^2 * S ) / ( 8 * PI * d^2 ) (2)orV = d * SquareRoot( (8 * PI * F ) / S ) (3)As F is expressed as a weight, and S and a as measures of area andlength, this gives a means of directly obtaining potential values inabsolute measure. (See Idiostatic Method--Heterostatic Method.)Synonyms--Attracted Disc Electrometer--Weight Electrometer.Fig. 152. SECTION OF BASE OF PORTABLE ELECTROMETER.In some forms the movable disc is above the other, and supported at theend of a balance beam. In others a spring support, arranged so as toenable the attraction to be determined in weight units, is adopted. Thecuts, Figs. 152 and 154, show one of the latter type, the portableelectrometer. The disc portion is contained within a cylindrical vessel.Fig. 153. DIAGRAM ILLUSTRATINGTHEORY OF ABSOLUTE ELECTROMETER.Referring to Fig. 152 g is the stationary disc, charged through thewire connection r; f is the movable disc, carried by a balance beampoised at i on a horizontal and transverse stretched platinum wire,acting as a torsional spring. The position of the end k of the balancebeam shows when the disc f is in the plane of the guard ring h h. Theend k is forked horizontally and a horizontal sighting wire or hair isfastened across the opening of the fork. When the hair is midway betweentwo dots on a vertical scale the lever is in the sighted position, as it