Earth, Dead.

A fault, when a telegraph or other conductor is fully connected to earth or grounded at some intermediate point.

Synonyms--Solid Earth--Total Earth.

Earth, Partial.

A fault, when a telegraph or other conductor is imperfectly connected to earth or grounded at some intermediate point.

Earth Plate.

A plate buried in the earth to receive the ends of telegraph lines or other circuits to give a ground, q. v. A copper plate is often used. A connection to a water or gas main gives an excellent ground, far better than any plate. When the plate oxidizes it is apt to introduce resistance.

Earth Return.

The grounding of a wire of a circuit at both ends gives the circuit an earth return.

Earth, Swinging.

A fault, when a telegraph or other conductor makes intermittent connection with the earth. It is generally attributable to wind action swinging the wire, whence the name.

Ebonite.

Hard vulcanized India rubber, black in color. Specific resistance in ohms per cubic centimeter at 46? C. (115? F.): 34E15 (Ayrton); specific inductive capacity, (air = 1): 2.56 (W?llner); 2.76 (Schiller); 3.15 (Boltzmann). It is used in electrical apparatus for supporting members such as pillars, and is an excellent material for frictional generation of potential. Its black color gives it its name, and is sometimes made a point 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 place between a terminal of an incandescent lamp filament and a plate placed near 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 lamp used 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 potential electricity, giving painful or dangerous shocks. Its habitat is the fresh water, in South America. Faraday investigated it and estimated its shock as equal to that from fifteen Leyden jars, each of 1.66 square feet 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 perfect machine would have the maximum efficiency in which the two qualities named 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 produced but half the work represented by the energy it absorbed, the rest disappearing in wasteful expenditure, in heating the bearings, in overcoming the resistance of the air and in other ways, its efficiency would be expressed by the coefficient 1/2 or .5, or if one hundred was the basis, by fifty per centum. There are a number of kinds of efficiencies of an electric generator which are given below.

Efficiency, Commercial.

Practical efficiency of a machine, obtained by dividing the available output of work or energy of a machine by the energy absorbed by the same machine. Thus in a dynamo part of the energy is usefully expended in exciting the field magnet, but this energy is not available for use in the outer circuit, is not a part of the output, and is not part of the dividend.

If M represents the energy absorbed, and W the useful or available energy, the coefficient of commercial efficiency is equal to W/M. M is made up of available, unavailable and wasted (by Foucault currents, etc.,) energy. Calling available energy W, unavailable but utilized energy w, and wasted energy m, the expression for the coefficient of commercial efficiency becomes

W / ( W + w + m ) when M = W + w + m

Synonym--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 available electrical energy. If we call W the useful electric and w the wasted electric energy, the coefficient of electrical efficiency is equal to

W / ( W + w )

Synonyms--Intrinsic Efficiency--Economic Coefficient--Coefficient of Electrical Efficiency.

Efficiency of Conversion.

In a dynamo or generator the relation of energy absorbed to total electric energy produced. Part of the electric energy is expended in producing the field and in other ways. Thus a generator with high efficiency of conversion may be a very poor one, owing to the unavailable electric energy which it produces. The coefficient of Efficiency of Conversion is obtained by dividing the total electric energy produced by the energy absorbed in working the dynamo. If M represents the energy absorbed, or work done in driving the dynamo or generator, W the useful electric, and w the wasted electrical energy, then the coefficient of efficiency of conversion is equal to

(W + w ) / M

In the quant.i.ty 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 the alternating system. Synonym--Gross Efficiency.

Efficiency of Secondary Battery, Quant.i.ty.

The coefficient obtained by dividing the ampere-hours obtainable from a secondary battery by the ampere hours required to charge it.

Efficiency of Secondary Battery, Real.

The coefficient obtained by dividing the energy obtainable from a secondary battery by the energy absorbed in charging it. The energy is conveniently taken in watt-hours and includes the consideration of the spurious voltage. (See Battery, Secondary.)

206 STANDARD ELECTRICAL DICTIONARY.