Equipotential Surface, Magnetic and Electro-magnetic.

A surface bearing the same relation to a magnetic or electro-magnetic field of force that an electrostatic equipotential surface (see Equipotential Surface, Electrostatic,) does to an electrostatic field of force.

Equivalent, Chemical.

The quotient obtained by dividing the atomic weight of an element by its valency.

Equivalents, Electro-chemical.

The weight of any substance set free by one coulomb of electricity. The following give some equivalents expressed in milligrams:

Hydrogen .0105 Mercury (mercurous) 2.10 Gold .6877 Iron (ferric) .1964 Silver 1.134 Iron (ferrous) .294 Copper (cupric) .3307 Nickel .3098 Mercury (mercuric) 1.05 Zinc .3413 Lead 1.0868 Chlorine .3728 Oxygen .89

245 STANDARD ELECTRICAL DICTIONARY.

Equivalent, Electro-mechanical.

The work or energy equivalent to unit quant.i.ties of electric energy, q.

v.; or equivalent to a unit current in a conductor whose ends differ one unit of potential. The unit of electric energy taken is the watt-second or volt-coulomb. One volt-coulomb is equal to Ergs 1E7 [10000000]

Foot Pound .737337 Gram-degree C. .24068 Horse Power Second .0013406 Pound-degree F. .000955 One horse power is equal to 745.943 volt coulombs per second.

Equivalent, Electro-thermal.

The heat produced by a unit current pa.s.sing through a conductor with unit difference of potential at its ends; the heat equivalent of a volt-coulomb or watt-second. It is equal to Gram-degree C. .24068 Pound-degree F. .000955

Equivalent, Thermo-chemical.

The calories evolved by the combination of one gram of any substance with its equivalent of another substance being determined, the product obtained by multiplying this number by the equivalent (atomic or molecular weight / valency) of the first element or substance is the thermo-chemical equivalent. If expressed in kilogram calories, the product of the thermo-chemical equivalent by 0.43 gives the voltage required to effect such decomposition.

The following are thermo-chemical equivalents of a few combinations: Water 34.5 Zinc oxide 43.2 Iron protoxide 34.5 Iron Sesquioxide 31.9 X 3 Copper oxide 19.2

Equivolt.

"The mechanical energy of one volt electro-motive force exerted under unit conditions through one equivalent of chemical action in grains."

(J. T. Sprague.) This unit is not in general use as the unit of electric energy, the volt-coulomb and (for rate of electric energy) the volt-ampere being always used.

Erg.

The absolute or fundamental C. G. S. unit of work or energy. The work done or energy expended in moving a body through one centimeter against a resistance of one dyne.

Erg-ten.

Ten millions of ergs, or ten meg-ergs.

Escape.

A term applied to leakage of current.

Etching, Electric.

A process of producing an etched plate. The plate is coated with wax, and the design traced through as in common etching. It is then placed in a bath and is connected to the positive terminal from a generator, whose negative is immersed in the same bath, so that the metal is dissolved by electrolytic action. By attaching to the other terminal and using a plating bath, a rough relief plate may be secured, by deposition in the lines of metal by electroplating.

Synonym--Electric Engraving.

246 STANDARD ELECTRICAL DICTIONARY.

Ether.

The ether is a hypothetical thing that was invented to explain the phenomena of light. Light is theoretically due to transverse vibrations of the ether. Since the days of Young the conception of the ether has extended, and now light, "radiant heat," and electricity are all treated as phenomena of the ether. Electrical attraction and repulsion are explained by considering them due to local stresses in the ether; magnetic phenomena as due to local whirlpools therein. The ether was originally called the luminiferous ether, but the adjective should now be dropped. Its density is put at 936E-21 that of water, or equal to that of the atmosphere at 210 miles above the earth's surface. Its rigidity is about 1E-9 that of steel (see Ten, Powers of); as a whole it is comparable to an all-pervading jelly, with almost perfect elasticity.

The most complete vacuum is filled with ether.

All this is a hypothesis, for the ether has never been proved to exist.

Whether gravitation will ever be explained by It remains to be seen.

[Transcriber's note: The Michelson-Morley experiment in 1887 (five years before this book) cast serious doubt on the ether. In 1905 Einstein explained electromagnetic phenomenon with photons. In 1963 Edward M.

Purcell used special relativity to derive the existence of magnetism and radiation.]

Eudiometer.

A graduated gla.s.s tube for measuring the volumes of gases. In its simplest form it is simply a cylindrical tube, with a scale etched or engraved upon it, closed at one end and open at the other. The gas to be measured is collected in it over a liquid, generally water, dilute sulphuric acid in the gas voltameter, or mercury. Many different shapes have been given them by Hoffmann, Ure, Bunsen and others.

Evaporation, Electric.

The superficial sublimation or evaporation of a substance under the influence of negative electricity. It is one of the effects investigated by Crookes in his experiments with high vacua. He found that when a metal, even so infusible as platinum, was exposed to negative electrification in one of his high vacuum tubes, that it was volatilized perceptibly. A cadmium electrode heated and electrified negatively was found to give a strong coating of metal on the walls of the tube. Even in the open air the evaporation of water was found to be accelerated by negative electrification.

Exchange, Telephone.

The office to which telephone wires lead in a general telephone system.

In the office by a multiple switch board, or other means, the different telephones are interconnected by the office attendants, so that any customers who desire it may be put into communication with each other.

The exchange is often termed the Central Office, although it may be only a branch office.

Excitability, Faradic.

The action produced in nerve or muscle of the animal system by an alternating or intermitting high potential discharge from an induction coil.

247 STANDARD ELECTRICAL DICTIONARY.

Excitability, Galvanic.

The same as Faradic excitability, except that it refers to the effects of the current from a galvanic battery.

Excitability of Animal System, Electric.

The susceptibility of a nerve or muscle to electric current shown by the effect produced by its application.