234 STANDARD ELECTRICAL DICTIONARY.

Electroscope, Pith Ball.

Two pith b.a.l.l.s suspended at opposite ends of a silk thread doubled in the middle. When charged with like electricity they repel each other.

The extent of their repulsion indicates the potential of their charge.

Electrostatic Attraction and Repulsion.

The attraction and repulsion of electrostatically charged bodies for each other, shown when charged with electricity. If charged with electricity of the same sign they repel each other. If with opposite they attract each other. The cla.s.sic attraction and subsequent repulsion of bits of straw and chaff by the excited piece of amber is a case of electrostatic attraction and repulsion. (See Electricity, Static--Electrostatics--Coulomb's Laws of Electrostatic Attraction and Repulsion.)

Electrostatic Induction, Coefficient of.

The coefficient expressing the ratio of the charge or change of charge developed in one body to the potential of the inducing body.

Electrostatic Lines of Force.

Lines of force a.s.sumed to exist in an electrostatic field of force, and to const.i.tute the same. In general they correspond in action and attributes with elcctro-magnetic lines of force. They involve in almost all cases either a continuous circuit, or a termination at both ends in oppositely charged surfaces.

Fig. 161. ELECTROSTATIC LINES OF FORCE BETWEEN NEAR SURFACES.

Fig. 162. ELECTROSTATIC LINKS OF FORCE BETWEEN DISTANT SURFACES.

235 STANDARD ELECTRICAL DICTIONARY.

The cut, Fig. 161, shows the general course taken by lines of force between two excited surfaces when near together. Here most of them are straight lines reaching straight across from surface to surface, while a few of them arch across from near the edges, tending to spread. If the bodies are drawn apart the spreading tendency increases and the condition of things shown in the next cut, Fig. 162, obtains. There is an axial line whose prolongations may be supposed to extend indefinitely, as occupying a position of unstable equilibrium. Here the existence of a straight and unterminated line of force may be a.s.sumed.

A direction is predicated to lines of force corresponding with the direction of an electric current. They are a.s.sumed to start from a positively charged and to go towards a negatively charged surface. A positively charged body placed in an electrostatic field of force will be repelled from the region of positive into or towards the region of negative potential following the direction of the lines of force, not moving transversely to them, and having no transverse component in its motion.

[Transcriber's note: More precisely, "A positively charged body placed in an electrostatic field of force will be repelled from the region of positive into or towards the region of negative potential ACCELERATING in the direction of the lines of force, not ACCELERATING transversely to them, and having no transverse component in its ACCELERATION."

Previously acquired momentum can produce a transverse component of VELOCITY.]

Electrostatics.

The division of electric science treating of the phenomena of electric charge, or of electricity in repose, as contrasted with electro-dynamics or electricity in motion or in current form. Charges of like sign repel, and of unlike sign attract each other. The general inductive action is explained by the use of the electrostatic field of force and electrostatic lines of force, q. v. The force of attraction and repulsion of small bodies or virtual points, which are near enough to each other, vary as the square of the distance nearly, and with the product of the quant.i.ties of the charges of the two bodies.

Electrostatic Refraction.

Dr. Kerr found that certain dielectrics exposed to electric strain by being placed between two oppositely excited poles of a Holtz machine or other source of very high tension possess double refracting powers, in other words can rotate a beam of polarized light, or can develop two complimentary beams from common light. Bisulphide of carbon shows the phenomenon well, acting as gla.s.s would if the gla.s.s were stretched in the direction of the electrostatic lines of force. To try it with gla.s.s, holes are drilled in a plate and wires from an influence machine are inserted therein. The discharge being maintained through the gla.s.s it polarizes light.

Synonym--Kerr Effect.

Electrostatic Series.

A table of substances arranged in the order in which they are electrostatically charged by contact, generally by rubbing against each other. The following series is due to Faraday. The first members become positively excited when rubbed with any of the following members, and vice versa. The first elements correspond to the carbon plate in a galvanic battery, the succeeding elements to the zinc plate.

Cat, and Bear-skin--Flannel--Ivory--Feathers--Rock Crystal--Flint Gla.s.s--Cotton--Linen--Canvas--White Silk--the Hand--Wood--Sh.e.l.lac--the Metals (Iron-Copper-Bra.s.s-Tin-Silver-Platinum)--Sulphur. There are some irregularities. A feather lightly drawn over canvas is negatively electrified; if drawn through folds pressed against it it is positively excited. Many other exceptions exist, so that the table is of little value.

236 STANDARD ELECTRICAL DICTIONARY.

Electrostatic Stress.

The stress produced upon a transparent medium in an electrostatic field of force by which it acquires double refracting or polarizing properties as regards the action of such medium upon light. (See Electrostatic Refraction.)

Electro-therapeutics or Therapy.

The science treating of the effects of electricity upon the animal system in the treatment and diagnosis of disease.

Electrotonus.

An altered condition of functional activity occurring in a nerve subjected to the pa.s.sage of an electric current. If the activity is decreased, which occurs near the anode, the state is one of anelectrotonus, if the activity is increased which occurs near the kathode the condition is one of kathelectrotonus.

Electrotype.

The reproduction of a form of type or of an engraving or of the like by electroplating, for printing purposes. The form of type is pressed upon a surface of wax contained in a shallow box. The wax is mixed with plumbago, and if necessary some more is dusted and brushed over its surface and some iron dust is sprinkled over it also. A matrix or impression of the type is thus obtained, on which copper is deposited by electroplating, q. v.

Element, Chemical.

The original forms of matter that cannot be separated into const.i.tuents by any known process. They are about seventy in number. Some of the rarer ones are being added to or cancelled with the progress of chemical discovery. For their electric relations see Electro-chemical Equivalents--Electro-chemical Series.

The elements in entering into combination satisfy chemical affinity and liberate energy, which may take the form of electric energy as in the galvanic battery, or of heat energy, as in the combustion of carbon or magnesium. Therefore an uncombined element is the seat of potential energy. (See Energy, Potential.) In combining the elements always combine in definite proportions. A series of numbers, one being proper to each element which denote the smallest common multipliers of these proportions, are called equivalents. Taking the theory of valency into consideration the product of the equivalents by the valencies gives the atomic weights.

237 STANDARD ELECTRICAL DICTIONARY.

Element, Mathematical.

A very small part of anything, corresponding in a general way to a differential, as the element of a current.

Element of a Battery Cell.

The plates in a galvanic couple are termed elements, as the carbon and zinc plates in a Bunsen cell. The plate unattacked by the solution, as the carbon plate in the above battery, is termed the negative plate or element; the one attacked, as the zinc plate, is termed the positive plate or element.

Synonym--Voltaic Element.

Elements, Electrical Cla.s.sification of.

This may refer to Electro-chemical Series, Electrostatic Series, or Thermo-electric Series, all of which may be referred to.

Element, Thermo-electric.

One of the metals or other conductors making a thermo-electric couple, the heating of whose junction produces electro-motive force and a current, if on closed circuit. The elements of a couple are respectively positive and negative, and most conductors can be arranged in a series according to their relative polarity. (See Thermo-electric Series.)

Elongation.