Definitions and Explanations of Electrical Terms

In the last chapter we explained various terms relating to magnetism. Just as in the neighbourhood of a magnet we have a field of magnetic force, so, too, in the neighbourhood of an electrified body there is a field of electric force. We proceed to consider certain facts, and to explain some of the terms connected with the theory of electricity, a clear comprehension of which will be necessary in order to understand rightly the experiments which follow.

Most bodies can by friction, chemical action, or by various other means, be made to exert forces on other bodies which have been similarly treated. The phenomena in question are classed together as electrical, and the bodies are said to have been electrified. By experiments with Faraday's ice-pail among others (vide Maxwell's 'Elementary Electricity,' p. 16, &c.), it has been shown that these effects can be accounted for by supposing the bodies to be charged with certain quantities of one of two opposite kinds of electricity, called respectively positive and negative, and such that equal quantities of positive and negative electricity completely annihilate each other.

An electrified body exerts force on other electrified bodies in its neighbourhood - in other words, produces a field of electrical force - and the force at any point depends on the position of the point, on the form and dimensions of the electrified body, and on the quantity of electricity on the body. By doubling the charge we can double the force. We are thus led to look upon electricity as a quantity which can be measured in terms of a unit of its own kind, and we may speak of the quantity of electricity on a body, in somewhat the same way as we use the term quantity of magnetism for the strength of a magnetic pole. The magnetic forces produced by a magnetic pole are due to a quantity of magnetism concentrated at the pole. The electrical forces produced by an electrified body are due to a quantity of electricity distributed over the body. By supposing the body to become very small while the quantity of electricity on it still remains finite, we may form the idea of an electrified point or a point charged with a given quantity of electricity.

With regard to the transmission of electrical properties bodies may be divided into two classes, called respectively conductors and non-conductors. To the latter the name 'dielectric' is also applied.