Wrinkles in Electric Lighting

E. & F. N. SPON, 125, STRAND, LONDON.
NEW YORK: 12, CORTLANDT STREET.
1888.

In the following pages it is my intention to give engineers on board ship, who may be put in charge of electric lighting machinery without having any electrical knowledge, some idea of the manner in which electricity is produced by mechanical means; how it is converted into light; what precautions must be used to keep the plant in order, and what to do in the event of difficulties arising. I do not therefore aim at producing a literary work, but shall try and explain everything in the plainest language possible.
Fig. 1.
Action of current is instantaneous. The action of electricity is practically instantaneous in any length of wire, so that if the current is used to ring two bells a mile apart, but connected by wires, they will commence to ring simultaneously. I have so far not said anything about resistance to the passage of the current through the wires. I shall therefore refer again to our comparison of the current to water forced through a pipe, and you will agree that a certain sized pipe will only convey a certain amount of water in a given time. If a larger quantity is to be conveyed in the same time, a greater pressure must be applied, or a larger pipe must be used.
It is evident that increasing the size of the pipe will get over the difficulty more readily than increasing the pressure of the water. The pipes themselves offer a certain resistance to the passage of the water through them, in the shape of friction; so that if an effect is to be produced at a distance, rather more pressure is required than if it is done close at hand, so as to make up for the loss sustained by friction.
Resistance to the passage of the current. Much the same may be said of the electric current; a certain sized wire will only carry a certain current, and if more current is required, a thicker wire must be used to convey it, or it must be of a greater E.M.F. It is usually more convenient to increase the thickness of the wire than to increase the E.M.F. of the current. The wire offers a certain resistance to the passage of the current through it, which may be compared to friction, and this resistance varies according to the metal of which it is composed. Copper the usual metal for conductors. Copper is the metal in ordinary use for wires for electric lighting purposes, and the purer it is the better will it convey the current. Iron is used for telegraph wires on account of cheapness, the current used being so small that this metal conveys it readily enough; if copper were used, the wires will only require to be about one-third the diameter of the iron ones. The following are the respective values for electrical conductivity of various metals when pure, taking silver as a standard:—Silver 100, copper 99·9, gold 80, zinc 29, brass 22, iron 16·8, tin 13·1, lead 8·3, mercury 1·6.