We have, in a former portion of this work, explained the construction of the telephone and phonograph with other inventions to make sounds audible at a distance, so we need not repeat the explanations here. A brief reference to them will, however, be found in this chapter, in which the electro-magnet and the methods of lighting by magneto-electric machines are treated of. We will proceed to give some particulars concerning the electric light before considering the means by which it is produced, as such an arrangement is more convenient.
The light is very easily produced by uniting and then separating the terminals of a strong battery. The passage of the electric current induces intense heat and a most brilliant light. But if this were continued the wires would melt, and therefore some non-fusible substance is placed at the ends of the wires, which will be at once a conductor and infusible. Now in gas-carbon (the deposited substance found in gas retorts) we have a substance suited to these conditions. The carbon is heated to an intense brightness, and particles of it are passed across the arc of flame almost in a state of fusion. Combustion does not actually take place, because it has been proved that the wires will give out light under water, and in the vacuum of an air-pump the light is even increased, so that had the oxygen of the air any part in the production of the light it would not remain unaffected under these conditions. The heat arising from this Voltaic arc is intense, and even platinum may be fused with the assistance of the gas carbon. The carbon points are of course liable to be worn away, and one side more than another. The positive pole is generally more concave than the other, for it sheds its particles in a greater degree, and is the more intensely heated. The electric light first appeared in public at the opera in Paris in 1836, to illustrate a sunrise, but it was not till 1843 that it was experimented upon in the open air. We need not trace it farther at present, for a full account of its origin, rise, and progress is published in a small shilling volume by Messrs. Ward, Lock, & Co. We will proceed to the methods of bringing out the light.
[Illustration: Fig. 267.—The Maxim light.]