Page:Popular Science Monthly Volume 59.djvu/352

342 deforms it, drawing it out into a conical shape. He even experiments with smoke, concluding that the small carbon particles are attracted by an electrified body. It was only a few years ago that Dr. Oliver Lodge, extending this observation, proposed to lay the poisonous dust floating about in the atmosphere of lead works by means of large electrostatic machines. He even hinted in his Royal Institution lecture that they might be useful in dissipating mists and fogs, recommending that a trial be made on some of our ocean-bound steamers.

Gilbert next tries heat as an agent to produce electrification. He takes a red-hot coal and finds that it has no effect on his electroscope; he heats a mass of iron up to whiteness and finds that it too exerts no electrical effect. He tries a flame, a candle, a burning torch, and concludes that all bodies are attracted by electrics save those that are afire or flaming, or extremely rarefied. He then reverses the experiment and brings near an excited body the flame of a lamp, and he ingenuously states that the body no longer attracts the pivoted needle. He thus discovered the neutralizing effect of flames, and supplied us with the readiest means we have to-day of discharging non-conductors.

He goes a step further; for we find him exposing some of his electrics to the action of the sun's rays in order to see whether they acquired a charge; but all his results were negative. He then concentrates the rays of the sun by means of lenses, evidently expecting some electrical effect; but finding none, he concludes with a vein of pathos that the sun imparts no power, but dissipates and spoils the electric effluvium.

Professor Righi has shown that a clean metallic plate acquires a positive charge when exposed to the ultra-violet radiation from any artificial source of light, but that it does not when exposed to solar rays. The absence of electrical effects in the latter case is attributed to the absorptive action of the atmosphere on the shorter waves of the solar beam.

Of course, Gilbert permits himself some speculation as to the nature of the agent he was dealing with. He thought of it, reasoned about it, pursued it in every way; and came to the conclusion that it must be something extremely tenuous indeed, but yet substantial, ponderable, material. "As air is the effluvium of the earth," he says, "so electrified bodies have an effluvium of their own, which they emit when stimulated or excited;" and again: "It is probable that amber exhales something peculiar that attracts the bodies themselves."

In 1862, another Gilbert, Sir Wm. Thomson (now Lord Kelvin), writing to his friend. Professor Tait, of Edinburgh, said: "Tell me what electricity is and I'll tell you everything else"; and in April, 1893, the same Lord Kelvin, replying to the writer, added: "I see no reason to say otherwise than what you tell me I said to Professor Tait in 1862." Despite, then, the great work of Clerk Maxwell and the corroborative