342 POPULAR SCIENCE MONTHLY. 



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 Eoyal 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 con- 

 cludes 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 dis- 

 covered 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 elec- 

 trics 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 meaus 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 eftluvium. 



Professor Eight 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, jjonderable, 

 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 111 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 



