Page:Popular Science Monthly Volume 13.djvu/710

690 deposition of rain. To this there is no exception. There is, indeed, a manifest relation between the two. The more sudden and rapid the condensation, the more violent and terrific the explosion.

Sometimes, in thunder-storms we hear a loud crash, and then, soon after, comes an increased pouring down of water. Sound travels more rapidly than rain, and, although the report reaches us first, the interval between the events and the distance traveled plainly indicate that the explosion succeeded the condensation; and we naturally infer that it was caused by it. The loud crash and simultaneous lightning show the nearness of the explosion, at the origin of the rain-drops.

I next inquire whether we have experimental proofs corroborating these views.

A few years since an accidental escape of steam from a steam-boiler was found to strongly electrify a person who stood upon an insulator and held one hand in the escaping steam. This excited much interest at the time, and it was investigated by Armstrong and others, and led to our present steam-boiler electrical machine. The phenomena were at first supposed to throw much light upon the causes of atmospheric electricity. The subject was subsequently taken up by Faraday, who instituted a series of experiments, and came to a different conclusion. His theory, using his own words, was:

"The electricity is due to the friction of the particles of water which the steam carries forward against the surrounding solid matter of the passage, . . . and is in its nature like any other ordinary case of excitement by friction."

Again (section 2145), he says:

"Finally, I may say that the cause of the evolution of electricity by the liberation of confined steam is not evaporation; and, further, being I believe friction, it bas no effect in producing and is not connected with the general electricity of the atmosphere."

The great authority of Faraday has made this, ever since, to be the generally-accepted explanation of the phenomena. It may seem presumptuous to question it, but I cannot think that a careful examination of his experiments will justify all of his conclusions.

Faraday's apparatus consisted of a small steam-boiler, which he insulated, and for the discharge of steam he attached a pipe about four feet long, terminating in an iron globe. This had an orifice to which other appendages could be attached, and there was also a device for injecting water into the exit-pipe. His first experiments were directed to evaporation. He found that when the steam was at full pressure, and the valve was suddenly raised and taken out, and the evaporation was very rapid, no electricity was produced. He charged the boiler with electricity by an electrical machine before the valve was raised, and found that the escape of steam did not affect the charge. It was hence inferred that no electricity was produced by evaporation.