Page:Popular Science Monthly Volume 13.djvu/713

From Wikisource
Jump to: navigation, search
This page has been validated.
693
ELECTRICITY IN THUNDER-STORMS.
steam was freely escaping, and then advancing the other hand toward any conducting body, sparks of about an inch in length were obtained. But it was soon observed that, by elevating the rod in the steam, the electricity was gradually increased, and that the maximum effect was not obtained until the end of the rod was raised five or six feet above the valve, at which point the length of the sparks occasionally reached two inches. Small sparks were even obtained when the rod was wholly removed from the steam and held in the atmosphere at the distance of two or three feet from the jet; and the electricity thus drawn from the air was positive like that of the steam. When the rod was extended into the cloud of vapor which accumulated in the upper part of the shed, electricity was drawn down as by a lightning-conductor from a thunder-cloud."

These results seem to me to point out very clearly the cause of the electrical excitement. If it were the friction of steam against the sides of the exit-pipe, then at that point should be the greatest manifestation. If, on the contrary, it be condensation, then at a distance from the exit, where the greatest condensation takes place, should be the greatest development—and such is the fact. At the valve, Faraday found no electricity. At five or six feet from it, according to Armstrong and to Patterson, its development was abundant. The conclusion seems to me inevitable. All the facts point to condensation as the cause of the excitement.

A phenomenon that occurs daily at Pike's Peak has been described to me. The tops of the mountain, are covered with perpetual snow. During the summer months the snow-line gradually recedes up the sides of the mountain, and from it flow considerable streams of water, that are finally lost in the plains below. The winds coming from the prairies take up this moisture, and, ascending the mountain, reach the frozen regions above. At about eleven o'clock each day, black clouds begin to gather about the tops of the mountain, and soon thereafter pour down floods of rain. Flashes of lightning are almost incessant, with peals of thunder that seem to shake the mountains. I am informed that we have nothing in Eastern States that can compare with the terrific violence of these storms.

Here, certainly, is no friction, but condensation on a large scale; and it is attended with the same electrical effects that were observed in the condensation of steam from the steam-boiler.

Volcanoes sometimes emit great volumes of steam and smoke, and these are usually attended with flashes of lightning in every direction. Were the electricity due to friction, it would be found at the mouth of the crater, where the steam issues; but, instead of that, it is found on the sides of the column, where the steam meets with colder air, and is condensed to water. The effects are analogous in every respect to those of steam from the steam-boiler.

In thunder-storms we have no friction, but condensation, and we need not go beyond the usual effects of condensation to explain all the electrical phenomena.