Page:Popular Science Monthly Volume 43.djvu/473

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457
PROTECTION FROM LIGHTNING.

There was a certain amount of energy which they must dissipate somehow, and they could not expect to hocus pocus it out of existence by saying they could conduct it to the earth. The quicker they tried to conduct it down to the earth the more searching and ramifying disturbances they were likely to get. It might be better to let it trickle down slowly by using a moderately bad conductor than to rush it with extreme vehemence down a good conductor, just as it would be safer to let a heavy weight suspended in a dangerous position down slowly rather than let it drop as quickly as possible. . . . If a man holds a lightning conductor when a flash passes down it, he will most likely be killed. . . . It did not matter about the earth; . . . a spark was likely to occur. . . he had made experiments in the laboratory with a rod very thick and a yard long, in circuit with a Leyden-jar discharge. He took a platinum wire as fine as possible to make the contrast greater, and arranged it so as to make a kind of tapping circuit; if, then, the bottom end was arranged so as to be in contact with the rod and then let the top end be an eighth of an inch away, then they would have a splendid conductor, better than any lightning conductor ever was. They would have no trouble about earth. It seemed absurd for any portion of the discharge to leave this conductor to jump across and make for the little strip of wire. Nevertheless, a portion of it did, and from every spark that went to the conductor, a side branch went to that little wire. . . . What are the conditions of a flash? He assumed that a flash behaved like experiments in the laboratory, but it was a question whether a cloud discharge was of this kind, A cloud is not like a conductor; it consists of globules of water separated from one another by interspaces of air; it may be compared to a spangle jar: when a spangle jar discharges, you have no guarantee that the whole of it discharges—it discharges in a slowish manner. It might be that there was with a cloud first a bit of a discharge and then another bit, and so on, so that there might be a kind of dribbling of the charge out of it, and they might therefore fail to get these sudden and oscillatory rushes. . . But we must provide for the possibility of a sudden discharge."

Hon, Ralph Abercromby contributed to the discussion facts brought out by an examination of some ninety photographs of lightning flashes in different parts of the world. In one instance the whole air was filled with threads of lightning coming down like the roots of a tree from the sky. He thought it was very much a question where the area of protection would be when the whole air seemed to be pouring lightning down upon you. He would also like to find out whether buildings were struck during rain or when it was not raining. In connection with the fact that thunderstorms were confined to the lower ten thousand