Page:Popular Science Monthly Volume 42.djvu/375

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his work had met in Berlin, but went on to construct his lightning-rod. After all that was necessary had been prepared, the conductor was erected on the 15th of June, 1754, near the residence of the parson, for Divis, in order to avoid all risks, gavePSM V42 D375 Divis lightning rod cross bars.jpgFig. 2.—A Horizontal View of the Cross-bars.up the idea of placing the lightning-rod upon the building, but built it separately in the free field near the building. The lightning-rod of Divis was constructed as follows:

A pointed, slender iron bar formed the main part of the machine. Fastened to it were two cross-bars, thus making four arms, across each of which, in turn, a shorter bar was laid. And each of the twelve extremities so effected bore a box filled with shavings of iron in which twenty-seven brass needles were stuck, making three hundred and twenty-four needles in all. The main bar was supported by a wooden column sufficiently high (forty-eight feet at first, afterward one hundred and thirty-two feet) to secure protection for the building and its immediate surroundings. Several iron chains connected the main bar with the earth. The effect of the machine was to divide the lightning into as many sparks as there were needles (three hundred and twenty-four), and thus to lessen its force. It might, therefore, more properly be called a lightning-divisor.

Scarcely had the rod been erected when a storm came rushing on from the north. Thunder-clouds hung over Prendice, and occasionally white shafts of lightning were seen darting from the clouds and flying toward the conductor. In a few minutes a white cloud enveloped the machine, and the storm soon passed away without doing any damage. For two years Divis continued experimenting with his lightning-rod; the results were published by Dr. Scrinci in the Prague News (1754). Having satisfied himself in regard to the utility of his new machine, Divis offered to the emperor a plan for erecting a number of conductors in various parts of his empire. The emperor submitted the plan to Viennese mathematicians, who were, unfortunately, a little behind the times, and reported unfavorably upon the Bohemian's proposition. The plan was consequently never carried out. Abbot Marci, speaking about the report of the Viennese "connoisseurs," says, in a letter to Divis, "Blasphemant, quae ignorant" (They blaspheme that which they do not understand). And at last, in 1756, Divis was compelled to remove his lightning-rod. There had been a very dry summer that year, which the farmers