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Page:Popular Science Monthly Volume 56.djvu/263

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of electricity, and Franklin charged a Leyden jar from the key, thus achieving the actual storage of "lightning."

He continued his investigations in atmospheric electricity, and discovered that the electrification of the clouds (or of the upper atmosphere) was sometimes positive and sometimes negative. The invention of the lightning rod is due to him.

Franklin sided with Watson in his belief in the single nature of the electric fluid.

As intimated above, atmospheric electricity appears to have been collected independently about the same time in Europe, and certain very daring and dangerous experiments were performed there. One sad occurrence, as a result, was the death of Professor Richman, in St. Petersburg, in 1753. Richman, in company with a friend, Sokolow, was taking observations on an electroscope connected with an iron rod which terminated in the apartment and extended in the other direction above the roof of the building. During the progress of their experiments a violent peal of thunder was heard in the neighborhood, and Richman bent to examine the instrument. In doing so he approached his head to within a foot of the end of the rod, and Sokolow saw a ball of fire "about the size of a man's fist" shoot from it to Richman's head with a terrific report. The stroke was, of course, immediately fatal, and what we now know as the return shock stupefied and benumbed Sokolow. The unfortunate event served as a warning to other daring experimenters.

Canton, another prominent worker in this field, discovered that the so-called vitreous electricity was not necessarily always developed by the friction of glass, as had hitherto been believed to be invariably the case. By applying different rubbers to glass he obtained either positive or negative at pleasure. This at once disposed of the idea that one kind of electricity resided in certain bodies and its opposite in others. Canton also made the interesting discovery that glass, amber, rock crystal, etc., when taken out of mercury, were all electrified positively. He was thus enabled to make the improvement in the electrical machine of coating its rubber with an amalgam rich in mercury, which greatly enhanced. its powers.

Among the numerous names now coming into prominence must be mentioned those of Beccaria, Symmer, Delaval, "Wilson, Kinnersley, Wilcke, and Priestley.

The first named, Father Beccaria, was a celebrated Italian physicist who did most valuable work in connection with atmospheric electricity, and who published several classical works on that and allied subjects. Among these may be mentioned his Lettre del Elettricitá, 1758, and Experimenta, 1772. He ascertained that water is not by any means a good conductor, as it had previously been sup-