A History of Science-2 [100]
to those of Hauksbee. While experimenting with a glass tube for producing electricity, as Hauksbee had done, he noticed that the corks with which he had stopped the ends of the tube to exclude the dust, seemed to attract bits of paper and leaf-brass as well as the glass itself. He surmised at once that this mysterious electricity, or "virtue," as it was called, might be transmitted through other substances as it seemed to be through glass. "Having by me an ivory ball of about one and three-tenths of an inch in diameter," he writes, "with a hole through it, this I fixed upon a fir-stick about four inches long, thrusting the other end into the cork, and upon rubbing the tube found that the ball attracted and repelled the feather with more vigor than the cork had done, repeating its attractions and repulsions for many times together. I then fixed the ball on longer sticks, first upon one of eight inches, and afterwards upon one of twenty-four inches long, and found the effect the same. Then I made use of iron, and then brass wire, to fix the ball on, inserting the other end of the wire in the cork, as before, and found that the attraction was the same as when the fir-sticks were made use of, and that when the feather was held over against any part of the wire it was attracted by it; but though it was then nearer the tube, yet its attraction was not so strong as that of the ball. When the wire of two or three feet long was used, its vibrations, caused by the rubbing of the tube, made it somewhat troublesome to be managed. This put me to thinking whether, if the ball was hung by a pack-thread and suspended by a loop on the tube, the electricity would not be carried down the line to the ball; I found it to succeed accordingly; for upon suspending the ball on the tube by a pack-thread about three feet long, when the tube had been excited by rubbing, the ivory ball attracted and repelled the leaf-brass over which it was held as freely as it had done when it was suspended on sticks or wire, as did also a ball of cork, and another of lead that weighed one pound and a quarter." Gray next attempted to determine what other bodies would attract the bits of paper, and for this purpose he tried coins, pieces of metal, and even a tea-kettle, "both empty and filled with hot or cold water"; but he found that the attractive power appeared to be the same regardless of the substance used. "I next proceeded," he continues, "to try at what greater distances the electric virtues might be carried, and having by me a hollow walking-cane, which I suppose was part of a fishing-rod, two feet seven inches long, I cut the great end of it to fit into the bore of the tube, into which it went about five inches; then when the cane was put into the end of the tube, and this excited, the cane drew the leaf-brass to the height of more than two inches, as did also the ivory ball, when by a cork and stick it had been fixed to the end of the cane.... With several pieces of Spanish cane and fir-sticks I afterwards made a rod, which, together with the tube, was somewhat more than eighteen feet long, which was the greatest length I could conveniently use in my chamber, and found the attraction very nearly, if not altogether, as strong as when the ball was placed on the shorter rods." This experiment exhausted the capacity of his small room, but on going to the country a little later he was able to continue his experiments. "To a pole of eighteen feet there was tied a line of thirty-four feet in length, so that the pole and line together were fifty-two feet. With the pole and tube I stood in the balcony, the assistant below in the court, where he held the board with the leaf-brass on it. Then the tube being excited, as usual, the electric virtue passed from the tube up the pole and down the line to the ivory ball, which attracted the leaf-brass, and as the ball passed over it in its vibrations the leaf-brass would follow it till it was carried off the board." Gray next attempted to send the electricity over a line suspended horizontally. To do this he suspended the