In order to ascertain the speed at which the electric force traversed space, Dr. Watson and his friends next entered upon a series of experiments at Shooter’s Hill, near London. They sent an electric discharge a distance of four miles, observers being stationed at each end, and a gun fired at the touch of the Leyden jar, when it was shown conclusively that the movement of the electric force was instantaneous. This was an important step in advance, in overthrowing all formerly established conclusions as to the agency being produced by a succession of waves, like sound, and as such, moving slowly through space.
The field for electrical experiments was now becoming gradually more extensive, and a few more practical tests of Mr. Watson and his coadjutors led the way to the greatest knowledge of the all-pervading force that had yet been achieved, in the clear apprehension that lightning was but a manifestation of electricity. The new experiments were chiefly made with the so-called electrical tube, a glass rod, from two and a half to three feet in length and about an inch in diameter. It had been known for some time that the tube, when gently warmed, so as to be perfectly dry, and rubbed with a silk handkerchief, exhibited strong symptoms of electricity, to the extent of throwing off luminous sparks, which obtained the name of ‘electric fire.’ Dr. Watson found, to his surprise, that this electric fire was not general and always obtainable, but conditional upon circumstances. Having rubbed a glass tube while he was insulated by standing upon a cake of wax, he found that no electricity could be drawn from him by another person who touched any part of his body, but that the same person could obtain sparks from the tube by putting his hand near it. Dr. Watson likewise observed, in the same train of experiments, that if an electrical machine, together with the person turning the handle, were suspended by silk, electric fire was not apparent until he touched the floor with one foot, when the fire appeared upon the conductor. Having made a great number of trials of a like nature, Dr. Watson made known the important conclusion derived from them, namely, that glass tubes and all similar ‘electrifiers’ did not contain within themselves the subtle agent known as electricity, but formed only its temporary place of rest, as a sponge would that of water. Dr. Watson was near proclaiming the fact that electricity resides everywhere throughout the universe; but for a moment he only touched the fringe of it. The discovery of this grand truth was left to later investigators.