Thursday, October 06, 2005

Men Who Found Electricity - Part Two

The Bluecoat Boy Who Sent Electricity Along a Line of Thread

An ivory ball did not seem a promising thing with which to work, but Gray got a glass tube, and into its ends he fitted two corks. Into one cork he fixed his ivory ball, and, to his delight, he found that when the glass was rubbed it passed on its electricity through the cork to the ivory ball, and the ivory ball would now attract little light things just as the glass itself would.

This led Gray to many splendid experiments - little in themselves, but dazzling by their results, considering how he was working in the dark. He tried if silk would conduct electricity, and found that it would not. So he tried pack-thread, and found that that did. He put up a line of pack-thread, and supported it by loops of silk, which would not conduct the current away from the cotton. He was able to send a current of electricity along his line of thread for a distance of 886 feet. That was a wonderful achievement.

An industrious Frenchman was at work on similar lines at this time. This was a man named Dufay, who, born in 1699, died when only forty years of age, in 1739, three years after Gray. Dufay went over Gray's experiments, and went beyond them. He found that glass tubes could be used to hold up the pack-thread, and he found, too, that by connecting himself with the electrified thread he himself became electrified, and that when another person touched him there was a crackling sound, accompanied by a spark. But the great thing which Dufay did was to find out that there are two kinds of electricity, what we now call positive and negative.

How Men's Knowledge of Electricity Began to Grow

The two kinds exist in a substance, and are at rest until that body is rubbed. Thus two electrified silks will not come together, but silk and worsted will, though two electrified woollen threads will keep as far apart as possible. This is like the loadstone or magnet. That part of the loadstone which points to the north will drive away the north pole of another magnet, but will attract the other magnet's south pole, as if it loved it. North and south go together in the magnet, and opposite kinds go together in electricity.

Inventions now went forward rapidly. Machines were made for rubbing glass cylinders with cushions and other things, and they produced so much electricity that sparks could be formed which would set light to spirits, to wax, to pitch, and other things which were thoroughly heated by friction. The increase of knowledge was now turned to account in a new way. Several men saw that, if electricity could be so easily produced in the open air, it ought to be still stronger if produced in a vessel, away from the free air, where it could be kept and tapped as required, instead of being allowed to escape. This was near the middle of the eighteenth century.

The Shock That Surprised the Professor with a Jar of Water

A monk living abroad, a foreign inventor, and a professor named Muschenbroek, of Leyden in Holland, each seem to have had the same idea about the same time, and the outcome was what is called the Leyden jar. The professor electrified some water in a bottle or jar, which was covered with a metal stopper, through the centre of which ran an iron rod.

From this the electricity could be conducted as it was wanted. The professor made his discovery of the power of the electricity by accident. Holding the jar in one hand, he chanced to touch the iron rod with the other hand, and received such a shock that he declared that he would not for the crown of France risk such another.

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