Nollet sent a discharge from a jar through a regiment of 1500 men holding each other’s hands, and they were all shocked in the arms and shoulders. But perhaps the best known experiment is that of Franklin with his kite.
Two strips of cedar, fixed crosswise, with a large silk handkerchief tied at the corners, and a sharp-pointed wire projecting a foot above the upright, was all that Benjamin Franklin’s famous kite consisted of. It had an ordinary paper tail, a bellyband, and a long fine string, with a short piece of silk ribbon tied at the end. Just where the ribbon was knotted to the string he hung a key.
It was in June, 1752, when he let his kite up in the thunderstorm. He and his son, after some little difficulty, got it out to the full length of the string, and then stood up inside a doorway to keep the ribbon dry. A thundercloud passed over, and nothing seemed to happen. The experiment promised to be a failure. Gradually, however, the loose filaments of twine began to stand out at right angles, and were found to be attracted by the fingers; then a knuckle held to the key extracted a spark from it, and as the string got thoroughly wet in the pouring rain the electricity became abundant. With it the experimenters charged the Leyden jar, whose discharges afterwards proved the identity of the electricity of the thundercloud with the electricity of the machine.
Another famous experiment is that known as Lichtenberg’s figures. It is generally performed as follows. Hold the jar, charged positively, in the hand, and with the knob draw on a glass plate, cake of resin, or sheet of vulcanite, a series of patterns. Then put the jar on an insulator, and, lifting it by the knob, trace another series of patterns with the outer coating, so as to cross and intertwine with those made by the knob. Having designed the patterns, make a mixture of red lead and flowers of sulphur and dust it on to the slab. A curious thing will happen. The red and yellow will sort themselves out. The sulphur will stick to the positive lines, the lead to the negative ones, and the pattern will be given in two well-marked colours. The sulphur will be in tufts, the lead in spots. In mixing the powder the sulphur became negatively electrified, the red lead positively so, and hence the disposition of the materials.
The terms negative and positive were first used by Symmer as alternatives for resinous and vitreous. Symmer was the man who discovered the electricity in his stockings and charged the jar by their aid. His experiments were the same in principle as those of Cigna with his silk ribbons, but were much more astonishing.
When Symmer pulled off his stockings he noticed that they often gave a crackling sound, and when he undressed in the dark he saw sparks issuing from them. When he wore silk stockings for show and worsted beneath them for warmth the effects were more powerful. When one stocking was drawn out of the other they appeared inflated, and attracted and repelled each other like electrified bodies!
He experimented with a pair of white silk stockings and a pair of black silk stockings. When he wore both white or both black on the same leg, nothing happened; but when he wore a white and black on the leg, and pulled them off after ten minutes or so, they remained inflated, and showed the shape of his leg! Brought within eighteen inches of each other, they rushed together; then they were separated, and again became inflated, and again rushed together.
Experimenting with the two pairs held against each other, he found that they sorted themselves out, rushing each to each, until they gradually wasted away, and from legs substantial enough for the foundation of a family ghost story—a ghostly legacy—dwindled down into mere flabby pieces of silk. The electricity he obtained from these classical stockings was considerable. He charged a Leyden jar from the four of them, and secured enough electricity to shock himself up to his elbows, and to light a teaspoonful of spirits of wine!
One caution before we conclude. In every experiment, whether it be merely in shocking, in rendering luminous half-a-dozen eggs placed end to end by sending the shock through them, in perforating a card by passing a spark through it as it rests on the foil, in splitting wood by driving the wires in until their points are close to each other, in breaking a glass by passing a spark from knob to knob in water, however simple it may be, remember always to discharge by touching the outside first. Otherwise you may receive an unpleasant surprise, and, like Cuneus, come to grief with your Leyden jar.