Page:Popular Science Monthly Volume 9.djvu/359

Rh by warm tumblers. Hold in your right hand a sheet of vulcanized India-rubber, and clasp, with it between you, the left hand of a friend. Place your left hand on the conductor of the machine, and let it be worked. You and your friend soon feel a crackling and a tickling of the hands, due to the heightening attraction of the opposite electricities across the India-rubber. The hand-jar is then charged. To discharge it you have only to bring your other hands together: the shock of the Leyden-jar is felt.

By the discharge of the hand-jar you can fire gunpowder. But this will be referred to more particularly further on.

20. Physiological Effects of the Shock.—The physiological effect of the shock was variously studied. Graham caused a number of persons to lay hold of the same metal plate, which was connected with the outer coating of a charged Leyden-jar, and also to lay hold of a rod by which the jar was discharged. The shock divided itself equally among them.

The Abbé Nollet formed a line of one hundred and eighty guardsmen, and sent the discharge through them all. He also killed sparrows and fishes by the shock. The analogy of these effects with those produced by thunder and lightning could not escape attention, nor fail to stimulate inquiry.

Indeed, as experimental knowledge increased, men's thoughts became more definite and exact as regards the relation of electrical effects to thunder and lightning. The Abbé Nollet thus quaintly expresses himself: "If any one should take upon him to prove, from a well-connected comparison of phenomena, that thunder is, in the hands of Nature, what electricity is in ours, and that the wonders which we now exhibit at our pleasure are little imitations of those great effects which frighten us, I avow that this idea, if it was well supported, would give me a great deal of pleasure." He then points out the analogies between both, and continues thus: "All those points of analogy, which I have been some time meditating, begin to make me believe that one might, by taking electricity as the model, form to one's self, in relation to thunder and lightning, more perfect and more probable ideas than what have been offered hitherto. "

These views were prevalent at this time, and out of them grew the experimental proof by the great physical philosopher, Franklin, of the substantial identity of the lightning-flash and the electric spark.

Franklin was twice struck senseless by the shock. He afterward sent the discharge of two large jars through six robust men; they fell to the ground and got up again without knowing what had happened; they neither heard nor felt the discharge. Priestley, who made many valuable contributions to electricity, received the charge of two jars, but did not find it painful.