Continuing onr electrical experiments, we have, in the accompanying illustration, two pieces of apparatus that will serveio illustrate the principal laws which this force obeys. The first is a bottle, covered inside and outside, about three-quarters its hight, by tin-foil, and having a metal rod passing through its cork, being connected by a piece of chain with the round ball or loop outside. It is called the iMt/den jar, because it was supposed to have been contrived by M. Cunocus, of the city of Leyden, at tlie close of the year 1745 ; but Dr. Priestley ascribes its discovery to Mr. Von Kleist, dean of the cathedral of Cam in, who announced its phenomena in the sarn year. It acts as a, reservoir of electricity. If the ball be presented to the prime conductor of the electrical machine, a series of sparks will pass from the machine to the jar, and will, so to speak, accumulate on the interior tinfoil. It would be more proper, perhaps, to say that the inside of the jar becomes in a higher state of excitement than the outside, find in consequence, if, after many sparks have passed into it, the outside is grasped in one hand and the finger of the other presented to the ball, a powerful shock will be felt, having just the force of the sura of the small shocks which have passed into it. The force being in a morn active state inside than out, so.eks through the hest conductors (your arms) to regain its equilibrium ; and so powerful is the effort which electricity makes to be always equal, that should you go on charging a Leyden jar, without discharging also, it would discharge itself through the air, making that its conductor. The little stand also in the illustration is for the demonstration of attraction and repulsion. A bent wire may be inserted in a piece of wood, and two pith balls connected by a bit of silk may be thrown over a hook at its extremity. Take a piece of "sealing-wax and rub it on your coat sleeve, then apply it to one ball, which will instantly Hy to it, and then as suddenly fiy away, and communicate its electricity to the other ball. The explanation of this is, that the sealing-wax, having more electricity than it wants, attracts the pith ball, and when that has got its fill of the same kind of electricity, repels it, thus demonstrating a great, if not the greatest law of tills force, and which, with the simple apparatus we have described, our young readers can prove in a variety of ways ; this law is, that bodies similarly electrified repel each other, while bodies differently electrified attract each other. To change the subject entirely to a seeming wonder, we will tell you how to support a pail of water by a stick, only half of which, or less, rests upon the table. Let A B be the top of the table, and C D the stick which is [to support the bucket. Place the handle of the bucket on the stick in such a manner that it may rest on it in an inclined position, as H ', and let the middle of the bucket be a little within the edge of the table; to keep this apparatus properly in its situation, place another stick, E F G, with the end resting against the bucket at the bottom, its middle, V, resting on the opposite top edge of the bucket, and its other extremity, E, against the first stick, C D, in which a notch must be cut to retain it. The bucket will thus be kept in its situation without inclining to either side, and if not already filled with water, it may be filled with safety.
This article was originally published with the title "Science in Sport" in Scientific American 13, 26, 208 (March 1858)