A Large Leyden-jar
When experimenting with this machine it would be well to have one or more Leyden-jars to accumulate static charges. A large one of considerable capacity is easily made from a battery jar, tin-foil, brass rods and chain, and some other small parts.
Obtain a bluestone battery jar, and after heating it to drive all moisture from the surface, give it a coat of shellac inside and out. With tin-foil, set with shellac, cover the bottom and inside of the jar for two-thirds of its height from the bottom, as shown in [Fig. 11]. Cover the outside and bottom in a similar manner, and the same height from the bottom, and provide a cork, or wooden cap, for the top. If a large, flat cork cannot be had, then make a stopper by cutting two circular pieces of wood, each half an inch thick, the inner one to fit snugly within the jar, the other to lap over the edges a quarter of an inch all around. Fasten these pieces together with glue, as shown at [Fig. 13], and give them several good coats of shellac. Make a small hole at the middle of this cap and pass a quarter-inch rod through it, leaving six inches above and below the cap. To the top of the rod solder a brass ball. At the foot a piece of brass chain is to be made fast, so that several links of it rest on the tin-foil at the bottom of the jar.
To charge a jar from the Wimshurst machine, stand the jar on a glass-legged stool, and connect a copper wire between one of the overhead balls on the machine and the ball at the top of the rod in the stopper of the jar. Make another wire fast to the other ball at the top of the machine, and place it under the jar so that the tin-foil on the bottom touches it. By operating the machine the jar is charged.
To discharge the jar make a T-yoke, as shown at [Fig. 14], by nailing a brass rod fast to a wooden handle and soldering brass knobs, or hammering a lead bullet, on the ends of the rod. Hold one knob against the top knob of the jar and bring the other near the foil coating at the outside, when a spark will jump from the foil to the knob with a loud snap.
A Glass-legged Stool
One of the most useful accessories in playing with frictional electricity will be a glass-legged stool. A stool with glass feet is perhaps too expensive for a boy to purchase, but one may be made at little or no cost from a piece of stout plank, four glass telegraph line-insulators, and the wooden screw-pins on which they rest when attached to a pole.
The general plan of the stool is shown at [Fig. 15], and the top measures twelve by fifteen by two inches. Under each corner a screw-pin is made fast by boring a hole in the wood and setting the pin in glue. The pins are cut at the top, as shown in [Fig. 16], and when they are set in place the glass insulators may be screwed on. The wood-work should be given a few coats of shellac to lend it a good appearance and help to insulate it.