Now this repulsion of similarly charged particles is demonstrable by a straightforward experiment, whose simplicity of description is in nowise proportionate to its entertainment. In truth, it consists merely of blowing a soap-bubble and catching it upon an excited stick of glass or wax. The bubble becomes electrified, its myriads of particles repel one another, and the beautiful globe expands in size, possibly to breaking point.
7. Scratch any design or word upon a small sheet of indiarubber—such as is used in the manufacture of mats—and then dust over the surface a thoroughly-shaken mixture of red-lead and sulphur. When all excess of the powder has been blown away, the design should appear in grains of red-lead, showing to excellent effect on the gray rubber ground.
8. By the following method a spark of sufficient intensity to light house gas may be obtained from brown paper. Support a salver on four well-dried inverted tumblers, placing a rubber ring between the tray and each glass, and twist a copper wire round a spoon which rests on the tray. The other end of this wire must be held—insulated from the fingers by a piece of indiarubber or by the ordinary covering of the wire—just over the gas-jet, whilst about 1⁄8-inch away is held another piece in metallic connection with the hand; that is, in reality, via the operator’s body with the earth.
Now, if the gas be turned on slightly and a piece of warm brown paper, electrified by stroking vigorously with a dry brush, be placed on the salver, a spark should pass across the 1⁄8-inch gap and ignite the escaping gas. If the spark does not pass at once, approach the wire extremities slightly closer together.
Fig. 1.—Raising paper by touching wooden lath with electrified sealing-wax.
9. The following experiment owes its origin to Gray—an early worker in the field of static electricity: Erect two dry tumblers with a piece of waxed cardboard between, after the fashion shown in [Fig. 1], and lay a lath on the top glass. Beneath one end of the lath spread small pieces of paper, over an ebonite or wood surface supported on another inverted glass. Then if a stick of sealing-wax, which has been vigorously rubbed with flannel, be approached to the other end of the lath, the particles of paper will fly backwards and forwards between the lath and the ebonite surface—on which they would normally rest.
10. A simple trick, but one nevertheless causing considerable amusement to spectators, may be arranged in the following manner: Bore a hole carefully at the middle of a wooden meat skewer (A, [Fig. 2]), of such size as to take a bone knitting-needle tightly (B, [Fig. 2]).
Sharpen the blunt end of the skewer and mount it so as to turn easily between bearings erected on inverted wine-glasses. These may consist of two wood blocks (C, [Fig. 2]), in each of which a shallow conical hole is made to receive the points of the skewer. On these stand weights (E, [Fig. 2]) to keep wood-bearings firm. When this is in position and swings easily, adjust the needle until it balances exactly. It should be at right angles to the skewer, and may be fixed in position, if necessary, with glue or sealing-wax.
