Fig. 6.—The electrophorus.
Electrophorus
Our Leyden jars have been constructed to store electrical energy, and the gold leaf electroscope to indicate its presence. But we do not yet possess the means of producing this energy in any considerable quantity.
To make an instrument for this purpose proceed as follows: Clean the inner surface of a circular tin lid—diameter 6 inches or 7 inches, and about 5⁄8-inch deep—(A, [Fig. 6]), and in the center stand upright on its head a brass screw, whose point has been filed down until it nearly reaches to the level of the upper edge of the lid (B, [Fig. 6]). Then carefully pour in melted lead or zinc to a depth of 1⁄8-inch. This process is not absolutely necessary, but is advisable if the metal be available and the extra trouble is not distasteful.
When this metal has thoroughly cooled, melt up sufficient rough resin to just overflow the tin, pour it in and allow to solidify properly without the least disturbance (D, [Fig. 6]).
For the upper part of the electrophorus, take a disc of tin or brass, absolutely flat, and of the same diameter as the resin surface (E, [Fig. 6]). In the center of its upper side solder a short piece of brass tube (F, [Fig. 6]), the correct internal width to fit tightly on a 12-inch length of polished wood rod, cut, say, from a walking-stick (G, [Fig. 6]).
The drawing shows the general arrangement of this electrophorus, wherewith, by the help of a piece of fur, electricity may be generated. A small cavity must be made in the resin, just above the screw (H, [Fig. 6]), so that the point of the latter may be clearly seen.
Fig. 7.—The discharger.