When making the cover, observe the directions on [page 20], then round the edge to a good half-circle. Test the cover also to see that it is flat, especially on its under side, for to get good sparks, the tinfoil and rosin must come just as close together as possible. Cut two circles of tinfoil 4-1/2" in diameter. Smooth them carefully on a piece of paper, spread glue thinly on the cover, lay the tinfoil on the glue, and smooth it with the fingers. Press the edges as smooth as possible because electricity escapes easily from sharp corners. Cover the larger open spaces with bits of tinfoil. Hard rubber (ebonite), being a non-conductor of electricity, makes the best handle. A piece of an old rubber comb or a fountain pen can be used for this purpose.
To get a spark of electricity, rub the rosin with soft leather, fur, or woolen; place the cover on it; touch the top of the cover with the finger (to remove the negative electricity); lift the cover by the top of the handle; bring the edge of the cover near a finger, or other conductor, and a spark will fly off with a snap. It is a miniature flash of lightning. Some books on electricity describe many other experiments which can be tried.
ELECTROPHORUS — Plate 18
[WATERWHEEL—][Plate 19].
This waterwheel is designed to be placed in a flowing stream. A longer trough might well lead the water into this one so as to get greater speed.
Make the trough first, being careful to make a good fit where the sides nail to the bottom. Nail the top 5" from the end where the wheel is placed. The upper corners of the axle blocks are to be cut off 1". The center of the 5/16" hole for the axle is 7/8" from the lower edge. When nailing the axle blocks in place, put a dowel or lead pencil thru the holes to help in nailing the blocks exactly opposite each other.