The Driving-Wheels are turned out of wood on a lathe. They are seven inches in diameter and seven-eighths of an inch thick. A groove should be turned in the edge to carry a small round leather belt. The wheels are mounted on a wooden axle made from a round curtain-pole. They are glued to the axle and arranged so that the grooves will fall directly underneath the pulleys turned in the bosses.
Fig. 39.—The Driving-Wheels and Axle.
The ends of the axle pass through the uprights, five inches above the bottom.
The front end of the axle is fitted with a crank and a handle.
Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.
The plates are mounted on short iron axles passing through the top of the upright into the brass bushings. One end of each of the axles is filed flat where it passes through the wood upright so that it may be firmly held by a set-screw and prevented from revolving.
Fasten a small fiber washer to the center of one glass disk so that it will separate the plates and prevent them from touching when revolving.
The collectors, quadrant rods, etc., are mounted on glass rods one inch in diameter. The bottoms of the rods fit in holes (H H) bored in the cross-pieces of the base, Figure 37. The upper ends are each fitted with a brass ball two inches in diameter. The balls are mounted on the rods by soldering a piece of brass tubing to the ball and slipping it over the rod. The rods should be of the proper length to bring the center of the balls on a line with the center of the plates.