We will now take up the method of revolving the two plates in opposite directions. Purchase two cast-iron screw wall pulleys 4" diameter and remove the grooved wheels by knocking out the pins. Get a piece of iron rod 12" long which will fit tightly into the holes in the wheels. Bend the rod in the middle at right angles for 3" and then straight again for 3", making a crank. Take a piece of pine 5" wide and 10" long and 1" thick, D' (Fig. 7), and screw it to the bottom of the base H, allowing it to project 6" beyond the end of the base. Two upright supports, E' (Fig. 7), 3" wide, 5" high and 1/2" thick are now screwed to the sides of D' at the far end, and \" round notches are cut in the center of the top edges to hold the axle of the pulleys. The pulleys are now driven on the iron rod, the first two within 1" of the crank and the second 1" from the other end with 4" between them. A 3" piece of broomstick is now bored and forced on the crank for a handle. The whole thing can then be placed in the notches provided, and held in place with small strips of wood, previously notched, screwed over them.

Fig. 5.

Having revolved the pulleys with the crank and found that they turn truly and easily, we will remove them from the standards and put them aside while we assemble the machine. Take the base H (Fig. 7) and screw the rear standard I firmly in its place. The steel axle K (Fig. 3) is now slipped into the hole in I, and the two glass plates and spools are slipped onto the rod K, with enough cardboard washes between them to separate them 3/16". The plates are set face to face with the spools outward. Support the loose end of K and guide it into the hole in the front standard I', which is then moved into position and screwed in place. The ends of K should project 1" beyond the outside faces of the two standards. The two neutralizing bars must now be tipped at each end with a small metallic brush. This can be made of either tinsel from a card of pearl buttons, or of very thin sheet copper. The tinsel or copper is cut into strips 1/16" wide and \\" long, about 15 being needed for each brush. They are hunched together and 1/2" of the length is fastened to the ends of the bars by whipping them with fine wire. The bars having been thus prepared, the wooden block C, to which they are attached, is thrust onto the end of K until the tinsel brushes just touch the tin-foil sectors on the plates. They should touch the middle of the sectors, and any adjustments should be made by bending the wire arms. The lighter they touch the sectors, the better, so long as they are in contact during the entire revolution of the plates.

Fig. 6.

The blocks C should be turned on the axle K until the bars lie at an angle of 45 degrees from the perpendicular and 90 degrees with each other. The front bar should slant from right to left and the rear bar vice versa. The hand rubber rods S (Fig. 4) are now set in the holes at each end of the base, H, being forced to the bottom and glued. When these are dry, insert the two plugs T (Fig. 4) in the tips of the tubes, allowing the end of the machine screw to project 1/2". Slide the combs U, Fig. 4, into place, so that they embrace the sides of the glass plates, and slip the rings of U over the projecting ends of the screws. The rings in the ends of the arms, W, are set on top of those of thecombs, and one of the brass balls is screwed down on both, clamping all firmly.

A convenient method of swinging the arm Y is shown in Fig. 7. A small hole is drilled at the bend of Y, and a copper wire having a short cylinder of wood attached, is inserted in this hole and soldered. One handle is sufficient. In order to take the strain off the arms, W, they may rest on a length of 1/2" glass tube, as shown in Fig. 7, the tube being clamped to the face of the standard, I, with a strip of brass.

Fig. 7.

The only thing that now remains to be done to complete the machine is to connect the spools and pulleys by belts. Get two pieces of \" round sewing-machine belt 32" long each. String the belt around the spools and in the grooves of the pulleys, and draw the ends of each belt together until within an inch of each other, having the rear belt crossed. Punch a little hole 1/4" from the two ends of each belt, and, having thrown them off the grooved pulleys, put the ends together and stick the point of a large double-pointed tack through the holes, and bend the points together with a pair of pliers. The belts may now be sprung back onto the grooved pulleys, and should then be fairly tight, but not so much as to spring the shaft K. As the belts must remain parallel to the plates while running, it is desirable to cut round grooves in the spools with a half-round file to keep the belts from wandering from the center. The machine itself is now completed, but as in experimenting it is much more satisfactory to have condensers, I will describe a simple method of making them.

Get two wide-mouth pint jars, such as candy dealers use for storing stick candy. They should be of white glass and fairly thick. These jars should be washed clean and then shellacked all over and covered with tin-foil inside and outside, including the bottoms, up to 2/3 of their height. Two flat, thick corks to fit the mouths of the jars are now procured, and two circular pieces of cigar-box wood, a little larger than the mouths of the jars, are cut out. The wooden circles are glued to the tops of the corks, and both are shellacked.

From the remainder of your No. 10 brass wire cut two pieces 8" long, and tip with the two remaining brass balls, as described before. A hole is pierced in the center of each cork and cap, and the brass rods are pushed through the holes to a depth of three inches. The rods should fit tightly in the corks, so that they cannot drop down. A piece of thin, bare copper wire about 8" long is now soldered to the lower end of each brass rod, and the corks and rods are set in the mouths of the jars, taking care that the copper wires touch the inside coatings of the jars. The condensers being now completed are set on the base H, as shown in Fig. 7, the brass rods being in contact with the arms W, and the bottoms connected with each other by a strip of tin foil pasted on the base.