ssary to
make this machine, and the glass should be of sufficient size to
cut a circular plate 16-in. in diameter. A hole must be made
exactly in the center of each plate, and this should be done
before cutting the circle. One of the best ways to make the hole
is to drill the glass with a very hard-tempered drill, the cutting
edge of which should be kept moistened with 2 parts turpentine and
1 part sweet oil while drilling. The hole is to be made 3/4 in. in
diameter. The circle is then marked on each plate and cut with a
glass cutter. The plates are trued up, after they are mounted, by
holding a piece of emery wheel to the edges while they are
turning. Water should be applied to the edges while doing the
work.

The sectors are cut from tinfoil, 1-1/2 in. wide at one end, 3/4
in. at the other, and 4 in. long. A thin coat of shellac varnish
is applied to both sides of the plates, and 16 sectors put on one
side of each plate, as shown in Fig. 1. The divisions can be
marked on the opposite side of the plate and a circle drawn as a
guide to place the sectors at proper intervals.

The sectors should lie flat on the glass with all parts smoothed
out so that they will not be torn from their places as the plates
revolve. The shellac should be tacky when the pieces of tinfoil
are put in place.

The collectors are made, as shown in Fig. 2, from about 1/4-in.
copper wire with two brass balls soldered to the ends. The fork
part is 6 in. long and the shank 4 in. Holes are drilled on the
inside of the forks, and pins inserted and soldered. These pins,
or teeth, should be long enough to be very close to the sectors
and yet not scratch them when the plates are turning.

The frame of the machine is made from any kind of finished wood
with dimensions shown in Fig. 3, the side pieces being 24 in. long
and the standards 3 in. wide. The two pieces, C C, Fig. 3, are
made from solid, close grained wood turned in the shape shown,
with the face that rests against the plate 4 in. in diameter, and
the outer end 1-1/2 in. in diameter, the smaller end being turned
with a groove for a round belt. Before turning the pieces a hole
is bored through each piece for the center, and this hole must be
of such a size as to take a brass tube that has an internal
diameter of 3/4 in. The turned pieces are glued to the glass
plates over the center holes and on the same side on which the
sectors are fastened. Several hours' time will be required for the
gl