is bent as
shown. On this horizontal part is fastened the leaf. These should be
made of aluminum leaf, or of Dutch metal. The former will stand more
rough handling than the latter. Goldleaf is used for very sensitive
instruments. It is a little too delicate for unskilled hands.

[Illustration: Fig. 113.]

[Illustration: Fig. 114.]

246. To cut the aluminum leaf, place it between two pieces of paper,
then cut paper and all into the desired shape. The piece should be about
3 in. long and 1 in. wide. Fold this across the middle, and stick it to
the underside of the wire (Fig. 113). Saliva will make it adhere to the
wire, if you have nothing better.

APPARATUS 142.

_247. To Show Where a Charge of Static Electricity Resides._ Fig. 114.
This shows a tin baking-powder box placed upon a hot tumbler. A moist
cotton thread is hung over the edge of the box. (See experiments in
text-book.) The box will become charged by touching it with a charged
body. The thread will show whether the charge resides upon the inside or
upon the outside of the box.

APPARATUS 143.

[Illustration: Fig. 115.]

_248. Support for Electrified Combs._ Fig. 115. In the study of static
electricity, ordinary ebonite combs can be used to great advantage. A
bent hairpin will serve as a cradle to support them. A silk thread may
be tied to the wire, but a narrow silk ribbon is better than thread, as
it will hold the comb steady.

CHAPTER XIX.

ELECTRIC MOTORS.

_249. An Electric Motor_ is really a machine. If it be supplied with a
proper current of electricity, its armature will revolve; and, if a
pulley or wheel be fastened to the revolving shaft, a belt can be
attached, and the motor made to do work. There are many kinds of motors,
and many simple experiments which aid in understanding them. All that
can be done here, however, is to show how to make simple motors. (See
text-book for experiments.)

APPARATUS 144.

_250. Electric Motor._ Fig. 116, 117. Fig. 116 shows a plan or top view,
and Fig. 117 shows a side view, with a part of the apparatus removed,
for clearness.

The base, B, is 5 x 4 x 7/8 in. The upright, U, is 3-1/2 x 1-1/2 x 1/2
in., and is nailed or screwed to B. The binding-posts, X and Y are like
App. 46. 4 is a screw binding-post.

251. The Field-Magnets, as the large electro-magnets on a motor are
called, are made of 5/16 machine-bolts, 2-1/2 in. long. The washers are
1-1/2 in. apart inside. (See App. 88 for f