aratus. The base is 5 x 4 x 7/8 in. At its front end are three
binding-posts. The pasteboard band, G, is 1-1/4 in. wide and 6 in. in
diameter. Cut the pasteboard 21 in. long and 1-1/4 in. wide, then bend
it into the form of a circle. There will be a lap of about 3 in., and
you can make it solid by sewing the two ends together at the lap.

[Illustration: Fig. 90.]

183. The Coils maybe made of No. 24 insulated copper wire, which should
be wound on before fastening G to the base. There are two separate
coils, one having five turns and the other ten turns. Leaving a 6-in.
length, A, for connections, wind five turns of wire on to G, putting
them on clockwise; that is, pass them over the top of G from left to
right. Tie thread around G and the wire to hold them together after you
have five turns on, and cut a 6-in. end, B. Now begin with C, and wind
on ten turns, bringing the end of them out at D. Punch holes, F, through
G on each side of the coils, run twine, T, through them, and tie T on
the outside of G. Do this in three or four places, to firmly hold the
coils.

184. Fastening Coils to Base. The band and coils will not rest squarely
upon the base, so cut two pieces of wood, E, about 2 x 1/4 x 1/4 in., to
be put under G, one being on each side of the coil. Make holes through
the base, pass strong cord, H, through them, and over the inside of G,
then tie under the base. This should tightly squeeze E, and hold G
upright and firm.

185. The Connections. A and B are the ends of the five-turn coil; C and
D are the ends of the ten-turn coil. If the battery-wires are connected
with X and Y, the current will pass through five turns of wire; if
connected with Y and Z, it will pass through ten turns; if with X and Z,
the current will pass through the entire fifteen turns. In this way the
strength of the magnetic field about the coil can be regulated, and its
effect upon the magnetic needle, M, changed.

186. To Support the Needle, glue or sew two strips, I, to G. They must
be in such a position that the poles of M will be as nearly as possible
in a horizontal line drawn through the center of the circle, G. After
you have made M (App. 66), and have found where the pieces, I, should
be, fasten them to G, and then to I glue a pasteboard strip, J, about
1-1/4 in. wide. Run a pin, P, up through the center of J to support M.

187. The Magnetic Needle, M, should not be over 1 in. long for this kind
of an instrument. (See App. 66 for