(See App. 9.)

203. Hints About Adjusting. If you have the right spring to the part F,
of the armature, you will have no trouble. It must not be so weak that
it allows L to strike upon the poles, as the residual magnetism
(Text-book) will hold L down after the current has ceased to pass. No
springs are necessary, if your tin is right. Do not have L too far away
from the poles. The distance is regulated by the position of V. If you
have trouble in getting it to work see App. 122. The poles must be
opposite in nature.

APPARATUS 122.

[Illustration: Fig. 96.]

_204. Telegraph Sounder._ Fig. 96. The magnets, connections, etc., are
like those of App. 121, no binding-posts, etc., being here shown. The
armature is straight, however, the part F resting upon D. A hole is made
in the end of F, and through this is a screw or nail, S. The hole must
be large enough to allow S to pass through easily. This acts as a
bearing or pivot. L is kept up against V by the rubber-band, J, one end
of which passes around the end of L; to the other end of J is a thread,
which is tied around a screw-eye, K. By turning the screw-eye, the band
may be made to pull more or less upon L. In this way the apparatus may
be regulated according to your battery. The general dimensions and
explanations are given in App. 121. D is made of such a height that it
will bring L about 1/8 or 3/16 in. above the poles.

APPARATUS 123.

[Illustration: Fig. 97.]

_205. Telegraph Sounder._ Figs. 97 and 98. This apparatus looks a little
more like a regular sounder than App. 121 and 122, but it is much harder
to make and adjust. In this the lower nuts of the bolts are not sunk
into the base, and the magnets are made of 2-in. bolts. If you change
this and fasten them like App. 89 and 90, it will simply change the
dimensions of the small parts. The sizes given are for this particular
instrument.

Fig. 97 shows a perspective view, and Fig. 98 is a plan or top-view of
it, with dimensions.

[Illustration: Fig. 98.]

206. The Base, B, is 6 x 4 x 7/8 in. The magnet, M, is explained in App.
89. Its wires are attached to the binding-posts like App. 46. The
armature, A, is 2-1/2 x 3/4 x 1/8 in., and made as described in App. 71.
The piece, D, is 2-1/2 x 1-3/8 x 1/2 in., and is screwed to B from
below, after the two uprights, C, are nailed to it. The uprights, C, are
2-3/4 x 7/8 x 1/2 in. They are nailed to D. The nail, N, runs through
both uprights, and acts as the