e base. Through its center is a hole for the
screw-eye, S I, which is the regulating-screw. F is a piece of copper,
brass, or tin, 5/8 x 1-3/4 in. It is held to the base by the screw, S,
and is bent so that it presses tightly against S I. Through F is a
screw, R, to hold one end of the primary coil.

149. Adjustment and Use. The battery wires should be joined to W and X,
and the handles to the secondary coil at Y and Z, unless a regulator
(App. 103) is used. Let us consider the primary circuit. If the current
enters at W it will pass through the primary coil and out at X, after
going through 5, R, F, S I, B, E, and C. The instant that the current
passes, the bolt becomes magnetized; this attracts A, which pulls B away
from the end of S I, thus automatically opening the circuit. B at once
springs back to its former position against S I, as A is no longer
attracted; the circuit is closed and the operation is rapidly repeated.
B should press gently against S I, which must be screwed back and forth,
until the best results are obtained. While not in use A should be about
1/8 or 3/16 in. from the bolt-head. The armature, A, should vibrate back
and forth very rapidly. If this coil gives too much shock with one cell
of App. 3 or 4, put a regulator (App. 103) between Y and one of the
handles (App. 101).

APPARATUS 101.

_150. Handles for Shocking Coils._ Fig. 79. Ordinary sheet-tin makes
good handles. Cut 2 pieces, each 6 x 4-1/2 in., and connect a stout
copper wire to each. This may be done as suggested in Fig. 79, where the
tin laps tightly over the bare end of the wire, or by punching 4 or 5
holes through the tin, and weaving the wire back and forth through the
holes. Be sure that a tight and permanent connection is made. The wires
joined to the handles should be about No. 20, and be 4 or 5 feet long.
Roll the tin into a cylinder, so that the connection will be on the
inside.

[Illustration: Fig. 79.]

APPARATUS 102.

_151. Handles for Shocking Coils._ Very neat handles may be made from
4-in. lengths of brass tubing that is about 3/4 in. in diameter. The
wires leading to the coil may be soldered to the handles.

APPARATUS 103.

_152. Current Regulator for Induction Coils._ Fig. 80. If your coil
gives too much of a shock with one cell of App. 3 or 4, you can pull the
carbon and zinc partly out of the solution to weaken the shock, or you
can use a water regulator. T is an ordinary tin tomato can nearly filled
w