DIRECTION OF CURRENT.--If the current should go through the wire (A)
from right to left, as shown in Fig. 34, the magnet (B) would swing in
the direction taken by the hands of a clock and assume the position
shown in Fig. 34. If, on the other hand, the current in the wire (A)
should be reversed or flow from left to right, the magnet (B) would
swing counter-clock-wise, and assume the position shown in Fig. 36. The
little pointer (G) would, in either case, point in the direction of the
flow of the current through the wire (A).

[Illustration: _Fig. 37._ INDICATING DIRECTION OF CURRENT]

SIMPLE CURRENT DETECTOR.--A simple current detector may be made as
follows:

Prepare a base 3' x 4' in size and 1 inch thick. At each corner of one
end fix a binding post, as at A, A', Fig. 37. Then select 20 feet of No.
28 cotton-insulated wire, and make a coil (B) 2 inches in diameter,
leaving the ends free, so they may be affixed to the binding posts (A,
A'). Now glue or nail six blocks (C) to the base, each block being 1" x
1" x 2", and lay the coil on these blocks. Then drive an L-shaped nail
(D) down into each block, on the inside of the coil, as shown, so as to
hold the latter in place.

[Illustration: _Fig. 38._ THE BRIDGE]

Now make a bridge (E, Fig. 38) of a strip of brass 1/2 inch wide, 1/16
inch thick and long enough to span the coil, and bend the ends down, as
at F, so as to form legs. A screw hole (G) is formed in each foot, so it
may be screwed to the base.

Midway between the ends this bridge has a transverse slot (H) in one
edge, to receive therein the pivot pin of the swinging magnet. In order
to hold the pivot pin in place, cut out an H-shaped piece of sheet brass
(I), which, when laid on the bridge, has its ends bent around the
latter, as shown at J, and the crossbar of the H-shaped piece then will
prevent the pivot pin from coming out of the slot (H).

[Illustration: _Fig. 39._ DETAILS OF DETECTOR]

The magnet is made of a bar of steel (K, Fig. 39) 1-1/2 inches long, 3/8
inch wide and 1/16 inch thick, a piece of a clock spring being very
serviceable for this purpose. The pivot pin is made of an ordinary pin
(L), and as it is difficult to solder the steel magnet (K) to the pin,
solder only a small disc (M) to the pin (L). Then bore a hole (N)
through the middle of the magnet (K), larger in diameter than the pin
(L), and, after putting the pin in the hole, pour sealing wax into the
hole, and thereby secure the t