pindle. About 1/2 in.
from each end of this wire are soldered two smaller brass wires
which in turn are soldered to a strip of light tin 1/4 in. wide
and 2-5/8 in. long. The lower edge of this tin should be about 1/2
in. from the spindle. The pointer is soldered to the spindle 1/4
in. from one end. All of these parts should be brass with the
exception of the strip of tin. Another strip of tin, the same size
as the first, is soldered to two brass wires as shown in Fig. 4.
These wires should be about 1 in. long.

The spindle of the pointer swings freely between two bars of
brass, G, 1/16 in. thick, 1/4 in. wide and 2-1/2 in. long. A small
hole is countersunk in one of the bars to receive one end of the
spindle and a hole 1/8 in. in diameter is drilled in the other and
a thumb nut taken from the binding-post of an old battery soldered
over the hole so the screw will pass through when turned into the
nut. The end of the screw is countersunk to receive the other end
of the spindle. A lock nut is necessary to fasten the screw when
proper adjustment is secured. A hole is drilled in both ends of
the bars for screws to fasten them in place. The bar with the
adjusting screw is fastened on the back so it can be readily
adjusted through the hole H, bored in the back. The pointer is
bent so it will pass through the U-shaped cut-out and up back of
the board B. A brass pin is driven in the board B to hold the
pointer from dropping down too far to the left. Place the tin,
Fig. 4, so it will just clear the tin, Fig. 5, and fasten in
place. The magnet is next placed with the ends of the coil to the
back and the top just clearing the tin strips. Two binding screws
are fitted to the bottom of the back and connected to the
extending wires from the coil.

The instrument is now ready for calibrating. This is done by
connecting it in series with another standard ammeter which has
the scale marked in known quantities. In this series is also
connected a variable resistance and a battery or some other source
of current supply. The resistance is now adjusted to show .5
ampere on the standard ammeter and the position of the pointer
marked on the scale. Change your resistance to all points and make
the numbers until the entire scale is complete.

When the current flows through the coil, the two tinned strips of
metal are magnetized, and being magnetized by the same lines of
force they are both of the same polarity. Like poles repel each
other,