thick 5/8-in. wide and 11 in.
long across the sides of the ring with their upper edges passing
exactly through the center of the ring. An ordinary pocket
compass, about 1-1/4 in. in diameter, is fitted in these strips so
that the center of the needle or pointer will be exactly in the
center of the ring and its zero point mark at the half-way point
between the two strips. Put the ring in place on the base, as
shown in the sketch, and connect the two ends of the wire to two
binding-posts that are previously attached to the base. Coat the
entire surface with brown shellac. Any deviation from the
dimensions will cause errors in the results obtained by its use.
Remove all pieces of iron or steel and especially magnets in the
near vicinity of the instrument when in use. Place the
galvanometer on a level table and turn it until the needle,
pointing north and south, and swinging freely, lies exactly in the
plane of the coil, as shown in the cut. The needle then will point
to zero if the directions have been followed closely. Connect one
[Illustration: Tangent Galvanometer]
cell of battery to the instrument and allow the current to flow
through the coils.
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