Fig. 184. SINE GALVANOMETER.
Galvanometer, Sine.
A galvanometer whose measurements depend upon the sine of the angle of
deflection produced when the coil and needle lie in the same vertical
plane.
The needle, which may be a long one, is surrounded by a coil, which can
be rotated about a vertical axis passing through the point of suspension
of the needle. Starting with the needle at rest in the plane of the
coil, a current is passed through the coil deflecting the needle, the
coil is swung around deflecting the needle still more, until the needle
lies in the plane of the coil; the intensity of the current will then be
in proportion to the sine of the angle through which the coil and needle
move.
In the galvanometer M is a circle carrying the coil, N is a scale over
which the needles, m and n, move, the former being a magnetic needle,
the latter an index at right angles and attached thereto; a and b are
wires carrying the current to be measured. The circles, M and N, are
carried by a base, O, around which they rotate. H is a fixed horizontal
graduated circle. In use the circle, M, is placed in the magnetic
meridian, the current is passed through the coil, M; the needle is
deflected; M is turned until its plane coincides with the direction of
the needle, m. The current strength is proportional to the sine of the
angle of deflection. This angle is measured by the vernier, C, on the
circle, H. The knob, A, is used to turn the circle, M.