Usage/History: The tangent galvanometer was introduced
by Servais Mathias Poullet in 1837. A current flowing through
the coils will deflect the needle of the compass. The current
strength is proportional to the tangent of the angle of the deflection.
The present instrument could be used as a teaching device for
physics classes, for demonstration of the tangent law (the relation
between the current flowing through the coils and the tangent
of the angle of deflection of the compass). Such instruments
would also be used to plot the horizontal component of the earths
magnetic field in the laboratory-an important consideration in
any laboratory where studies involving magnetism are to be conducted.
Some contemporary/early descriptions of the Tangent Galvanometer
and its use are provided below:
Description: The windings (20, 40, 80, and 160) are
wrapped in a U-shaped channel in an 8 7/8" o.d. cast aluminum
ring. Slots in the back of the ring allow the coil diameters
to be measured. There is a 3 1/4" diameter chrome finished
compass with raised polished metal numbers and divisions against
a black plate, mounted on a center rod centered in the coils,
the whole mounted in the center of an 8"diameter black painted
wood base. Two chromed brass posts at the front of the base connect
through contact plugs on a hard rubber rectangle on the base.
An additional set of heavy coils are provided with separate binding
posts at the back of the instrument. The entire instrument is
mounted on a heavy cast brass tripod equipped with leveling screws.
The tripod and ring are finished in black wrinkle enamel. Humboldt
S-T-C brass tag: 3877.
References:
1. Turner, 19th Century Scientific Instruments, pg
177.
2. Minor, Ralph S., Physical Measurements, A Laboratory
Manual in General Physics for Colleges: Part 2, Magnetism and
Electricity, Sound and Light 3rd ed, Associated Student's
Store, Berkeley (1956) pp 9-13, 27-35.
