Humboldt State University
Robert A. Paselk Scientific Instrument Museum
W.M. Welch Scientific Company
Provenance: Humboldt S-T-C; c.1930
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.
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.
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.