| The Iron Vane Galvanometer is a simple instrument, primarily
designed for demonstration lecture use. The example at the right, probably
locally-built at Washington and Jefferson College in Washington, Pennsylvania,
shows a compass needle pivoted in the middle of a coil. Passing a current
through the coil exerts a torque on the needle, which tries to align itself
with the resulting magnetic field. A gravitational counter-torque eventually
produces an equilibrium. The calibration of the instrument is clearly non-linear.
In the three instruments below a small (hidden) bar magnet is placed horizontally within the coil.
| The three iron-vane instruments at the right and below
are examples of the Breguet upright galvanometer. These small, table-top
instruments are designed to be used with a glass dome to protect them against
The bar magnet is pivoted in the middle of the circular coil. Usually the magnet is covered with a copper disk (just visible in the Amherst instrument) which supplies eddy-current damping.
The St. Mary's and Amherst instruments were made by Ducretet of Paris. The letters "A.C.P.L." on the Amherst galvanometer stand for "Amherst College Physics Laboratory"; as an undergraduate at Amherst in the 1950's we had to record these numbers on circuit diagrams, "in case we needed to repeat the experiment." We never did.
Breguet's name is also associated with a form of dial telegraph.
The iron-vane galvanometer at the right is simlar to those immediately above. It was made by J. H. Bunnell & Co. of New York, and is 10 cm high. The faint ring left by the missing glass dome can be seen faintly on the base, just outside the current-carrying coil.
This instrument is at Westminster College in western Pennsylvania.
||The dual-range lecture table galvanometer at the left has been given a new lease on life by having its scale repainted so that students in lecture rooms at Cornell University can see the effects of a electric current. This iron vane galvanometer can be found in the 1900 Max Kohl catalogue. It cost 45 marks (about $10); the original catalogue description noted that the coil was wound with "stout and thin wire" to get the two sensitivities.|