Iron Vane Galvanometers
   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 instrument from Denison University at the left below is typical of German practice ca. 1900. In the middle is a galvanometer made by the L.E. Knott Apparatus Co. of Boston; in the 1916 catalogue a similar instrument, executed in metal instead of wood, is listed at $6.50. The Transylvania instrument is unmarked. All three pieces of apparatus were designed to be used on the lecture bench, unprotected from air currents
              Denison University                                  St. Mary's College                                  Transylvania University
 
   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 air currents. 

   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.

                                                                                                                             St. Mary's College
 
                                Amherst College                                                                         Denison University

The Breguet-type galvanometer at the right, above was bought by Denison University about 1887
from J.W. Queen & Co. of Philadelphia, and was made by Deprez et Carpentier of Paris.




  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. 
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