Ampere's Frame

   Ampere's Frame (or stand) is a device for demonstrating the effect of the earth's magnetic field on current-carrying coils of wire. The apparatus at the University of Cincinnati, made by Max Kohl of Chemnitz about 1900, is part of a larger set of apparatus with other configurations of conductors. Similar pieces of apparatus can still be purchased, although the contact to the rotating conductor is no longer made through pools of mercury.
         University of Cincinnati                          University of Cincinnati                          Allegheny College

   The four pictures below show the same piece of apparatus with different conductors. The system was made by the firm of Ferdinand Ernicke and is in the collection at the Virginia Military Institute in Lexington, Virginia. Once more, the contact to the freely-rotating conductors is through mercury contacts. In one of the four cases, the dipole magnetic moment of the wire frame is zero. Note the switch for reversing the current through the wire frame.
   The Ampere's frame at the left was made by Leybold of Germany toward the beginning of the twentieth century. 
Current passes through the two parts of the coil in opposite directions, and hence the net magnetic moment of the combination is zero; it can be oriented in any position relative to the horizontal component of the earth's magnetic field, and will not experience any torque.

   The apparatus is in the collection of the University of Vermont.

   At the left is Pouillet's version of Ampere's frame, listed in the 1853 catalogue of Lerebours et Secretan of Paris. It was purchased in the second half of the 1850s by Prof. Frederick Barnard, the second Professor of Natural Philosophy at the University of Mississippi, 1854-1861.

   It is currently on display at the University Museum in Oxford, and forms part of the Millington/Barnard Collection. 

   Pouillet was the inventor of the tangent galvanometer in 1837.

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