Mechanical Equivalent oj Heat 



149 



•agreement with the electrical equivalent would be an indication of 

 the accuracy with which the practical electrical units realise tlieir 

 intended values. 



Principle of the Experiment. 



The method to be described,^ we l)elieve, has not, \ycon previously 

 applied. Bailie and Fery^ proposed to generate heat, not by stir- 

 ring water, but by placing a copper cylinder in a rotating mag- 

 netic field produced by polyphase currents. Their proposal is 

 open to the objection that the lines' of magnetic force would ])rol>- 

 ably have a component of motion in the direction of the axis of 

 the copper cylinder. Heat would then be generated to which there 

 was no corresponding couple. We have obtained a rotating mag- 

 netic field with a known and fixed axis, A, by the rotation of an 

 electro-magnet. A copper cylinder is mounted (see Figs. 1 and 2) 

 .so as to be capable of rotation a.bout a vertical axis, B, and is 



2. Comptes Rendus., Vol. CXXVI., p. 1494 (1S9S). 



Fig. 1 



