MAGNETISM AND HEAT. 355 



ON THE DIRECT PRODUCTION OF HEAT BY 

 MAGNETISM. 



Ptoc. R. S. May 24, 1849. 



THE author recites the experiments of Messrs. Marrian, Beat- 

 son, Wertheim, and De la Rive on the phenomenon made 

 known some years ago, that soft iron when magnetised emitted 

 a sound or musical note. 



He also mentions an experiment of his own, published in 

 January 1845, where a tube was filled with the liquid in which 

 magnetic oxide had been prepared, and surrounded by a coil ; 

 this showed to a spectator looking through it a flash of light 

 when the coil was electrised. 



These experiments led to the supposition that when iron 

 is magnetised a molecular change is produced throughout its 

 mass ; if this be the case, a species of molecular friction might 

 be expected to obtain, and by such molecular friction heat 

 might be produced. 



Difficulties present themselves in proving this result, the 

 principal of which is that with electro-magnets the heat pro- 

 duced by the electrised coil surrounding them, might be 

 expected to mask any heat developed by the magnetism. 



This interference, after several experiments, the author con- 

 siders he entirely eliminated by surrounding the poles of an 

 electro-magnet with cisterns of water, and by this means, and 

 by covering the keeper with flannel and other expedients, he 

 was enabled to produce in a cylindrical soft iron keeper, when 

 rapidly magnetised and demagnetised in opposite directions, 

 a rise of temperature several degrees beyond that which ob- 

 tained in the electro-magnet, and which therefore could not 

 have been due to conduction or radiation of heat from such 

 magnet. A series of experiments is given with this apparatus. 



By filling the cisterns with water colder than the electro- 

 magnet, the latter could be cooled by the water while the 

 keeper was being heated by the magnetisation. 



The author subsequently obtained distinct thermic effects 

 in a bar of soft iron placed opposite to a rotating permanent 



A A 2 



