4G2 PROCEEDINGS OF THE AMERICAN ACADEMY 



IN'TESTIGATIONS ON LiGlIT AND IIeAT, MADE AND PUBLISHED WHOLLY n DJ PABT WITH 



Appuopriation from tue Kumfoed Fund. 



XXII. 



THE EFFECT OF TEMPERATURE ON THE MAGNETIC 

 PERMEABILITY OF IRON AND COBALT. 



By John Trowbridge and Austin L. McRae. 



Communicated May 13, 1885. 



These experiments were made with a view, — 



1. To repeat Professor Rowland's experiments.* 



2. To determine the change of the magnetic permeability with 



a. The change of temperature. 



b. The variation of the size and thickness of the rinjrs. 



c. Tlie temper of the substance. 



3. To determine whether the outer layer of the substance shielded 

 the inner layers from magnetic influence. 



The method of experiment was the same as Rowland's, except that 

 the small coil around the horseshoe magnet used to bring the needle 

 to rest was taken out of the circuit of the induced current, and a 

 thermal junction of copper and german silver was placed iu the lamp 

 used with the mirror galvanometer, and the circuit made through the 

 galvanometer and a key. This circuit was independent of the induced 

 current circuit. By closing the key, a thermal current could be sent 

 throu»li the galvanometer. This arrangement served the same pur- 

 pose as the .sliding coil on the magnet, and was more convenient. 



The measurements are made iu the C. G. S. system of absolute 

 units. 



The symbols used are : 



II = intensity of the magnetizing force. 



B = magnetic induction, or the number of lines of force passing 



throuerh a unit of area. 

 M = magnetic permeability. 



» Phil. Mag., 1873, 1874. 



