CHANGE OF LENGTH BY MAGNETIZATION. 7 



more, till, the temperature became nearly constant. The current- 

 supply from the dynamo was then changed for that from the ac- 

 cumulator to repeat the same subsequent processes. In this way, 

 experiments at successively increasing temperatures from the ordinary 

 to the highest were carried out. Our heating coil gave a rise of 

 temperature of about 1000°C in the core by passing a current of 11 

 amperes. 



When the specimen was once heated to a high temperature, it 

 underwent a permanent change with regard to the magnetic change 

 of length ; thus it was necessary to try the experiment at low tem- 

 peratures before our specimens had been heated to high temperatures. 



The sensibility of our apparatus was such that an elongation or 

 contraction of 5 x 10~ 8 of our specimens could easily be observed. 



We tested 6 différent samples shown in the following table : — 



§ 3. RESULTS OF EXPERIMENTS- 



The change of length of our specimen at the temperature of the 

 room (cS c C-17°C) is shown in Fig. 1. 



The full lines represent the curves of the change of length plotted 

 against the internal field (H'= IT — IX) ; the dotted lines refer to 

 the external field. The comparison of the corresponding curves shows 

 us the influence of the demagnetizing force. 



