4 Dr. J. G. Gray and Mr. A. D. Ross 



seen that the necessity for rendering the specimen neutral is 

 brought about by the thermal treatment, and not by any 

 magnetic treatment to which the specimen has been exposed. 



Table I. 



Yalue of H in 

 c.g.s. units. 



Value of I in c.g.s. units. 



Given by specimen Given by specimen 

 after thermal treatment.! in neutral condition. 



2 

 4 

 6 

 8 

 9 



22 



67 



13(> 



220 



275 



15 



47 



100 



17-3 



206 



So far, in describing the phenomena of this " Sensitive 

 State," attention has been confined to the case o£ steel 

 annealed at 900° C. It is not necessary, however, for the 

 production of this state that the temperature change should 

 be great : even a moderate alteration in the temperature is 

 sufficient to bring about the effect to a marked extent. 

 Moreover, it is not necessary that the alteration should 

 consist o£ a step up in temperature followed by a step down 

 of the same amount. Experiment Las shown that if the 

 temperature of a specimen, which is initially neutral, is 

 altered from any one temperature to a second, the specimen 

 assumes the '• Sensitive State " at the second temperature. 

 The further f.act was established that once the specimen was 

 rendered neutral it remained neutral provided that the 

 temperature was maintained constant. In other words, the 

 " Sensitive State " cannot be induced by prolonged exposure 

 of the specimen to either a high or a low temperature ; it is 

 brought on in the process of heating or cooling the specimen. 



Reference may here be made to the interesting fact that 

 once the " Sensitive State " has been induced in a specimen, it 

 cannot be got rid of except by submitting the specimen to the 

 demagnetizing process. Thus a specimen of annealed steel 

 was tested after having been laid aside for a period of several 

 weeks, and gave results precisely similar to those yielded by 

 it when in the freshly annealed condition. Further experi- 

 ments revealed the fact, which is of great importance in 

 connexion w T ith what immediately follows, that once a spe- 

 cimen of steel in the sensitive condition has been exposed to 

 a magnetizing force in one direction, th? " Sensitive State " 



