On the Time-Lag in the Magnetisation 

 of Iron. 



By 

 Yoshijiro Kato, Rigakushi. 



"With Plates VII— XV. 



Preliminary Remarks. 



A piece of soft iron, subjected to a change in the weak magnetic 

 field in which it has been exposed, does not obtain its magnetic 

 state corresponding to the change at once. When the intensity 

 of the field is increased, a certain immediate increase in the masrne- 

 tisation is apparent, but after that the magnetisation increases gradu- 

 ally, if the intensity of the field is kept constant. A quite similar 

 but contrary effect is produced when the intensity of the field is 

 decreased. This fact has been observed long since by several physicists 

 (see Wiedemann's Electricitat, IA 7 , p. 236.), most of whom thought, 

 however, that it was rather more due to the action of induced currents, 

 than to the condition of the iron itself. A different view was taken 

 by Prof. Ewing, F. R. S., who made a careful investigation 1 of this 

 time-lag in magnetisation, as the phenomenon is called. 



He took a piece of soft iron in the form of a wire -1 mm. thick, 

 and starting every time from the magnetically neutral state, he applied 

 small magnetic forces, and determined the amount of "creeping" of 

 the magnetisation. The greatest magnetising force he used was only 

 0*34 C.G.S. He also tried the effect of increasing the magnetising 

 force by a small step, when the iron was kept under the influence of a 



1 Proc. Royal Society, 46 p. 269 (18S9). 



