1895.] on the Effects of Electric Currents in Iron, &c. 



547 



magnetisation. The vertical ordinates represent the induction, and 

 the horizontal abscissas the magnetising force. You will observe 

 that when the magnetising force is small the ratio of induction to 

 magnetising force is also small ; that as the magnetising force 

 increases this ratio is also increased for a time, but that, finally, it 

 again becomes small. You will observe, further, that when the 

 magnetising force is great the curve of magnetisation begins with a 

 small rate of change, which then becomes large, and which again 

 becomes finally small. Now the slowness of changes of induction 

 depends upon the largeness of the ratio of induction to magnetising 

 force, and, therefore, we should expect that when this ratio is small 

 the changes would occur with comparative rapidity, and that when 

 it is large they would occur more slowly. This is exactly what we 



Fig. 10. 



have seen. With a small force the change shows itself almost at 

 once ; with an intermediate force the principal maximum occurs 

 much later, and with a large force it is continuously being accele- 

 rated as the force becomes larger. The first rise that occurs with 

 a large force is due to the early part of the curve of induction, where 

 changes of induction are comparatively small, and where consequently 

 the effects rush in rapidly. This first maximum is followed by a 

 time of comparative quiescence, which is again succeeded by a 

 second and large maximum caused by the full effect of the great 

 changes of induction which have occurred, but which have passed in 

 comparatively slowly ; and then, finally, the change drops away to 

 zero quite suddenly, owing to the great rate at which the last part of 

 the change has rushed in and pressed upon the parts which had 

 occurred before it. 



