278 



Prof. J. A. Ewing. 



[June 20, 



great that this immediate effect is less than, one-fourth of the 

 whole change which the magnetisation has suffered by the time 

 1 minute has elapsed. 



Fig. 5. 



To show clearly the region in the curve of magnetisation at which 

 the experiment of Table III and fig. 5 was made, a curve is drawn in 

 fig. 6, showing, as the result of a separate experiment, the relation in 

 absolute measure of the intensity of magnetism to the magnetising 

 force produced by the solenoid. The region dealt with in Table III 

 is at the place marked Q (g = about 40 c.g.s.), and the dotted line 

 drawn there shows the immediate value of d^/d^ after a 1-minute 

 pause. The dotted line P shows the corresponding initial gradient, or 

 immediate value of d^/d^, when there is no previous magnetisation. 



Another step-by-step experiment of the same kind, made at a place 

 higher up, where the magnetising force of the solenoid was about 

 4 c.g.s. and §f about 320, gave again about 13 for the immediate effect 

 (difcFf) ; and this was followed by a creeping to the extent of six or 

 seven times the immediate effect. 



The immediate magnetic effect of a small step is substantially the 

 same whether the step is made quite suddenly by short-circuiting a 

 resistance coil in the circuit of the magnetising solenoid, or compara- 

 tively gradually by means of the liquid slide, so that the process 

 occupies a sensible fraction of a second, or even as much as a whole 

 second. 



