1889.] On Time-lag in the Magnetisation of Iron. 281 



• Fig. 7. 



which, shook the wire very perceptibly and caused a comparatively 

 sudden increase of magnetism (indicated by the dotted part of the 

 curve), after which the time-rate of creeping became specially slow 

 for 1 or 2 minutes : finally, however, the rate appeared to recover 

 from this disturbance. The curves a and b of fig. 7 are the first parts 

 of A and B drawn to a ten-fold coarser scale of times. 



In confirmation of the above, another experiment was made in 

 which the magnetic force was increased by three successive small and 

 very nearly equal steps. The first step was made after 5 minutes of 

 constant force, the second after 1 hour of constant force, and the 

 third again after 5 minutes of constant force. Time-curves of the 

 growth of magnetism were drawn in all three cases. The first and 

 third curves were not far from coincident: but the second curve lay 

 very much below them, as B lies below A. 



In the experiments to which figs. 4, 5, and 7 relate, the increment 

 of magnetic force whose effects were measured was preceded by 

 increasing magnetic forces : in other words, it was a step-up from a 

 point on the up curve of magnetisation. I have also examined the 

 effect of a small step-down from a point on the up curve — that is to 

 say, a small decrement of previously increasing force — and find, as 



