ON THE MAGNETISATION OF COBALT. 
373 
the residual magnetisation, as measured by the percentage got rid of, continually 
diminishes as the strength of the field is increased. According to the seventh columns 
of Tables VI. and VII., and the sixth column of Table VIII., on which the curves 
are based, this diminution most probably goes on up to fields of 400 C.G.S. units 
at least. The difference, however, between the percentages shaken out in the case of 
fields of 100 and 400 C.G.S. units is under all conditions very small. 
Comparing curves b and c, in figs. 14 and 15, and the seventh columns of Tables VI. 
and VII., we see that while in fields below 15 C.G.S. units an absolutely larger 
amount of residual magnetisation is shaken out by the first jiressure when pressure 
cycles have been applied during the flow of the current, still in these and in all 
higher fields within the experimental limits a greater percentage is removed by the 
first pressure when no pressures have been applied during the current. 
We thus see that in fields below 100 C.G.S. units, pressure cycles during the flow 
of the current diminish simultaneously the percentage of the induced magnetisation 
got rid of by breaking the current, and the percentage of residual magnetisation got 
rid of by the subsequent application of a pressure. In fields from 130 to at least 
400 C.G.S. units pressure cycles during the flow of the current appear slightly to 
increase the percentage of induced magnetisation got rid of by breaking the current, 
while simultaneously diminishing the percentage of residual magnetisation got rid of 
by the subsequent application of a pressure. In these strong fields, however, both 
these effects are comparatively insignificant. 
§ 55. In the experiments on which the curves h and c are based the effects of 
removing the first pressure applied after the break of the current were also observed. 
The invariable result was a loss of magnetisation, and its magnitude is recorded in the 
fifth columns of Tables VI. and VII. In considering how much of this loss is perma¬ 
nent, the cyclic effect of the change of pressure must be allowed for. This has been 
done in calculating the eighth columns of Tables VI. and VII., which give the 
relative importance of the first pressure and its removal in permanently reducing the 
magnetisation. 
When no pressures have been applied during the flow of the current we see from 
Table VI. that, in fields between 18 and 75 C.G.S. units, the removal of the first 
pressure produces uniformly about one-ninth of the effect of its application. In the 
higher fields the relative importance of the removal of pressure shows a distinct 
diminution. 
Comparing Tables VI. and VII. we see that in fields below 50 C.G.S. units the 
importance of the removal of the first pressure after the break of the current relative 
to its application is largely increased by the application of pressure cycles during the 
flow of the current. In fields over 50 C.G.S. units the effect of the removal bears to 
that of the application of the first pressure in the case of Table VII. the appa¬ 
rently nearly constant ratio of 1 :9, which still somewhat exceeds the ratios found in 
the corresponding fields of Table VI. 
