ON THE MAGNBTISATrON OF COBALT. 
875 
that for the induced magnetisation, and the intensity of the critical magnetisation in 
the former case is less than an eleventh of that in the latter. Table VII. shows no 
sensible variation in the magnitude of the effect as the field is raised from 70 to 400 
C.G.S. units. 
Taking next the case when no pressures were applied during the flow of the current, 
we see from Table VI. that in a field of 18 C.G.S. units—the lowest in which observa¬ 
tions of the effect were taken—no sure cyclic effect was detected. Thus a critical 
field must exist at or very close to this field. In higher fields there is a clear diminu¬ 
tion of magnetisation accompanying pressure on,” and in fields over 100 C.G.S. 
units the results agree as closely with those of Table VII. as they well could. Thus, 
the only conspicuous difference in the cyclic effect produced by pressure cycles during 
the flow of the current is a rising of the critical field. 
Table VIII., however, shows that a truly remarkable difference occurs in the 
phenomena when pressure exists during the break of the current. In this case, in 
fields from 11‘5 to 400 C.G.S. units, the residual magnetisation in the cyclic state 
is invariably greater when pressure is “ on ” than when it is “ off” The magnitude 
of the cyclic effect apparently diminishes at first as the field is raised, but in fields 
of from 70 to 400 C.G.S. units, it is at least approximately constant. 
It thus appears that the sign even of the cyclic change of the residual magnetisation 
accompanying cycles of pressure, is altered by such a seemingly trifling circumstance 
as the existence of pressure during the break of the pre-existing current. 
It seems almost unnecessary to point out that the facts stated in this paragraph 
convincingly show that the effect on the magnetisation of cyclic applications of 
pressure is not determined solely, or in some circumstances even principally, by 
the measure of the rod’s magnetic moment, or its so-called intensity of magnetisation. 
§ 58. As the conclusions of the last paragraph as to the cyclic effect seem of 
considerable importance, it may not be out of place to supply data by which the value 
of the evidence on which they are based may be fairly judged. 
The precautions taken in varying the order of the experiments have been already 
mentioned in explaining the Tables VI., VII., and VIII. 
Now in fields stronger than the critical field of Table VII., there were, in all, 46 
separate experiments of the types L, M, and N. Answering to pressure “ on,” there 
appeared a minimum of magnetisation in each of the 31 experiments of the types L 
and M, a maximum in each of the 15 experiments of type N. As the difference was 
wholly unexpected, and the observer had no preconceived ideas on the subject, it is 
difficult to conceive how the evidence could be stronger. 
§ 59. The ordinates of Curve II. of fig. 13, give the fraction of the residual 
magnetisation, which is removed by a definite number of pressure cycles iii the 
experiments of Table VI., or type L. 
The percentage removed continually diminishes as the strength of the pre existing 
field rises. The rate of diminution in the percentage removed is very rapid as the 
