ON THE MAGNETISATION OF COBALT. 
385 
of the magnetisations answering to the V/endepunkte of the stretched iron wires 
were on an average nearly thrice that answering to the Wendepunkt in the cobalt 
rod, that the wires were practically of infinite length, and that the critical fields 
observed in them answer, as a rule, to stresses considerably more severe than the 
normal stress appjlied to the cobalt, it seems not unlikely that by taking the position 
of the Wendepunkt in the absence of stress as a standard for comparison, it may be 
possible to trace general laws underlying the varied phenomena occurring in the 
different magnetic metals, and thus throw light on the material changes in which the 
process of magnetisation consists. 
Note. 
[The referees to whom the paper was submitted having suggested the desirability 
of an examination into the chemical character of the rod, I add the following analysis, 
for which I am indebted to Mr. R. H. Adie, of Trinity College, Cambridge, wdm 
kindly undertook the work :— 
Percentages. 
Cobalt. 91'99 
Nickel. 4‘3G 
Manganese. 1‘86 
Iron. ] '37 
Carbon, &c. ‘42 
100-00 
The rod is thus not a pure specimen of cobalt. The principal impurity, however, is 
nickel, which closely resembles cobalt in its magnetic properties, though in general 
regarded as less strongly magnetic. The effects of pressure on the magnetisation of 
nickel are of the same general character as in the case of cobalt in fields below the 
critical, though probably more intense. One would thus expect the critical field to 
be slightly raised in consequence of the presence of the nickel.— April 16, 1890.] 
3 D 
MDCCCXC.-A. 
