﻿of Ferro-magnetic Elements in Corresponding States. 41 



diminution begins, while on cooling the magnetism rises to a 

 value higher in the vicinity of 100° C. than what it is at the 

 temperature of the room. These effects are, however, nearly 

 obliterated on repeating the heating and cooling many times, 

 although there is always a tendency for the intensit}^ to be 

 higher at about 100° on cooling than at lower temperatures. 

 In other respects cobalt behaves regularly up to 750° C. 

 The numbers which have been used in the construction of 

 the curve for cobalt are mean values of experiments on 

 electrolytic deposits of cobalt on copper and on platinum. 

 Since the expansion of cobalt is intermediate between that of 

 copper and platinum, it was considered justifiable to take the 

 mean as the rinal result. - 



4. Experiments on the change of residual magnetism of 

 nickel, iron, and cobalt over so extended a range of tempe- 

 rature do not appear hitherto to have been carried out, and 

 it is useful to compare the results now arrived at with those 

 which have been obtained in very intense fields by P. Curie *, 

 Du Bois f, Honda and Shimizu J, and others. Curie's 

 observations on iron were made in a field of 1300 c.G.s. units 

 from air temperature to the critical temperature and beyond, 

 and his curve agrees with the one for iron given above at 

 the extremities, but is a little higher at intermediate points. 

 There is no evidence of a halt at 400° to 600°. 



Du Bois, using an optical method with ellipsoids of a 

 dimension ratio of 30, has experimented upon nickel and 

 cobalt as well as iron in intense fields, but has not carried 

 the temperature beyond 300° C. His curves take rather 

 an abrupt downward bend at temperatures beyond 200°, but 

 in other respects are similar to those in Diagram 1. He 

 does not give numerical results, but from the curves traced 

 in his paper I have deduced the following approximate 

 values of the temperature coefficient : 



Temp. Nicltel. Iron. Cobalt. 



0°-100° 0-0CJ05 0-00014 -00005 

 100°-200° 0-0017 0-00033 '00015 



The coefficients are largest in nickel and least in cobalt, and 

 "in all cases increase with the temperature. 



Honda and Shimizu by means of the magnetometrie 

 method and employing ellipsoids having a dimension ratio of 

 20 have made experiments on annealed iron, nickel, and 

 cobalt over a range of temperature which extended from 



* Ann. Chim. et Pki/s. ser. 7, vol. v. 1S ( J5, p, 289. 



t Phil. Mag. ser. 5," vol. xxix. 1890, p. 298. 



j Phil. Mag. ser. 6, vol. x. 1905, p, 548. 



