74 HENRY A. EOWLAND 



applies to the permanent state finally attained after several reversals of 

 magnetizing-f orce ; but if we strongly magnetize a bar in one direction 

 and then afterwards apply a weak magnetizing-force in the opposite 

 direction, the change of magnetization will be very great. 



(5) The resistances of nickel and cobalt to magnetization vary with 

 the temperature; but whether it is increased or not in nickel depends 

 upon the amount of magnetization : for a moderate amount of magneti- 

 zation it decreases with rise of temperature very rapidly; but if the 

 magnetization is high the resistance is increased. In cobalt it appar- 

 ently always decreased, whatever the magnetization. The resistance 

 of iron to magnetization is not much affected by the temperature. 



(6) The resistance of any specimen of metal to magnetization de- 

 pends on the kind of metal, on the quality of the metal, on the amount 

 of permanent magnetization, on the temperature, and on the total 

 amount of magnetization, and, in at least iron and nickel, decreases 

 very much on careful annealing. The maximum of magnetization 

 depends on the kind of metal and on the temperature. 



(7) Iron, nickel, and cobalt all probably have a maximum of magneti- 

 zation, though its existence can never be entirely established by experi- 

 ment, and must always be a matter of inference; but if one exists, the 

 values must be nearly as follows at ordinary temperatures. Iron when 

 33 = 175,000 or when 3 = 13,900; nickel when 33 =63,000 or when 

 3 = 4940; cobalt when 33 = 100,000( ?) or when 3 = 8000 (?). 



(8) The maximum of magnetization of iron and nickel decreases with 

 rise of temperature, at least between 10 C. and 220 C., the first very 

 slowly and the second very rapidly. At 220 C. the maximum for iron 

 is when 33 = 172,000 and 3 = 13,600, and for nickel when 33 = 49,000 

 and 3 = 3800. 



The laws which govern temporary and residual magnetism, except so 

 far as they have been hitherto given, I leave for the future, when I 

 shall have time for further experiment on the subject to develop some 

 points which are not yet quite clear. 



Troy, New York, U. S. A., April, 1874. 



