550 



PROFESSOR C. G. KNOTT ON MAGNETIZATION 



continuing to diminish, however, the resistance change passes through a minimum as 

 the temperature rises through 295° and thereafter experiences an abrupt rise in value, 

 reaching a sharp maximum at 310°. At higher temperatures the value of the resistance 

 change falls off rapidly to a comparatively low value at 344°. At this temperature, 

 as is well known, the nickel loses its strong magnetic qualities and becomes practically 

 a non-magnetic metal. 



The peculiarity was first noticed in the experiment of 27th May, when, by applica- 

 tion of fields about 3700 (see Appendix), I obtained for the resistance changes at 331°, 

 250°, and 203° the values 226, 213, and 376. That is to say, the smallest effect was 

 obtained with the intermediate temperature. The same result was given with the 

 other fields used. The first impression was that this quite unexpected result was due 



240 



260 



"280* 



300° 



320° 



340" 



The ordinates measure in the units indicated either Decrease of Resistivity or Increase of Conductivity. 



to some error of experiment. Accordingly, I proceeded to make a great many other 

 experiments so as to get as many measurements as possible in the neighbourhood of 

 the minimum and maximum points. The experiment of 2nd June (see Appendix) is 

 particularly instructive. To show how closely the various points cluster along the 

 respective curves, I have plotted on an enlarged scale those parts which lie between 

 the temperatures 240° and 344°. 



The effect is undoubted in the three highest fields. It is also hinted at in the lower 

 fields ; but the smallness of the effects in these lower fields make the errors of observa- 

 tion more conspicuous, and the digits in the numbers tabulated may be in error easily 

 by three or four. 



The question at once suggests itself as to whether any analogous peculiarity can be 

 detected in other electrical and magnetic properties of nickel. Thus, to take the very 

 simplest case, is there any peculiarity in the relation between permeability and tempera- 

 ture in the neighbourhood of the temperatures 260° to 300°? According to Tait's dis- 



