Strong Fields at Different Temperatures. 297 



referred to unit mass, which always contains the same number 

 of molecules, than to unit volume, which does not. In PL VIII. 

 fig- 1 the long curves represent @ = funct. (.0') over a range 

 evident from the scale of abscissae. The origins do not occur 

 in the diagrams, excepting that for nickel, which is joined 

 to the first experimental point © in a manner approximately- 

 estimated from known data. From these curves others may 

 readily be calculated ; in particular, those representing 3 = 

 funct. QB'), which will be referred to below. 



§ 1. Effect of temperature. — The upper curves of magneti- 

 zation for iron and steel correspond to 0°. It will be seen 

 that at first they almost coincide with those for 100°, bat that 

 the difference increases towards larger abscissae. For ,0' con- 

 stant*, equal to about 900 C.G.S., © = funct. (0) was then 

 determined. It is represented by the short temperature- 

 curves to the left of fig. 1, plotted to the separate scale of 

 abscissae. They all show a decrease of © ; the latter evidently 

 always being above its critical value, below which it is known 

 to increase on heating. The nickel curve falls off less abruptly 

 than it is known to do for weaker magnetizing fields. 

 Hence in an infinitely strong field the magnetization of all 

 these metals would probably begin by decreasing at a quicker 

 rate still ; then to fall off without any abruptness towards 

 practically vanishing values (see § 13). 



On the hypothesis of magnetic molecules, this case corre- 

 sponds to the temperature-variation of the individual molecular 

 moments, because the supposed infinite field would direct the 

 axes of all the molecules parallel to itself. It is the simplest 

 case ; the abrupt changes and other complications observed 

 with ordinary fields being due to the action of temperature 

 on the direction of the molecular axes. All this was theoreti- 

 cally pointed out by Prof. G. Wiedemann f. As far as I 

 can see, my results nowhere contradict any previous thermo- 

 magnetic researches, conducted with much lower fields, though 

 partly at higher temperatures, by Gr. Wiedemann, Rowland, 

 Baur, Wassmuth, Ewing, Berson, Ledeboer, Tomlinson, 

 J. Hopkinson, and others. 



§ 8. Additional experiments were made on material slightly 

 differing in condition or quality from that above defined 

 (in § 3). Annealing the hard-drawn nickel caused the 



* Of course it was the current, and with it the field §, which was 

 actually kept constant ; hut the increase of §'=$ — -05-J3, amounts to but 

 2 per cent, even when, as with nickel, 3 foils oil' from 500 to 0. 



t Leh re v. d. Elektrizitiit, iii. § 802. 





