CONTEMPORARY ADVANCES IN PHYSICS 



337 



the earlier part is exalted, the later part is depressed, so that the 

 susceptibility increases in low fields and diminishes in high; curves 

 obtained at different temperatures, not too far apart, intersect one 

 another somewhere upon the "second segment" (Fig. 7). On 

 plotting / or I/H for individual fieldstrengths as functions of tempera- 

 ture, one obtains curves which for very low fieldstrengths, such as 

 0.3 gauss for instance, are remarkably shaped (Fig. 8). The initial 

 susceptibility rises to an enormous height at a temperature slightly 

 above 700° C, and then precipitately falls almost to nothing — it does 

 not quite vanish, but instruments of a much higher order of sensi- 

 1.0 



.8 



.7 



1.0 



Fig. 9 — Saturation-vs. -temperature data for iron, cobalt, nickel, and magnetite 

 below their respective Curie-points, with a theoretical curve. Abscissa is ratio of 

 absohite temperature to Curie-point temperature for each substance individually. 

 (After P. Weiss.) 



tiveness are required to detect or measure it beyond say 770°. At a 

 somewhat higher fieldstrength, about 4 gauss, the I-vs.-T curve is 

 nearly horizontal for a long way, and then declines gradually to the 

 axis of H, which it reaches near 770°. At higher fieldstrengths the 

 decline sets in progressively earlier (Fig. 8). At very high fields one 

 obtains what is substantially the curve of /max. versus T (here the 

 analogy with the effect of tension breaks down) which is shown in 

 Figure 9. 



