454 



made oiil}^ one measurement at temperatures Iiiglier than those given 

 in table 2. 



Althougli this measurement is the only one it may be considered 

 sufficient together with the observations by Zeleny and Smith ^j to 

 infer a considerable deviation from the formula at this temperatui'e. 



In conclusion I am glad to record my gratitude to Prof. H. Kamek- 

 LiNGH Onnes for his kind assistance and his ever ready interest in 

 mv work. 



Physics. — "On the magnetization of ferromagnetic substances 

 considered in connection irith the assumption of a zero-point 

 energy'. By Dr. W. H. Keesom. Supplement N". 32a to the 

 Communications from the Physical Laboratory at Leiden. 

 (Communicated by Prof. H. Kamerlingh Onnes). 



(Communicated in the meeting of September 27, 1913). 

 L On the .•spontaneous magnetization. 



§ 1. Introduction. Nernst ") was the first who suggested that 

 the quantum-theory has to be applied also to the rotations of gas 

 molecules. Since that time the measurements by Eucken ^) and those 

 by Scheel and Heuse''} have confirmed the anticipation expressed 

 by Kamerlingh Onnes"), that the decrease which according to that 

 application is to be expected in the specific heat at constant volume 

 of hydrogen in the gas state, would already occur at realisable 

 temperatures. By this result they ha\'e demonstrated very clearly 

 the necessity of that application. At the same time they have given 



1) Zeleny u. Smith. Phys. Z. S. pag. 667, 1906. 



•2) W. Nernst. ZS. f. Elektrochem. 17 (1911), p. 270 W. Neknst and K. A. 

 LiNDEMANN, ibid. p. 825. Gf. &lso A. Einstein, Rapports conseil Solvay 1911, p. 432, 



'^) A. Eucken. Berlin Sitz.-Ber. 1912, p. 141. 



4) K. Scheel and W. Heuse. Berlin Sitz.-Ber. 1913, p. 44. Ann. d. Phys. (4) 

 40 (1913;, p. 473. 



5j Rapports conseil Solvay 1911, p. 301. ZS. f. Elektrochem. 17 (1911), p. 

 826. Gf. also H. Kamerlingh Onnes and W. H. Keesom. Math. Enz. V 10, 

 Leiden Gomm. Suppl. N". 23, § 57 f. 



