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Physics. — "Mdgnetic researches. IX. The deviations from Curie's 

 laiv in connectio7i with the zero-point energy''''. By E. 

 OosTERHUis. Supplement N". 31 to the Communications from 

 the Plijsical Laboratory at Leiden. (Communicated by Prof. 



H. KAMERlilNGH OnNES). 



(Communicated in the meeting of June 28, 1913). 



§ 1. Curie ^) found that for a number of paramagnetic substances 

 the susceptibility is inversely proportional to the absolute temperature. 

 Later measurements have shown, however, that with many substances 

 considerable deviations from Curie's law occur. They were first 

 disclosed about simultaneously by an investigation of Honda ^) fafter- 

 wards continued by Owen')) who showed that the majority of para- 

 magnetic elements does not obey Curie's law and by an investigation 

 of liquid and solid oxygen by Kamerlingh Onnes and Perrier'), which 

 proved that a substance which follows the law at higher tempera- 

 tures, may begin to deviate from it at lower temperatures. Liquid 

 oxygen showed an increasing deviation with falling temperature 

 approximately in accordance with the relation )i=:CT—^ (x : sus- 

 ceptibility per gramme, 2-. absolute temperature); with solid oxygen 

 at hydrogen temperatures the susceptibility deviated even more and 

 seemed to approach a constant value. The investigation at low 

 temperatures which promised to give an insight into the nature of 

 paramagnetism ^) was continued by Kamerlingh Onnes and Perrier ") 

 with several other substances. By the results obtained they were led 

 to the conception that for all paramagnetic substances or at least 

 for one class of them the deviations from Curie's law are governed 

 by a law of corresponding states, the corresponding temperature for 

 each substance to be taken proportional to a certain temperature 

 characteristic of that substance. The data obtained later on by 

 Kamerlingh Onnes and the author ') may serve to confirm this view, 

 as will be shown in § 7. 



The majority of the substances investigated in the cryogenic labo- 

 ratory at Leiden may be reduced to the following three types : 



1) P. Curie. Ann. chim. pliys. (7). 5, p. 289; 1895. 



2) K. Honda. Ann. d. Phys. 32. p. 1027. 1910. 



3) M. Owen. Ann. d. Phys. 87. p. 657. 1912. 



•*) H. Kamerlingh Onnes and A. Perrier. Gomm. N**. 116 (April 1910). 

 B) Comp. H. Kamerlingh Onnes, Comm. Suppl. N^. 216. 



6) H. Kamerlingh Onnes and A. Perrier, Comm. Nos 122a, 124a. 



7) H. Kamerlingh Onnes and E. Oosterhuis. Comm. Nos. 129Ö, 132e, 134rf. 



