112 



Was always ^) supposed to be contained in the same \olnme. and 

 in the comparison with experimental data no account was taken of 

 the inthience which the relatively small changes of density connected 

 with the teniperatnre changes exert on the parameter 0^ , which 

 occurs in the formulae of that commnnication, and which [ will 

 call the dKiracteristic zero-temperdture. 



Since then the measurements by Perhikk and Kamerlingh (3nnes ^) 

 concerning the susceptibility of liquid mixtures of oxygen and nitro- 

 gen have furnished very important data, wdiich, wiien considered 

 from the point of view taken in the paper quoted above, allow a 

 conclusion as to the manner in which the characteristic zero-tempp- 

 rature 6^ depends on the composition of those mixtures. If it is 

 further assumed with Perkier and KAMERLI^GH Onnes, that to a 

 first approximation the presence of the nitrogen molecules in these 

 mixtures does not exert a direct influence on the statistical distri- 

 bution of the orientations, nor on the magnetic moment of the oxygen 

 molecules, so that it is only the changes in density of the oxygen, 

 which determine the changes in the susceptibility, then those mea- 

 surements furnish at the same time data lor a discussion of the 

 question how ('^ depends on the density. 



We will in the tirst place treat the ([uestion whether the results 

 of the measurements by Perriek aiul Kameki.ingh Onnks mentioned 

 above can be represented with the aid of the relations of Suppl. 



value of X, may then bo pal into the form : 



(c) 



"lO "i".l 



For nickel (T, i =033. ^Vci = 2100, cf. Suppl. N". 32a § 4)^^= 1.30. From 



"r(t.l 



— llie value of— can be derived, and then with /7o h'om {b) the value of 1\- 



corresponding to x can be fomid. 



A continuation of the investigation of the magnetisation of alloys such as those 

 mentioned above, particiilai-ly for compositions, for which the GuRiE-point lies 

 below 0° C, would be of great mteresl, on the one hand for putting tlie apph- 

 calion of the cjnantum-theory to a test (according to this with such alloys the 

 different cases indicated in Fig. o of Suppl. N'. 32/) might be realised^ on the 

 other hau'-l for increasing our knowledge of the molecular field [In the mean 

 time I have received an article by P. Weiss, Ann. de physique (9) 1 (Febr. 1914) 

 p. 134, in which is mentioned, that, with a view to the investigation of the 

 molecular held, a series of measurements concerning alloys of nickel and copper 

 has already been imderlaken. (Added in correcting the proof of the Dutch edition)]. 



1) \\\{\\ the exception of the note added in Leiden Comra. : note 2, p. 6. 



2) Alb. Perkier and H. Kamerlingh OsjsES. Gomm. No. 139(/ (Febr. '14). 



