Physics. — "Magnetic Resenrclies. XXII. On the determination of 

 the magnetisntion at very low temperatures and on the 

 susceptibility of gadolinium sulphate in the region of tempe- 

 ratures obtainable with liquid hydrogen'. By H. R. Woltjer. 

 (Communication N°. 1676 from llie Physiral Laboratory at 

 Leiden). (Cominnnicated by Prof. H. Kamekijngh Onnes). 



(Gommuuicated at ttie meeting of September 29, 19:i3). 



^ 1. Introduction. Tlie significance of extending- the investigation 

 on tiie magnetisation of paramagnetic substances to the temperatures 

 obtainable with liquid lieiium, tliat inigiit l)e expected a priori, has 

 been confirmed in a convincing way l)y tiie preliminary reseaicli 



on tiie magnetisa- 

 tion of gadolinium 

 sulphate in liquid 

 helium carried out 

 by KamermnghOn- 

 NKS in 1914 '). The 

 results then ob- 

 tained showed the 

 interest of conti- 

 nuing the research 

 on gadolinium sul- 

 phate and com- 

 pleting tlie preli- 

 minary qualitative 

 results by more 

 accurate quantita- 

 tive ones. Other 

 substances, such 

 as the paramag- 

 netic chlorides') presented themselves also for investigation in helium. 

 However, closer inspection of the work of 1914 showed, that it 

 was of little use repeating the work without detailed investigation 



') H. Kamerungh Onnes, these Proceedings, 17 p 283; Leiden Gomm. N". 140d. 

 Gf. also idem, Rapport Solvay 1921, p. 131. Leiden Gomm. Suppl. N». 44a. 

 ') 1. 'c. p. 154, resp. p. 25. 



