Physics. — "Magnetic Researches. W\^\. Measurements of Magnetic 

 Fernieabi/itie.^ of Clirommm Chloride and Gadolinhnn Sulphate 

 (It the Boiling Point of Liquid Hydrogen in Altermiting Fields 

 of Frequency 369,000 ijer Second." Bv G. Brkit, National 

 Re.seairli Fellow, U.S.A., and H. Kamerlingh Onnes. (Comniu- 

 iiicatioii N'. 168c from the Physical Laboratory at Leiden.) 



(Communicated at the meeting of December 29, 1923). 



§ I. fntroduction. It has l)een suggested hy Ehrenfest') tlial at 

 very low temperatures paramagnetic substances may show pheno- 

 mena of hysteresis. The experiments reported on in this communi- 

 cation weie made in order to see whether this efllecl is present at 

 reasonably high frequencies. The quantities measured wei'e magnetic 

 susceptibilities. The measurements were made on samples previously 

 used in steady (ield determinations to as to enable a direct compa- 

 rison. The measurements made do not give one sufficient confidence 

 to claim great numerical accuracy of the results. However, tiiey 

 seem to indicate definitely that the order of magnitude of the sus- 

 ceptibilities for steady and alternating fields is the same. The nume- 

 rical values obtained for both salts are smaller than the values 

 obtained in direct fields and the apparent consistency of trial measure- 

 ment given below suggests that this discrepancy may be not due 

 to experimental error. 



§ 2. Methods and Apparatus. The method was similar to that 

 described by Beltz'). Two electron tube circuit.s (Ni'. 1, Nr. 2) 

 were set up to generate sustained oscillations of high frequency. 

 The frequencies of the two were adjusted so as to be nearly 

 integral multiples of each other. A two stage audio frequency 

 amplifier was coupled loosely to both. The audible beats produced 

 in the amplifier were made to give beats with an audible note 

 produced by a third electron tube circuit, say Nr. 3. The para- 

 magnetic sample was put into the inductance of circuit Nr. 1. 

 The cryogenic apparatus surrounding the .sample was placed inside 

 the same coil. The coil was shielded on its inside by means of 

 tinfoil. The tinfoil was cut into 8 segments so as to allow the 

 magnetic field to pass to the inside of the shield. The cryogenic 



') P. Ehrenfest, these Proc. 23, p. 989; Leiden Coram. Suppl. N". 446. 

 ') Phil. Mag. 44 (1922) p. 479. 



