rÈAN BECQUEREL and H. KAMERLINGH ONNES. On [the absorpiionspectra of the compounds of the 

 rare earths at the temperatures obtainable by liquid hydrogen and their change by the magnetic 

 field. 



>17.6 



523.5 



PI. II. 



r= 293^ abs. 



T= %b' 



T=20° 



T= 14" 



Fig. 1. Anomalous birefrigency, tysonite, group in the green 2d spectrum (RowLAND^grating), thickness op plates 

 71 mM. in I, 2, 3, 4 and 0.41 mM. in 2 (in 2 the ordinary and extraordinary ray are interchanged). 



520.6 523.7 



537 



r= 293^ abs. 



7 = 85^ 



r = 2o^ 



T= 14^ 



522.1 



^ig. 2. Left- and righthanded vibrations in a field of 18000 Gauss nearly. Xenotime, group in the green, 2^ 

 2ctrum (Rowland grating). 



