( 599 ) 



§ 9. P(trtï<il polarisation of the components of soive hands. In a 

 foregoing communication (JGR. 19 Aoiit J 907) one of us (J. B.) has 

 demonstrated, that the band 624,97 of tysonite becomes double 

 in each of tiie two spectra of left-handed and right-handed circu- 

 larly {)olarized light, which are obtained by means of a plate of 

 a quarter wavelength and a rhombohedron. Therefore in both com- 

 ponents of the magnetic doublet of the band the polarisation is not 

 perfectly circular. The band behaxes as if it were owing both to 

 positive and to negative electrons with the same period of vibration, 

 and the same ratio efm, in which the number of positive electrons is 

 to be put as the largest, because the strongest component belongs to it. 



At the temperature of liquid hydrogen the same phenomenon is 

 observed with some bands which become at the same time tine 

 and bright (fig. 2 PI. I band 522. 1). In general the same thing 

 is found on reexamining the spectra at the temperature of liquid air 

 and at the ordinary temperature, though it is more difficult to see. 

 Some time ago Dufour again found the same phenomenon in emission 

 bands of fluorcalcium put into the flame. 



§ 10. Asymmetry of the right- and left-handed components. The 

 experiments at the temperature of liquid air had proved ^) that 

 when the rays of light run parallel to the lines of force the right- 

 and left-handed components very often differ in strength. No regu- 

 larity had been found in these differences, the asymmetry was now 

 in one, then in the other sense. 



If we pass to the temperature of liquid, or better still, to that of 

 solid hydrogen, the asymmetries, which sometimes change their sign, 

 become exceedingly great; one component increases in intensity at 

 the expense of the other, even to such a degree, that some compo- 

 nents vanish almost entirely on the side of the greater wave lengths. 

 An example is furnished by fig. 3, PI. Ill refen-ing to ^54,2 and 

 643,4 of xenotime, one component of which is very intense, the 

 other very faint. Apatite shows the same thing. 



In solid hydrogen almost all the components which divei'ge towards 

 the small wave lengths, become very sensibly intenser than those of 

 opposite sign. 



§ Jl. Variation of the magnetic rotation of the plane of pola- 

 risation in the ?ieighboiirhood of the absorption bands. 



a. Simple bands. The experiments of Macaluso^), H. Becquerel '), 



^) Jean Becquerel Le Radium V. No. 1. p. 9. 1908. 



2) CR. GXXVII p. 548, 1898. 



3) GR. CXXV p. 679. 1897 GXXVll p. 899. 1891. 



41 

 Proceedings Royal Acad. Amsterdam. Vol. X. 



