( 571 ) 



interest to compare with this result some consequences issuing from 

 work done in the Amstercham laboratory by Hallo on the magnetic 

 rotation of the piano of polarisation in sodium vapour^), and by 

 (tkkst on magnetic double refraction in the same substance ^), and 

 from one of the results of Jean I^ecqub^rel ") in his remarkable 

 experiments concerning the behaviour of tysonite and other crystals 

 at low temperature and in a magnetic tield. 



These physicists come to the conclusion that in the substances 

 they have experimented on, only a small part of the atoms are 

 participating simultaneously in the emission or absorption phenomena. 



Of course there is not the least improbability in accepting that in 

 a Geissler tube the circumstances are quite ditferent, and to admit 

 that in a vacuum tube the number of atoms vibrating at a given 

 instant is very large. 



Asi/inuictries of Wolfraiiimm and Molybdenum lines. 

 Observations of Mr. Jack. 



6. Not only the lines of mercury and iron, which I investigated, but 

 also those of other substances give in the magnetic tield asymmetrical 

 ti-iplets. Some examples of very pronounced asymmetries, have been 

 met with by Mr. Jack in the physical laboratory at Göttingen, and 

 1 am indebted to the kindness of Prof. Voigt in being able to com- 

 municate these here. In the annexed table the wavelengths are given 

 in Angstrom units, the separations however in m.m. as measured 

 on the plates. For a knowledge of the relative asymmetry this is 

 sufficient. 



With some lines the asymmetry is reversed, the component towards 

 the red being at a larger distance. According to the remarks of 

 Mr. Jack it is not excluded however that in these cases the structure 

 of the lines is not quite simple. 



The intensities given can only have a relative value according to 

 the results of my paper in these Proceedings of October 1907. 



Observation parallel to the lines of force. 



7. In a direction parallel to the magnetic force the two com- 

 ponents of the doublet must be placed, according to the elementary 

 theory, symmetrically relatively to the unmodified line. It seemed 

 rather superfluous to test this point. However at the \ery outset 



1) Hallo. Thesis, Amsterdam 1902. Arch. Néerl. (2) T. 10 p. 148. 1905. 

 2j Geest. Thesis, Amsterdam 1904 Arch. Néerl. (2). 1'. 10, p. 291, 1905. 

 '^) See especially Jean Becquerel. Influence des variations de Temperature sur la 

 dispersion. Le Radium. 1907. 



