CH. XT.] MAGNETISATION OF LIGHT 121 



Even the two constituents of the double sodium 

 line behave differently, when the source is magnet- 

 ised and the light thus examined as illustrated in 

 fig. 15 : one of the sodium lines, D 2 , which had 

 appeared only broadened to Zeeman at first, really 

 becomes a sextet. The other sodium or D x line 

 becomes a quartet ; and a complete study of the 

 behaviour, under magnetism, of all the lines and 

 groups of lines given by different substances must 

 result in a great extension of our knowledge in many 

 directions ; in fact it is hardly too much to say that 

 the discovery of Zeeman, in the light of the theory of 

 Lorentz, has doubled the power of spectrum analysis 

 to throw light upon the processes of radiation and the 

 properties of atoms, and has opened up a new branch 

 of physics a new department, as it were, of atomic 

 astronomy, with atoms and electrons instead of 

 planets and satellites. 





