CH. XL] MAGNETISATION OF LIGHT 



119 



resolved into a quartet, and D 2 into a sextet, when 

 the light travels across the magnetic field. 



Directly Zeeman had demonstrated the fact that a 

 magnetic field applied to a source of light was able 

 to act as a perceptible perturbing cause, Professor 

 Lorentz was at once able to predict the main part of 

 that which has been here stated, about the tripling 

 of the line seen sideways to the lines of force, and 

 the doubling of the line seen endways, with all the 

 polarisations as just stated ; because the lines of 



n 



tt 



FIG. 15. 



magnetic force constitute the precessional axis. And 

 all these effects were shortly afterwards seen by 

 Zeeman and others, and are characteristic of the 

 simplest circular orbit. 



As already stated, the full meaning of these very 

 exquisite phenomena is still very far from being 

 unravelled. The most general theoretical result is 

 that of Larmor (Phil. Mag., Dec. 1897) that for any 

 atomic system, however complex, if the effectively 

 moving electrons are all negative, while the attraction 

 of the positive on them is centrical, each line will be 

 divided into three, exactly as in the provisional theory 

 of Zeeman and Lorentz. 





