XII.] THE MAGNETIC PERTURBATION OF LINES. 115 



the spectra of elementary substances are not produced by the vibra- 

 tion of similar " atoms " or " ions," but by a series of different ones. 



It is already pretty obvious that .when ordinary spectroscopic obser- 

 vations, and the evidence supplied by " series," and these magnetic per- 

 turbations are completely correlated, we shall have taken a long step 

 forward. 



I 2 



