Electric and Magnetic Fields on Spectral Lines. 523 



gradually alters. The single lines get diffuse and grow 

 together; and when the field is increased still more the whole 

 system o£ lines tends to shrink into three homogeneous com- 

 ponents, with the same relative positions as the components 

 of a simple Zeeman triplet. 



An analogy to these results is obtained by considering the 

 simultaneous effect of an electric and a magnetic field on a 

 system consisting of an electron rotating round a nucleus of 

 infinite mass. In section 2 we assumed that the effect of an 

 external electric field is to increase the eccentricity of the 

 orbit of the electron and to direct the major-axis parallel to 

 the electric force. According to section 3, the effect of a 

 magnetic field is to superpose a rotation of uniform frequency 

 on the orbit of the electron, To consider the simultaneous 

 effect of electric and magnetic fields the axes of which are 

 perpendicular to each other, let us first suppose that the 

 effect of the electric force is large compared with the effect 

 of the magnetic force. In this case, the directing effect of 

 the electric force will oppose the rotatory effect of the 

 magnetic force, and the result may be the appearance of a 

 number of stationary orbits close to the orbits to be expected 

 when the electric field acts alone. If, on the other hand, the 

 effect of the magnetic field is large compared with that of 

 the electric field, the directing effect of the latter cannot 

 prevent the general rotation of fhe system, and it is easily 

 seen that the case will be very similar to that due to the 

 magnetic field alone. The necessary condition for the appli- 

 cation of this analogy to the case of the magnetic effect on 

 double lines, is that the configuration of the inner electrons 

 does not rotate in the field with the same frequency as the 

 orbits of the outer electrons. It may be noticed that these 

 considerations bear an analogy to the theory of Sommerfeld 

 (cf. p. 519), which corresponds to the analogy between the 

 considerations of the former section and the theory of 

 Lorentz. 



Concluding Remarks. 



In the deductions of this paper the following general 

 assumptions are used : — 



1. That an elementary system containing rotating electrons 

 will not emit energy radiation in the continuous way assumed 

 in ordinary electrodynamics, but that radiation is only emitted 

 during the passing of the system between a certain number of 

 stationary states. 



'I. That the dynamical equilibrium of the system in fhe 



