(2) 



Physics. — ''Considerations concerning light radiation under the 

 simultaneous influence of electric and magnetic forces and some 

 experiments therehy suggested. (First Part) bj Prof. P. Zeeman. 



(Communicated in the meeting of January 28, 1911). 

 /. Theoretical considerations. 



1. After the discovery of the influence of magnetic forces on 

 radiation frequency in J 896, many physicists certainly have put 

 the question to themselves whether electric fields also influence the 

 emission of light. We may imagine an atom or molecule containing 

 one single electron, which is drawn back to its position of equilibrium 

 by quasi-elastic forces — hx, — hy, — kz, where x, y, z, are the com- 

 ponents of the displacement of the electron. This is just as in Lohentz's 

 elementary theory of magnetic separation. Let our molecule be placed 

 in a uniform electric field parallel to the axis of A"^. If the force on 

 the electron be denoted by A', then the displacement ^o of the electron 

 is given by 



X = + kx, . 



In the new position there is equilibrium. If the electron performs 

 vibrations about the new position, then the coordinates may be 

 represented by 



§1 >i, ^ being supposed to be infinitely small. The components A^', Y',Z' 

 of the quasi-elastic force become 



— ^(.r„-f§), - h^, — kC, 

 and therefore the components of the total force {X-\-X', etc.) 



-kl -kri, —k^ (1) 



In the new position the electron is subjected to infinitely small 

 forces, which are independent of the direction of the displacement. 

 The frequency of the vibrations of the electron, being determined 

 by k, has the same value as before the application of the electric field. 



2. VoiGT developed the consequences of the hypothesis, which 

 presents itself, if the simple law followed by the quasi-elastic force 

 of ^ 1 no longer holds. 



The potential energy of a displacement {x, y, z) is represented in 

 the supposition of § 1 by 



ip=.^k{.v"--{-y^ + z') = ^kr' (2) 



k being a constant. 



