110 



of r, we may assume, however, that already for values of the electric force small 

 compared with those applied by Stark, the orbits in the corresponding stationary 

 states will be perturbed very nearly in the same wa}' as an orbit of the electron 

 in the hj'drogen atom. This explains the fact that for the fields applied the relative 

 intensities of the components remained approximately constant, while their displace- 

 ments were found to increase nearly linearly with the electric force, as in the case 

 of the components of the Stark effect of the hydrogen lines discussed in the pre- 

 ceding section. 



While a general interpretation of the efïects of electric fields on the spectra of 

 the elements of higher atomic number as regards the appearance of new lines may 

 be obtained from a comparison with the effect to be expected on a spectrum ori- 

 ginating from an electron moving in a central field of force, the detailed discussion 

 of the displacement and splitting up of the components for increasing field, how- 

 ever, claims a closer consideration of the perturbations of the orbits of the inner 

 electrons during the perturbations of the orbit of the outer electron in the presence 

 of the external field. This problem will be considered at a later occasion in connec- 

 tion with the calculations on the helium spectrum mentioned above. 



§ 4. Effect of magnetic fields on series spectra. 



As regards the effect of an external magnetic field on the spectra of elements 

 of higher atomic number it would at first sight seem natural to assume that, in the 

 presence of a magnetic field, just as in the case of hj'drogen, the motion of the 

 atom in a stationary state would differ from the motion in a stationary state without 

 the field only by a superposed uniform rotation of frequency wh, given by (79), round 

 an axis through the nucleus parallel to the magnetic force. Bj' applying as in 

 Part II § 5, the general considerations of Part II § 2 about the relation between the 

 energj' and frequencies of an atomic system we should further conclude that the 

 additional energy of the system due to the presence of the field was again given 

 by the formula (80), and proceeding as in the paragraph mentioned we should expect 

 that the effect of the field on the spectrum would, also for the spectra under con- 

 sideration, consist in the resolution of every line in a normal Zeeman triplet. As 

 well known this is not in general agreement with the observations, Although in 

 certain cases, for instance in helium and lithium where the spectra consist of 

 single lines or verj' naiTow doublets, the resolutions observed to a high approximation 

 are the same as those in hj'drogen, we meet with far more complex effects, when 

 we proceed for instance to the spectra of the alkali metals of higher atomic numbers, 

 where the lines consist of doublets of considerable width. In the presence of a 

 magnetic field each member of these doublets is resolved in a large number of com- 

 ponents the displacements of which are proportional to the magnetic force, but 



