98 



angular momentum of the electron round the axis of the magnetic field changes 

 by two times ^2-, will lie at a distance from the original hydrogen line, which is 

 approximately twice as large as that of the outer components of the normal Zeeman 

 effect, and wùU therefore be distinctly separated from the strong components into 

 which each of the components of the normal Zeeman effect is split up in the pre- 

 sence of the small electric field. We must be prepared, however, to find that the 

 weak components will not, as it might be expected at first sight, form two sets of 

 distinctly separated lines, but that they will only appear as two diffuse lines of cir- 

 cular polarisation in opposite directions and of a spectral width proportional to /. u. *) 



§ 6. The continuous hydrogen spectrum. 



We shall conclude the considerations of this Part by a brief discussion of the 

 characteristic continuous spectrum of hydrogen in the ultra violet region, which is 

 intimately connected with the series spectrum given by (35). This spectrum consists 

 of a radiation, the frequencies of which are continuously distributed over a spectral 

 interval extending from the head of the Balmer series in the direction of higher 

 frequencies.'^) The existence of a continuous spectrum of this type is just what 

 should be expected from a natural generalisation of the principles underlying the 

 quantum theory of series spectra. ') Thus the spectrum under consideration may be 

 directly explained by application of relation (1), if we assume that the complete 

 spectrum, emitted by a sj'stem consisting of a nucleus and of an electron, originates 

 not only from radiations, emitted during transitions between two states belonging 

 to the multitude of stationary states in which the electron describes a closed orbit, 

 characterised by the condition I = nh, but also from radiations emitted during 



') \o experiments, which allow to test the preceding results in detail, seem to ha%'e been recorded, 

 but it would appear that the above considerations afford an explanation of the general character of the 

 remarkable deviations from a normal Zeeman effect, observed bj- F. Pasche.n and E. Back (Ann. d. Phys. 

 XXXIX, p. 897 (1912)1 in experiments in which the hydrogen lines were excited b}- passing a powerful 

 condensed discharge through a capillary tube placed at right angles with the direction of the magne- 

 tic field. Besides the characteristic want of sharpness of the polarisation of the middle component, 

 exhibited by all the spectrograms published by Paschen and Back, especially one of their photographs 

 (Tafel VIII, Bild 4) seems to suggest the presence of a weak, perpendicular!}' polarised, diffuse line on 

 each side of the original line and at a distance from it twice that of the outer components of the 

 normal effect. 



-j This spectrum has been observed as an emission spectrum in spectra of solar protuberances 

 and planetary nebulæ (See ,1. Evershed, Phil. Trans. Roy. Soc. 197 A, p. 399 Il901i and W. H. Wright, 

 Lick Obser\'atory Bulletin, No. 291 (1917)) as well as in direct laboratorj' experiments on spectra ex- 

 cited by positive rays (See J. Stark, Ann. d. Phys. LII. p 255 (1917)). Further it has been observed 

 as an absorption spectrum in the spectra of several stars (see W. Hcggins, An Atlas of Representative 

 Stellar Spectra, p. 85 (1899) and J. Hartmann, Phys. Zeitschr. XVIII p. 429 (1917)). 



äj Compare N. Bohr, Phil. Mag. XXVI, p. 17 (1913); and also P. Debye. Phys. Zeitschr. XVIII, p. 

 428 (1917). 



