( 573 ) 



Looking at the doublets of the lines 5791 and 5770, whicii were 

 very brilliant, I ol)served a narrow and extremely weak^line between 

 the components of the two lines. This weak line seemed with 5770 

 precisely midway between the components, with 579 L however it 

 seemed to be displaced somewhat towards the red. 



These weak lines evidently are dne to reflection of light, radiat- 

 ing nearly at right angles to the directio]i of the magnetic force, 

 from the inner surface of the capillary of the Geissler tube. Lohmann ^) 

 investigating the neon lines, observed a similar, but in his case 

 entirely symmetrical perturbation. I found the weak [line to^ be 

 linearly polarized, as was to be expected. 



The whole image, apart then from the ratio of intensities and 

 the character of the polarization, strikingly resembles the type of 

 effect observed at right angles to the magnetic force. No good photo- 

 graphs showing the extremely weak line at the same timejwith the 

 two components of the doublet were obtained. 



I therefore tried to bring into the field of view the unmodified 

 line at the same time with the doublet. It is well known that the use 

 of a spectrum of comparison in measurements where a high degree 

 of precision is wanted, is not without serious objections. Kayser ^) 

 therefore recommends as the most suitable method to produce the lines 

 necessary for comparison in the source itself. In our case this is 

 naturally out of question. 



The sidelong displacement, which the lumiuous line in the vacuum 

 tube undergoes by the action of the field, makes it already impos- 

 sible, even if the position of the vacuum tube remains unchanged, 

 accurately to compare a negative taken with the field off, with one 

 taken when the field is on. 



The best manner of procedure in the given circumstances therefore 

 seemed to reflect into the spectroscope by means of a semi-silvered 

 mirror the light of a separate vacuum tube placed sideways and to 

 analyse this light simultaneously with that of the tube between the 

 poles. However also this comparison succeeded onlj^ incompletely in 

 view of the extreme accuracy wanted. In some comparisons the line 

 of the unmodified source seemed to be in a symmetrical position for 

 line 5770 as well as for 5791. I hesitate however to attach even a 

 very moderate value to this result. The experiments however forcibly 

 suggested the question : 



1) LoHMANN, Beiti'age zar Kenntniss des ZEEMAN-Phanomens. Dissertation. Halle 

 a. d. S. S. 62. 1907. Zeitschr. f. Wissensch. Photographie. Band Ü. Heft 1 u. 2. 1908. 

 ^) Kayser, Handbuch der Spectroscopie. Band I. p. 732. 



