Mr Purvis, The radiation of various spectral lines of neon, etc. 45 



The radiation of various spectral lines of neon, helium and 

 sodium in a magnetic field. By J. E. Purvis, M.A., St John's 

 College. 



[Read 23 November 1908.] 



Neon. The author had already photographed the principal 

 lines of neon vibrating in a magnetic field, when a paper by 

 Lohmann appeared giving a short account of the effect on the 

 lines when observed by means of an echelon spectroscope* : and 

 since then, Lohmann has completed the measurements f. He used 

 an echelon of 32 plates, the thickness of each plate being 1 cm., 

 and the strength of the magnetic field was usually 11,000 units. 

 He states he was able to see and to photograph the lines divided 

 into 9, 12 and 15 constituents. 



Field strengths were used in the author's experiments of 26,100 

 and 24,000 units respectively, as the distances between the poles 

 of the magnet had to be adjusted to the diameters of the neon 

 tubes. In the first series of experiments, the first order of 

 Professor Liveing's 21-foot radius grating spectroscope was used, 

 and, usually, there was an exposure of 20 minutes of the photo- 

 graphic plates. On examining the photographs with a low power 

 microscope, the author was unable to see the more complicated 

 divisions of some of the lines described by Lohmann. 



Lately, the author has repeated the experiments with an echelon 

 of 18 plates, the thickness of each plate being 7 J mm. ; and using 

 the same field strengths as were used in the Rowland grating 

 experiments. But, when the lines were divided into more than 

 three or six constituents, there was a great difficulty in distinguish- 

 ing clearly between the images of other orders and the images of 

 some of the constituents of the divided lines. For instance as 

 regards the line 6402, described by Lohmann as giving 15 con- 

 stituents, one could only be sure of five constituents ; and of the 

 line 5944 divided into 12 constituents by Lohmann, four constituents 

 could be distinguished, of which there were two fairly sharp ones 



"' Physik. Zeits. 7 Jahrgang, No. 22, Seite 809—811. 



t " Beitr. zur Kennt. des Zeeman-phanomens," Inaug. diss., Halle, 1907. 



