Ultra-violet Spectra of Magnesium and Selenium. 453 



The wave-lengths of the lines measured and their relative 

 intensities are given in Table I. (p. 454). In the same table 

 the lines recorded by other observers for the range of wave- 

 lengths shorter than \ = 2852*22 A.U. are included. 



II. Series Relations. p, 



The most recent work on the series spectra of magnesium is 

 the Inaugural Dissertation recently published by E. Lorenser 

 of Tubingen. In this paper he draws attention to a series 

 calculated from the formula 



A— v={m, X) 



(«+*t=) 



where A= 56098*8, and for which the wave-lengths of the 



different members are : — 



I 

 m = 2 3 4 5 6 K\ 



X = 2852-22 2219-8 (?) 2019-2 (?) 1930-9 1886-3 



The first member of this series is well known, and the fifth 

 and sixth it will be noted were observed by Handke. 

 Lorenser, however, was not able to observe the second and 

 third members, and concluded that the series as calculated 

 was based on false assumptions. The results of the present 

 investigation, as the table of wave-lengths shows, goes to 

 support Lorenser's view, for no lines were observed with 

 wave-lengths which could be supposed to represent \ = 2219*8 

 A.U. andX = 2019*2 A.U. 



A series of single lines and represented by v = (l*5, S) 

 — (m, P) has been calculated by Lorenser as follows : — 



m= 2 3 4 5 6 7 8 



a = 2852-22 2025-08 1828-1 1748-09 1707*3 1683'64 1668 04 



o 



For this series \ = 2852*22 A.U. is well known. The line 

 \= 2025*08 A.U. was observed by Saunders and is brought 

 out clearly in the present investigation as a prominent 

 line. Both Lyman and Saunders have observed the line 

 X = 1828*1 A.U. No line has been observed as yet exactly at 

 X= 1748*09 A.U., but Handke gives two which are close 

 to it. The lines X = 2852*22 A.U. and \ = 2025*08 A.U. have 

 been shown by one of us to be strongly absorbed by Q non- 

 luminous magnesium vapour, and the line \ = 2852*22 A.U., 

 it will be recalled, is easily reversed. 



Moreover, it will be recalled that when magnesium vapour 

 is bombarded by electrons*, the line \ = 2852*22 A.U. is the 



* McLennan, Proc. Roy. Soc. A. vol. xcii. p. 574. 



M 



I 



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