460 Ultra-violet Spectra of Magnesium and Selenium. 



A = 3200 A.U. The approximate wave-lengths of the bands 

 found in the ultraviolet are given as A = 3240, 3255, 3280, 

 3295, 3317, 3338, 3363, 3387,3412, 3435, 3460, 3483, 3510, 

 3537, 3592, 3614, 3640, 3663, 3684,3700,3715, 3730, 3742, 

 3755, 3763, 3774, and 3802 A.U. 



As none of these bands are in the region in which the 

 emission lines, given above, were found, some experiments 

 were performed to find if absorption did take place at any 

 of these wave-lengths. Some selenium metal was enclosed 

 in a fused quartz tube, highly exhausted and sealed off'. 

 But owing to the difficulty of obtaining a continuous 

 spectrum in the region from A = 2200 A.U. to X=1850 A.U., 

 this method was abandoned. The photograph (/) on the 

 plate showing a clear reversal of the selenium line X=1960 

 A.U. was obtained in the carbon arc. Two solid carbons 

 with flat ends were used. A large bead of selenium met;il 

 was placed on the vertical carbon and then the arc was 

 struck behind the selenium metal. As the carbons became 

 hot the selenium boiled up in front of the arc and gave a 

 sharp but narrow reversal-band at \=1960 A.U. This was 

 the only absorption band observed, and it is possible that this 

 frequency on account of its intensity and easy reversal is 

 intimately connected with one of the series i/ = (l*5, S) 

 — (m, P) or y=(l"5, S)— (??i, p 2 ), the remainder of the series 

 lying below A, = 1850 A.U. To investigate this further 

 work with a fluorite or a vacuum grating spectrograph will 

 be necessary. 



Summary. 



1. Twelve new lines have been recorded in the selenium 

 spark spectrum between A, = 2200 A.U. and X = 1850 A.U. 



2. Five lines in the selenium arc have been found between 

 the same limits. 



3. In the sources used no o part of the spectrum longer in 

 wave-length than A,= 2200 A.U. was present. 



4. The absorption spectrum of selenium metal in the 

 carbon arc was investigated and a reversal was found at 

 A,= 1960 A.U., which is the strongest line in both the arc 

 and spark spectra. 



5. If the absorption of selenium vapour should prove to 

 be analogous to that of mercury, zinc, and cadmium, this 

 would indicate that the two series v=(l*5,S) — (w,P) and 

 v = (l'5, S) — (jn,p 2 ) for selenium are in the extreme ultra- 

 violet. 



The Physical Laboratory, 

 University of Toronto. 



