450 



Sir J. Norman Lockyer. 



Very few records of work on the silicium spectrum have been pub- 

 lished by later spectroscopists, but Eder and Valenta* give lines agree- 

 ing in wave-length with those mentioned^ as shown in the accompanying 

 table. 



A. 



(Lockyer) . 



Int. 



X. 



(Eder and 

 Valenta). 



Int. 



Eemarks. 



3856-1 



6 



3855*7 



! 





3862 -7 



4 



3862 -5 







4128-1 



3 



4126 -5 



4 



Probably a misprint for 4128 *5. 



4131 -1 



4 



4131-5 



4 



Later experiments on the spark spectrum of silicium with the aid of 

 the large Spottiswoode coil, and on the spectra of silicium compounds 

 in vacuum tubes, reveal other lines of that element no less interesting 

 from a stellar point of view than those previously mentioned. 



We learn from these recent observations that the lines of silicium 

 may be divided into three sets, no two of which behave alike under 

 varying electrical conditions. The wave-lengths of the lines composing 

 the different sets are : — 



4552-8 *| 

 4568-0 VC. 

 4575-3 J 



There is a line at A 3905-8 which is associated in the spark spectrum 

 of silicium with the lines in set A, but while these are entirely absent 

 from the arc spectrum of silicium, 3905*8 is a strong line in the arc 

 spectrum. This line differs from the others, therefore, in not being 

 enhanced in intensity in passing from the conditions of the arc to those 

 of the spark. So far as is known, the lines in sets B and C have not 

 been recorded by any other observers of the silicium spectrum. 



The behaviour of the three sets of lines in terrestrial spectra is 

 shown in the following figure. 



It is found, on investigating the occurrence of these silicium lines in 

 stellar spectra, that the three sets of lines respectively attain a maximum 

 intensity at the three different levels of stellar temperature represented 

 by /3, y, and £ Orionis. 



poles of the "steeple" used in lliat particular case had broken off close to the 

 glass, and the latter was fused by the heat from the spark. This is the more likely 

 as the double line only appeared on one edge of the spectrum. 

 * ' Denkschr. Kais. Akad. Wissensch., Wien.,' vol. 60, 1893. 



3856-1-j 



3862-7 I 4089-1 1 



4128-1 [ 4116-4 J 

 4131-1 J 



