Further Nutc on the Spcctm:n of Silicium. 405 



common to the two spectra, the relative intensities of the lines differ 

 greatly. 



These later photographs show all the lines enumerated in my former 

 communication, with the addition of several fainter lines and a strong 

 double in the green, the latter falling outside the region previously 

 investigated. 



Lines in the spark spectrum of silicium have been recorded by Eder 

 and Valenta* and by Exner and Hasehekf. A comparison of these with 

 the lines photographed at Kensington is given in the following table. 



Better photographs of the spectra of the type stars have been 

 recently obtained, and we are now in a more satisfactory position to 

 trace the various silicium lines through successive stages of stellar 

 temperature. The lines in the spectra of a. Cygni, /? Orionis, y Orionis, 

 and Orionis which correspond with lines of silicium are indicated in 

 the table by their intensities. 



In my former note the lines were divided into three sets, A, B, C, 

 and the behaviour of the different sets in terrestrial and celestial 

 spectra was described. The groupings were then made, roughly 

 speaking, in order of wave-length. For my present purpose, it is 

 important to divide them according to the conditions under which they 

 become prominent lines ; this only involves the changing of the order 

 of the groups, and involves no interchange of any of the lines from 

 one group to another. Reference was also made previously to a line at 

 A 3905-8 special to the arc, but as this is not an enhanced line it was 

 not included in any of the sets A, B, C. Hence, I now add another 

 group consisting of lines most prominent in the arc spectrum. The lines 

 constituting the various groups will then be as given below, arranged 

 in order of ascending temperature, Group I being the lowest : 



f 4089-1- 



Group IV < 4096 9 Set B of previous note. 

 Ull6-4_ ! 

 |- 4552 -8 



Group III J 4568-0- Set C 

 1 4574- 9- 

 f 3853 -9 



3856-1 | 

 ( 3862-7 , 

 Group II <j 4128' 



4131-1- 

 5042 

 1^5057 

 T f 3905 -8 

 1 * 1 1 4103-2 



' Sitz. Kais. Aksd. der \Viss. Wien,' vol. 107, p. 41. 

 ' Ast. Phvs. Jour.,' vol. 12, p. 48. 



