296 Sir N. Lockyer and Mr. F. E. Baxandall. [Oct. 11, 



"On the Group IV Lines of Silicium." By Sir NOKMAN LOCKYER, 

 K.C.B., LL.D., Sc.D., F.B.S., and F. E. BAXANDALL, A.RC.Sc. 

 Keceived October 11, Bead November 17, 1904. 



[PLATES 11 AND 12.] 



In previous communications to the Koyal Society* an account was 

 given of the behaviour of the lines of silicium under varying experi- 

 mental conditions, and as a result of this enquiry, the lines were 

 divided into four distinctive groups. 



In these papers no reproductions of the silicium spectra were given, 

 a description of the behaviour of the lines in the various photographs 

 being at the time considered sufficient. 



The genuineness of the lines of Group IV, as silicium lines, has 

 recently been questioned by M. de Gramont. In his paper f he gives 

 *n account of the effect of self-induction on the various groups of lines 

 into which the silicium spectrum was divided from a study of the 

 Kensington photographs. He also gives an analysis of these lines 

 with regard to their appearance in stellar spectra. He agrees as to 

 Groups I, II, and III, but states that the lines of Group IV always 

 disappear from his spectra with the air lines, and he concludes from 

 this that they are not genuine lines of silicium, but belong to either 

 oxygen or nitrogen. This conflicts so much with the conclusions 

 arrived at from the investigations of the Kensington photographs 

 that it becomes necessary to give the photographic evidence on which 

 the lines were accepted as being due to silicium. 



The wave-lengths of the lines of Group IV are 4089' 1, 4096-9, and 

 4116-4. Of these three, 4096*9 is quite insignificant in intensity 

 compared with the other two, and as it is so weak as not to be shown 

 in the reproductions of the photographs, it may well be left out of the 

 present discussion. It may here be stated that, according to Neovius, 

 there is a weak and diffuse oxygen line (Intensity 1) at X 4089-2, and a 

 weak nitrogen line (Intensity <l)atA4116'7; which are very nearly 

 the positions of the silicium lines. Whether these are the lines which 

 M. de Gramont gets in his spectra he records both in his lists as very 

 faint it is not possible to say, but that they are not the lines which 

 appear in the Kensington photographs will probably be readily 

 admitted when the reproductions of the spectra in the present paper are 

 carefully examined. 



The spectrum A shown in Plate 11 is that given by an electric- 

 discharge in a vacuum tube containing silicium tetra-fluoride. The 

 bottom portion is that from the incandescent gases in the bulb of the 



* ' Hoy. Soe. Proc.,' vol. 65, p. 449 ; vol. 67, p. 403. 

 t ' Comptes Kendu,' vol. 139, p. 188. 



