1887.] On Radiant Matter Spectroscopy. 



123 



Professor Cleve's ytterbia, in the form of sulphate, gives in the 

 radiant-matter tube a blue phosphorescence, the spectrum of which 

 shows a strong double blue band,* together with traces of the GrS and 

 the erbia green lines. The addition of lime broadens the blue band 

 and makes it single. Professor Cleve writes that this ytterbia may 

 contain some traces of thulia, perhaps also of erbia, but scarcely any 

 other impurities. Measurements in the spectroscope give the follow- 

 ing approximate results. 



Scale of 

 spectroscope. 



A. 



1 



A 2 ' 



Remarks. 



8-63 



4626 



4673 



Commencement of first blue line. 









This edge is very hazy. 



8-54 



4574 



4780 



Centre of the first blue Hue. 



8-45 



4524 



4885 



End of first blue line. 



8-44 



4518 



4898 



Centre of dark interval between the 









two blue lines. 



8-40 



4475 



4994 



Centre of second blue line. This 









line is narrower than the first 









line. 



The following are measurements taken with the mixture of this 

 ytterbia and lime : — 



Scale of 



A. 



1 



Remarks. 



spectroscope. 



A 2 ' 



8-71 



4674 



4577 



Up to this point there is the con- 









tinuous spectrum of li-calcium. 









Here a black space commences. 



8-515 



4555 



4819 



Commencement of a hazy blue band. 



8-475 



4538 



4855 



End of hazy blue band. This band 









is of considerable brilliancy. 



These blue bands are seen much fainter without lime, and are about 

 as strong in the mixture of thulia and erbia with lime described above. 

 I had ascribed them to ytterbia, when Professor Nilson kindly 

 forwarded me a small specimen of ytterbia, considered by him 

 perfectly pure, and used for his atomic weight determinations. 

 This ytterbia gives absolutely no blue bands. The origin of these 

 bands therefore remains uncertain. 



* This is the band spoken of in my Royal Society paper of 9th June last (' Roy. 

 Soc. Proc.,' vol. 40, 1886, p. 507), provisionally called Sy, and ascribed to ytterbia. 

 If it is not due to ytterbia it is evidence of a new body. 



