422 



Messrs. D. Herman and F. Rutley. [June 18, 



by the darkening in the yellow portion of what; otherwise would be a 

 continuous spectrum. ' 



The calcium phosphorescent spectrum by itself is continuous, with 

 no break, lines, or bands in it. 



The Anomalous Line rj 2693. 



A, 



On several occasions I have spoken of an ors.ngo line, 2693, which 

 by its brilliancy and sharpness is a prominent object in most of the 

 samarium-yttrium spectra. With pure samaric sulphate it is exceeding 

 faint. With samaria containing 5 per cent, of yttria it is very little 

 brighter ; with 10 per cent, of yttria it gain3 a little ; with 1 5 per 

 cent, it is brighter still, and with a mixture of 80 parts samaria and 

 20 parts yttria it is at its maximum intensity. It continues to be the 

 most striking feature in the spectra of the variois mixtures of samaria 

 and yttria until the proportion becomes samaria 3, yttria 97, when it 

 begins to get less bright, and only when pure yttria is reached does it 

 altogether vanish. 



It is noteworthy that so long as this bright line is a component of 

 the spectrum, the other bands manifest decidedly less intensity, and 

 many of them are suppressed. The profound modification in the 

 spectra of samaria and yttria developed by their mixture is, I believe, 

 without precedent in spectrum analysis. It is difficult to realise the 

 character of the modification which converts somewhat faint diffused 

 bands into one intensely sharp and brilliant line. 



One important lesson taught by the many anomalies unearthed in 

 these researches is, that inferences drawn from spectrum analysis per 

 se are liable to grave doubt, unless at every step the spectroscopist 

 goes hand in hand with the chemist. Spectroscopy may give valuable 

 indications, but chemistry must after all be the court of final appeal. 



VI. " On the Microscopic Characters of some Specimens of 

 Devitrified Glass; with Notes on certain enalogous Struc- 

 tures in Rocks.*' By Douglas Herman and Frank Rutley. b 

 Communicated by Professor T. G. Bonney, D.Sc, F.R.S.* 

 Received May 28, 1885. 



(Abstract.) 



This paper relates first to the changes brought about in glass solids 

 bounded by plane surfaces, by exposure to high temperatures, the 

 main object of the paper being to elucidate the changes which have 

 taken place in vitreous, and once vitreous, rocks by comparing the 

 phenomena of natural devitrification with similar phenomena effected 



