Note on the Spectrum of Silicium. 449 



•I. " Xote on the Spectrum of Silicium." By Sir J. Norman Lockyer, 

 K.C.B., F.K.S. 



II. "Preliminary Table of Wave-lengths of Enhanced Lines." By 

 Sir J. Norman Lockyer, K.C.B., F.KS. 



III. " The Colour-Physiology of Hippolyte varians " By F. W. Keeble, 



and F. W. Gamble. Communicated by Professor S. J. Hickson, 

 F.E.S. 



IV. " The Medusae of Millepm-a." By Professor S. J. Hickson, F.R.S. 



f Note on the Spectrum of Silicium." By Sir Norman Lockyee, 

 K.C.B., F.B.S. Received November 9 — Read November 23, 

 1899. 



In 1895, during the course of an investigation of the spectra of 

 gases distilled from the mineral Eliasite, a double line at AA 4128*3 and 

 4131*4 was found in one of the photographs, which could not at the 

 time be traced to any terrestrial substance. It was thought that it 

 might belong to some new gas, especially as there was a well-marked 

 double in the corresponding region of a Cygni. 



Some time later, shortly after the discovery by Professor Pickering 

 of a new series of probable hydrogen lines in the spectrum of ( Puppis, 

 an attempt was made to produce this series of lines in the laboratory, 

 and the spectrum of hydrogen was examined under different electrical 

 conditions. During this research it was found that with the use of the 

 spark in vacuum tubes of very narrow bore, with large jars in circuit, 

 the same double line noted in the eliasite photograph made its appear- 

 ance, and as in these experiments the glass on the inside of the capil- 

 lary of the vacuum tube had become partially fused, silicium suggested 

 itself as being the origin of this so-called " unknown" double. That 

 this was correct was proved directly afterwards by photographing the 

 spectrum of a spark over SiCh in a retort, the double in question being 

 the most prominent feature of the spectrum.* 



In addition to this double, a wider one at XX 3856*1 and 3862*7 was 

 noticed, and as the two components also agreed very closely in position 

 with lines in the spectrum of a Cygni, it was concluded that silicium 

 was the true origin of the lines, f 



* A list of the spark lines of silicium was published by Eder and Valenta in 

 1893, and the identity of the strange double would probably have been established 

 before by a reference to that list, had it not been for a large error in the wave- 

 length of one of the components of the double as recorded by them. 



f The probable explanation of the appearance of the silicium double in one of 

 the photographs of the spectrum of the eliasite gases is that one of the platinum 



