\= 



= 1990 57 A.TJ. 





35-9 „ 





31-15 „ 





1862-81 „ 





58-2 „ 





54*8 ... 



On the Ultraviolet Spectrum of Elementary Silicon. 483 



these were carefully measured up to arrive at the wave- 

 lengths of the different lines which came out. 



hi taking the photographs the spark spectrum of zinc was 

 first taken on the plate, then the spark spectrum of silicon, 

 and finally the spark spectrum of aluminium. 



The prominent zinc and aluminium lines in the region 

 examined were : — 



Zinc lines*. Aluminium lines f. 



\=213866 A.U. 



02-35 „ 

 00-08 „ 

 2064-32 „ 

 02-08 „ 

 25-51 „ 



and these were used as standards when determining the 

 wave-lengths of the silicon lines. In measuring up a plate 

 the distances of the various zinc, silicon, and aluminium 

 lines from the edge of the plate were carefully measured 

 with a Hilger comparator. The distances of the above- 

 mentioned zinc and aluminium lines from the edge of the 

 plate were used for the abscissae of a calibration curve, and 

 the wave-lengths of the lines as ordinates. This calibration 

 curve was then used to determine the wave-lengths of the 

 silicon lines. Photographs were also taken of the spark 

 spectra of iron and aluminium to make certain that no lines 

 of these elements were included in those obtained with the 

 samples of silicon, but as we had no samples of titanium at 

 hand we were not able to take the precaution of making 

 absolutely certain that no lines of that element were included 

 in those ascribed to silicon. However, the high purity of 

 the silicon used, and the fact that the same spectrum came 

 out on the plates when different pieces of the metal and 

 different points on the same pieces were used as sparking 

 terminals, would seem to guarantee the purity of the spectrum 

 observed. 



The mean values of the measurements made on the wave- 

 lengths of all the lines observed in the spark spectrum of 

 silicon are : — 



* Eder and Valenta, Atlas Ti/piscJwr Spectrin, Wien. 

 t Handke, Inaugural-Dissertation, Berlin, 1909, p. 18. 



212 



