3IO 



NATURE 



[Attgust 5, 1880 



the experiments were being made to get my observations 

 confirmed. He has been good enough to write me the 

 following letter and to allow me to give it here :— 



" March 2 1 



" Mv Dear Lockyer, — The following is an account of 

 the experiment which I saw performed in your laboratory 

 on Monday, March 15 : — 



"A tube containing carbon-tetrachloride was attached to 

 the Sprengel pump. As exhaustion proceeded the air was 

 gradually displaced by the vapour of the tetrachloride. 

 The electrodes were a few millimetres apart. If the spark 

 was taken without a condenser in the vapour the well- 



known carbon bands first observed by Swan in the 

 spectrum of a candle were seen with great brilliancy ; I 

 also saw the blue band which you said was identical in 

 position with one of the blue bands seen in the flame of 

 cyanogen or in the spectrum of the electric arc. When 

 the condenser and air-break were introduced this spectrum 

 gave way to a line spectrum in which I could recognise 

 the lines of chlorine. The lines of nitrogen were absent, 

 not a trace of the principal double line in the green bein^ 

 seen. The hydrogen line Ha(C) was faintlv visible when 

 I first observed the spectrum, but it got gradually weaker 

 and Jinally disappeared altogether. When this line -was 

 no lonoer visible the condenser was taken out of circuit 



again, and the same carbon bands were seen as before. 

 These bands, therefore, show themselves with great 

 brilliancy when a strong and powerful spark doej not 

 reveal the presence either of hydrogen or nitrogen. 

 "March 21, 18S0 (Signed) Arthur Schuster " 



This result, which entirely endorses the workof Attfield 

 and Watts, has been controlled by many other experi- 

 ments. I have also repeated Morren's experiment and 

 confirm it, and I have also found that the undoubted 

 spectrum of cyanogen is visible neither in the electric arc 

 nor in the surrounding flame. 



Hence then in the case of carbon, as in the prior cases 



of hydrogen, nitrogen and the like, those who hold that 

 the flutings are due to impurities must, it would seem, 

 abandon their position ; for the flutings are undoubtedly 

 produced by carbon vapour. Nor is this all ; the sugges- 

 tion that the various difficulties which have always been 

 acknowledged to attend observations of this substance 

 may in all probability be due to the fact that the sets of 

 carbon flutings represent diflerent molecular groupings of 

 carbon, in addition to that or those which give us the line 

 spectrum, and that the tension of the current used now 

 brings one set of flutings into prominence and now 

 another, seems also justified by the facts. This suggests 



the view that a body may have a fluted spectrum of 

 compound origin as well as a line spectrum. 



This conclusion is greatly strengthened by the prelimi- 

 nary discussion of a considerable number of photographs of 

 the spectra of various carbon compounds. 



A general comparison of the photographs first enables 

 us to isolate the lines in the blue and ultra-violet portions 

 of the spectrum (wave-lengths 4300-3S00) of the substance 

 associated with the carbon in each case. 



In this manner the lines seen in the photographs of 

 the spectra of CClj, Ci„Hs, CN, CHI3, CSj, CO.,, CO, 

 &c., have been mapped, and both the common and special 

 lines and flutings thus determined. 



The phenomena seen with more or less constancy are 

 a blue line, with a wave-length of 4266 ; a set of blue 

 flutings, extending from 4215 to 415 1 ; and another set of 

 ultra-violet flutings, which extend from 3885 to 3S43 (all 

 approximate numbers). 



