4 Br. Euggins [Jan. 20, 



the induction spark in defiant gas with the comet's spectrum, in the 

 manner shown upon the screen. 



The next diagram shows the result of this direct comparison.* 

 There could be no longer any doubt of the oneness of chemical nature 

 of the cometary stuff with the gas we were using,^ in fact, that carbon, 

 in some form or in some state of combination, existed in the cometary 

 matter. From that time some twenty comets have been examined by 

 different observers. The general close agreement, notwithstanding 

 some small divergencies, of the positions of the three bands with those 

 seen in the flame spectrum of hydrocarbons, leaves no doubt whatever 

 that the original light of comets is really due to matter containing 

 carbon in combination with hydrogen. 



At first, indeed, for certain reasons, I was led to consider this 

 spectrum to be that of carbon itself in the form of gas, a view still 

 held by some physicists ; but subsequent researches by several 

 experimentalists on this point appear to me to be strongly in favour 

 of carbon combined with hydrogen. f 



Last year another advance was made. For the first time since the 

 spectroscope has been in the hands of the astronomer the coming of a 

 bright comet made it possible to extend this mode of research into 

 the more refrangible region of the spectrum. Making use of the 

 apparatus and arrangements which I employed for photographing the 

 spectra of stars,| I succeeded in obtaining a photograph of the spectrum 

 of the head of comet h. 



A copy of this spectrum is now upon the screen (see plate). There 

 is a continuous spectrum which can be traced from about G to beyond 

 K, in which are seen distinctly several of the Fraunhofer lines, G, \ 

 H, K, and many others. The presence of these lines was crucial, 

 and made it certain that this continuous spectrum was really duo to 

 reflected solar light.§ 



But there was also present a second spectrum consisting chiefly of 

 two groups of brigJd lines. These evidently were due to the same 

 light which is resolved, in the visible region, into the three bright 

 groups. 



I regarded them with intense interest, for there was certainly 

 hidden within these hieroglyphics some new information for us. 

 Measures of their position in the spectrum, taken under the micro- 

 scope, brought out that these groups were undoubtedly the same 



* These hydrocarbon groups may be seen with a pocket spectroscope in the 

 blue base of a candle flame or in the flame of a Bunsen burner. 



t Among many papers, I may refer to * Ueber die Spectra der Cometen,' Dr. 

 Hasselberg, Mem. Acad, des Sciences, St. Pe'tersbourg, vii. ser. tome xxviii. 

 No. 2; and papers by Professors Liveiug and Dewar and by Mr. Lockyer in 

 recent volumes of the ' Proceedings of the Royal Society.' 



X ' Trans. R. S.' 1880, part 2, p. G71. ' Proceedings R. Instit.' vol. ix. part 3, 

 p. 285. 



§ See observations of the visible spectrum of this comet by Professor Young, 

 the Astronomer Royal, Professor Yogel, Professor Wright, Dr. Von Konkoly, 

 Dr. Hasselberg, and others. 



