Received since the End of the Session. 



Preliminary Note on the Photographic Spectrum of Comet 

 b 1881. By William Huggins, D.C.L., LL.D., F.R.S. 

 Received June 27, 1881. 



On the evening of June 24, I directed the reflector furnished with 

 the spectroscopic and photographic arrangements described in my 

 paper " On the Photographic Spectra of Stars "* to the head of the 

 comet, so that the nucleus should be upon one half of the slit. After 

 one hour's exposure the open half of the slit was closed, the shutter 

 withdrawn from the other half, and the instrument then directed 

 to Arcturus for fifteen minutes. 



After development, the plate presented a very distinct spectrum of 

 the comet, together with the spectrum of the star, which I have 

 already described in the paper referred to above. 



The spectrum of the comet consists of a pair of bright lines in the 

 ultra-violet region, and a continuous spectrum which can be traced 

 from about F to some distance beyond H. 



The bright lines, a little distance beyond H, with an approximate 

 wave-length from 3870 to 3890, appear to belong to the spectrum of 

 carbon (in some form, possibly in combination with hydrogen), which 

 I observed in the spectra of the telescopic comets of 1866 and 1868. 



In the continuous spectrum shown in the photograph, the dark 

 lines of Fraunhofer can be seen. 



This photographic evidence supports the results of my previous 

 observations in the visible spectra of some telescopic comets. Part of 

 the light from comets is reflected solar light, and another part is light 

 of their own. The spectrum of this light shows the presence in the 

 comet of carbon, possibly in combination with hydrogen. 



On the next night, June 25, a second photograph was obtained with 

 an exposure of an hour and a half. This photograph, notwithstanding 

 the longer exposure, is fainter, but shows distinctly the two bright 

 lines and the continuous spectrum, which is too faint to allow the 

 Fraunhofer lines to be seen. 



(Postscript, July 9, 1881.) 



I have since measured the photographs of the comet's spectrum, 

 and I find for the two strong bright lines the wave-lengths 3883 and 

 3870. The less refrangible line is much stronger, and a faint lumi- 

 nosity can be traced from it to a little beyond the second line 3870. 

 There can be, therefore, no doubt that these lines represent the 

 brightest end of the ultra-violet group which appears under certain 



* "Phil. Trans.," 1880, p. 669. 



