388 Mr. W. Huggins on the Spectrum of Brorsen's Comet. [May 14, 



bands. The length of the bands in the instrument shows that they are not 

 due alone to the stellar nucleus, but are produced by the light of the 

 brighter portions of the coma. 



I took some pains to learn the precise character of these luminous bands. 

 When the slit was wide they resembled the expanded lines seen in some 

 gases ; for example, the line F in the spectrum of hydrogen at the atmo- 

 spheric pressure. As the slit was made narrow the two fainter bands, 

 namely the one in the yellow and the one in the blue, appeared to fade out 

 without becoming more defined. I was unable to resolve these bands into 

 lines. In this respect they are very different from the bright lines of the 

 nebulae, which become narrow as the slit is made narrow. 



The middle band, which is so much brighter than the others that it may 

 be considered to represent probably three-fourths, or nearly so, of the whole 

 of the light which we receive from the comet, appears to possess similar 

 characters. In this nebulous band, however, I detected occasionally two 

 bright lines, which appeared to be shorter than the band, and may be 

 due to the nucleus itself. This suspicion seems to be strengthened by the 

 circumstance that when by moving the telescope the image of the comet 

 was made to pass before the slit, these brighter lines were only observed 

 .when the middle of the comet was upon the slit, while the nebulous band 

 continued as long as any part of the comet, except its extreme margin, was 

 upon the slit. 



Besides these three bright bands there was a very faint continuous spec- 

 trum. This spectrum is omitted in the diagram, as it could scarcely be 

 represented without_.making it appear too strong relatively to the bright 

 bands. 



The position in the spectrum of the bands was determined by micro- 

 metrical measures, and also by simultaneous comparison, of the bands with 

 the bright lines of magnesium, sodium, hydrogen, and nitrogen. The 

 brightest band, which is in the green part of the spectrum, is nearly in the 

 position of the brightest line of the nebulae, which coincides with the double 

 line of the spectrum of nitrogen ; but, as the diagram shows, the band in 

 the comet is in a small degree less refrangible than the line of nitrogen. 

 This difference of refrangibility cannot be attributed to the comet's 

 motion, since at the time the observations were made the comet was ap- 

 proaching the earth. 



The band in the blue is considerably more refrangible than F, and is 

 nearly as refrangible as the group of bright lines in the air-spectrum, which 

 have the numbers 2642, 2669 in the map and tables of my paper '*0n 

 the Spectra of the Chemical Elements" 



The least refrangible of the bands occurs in the yellow part of the spec- 

 trum, at about the distance from E of one-third of the interval which sepa- 

 rates E from D. 



The spectrum of this comet resembles the diagram given by Donati of 



* Astronomische Nachrichten, No. 1488. 



