Mr. W. Huggins on the Spectrum o/Brorsen's Comet. 61 



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

 bands. When the slit was wide they resembled the expanded lines 



i-rH- 



I 1 I I 1 



seen in some gases — for example, the line F in the spectrum of hy- 

 drogen at the atmospheric 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 denned. 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 suspi- 

 cion seems to be strengthened by the circumstance that when by 

 moving the telescope the image of the comet was made to pass be- 

 fore 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 

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

 scarcely be represented without making it appear too strong rela- 

 tively to the bright bands. 



The position in the spectrum of the bands was determined by 

 micrometrical 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, 



