SPECTRUM ANALYSIS OF THE HEAVENLY BODIES. 159 
§ III. Ossrrvarions oF Comers, 
As soon as I had successfully applied the analysis by the prism to the 
light of the nebulie, it appeared to me to be of great importance to subject 
the light of comets to a similar examination, especially as we possessed no 
certain knowledge of the intimate nature of these singular and enigmatical 
bodies, or of the cosmical relations they may sustain to the solar system. 
Several attempts which I made to obtain a prismatic observation of Comet I., 
1864, were rendered unsuccessful by the position of the comet, and by un- 
fayourable weather. M. Donati succeeded in making an observation of its 
spectrum. He describes it as consisting of three bright bands *. 
In the discourse I had the honour to give before the Association at Not- 
tingham, I described the results of the analysis of a very small and faint 
comet, Comet I. 1866. Its spectrum was compound, and showed that the 
nucleus was self-luminous, and the surrounding coma was visible by reflect- 
ing solar light. ‘The position of the bright line, into which the light of the 
nucleus was resolved, appeared, as far as the faintness of the object per- 
mitted a determination, not to differ greatly from that of the brightest line 
of the nebule. I was led by this circumstance to suggest that possibly the 
material of the comet was similar to the matter of which the gaseous nebulz 
consist. A subsequent examination of three other comets, of which the 
principal results will be given in this paper, shows that this suggestion of 
the identity of the material of comets with that of some of the nebule can- 
not be maintained. 
The spectrum of a faint comet examined in May 1867 resembled that of 
Comet I., 1866. The light of the self-luminous nucleus gave a line between 
b and F, and the coma was represented by a continuous spectrum, which 
showed that it reflected solar light. 
Brorsen’s Comer. 
From May 2 to May 13 I examined the spectrum of Brorsen’s comet at 
its reappearance in 1868, This comet was brighter than the two comets I 
had previously examined; and IT was, from this cause, enabled to obtain a 
fuller and more complete analysis of its light. 
Its spectrum, as seen in a spectroscope furnished with two prisms of dense 
flint glass, with a refracting angle of 60°, is represented in fig. 2. Pl. V. 
The comet appeared in the telescope as a nearly round nebulosity, in 
which the light increases rapidly towards the centre, where on some occasions 
I detected, I believe, a small nucleus. 
The spectrum consisted, for the most part, of three bright bands, into 
which the light of the brighter portions of the coma was dispersed. These 
bands I was unable to resolve into lines, even when the slit was made narrow. 
The position of the bands was determined by micrometrical measures, and 
also by the simultaneous comparison of them with the bright lines of mag- 
nesium, sodium, hydrogen, and nitrogen. The brightest band, which may be 
considered to represent about three-fourths of the whole light of the comet, 
occurs between 6 and F, and is, in a small degree, less refrangible than the 
line of nitrogen with which the brightest of the three lines of the nebule is 
coincident. The band in the blue was considerably more refrangible than 
F, and was nearly as refrangible as the group of bright lines in the air- 
spectrum which have the numbers 2642 to 2669 in the maps and tables of 
* Monthly Notices of the Royal Astronomical Society, vol. xxv. p.490; and Astrono- 
mische Nachrichten, No. 1488. 
