OE SOME OE THE STARS AND NEBTTL2E. 
557 
of the middle band near its less refrangible limit. This part would consist chiefly of 
light from the bright central spot. 
As has been stated, the middle band commences probably with a bright line ; for the 
limit of the band is here abrupt and distinct. On the contrary the exact point of com- 
mencement and termination of the other bands could not be observed with certainty. 
I could perceive no other bands, nor light of any kind beyond the three bands, in the 
parts of the spectrum towards the red and the violet. 
When the marginal portions of the coma were brought upon the slit, the three bands 
of light could still be traced. When, however, the spectrum became very faint, it ap- 
peared to me to become continuous ; but the light was then so very feeble that it could 
not be traced beyond the three bands towards the violet or the red. 
On this evening I observed the spectrum of the comet in a larger spectroscope, which 
gives a dispersion equal to about five prisms. In this instrument the middle band was 
well seen. It retained its nebulous, unresolved character, and the abrupt commencement, 
as if by a bright line, already mentioned, was distinctly seen. 
For convenience of comparison, the spectrum of Brorsen’s comet, and that of the 
gaseous nebulae, have been added to the diagram, fig. 2, Plate XXXIII. The spectrum 
of Brorsen’s comet consisted of three bright bands and a faint continuous spectrum. 
These bands appeared, as represented in the diagram, narrower than those of the comet 
now under examination. It is not possible to say to what extent this circumstance 
may be due to the much feebler light of this comet. Though the bands of Brorsen’s 
comet fall within the limits of position occupied by the broad bands of Comet II., they 
do not correspond to the brightest parts of these bands. In the middle band I sus- 
pected two bright lines, which appeared shorter than the band, and may be due to the 
nucleus. Brorsen’s comet differed from the two small comets which I had previously 
examined* in the much smaller relative proportion of the light which forms a conti- 
nuous spectrum. In Brorsen’s comet the bright middle part of the coma seemed to 
emit light similar to that of the nucleus, in the other comets the coma appeared to 
give a continuous spectrum. The three comets resembled each other in the circum- 
stance that the light of the central part was emitted by the cometary matter, while the 
surrounding nebulosity reflected solar light. 
It will be seen in the diagram that the bands of Brorsen’s comet, and those of 
Comet II., occupy positions in the spectrum widely removed from those in which the 
lines of the nebulae occur. The spectra of the gaseous nebulae consist of true lines, which 
become narrow as the slit is made narrower. 
The following day I carefully considered these observations of the comet with the 
hope of a possible identification of its spectrum with that of some terrestrial substance. 
The spectrum of the comet appeared to me to resemble some of the forms of the spectrum 
of carbon which I had observed and carefully measured in 1864. On comparing the 
* Comet I., 1866. Proceedings, vol. xv. p. 5, and Comet 1867, Monthly Notices of Royal Astronomical 
Society, vol. xxvii. p. 288. 
