560 
MR. W. HUGGINS ON THE SPECTRA 
exact coincidence could not be obtained. We considered these bands to agree precisely 
in position with the bands corresponding to them in the spectrum of the spark. 
The apparent identity of the spectrum of the comet with that of carbon rests not 
only on the coincidence of position in the spectrum of the bands, but also upon the very 
remarkable resemblance of the corresponding bands in their general characters, and in 
their relative brightness. This is very noticeable in the middle band, where the grada- 
tion of brightness is not uniform. This band in both spectra remained of nearly equal 
brightness for the same proportion of its length. 
On a subsequent evening, June 25, I repeated these comparisons, when the former 
observations were fully confirmed in every particular. On this evening I compared the 
brightest band with that of carbon in the larger spectroscope, which gives a dispersion 
of about five prisms. 
The remarkably close resemblance of the spectrum of the comet to the spectrum of 
carbon necessarily suggests the identity of the substances by which in both cases the 
light was emitted. 
It may be well to state that some phosphorescent and fluorescent bodies give discon- 
tinuous spectra in which the light is restricted to certain ranges of refrangibility. There 
are, however, several considerations which seem to oppose the idea that the light of 
comets can be of a phosphorescent character. Phosphorescent bodies are usually so 
highly reflective that the phosphorescence emitted by them is not seen so long as they 
are exposed to light. This comet was still in the full glare of the sun, and yet the 
continuous spectrum corresponding to reflected solar light was of extreme feebleness 
compared with the three bright bands which we have under consideration. The pheno- 
menon of phosphorescence seems to be restricted to bodies in the solid state, a condition 
which is not apparently in accordance with certain phenomena which have been observed 
in large comets, such as the outflow of the matter of the nucleus, and the formation of 
successive envelopes. 
There are, indeed, some phenomena of fluorescence, such as that of a nearly transparent 
liquid becoming an object of some brightness by means of the property which it pos- 
sesses of absorbing the nearly invisible rays of the spectrum, and dispersing them in a 
degraded and much more luminous form, which are less obviously inconsistent with 
cometary phenomena than are those of phosphorescence. 
The violent commotions and internal changes which we witness in comets when near 
the sun seem, however, to connect the great brightness which they then assume more 
closely with that part of the solar force we call heat. There is also to be considered 
the fact of the polarized condition of the light of the tail and some parts of the comae 
of comets, which shows that a part of their light is reflected. 
The observations of the spectrum of Comet II. contained in this paper, which show 
that its light was identical with that emitted by highly heated vapour of carbon, appear 
to be almost decisive of the nature of cometary light. The great fixity of carbon seems 
indeed to raise some difficulty in the way of accepting the apparently obvious inference 
