564 MR. W. HTJG-GTNS ON THE SPECTRA OF SOME OF THE STARS AND NEBULA. 
in this condition only. It may be that this apparent repulsion takes place at the time 
of the condensation of the gaseous matter of the coma, into the excessively minute solid 
particles of which the tail probably consists. There is a phenomenon occasionally seen 
which must not be passed without notice, namely, the formation of faint narrow rays 
of light, or secondary tails, which start off usually from the brightest side of the 
principal tail, not far from the head. Sir John Heeschel* considers that “they 
clearly indicate an analysis of the cometic matter by the sun’s repulsive action, the 
matter of the secondary tails being darted off with incomparably greater velocity (indi- 
cating an incomparably greater intensity of repulsive energy) than that which went to 
form the primary one.” The important differences which exist between the spectrum of 
Beoesen’s comet and that of Comet II., 1868, appear to show that comets may vary 
in their constitution. If the phenomenon of the secondary tails were observed in a 
comet which, like Comet II., 1868, appears to consist of carbon, the analytical action 
supposed by Sir John Heeschel might be to separate between particles of carbon in 
different conditions, or possibly in a state of more or less subdivision. The enormous 
extent of space, sometimes a hundred millions of miles in length, over which a compara- 
tively minute portion of cometary matter is in this way diffused, would suggest that we 
have in this phenomenon a remarkable instance of the extreme division of matter. 
Perhaps it would be too bold a speculation to suggest that, under the circumstances 
which attend the condensation of the gaseous matter into discrete solid particles, the 
division may be pushed to its utmost limit, or nearly so. If we could conceive the 
separate atoms to be removed beyond the sphere of their mutual attraction of cohesion, 
it might be that they would be affected by the sun’s energy in a way altogether different 
from that of which we have been hitherto the witnesses upon the earth. 
Though comets may differ in their constitution, reference may be permitted to the 
periodical meteors which have been shown to move in orbits identical with those of some 
comets. If these consist of carbon, we might have some explanation of the appearances 
presented by these meteors, though their light is doubtless greatly modified by that of 
the air rendered luminous by their passage, as well as by the degree of temperature to 
which they are raised. Carbon is abundantly present in some meteorites, but we have 
no certain evidence at present that the periodical meteors belong to this class of celestial 
bodies. 
Note to Plate XXXIII. 
In fig. 2, the bright line at the beginning of the middle band of the spectrum of 
.olefiant gas is made too strong. 
* Familiar Lectures on Scientific Subjects, p. 129. 
