162 W. A. Norton—Coggia’s Comet. 
dioxide of carbon (carbonic acid gas). Other experiments 
have shown that the volatile hydro-carbons give, with the 
electric spark, the same spectroscopic bands; and that these 
are wholly due to the momentary incandescence of the carbon 
molecules of the compound. - Several other comets have given 
the same “carbon bands.” Brorsen’s comet, a faint circular 
nebula, invisible to the naked eye, proved to be an exception. 
Three bright bands were observed in its spectrum, but they 
differed in position and other features from the carbon bands. 
(3.) “The spectrum of the nucleus was continuous, but it 
appeared to have traces of numerous bright bands, and three 
or four dark lines also were seen.” 
(1.) From the bright bands observed we may infer that the 
vapor of some hydro-carbon. ; 
‘ é e light of incandescence of the gaseous particles, 
which furnished the bands, must have been of electric origin; 
since the heat of the sun could not have been sufficient to 
ignite the most inflammable vapor. 
(3.) The continuous spectrum on which the three, carbon 
bands were seen, affords no decisive evidence of the presence 2 
the coma of discrete solid particles, since it may have resulted 
from the solar light reflected from the gaseous particles. Such 
light would not have been sufficiently intense to give the dark 
solar lines. 
(4.) The “traces of bright bands” seen in the spectrum of 
the nucleus reveal the presence of vapors at its surface shining 
by electric light. The bright continuous spectrum may have 
wholly due to reflected solar light (since dark solar lines 
were not wanting), or partly to discrete solid particles render 
luminous by electric discharges. The light reflected from the 
solid nucleus, or from dense vapors or clouds near its surface, 
may well have been of sufficient intensity to make the gaseous 
n bands resulting from electric discharges inconspicuous. 
(5.) The spectroscope did not give any decisive evidence 
with to the state of the matter in the tail—whether 
gaseous or composed more or less of discrete solid particles; 
but since the tail was formed of matter flowing in continuous 
streams from the head, we must suppose that it was made up 
chiefly of gaseous particles, like the head. 
j (6.) The light of the tail was exclusively reflected solar 
ight. Si 
- 
