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PROCEEDINGS OE THE PERTHSHIRE SOCIETY OE NATURAL SCIENCE. 
strange and mysterious objects are confined to our region | 
of the universe. Away out in the vast interstellar re¬ 
gions,—those vast fields through which our sun with his 
attendant train of planets is now sweeping,—they are rush¬ 
ing in all directions, and would be found in various condi¬ 
tions. Some we may suppose to be in a formative state, 
the matter of which the future comet is to be composed 
being enormously diffused, and in the act of being 
drawn together and condensed, in order that, in its 
more compacted state, it may feel the influence of some 
far-distant attraction, and start from its former quiescence 
upon an impetuous course, as a comet around some distant 
sun. But whilst enormous areas of interstellar space may 
contain this cometic matter from which new comets are 
being formed, other spaces may—indeed, we know, must— 
contain comets which have lost themselves. Astronomers 
know that many years ago a comet got entangled among 
the satellites of Jupiter and was thrown completely out of 
its course, and sent at last along the arm of a parabola, 
never again to return to this region of the universe. Such 
an accident must be no uncommon occurence, when we 
consider the number of comets, and the risks they run in 
rushing through the planets of a system. A very small 
planet—or even a satellite—would be quite sufficient to de¬ 
flect their path if they came near it, so that they would 
never return upon themselves. Even two of them passing 
near each other might so alter their orbits as to send one 
or both of them out into those vast abysses of space, where 
they would be lost,—where they could only wander aim¬ 
lessly, waiting, as it were, for some new attraction to in¬ 
fluence them. A lost comet being all but entirely freed 
from the forces which formerly impelled it, and as it were 
held it together, and being away out into those abysses of 
space where it was feebly assailed by distant and opposing 
attractions from the nearer surrounding suns, may be 
supposed to expand itself, and go back again to the 
nebulous mass, from which it was originally formed. The 
forces which compacted it, and sent it on its impetuous 
course, being spent, it would naturally return to its pris¬ 
tine state. Such appears to be the only condition in which 
a lost comet may be expected to be found. 
If we have succeeded in shewing it possible—if not 
probable—that these cometic masses exist in the inter¬ 
stellar spaces, we have to some extent prepared the way 
for the understanding of the theory we have advanced, as 
an explanation of the phenomena of the after-glow. We 
suppose that the sun in his gigantic sweep southward, 
passed, with his attendant train of planets, during the 
continuance of the glow, through cne of these vast cometic 
fields; and that during that time the upper regions of our 
atmosphere were in contact with the cometic matter, by 
which it was practically enormously deepened, and the 
light of the sun was for a much longer time refracted or 
bent down towards the earth. The theory we have advanced 
will neither be understood nor appreciated unless the 
enormous difference in density between the atmosphere and 
cometic matter, as we know it to exist, be kept in view. 
Living as we do at the bottom of an atmospheric ocean 50 
miles deep, we are apt to think of atmospheric effects as 
they are seen and felt around us, forgetting that the 
atmosphere becomes thinner and rarer as we ascend, until 
it ceases altogether, and absolute vacuum (so far as the 
atmosphere is concerned) prevails; so that phenomena 
which are possible in one depth, are absolutely impossible 
in another. In the extremely rarified air of the upper 
regions, where vacuum was being approached, even such 
rare and attenuated matter as that of which comets are 
composed could be absorbed for a certain depth into it. 
They could for miles downward be blended together, and 
that so gradually that it would be impossible to tell where 
the effects produced by the one ended, and those by the 
other began. It was the practical .deepening of the atmos¬ 
phere for man3' miles, by its being overlaid with the cometic 
matter, and being blended with it, which refracted or bent 
down the rays of the sun (which after sunset ordinarily 
pass clean over the atmosphere), causing the twilight 
glories to be continued for nearly an hour longer than they 
usually are, and which occasioned the extraordinary 
brilliancy of colour which was one of the most striking 
characteristics of the glow. 
In confirmation of the theory we have advanced, it may 
be mentioned that, during the continuance of the glow, 
telescopes, when applied to celestial observation, came 
short of their usual definition. The best instruments 
wanted that clear and sharp distinctness which is one of 
their highest properties—a circumstance which the contact 
of nebulous matter with the atmosphere easily accounts for. 
But it may be said that the nebulous or cometic field, 
the theory supposes, must have been very large, since the 
earth and sun required nearly two years to sweep through 
it. But this objection will not be formidable to those w’ho 
in any way have tried to apprehend astronomical distances 
and magnitudes. Though 20 years instead of two had been 
required, the field would have been a small one compared 
with many we know to exist in the depths of space. 
