PROCEEDINGS OF THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
231 
glow passed through one of them. That the vast inter¬ 
planetary, and the still vaster inter-stellar, spaces, are not 
absolutely void, is now conceded by our highest authorities. 
Ether, or whatever else we choose to call the medium 
through which light is transmitted, manifestly fills all 
space. However far in imagination we may extend the 
confines of the universe,—reaching outward in every 
direction,—beyond one star system after another, all but 
indefinitely, we cannot imagine our reaching a region 
through which light cannot pass, or where this all-pervading 
element does not exist. Certainly, also, matter in a much 
grosser form than this impalpable element exists in the 
interplanetary spaces, for, in her flight round the sun, the 
earth is continually peppered or battered with mioute 
masses of matter, which are known as meteors, or aerolites, 
as shown by the meteoric shower on the night of the 27th 
November last, and many other occasions. These bodies, 
varying in size from a boy’s marble to masses a couple of 
tons in weight,—though generally of very small dimensions, 
—have a high velocity, and move in regular eliptical orbits 
around the sun. Occasionally the earth’s orbit crosses the 
orbit in which a great stream of them is moving, taking 
about five hours to pass through it; and as the earth and 
they meet each other, and both when they do so 
are moving at the rate of 18 miles a-second, the 
prodigious velocity with which they plunge into the 
earth’s atmosphere induces such a heat from friction 
that they are in a second or two sublimated into 
vapour. They are only seen by us when they are in 
the act of perishing. When the original mass, how¬ 
ever, is so great that it has not time to be burnt up in its 
rush through the atmosphere, it falls with terrific force to 
the earth,—fortunately for the earth, the fall of such 
bodies is extremely rare. But whilst such bodies are 
known to exist, and to move individually and in groups 
around us and through the interplanetary spaces, it is 
well known that there are enormous fields of nebulous- 
looking matter existing in the celestial abysses, which, 
because they cannot be resolved into star systems by our 
finest and most powerful telescopes, are believed to be 
composed of matter in its most rudimentary state. It is 
seen in large instruments as a faint puff of smoke against 
the black void beyond, from which no light comes. It is 
supposed to be prodigiously attenuated, so that the lightest 
of our known gases are dense when compared with it. 
From these enormous nebulous masses which lie away 
out into the prodigious depths of space, according to the 
theories of La Place and Herschell, suns and worlds have 
been evolved, and are now being evolved, in those mighty 
cycles through which the work of cieation is supposed to 
extend. The nearest approach to this nebulous matter of 
which we have any knowledge is the matter of which 
those comets which visit our region of the universe are com¬ 
posed ; though it must be confessed that our knowledge is 
limited indeed. We can only conceive of nebulous matter 
by giving to it a somewhat similar consistancy and 
similar properties to that which we are led to give to comets, 
from the observations made in recent years upon these 
strange wanderers. The main difference between them 
is that the nebulons mass is comparatively quiescent, 
whilst the comet is usually—though, as we shall after¬ 
wards shew, not always—in a high state of motion. 
The few properties we know cometic matter to possess 
are the following. It has in a high degree the power of 
reflecting the light of the sun which falls on it; hence the 
extraordinary splendour many comets discover when 
placed in a favourable position. It is attenuated, and 
thin, and rare, beyond any form of matter of which we 
have any experience. A striking illustration of its rarity 
is furnished by the fact that in 1858 Donati’s comet passed 
over the star Arcturus on a beautiful October evening, but 
the faint light of the star was not obliterated even when 
the nucleus, or head of the comet, passed over it. Now 
we know that the feeble light of Arcturus must have 
passed through 1,200,000 miles of the densest part of the 
comet; yet there the star twinkled on, but little dimmed 
by the intervention. How inexpressibly thin and rare, 
then, must the matter of the comet have been to enable it 
to do so. The thinnest and most fleecy cloud will obscure 
Arcturus, a puff of smoke from a workman’s pipe will do 
it, yet more than a million miles of the comet’s head failed 
to do so. As an illustration of the lightness of comets, we 
may mention that some 30 years ago a comet passed near 
the planet Venus ; and although the most careful observa¬ 
tions were made, with the most delicate instruments, it 
was found that the planet was not in the slightest degree 
deflected from its course by the vicinity of the ethereal 
wanderer. The planet disturbed the comet,—but the 
comet had so little solid matter in it that it could not dis¬ 
turb the planet. Many, even in modern times, have been 
alarmed for the consequences of the earth coming in con¬ 
tact with a comet,—but the apprehension is groundless, 
since the earth’s atmosphere, which is so much more dense 
than a comet, would effectually protect it. The most that 
could happen would be a few and harmless atmospheric 
disturbances, and possibly a series of glorious after-glows 
so long as the collision lasted. The number of comets 
connected with the solar system is known to be above 200, 
though there may be many more which have not been ob¬ 
served. But we have no reason to suppose that these 
