Is, as usual, a multifarious volume, and abounds with reading that must
please all tastes. It has, moreover, to meet the exigencies of the day, a
pretty sprinkling of cuts and plates, respecting the number of which we do
not quarrel; in the choice of some of them we must, however, dissent from
the editor. The Astronomical portion, by Mr. Barker, is unusually copious,
and the cometary plates are well executed. We quote a passage:
_On the probability of a concussion of a Comet with the earth_.
It has been stated that the comet of 1770, passed through the system of
the planet Jupiter, without in the slightest degree affecting the motions
of either the primary or his satellites; also, that it passed sufficiently
near our planet to have shortened the length of the year had its mass been
equal to that of the earth. No effect whatever was produced, from whence
it may be concluded, that the neighbourhood of a comet is not of
sufficient importance to excite any alarming apprehensions for the safety
of the habitation of man.
Most of the calculations that have been made respecting the effect of the
proximity of a comet to our earth have proceeded on erroneous
principles,--over-rating the quantity of matter in comets, and losing
sight of their great velocity when in this part of the system. For a comet
to produce any direful effect, it ought to contain not merely a
considerable quantity of matter, but also ought to be vertical and
stationary to the earth's surface for several hours; instead of which, we
have sufficient reason to believe that though vast in volume, comets
contain but little matter in proportion, consequently, their attractive
energy would be inconsiderable; also their velocity would, in a very short
period, carry them beyond the limit of exerting any influence on the
waters of the globe. Of course, this general statement would be modified
by the rate and direction of a comet's motion, and also the earth's
rotation.
It may, then, be asserted with safety that the close appulse of a comet
would not be attended with any fatal results; and that this security
principally consists in its great velocity, which would so swiftly remove
it to a distance. But, the very circumstance which, in the case of
_proximity_, would be the security of our globe, (its velocity,) would, in
the event of a _contact_, be attended with the direst effects. It is true
that the probability of a contact is less, in an almost infinite degree,
than the proximity of a comet, which, notwithstanding, is an event which
every astronomer is fully aware, is within the verge of possibility.
The effects of a contact would be greatly modified by circumstance. Should
the comet strike the earth obliquely, it would glance off, and the
consequences would be partial. If the point of collision were on a
continent of the globe, mountains would be hurled from their bases, and
new ones would elevate their ridges towards the clouds. Were the place of
meeting on either of the great oceans, some regions would be deserted, and
others would be inundated by the waters of the sea. These dreadful
consequences would be increased, in an indefinite proportion, if the point
of contact were in the direction of the earth's centre; the meeting would
be terrific; the earth's period of revolution would, in all probability,
be altered, either by carrying it nearer to or farther from the sun; a
different inclination of the axis might be given, and there would be a
consequent change of seasons; the diurnal motion might be either
accelerated or retarded, by which the length of the day would be affected;
the vast continents of the globe would be again covered with the ocean,
which, deserting its bed, would rush towards the new equator.
Infinitely more tremendous would be the catastrophe if the earth were
struck by a _retrograde comet_ in the direction of the terrestrial centre,
the comet making up, by its velocity, the deficiency of mass: in this case
the centrifugal force of both bodies might be annihilated,--the
centripetal principle alone obeyed, and both comet and earth rush to the
sun!
It must, however, be stated, that the probability of such an event is all
but infinitely removed: the most likely of any that is known, to effect
such a consummation, is the comet of Encke, which it has been calculated
would come in collision with our earth after a lapse of 219 millions of
years! This calculation proceeds on the soundest principles of reasoning,
and proves not so much the safety of our globe from cometary destruction,
(for some comet, hitherto unseen by mortal eyes, may _now_ be winging its
flight directly towards our globe,) as the astonishing powers of the mind
of man, which can thus essay to penetrate the veil of futurity, and read
the destiny of a world.
But destruction to this terrestrial orb and its teeming inhabitants, may
be more speedily brought about than by a concussion with these celestial
agents. A single principle of motion annihilated, evaporation suspended,
or a component part of the atmosphere abstracted, and "final ruin would
drive her ploughshare o'er creation;" universal conflagration would
instantly ensue from the separation of the oxygen from the nitrogen of the
atmosphere,--the former exerting its native energies without control
wherever it extends,--solid rocks, ponderous marble, metals, and even
water itself, would burst into an intensity of flame, and change the
aspect of all sublunary things.
But all these vast bodies of the universe are, doubtless, kept in their
prescribed limits as with so many "reins and bridles," and when this earth
has completed its destined circles, and fulfilled the purposes for which
it was called out of nothing, it will need but the command of the glorious
Creator who at first spoke this beautiful frame into being, bliss, and
light, to return it to its primeval gloom, or bid it shine forth with new
resplendent beauty and lustre.
The "Notes of a Naturalist" are stated to be by Professor Rennie; but we
question if they have been written expressly for this volume, as we
recognise many passages from other works.
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