cannot imagine a part of space where some light would not strike the
eye: but as the fixed stars would not be visible at such distances, if
they did not shine by their own light, it is reasonable to infer that
they are suns; and if so, they are in all probability attended by
systems of opaque bodies, revolving about them as the planets do about
ours. But although there be no proof that planets not seen by us revolve
about these remote suns, certain it is, that there are many invisible
bodies wandering in space, which, occasionally coming within the sphere
of the earth's attraction, are ignited by the velocity with which they
pass through the atmosphere, and are precipitated with great violence on
the earth. The obliquity of the descent of meteorites, the peculiar
matter of which they are composed, and the explosion with which their
fall is invariably accompanied, show that they are foreign to our
planet. Luminous spots altogether independent of the phases have
occasionally appeared on the dark part of the moon, which have been
ascribed to the light arising from the eruption of volcanoes; whence it
has been supposed that meteorites have been projected from the moon by
the impetus of volcanic eruption; it has even been computed, that if a
stone were projected from the moon in a vertical line, and with an
initial velocity of 10992 feet in a second, which is more than four
times the velocity of a ball when first discharged from a cannon,
instead of falling back to the moon by the attraction of gravity, it
would come within the sphere of the earth's attraction, and revolve
about it like a satellite. These bodies, impelled either by the
direction of the primitive impulse, or by the disturbing action of the
sun, might ultimately penetrate the earth's atmosphere, and arrive at
its surface. But from whatever source meteoric stones may come, it seems
highly probable, that they have a common origin, from the uniformity, we
may almost say identity, of their chemical composition.
The known quantity of matter bears a very small proportion to the
immensity of space. Large as the bodies are, the distances that separate
them are immeasurably greater; but as design is manifest in every part
of creation, it is probable that if the various systems in the universe
had been nearer to one another, their mutual disturbances would have
been inconsistent with the harmony and stability of the whole. It is
clear that space is not pervaded by atmospheric air, since its
resistance would long ere this have destroyed the velocity of the
planets; neither can we affirm it to be void, when it is traversed in
all directions by light, heat, gravitation, and possibly by influences
of which we can form no idea; but whether it be replete with an ethereal
medium, time alone will show.
Though totally ignorant of the laws which obtain in the more distant
regions of creation, we are assured, that one alone regulates the
motions of our own system; and as general laws form the ultimate object
of philosophical research, we cannot conclude these remarks without
considering the nature of that extraordinary power, whose effects we
have been endeavouring to trace through some of their mazes. It was at
one time imagined, that the acceleration in the moon's mean motion was
occasioned by the successive transmission of the gravitating force; but
it has been proved, that, in order to produce this effect, its velocity
must be about fifty millions of times greater than that of light, which
flies at the rate of 200000 miles in a second; its action even at the
distance of the sun may therefore be regarded as instantaneous; yet so
remote are the nearest of the fixed stars, that it may be doubted
whether the sun has any sensible influence on them.
The analytical expression for the gravitating force is a straight line;
the curves in which the celestial bodies move by the force of
gravitation are only lines of the second order; the attraction of
spheroids according to any other law would be much more complicated; and
as it is easy to prove that matter might have been moved according to an
infinite variety of laws, it may be concluded, that gravitation must
have been selected by Divine wisdom out of an infinity of other laws,
its being the most simple, and that which gives the greatest stability
to the celestial motions.
It is a singular result of the simplicity of the laws of nature, which
admit only of the observation and comparison of ratios, that the
gravitation and theory of the motions of the celestial bodies are
independent of their absolute magnitudes and distances; consequently if
all the bodies in the solar system, their mutual distances, and their
velocities, were to diminish proportionally, they would describe curves
in all respect similar to those in which they now move; and the system
might be successively reduced to the smallest sensible dimensions, and
still exhibit the same appearances. Experience shows that a very
different law of attraction prevails when the particles of matter are
placed within inappreciable distances from each other, as in chemical
and capillary attractions, and the attraction of cohesion; whether it be
a modification of gravity, or that some new and unknown power comes into
action, does not appear; but as a change in the law of the force takes
place at one end of the scale, it is possible that gravitation may not
remain the same at the immense distance of the fixed stars. Perhaps the
day may come when even gravitation, no longer regarded as an ultimate
principle, may be resolved into a yet more general cause, embracing
every law that regulates the material world.
The action of the gravitating force is not impeded by the intervention
even of the densest substances. If the attraction of the sun for the
centre of the earthy and for the hemisphere diametrically opposite to
him, was diminished by a difficulty in penetrating the interposed
matter, the tides would be more obviously affected. Its attraction is
the same also, whatever the substances of the celestial bodies may be,
for if the action of the sun on the earth differed by a millionth part
from his action on the moon, the difference would occasion a variation
in the sun's parallax amounting to several seconds, which is proved to
be impossible by the agreement of theory with observation. Thus all
matter is pervious to gravitation, and is equally attracted by it.
As far as human knowledge goes, the intensity of gravitation, has never
varied within the limits of the solar system; nor does even analogy lead
us to expect that it should; on the contrary, there is every reason to
be assured, that the great laws of the universe are immutable like their
Author. Not only the sun and planets, but the minutest particles in all
the varieties of their attractions and repulsions, nay even the
imponderable matter of the electric, galvanic, and magnetic fluids are
obedient to permanent laws, though we may not be able in every case to
resolve their phenomena into general principles. Nor can we suppose the
structure of the globe alone to be exempt from the universal fiat,
though ages may pass before the changes it has undergone, or that are
now in progress, can be referred to existing causes with the same
certainty with which the motions of the planets and all their secular
variations are referable to the law of gravitation. The traces of
extreme antiquity perpetually occurring to the geologist, give that
information as to the origin of things which we in vain look for in the
other parts of the universe. They date the beginning of time; since
there is every reason to believe, that the formation of the earth was
contemporaneous with that of the rest of the planets; but they show that
creation is the work of Him with whom 'a thousand years are as one day,
and one day as a thousand years.'