A Preliminary Dissertation on the Mechanisms of the HeavensSomerville, Mary
Science
A Preliminary Dissertation on the Mechanisms of the Heavens
Somerville, Mary
Celestial mechanics
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.
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