Jacobi, in his researches on the mathematical knowledge of the
Greeks, comments on “the profound consideration of nature evinced by
Anaxagoras, in whom we read with astonishment a passage asserting that
the moon, if the centrifugal force were intermitted, would fall to the
earth like a stone from a sling.” Anaxagoras likewise applied the same
theory of “falling where the force of rotation had been intermitted”
to all the material celestial bodies. In Aristotle and Simplicius may
also be traced the idea of “the non-falling of heavenly bodies when the
rotatory force predominates over the actual falling force, or downward
attraction;” and Simplicius mentions that “water in a phial is not
spilt when the movement of rotation is more rapid than the downward
movement of the water.” This is illustrated at the present day by
rapidly whirling a pail half-filled with water without spilling a drop.
Plato had a clearer idea than Aristotle of the _attractive force_
exercised by the earth’s centre on all heavy bodies removed from
it; for he was acquainted with the acceleration of falling bodies,
although he did not correctly understand the cause. John Philoponus,
the Alexandrian, probably in the sixth century, was the first who
ascribed the movement of the heavenly bodies to a primitive impulse,
connecting with this idea that of the fall of bodies, or the tendency
of all substances, whether heavy or light, to reach the ground. The
idea conceived by Copernicus, and more clearly expressed by Kepler,
who even applied it to the ebb and flow of the ocean, received in 1666
and 1674 a new impulse from Robert Hooke; and next Newton’s theory
of gravitation presented the grand means of converting the whole of
physical astronomy into a true _mechanism of the heavens_.
The law of gravitation knows no exception; it accounts accurately for
the most complex motions of the members of our own system; nay more,
the paths of double stars, far removed from all appreciable effects
of our portion of the universe, are in perfect accordance with its
theory.[8]