r daily
observation, with greater precision than had been before attained;
and, by following out, with marvellous power and subtlety, the
mathematical consequences of these rules, he almost created the modern
science of pure mechanics. In the second place, applying exactly the
same method to the explication of the facts of astronomy as that which
was applied a century and a half later to the facts of geology by
Lyell, he set himself to solve the following problem. Assuming that
all bodies, free to move, tend to approach one another as the earth
and the bodies on it do; assuming that the strength of that tendency
is directly as the mass and inversely as the squares of the distances;
assuming that the laws of motion, determined for terrestrial bodies,
hold good throughout the universe; assuming that the planets and
their satellites were created and placed at their observed mean
distances, and that each received a certain impulse from the Creator;
will the form of the orbits, the varying rates of motion of the
planets, and the ratio between those rates and their distances from
the sun, which must follow by mathematical reasoning from these
premisses, agree with the order of facts determined by Kepler and
others, or not?

Newton, employing mathematical methods which are the admiration of
adepts, but which no one but himself appears to have been able to use
with ease, not only answered this question in the affirmative, but
stayed not his constructive genius before it had founded modern
physical astronomy.

The historians of mechanical and of astronomical science appear to be
agreed that he was the first person who clearly and distinctly put
forth the hypothesis that the phenomena comprehended under the general
name of "gravity" follow the same order throughout the universe, and
that all material bodies exhibit these phenomena; so that, in this
sense, the idea of universal gravitation may, doubtless, be properly
ascribed to him.

Newton proved that the laws of Kepler were particular consequences of
the laws of motion and the law of gravitation--in other words, the
reason of the first lay in the two latter. But to talk of the law of
gravitation alone as the reason of Kepler's laws, and still more as
standing in any causal relation to Kepler's laws, is simply a misuse
of language. It would really be interesting if the Duke of Argyll
would explain how he proposes to set about showing that the elliptical
form of the orbits o