human mind the vast in the minute, the
general in the particular, it had been inferred, that the force by
which bodies fall to the earth might also be an attraction. Newton
pondered all these things. He looked, as was his wont, into the
darkness until it became entirely luminous. How this light arises we
cannot explain; but, as a matter of fact, it does arise. Let me
remark here, that this kind of pondering is a process with which the
ancients could have been but imperfectly acquainted. They, for the
most part, found the exercise of fantasy more pleasant than careful
observation, and subsequent brooding over facts. Hence it is, that
when those whose education has been derived from the ancients speak of
'the reason of man,' they are apt to omit from their conception of
reason one of its most important factors.

Well, Newton slowly marshalled his thoughts, or rather they came to
him while he 'intended his mind,' rising like a series of
intellectual births out of chaos. He made this idea of attraction his
own. But, to apply the idea to the solar system, it was necessary to
know the magnitude of the attraction, and the law of its variation
with the distance. His conceptions first of all passed from the
action of the earth as a whole, to that of its constituent particles.
And persistent thought brought more and more clearly out the final
conclusion, that every particle of matter attracts every other
particle with a force varying inversely as the square of the distance
between the particles.

Here we have the flower and outcome of Newton's induction; and how to
verify it, or to disprove it, was the next question. The first step
of the philosopher in this direction was to prove, mathematically,
that if this law of attraction be the true one; if the earth be
constituted of particles which obey this law; then the action of a
sphere equal to the earth in size on a body outside of it, is the same
as that which would be exerted if the whole mass of the sphere were
contracted to a point at its centre. Practically speaking, then, the
centre of the earth is the point from which distances must be measured
to bodies attracted by the earth.

From experiments executed before his time, Newton knew the amount of
the earth's attraction at the earth's surface, or at a distance of
4,000 miles from its centre. His object now was to measure the
attraction at a greater distance, and thus to determine the law of its
diminution. B