third, 'why not as far as the moon?' And he proceeds to assign the
motion of the moon to the same cause as that which produced the motion
of the apple. Taking this as a working hypothesis, he examines what
would be the motions of all the planets if this were true. And the
examination ends with establishing the high probability of the Law of
Gravitation.

Now this being the invariable process of Science, it follows that our
conception of cause must come originally from that cause which we have
within ourselves and with which we cannot but begin, the action of the
human will. It is from this action that is obtained that conception
which underlies the ordinary conception of cause, namely, that of force
or power.

This conception of force or power is derived from the consciousness of
our own power to move our limbs, and perhaps too of passions,
temptations, sentiments to move or oppose our wills. This power is most
distinctly felt when it is resisted. The effort which is necessary when
we choose to do what we have barely strength to do, impresses on us more
clearly the sense of a force residing in ourselves capable of overcoming
resistance. Having the power to move our limbs, and that too against
some resistance, we explain, and in no other way can we explain, other
motions by the supposition of a similar power. In so doing we are
following strictly the scientific instinct and the scientific process.
We are putting into the same class the motions that we observe in other
things and the motions that we observe in ourselves; the latter are due
to acts of our own wills, the former are assigned to similar acts of
other wills. Hence in infancy, and in the infancy of mankind, the whole
world is peopled with persons because everything that we observe to move
is personified. A secret will moves the wind, the sun, the moon, the