em
to be inconceivable--the proposition, that a body cannot
act where it is not. All the cumbrous machinery of
imaginary vortices, assumed without the smallest
particle of evidence, appeared to these philosophers a
more rational mode of explaining the heavenly motions,
than one which involved what appeared to them so great
an absurdity. And they, no doubt, found it as impossible
to conceive that a body should act upon the earth at the
distance of the sun or moon, as we find it to conceive
an end to space or time, or two straight lines inclosing
a space. Newton himself had not been able to realize the
conception, or we should not have had his hypothesis of
a subtle ether, the occult cause of gravitation; and his
writings prove, that although he deemed the particular
nature of the intermediate agency a matter of
conjecture, the necessity of _some_ such agency appeared
to him indubitable. It would seem that, even now, the
majority of scientific men have not completely got over
this very difficulty; for though they have at last
learned to conceive the sun _attracting_ the earth
without any intervening fluid, they cannot yet conceive
the sun _illuminating_ the earth without some such
medium.

"If, then, it be so natural to the human mind, even in
its highest state of culture, to be incapable of
conceiving, and on that ground to believe impossible,
what is afterwards not only found to be conceivable, but
proved to be true; what wonder if, in cases where the
association is still older, more confirmed, and more
familiar, and in which nothing even occurs to shake our
conviction, or even to suggest to us any conception at
variance with the association, the acquired incapacity
should continue, and be mistaken for a natural
incapacity? It is true our experience of the varieties
in nature enables us, within certain limits, to conceive
other varieties analogous to them. We can conceive the
sun or moon falling, for although we never saw them
fall, nor ever perhaps imagined them falling, we have
seen so many other things fall, that we have innumerable
familiar analogies to assist the conception; which,
after all, we should probably have some difficulty in
framing, were we not well accustomed to see the sun and
moon move, (or appear to move,) so that we are onl