Elements of the philosophy of the human mind. By Dugald Stewart. Rev. and abridged, with critical and explanatory notes, for the use of colleges and schools. By Francis Bowen ...

40 Ei XTERNAL PERCEPTION.
respect to ordinary events. The communication of motion by
impulse, (as I already hinted,) is as unaccountable as any phenomenon we know; and yet, most men are disposed to consider
it as a fact which does not result from will, but from necessity.
To such men, it may be useful to direct their attention to the
universal law of gravitation; which, although not more wonderful in itself than the common effect of impulse, is more fitted,
by its novelty, to awaken their attention, and to excite their
curiosity.
Contrary effect of erroneous theories. - If such, however, be
the effects of our philosophical pursuits when successfully cons
ducted, it must be confessed that the tendency of imperfect or
erroneous theories is widely different. By a specious solution
of insuperable difficulties, they so dazzle and bewilder the understanding, as, at once, to prevent us from advancing, with
steadiness, towards the limit of human knowledge; and from
perceiving the existence of a region beyond it, into which philosophy is not permitted to enter. In such cases, it is the business of genuine science to unmask the imposture, and to point
out clearly, both to the learned and to the vulgar, what reason
can, and what she cannot, accomplish. This, I apprehend, has
been done with respect to the history of our perceptions, in the
most satisfactory manner, by Dr. Reid. When a person little
accustomed to metaphysical speculation is told, that, in the case
of volition, there are certain invisible fluids, propagated from the
mind to the organ which is moved, and that, in the case of perception, the existence and qualities of the external object are
made known to us by means of species, or phantasms, or images,
which are present to the mind in the sensorium; he is apt to
conclude that the intercourse between mind and matter is much
less mysterious than he had supposed; and that, although these
expressions may not convey to him any very distinct meaning,
their import is perfectly understood by philosophers. It is
now, I think, pretty generally acknowledged by physiologists,
that the influence of the will over the body, is a mystery which
has never yet been unfolded; but singular as it may appear,
Dr. Reid was the first person who had courage to lay completely