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 ...

t IIIr7TION. 63
more quickly than other men, (for all tlle feats of legerdermanrl
suppose the exercise of observation, thought, and volition,) but
of performing a variety of movements with the hand, before the
eyes of a company, in an interval of time too short to enable
the spectators to exert that degree of attention which is necessary to lay a foundation for memory.*
M Mr. Locke, in his Essay on Hunman Understanding, has taken notice
of thfe quickness with which the operations of the mind are carried on, and
has referred to the acquired perceptions of sight as a proof of it.
"We are further to consider, concerning perception, that the ideas we
receive by sensation are often, in grown people, altered by the judgment,
without our taking notice of it. When we set before our eyes a round
globe of any uniform color, for example, gold, alabaster, or jet, it is certain
that the idea thereby imprinted on our mind is of a flat circle, variously
shadowed, with several degrees of light and brightness coming to our eyes.
But we, having by use been accustomed to perceive what kind of appearance convex bodies are wont to make in us, and what alterations are made
in the reflections of light by the difference of the sensible figure of bodies;
the judgment presently, by a habitual custom, alters the appearances into
their causes; so that, from that which truly is variety of shadow or color,
collecting the figure, it makes it pass for a mark of figure, and frames to
itself a perception of convex figure, and an uniform color; when the idea
we receive from thence is only a plane variously colored; as is evident in
painting."- Chap. ix. sec. 8.
"But this is not, I think, usual in any of our ideas but those received
by sight; because sight, the most comprehensive of all our senses, conveying to our minds the ideas of lights and colors, which are peculiar only to
that sense, and also the far different ideas of space, figure, and motion, the
several varieties whereof change the appearances of its proper object,
namely, light and colors, we bring ourselves by use to judge of the one by
the other. This, in many cases, by a settled habit in things whereof we
have frequent experience, is performed so constantly, and so quick, that
we take that for the perception of our sensation, which is an idea formed
by our judgment; so that one, namely, that of sensation, serves only to
excite the other, and is scarce taken any notice of itself; as a man who
reads or hears with attention and understanding, takes little notice of the
character or sounds, but of the ideas that are excited in him by them.
"/Nor need we wonder that this is done with so little notice, if we consider how very quick the actions of the mind are performed; for as itselt
is thought to take up no space, to have no extension, so its actions seem
to require no time, but many of them seem to be crowded into an instant,
I speak this in comparison with the actions of the body. Any one may