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 ...

ATTENTION. 61
to give us the same advantage in examining rapid events, which
the microscope gives for examining minute portions of extension, they would enlarge our views with respect to the intellectual world, no less than that instrument has with respect to the
material.
It may contribute to remove, still more completely, some of
the scruples which are naturally suggested by the foregoing
doctrine, to remark, that, as the great use of attention and memory is to enable us to treasure up the results of our experience
and reflection for the future regulation of our conduct, it would
have answered no purpose for the Author of our nature to have
extended their province to those intervals of time, which we
have no occasion to estimate in the common business of life.
All the intellectual processes I have mentioned are subservient
to some particular end, either of perception or of action; and it
would have been perfectly superfluous, if, after this end were
gained, the steps which are instrumental in bringing it about,
were all treasured up in the memory. Such a constitution of
our nature would have had no other effect but to store the mind
with a variety of useless particulars.
After all I have said, it will perhaps be still thought, that
some of the reasonings I have offered are too hypothetical; and
it is even possible, that some may be disposed rather to dispute
the common theory of vision, than admit the conclusions I have
endeavored to establish. To such readers, the following considerations may be of use, as they afford a more palpable instance
than I have yet mentioned, of the rapidity with which the
thoughts may be trained, by practice, to shift from one thing to
another.
Instances of the quickness of mental operation. - When an
equilibrist balances a rod upon his finger, not only the attention
of his mind, but the observation of his eye, is constantly requisite. It is evident that the part of his body which supports the
object is never wholly at rest; otherwise the object would no
more stand upon it, than if placed in the same position upon a
table. The equilibrist, therefore, must watch, in the very beginning, every inclination of the object from the proper position,
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