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 ...

190 DREAMING.
keep awake, re naturally fix our attention on some subject
which is calculated to afford employment to our intellectual
powers, or to rouse and exercise the active principles of our
nature.
It is well known, that there is a particular class of sounds
which compose us to sleep. The hum of bees; the murmur of
a fountain; the reading of an uninteresting discourse, have this
tendency in a remarkable degree. If we examine this class of
sounds, we shall find that it consists wholly of such as are fitted
to withdraw the attention of the mind from its own thoughts,
and are, at the same time, not sufficiently interesting to engage
its attention to themselves.
It is also matter of common observation, that children and
persons of little reflection, who are chiefly occupied about sensible objects, and whose mental activity is, in a great measure,
suspended, as soon as their perceptive powers are unemployed;
find it extremely difficult to continue awake, when they are
deprived of their usual engagements. The same thing has
been remarked of savages, whose time, like that of the lower
animals, is almost completely divided between sleep and their
bodily exertions.*
The powers dependent on volition suspended during sleep. —From a consideration of these facts, it seems reasonable to conclude that in sleep those operations of the mind are suspended,
which depend on our volition; for if it be certain, that before
we fall asleep, we must withhold, as much as we are able, the
exercise of all our different powers; it is scarcely to be
imagined, that, as soon as sleep commences, these powers should
again begin to be exerted. The more probable conclusion is,
that when we are desirous to procure sleep, we bring both mind
and body, as nearly as we can, into that state in which they are
* " The existence of the negro slaves in America, appears to participate
more of sensation than reflection. To this must be ascribed, their disposio
tion to sleep when abstracted from their diversions and unemployed in.heir labor. An animal whose body is at rest, and whllo does not reflect,
must be disposed to sleep, of course." — Notes on Virginia, by Mr. Jefferson, p. 225.