s assemblage of persons--as a reading-room, a
lecture-room, or a school-room--should be provided with apertures, adapted
to admit spontaneous supplies of fresh air, in such variable quantities as
may be required, on at least two of its opposite sides, and within three
feet from the floor; also, with apertures in the ceiling, or on a level
therewith, to promote the exit of the vitiated air. The apertures of both
descriptions may be quite distinct from those which admit light.

Suppose a room to be twenty-four feet square, and sixteen feet in height,
with two apertures for light on each side, each aperture being three feet
wide by eight feet in height, and rising from the floor. There are not many
rooms constructed on a plan so favourable to the admission of fresh
air--but it has some serious defects. 1. The air would enter in broad and
partial currents. 2. It would not reach the angular portions of the room.
3. The vitiated air might rise above the apertures, and so accumulate
without the means of escape.

Now, suppose the same room to have its apertures at eight feet from the
floor, and so to reach the ceiling. The escape of the vitiated air might
then take place--if not prevented by a counter-current. But whence comes
the fresh air for the occupants? There is no direct provision for its
admission. The elevated apertures are utterly insufficient for that
purpose; and _the perpetual requisite is no otherwise afforded than by the
occasional opening of a door!_

It being thus established that the same apertures can never effectually
serve for light and ventilation, I propose with regard to reading-rooms,
lecture-rooms, and school-rooms, which require accommodation for books,
maps, charts, and drawings, rather than a view of external objects, that
the windows should be placed in the upper part of the room--that the
admission of fresh air should be provided for by ducts near the floor--and
the escape of the vitiated air by openings in, or on a level with, the
ceiling.

The number of windows, and their size, must depend on the size of the room.
If windows are to admit light only, a smaller number may be sufficient, and
they may not be required on more than one side; a circumstance which
recommends the plan proposal, as we can seldom have windows on each side of
a room, or even on two of its opposite sides, but may devise a method of so
admitting air.

Rejecting the use of windows as a means of ventilation, and rejecting