252 Prof. Hosking on Ventilation. 
from low levels to high levels, open windows are not sufficient 
to effect thorough in-door ventilation. ‘There must for this pur 
pose. be in every room a way by which a draught can be obtained, 
and this draught must take effect upon the most impure air of 
the room, which is that of the highest level. The chimney 
opening may supply a way at a low level, and a draught may be 
established between it and the window, but the air removed from 
the room by such a dranght is not necessarily the spent or foul 
air. But make an opening into the chimney flue near the high- 
est level in the room, that is to say, as near as may be to the ceil- 
ing, and if a draught be established between the window and 
the flue by this opening, the ventilation is complete ; that is to 
say again, if there be draught enough in the chimney flue from 
any cause to induce an up-current through it, or if there be mo- 
tion of the external air to drive the air in at the window and 
force an up-current through the flue. 
Windows may not be put open in the long enduring colder 
season, however, and for the same reason in-draughts. of the 
outer air by any other channel are offensive and injurious. To 
open a door for the sake of air is but a modification of opening 
a window, and, if the door be an internal one, with the effect of 
admitting already enclosed, and, probably, contaminated air- 
Means of efficient in-door ventilation must therefore be indepen- 
dent of windows and doors; and the means should be such as 
will lead to a result at once wholesome and agreeable. 
_ Many plans have been suggested, and some have been carried 
into effect, of warming air, and then forcing it into or drawing it 
through buildings, and, in the process of doing so, removing the 
foul or spent air from the apartments to which it may be applied. 
Some of these plans are more and some are less available to 
wholesome and agreeable in-door ventilation, but even the 
churches, theatres, and assembly-rooms, than to private dwelling 
houses in which the rooms are small ‘and labor and cost are to be 
economized. : 
Plans have been proposed, too, for the economical ventilation 
of dwelling-houses: but they seem to be ail in a greater or ess 
degree imperfect. 
for the outer air directly to the fire in every apartment, to fee 
sometimes provided for the spent air of a room; sometimes, 
in its way to the inmates of the room, the objection to its direct 
ness ceases. If however the warmth is imparted to it with foul- , 
