On Ven tihthig and Warming HuikUngs. §61 
tky for ventilatioiij and an allowance for oilier causes of loss 
should be made. We then liave no difficulty in proportioning 
the quantity of heat, and reducing that to a regular system 
which has been conducted by guess. A minute is made the 
measure of time in both cases, and a cubic foot the measure of 
the quantity of air heated or cooled. That is, if there be 150 
cubic feet of air cooled per minute by the windows, and 400 
cubic feet per minute changed for ventilation, and. 50 cubic feet 
be allowed for loss by apertures ; then there must be 150 -f 
4- 50 = 600 cubic feet of air warmed per minute, to maintain 
the room at the proposed temperature. 
The bulk of air in a room has no concern in such calculations; 
.but the temperature is more slowly obtained, after setting the 
apparatus to work, when a room is large, both on account of 
the greater quantity of air to be heated, and the greater extent 
of walls, floors, &c. to be warmed. What an immense length 
of time it would require to warm the walls and air of a large 
cathedral, while its height must render it nearly impossible to 
warm.it by hot air. The only course that could be relied upon 
in such a case, would be to communicate the heat as directly as 
possible to the solid matter of the seats, kc. instead of expend- 
ing it upon air to rise to the upper regions of the building. 
But we have yet to consider how a hot body communicates its 
heat, and the temperature to which its surface should be limit- 
ed, when the air is to be warmed at that surface. 
A hot body radiates or projects heat through air from its sur- 
face ; and it also communicates its heat to any solids or fluids 
in contact with it. Both these methods of communicating heat 
are employed in warming buildings. There are cases in which it 
is not prudent to employ radiant heat, but in all cases where it 
can be employed with safety, the union of the two methods ren- 
ders the place which is warmed most healthy and agreeable. 
To afford radiant heat, we have a fire in an open grate, so 
constructed as to expose a considerable surface to send out heat; 
and all the other parts of the fire-place, in contact with the fuel, 
should be slow conductors of heat, such as fire-brick and the 
like. To understand the reason of this precaution, we have 
only to consider that fuel does not send out radiant heat freely 
till its temperature be about 800® ; and, as a given quantity of 
VOL. XII. NO. S4. APRIL 1825. S 
