78 NOTICES OF THE MEETINGS [May 23, 
freely over the heated surface; and there being little or no con- 
sumption of air, and consequently little or no draught, in connexion 
with heated bodies, such as close stoves and hot pipes, the heat from 
them is not freely diffused, and is not wholesome. There is with all 
the expense no ventilation. 
Stoves and hot pipes are, moreover, exceedingly dangerous inmates 
in respect of fire. Such things are the most frequent causes, directly 
or indirectly, of fires in buildings. Placed upon, or laid among or about 
the timbers and other wood-work of hollow floors, and hollow parti- 
tions, and in houses with wooden stairs, more conflagrations are 
occasioned by hot pipes and stoves, than by any thing else, and per- 
haps more than by all other things together. 
Open stoves with in-draught of air warmed by being drawn 
quickly (when it is drawn quickly) over heated surfaces may be 
made part of asystem of safe and wholesome in-door ventilation ; 
but to be perfect there must be also out-draught with power to 
compel the exit of spent or otherwise unwholesome air. But the 
arrangements for and connected with such stoves are special and 
therefore costly, unless the buildings in which they may be em- 
ployed have been adapted in building to receive them. An in- 
draught stove may however be applied with great advantage as 
it regards the general warmth and ventilation, in the lowest story of 
any house, if there be compelled out-draught at the highest level 
to which it will naturally direct itself ifit be not retained, so that the 
in-draughted air, tempered as it enters, may be drawn out as 
it becomes spent, or otherwise contaminated. 
But this must be considered in all endeavours to effect in-door 
ventilation, or the endeavour will fail. The air must be acted upon, 
and not be left, or be expected, to act of itself, and to pass in or 
out as may be desired merely because ways of ingress and egress are 
made for it. Make a fire in a room, or apply an air-pump to the 
room, and the outer air will respond to the power exerted by either 
by any course that may be open to it, and supply the place of that which 
may be consumed or ejected ; but open a window in an otherwise close 
room andno air will enter; no air can enter, indeed, unless force 
be applied as with a bellows, whereby as much may be driven out as 
is driven in, with the effect only of diluting not of purifying. 
Even at that short season of the year in which windows may be 
freely opened, unless windows are so placed as to admit of the 
processes of out-door ventilation being carried on through them 
by a thorough draught from low levels to high levels, open 
windows are not sufficient to effect thorough in-door ventilation. 
There must for this purpose 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 draught is not neces- 
