304 Professor Hosking on Ventilation. 



(when it is drawn quickly) over heated surfaces may be made part 

 of a system 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 bo employed 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 if it be not retained, so that the in-draughted air, tempered 

 as it enters, may be drawn out as it becomes spent, or otherwise con- 

 taminated. 



But this must be considered in all endeavours to effect in-door 

 ventilation, or the endeavour will fail. The air must he 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 other- 

 wise close room and no 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 necessarily the spent or foul air. But 

 make an opening into the chimney flue near the highest level in the 

 room, that is to say, as near as may be to the ceiling, 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 motion 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 sea- 

 son, 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, 



