. eee 
376 S. Webber on Ventilation. 
y sid which the outward curren 
warmth and force and a slight o 
dition to the actions of the great inward and outward cunend 
If the conditions be reversed, so will the performan ‘the 
changes ; that is, if. the close room n be colder that: the external air, 
of want of homogeneity i in the structure of the walls of the room, 
local currents will occur as before, only inversely. Generally 
speaking, the change will be effected by the substitution of the 
air without for that within, but not wholly so, for some of the 
internal air will be warmed or cooled by induction, from coming 
in —— with the external air of a different temperature from 
its 
The “completeness and quickness of the change will depend 
partly upon the-size of the e aperture, and partly upon its situation. 
Of course, the Ba the opening, the more quickly will the ex- 
change effected. But in cases where the dimensions of the 
aperture are the same, and the size of the apartment the same, 
tion has much effect. Thus, in the first supposition that the 
ait ¢ the room is warmer than the external air, an opening parid 
the top.of the room will most readily permit the warm air to € 
cape and the colder and denser external air to descend to take ns 
place, and leave but little to be cooled by induction, while with 
an opening of the same. size near the floor, the warm air would 
escape after a little while with much difficulty, and much more 
of it would remain in the room cooled down to the temperature 
of the external air. The results would be reversed on the secon 
supposition, that the air of the close room was colder than the 
ext Lair, 
So far then as to simply warm air and cold air Mr. Hosking’s 
doctrine seems to be correct, as to. the effect of a ventilating 
opening near nek collin: ofa room be 
ing thoroughly the a air of a 
he 
close room. uk 
These changes are otis ge: the teint in pres density of 
warm air and cold air; air being considered: homogeneous 
