16 LETTER concEeRNnING 
the corner is made to open againft the wall, which 
is common, as being there, when open, more out 
of the way, it follows, that when the door is on- 
ly opened in part, a current of air rufhing in paffes along 
the wall into and acrofs the opening of the chimney B, 
and flirts fome of the {moke out into the room. This 
happens more certainly when the door is fhutting, for then 
the force of the current is augmented, and becomes very 
inconvenient to thofe who, warming themfelves by the 
fire, happen to fit in its way. 
The Remedies are obvious.and eafy. Either:put an in- 
tervening {kreen from the wall round great part of the fire- 
place ; or, which is perhaps preferable, fhift the hinges of 
your door, fo as it may open the other way, and when 
open throw the air along the other wall. ; 
§. A room that has no fire in its chimney, is fome- 
times filled with /moke which is received at the top of 
its funnel and defcends into the room. In a former 
paper * I have already explained the defcending currents 
of air in cold funnels; it may not be amifs however 
to repeat here, that funnels without fires have an effect 
according to their degree of coldnefs or warmth, on the 
air that happens to be contained inthem. The furround- 
ing atmofphere is frequently changing its temperature ; 
but ftacks of funnels covered from winds and fun by the 
houfe that contains them, retain a more equal temperature. 
If, after'a warm feafon, the outward air fuddenly grows 
cold, the empty warm funnels begin to draw ftrongly up- 
ward; that is, they rarefy the air contained in them, which 
of courfe rifes, cooler air enters below to fupply its place, 
is rarefied in its turn and rifes; and this operation conti- 
nues, till the funnel grows cooler, or the outward air 
warmer, or both, when the motion ceafes. On the other 
hand, if after a cold feafon, the outward air fuddenly grows 
warm and of courfe lighter, the air contained in the cool 
funnels, being heavier, defcends into the room; and the 
warmer 
Plate I. 
Figure 4. 
* See Appendix, N° II, 
