1$ LET TER -concernine 
ftrong wind, paffes over the top of a chimney, its particles. 
have received fo much force, which keeps them in a hori- 
zontal direCtion and follow each other fo rapidly, that the 
rifing light air has not ftrength fufficient to oblige them 
to quit that direction and move upwards to permit its iffue: 
Add to this, that fome of the current pafling over that fide 
of the funnel which it firt meets with, viz. at A, 
Fewe's, Having been compreffed by the refiftance of the 
funnel, may expand itfelf over the flue, and ftrike 
the interior oppofite fide at B, from whence it may be re- 
fle&ted downwards and from fide to fide in the direGtion of 
the pricked lines cc c. 
Remedies. In fome places, particularly in Venice, where 
they have not ftacks of chimneys but fingle flues, the cuf- 
tom is, to open or widen the top of the flue round= 
ing in the true form of a funnel ; which fome think 
may prevent the effe&t juft mentioned, for that the 
wind blowing over one of the edges into the funnel may 
be flanted out again on the other fide by its form. Ihave 
had no experience of this; but. I have: lived in a windy 
country, where the contrary is practifed, the tops of the 
flues being uarrowed inwards, fo as to form a flit for the 
iffue of the {moke, long as the breadth of the funnel, and 
only four inches wide. This feems to have been contrived 
on a fuppofition that the entry of the wind would thereby 
be obftructed, and perhaps it might have been imagined, 
that the whole force of the rifing warm air being con- 
denfed, as it were, in the narrow opening, would thereby 
be ftrengthened, fo as to overcome the refiftance of the 
wind. ‘This however did not always fucceed ; for when 
the wind was at north-eaft and-blew frefh, the fmoke was 
forced down by fits into the room I commonly fat in, fo as 
to oblige me to fhift the fire into another. The pofition 
of the flit of this funnel was indeed north-eaft and fouth- 
weft. Perhaps if it had lain acrofs the wind, the effe& 
might have been different. But on. this I can give no cer- 
tainty, 
Plate I. 
Figure 6. 
