Anal'yfts of the Airl 257 
fires are continually carrying a large ftream 
of heated air out of the rooms up the chim- 
ney, which ftream muft neceflarily be fup- 
plied with equal quantities of frefti air, 
thro’ the doors and windows, or the cranies 
of them. 
And thus many of thofe who have weak 
lungs, but can breath well enough in the 
frefh country air, are greatly incommoded 
in their breathing, when they come into 
large cities where the air is full of fuliginous 
vapours, ariling from innumerable coal fires, 
and flenches from filthy lay-ftalls and fewers : 
And even the moft robuft and healthy in 
changing from a city to a country air, find 
an exhilarating pleafure, arifing from a more 
free and kindly infpiration, whereby the 
lungs being lefs loaded with condenfing air 
,and vapours, and thereby the veficles more 
dilated, with a clearer and more elaftick 
air, a freer courfc is thereby given to the 
blood, and probably a purer air mixed with 
it 5 and this is one reafon why in the coun- 
try a ferene dry conftitution of the air is 
more exhilarating than a moift thick air. 
And for the fame reafon, 'tis no wonder, 
that peftilential, and other noxious epide- 
S mical 
