Git Vw E YS. 235, 
the iron plate, by which the fpace was diminifhed one 
half, the door fhut to with the-greateft eafe. This éx- 
traordinary preflure of the air upon the door of the room, 
or fution of the chimney, | take to be owing in fome 
meafure to the unufual height of the houfe. 
Upon the whole, therefore, this fa& feems. clearly af- 
certained, viz. That the flue or fize of the chimney, 
ought always to be proportioned to the tightnefs and clofe- 
nefs of the room, fome air is undoubiedly neceffary to be 
admitted into the room in order to carry up the {fmoke, 
otherwife as you juftly obferved we might as well expect 
{moke to arife out of an exhaufted receiver; but if the 
flue is very large, and the room is tight, either the {moke 
will not afcend, in confequence of which will be, that the 
air of your room will be fo frequently and fo conftantly 
changed that as faft as it is heated, it will be hurried 
away, with the fmoke, up the chimney, and of courfe 
your room will be conftantly cold. 
One great advantage attending this method of curing 
{moky chimneys is, that, in the firft place, it makes no 
aukward or unfightly appearance, nothing being to be 
feen but what is ufual to chimneys in common; and in 
the fecond place that it is attended with very little ex- 
pence, a few bricks and mortar with a plate or covering. 
to the aperture, and a little labour, being all that is requi- 
fite. But in this new country where crops of houfes may. 
be expected to rife almoft as quick as fields of corn, when 
the principles upon which chimneys ought to be thorough- 
ly underftood, it is to be hoped, that not only this ex- 
pence, {mall as it is, but that all the other inconveniencies 
we have been {peaking of, will be avoided, by conftruat-- 
ing the flues of the chimneys fufficiently {mall. 
From your humble fervant, 
THOMAS RUSTON.. 
