APPENDIX. 29 
warmer in cold weather than they generally are, and with 
lefs fire. Itis this. The opening of the chimney is con- 
tracted, by brick-work faced with marble flabs, to about 
two feet between the jams, and the breaft brought down 
to within about three feet of the hearth.—An iron frame is 
placed juft under the breaft, and extending quite to the 
back of the chimney, fo that a plate of the fame metal 
may flide horizontally backwards and forwards in the 
grooves on each fide of the frame. This plate is jult fo 
large as to fill the whole fpace, and fhut the chimney en- 
tirely when thruft quitein, whichis convenient when there 
is no fire. Drawing it out, fo as to leave a {pace between its 
further edge and the back, of about two inches; this {pace 
is fufficient for the fmoke to pafs; and fo large a part of 
the funnel being ftopt by the reft of the plate, the paflage 
of warm air out of the room, up the chimney, is obftruct- 
ed and retarded, and by that means much cold air is pre- 
vented from coming in through crevices, to fupply its 
place. This effe& is made manifeft three ways. Firft, 
when the fire burns brifkly in cold weather, the howling 
or whiftling noife made by the wind, as it enters the room. 
through the crevices, when the chimney is open as ufual, 
_ceafes as {oon as the plate is flid in to its proper diftance. 
Secondly, opening the door of the room about half an inch, 
and holding your hand againft the opening, near the top 
of the door, you feel the cold air coming in againft your 
hand, but weakly, if the plate be in. Let another perfon 
fuddenly draw it out, fo as to let the air of the room goup 
the chimney, with its ufual freedom where chimneys are 
open, and you immediately feel the cold air rufhing in 
ftrongly. Thirdly, if fomething be fet againft the door, 
juft fufficient, when the plate is-in, to keep the door nearly 
fhut, by refifting the preffure of the air that would force 
it open: Then, when the plate is drawn out, the door will 
be forced open by the increafed preffure of the outward 
cold air endeavouring to get. in. to fupply the place of the 
warm) 
