30 APPENDIX. 
warm air, that now paffes out of the room to go up the 
chimney. In our common open chimneys, half the fuel 
is watted, and its effect loft; the air it has warmed being 
immediately drawn off. Several of my acquaintance hav- 
ing feen this fimple machine in my room, have imitated 
it at their own houfes, and it feems likely to become pretty 
common. I defcribe it thus particularly to you, becaufe I 
think it would be ufeful in Bo/fon, where firing is often dear. 
Mentioning chimneys puts me in mind of a property I 
formerly had occafion to obferve in them, which I have 
not found taken notice of by others; it is, that in the fum- 
mer time, when no fire is made in the chimneys, there is, 
neverthelefs, a regular draft of air through them; continu- 
ally paffing upwards, from about five or fix o’clock in 
the afternoon, till eight or nine o’clock the next morning, 
when the current begins to flacken and helitate a little, for 
about half an hour, and then fets as ftrongly down again, 
which it continues to do till towards five in the afternoon, 
then flackens and hefitates as before, going fometimes a 
little up, then a little down, till in about a half an hour it 
gets into a fteady upward current for the night, whichcon- 
tinues tilkeight or nine the next day; the hours varying a 
little as the days lengthen and fhorten, and fometimes va- 
rying from fudden changes in the weather; as if, after bes 
ing long warm, it fhould begin to grow cool about noon, 
while the air was coming down the chimney, the current 
will then change earlier than the ufual hour, dc. 
This property in chimneys I imagine we might turn to 
fome account, and render improper, for the future, the old 
faying, as ufele/s as a chimney in Jummer. If the opening 
of the chimney, from the breaft down to the hearth, be 
clofed by a flight moveable frame or two, in the manner 
of doors, covered with canvas, that will Jet the air through, 
but keep out the flies; and another little frame fet within 
upon the hearth, with hooks on which to hang joints of 
meat, fowls, &c. wrapt well in wet linen cloths, three or 
four 
