68 DESCRIPTION or a 
ftantly be itfelf extinguifhed. Smoke muft have a certain 
degree of heat to be inflammable. As {oon as it has ac- 
quired that degree, the approach of a candle will inflame 
the whole body, and you will be very fenfible of the dif- 
ference of the heat it gives. A ftill eafier experiment may 
be made with the candle itfelf. Hold your hand near the 
fide of its flame, and obferve the heat it gives; then blow 
it out, the hand remaining in the fame place, and obferve 
what heat may be given by the fmoke that rifes: from the 
fill burning fnuff. You will find it very little. And yet 
that {moke has in it the fubftance of fo much flame, and 
will inftantly produce it, if you hold another candle above 
it fo as to kindle it. Now the {moke from the frefh coals 
laid on this ftove, inftead of afcending and leaving the fire 
while too cold to burn, being obliged to defcend through 
the burning coals, receives among them that degree of 
heat which converts it into flame, and the heat of that 
flame is communicated to the air of the room, as above: 
explained. 
4. The flame from the frefh coals laid on in this: ftove, 
defcending through the coals already ignited, preferves 
them long from confuming, and continues. them in the 
ftate of red coals as. long as the flame continues that fur- 
rounds them, by which means the fires made: in this ftove 
are of much longer duration than in any other, and fewer 
coals are therefore neceflary for a day. This is a very 
material advantage indeed.. That flame fhould be a kind 
of pickle, to preferve burning coals from confuming, may 
feem a paradox to many, and very unlikely to be true, as 
it appeared to me the firft time L obferved the fact... I muft 
therefore relate the circumftances, and {hall mention an 
eafy experiment, by which my reader may be in poffeflion 
of every thing neceflary to the underftanding of it. In 
the firft trial I made of this kind.of ftove, which was con- 
ftructed of thin plate iron, I had inftead of the vafe a kind 
of inverted pyramid like a mill-hopper; and see at 
rift 
