Anahjfts of the Air. 275 
the Nitre detonizc in a very rare , nor a 
very thick air 5 whence the reafon why the 
Nitre detonized, and the Candle burnt, 
when placed in the receiver, after frefh air 
was let in upon the fumes which were 
made in vacuo^ was that thofe fumes were 
much difperfed and condenfed on the fides 
of the glafs, upon the rufliing in of the 
frefh air, for the fumes were then much 
more rare aud tranfparent, than before the 
air was let in. 
That a Fire which is fupplied with a hot 
air will not burn fo briskly as a Fire which 
is fed by a cool air is evident from hence 5 
that when the Sun fhineson aFire, and there- 
by too much ratifies the ambient air, that 
Fire will not burn well, nor will a fmall 
Fire burn fo well near a large one as at 
fome diftance from it. And e conlra^ it is a 
common obfervation, that in very cold frofty 
weather Fires burn moft briskly $ the reafon 
of which feems to be this, that the elaftick 
expanfion of the cold condenfed air to a 
ratified ftate, when it enters the Fire, is much 
brisker than that of an air already ratified in 
1 a good meafurc by heat, before it enters the 
i Fire % and conlequently a continued fuc- 
i T % cellion 
