Anahfis of the Air. 27 j 



the Nitre detonize 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 frefli 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 rufhing 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 $ 

 that when the Sun dunes on a Fire, and there- 

 by too much rarifies 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 con1ra> it is a 

 common obfervation, that in very cold frofty 

 weather Fires burn mod briskly 5 the reafon 

 of which feems to be this, that the elaftick 

 expanfion of the cold condenfed air to a 

 rarified ftate, when it enters the Fire, is much 

 brisker than that of an air already rarified in 

 a good meafure by heat, before it enters the 

 Fire $ and confequently a continued fuc- 

 T z ceffioa 



