Anahjfis of the Air. 27 y 



the Nitre dctonizc in a very rare , nor a 

 very thick air 5 whence the rcafon why the 

 Nitre dctonized, 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 nulling in of the 

 frefh air, for the fumes were then much 

 more rare aud tranfparcnt, 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 mines on a Fire, and there- 

 by too much rarities 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 contra, 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 

 cxpanfion of the cold condenfed air to a 

 rarined ftate, when it enters the Fire, is much 

 hriskcr than that of an air already rarified in 

 a good meafure by heat, before it enters the 

 Fire j and confequently a continued fuc- 



X 2 ceffion 



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