[ i 66 ] 



of longer continuance, did by no means rcftore this 

 kind of air : for when I have expofed the phials which 

 contained It a whole night, in which the froft was 

 -very intenfe j and alfo when I kept it furrounded with 

 a mixture of fnow and fait, I found it, in all re- 

 fpects, the fame as before. 



It is alfo advanced, in the fame Memoir, p. 41. 

 that heat only, as the reverfe of cold, renders air 

 unfit for candles burning in it. But I repeated the 

 experiment of the Count for that purpofe, without 

 tfinding any fuch effect from it. I alio remember that, 

 many years ago, I filled an exhaufted receiver with: 

 air, that had paffed through a glafs tube made 

 red-hot, and found that a candle would burn in it 

 perfectly well. Alfo, rarefaction by the air-pump 

 does not injure air in the leaft degree. 



Though this experiment failed, I flatter myfelf 

 that I have accidentally hit upon a method of re- 

 ftoring air which has been injured by the burning 

 of candles, and that I have difcovered at leaft, one 

 of the reftoratives which nature employs for this 

 purpofe. It is vegetation. In what manner this pro- 

 cefs in nature operates, to produce fo remarkable an 

 effect, I do not pretend to have difcovered; but a 

 number of facts declare in favour of this hypothefis. 

 I mall introduce my account of them, by reciting 

 fome of the obfervations which I made on the grow- 

 ing of plants in confined air, which led to this dif- 

 covery. 



One might have imagined that, fince common 

 air is neceffary to vegetable, as well as to animal 

 life, both plants and animals had affected it in the 

 fame manner, and I own I had that expectation, 



when 



