On Sal Nitrum and Nitro- Aerial Spirit 91 



region is extremely cold and that vapours to some 

 extent freeze in it. For the air in the middle region 

 is at least as cold as that which rests on the top of the 

 loftier mountains, which in fact does not permit the 

 snow there to melt even in mid-summer, as was 

 remarked by the illustrious Descartes. But I have 

 endeavoured to show above that intense cold and the 

 congelation of vapours are due to nitro-aerial particles. 

 Further, that nitro-aerial particles are crowded in the 

 highest region of the air seems to be confirmed by the 

 blue colour of the sky ; for as nitro-aerial particles, 

 when urged with swiftest motion, glow and flame, so 

 when they move more slowly, or when their motion 

 ceases altogether, they assume a blue colour. And it 

 is an indication of this that the flame of sulphur is 

 blue ; for the nitro-aerial particles do not move so 

 swiftly in it as in other flames, as has been elsewhere 

 stated. And hence it would seem that when flame is 

 about to expire in subterranean crypts, or even from 

 the lack of sulphureous nutriment, the nitro-aerial 

 particles in it do not shine brightly as in other 

 circumstances, but take a blue colour on account of 

 their diminished motion. To these I add, lastly, that 

 iron and other very rigid substances of the same kind 

 appear blue when polished on account of the nitro- 

 aerial particles densely fixed in them. 



These things being admitted, it is reasonable to 

 suppose that aerial particles when deprived, whether 

 by the burning of fire, or by the breathing of animals, 

 or in any other way, of their nitro-aerial particles and 

 consequently of their weight and elasticity, are driven 

 upwards by the pressure of the rest of the air, and 

 that they ascend until they arrive where nitro-aerial 

 particles moving with the greatest rapidity constitute 

 the element of fire : further, that the aerial particles on 



