92 Mayow 



-entering the fiery element in the manner described, 

 immediately glow and are impregnated anew with 

 nitro-aerial particles, and are moreover rendered heavier 

 by the accession of the nitro-aerial particles (just as 

 antimony when calcined by the solar rays is in- 

 creased in weight on account of the nitro-aerial 

 particles infixed in it, as has been elsewhere shown) : 

 and, finally, that the nitro-aerial particles when impreg- 

 nated in that way and made heavier are by their own 

 weight borne downwards to the coldest region of the 

 air, and being rapidly cooled there become extremely 

 rigid and acquire anew resilient force. For the case 

 here seems not to differ much from what happens 

 when soft and inelastic iron is made to glow by putting 

 it into the fire, and i^ then immediately cooled by 

 plunging it into cold water, so that it thus recovers 

 its rigidity and resilient force. 



It is besides probable that the aerial particles, when 

 made rigid in the manner aforesaid and borne down- 

 wards by their weight, are likewise in some degree 

 bent by the weight of the superincumbent air, so that 

 they no longer move straight like arrows but begin to 

 rotate. Hence it is that they at last, like the steel 

 spring which sets automata in motion, are bent in 

 multiple convolutions and crowded together. And 

 thus, it seems, there ultimately arises in the aerial 

 particles that conspicuous elasticity and tendency to 

 expand indefinitely. 



As regards the descent of aerial particles they are 

 probably not borne straight down, but obliquely 

 towards the poles. For the continual ascent of 

 vapours and of air which goes on in the meridional 

 region, on account of the very intense heat there and 

 the rarefaction of the air, hinders their straight 

 •descent ; so that, returning obliquely from the poles, 



