xv THE MOLECULAR THEORY 323 



this : That our Air either consists of, or at least abounds with, 

 parts of such a nature, that in case they be bent or com- 

 press'd by the weight of the incumbent part of the Atmo- 

 sphere, or by any other Body, they do endeavor, as much 

 as in them lies, to free themselves from that pressure, by 

 bearing against the contiguous Bodies that keep them bent ; 

 and, as soon as those Bodies are remov'd or reduced to 

 give them way, by presently unbending and stretching out 

 themselves, either quite, or so far forth as the contiguous 

 Bodies that resist them will permit, and thereby expanding 

 the whole parcel of Air, these elastical Bodies compose. 



" This Notion may perhaps be somewhat further explain'd, 

 by conceiving the Air near the Earth to be such a heap of 

 little Bodies, lying one upon another, as may be resembled 

 to a Fleece of Wool. For this (to omit other likenesses 

 betwixt them) consists of many slender and flexible Hairs ; 

 each of which may, indeed, like a little Spring, be easily 

 bent or rolled up ; but will also, like a Spring, be still 

 endeavouring to stretch itself out again. ..." 



" There is yet another way to explicate the Spring of the 

 Air, namely, by supposing with that most ingenious Gentle- 

 man, Monsieur Des Cartes, that the Air is nothing but a 

 Congeries or heap of small and (for the most part) of flexible 

 Particles ; of several sizes, and of all kind of Figures which 

 are rais'd by heat (especially that of the Sun) into that fluid 

 and subtle Etherial Body that surrounds the Earth ; and by 

 the restless agitation of that Celestial Matter wherein those 

 Particles swim, are so whirl'd round that each Corpuscle 

 endeavours to beat off all others from coming within the 

 little Sphear requisite to its motion about its own Center ; 

 and (in case any by intruding into that Sphear shall oppose 

 its free Rotation) to expel or drive it away : So that accord- 

 ing to this Doctrine, it imports very little, whether the 

 particles of the Air have the structure requisite to Springs, 

 or be of any other form (how irregular soever) since their 

 Elastical power is not made to depend upon their shape or 

 structure, but upon the vehement agitation, and (as it were) 

 brandishing motion, which they receive from the fluid 

 Ether that swiftly flows between them, and whirling about 

 each of them (independently from the rest) not only keeps 



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