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eaten by time ; and in others they appear crumbling into* 

 dust. Gold alone seems to be exempted from this 

 general dissolution. It is never found to contract rust, 

 though exposed never so long : the reason is, that sea- 

 salt, which is the only menstruum of gold, is but very 

 little mixed with the air, being a very fixed body, and 

 not apt to volatilize. In the laboratories, however, 

 where the air is impregnated with it, gold is found to 

 rust, as well as other metals. 



By its elasticity air insinuates into the pores of bodies, 

 carrying with it this faculty of expansion ; whence it 

 must necessarily put all the particles it is mixed with 

 into perpetual oscillations. And as its elasticity is never 

 the same for two moments together, there must be an 

 incessant dilatation and^contraetion in all bodies. To this 

 is owing all putrefaction and. fermentation, neither of 

 which will proceed in vacuo. And indeed all natural 

 corruption and alteration seem to depend hereon : so 

 that metals, particularly gold, are so durable, only by 

 being impervious to air. And yet it may be doubted 

 whether air itself be the true, original, universal, dis- 

 solvent ; or rather the ethereal fire, which is intimately 

 united with every particle of it ; and without which air 

 is effete and useless, neither able to feed flame, nor to 

 sustain animal life. 



That there is some matter in the air much finer than 

 the air itself, appears from many considerations. In an 

 exhausted receiver something remains, which conveys the 

 heat near as readily as air. Now this must be a body, 

 and a body subtle enough to penetrate the pores of 

 glass. Doubtless then it penetrates the pores of all 

 other bodies, and consequently is diffused through the 

 universe. And this seems to be not only more subtle 

 than the air, but far more weighty and elastic. To the 

 weight of this may be owing the weight of the air, and 

 of all other bodies; to its elasticity, the elasticity of the 

 air, and of all other elastic bodies. This also may cause 

 the reflection and other phaenomena of light : as also sen- 

 sation, and muscular motion. Indeed it seems to be the 

 first spring of all the action in the universe. 



