NATURE OF THINGS. 433 



previously incorporated, or the possession by bodies of some 

 natural virtue (whatever it might be) of concentration and 

 diffusion within themselves. As relates to the extrusion 

 of the rarer body, it is a mode of reasoning that involves us 

 in an endless series of such expulsions. For true it is, that 

 sponges and the like porous substances, contract by the 

 ejection of the air. But with respect to air itself, it is clear 

 from manifold experiments that it can be condensed in a 

 known space. Are we then to suppose that the finer part 

 of air itself may be thus eliminated by compressure, and of 

 the eliminated part another part, and so on to infinity ? For 

 it is a fact most decidedly adverse to such an opinion that 

 the rarer bodies are they are susceptible of the more con 

 traction ; when the contrary ought to be the fact, if con 

 traction was performed by expressing the rarer portion of 

 the substance. As to that other mode of solution, namely, 

 that the same bodies without farther alteration undergo 

 various degrees of rarity and density, it is not worthy of 

 elaborate attention. It seems to be an arbitrary dictum, 

 depending on no cognizable reason, or intelligible principle, 

 like the generality of the dogmas of Aristotle. There remains 

 then the third way, the hypothesis of a vacuum. Should 

 any one object to this, that it appears a difficult and even im 

 possible supposition, that there should exist an interspersed 

 vacuity, where body is every where found ; if he will only 

 reflect calmly and maturely on the instances we have just 

 adduced, of water imbued with saffron, or air with odours, 

 he will readily discover that no portion of the water can be 

 pointed out where there is not the saffron, and yet it is 

 manifest by comparing the saffron and the water previous 

 to their intermixture, that the bulk of the water exceeds by 

 many times the bulk of the saffron. Now if so subtile an 

 interspersion is found to take place in different bodies, 

 much more is such interspersion possible in the case of a 

 body and a vacuum. 



Yet the theory of Hero, a mere experimentalist, fell short 

 of that of the illustrious philosopher Democritus in this 

 particular point, namely, that Hero not finding in this our 

 globe, a vacuum coacervatum, denied it therefore absolutely. 

 Now there is nothing to hinder the existence of a complete 

 vacuity in the tracts of air, where there are undoubtedly 

 greater diffusions of substances. 



And let me give this once the admonition, that, in these 

 and similar investigations, none be overpowered or des 

 pair, because of the surpassing subtilty of nature. Let 



VOL. xiv. F F 



