LUCRETIUS AND THE ATOMIC THEORY 181 



class ; but he has another argument in favour of a vacuum : 

 ' Why do we see one thing surpass another in weight, though not 

 larger in size ? ' How can things be of various densities unless 

 we admit empty pores in bodies ? His proof is insufficient ; 

 but here again modern research has confirmed his conclusion, so 

 far as it affects gross matter only, and Lucretius conceived no 

 other. His explanation of varying density is that which is 

 universally received and taught, and even the modern dis- 

 believers in a vacuum do not deny that some space may be un- 

 occupied by gross matter, but simply affirm, on grounds to be 

 hereafter stated, that all space is full of something, though not 

 of ponderable matter. In support of his proposition, Lucretius 

 points to the pores found in all bodies, and uses the following 

 ingenious though fallacious argument to prove a vacuum : ' If 

 two broad bodies after contact quickly spring asunder, the air 

 must surely fill all the void which is formed between the bodies. 

 Well, however rapidly it stream together with swift circling 

 currents, yet the whole space will not be able to be filled up in 

 one moment ; for it must occupy first one spot, and then 

 another, until the whole is taken up ; ' therefore, in the middle 

 a void must have existed for a sensible time. 



We are next informed by our author that matter exists, or, 

 in the language of Lucretius, l all nature, then, as it exists by 

 itself, has been founded on two things : there are bodies, and 

 there is void in which these bodies are placed, and through 

 which they move about.' In his first and second propositions, 

 Lucretius uses the word thing, res, which, as we have already 

 explained, comprehended all kinds of things, such as matter, 

 force, motion, thought, life, &c. He now states the existence 

 of matter, and few will be disposed to contradict him ; indeed, he 

 appeals to the general feeling of mankind in proof of his assump- 

 tion. Unless you grant this, he says, ' there will be nothing 

 to which we can appeal to prove anything by reasoning.' 



Lucretius now affirms that nothing exists but matter and 

 void, or, as put in Mr. Munro's translation, ' there is nothing 

 which you can affirm to be at once separate from all body and 

 quite distinct from void, which would, so to speak, count as the 

 discovery of a third nature.' Here at last we reach debatable 

 ground. Lucretius hardly adduces a single argument in support 



