LUCRETIUS AND THE ATOMIC THEORY 185 



tion as a dogma by itself is, that the proof could not as yet be 

 given ; but in discussing rival doctrines he is led to anticipate 

 his own views. 



He proceeds to assert that there is no limit to space, nor 

 yet to the total quantity of matter ; but these are rather meta- 

 physical than physical questions, although he seems to think 

 that, unless infinite space were full of matter, the universe 

 could not hold together, for he will not hear of gravitation, by 

 which ' all things press to the centre of the sum.' He is almost 

 comically unfortunate in denouncing the idea, that heavy bodies 

 which are beneath the earth shall press upwards, or that living 

 things walk head downwards, and that when these see the sun 

 we behold the stars of night ; but although it is very interesting 

 to observe that these doctrines were then held, we will examine 

 only the propositions strictly necessary for his theory of matter, 

 passing over also his assertion that atoms were not arranged by 

 design, until we examine how he himself conceived that they 

 were arranged. This explanation is given in the Second Book, 

 containing what we should term the Kinetic branch of his 

 theory, or, to use his own language, he next explains ' by what 

 motion the begetting bodies of matter do beget different things, 

 and, after they are begotten, again break them up, and by what 

 they are compelled so to do.' The book opens with the pro- 

 position that matter does not ' cohere inseparably massed 

 together ; ' it does not stick together as a mere inert mass. 

 Lucretius infers this from the continual change which we per- 

 ceive, and by which all things wax and wane, although the 

 sum remains constant. 



A modern physical treatise would attribute these changes to 

 chemical affinity, heat, gravitation, &c., or possibly, in more 

 general terms, to the various forms of what we term Energy. 

 Lucretius can only suppose this energy to be represented by 

 atoms in motion ; and if this be not universally true, it is pro- 

 bably true for many cases. This perpetual motion of the atoms 

 is next reasserted as a distinct proposition. ' No atom,' he 

 says, ' can ever stop, giving up its motion to its neighbour.' 

 At first sight, nothing can be more contrary to our ideas of the 

 laws of motion. We repeatedly see a ball strike another, and 

 set it in motion, remaining itself apparently quiescent after the- 



