LUCRETIUS AND THE ATOMIC THEORY 199 



full. The dust and round balls he calls the first and second 

 kind of materials of which the universe, as we know it, is com- 

 posed ; but besides the dust and balls there is a third material ; 

 all the edges of the first fragments of plenum did not get ground 

 into dust ; a fair number were merely rubbed into a kind of 

 snake-shape of triangular section such a shape as would slip 

 through the interstices in a pile of cannon-balls. These snake- 

 shaped pieces sometimes got entangled, and when so entangled 

 they composed the solid matter which is apparent to our senses. 

 The balls and dust fill all space, the dust forms the great vor- 

 tices which carry the planets round the sun, the balls are light 

 and go flying about, so do the snakes, which, getting entangled, 

 form gross matter. It is far more interesting to endeavour 

 to understand the views of great men, however removed they 

 may be from our own, than to look merely on the ludicrous side 

 which their ideas may happen to present ; but we are unable in 

 all Descartes's theory of matter to perceive anything beyond the 

 most childish fancy. It does not seem to have occurred to him 

 that there would be any difficulty in breaking up an absolute 

 plenum ; what would be the nature of the separation between 

 the fragments, what could define the boundary, he nowhere says ; 

 he sends his balls, dust, and snakes flying about in any direction 

 he may think convenient ; the balls and dust are imponderable, 

 the knotted snakes, made of the same stuff, and intermediate 

 between the two other kinds, are ponderable. Why three kinds 

 balls, dust, and snakes ? Why not rather fragments of 

 infinite variety of shape and size, from big bits of plenum to 

 dust ? No answer to all this, but long dissertation on the knot- 

 ting of snakes to form spots on the sun. His laws of motion are 

 false, and he knew it, but says we must not judge from our 

 experience of gross matter ; and yet, this man insisted on clear 

 conceptions as the very test of truth. 



Leibnitz about the same time declared against atoms, against 

 a vacuum, and against Descartes. He will have it to be inconsis- 

 tent with the perfection of God, that a vacuum can exist. It is 

 out of the question that God should leave any part of space 

 unemployed. John Bernoulli, in whose correspondence with 

 Leibnitz these questions are treated with much dexterity, very 

 properly replies that vacuum may be useful, since it may be a 



