46 SCIENCE IN GRECO-ROMAN ANTIQUITY 



senses reveal to us ? They result simply, answers 

 Anaxagoras, from the fact that the Nous intensifies 

 such or such a quality and makes it predominate over 

 some other in the constitution of the body. This is 

 the reason why objects which we perceive appear to 

 us to differ from one another, although they are com- 

 posed of exactly the same substance. The qualitative 

 atomism of Anaxagoras is a remarkable effort to 

 reconcile the unity and plurality of Being ; but it is 

 unfortunately a hypothesis which scarcely seems 

 susceptible of scientific verification. It had, never- 

 theless, a great influence on Plato and Aristotle. How, 

 asked Anaxagoras, can qualities, which sensation 

 shows to be irreducible (red and blue for example) 

 mix together ? Transferring this problem to the 

 world of ideas, Plato likewise examined in what 

 manner ideas, which each formed an indissoluble 

 whole, could form a group and partake of each other's 

 properties. As to Aristotle, if he borrowed from 

 Empedocles the theory of the four elements, under 

 the influence of Anaxagoras, he gave them a purely 

 qualitative signification, which persisted during the 

 Middle Ages and which hampered the progress of 

 physical science, as such a conception discards the 

 use of mathematics. 



About 460 B.C., Leucippus of Miletus, a disciple 

 of Parmenides, and a contemporary of Empedocles, 

 taught another system of atomic philosophy more 

 scientific and more important. His ideas were taken 

 up and developed by Democritus of Abdera (460-370 

 B.C.) who, according to tradition, travelled in Egypt 

 and as far as the Indies. Amongst the works attri- 

 buted to him, several were really written either by 

 his master or his disciples. The outstanding idea of 

 all these works is the following : In spite of the opinion 

 of the Eleatic school, the existence of empty space 



