62 A SHORT HISTORY OF SCIENCE 



almost nothing is known, but he was probably a contem- 

 porary of Empedocles and Anaxagoras, and possibly a pupil 

 of Zeno. Leucippus assumed the existence of empty space as 

 well as of matter, and held that of atoms all things are consti- 

 tuted. Space is infinite in magnitude, atoms infinite in number 

 and indivisible, with only quantitative differences. Atoms are 

 always in activity, and worlds are produced by atoms variously 

 shaped and weighted, falling in empty space and giving rise to an 

 eddying motion by mutual impact. 



DEMOCRITUS OF ABDERA was a pupil and associate of Leu- 

 cippus, whose theories of empty space and material atoms he de- 

 veloped and made so famous that his own name alone is often 

 associated with them. Of his life, his works, and his death little 

 is certainly known, but he may be regarded as marking the culmina- 

 tion and conclusion of the Ionian school ; and his reputation, both 

 in antiquity and in mediaeval times, was immense. Like contem- 

 porary and preceding philosophers, his writings were in verse, and 

 Cicero is said to have deemed his style worthy of comparison with 

 that of Plato. His somewhat boastful comparison of his own 

 geometrical power with that of the Egyptian rope-stretchers has 

 been quoted. 



Democritus appears to have agreed closely in his interpretation 

 of nature with Leucippus, and regarded empty space and atoms 

 as cosmic elements. He also held that by the motion of the atoms 

 was produced the world with all that it contains. Soul and fire 

 are of one nature, their atoms small, smooth, and round. By 

 inhaling them life is maintained. Hence the soul perishes with 

 and in the same sense as the body, - - a doctrine which made 

 Democritus odious to later generations. Dante, for example, 

 places him far down in hell as "ascribing the world to chance." 



The atomic theory of perception held that from every object 

 "images" of that object are being given off in all directions, some 

 of which enter the organs of sense and cause "sensations." De- 

 mocritus further held that sensations are the only sources of our 

 knowledge. He was regarded as one of the extreme sceptics of 

 antiquity, as e.g. in this saying, " We know nothing : not even 



