2 Clarke, TJie Atomic Theory. 



diversity. Is matter one thing, or many ? Is it con- 

 tinuous, or discrete? These questions occupied the 

 human mind before recorded history began, and their 

 vitaHty can never be exhausted. Final answers may be 

 unattainable, but Thought will fly beyond the boundaries 

 of knowledge, to bring back, now and then, truly helpful 

 tidings. 



To the early Greek philosophers we must turn for our 

 first authentic statements of an atomic theory. Other 

 thinkers in older civilisations, doubtless, went before 

 them ; perhaps in Egypt or Babylonia, but of them we 

 have no certain knowledge. There is a glimpse of some- 

 thing in India, but we cannot say that Greece drew her 

 inspiration thence. For us Leucippus was the pioneer, to be 

 followed later by Democritus and Epicurus. Then, in 

 lineal succession, came the Roman, Lucretius, who gave 

 to the doctrine the most complete statement of all. In 

 the thought of these men the universe was made up of 

 empty space, in which swam innumerable atoms. These 

 were inconceivably small, hard particles of matter, 

 indivisible and indestructible, of various shapes and sizes, 

 and continually in motion. From their movements and 

 combinations all sensible matter was derived. Except 

 that the theory was purely qualitative and non-mathe- 

 matical in form, it was curiously like the molecular 

 hypothesis of modern physics, only with an absolute 

 vacuum where an intermediary ether is now assumed. 

 This notion of a vacuum was repellent to many minds; to 

 conceive of a mass of matter so small that there could be 

 none smaller was unreasonable; and hence there arose the 

 interminable controversy between plenists and atomists 

 which has continued to our own day. It is, however, 

 essentially a metaphysical controversy, and some writers 

 have ascribed it to a peculiar distinction between two 



