514 



SCIENCE. 



[N. S. Vol. XVIII. No. 460. 



losophy men sought to discover the nature 

 of the material universe, and to bring unity 

 out of diversity. Is matter one thing or 

 many ? Is it continuous or discrete ? These 

 questions occupied the human mind before 

 recorded history began, and their vitality 

 can never be exhausted. Final answers 

 may be unattainable, but thought will fly 

 heyond 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 state- 

 ments of an atomic theory. Other thinkers 

 in older civilizations, doubtless, went be- 

 fore them ; perhaps in Egypt or Babylonia, 

 but of them we have no certain knowledge. 

 There is a glimpse of something in India, 

 but we can not say that Greece drew her 

 inspiration thence. For us Leucippus was 

 the pioneer, to be followed later by Democ- 

 ritus and Epicurus. Then, in lineal suc- 

 cession, 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 par- 

 ticles of matter, indivisible and indestruct- 

 ible, of various shapes and sizes, and con- 

 tinually in motion. From their movements 

 and combinations all sensible matter was 

 derived. Except that the theory was purely 

 qualitative and non-mathematical in form, 

 it was curiously like the molecular hypoth- 

 esis of modern physics, only with an abso- 

 lute vacuum where an intermediary ether 

 is now assumed. This notion of a vacuum 

 was repellant 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 con- 

 troversy between plenists and atomists 

 which has continued to our own day. It 

 is, however, essentially a metaphysical con- 



troversy, and some writers have ascribed 

 it to a peculiar distinction between two 

 classes of minds. The arithmetical thinker 

 deals primarily with number, which is, in 

 its nature, discontinuous, and to him a 

 material discontinuity offers no difficulties. 

 The geometer, on the other hand, has to 

 do with continuous magnitudes, and a lim- 

 ited divisibility of anything in space is not 

 easy for him to conceive. But be this as 

 it may, the controversy was one of words 

 rather than of realities, and its intricacies 

 have little interest for the scientific student 

 of to-day. It is always easier to reason 

 about things as we imagine they ought to 

 be, than about things as they really are, 

 and the latter procedure became practicable 

 only after experimental science was pretty 

 far advanced. The Greeks were deficient in 

 physical knowledge, and, therefore, their 

 speculations remained speculations only, 

 mere intellectual gj'mnastics of no direct 

 utility to mankind. They sought to de- 

 termine the nature of things by the exer- 

 cise of reason alone, whei'eas science, as 

 M^e understand it, being less confident, seeks 

 mainly to coordinate evidence and to dis- 

 cover the general statement which shall 

 embrace the largest possible number of ob- 

 served relations. The man of science may 

 use the metaphysical method as a tool, but 

 he does so with the limitations of definite, 

 verifiable knowledge always in view. In- 

 tellectual stimulants may be used tem- 

 perately, but they need not be discarded 

 altogether. 



From the time of Liicretius until the 

 seventeenth century of our era, the atom- 

 istic hypothesis received little serious at- 

 tention. The philosophy of Aristotle gov- 

 erned all the schools of Europe, and 

 scholastic quibblings took the place of real 

 investigation. All scholarship lay under 

 bondage to one master mind, and it was not 

 until Galileo let fall his weights from the 



