244 THK ATUMIC THEUKY. 



and Epicurus. Then, in lineal succession, came the Roman, Lucretius, 

 who gave to the doctrine the most complete statement of all. In the 

 thouj^ht of these men the universe was made up of empt}" space in 

 which swum imiumerable atoms. These were inconceivabl}^ 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 nonmathematical in form it was 

 curiously like th(> molecular hypothesis of modern physics, oidy with 

 an absolute 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 unrea- 

 sonable; 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 sonu'. 

 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, discoiitinuous, and to him a material disconti- 

 nuity ort'ei-s no difliculties. The oeometer, on the other hand, has to 

 do with continuous maj^'nitudes, and a limited 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 intrica- 

 cies have little interest for the scientific student of to-day. It is 

 always easier to reason about tilings as we imagine they ought to be, 

 than about things as the}" really are, and the latter procedure became 

 practicable only after experimental science was pretty far advanced. 

 The Greeks were deticient in phvsical knowledge, and, therefore, their 

 speculations remained speculations only, mere intellectual gymnastics 

 of no direct utility to mankind. They sought to determine the nature 

 of things ])V the exercise of reason alone, whereas science, as we under- 

 stand it, being less confident, seeks mainly to coordinate evidence and 

 to discover the general statement which shall embrace the largest 

 possible number of observed 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. Intellectual stimu- 

 lants may be used temperately, but they need not be discarded 

 altogether. 



From the time of Lucretius until the seventeenth century of our 

 era the atomistic hypothesis received little serious attention. The 

 philosophy of Aristotle governed all the schools of Europe, and scho- 

 lastic quibl)lings took the plai'C of I'eal investigation. All scholarship 

 lay under bondagi^ to one master mind, and it was not until (ialileo 

 let fall his weights from the leaning towei- of Pisa that the sp(dl of 

 the Stagirite was bi-oken. Experimental science now came to tlw? fore, 

 and it was seen that even Aristotelian logic must verify its premises. 



