THE ATOMIC THEORY/' 



By Prof. F. W. Clarke, D. Sc. 



One hundred years ag'o, on October 21, 1803, John Dalton gave this 

 society the first announcement of his famous atomic theory. Jt was 

 only a slight preliminary notice, a mere note appended to a memoir 

 upon another subject, and it attracted little or no attention. In ISO-i 

 Dalton communicated his discovery to Dr. Thomas Thomson, who at 

 once adopted it in his lectures, and in 1807 gave it still wider pub- 

 licit}^ in a text-book. A year later Dalton published his New System 

 of Chemical Philosoph}-, and since then the history of chemistry has 

 been the history of the atomic theory. To celebrate Dalton's achieve- 

 ment, to trace its influence upon chemical doctrine and discover}^ is 

 the purpose of my lecture. It is an old story, and yet a new one; for 

 ever}' year adds something to it, and the process of development shows 

 no signs of nearing an end. A theory that grows and is continually 

 fruitful can not be easily supplanted. Despite attacks and criticisms, 

 Dalton's generalization still holds the field; and from it, as from a 

 parent stem, spring nearly all the other accepted theories of chemistry. 



Every thought has its ancestry. Let us briefly trace the genealogy 

 of the atomic theory. In the very beginnings of philosophy 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 continu- 

 ous 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 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 civilizations 

 doubtless went before them; perhaps in Egypt or Bal)y Ionia, 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 Democritus 



«The Wilde Lecture, delivered IVIay 19, 1908, l)y Professor Clarke ])efore the INIan- 

 cbester Literary and Phil()soi)hica! Society. Reprinted from Memoirs and Proceed- 

 ings of the Society, Manchester, England, vol. 47, Part IV, No. 11, May 29, 1908. 



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