Manchester Memoirs, Vol. xlvii. (1903), No. 11. 



THE WILDE LECTURE. 



XL The Atomic Theory. 



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



Delivered May igtk, igoj. 



One hundred years ago, on October 21, 1803, John 

 Dalton gave this Society the first announcement of his 

 famous atomic theory. It was only a slight preliminary 

 notice, a mere note appended to a memoir upon another 

 subject, and it attracted little or no attention. In 1804 

 Dalton communicated his discovery to Dr. Thomas 

 Thomson, who at once adopted it in his lectures, and in 

 1807 gave it still wider publicity in a text-book. A year 

 later Dalton published his " New System of Chemical 

 Philosophy," and since then the history of chemistry has 

 been the history of the atomic theory. To celebrate 

 Dalton's achievement, to trace its influence upon chemical 

 doctrine and discovery, is the purpose of my lecture. It 

 is an old story, and yet a new one ; for every 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, cannot be easily supplanted. Despite 

 attacks and criticisms, Dalton's generalisation 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 



May 2gth, igoj. 



