Manchester Memoirs, Vol. lix. (191 5), No. \%. 



Part III. 

 The Lecture Sheets Illustrating the Atomic Theory. 



By Hubert Frank Coward, D.Sc, 



AND 



Arthur Harden, D.Sc, Ph.D., F.R.S. 



{Read May nth, 1Q15. Received for piiblicati on May jrst, ig^S-) 



Towards the end of the eighteenth century and 

 during the early part of the nineteenth, John Dalton 

 delivered courses of lectures on Natural Philosophy in 

 Kendal, Manchester, London, Edinburgh and Glasgow, 

 and other places. 14 During his development of the atomic 

 theory, from about 1803 onwards, Dalton's lectures dealt 

 more and more with chemistry, and were illustrated by 

 chemical experiments and by sheets of diagrams which 

 he prepared with considerable care. Recently some 150 

 of these lecture sheets were found in the rooms of the 

 Society, and- of these the 53 which illustrate the atomic 

 theory are described in the present Memoir. 



While no new view of the origin of the atomic theory 

 has been disclosed by them, they nevertheless present 

 some highly interesting points to the student of the 

 history of science. In general they show that Dalton 

 made much more use of his symbols in oral explanations 

 of the theory than in his published works or even in his 

 laboratory note-books. Thus, besides two tables of 

 atomic weights and symbols, some 34 of the sheets 

 14 For ;i list of these, see Part I. 



