4 MFLDRU^r, Devdopiuoit of the. Atomic Theory. 



what had been done by Richter on the same subject." 

 Again, " Nobody knows better than myself that Dalton 

 was ignorant of what Richter had done about ten years 

 before him.'"' This shows conclusively that Dalton said 

 nothing about Richter to Thomson. 



Now that we have access, thanks to Roscoe and 

 Harden's " New View of the Origin of Dalton's Atomic 

 Theory," to the valuable material contained in Dalton's 

 notebooks, we can carry the critical process further than 

 Henry and Thomson did. The notebooks show, as 

 Roscoe and Harden point out, that Dalton had been 

 busily engaged during the year 1803 on the atomic 

 theory, and that he was investigating the non-metallic 

 elements then, and not Richter's acids and bases at all. 



Dalton's knowledge of Richter can hardly have been 

 due to anyone but Berthollet. Richter's work had been 

 completely ignored till E. G. Fischer gave a resume of it, 

 and thus made it known throughout Germany. Ber- 

 thollet, by quoting this resume at the end of the " Essai 

 de Chimie Statique," made Richter known throughout 

 Europe. In the " Essai " Berthollet opposes Dalton's theory 

 of "mixed gases," but Dalton made no reply till 1808 in 

 the " New System of Chemical Philosophy." This helps 

 to date his knowledge of Richter. If Dalton was slow to 

 read new books, he was prompt in replying to criticisms 

 of his theory. He kept up the defence of it in a series of 

 papers which came to an end about October, 1805, without 

 any mention of BerthoUet's objections having been made. 

 It was presumably subsequent to this date that Dalton 

 read the "Essai," and learnt of Richter's work. In the 

 note-books the date of the earliest reference to Richter is 

 April 19th, 1807.'' There is really no room for doubt that 



*■' Pi-oc. Phil. Soc. Glasgow, vol. 2, pp. 86, 88, 1845-6. 

 ' Roscoe and Harden, " New View of ^tlie Origin of Dalton's Atomic 

 Theory,'" p. 79 ; see also pp. 7-10, 46, 91-94. 



