46 Coward & Harden, Dalton's Lecture Sheets. 



calculated from the composition of carbonic acid is 

 therein put 54. Evidently Dalton about this period 

 generally used whole numbers for his atomic weights ; 

 on this one occasion he showed more confidence 

 than usual in the analytical figures from which he had 

 deduced this atomic weight. An illustration of his atti- 

 tude of mind at the time is to be found in the third 

 laboratory note-book, page 76 {circa 1809), where he 

 writes, in reference to the atomic weight of nitrogen, 

 " From the above observations it seems probable that the 

 true ratio of hydrogen to azote in ammonia is nearly I to 

 5, or perhaps 1 to 4 J ; but as an integer is more easily 

 remembered, we shall prefer the ratio 1 to 5 till a more 

 accurate one can be ascertained/' 



There seems therefore to be little doubt that this 

 sheet was prepared at the latter end of 1806 or early in 

 1807 for illustrating the lectures in Scotland in April, 

 1807. ^ 1S therefore the second publicly presented list, 

 so far as is known. It was probably prepared by Dalton's 

 own hand. 



The atomic weights from Dalton's note-books and 

 publications of this period, starting from the earliest found 

 (in 1803) are collected for comparison in Table I. 



Sheet 2. 



Plate IV. 



This table of atomic symbols and weights is much 

 later than the previous one and is not very different from 

 the corresponding list of elements in Volume II. of the 

 "New System" (1827). The symbols are represented in 

 the book by the full names of the elements. The follow- 

 ing comparison shows those details where differences 

 between the two lists are found : 



