44 Coward & Harden, Daltorfs Lecture Sheets. 



Silver, which now appears to be 190, was originally 

 100. The 1 has at some time been covered and a tail 

 given to the first o to make it a 9. Some fibres of the 

 fragment of paper which had been pasted over the 1 still 

 adhere to the sheet. 



Gold, originally 140, was altered to 90. A slip of 

 paper pasted over the 1 is lost but has left the faint 

 outline of one corner, as shown by the small difference 

 of tint in the colour of the sheet in that region. 



Platina was 100, then altered to 90 in the same way 

 as the figure for silver. Fibre left by the covering slip 

 is readily noticed on the sheet. 



The date of the original preparation of this sheet 

 can be determined when the figures and symbols on it 

 are compared with those in Dalton's published works and 

 especially with those in his manuscript note-books. In 

 the first place it is evidently a very early list, although 

 quite different from the first published one, which was 

 appended to the paper " On the Absorption of Gases 

 by Water," published in 1805 (Memoirs 6, 287). It con- 

 tains, however, the names of the same twenty elements 

 (so-called) as the first part of the first volume of his " New 

 System of Chemical Philosophy," published in 1808. 

 Certain differences between the figures and symbols of 

 the sheet and the corresponding ones of the book are 

 apparent, and by comparison with others prove that the 

 sheet was the earlier of the two. Thus the symbols for 

 lime, magnesia and gold were not the same as those in 

 the book, and the atomic weights of sulphur and iron are 

 certainly earlier than those of the book. 



The published figures, therefore, point to the date of 

 the sheet as between 1805 and 1808. The atomic weights 

 found in the set of laboratory note-books kept by Dalton 

 and now preserved in the Society's library, were next 



