Manchester Memoirs, Vol. lix. (191 5), No. 12. 49 



This diagram obviously belongs to the very early 

 days of the atomic theory, when to Dalton the atmos- 

 phere of heat around the atoms was still the fresh and 

 vivid conception which had played so important a part 

 in the physical origin of the atomic theory. The original 

 sheet shows plainly that the formula for hydrogen sul- 

 phide (No. 2) is on a slip which has been pasted over an 

 earlier formula representing that compound by a central 

 sulphur atom surrounded by three atoms of hydrogen. 

 The new formula was adopted in 1809 (Third laboratory 

 note-book, page 185). The older one has been found in 

 1808 (" New System," I., i.), in 1807 (Edinburgh and Glas- 

 gow lecture-notes), and once as an alternative formula in 

 1806 (Laboratory note-book ii., p. 245, September, 1806). 

 Before 1806 Dalton gave only the formulae SH 2 and SH 4 . 

 The original compilation of the sheet therefore belongs to 

 the period 1806 to 1809. 



Another formula of interest is that for muriatic acid, 

 which is represented as H0 3 , a view held by Dalton in 

 the " New System," I., ii. (1810). 



Very interesting is the representation of methane, 

 ethylene, ether and alcohol as hydrocarbons : CH. 2 , CH, 

 CoH, and C 3 H respectively. This is exactly the idea 

 Dalton held at the time of the Edinburgh and Glasgow 

 lectures (1807), as shown in the Mss. notes. It seems 

 most likely that the table was prepared to illustrate those 

 lectures, and is the actual "scheme" mentioned in the 

 lecture notes for reference during the lectures. 



A further point of interest is the difference between 

 the mode of presentment in this early diagram and that 

 employed in the u New System," I., ii. (1810). In the 

 latter case (Plates 7 and 8) the atoms are represented by 

 squares, each containing 16 rays representing the atmos- 

 phere of caloric. 



In the early diagram the first eight atoms have nearly 



