the Genesis of Dalton' s Atomic Theory. 159 



its original form, and points to the inconsistency between the 

 two. Far from showing that Dalton at this time believed in 

 the theory that " M/S = C/' the first of these statements pre- 

 sents a striking proof to the contrary. It is in fact most 

 probable that this is the very " train of reasoning " which 

 convinced Dalton " that different gases have not their particles 

 of the same size." 



The fact that Dalton was not in this passage thinking of 

 the volume of the elastic particle is strikingly brought out by 

 a note which he had written on the page opposite to this 

 passage (Note-book, i. p. 245 ; R. & H. p 27) : — 



" N.B. — The ultimate atoms of bodies are those particles 

 which in the gaseous state are surrounded by heat; or they 

 are the centres or nuclei of the several small elastic globular 

 particles." 



As regards the second passage it may be noted that 

 although the heading is " Ultimate atoms of gases in the 

 order of their specific gravities/' and if the argument of 

 Debus is well founded the order of the specific gravities of the 

 gases should be identical with that of their relative weights, 

 this is not actually the case. The specific gravities (referred. 

 to air) of nearly all of these very gases are given only two 

 pages before this list by Dalton, and an inspection of them 

 at once shows that they do not follow the same order as the 

 relative molecular weights. 



Substance. 



Eelative mole- 

 cular weight 

 (Note-book, p. 260). 



Specific gravity 

 (Note-book, p. 258). 



Hydrogen 



1 

 4 



5-4 

 5-5 

 9-5 

 10-1 

 13-5 

 15-4 

 15-4 



•077 

 •966 

 •660 

 1-127 

 1-102 

 1-000 

 1-610 

 1-106 

 1-500 



Azote 



Carbonated Hydrogen Gas ... 

 Oxygen 



Nitrous Gas 



Gaseous Oxide of Carbon 



Nitrous Oxide 



Sulphuretted Hydrogen Gas . 

 Carbonic Acid Gas , 





A further and conclusive proof that Dalton (and Thomson) 

 did not (in 1803-4) believe in the hypothesis M/S = C is 

 afforded by the formula ascribed to water, which they in- 

 variably wrote in symbols equivalent to the formula OH, 

 although they were well aware that the volume relations 

 were nearly as 1 : 2, according to which, if the contention of 

 Debus were correct, the formula should have been H 2 0. 



