220 MEMOIR OF DR. DALTON, AND 



have built before, this is the existing ground on which Dalton 

 had to raise his edifice. 



To some extent this may be reckoned questionable, as the 

 discussion as to the definite proportions of compounds was 

 going on with Proust, a strong supporter of this doctrine, but 

 this exception only shows that the differences of opinion were 

 raised, not on the great theory, the history of which we are 

 discussing, but on the simplest preliminary facts ; the laws 

 themselves did not appear in the discussion from the cause 

 already given, viz., virtual non-existence, except in a state of 

 possible evolution from laws which themselves were not fully 

 proved. 



I shall now give those sentences from Proust's writings 

 which seem most nearly to affect our subject. 



* " As to those which have been announced by Thenard, 

 I will not contest results obtained by a chemist who knows 

 how to operate with that exactitude which characterizes a con- 

 summate worker. I will say, however, without attaching any 

 importance to my opinion, that in considering this almost 

 general law of nature which offers us everywhere only one or 

 two terms of oxidation of metals, and from which, in our arti- 

 ficial imitations, we cannot free ourselves, I fear that the six 

 terms which he recognises are not all sanctioned by nature. 



"If by the assistance of a high temperature we lower the 

 weight of an oxide which is at its maximum, and which does 

 not happen to be volatile, or if by a high continued heat we 

 elevate a metal to its highest oxidation, are we to believe 

 that all the ascending or descending terms of oxidation, 

 which may be inserted between the extremes, are to be taken 

 as so many different terms of oxidation ? Certainly not. I 

 do not recognise in that the ordinary course of nature, and I 

 venture to believe that in similar cases we only make mixtures 

 in all possible proportions of the oxide at minimum with the 

 oxide at maximum. 



• Journal de Physique. Tom. 50, page aSl- 1802. 



