250 MEMOIR OF DR. DALTON, ANU 



Part 1st. "At the time I formed the theory of mixed gases 

 I had a confused idea, as many have, I suppose, at this time, 

 that the particles of elastic fluids are all of the same size; 

 that a given volume of oxygenous gas contains just as many 

 particles as the same volume of hydrogenous." But he 

 arrived at the conclusion, "That every species of pure elastic 

 fluid has the particles globular, and all of a size ; but that no 

 two species agree in the size of their particles, the pressure 

 and temperature being the same." Then he concludes, in 

 Part 2nd, "The truth is, I believe, that gases do not unitg 

 in equal or exact measures in any one instance ; when they 

 appear to do so, it is owing to the inaccuracy of our experi- 

 ments. In no case, perhaps, is there a nearer approach to 

 mathematical exactness, than in that of 1 measure of oxygen 

 to 2 of hydrogen ; but here the most exact experiments I 

 have ever made, gave 1.97 hydrogen to 1 oxygen." 



This discussion brings out prominently some of the points 

 of Dalton's character. }f.e objected to the idea of bulk being 

 taken as a combining proportion ; it was his great object to 

 show the importance of weight and the completeness with 

 which it answered every purpose. He conceived the combi- 

 nation by bulk as accidental, evidently because he had not 

 examined the relations of the subject with sufiicient care, and 

 probably with some aversion, as his own discovery seemed 

 in question. He is strict in the examination of the analyses 

 of others, and seeks mathematical precision, when he could so 

 very easily, in his own researches, overleap a few per cent. Yet 

 no one would have been, on theoretical grounds, so likely to 

 arrive at Gay Lussac's law as Dalton himself, as he paid most 

 attention to the bulk of atoms, giving the relative diameters 

 of particles of the different gases after giving the relative 

 specific and atomic gravity. He did not always obtain an 

 analysis so correct as that mentioned above, he continually, 

 and to the last, insisted on the atomic weight of oxygen 

 being 7; and he gives the specific gravity as 14 times that 



