HISTORY OF THE ATOMIC THEORY. 25 1 



of hydrogen, and as he gave the specific gravity of oxygen at 

 1.127, he was compelled to raise very high that of hydrogen, 

 which he made .0805. We should have supposed Dalton to 

 be, of all men, the most fitted for seeing exactly the position 

 which Gay Lussac's law would take, and for extending our 

 view of it; but it was not so. His mind had probably be- 

 come too much engrossed with his own views of the case; 

 and the belief that the whole subject had been attained, came 

 in at last to shorten his vision. It is not in science only that 

 men show that they are not the best fitted for seeing their 

 own position, and without this knowledge a false step is not 

 easily prevented. 



His memoirs, after this period, were generally on less 

 important subjects. We see in them the same quality of 

 originality, the same inclination to strike at the root of a 

 subject, but it is done with less power ; the result is rather 

 an idea which he leaves to be worked out. Some of them 

 are hurried, some are careless, some are unfinished. Had it 

 lain within the scope of this memoir, I might have shown 

 many sentences full of latent beauty, which have since budded 

 and blossomed. 



Of these the following is not the least remarkable, although 

 it had gone farther than a mere idea;^ it was long put into prac- 

 tice by him. As far as 1 know, therefore, he is to be considered 

 as the originator of analysis by volume, which has long been 

 practised to a great extent in the manufactories of Lancashire. 

 In this respect chemists are still behind Dalton, and have not 

 yet got into the habit of using all those advantages which his 

 works have offered, although the actual knowledge on the sub- 

 ject has advanced far beyond the period of Dalton*s latest years. 



In one of these memoirs on the analysis of spring and 

 mineral waters, we find that he gives directions for the centi- 

 grade method of testing, and Mr. John Gough Watson, his 

 pupil, informs me that he used it constantly. Ho says,* 



* Mem. Phil. Soc, Vol. III., new scries, p. 59, 1>^I4. 



