Manchester Memoirs, Vol. xlvii. (1903), No. 11. 9 



menter he was crude, and excelled by several of his 

 contemporaries ; his tables of atomic weights, or rather 

 equivalents, were only rough approximations to the true 

 values. These defects, however, are only spots upon the 

 sun, and in no wise diminish his glory. Dalton trans- 

 formed an art into a science, and his influence upon 

 chemistry was never greater than it is to-day. The truth 

 of this statement will appear when we trace, step by step, 

 the development of chemical doctrine. The guiding clue, 

 from first to last, is Dalton's atomic theory. 



Although Dalton first announced his theory in 1803, 

 the publication of his "System" in 1808 marks the 

 culmination of his labours. The memorable controversy 

 between Proust and Berthollet had by this time exhausted 

 its force, and nearly all chemists were satisfied that the 

 law of definite or constant proportions must be true. The 

 idea of multiple proportions was also easily accepted ; 

 and as for the combining numbers, they, after various 

 revisions, came generally into use. The atomic con- 

 ception, however, made its way more slowly, for the fear 

 of metaphysics still governed many acute minds. Davy 

 especially was late in yielding to it, but in time even his 

 conversion was effected. Thomson, as we have already 

 noted, was the earliest and most enthusiastic disciple of 

 the new system, and Wollaston, although cautiously 

 preferring the term " equivalent " to that of atomic weight, 

 made useful contributions to the theory. These names 

 mark the childhood of the doctrine, before its vigorous 

 growth had thoroughly begun. 



The development of the atomic theory followed two 

 distinct lines, the one chemical, the other physical in 

 direction. On the chemical side the leader was Berzelius, 

 who began in 181 1 the publication of his colossal researches 

 upon definite proportions. At first he seems to have 



