414 LIFE OF DALTOX : 



the innumerable cases which Chemistry puts before us. We 

 are the more earnest in pressing these general views, inas- 

 much as they help us to comprehend the whole history of 

 this part of science. It is obvious that the processes of an 

 imperfect analysis could never substantiate doctrines which 

 have the numerical proportions of weight for their foundation. 

 It is the increasing exactness of analytical chemistry which 

 has furnished a basis for that new theory which we now have 

 under review. 



Certain questions as to priority of discovery meet us here, 

 even in the outset. This, it is well known, has happened in 

 almost every similar case ; the result sometimes of acci- 

 dent, sometimes the effect of a simultaneous direction of the 

 labour and genius of many to objects already indicated for 

 research. In the history of the greatest discoveries even 

 that of universal gravitation we find the record of men who 

 have seen the light before them, have approached near to it, 

 but have missed the sole path by which the lamp could be 

 seized. But the example which most bears on our present 

 subject is the controversy, actively revived of late, as to the 

 discovery of the composition of water the greatest single 

 step ever made in chemical science. We do not enter on the 

 question here ; but merely cite it as a striking instance of 

 that concatenation by which the labours of men of genius 

 are blended together for the advancement of knowledge and 

 the good of mankind. 



The closest anticipations of Dalton's discovery are doubt- 

 less to be found in the researches of Wenzel and Richter, 

 two Grerman chemists, and of Mr. Higgins of Dublin. Wen- 

 zel led the way, now nearly eighty years ago, by the execu- 

 tion of very exact analyses of neutral salts, which gave proof 

 that when two such salts decompose one another, the com- 

 pounds thence resulting are precisely neutral also. The two 

 bases and two acids are exchanged in proportions exactly 



