THE ATOMIC THEORY. 247 



opportunity cauie at the riolit niomont, and lie knew how to use it well. 

 Elements had ])een defined; the constancy of matter was established; 

 pneumatic chemistry was well developed, and great numbers of quan- 

 titative analyses awaited interpretation. The foundations were ready 

 for the master builder, and Dalton was the man. His theor}' could at 

 once be tested by the accunmlated data, and when that had been done 

 it was found to be worthy of acceptance. 



It is not my purpose to discuss in detail the processes of Dalton's 

 mind. The story is told in his own notebooks, which have been given 

 to the public by Roscoe and Harden,'^' and it has been sufficiently dis- 

 cussed b}^ others. We now know that Dalton was thoroughly imbued 

 with the corpuscular ideas of Newton and that, When studying the dif- 

 fusion of gases, he was led to the belief that the atoms of different 

 suV)stances must be different in size. Upon applying this hypothesis 

 to chemical problems he discovered that these differences were in one 

 sense measurable and that to every element a single, definite, com- 

 bining number, the relative weight of its atom, could be assigned. 



From this, the law of definite proportions logically followed, for 

 fractions of atoms were inadmissible; and the law of multiple propor- 

 tions, which Dalton worked out experimentally, completed the gen- 

 (M'alization. The conception that all comi)ination nuist take place in 

 lixed proportions was not new, and, indeed, despite the objections of 

 Herthollet, was generally assumed; ])ut the atomic theory gave a rea- 

 son for the laAV and made it intelligible. The idea of multiple propor- 

 tions had also occurred, although incompletely, to others; ))ut the 

 determination of atomic weights was altogether original and novel. 

 The new atomic theory, which figured chemical union, as a juxtaposi- 

 tion of atoms, coordinated all of these relations and gave to chemistrj^ 

 for the first time an absolutelv general ([uantitative basis. The tables 

 of Richter and Fischer, who preceded Dalton, dealt only with special 

 cases of combination, l)ut they established regularities which rendered 

 easier the acceptance of the new and l)roader teachings. The earlier 

 atomic speculations were all purely qualitative and incapable of exact 

 application to specific problems; Dalton created a working tool of 

 extraordinary power and usefulness. Between the atom of Lucretius 

 and the Daltonian atom the kinship is very remote. 



Dalton was not a learned man, in the sense of mere erudition, but 

 perhaps his limitations did him no harm. Too much learning is some- 

 times in the way, and clogs the flight of that imagination ])y which the 

 greatest discoveries are made. The man who could not see the forest 

 ])ecause of the trees was a good tj'pe of that scholarship which never 

 rises above petty details. It maj" compile encyclopa'dias, but it can 



«A New View of the Origin of Dalton's Atomic Theory, etc. By Sir Henry E, 

 Roscoe and Arthur Harden. London, 1S9(). See also Debus, in Zeits. Physikal. 

 Chenu, Bd. 20, p. 359, and a rejoinder by Roscoe and Harden in Bd. 22, p. 241. 



SM 1903 17 



