ATOMIC THEOEY. 419 



speak somewhat more in detail, as best illustrating the nature 

 and value of the objects attained, and the method of their 

 attainments. Two great steps of progress are especially to 

 be noted in the discovery. The first in order of time as well 

 as in order of thought and deduction, is the Law of multiple 

 proportions ; originally derived, as we have seen, from a cer- 

 tain class of compounds the neutral salts and afterwards 

 extended so largely to others as to assume the character of a 

 general law of chemical combination. The principle briefly 

 stated is, that when bodies, whatever their form, enter into 

 such combination or separate from it, they do so in the same 

 fixed proportions ; that these proportions are either equal or 

 multiples of one another ; and that intermediate quantities 

 or proportions are never found to exist. The earlier excep- 

 tions to this law have been gradually removed as chemical 

 analysis acquired greater exactness; a striking evidence in 

 itself of the truth and completeness of the discovery. Cogent, 

 however, as were the facts upon which it rested, there was at 

 first some hesitation among chemists in adopting it. The 

 eminent name of Berthollet had just given currency to the 

 doctrine that the mere quantity of a combining ingredient, 

 irrespectively of other conditions, was largely concerned in all 

 chemical affinities and combinations ; and this opinion was 

 ably defended by other chemical writers. The controversy, 

 however, could not long be maintained in the face of evidence 

 almost mathematical in kind, and all other views speedily 

 merged in the one doctrine we have just stated. 



Here, then, was a mighty gain effected not merely to 

 Chemistry, but to physical science in its every part. By 

 introducing the function of numbers in scrutinising the 

 wonderful changes which take place, invisibly to us, among 

 the molecules of bodies in chemical action, we may be said 

 to have gained nearer access to one of the great facts of 

 creative intelligence. For if these elementary molecules are 



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