292 REASONING. 



aspects of chemical phenomena, possesses within its 

 limited sphere this comprehensive character ; the 

 principle of Dalton, called the atomic theory, or the 

 doctrine of chemical equivalents : which by enabling 

 us to a certain extent to foresee the proportions in 

 which two substances will combine, before the experi- 

 ment has been tried, constitutes undoubtedly a source 

 of new chemical truths obtainable by deduction, as 

 well as a connecting principle for all truths of the 

 same description previously obtained by experiment. 



7. The discoveries which change the method of 

 a science from experimental to deductive, mostly con- 

 sist in establishing, either by deduction or by direct 

 experiment, that the varieties of a particular pheno- 

 menon uniformly accompany the varieties of some 

 other phenomenon better known. Thus the science 

 of sound, which previously stood in the lowest rank 

 of merely experimental science, became deductive 

 when it was proved by experiment that every variety 

 of sound was consequent upon, and therefore a mark 

 of, a distinct and definable variety of oscillatory mo- 

 tion among the particles of the transmitting medium. 

 When this was ascertained, it followed that every 

 relation of succession or coexistence which obtained 

 between phenomena of the more known class, 

 obtained also between the phenomena which corre- 

 sponded to them in the other class. Every sound, 

 being a mark of a particular oscillatory motion, 

 became a mark of everything which, by the laws of 

 dynamics, was known to be inferrible from that 

 motion ; and everything which by those same laws 

 was a mark of any oscillatory motion, became a mark 

 of the corresponding sound. And thus many truths, 

 not before suspected, concerning sound, became dedu- 



