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body were taken as a standard, every other could 

 have a number assigned to it as its proportional 

 combining weight. It was on this foundation of 

 fact that Dalton based his re-establishment of the 

 old atomic hypothesis on a new empirical founda- 

 tion. It is obvious, that if elementary matter 

 consists of indestructible and indivisible particles, 

 each of which constantly preserves the same 

 weight relatively to all the others, compounds 

 formed by the aggregation of two, three, four, 

 or more such particles must exemplify the rule of 

 combination in definite proportions deduced from 

 observation. 



In the meanwhile, the gradual reception of the 

 undulatory theory of light necessitated the assump- 

 tion of the existence of an " ether " filling all 

 space. But whether this ether was to be regarded 

 as a strictly material and continuous substance, 

 was an undecided point, and hence the revived 

 atomism escaped strangling in its birth. For it is 

 clear, that if the ether is admitted to be a con- 

 tinuous material substance, Democritic atomism 

 is at an end and Cartesian continuity takes its 

 place. 



The real value of the new atomic hypothesis, 

 however, did not lie in the two points which 

 Democritus and his followers would have con- 

 sidered essential namely, .the indivisibility of the 

 " atoms " and the presence of an interatomic 

 vacuum but in the assumption that, to the 



