I1ST THE LAST HALF-CEXTURY. 45 



foundation. It is obvious, that if ele- 

 mentary matter consists of indestructible 

 and indivisible particles, each of which 

 constantly preserves the same weight rela- 

 tively 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 recep- 

 tion of the undulatory theory of light ne- 

 cessitated the assumption of the existence 

 of an ' ether ' filling all space. But 

 whether this ether was to be regarded as 

 a strictly material and continuous sub- 

 stance 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 continuous ma- 

 terial substance, Democritic atomism is 

 at an end and Cartesian continuity takes 

 its place. 



The real value of the new atomic hy- The red 



