THE STRUCTURE OF THE WORLD-STUFF 271 



essentially the same. Indeed in some respects the older view has the 

 advantage, as it lays greater stress upon the motion of the atoms; a 

 forecast of the modern kinetic theory of matter. 



The lack of development of the atomic theory is to be ascribed largely 

 to the adverse criticism of Aristotle. The overwhelming influence of 

 the Aristotelian philosophy was thrown against it, and it made little 

 headway down through the middle ages. Not until the downfall of 

 scholasticism do we find any extensive revival of the system; a revival 

 culminating in the seventeenth century school of atomists, among 

 whom are to be noted Gassendi, Boyle and, as we have seen, Newton. 

 But still another century of stagnation was to elapse before it was to 

 be transformed and modernized at one stroke by the genius of the 

 English chemist John Dalton. 



The modern atomic theory founded by Dalton and developed during 

 the nineteenth century must not be regarded merely as an extension 

 of the older theory, but as a new structure built upon the old one as a 

 foundation. That was speculative, this was scientific. That was 

 vague, this was definite. That was based merely upon observation and 

 introspection, this upon experiment and calculation. The theory of 

 the elements and the theory of atoms was blended into a single com- 

 prehensive whole. The prime distinction between the different kinds 

 of atoms was found in a single property — that of their relative mass. 

 The older theory was not inadequate in the early days of science; but 

 it failed when the quantitative relations of phenomena were brought 

 into prominence by the development of experimental methods; and 

 such was the case when the principle of the indestructibility of matter 

 was raised by Lavoisier from a philosophic dogma to a scientific truth, 

 and emphasis was thus laid upon mass as the fundamental property 

 of matter. 



I need not detail to you the marvelous growth of the theory during 

 the past century; how it met every demand made upon it by modern 

 chemistry, and indeed inspired much of the development of that 

 6cience; how, on the other hand, it has lent its aid to the progress of 

 physics and especially how by the founders of the kinetic theory of gases, 



the flaring atom streams 

 And torrents of her myriad universe 

 Ruining along the illimitable inane 



were marshaled to the defense of the great principle of the conservation 

 of energy, and the science of heat was annexed to the domain of 

 mechanics. Let me rather recall to you the salient points of the theory 

 as held by the close of the century, for comparison on the one hand 

 with the theory of the past and on the other with its developments in 

 the future. 



8 Opticks, 4th edition, p. 375. 



