206 SPECULATIVE SCIENCE 



the explanation of heat ; and although it cannot be said that 

 we yet know with any certainty what motions are required for 

 the explanation of these phenomena, we do begin to know some 

 of the relations which must exist between the several motions ; 

 nor need we despair even of explaining light and gravitation 

 with the same machinery. Having traced the theory of a con- 

 tinuous fluid to its development in the hands of Thomson, we 

 find that this school too has arrived at indestructible elastic 

 atoms as the secondary constituents of gross matter, though 

 they reject the crude atoms of Lucretius as a primary material. 



Bacon was very cautious about atomic theories, but on the 

 whole believed in atoms. He devised the idea of groups or 

 knots of atoms, saying, in reference to the argument of Demo- 

 critus, that if only one kind of atom existed, all things could 

 be made out of all things ; there is no doubt but that the 

 seeds of things though equal, as soon as they have thrown 

 themselves into certain groups or knots, completely assume the 

 nature of dissimilar bodies till those groups or knots are dis- 

 solved.' 



Newton, while approving of some form of the atomic theory, 

 was very guarded in expressing his opinions ; but his discovery 

 of the laws of gravitation exercised great influence on most 

 subsequent hypotheses as to the constitution of matter. The 

 conception of atoms having the property of exerting various 

 forces across a void space, followed as a matter of course from 

 the idea of universal gravitation. A school arose which taught 

 that atoms might have the property of exerting force at a dis- 

 tance, and that this property might be inherent in the atoms, 

 just as Lucretius taught that hardness and elasticity were ori- 

 ginal indefeasible properties of the seeds of things. Force came 

 to be considered as having a real existence apart from matter ; 

 but this idea, though very popular now, was not established 

 without a hard struggle, and may yet have to be abandoned. 



This view is in direct contradiction with the old axiom that 

 matter could not act where it was not, or, as Hobbes put it, 

 1 there can be no cause of motion except a body contiguous and 

 moved 'no unnatural idea, but, on the contrary, universally or 

 almost universally believed till Newton's time. We do not 

 think that the fact of gravitation justifies the assumption that 



