THEORY OF MATTER. 43 



secondary qualities having disappeared, and all primary ones* 

 having been resolved into motion and tendency to motion, the 

 sciences which relate to phenomena appear to be resolved into 

 the general doctrine of motion. But if this be true the universe 

 can it is said present to us nothing but one great dynamical 

 problem. Motion, and force the cause of motion, belong essen- 

 tially to the domain of mechanics: and if chemical affinity be a 

 cause of local motion, that is, if in virtue of its action f a 

 particle of matter finds itself at a given time in a position dif- 

 ferent from that which it would else have occupied, chemical 

 affinity is not really distinct from mechanical force (which 

 looked at from the dynamical point of view includes everything 

 which is a cause of motion); whereas if it be not a cause of 

 motion the enquiry at once presents itself of what is it? In illus- 

 tration of this view we may refer to any chemical experiment. If 

 an acid is dropped into a glass containing any vegetable blue, the 

 colour is changed to red. But to say this is to say that the liquid 

 when the acid is introduced into it begins to act on the luminifer- 

 ous vibrations which exist near it in a different manner from that 

 in which it had previously acted. The whole change, whether we 

 call it a chemical phenomenon or not, consists in the introduction 

 of new forms of motion in virtue of the action of mechanical force. 



7. From considerations of this kind it appears to follow 

 that a complete explanation of all phenomena would introduce 

 no principles beyond those with which the science of mechanics 

 is conversant. And in truth if the conclusion drawn had been 

 that all phenomena might, if our knowledge of nature were 

 sufficiently extensive, be reduced to cinematical considerations 

 (using the word cinematics in the large sense in which it is 

 equivalent to the doctrine of motion), I do not see how on our 

 fundamental hypothesis we could refuse to assent to it. But the 

 conclusion drawn by the maintainers of the all-sufficiency of a 

 mechanical philosophy is something different from this and as 

 I conceive the error they appear to have committed is to be 

 sought for in this discrepancy. But before entering into the 

 discussion of this point, I will make a few remarks on certain 

 points in the history of what may be called the theory of matter. 



* That is, all that are commonly enumerated as primary qualities, 

 t As, for instance, in the phenomenon of crystallization. 



