ON MATTER AND FORCE. 27 



excited and communicated in these experi- 

 ments, except motion." 



In 1799, Davy published a paper on heat 

 and light, in which he said : " 1 conclude that 

 heat or the power of repulsion is not matter." 

 " Again," he says, " heat, then, or that power 

 which prevents the actual contact of the cor- 

 puscles of bodies, and which is the cause of our 

 peculiar sensations of heat and cold, may be 

 defined as a peculiar motion, probably as a 

 vibration of the corpuscles of bodies tending to 

 separate them. It may, with propriety, be 

 called the repulsive motion." 



" I am obliged," says Mr. Grove, " in order 

 to be intelligible, to talk of heat as an entity, 

 and of its conduction, radiation, etc. ; yet these 

 expressions are, in fact, inconsistent with the 

 dynamic theory, which regards heat as motion, 

 and as nothing else. Thus conduction would 

 be simply a progressive dilatation or motion of 

 the particles of the, conducting substance." 

 " The phenomena depend upon the molecular 

 structure of the matter affected ; and, although 

 these facts are not absolutely inconsistent with 

 the theory which supposes them to be fluids or 

 entities, it will, I think, be found to be far 



