on Dr. Faraday's Paper on Ray-vibrations. 535 



know. I am perfectly aware that the theory is merely 

 sketched by Dr. Faraday as the result of hasty thought, and 

 that it might be in some measure modified in its details on 

 further consideration by its author. But while the distinctive 

 features of the theory are retained, it will be, for the reasons 

 which I have given, inadmissible to me. The theory is how- 

 ever, in my opinion, a fair subject for the consideration of the 

 natural philosopher. 



2. With regard to the substitution of centres of force for 

 matter. 



This speculation, in its general character, differs little from 

 the celebrated inquiry regarding Substance and Accidents. 

 In the latter the question is, whether, when we have found a 

 lump of matter to possess certain form, colour, weight, and 

 other properties, we can satisfy ourselves by saying that this 

 lump of matter is a combination of such a form, such a colour, 

 such a weight, &c. ? And the answer has usually been that 

 the mind is not satisfied unless we describe the lump of 

 matter as something possessing the properties of such a form, 

 such a colour, such a weight, &c. In the speculation before 

 us, the question is, whether instead of matter which exerts 

 certain actions upon other matter, we may assume that there 

 is nothing but a number of centres of force producing these 

 actions? I think that most persons would say that the mind 

 is not satisfied with this assumption, and that it requires the 

 idea of a something as foundation for these centres of force. 

 But this question, in my opinion, is purely a metaphysical 

 question, entirely removed from the province of the natural 

 philosopher. 



To a great extent I am willing to admit that the supposi- 

 tion of centres of force is satisfactory. Mechanical attraction 

 or repulsion (including weight under the former term), colour, 

 radiation of every kind where the existence of something in- 

 termediate between the radiating body and the body receiving 

 the radiation is not apparently demonstrated ; all these may, 

 I think, be received without scruple as the results of mere 

 centres of force. But there is one property, to which by 

 chance Dr. Faraday has not alluded in his paper, that ap- 

 pears to me irreconcileable with the notion of centres of 

 force; I mean the property of inertia. And I believe that 

 the general notion of substance is really founded upon the per- 

 ception of inertia. Construct for any one a mass of matter 

 possessing invariable form, colour, and other attributes, even 

 attraction ; if he finds that this mass yields to muscular or 

 other force without perceptible resistance (it matters not whe- 

 ther it continually retain the same velocity or not), he will 



