Feanexand, — On the Doctrine of Mind- Stuff. 213 



Our first step will show us how thoroughly interdependent all these con- 

 ceptions are. Matter can only be defined as that which possesses inertia — 

 as that which requires a force proportional to its amount (designated its 

 mass) to effect a given change in its motion (either a change in velocity, or a 

 change in direction, or both) in a given time. Force, again, can only be 

 defined as that which causes a change in the velocity or direction of the 

 motion of matter. It is tacitly assumed, though not often expressed, that 

 the only thing which can cause such a change in velocity or direction is the 

 co-existence of other matter. This amounts to saying that force is a rela- 

 tion of co-existence between different portions of matter. But every relation 

 of co-existence in the material or phenomenal world is a relation of mutual 

 position in space. Hence force is a relation of mutual position between 

 different portions of matter. Motion, in the kinetic, or dynamical, as 

 opposed to the merely kinematical sense, is a change in the position of 

 matter, and is completely determined when the mass of the moving body 

 and the kinematical conditions of the case are given. The notion of energy 

 does not require the introduction of any fundamentally new conception. 

 Hence the phenomenal world is accurately described if we speak of it as a 

 complex of motions, varying in infinite ways as regards mass on the one 

 hand, and velocity and the other kinematical aspects on the other, tendmg 

 severally to constancy in all these respects, but having a mutual action on one 

 another, determined by their relations of co-existence, and, therefore, under- 

 going perpetual transformations. Now mark the parallelism. The noumenal 

 world, we have seen, may be described as a complex of feeling-elements, or 

 Mind- Stuff units, having, jtist as motion has, extension in Time, varying in 

 infinite ways as regards volume, intensity, and quality or timbre, having a 

 mutual action on one another, determined by their mutual relations of 

 co-existence, and undergoing perpetual transformations. Is this parallelism 

 something more than a parallelism ? "Without attempting to justify it in this 

 paper, I would hazard the conjecture that motion is Mind- Stuff, that volume 

 of feeling is mass, and intensity of feeling velocity. Professor Clifford seems to 

 have believed that motion and Mind-Stuff were identical, and indeed to have 

 held the belief in a much more dogmatic form than I should be inclined to 

 do ; but the other two identifications are, as far as I am aware, quite new. 

 The degree of hght which cerebral physiology may be capable of throwing 

 on the question must be estimated by abler minds than my own : but one 

 implication of my hypothesis has struck me as favourable to it. If matter 

 in MOTION be Mind- Stuff, it follows that if matter were ever at absolute rest, 

 it would no longer correspond to any noumenal existence. It would become 

 a pure abstraction — one term of a product, the other term of which was 

 zero. Does not this appear in harmony with the hypothesis of Sir Wm. 



