4 On PoTce. 



causes are all we are concerned with, and whether the earth 

 really exerts a pnll on the stone or not is a question which 

 neither common sense nor science can solve, nor, in my 

 opinion, need desire to solve ; let the metaphysician under- 

 take the impossible and unprofitable task if he will. 



The answers I have given to the above questions concern- 

 ing Force would probably be accepted by all disciples of the 

 modern Experience school of philosophy, but many able 

 investigators of nature and powerful reasoners have not 

 been content with the bounds which it sets to the kingdom 

 of knowledge. Thus Sir John Herschel has said — and his 

 dictum is quoted with approval in a very clever and 

 eloquent article by the late Mr. Martineau (Contemporary 

 Review, March, 1876), which has important bearings on the 

 question at issue : — 



"It is our own immediate consciousness of effort when 

 we exert force to put matter in motion, or to oppose and 

 neutralise force, which gives us this internal conviction of 

 poiuer and causation so far as it refers to the material world, 

 and compels us to believe that whenever we see material 

 objects put in motion from a state of rest, or deflected from 

 their rectilinear paths, and changed in their velocities if 

 already in motion, it is a consequence of such an effort 

 soonehoiu exerted, though not accompanied with our con- 

 sciousness." 



Mr. Martineau also quotes Du Bois-Reymond, a philosopher 

 of a very different way of thinking, who says : — 



" Power, regarded as the cause of motion, is nothing but 

 a more recondite product of the irresistible tendency to 

 personify which is impressed upon us. What do we gain 

 by saying that it is reciprocal Attraction whereby two par- 

 ticles of matter approach each other ? Not the shadow of 

 any insight into the nature of the process." 



And Mr. Martineau is forced to admit that Du Bois-Rey- 

 mond is justified in his criticism if the human mind has 

 nothing to do but to become an accomplished Natur 

 forscher ; which is, I presume, the only aim of the human 

 mind which Physical Science is concerned with. 



The question under discussion may be not unprofitably 

 illustrated by an analogy from the undulatory theory of 

 light. As that theory is commonly taught in the text- 

 books, it supposes that at each point of space through 

 which light is being propagated there goes on a backward 



