154 THE POPULAR SCIENCE MONTHLY. 



final analysis of them discloses, to have no likeness to the realities. 

 But the proposition that objective existence cannot be rendered in 

 terms of subjective existence, the reviewer thinks adequately expressed 

 by saying that " our fundamental conceptions" (subjective products) 

 " are inconceivable " (cannot be framed by subjective proce-sses) ! 

 Giving this as a sample from which may be judged his fitness for dis- 

 cussing these ultimate questions, I pass over his physico-metaphysical 

 criticisms, and proceed at once to those which his special discipline 

 may be assumed to render more worthy of attention. 



Quoting a passage relative to the law that " all central forces vary 

 inversely as the squares of the distances," he derides the assertion 

 that " this law is not simply an empirical one, but one deducible 

 mathematically from the relations of space — one of which the nega- 

 tion is inconceivable." Now, whether this statement can or cannot be 

 fully justified, it has at any rate none of that absurdity alleged by the 

 reviewer. When he puts the question : " Whence does he [do I] get 

 this ? " he invites the suspicion that his mind is not characterized by 

 much excursiveness. It seems never to have occurred to him that, if 

 rays like those of light radiate in straight lines from a centre, the 

 number of them falling on any given area of a sphere described from 

 that centre will diminish as the square of the distance increases, be- 

 cause the surfaces of spheres vary as the squares of their radii. For, 

 if this has occurred to him, why does he ask whence I get the infer- 

 ence ? The inference is so simple a one as naturally to be recognized 

 by those whose thoughts go a little beyond their lessons in geometry.^ 

 If the reviewer means to ask whence I get the implied assumption 

 that central forces act only in straight lines, I reply that this assump- 

 tion has a warrant akin to that of [NTewton's first axiom, that a moving 

 body will continue moving in a straight line, unless interfered with. 

 For that the force exerted by one centre on another should act in a 

 curved line, implies the conception of some second force, complicating 

 the direct eflect of the first. And, even could a central force be truly 

 conceived as acting in lines not straight, the average distribution of 

 its effects upon the inner surface of the surrounding sphere would 

 still follow the same law. Thus, whether or not the law be accepted 

 on a priori grounds, the assumed absurdity of representing it to have 

 a priori grounds is not very obvious. Respecting this statement of 

 mine, the reviewer goes on to say : 



"This is a wisdom far higher than that possessed by the discoverer of the 

 great law of attraction, who was led to consider it from no cogitations on the 

 relations of space, but from observations of the movements of the planets ; and 



* That I am certainly not singular in this view is shown to me, even while I write, by 

 the just-issued work of Prof. Jevons on the " Principles of Science : a Treatise on Logic 

 and Scientific Method." In vol. ii., p. 141, Prof. Jevons remarks respecting the law of 

 variation of the attractive force, that it " is doubtless connected at this point with the 

 primary properties of space itself, and is so far conformable to our necessary ideas." 



