Mr. S. T. Preston on Action at a Distance. 219 



lie assumes, explains gravity. Gravity as we know, is found 

 to vary as the square of the distance (and not in some other 

 ratio). This peculiar circumstance is supposed by Mr. 

 Browne to be explained by merely stating it to be a fact. 

 What would be thought of any one saying that the " law " of 

 light, which also varies in intensity as the square of the 

 distance, were explained, without considering the existence of 

 the aether, or the physical basis of light — without reflecting on 

 the fact that the area of the spherical wave over which the 

 energy is spread varies as the square of the distance (and not in 

 some other ratio). By a knowledge of the physical conditions 

 determining light, the fact that the intensity of light varies 

 as the square of the distance admits of being predicted before- 

 hand. So the " law " of gravity will admit of being pre- 

 dicted beforehand from the determining physical conditions, 

 as soon as these are known. This capability of prediction 

 beforehand, by a knowledge of the physical conditions, is one 

 test of the explanation of a physical fact. Yet some would 

 teach us to swallow the bare statement that gravity varies as 

 the square of the distance, as an explanation. The same may 

 be said of magnetism (which will never be explained until 

 the determining physical conditions are known) *. Surely 

 no argument is necessary to establish such points as these, 

 which (as matters of scientific principle) should really permit 

 no difference of opinion, were it not for the absence of the 

 " competent faculty of thinking," so strongly insisted on by 

 Newton, — or absence of due reflection. It is needless to lay 

 stress on the fact that an intellect which on the wliole may be 

 more competent than another, may yet be particularly incom- 

 petent in some given direction (and perhaps in this one). 

 For minds are so differently constituted. 



Finally, Mr. Browne appears to find difficulty in realizing 

 the fact that if we take ultimate atoms, and if we suppose the 

 atoms of a bar of iron to be elastic (as according to the 

 modern theory of matter, for example), and, finally, if these 

 atoms be of open structure (say something of a ring form), 

 then they can obviously bend when the bar is compressed; 

 so that it is not necessary to assume the constituent atoms of 

 the bar to be normally at a distance from each other, in order 

 to explain the contraction of the bar (within certain limits) 

 under an applied pressure. It is so far evident that me- 

 chanical considerations are independent of scale, and atoms of 



* It seems to have been overlooked by Mr. Browne, that no doubt is 

 now entertained by competent judges as to the essentially physical nature 

 of magnetism, as it appears that there are grounds for believing- that the 

 velocity of propagation of the magnetic influence has been approximately 

 determined. 



