[ 38 ] 



IV. On Action at a Distance. By S. Tolver Preston*. 



IN the last Number of the Philosophical Magazine is a paper 

 by Mr. Walter R. Browne, " On Action at a Distance "f, 

 in which some conclusions of mine relating to the explanation 

 of gravitation, or the general phenomena of approach, under 

 the kinetic theory of the aether, are noticed. 



Although some of the objections cited by Mr. Browne do 

 not appear to me to be of much weight, and some will, I think, 

 be found to be answered in my previous papers J, I will never- 

 theless comment upon a few points here. 



First, on page 440, a difficulty originally brought forward 

 by Dr. Croll§, in a notice of my papers, is alluded to, relating, 

 to the porosity of matter required by the kinetic theory of 

 gravity. It should be observed, however, that this difficulty 

 was considered by me (Philosophical Magazine, Feb. 1878), 

 and a means suggested for surmounting it||. 



Secondly, Mr. Browne concludes, apparently rather gra- 

 tuitously, on page 441 as follows, viz.: — " Hence our concep- 

 tion of the gravity-gas must practically be that of an indefinite 

 number of indefinitely small particles moving in all directions 

 with indefinitely high velocities — a conception from which it 

 hardly seems safe to draw any definite conclusion whatever." 



It is scarcely necessary to add that the number of particles 

 in unit of volume, their dimensions, and meanll velocity, are 

 not actually assumed by me to be indefinite (but strictly 

 finite). Any finite values, however great, are still an unli- 

 mited distance from indefinite values. 



Thirdly, on page 442, the fact is seemingly overlooked that, 

 according to the vortex-atom theory (alluded to in the context), 

 it appears that molecules would be elastic**; so that it would 

 not seem necessary to assume that the molecules of a solid bar 

 are normally at a distance from each other in order to explain 



* Communicated by the Author. 



t Read before the Physical Society, November 13, 1880. 



% Philosophical Magazine, Sept. and Nov. 1877, Feb. 1878. 



§ Ibid. Jan. 1878. 



|| It is obvious that if the molecules of matter themselves have an open 

 structure, then matter may possess any degTee of porosity (or permeability 

 to the particles of the gravific sether) that observed facts may require. 

 The open structure of molecules is only a priori natural, since a solid 

 (block) structure of molecules would involve useless waste of material. 



% The high velocity of the particles is the perfectly natural consequence 

 of their minute mass. 



** It is sufficiently clear that if u elasticity "were not yet explained, the 

 first step towards this end would have to be the rejection of "action at a 

 distance," since the retention of an occult quality would render any expla- 

 nation hopeless. 



