140 THE LE SAGE THEORY OF GRAVITATION. 



evident that the particles in question could vibrate in long closed paths 

 with the same effect as if they came in from outer space and returned 

 to it in straight lines, as the author originally supposed; and as to their 

 infinitesimal srnallness, our purely physical conceptions of space and 

 even of time are not only still, as is well known, relative, but have 

 received a curious extension since Le Sage wrote, so that our limit of 

 the physically infinitesimal has been pushed farther back by studies 

 into the nature of the molecule and the atom until we have before 

 us actual things of an order of magnitude incomparably below anything 

 known to the physicists of our author's time. 



On the whole, then, the tenor of modern thought goes in the direc- 

 tion in which we are led by this theory, if by that we understand it, 

 not in its first crude enunciations, but with the modifications which 

 can now be legitimately associated with it, and which tend to make it 

 both more suggestive and to maintain a continued interest in it — an 

 interest which seems to justify the present publication of a paper with 

 which so few are familiar at first hand. 



S. P. Langley. 



