146 Dr. S. Tolver Preston on some 



of material points, which, without anything intervening, act 

 on each other directly at a distance, according to a mathe- 

 matically exact formulated law. If the initial positions and 

 velocities of all the atoms are given, then their motions can be 

 calculated for any periods of time from the equations formulated 

 by Newton, and so a clearly defined mathematical problem 

 is presented. 



It is, however, well to observe that Newton did not believe 

 in such an action at a distance without the intervention of 

 something, as appears from his third letter to Bentley, where 

 he says : — 



" That gravity should be innate, inherent, and essential to 

 matter, so that one body may act upon another at a distance 

 through a vacuum, without the mediation of anything else, 

 by and through which their action and force may be conveyed 

 from one to another, is to me so great an absurdity, that I 

 believe no man who has in philosophical matters a competent 

 faculty of thinking, can ever fall into it" (Newton's third 

 letter "to Bentley, February 25, 1692-3). 



In the same sense speak many subsequent important 

 scientists. For instance Count Rumford remarks : — 



" Nobody surely in his sober senses has ever pretended 

 to understand the mechanism of gravitation, and yet what 

 sublime discoveries has our immortal Newton been enabled to 

 make, merely by the investigation of the laws of its action " 

 (" An Inquiry concerning the Source of the Heat which is 

 excited by Friction/' by Count Rumford, Phil. Trans. 1798). 



These last scientists are therefore not satisfied with the 

 Boscovich-Mosotti explanation of natural phenomena ; they 

 demand rather an explanation (by the intervention of a 

 medium) of the seeming action at a distance. To give such 

 an explanation was never seriously attempted by Newton : 

 the first attempt of that kind is to be found in the mechanical 

 gravitation theory of Le Sage, born at Geneva in 1724. This 

 theory is contained in a memoir published in the Transactions 

 of the Royal Berlin Academy for 1782, under the title 

 Lucrece Newtonien. There is also a book, Deux Traitds 

 de Physique mecanigue, edited by Pierre Prevost, Paris, 

 1818, which contains a full description of Le Sage's theory. 



Le Sage lays emphasis on the probability of the existence 

 of a mechanism of gravitation, and devoted his life to the 

 development of his idea. The introductory paragraph of his 

 memoir (entitled Lucrece Newtonien) is as follows, translated 

 from the French original, viz. : — 



" I propose to show that if the first Epicureans had had as 

 healthy ideas of Cosmography as several of their contem- 



