218 KINETIC THEORIES OF GRAVITATION. 



his system of nature; and it is related in his biography that in the 

 enthusiasm of his supposed discovery of so august a secret, he cried out, 

 in the words of the Syracusian Sage, " eureka! eureka /" and though 

 late at night, ho immediately wrote to his father, under date of January 

 15, 1747, " Eupr t y.a! suprf/.a! Xever have I felt such satisfaction as at 

 this moment, in which 1 have just succeeded in explaining completely, 

 by the simple laws of rectilinear movement, the principle of universal 

 gravitation /" 



His first production (written in unsuccessful competition for a prize 

 of the Academy) was an Essal sur Vorigine des forces mortes, in 1749. 

 This memoir was principally occupied with his mechanical basis of grav- 

 itation. Lesage wrote much, and published little. A memoir by him 

 entitled Essai de Chimie Mecanique, which explained the phenomena of 

 elective affinities by currents of ultramundane corpuscles of unequal 

 size, was crowned by the Academy of Rouen in 1758. Another essay 

 by him entitled Loi qui comprend toutes les Attractions et Repulsions, was 

 published in the Journal des Savants, for April, 17G4. Eighteen years 

 later, he wrote a dissertation entitled Lucrece Neutonien, more fully 

 developing his system, and comprising a response to the objections 

 which had been urged against it. This treatise was published in the 

 MSmoires de VAcademie de Berlin, for 1782. He also left a Traite des 

 Corpuscles ultramondaines, alluded to with high praise by Prevost in his 

 account of Lesage's life and works, but which appears never to have 

 been published. 



For more than fifty years did Lesage, with unwavering faith, proclaim 

 his doctrine of what he called the " gravific fluid," and urge upon his 

 contemporaries its adoption ; but without success. The scheme has been 

 rejected by intelligent physicists and astronomers as valueless in deal- 

 ing with the complex facts of nature. 



Of the six requirements heretofore specified, it will be found to satisfy 

 but two, — the first and the third. So far from fulfilling for example 

 the second condition, (the ratio of mass,) on which Lesage himself most 

 confidently expatiated, it can apparently give no true account of the 

 behavior of a series of atoms placed in a line between two outer ones. 

 The author supposed that he had covered the ground by the assump- 

 tion that material atoms are so exceeding small in comparison with their 

 interspaces that but few of the flying " corpuscles" will encounter the 

 atoms. Professor Tait, of the University of Edinburgh, has remarked : 

 " It is necessary also to suppose that particles and masses of matter 

 have a cage-like form, so that enormously more corpuscles pass through 

 them than impinge upon them ; else the gravitation action between two 

 bodies would not be as the product of their masses."* While this sup- 

 position fails notably to give a satisfactory mathematical representation 

 of the observed facts, (on any assignable ratio of impact to percolation,) 

 it is of course quite inadmissible with respect to atoms themselves. Iu- 



" Lectures ou Recent Advances iu Physical Science, Loudon, 1876, Lect. xii. p. 300. 



