Corpuscules o/Le Sage. 327 



and giving them suitably small masses, they may produce the 

 actual forces of gravitation, and not more than the amount of 

 resistance which observation allows us to suppose that the planets 

 experience. It will be a very interesting subject to examine 

 minutely Le Sage's details on these points, and to judge whether 

 or not the additional knowledge gained by observation since his 

 time requires any modification to be made in the estimate which 

 he has given of the possible degrees of permeability of the sun 

 and planets, of the possible proportions of diameters of corpuscules 

 to interstices between them in the " gravific fluid," and of the 

 possible velocities of its component corpuscules. This much is 

 certain, that if hard indivisible atoms are granted at all, his 

 principles are unassailable, and nothing can be said against the 

 probability of his assumptions. The only imperfection of his 

 theory is that which is inherent to every supposition of hard, 

 indivisible atoms. They must be perfectly elastic or imperfectly 

 elastic, or perfectly inelastic. Even Newton seems to have ad- 

 mitted as a probable reality hard, indivisible, unalterable atoms, 

 each perfectly inelastic. 



Nicolas Fatio is quoted by Le Sage and Prevost as a friend 

 of Newton, who in 1689 or 1690 had invented a theory of gravity 

 perfectly similar to that of Le Sage, except certain essential 

 points, had described it in a Latin poem not yet printed, and 

 had written, on the 30th March, 1694, a letter regarding it, 

 which is to be found in the third volume of the works of Leibnitz, 

 having been communicated for publication to the editor of those 

 works by Le Sage. Redeker, a German physician, is quoted by 

 Le Sage as having expounded a theory of gravity of the same 

 general character, in a Latin dissertation published in 1736, 

 referring to which Prevost says, a Ou Ton trouve F expose d'un 

 systeme fort semblable a celui de Le Sage dans ses traits prin- 

 cipaux, mais depourvu de cette analyse exacte des phenomenes 

 qui fait le principal merite de toute espece de theorie." Fatio 

 supposed the corpuscules to be elastic, and seems to have shown 

 no reason why their return velocities after collision with mundane 

 matter should be less than their previous velocities, and therefore 

 not to have explained gravity at all. Redeker, we are told by 

 Prevost, had very limited ideas of the permeabilities of great 

 bodies, and therefore failed to explain the law of the propor- 

 tionality of gravity to mass : " he enunciated this law very cor- 

 rectly in section 15 of his dissertation; but the manner in which 

 he explains it shows that he had but little reflected upon it. 

 Notwithstanding these imperfections, one cannot but recognize 

 in this work an ingenious conception which ought to have pro- 

 voked examination on the part of naturalists, of whom many at 

 that time occupied themselves with the same investigation. 



