584 Proceedings of the Royal Society 
of his assumptions. The only imperfection of his theory is tha 
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 admitted 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 communi- 
cated for publication to the editor of those works by Le Sage. 
Eedeker, 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, “ Oil l’on trouve l’expose d’un systeme fort semblable a celui 
“ de Le Sage dans ses traits principaux, 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 pre- 
vious velocities, and therefore not to have explained gravity at all. 
Eedeker, we are told by Prevost, had very limited ideas of the per- 
meabilities of great bodies, and therefore failed to explain the law 
of the proportionality of gravity to mass ; u he enunciated this law 
“ very correctly in section 15 of his dissertation ; but the manner 
“ in which he explains it shows that he had but little reflected upon 
11 it. Notwithstanding these imperfections, one cannot but recog- 
“ nise in this work an ingenious conception which ought to have 
“ provoked examination on the part of naturalists, of whom many 
u at that time occupied themselves with the same investigation. 
“ Indeed, there exists a dissertation by Segner on this subject.* 
“ But science took another course, and works of this nature gradu- 
u ally lost appreciation. Le Sage has never failed on any occasion 
il to call attention to the system of Eedeker, as also to that of Fatio.” f 
* De Causa gravitatis Redekeriana. 
f Le Sage was remarkably scrupulous in giving full information regarding 
11 who preceded him in the development of any part of his theory. 
