Corpuscules of Le Sage. 331 



the same after collision with molecules different from them in 

 form or in elastic rigidity as after collision with molecules only 

 of their own kind. All that is necessary to complete Le Sage's 

 theory of gravity in accordance with modern science, is to assume 

 that the ratio of the whole energy of the corpuscules to the trans- 

 lational part of their energy is greater, on the average, after 

 collisions with mundane matter than after intercollisions of only 

 ultramundane corpuscules. This supposition is neither more nor 

 less questionable than that of Clausius for gases, which is now 

 admitted as one of the generally recognized truths of science. 

 The corpuscular theory of gravity is no more difficult in allow- 

 ance of its fundamental assumptions than the kinetic theory of 

 gases as at present received; and it is more complete, inasmuch 

 as, from fundamental assumptions of an extremely simple cha- 

 racter, it explains all the known phenomena of its subject, which 

 cannot be said of the kinetic theory of gases so far as it has 

 hitherto advanced. 



Postscript, April 1872. 



In the preceding statement I inadvertently omitted to remark 

 that if the constituent atoms are seolotropic in respect of perme- 

 ability, crystals would generally have different permeabilities in 

 different directions, and would therefore have different weights 

 according to the direction of their axes relatively to the direction 

 of gravity. No such difference has been discovered ; and it is 

 certain that, if there is any, it is extremely small. Hence the 

 constituent atoms, if seolotropic as to permeability, must be so 

 but to an exceedingly small degree. Le Sage's second funda- 

 mental assumption, given above under the title " Constitution of 

 Heavy Bodies," implies sensibly equal permeability in all direc- 

 tions, even in an seolotropic structure, unless much greater than 

 Jupiter, provided that the atoms are isotropic as to permeability. 



A body having different permeabilities in different directions 

 would, if of manageable dimensions, give us a means for drawing 

 energy from the inexhaustible stores laid up in the ultramundane 

 corpuscules, thus :- — First, turn the body into a position of mini- 

 mum weight; secondly, lift it through any height; thirdly, 

 turn it into a position of maximum weight ; fourthly, let it down 

 to its primitive level. It is easily seen that the first and third 

 of those operations are performed without the expenditure of 

 work; and, on the whole, work is done by gravity in operations 

 2 and 4. In the corresponding set of operations performed upon 

 a movable body in the neighbourhood of a fixed magnet, as 

 much work is required for operations 1 and 3 as is gained in 

 operations 2 and 4 — the magnetization of the movable body 

 being either intrinsic or inductive, or partly intrinsic and partly 



