474 



the effective area* of the bodies are proportional to their masses, we shall make 

 tfce two laws coincide. Here, then, seems to be a path leading towards an 

 of tlie law of gravitation, which, if it can be shewn to be in 

 consistent with (acts, may turn out to be a royal road into the 

 aroana of science. 



La Sage himself shews that, in order to make the effective area of a body, 

 in virtue of which it acts as a screen to the streams of ultramundane cor- 

 puscules, un>|x>rtional to the mass of the body, whether the body be large or 

 nnH we must admit that the size of the solid atoms of the body is exceed- 

 ingly small compared with the distances between them, so that a very small 

 proportion of the corpuscules are stopped even by the densest and largest bodies. 

 W may picture to ourselves the streams of corpuscules coming in every direc- 

 tion, like light from a uniformly illuminated sky. We may imagine a material 

 body to consist of a congeries of atoms at considerable distances from each other, 

 and we may represent this by a swarm of insects flying in the air. To an 

 observer at a distance this swarm will be visible as a slight darkening of the 

 ky in a certain quarter. This darkening will represent the action of the 

 material body in stopping the flight of the corpuscules. Now, if the proportion 

 -I* light stopped by the swarm is very small, two such swarms will stop nearly 

 the same amount of light, whether they are in a line with the eye or not, but 

 if one of them stops an appreciable proportion of light, there will not be so 

 much left to be stopped by the other, and the effect of two swarms in a line 

 with the eye will be less than the sum of the two effects separately. 



Now, we know that the effect of the attraction of the sun and earth on 

 the moon is not appreciably different when the moon is eclipsed than on other 

 occasions when full moon occurs without an eclipse. This shews that the number 

 .f the corpuscules which are stopped by bodies of the size and mass of the 

 earth, and even the sun, is very small compared with the number which pass 

 straight through the earth or the sun without striking a single molecule. To 

 tlie streams of corpuscules the earth and the sun are mere systems of atoms 

 scattered in space, which present far more openings than obstacles to their recti- 

 linear flight. 



Such is the ingenious doctrine of Le Sage, by which he endeavours to 

 explain universal gravitation. Let us try to form some estimate of this con- 

 tinual bombardment of ultramundane corpuscules which is being kept up on all 

 sides of us. 



