258 THE POPULAR SCIENCE MONTHLY 



ences an impetus on all sides; but if we take two bodies each screens 

 the other and they are pushed together. Notice the force is one of 

 pressure and not of tension. At first sight the impulse due to the 

 impact would seem to be proportional to the effective area whereas 

 according to Newton's law it ought to be proportional to the mass; but 

 when we compare the diameter of a molecule with the distance between 

 molecules, we see that only a small portion of the particles are arrested 

 and that the number arrested is proportional to the number of mole- 

 cules in the body (the mass). 



The objections to Le Sage's theory are almost too numerous to 

 mention. First and foremost, the enormous speed at which these cor- 

 puscles must travel not to resist planetary motion involves an enormous 

 supply of energy from a source outside our universe. On this theory 

 the source of gravitation is ultramundane. Again if these corpuscles 

 are elastic there would be no screening action on the part of a body as 

 the corpuscles would carry away their energy in reflexion. If the cor- 

 puscles are inelastic, bodies ought to increase in size. As the corpuscles 

 transfer their momentum to bodies they lose kinetic energy, and accord- 

 ing to Maxwell the loss sufficient to account for gravitation if converted 

 into heat would keep the body white hot. Sir J. J. Thomson has shown 

 that it is not necessary to suppose the energy is transformed into heat. 

 In place of heat rays he suggests that the particles might give rise to a 

 very penetrating radiation just as the cathode particles are supposed to 

 give rise to the short ether-pulse known as Eontgen rays. 



The fact that a physicist of Kelvin's rank has tried to patch up a 

 theory that is so superficial shows how hard put to we are when we 

 attempt to explain gravitational attraction. 



About thirty years ago Zollner explained gravitation on the assump- 

 tion that the molecules carry positive and negative charges and the 

 attraction between two unlike charges exceeds the repulsion between 

 like charges. Lorentz, assuming a neutral body to be an assemblage of 

 positive and negative electrons, has used the same hypothesis. 



At Cambridge University during the fall term of 1908, Sir J. J. 

 Thomson gave a course of lectures on " Ether and Matter " and in that 

 course he devoted about three lectures to gravitation. Take two charged 

 plates and in place of drawing the resultant Faraday lines of force (a 

 Faraday line is a line beginning on a unit positive charge and termi- 

 nating on a unit negative charge) consider the components (see Fig. 1). 



Fia. 1. 



