Very — On a Possible Limit to Gravitation. 35 



action of waves in the medium which constitute the 

 external gravitational field of the electronic movements 

 which are matter. We admit that matter is first of all 

 a circulatory movement of the two sorts of electricity 

 (equivalent to an electric doublet) whose least com- 

 ponents are everywhere accompanied by indefinitely 

 extended and dynamically proportional vortices in the 

 magnetic medium. It would appear, however, that, 

 though no other than the magnetic medium can be con- 

 cerned in the action, and though the gravitational lines 

 of force are ultimately controlled by magnetic vortices, 

 the gravitational forces are not to be confounded with 

 magnetic forces. 



Rutherford maintains that the positive electricity in 

 an atom is a central mass of very minute size, placed 

 there like a sun (as in Larmor's atom) to guide the 

 orbital motions of the electrons. It has been supposed 

 that the positive nucleus of an atom must be very minute, 

 because collisions of alpha particles with them are infre- 

 quent ; but contact in this case does not mean hitting the 

 bull's-eye of a target. It means a sufficiently close juxta- 

 position of two interpenetrating fields of motion in the 

 magnetic universal atmosphere to produce reaction; 

 somewhat as the fields of force of light-rays everywhere 

 interpenetrate without interfering, except where there is 

 an exceptionally precise superposition of the extended 

 fields, with similar, or with opposing phases, reinforcing 

 the movement on the one hand, or destroying it on the 

 other. 



Now this assumption of central position is unnecessary ; 

 because Newton showed that the gravitational attraction 

 of a spherical shell of matter is precisely the same as if 

 all of the matter in the shell were concentrated at the 

 center. Nor do we know just what it is that constitutes 

 what we call an " attraction. ' ' A soap bubble is held 

 together as one piece by a circumferential pressure 

 everywhere centripetally directed. We explain this as 

 the result of surface tension in a liquid ; but if we were 

 ignorant of the existence of the surface tension, there 

 would be nothing to distinguish this from a case of cen- 

 tral " attraction. " Moreover, if all of the positive elec- 

 trification is concentrated in a single electric mass, it 

 would follow that the heaviest atoms must have the 

 smallest central nuclei (because intensity of electrifica- 



