40 Very — On a Possible Limit to Gravitation. 



turning the axial pose of a particular electron which, 

 although the direction of motion is not changed, is as if 

 the orbital velocity had been reversed. Except for these 

 instantaneous reversals in the generation of light- 

 quanta, the electronic revolutions never cease, for the 

 atom is a form of extraordinary or almost perpetual 

 endurance, and of relatively enormous energy. The 

 agreement of Bydberg's frequency constant N with the 

 value derived from an application of Kepler's laws to 

 the electronic orbits constitutes, as Millikan remarks, 

 "most extraordinary justification of the theory of non- 

 radiating electronic orbits," and verifies at least this 

 much of Bohr's theory. 



The External Gravitational Potential. 



It is now evident that every atom consists of two parts : 

 (1) the very circumscribed space in which the above 

 mentioned electronic movements are carried on; and (2) 

 the indefinitely extended field of gravitational potential, 

 or strain, in that universal medium which, following 

 Swedenborg, I shall call the magnetic aura, or simply the 

 aura. 



The first requisite for any proposed explanation of the 

 facts of gravitation, if it be admitted that a genuine 

 explanation will be of a mechanical nature, is some tenta- 

 tive scheme of a gravitational unit, which shall be capable 

 of generating a longitudinal wave of alternating expan- 

 sion and compression in the universal magnetic aura. In 

 seeking for such a possible working model, I shall further 

 assume that the aura is divided into complex vortices of 

 galactic dimensions, and that an individual complex vor- 

 tex constitutes a single independent aural "cell" within 

 which the gravitational motions of its combined masses 

 are confined. 



Since all of the motions of the aura are vorticose, this 

 may apply equally to the ultimate direction of propa- 

 gation of a gravitational wave in the medium. This 

 point may be open to discussion, but is here adopted ten- 

 tatively on the plea that the electron is probably a polar 

 vortical particle. 4 The wave, therefore, though at first 



4 In another paper ("The Luminiferous Ether," Occasional Scientific 

 Papers of the Westwood Astrophysical Observatory, No. 2, p. 36) I have 

 suggested that the electron itself probably has an internal vorticose motion 

 and polar structure -which adapt it to the required function even in its 

 pulsations. But the electronic complex, the atom, is always a perfect 

 sphere. 



