44 Very — On a Possible Limit to Gravitation. 



tional fields, each of which extends, if not to the ultimate 

 limits of the aura, still at least within a sphere of aura 

 appertaining to a particular galaxy, which draws the 

 particles together. There is no way of telling whether 

 the gravitational force of a particular galaxy extends to 

 infinity, or only to the boundary of its own sphere of 

 interacting aura, except that which may be inferred from 

 the geometrical structure; but the latter hypothesis, 

 namely, that the sphere of interaction is limited, seems 

 to me the more reasonable one, and we may even suppose 

 that, while there is universal attraction within each 

 aural sphere, the separate spheres mutually repel each 

 other, just as similarly electrified bodies do. In this case 

 the galaxies will be somewhat equably spaced without 

 danger of clashing. The galactic planes, however, lie in 

 every direction without any special preference, or they 

 are apparently wholly independent. 



A Crucial Test. 



Dr. See assumes that the motion within a spiral nebula 

 is along casual somewhat spiral paths towards the center 

 under the attraction of universal gravitation. A. Van 

 Maanen, on the contrary, finds in his research described 

 in the Astrophysical Journal for November, 1916, 9 "Pre- 

 liminary Evidence of Internal Motion in the Spiral 

 Nebula Messier 101," that the motion is outward. 10 He 

 also finds evidence of rotation; but whereas, under the 

 gravitational attraction of a massive central nucleus, 

 orbital motions at radial distances of 2-'2 and 8'9 should 

 be in the ratio of the inverse squares of the distances, or 

 as 16 to 1, Van Maanen obtains : 



At mean distance 2-'2, rotational component = 0"024, 

 At mean distance 8'9, rotational component = 0"019, 



or very nearly the same curved-line speed at both points, 

 and along the paths of the spirals; that is to say, the 

 nebula rotates not as if it were in one piece, but as if 

 there were also uniform stream-motion along the radius 

 away from the center; whence I infer that the motion 

 which we see is not that of matter under gravitational 



9 Vol. 44, pp. 210-228. 



10 For other facts which indicate that development of stellar systems is 

 expansive, rather than concentrative, reference may be made to the author's 

 paper: A Cosmic Cycle, this Journal, vol. 13, pp. 47-58, 97-114, 185-196. 



