12 FEOM NEBULA TO NEBULA 



centers of attraction already developed, while the fine dust alone 

 is diffused and carried away under repulsive forces to form 

 other nebluse which will sometime condense into cosmical sys- 

 tems. 



The assumption that rectilinear motions are inher- 

 ent is made to do duty to explain the flight of the sun, 

 and, indeed, of the so-called "proper motions" of stars 

 in general. How with every star, by hypothesis, moving 

 at random there can exist so concerted a phenomenon as 

 "star streams" has, so far as I am aware, remained not 

 only unexplained, but even gone unremarked as food for 

 reflection. As for the cause of the sun's flight, this is 

 so far beyond the powers of Newtonian theory to cope 

 with that the idea has seemingly never suggested itself; 

 and the sun's velocity and the apparent direction of his 

 course bare facts in themselves devoid of philosophi- 

 cal interest are all that Newtonianism can show for 

 generations of laborious effort in this direction. Attend 

 to this cheerless statement, if you please, from Doctor 

 William Wallace Campbell's recent work (Stellar 

 Motions, p. 194) : 



These are frequent and legitimate questions: Is the solar 

 system moving in a simple orbit, such as a conic section? Will 

 it eventually complete a circuit in this orbit and return to the 

 part of its orbit where it is now? The idea of affirmative answers 

 to these questions appears to be prevalent in the human mind. 

 It is natural to think that we must be moving on a great curve 

 perhaps closed like an ellipse, or open like a parabola the centre 

 of mass of the universe being in the curve's principal focus. The 

 attraction which any individual star is exerting upon us is cer- 

 tainly slight, owing to its enormous distance, and the resultant at- 

 traction of all the stars may not be very much greater ; for since 

 we are believed to be somewhere near the centre of our stellar, 

 system, the attractions of the stars in the various directions should 

 nearly neutralize one another, in accordance with the principle 

 that a body situated within a concentrically homogeneous sphere 

 is effectively acted upon only by the gravitational matter nearer 

 the centre of the sphere than itself. Even though we may be 

 following a definite curve at the present time, there is, in my 

 opinion, little doubt that we shall be prevented from continuing 

 upon it indefinitely. In the course of our travels we should be 

 carried, sooner or later, relatively close to some individual star 

 whose attraction would be vastly more powerful than that of all 



