96 FROM NEBULA TO NEBULA 



attraction between them constantly tends to deflect them 

 from their rectilinear courses, and to offset it the birds 

 are obliged to resort to the use of their wings. At this 

 stage, imagine the earth-bird to be struck fairly in the 

 breast by a great comet with a violence, not only suf- 

 ficient to slay it instantly, but also to bring it to a dead 

 stop. 



Up to this point, I take it, we are all in accord ; but 

 here we begin to disagree. According to the Newtonian 

 view, the moon-bird may now fold its wings and cease its 

 resistance to the earth-bird's attraction (which, of course, 

 persists in spite of the creature's death), with the result 

 of causing the former to circulate around the latter in- 

 definitely; whereas I hold that in order to maintain its 

 aloofness the living bird will have to exert its wing- 

 power precisely as much as before. In a word, Newtonians 

 while ostensibly representing the circulating body as 

 traveling on the strength of its inertia, actually treat it as 

 self -motored, i. e., as persistent, while I frankly face the 

 truth and cite the Prime Resultant as the centrifugal 

 agent. 



As suggested before in. the introductory chapter, it 

 has been the habit of those who make a study of the 

 heavens, from time immemorial, to anticipate finding a 

 good deal of mystery and miracle intermingled with 

 prosaic fact. The supposition that nebulae rotate of 

 themselves is a modern example of this primitive instinct. 

 So is the crude belief in the spontaneity of celestial mo- 

 tions in general, and in the inherence in them of persis- 

 tency as an abstract quality. Perhaps, however, the most 

 typical instance of this superstitious streak in modern 

 astronomers is their conception of the significance of the 

 law of the conservation of moment of momentum. By ob- 

 servation and computation, the astronomers have dis- 

 covered the fact (for such it is, subject to a modification 

 to be explained later on) that the sum of the momenta, 

 axial and orbital together, of any given system remains 

 the same from year to year. (Upon this rock it was that 

 the Nebular Hypothesis met final shipwreck, but of this in 



