' AND ITS INHABITANTS 21 



mean plane of the planets' orbits. To explain this, Chamber- 

 lin supposes that the sun had originally a rotation in a plane 

 not greatly different from that in which the passing star ap- 

 proached, but rotated in the opposite direction. The whirl 

 given to the solar mass by the tidal disruption is assumed to 

 have been a little greater than its initial rotation, but, being 

 in the opposite direction, the resultant was at a slow speed 

 and yet nearly in the plane of the planetary orbits. 3 Campbell 

 points out that the chances are highly against such a special 

 arrangement. If in a number of solar systems such an arrange- 

 ment prevailed, it would constitute a conclusive proof against 

 the hypothesis, but in the one example the exceptional com- 

 bination may have occurred and it cannot be urged as a 

 disproof. 4 



Turning to another aspect of the hypothesis, the innumer- 

 able spiral nebulae of the heavens, although good illustrations 

 of the initial hypothetical form of the solar planetary system, 

 do not appear to be stages in a similar evolution in the way 

 that Chamberlin and Moulton have conceived them to be. 

 They are, as previously stated, of a much vaster order of 

 magnitude, they avoid the region where the stars are clustered, 

 are at remote stellar distances, and by their very number show 

 a notable duration of their form. On the other hand, the 

 postulated originally spiral form of the solar nebula would 

 have been evanescent. Within a century from the time of 

 origin all except the outer nuclei would have completed many 

 revolutions about the sun. But the different periodic times of 

 the nuclei would in a few revolutions have caused the initial 

 spiral form to disappear. It would become wound up and 

 further blended together owing to the high ellipticities of the 

 constituent orbits. 



3 Chamberlin, T. C, The origin of the earth, 1916, pp. 130-132. 



4 Campbell, W. W., The evolution of the stars and the formation of the 

 earth. Scientific Monthly, vol. 1, 1915, p. 241. 



