358 SEE— ORIGIN OF ZONE OF ASTEROIDS. [November 4, 



12. Any one who calculates the moment of momentum of orbital 

 motion of a satellite such as the moon, which is 4.8 times larger 

 than the present total moment of momentum of the earth's axial 

 rotation, will perceive how powerfully the rotation of a planet may 

 be accelerated by the impact of satellites against its surface. To 

 be sure, the case of the moon is by far the most extreme in the solar 

 system, owing to its large mass, but the tendency is the same every- 

 where, and really rapid rotations can be acquired only by the gather- 

 ing in of quantities of satelHtes in the sun's field of force by large 

 planets, as in the observed cases of Jupiter and Saturn. 



The planets were formed at great distances from the sun, where 

 the field of attraction would be much feebler than in their present 

 situations ; and hence nebulous matter collecting to such secondary 

 centers in the outer parts of our nebula would give but feeble rota- 

 tions of these masses about their axes ; so that at no time in the 

 past history of the solar system could a planet have rotated with 

 sufificient rapidity to develop an appreciable tendency to detach a 

 satellite. Such an hypothesis is wholly untenable, because it is 

 found by calculation that the rapid rotations develop only when the 

 planets are comparatively near the sun, and the relative moment of 

 momentum of impinging particles therefore large. 



Accordingly the simple considerations here adduced confirm from 

 another independent point of view the results already obtained in 

 second volume of my " Researches " ; namely, that the moon and 

 other satellites are merely captured planets, originally describing in- 

 dependent orbits about the sun; and show that the Capture Theory 

 unquestionably is an ultimate law of nature. 



U. S. Naval Observatory, 



Mare Island, California, 

 October 17, 1910. 



