I9I0.] SEE— ORIGIN OF ZONE OF ASTEROIDS. 353 



which must occasionally be encountered by the asteroids as well as 

 by Jupiter. In the long run the secular effects of collisions with 

 comets and similar isolated bodies is exactly the same as the effects 

 of a medium of cosmical dust of nearly continuous character; so 

 that we need not dwell on the character of the medium. 



4. It is important to notice that as the small masses approach the 

 center most rapidly, they would tend in time to overtake the 

 larger planets nearer the sun. Thus the moon may have had 

 originally a greater mean distance than the earth, but by degrees it 

 was brought so near our planet that it passed under the earth's 

 control and became a satellite. A similar conclusion holds for all 

 the other satellites of the solar system. Besides crossing over the 

 orbits of the larger planets, owing to larger eccentricity, these 

 smaller bodies were originally at greater distances than their several 

 planets, and in approaching them by degrees were at length brought 

 within the range of the planetary attraction and captured, as ex- 

 plained in Volume II. of my " Researches on the Evolution of 

 Stellar Systems." 



5. In the Proceedings of this society, 1910, p. 213, we have 

 explained the process of capture by a direct and simple method of 

 reasoning, and in view of the considerations just adduced, one 

 cannot doubt that this represents essentially the process of nature. 

 The lesson taught by the great width of the zone of the asteroids 

 is so very significant that it may serve as a practical demonstration 

 of certain tendencies in the physical universe. The same conclusion 

 may be otherwise verified, from a new and independent point of 

 view, as follows. 



It is shown by the exact data calculated from Babinet's criterion 

 that the planets never could have been detached or thrown off from 

 the central mass of our system, but were formed at great distances 

 and have gradually neared the sun, as its mass increased and they 

 revolved in the nebular resisting medium and gathered up more and 

 more cosmical dust. 



6. Since, therefore, the solar nebula as a whole did not rotate 

 fast enough to detach the planets, or even exert a sensible centri- 

 fugal force, but they were originally independent nuclei formed in 



