1910.] RESEARCHES IN COSMICAL EVOLUTION. 215 



physical history. All the details of the lunar terrestrial system are 

 known to accord with the theory that the moon is a captured planet, 

 (a) It is shown by rigorous calcxdation from the theory of prob- 

 ability that the chances are infinity to one that the moon was cap- 

 tured like the other satellites, (b) It is likezvise shown that the 

 probability is infinity to one that the earth could not have rotated 

 zvith sufficient rapidity to detach the moon. As the theoretical 

 possibility of the capture of the moon is beyond doubt, it is there- 

 fore certain that it actually occurred. 



With this brief outline of the process of capture, we shall now 

 sum up the conclusions at which we have arrived. 



1. The planets never were detached from the sun by acceleration 

 of rotation, as held by Laplace, but had their origin in the outskirts 

 of the solar nebula, and have since neared the sun and had their 

 orbits reduced in size and rounded up into almost perfect circles by 

 moving for long ages against the resisting medium of nebulosity 

 formerly pervading our system. 



2. The view that the planets were formed at a great distance 

 from the sun was advanced by the great Swiss mathematician Euler 

 in 1749, before the theories of Kant (1755) and Laplace (1796) 

 were promulgated ; and he, too, based his conclusion on the secular 

 effects of a resisting medium. Euler considered only the effect on 

 the mean distance, but in 1805 Laplace showed by a more general 

 investigation that the eccentricity also would be diminished ; and it 

 is this latter effect in producing the observed roundness of the orbits 

 that gives us the principal clue to the true mode of formation of 

 the solar system. 



3. It therefore follows that the planets were developed in the 

 solar nebula, but are in no sense of the word children of the sun ; 

 for they never were connected with the sun by any form of hydro- 

 static pressure and afterwards thrown off by acceleration of rota- 

 tion, as has been generally believed. 



(4) The satellites likewise never were mechanically connected 

 with their several planets through any form of pressure and fluid 

 equilibrium, but were originally independent planets, moving in regu- 

 lar elliptical orbits, and were afterwards captured and attached to 



