58 



particle is, in time, bound to conic close to many others, and eventually to 

 collide with many. 



II' any one particle were Large enough to Btarl with, ii would therefore 



grow by collision with other particles, and the more it grew the more power of 

 growing it would have by reason of its increasing mass. It seems likely 

 then, that loose, Avidely extended nebulae of this sort musl eventually come 

 into a system of small bodies revolving about a large central mass. It can 

 be shown that a mass revolving in this way and suffering collision with other 

 masses must move in an orbit whose eccentricity is continually diminishing. 

 We should therefore expect to find, if our system has been formed in this 

 way, that the more massive planets have the least eccentric orbits and thai 

 the smaller ones have the greatest eccentricity. As a matter of fact all of 

 the large outer planets have low eccentricity and the smaller planets a 

 higher amount. The greatest eccentricity is found among the planetoids, 

 or asteroids, many of which are only a few miles in diameter. 



It has also been shoAvn that a close approach of two masses in the arms 

 of the spiral might not result in collision, but under conditions which might 

 easily arise, the smaller might be made to revolve in an elliptical orbit about 

 the larger, thus giving rise to a satellite, or system of satellites, and these 

 satellites might revolve in one direction as easily as another. We can 

 therefore account for the retrograde motion of the satellite of Neptune, 

 those of Uranus, for the fact that Jupiter has some going in one direction and 

 others in the reverse direction, for the widely scattered zone of the Asteroids 

 and even for the very rapid motion of the inner satellite of Mars. 



These, and many other features are not speculations as to what may have 

 happened. They have all been made the subject of rigorous mathematical 

 calculations, and with the supposed initial conditions are all entirely possible. 



As to whether these initial conditions that we have supposed, actually 

 existed or not — whether or not our earth and the other bodies revolving 

 about the sun ever developed from a spiral nebula, we can not be so sure. 

 Here it is a question of what is most probable. We are practically certain 

 that it did not come about as La Place supposed. There are too many 

 things mathematically impossible about that. By this theory, the develop- 

 ment into the present system was entirely possible, and certainly no more 

 probable evolution has been proposed. 



La Place did not and could not account for his nebula. On this plan we 

 can. I have said that the spirals far outnumber any other class in the sky. 



