PLANETARY EVOLUTION 



like long luminous streaks. And while all these 

 would ultimately be compelled bv gravitation 

 to revolve about the centre of the mass, never- 

 theless the lightest and outermost shreds would 

 be a long time in acquiring a definite direction 

 of revolution. While the greater number would 

 be doubtless drawn in and absorbed by the 

 main mass at an early stage, the chances are 

 that some would not arrive until the main mass 

 had become considerably contracted. Now it is 

 easy to see that such late arriving flocculi, com- 

 ing toward the centre of gravity from a great 

 distance, and therefore having small angular 

 velocities, will move in very eccentric ellipses. 

 In the next place, while they will come from 

 all parts of the space which the mass originally 

 occupied, they will come chiefly from regions 

 remote from the plane in which integration has 

 been most marked, — that is, from the poles 

 of the nebula rather than from its equatorial 

 regions. And thirdly, having failed to accom- 

 pany the retreating mass of the nebula while it 

 was first acquiring a definite direction of rota- 

 tion, their own revolutions will be determined 

 chiefly by their irregular shapes, and they will 

 be as likely to be retrograde as direct. 



All this is true of comets : they come chiefly 

 from high solar latitudes, along immensely ec- 

 centric orbits, and in directions which are indif- 

 ferently direct or retrograde. And when we add 

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