PROGRESS OF MODERN ASTRONOMY 



the formation of a body at this centre of attraction, 

 which, so to speak, grows from an infinitely small nu- 

 cleus by rapid strides ; and in the proportion in which 

 this mass increases, it also draws with greater force 

 the surrounding particles to unite with it. When the 

 mass of this central body has grown so great that the 

 velocity with which it draws the particles to itself with 

 great distances is bent sideways by the feeble degree 

 of repulsion with which they impede one another, and 

 when it issues in lateral movements which are capable 

 by means of the centrifugal force of encompassing the 

 central body in an orbit, then there are produced 

 whirls or vortices of particles, each of which by itself 

 describes a curved line by the composition of the at- 

 tracting force and the force of revolution that had been 

 bent sideways. These kinds of orbits all intersect 

 one another, for which their great dispersion in this 

 space gives place. Yet these movements are in many 

 ways in conflict with one another, and they naturally 

 tend to bring one another to a uniformity that is, 

 into a state in which one movement is as little ob- 

 structive to the other as possible. This happens in 

 two ways : first by the particles limiting one another's 

 movement till they all advance in one direction; and, 

 secondly, in this way, that the particles limit their 

 vertical movements in virtue of which they are ap- 

 proaching the centre of attraction, till they all move 

 horizontally i. e., in parallel circles round the sun as 

 , no longer intercept one another, and by 

 the centrifugal force becoming equal with the falling 

 force they keep themselves constantly in free circular 

 orbits at the distance at which they move. The result, 



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