Solar and J'/ainfm-// J£r<ih(t'ioii. ;")'.) 



of matter separates oif and is left suspended around the cou- 

 traeting nucleus. Otlier rings form in the same way, until 

 a series of them surrounds the central mass which has con- 

 tracted into a sphere. But these rings are not everywhere 

 of ecjual thickness, and the tendency of their constituent 

 ])articles to gravitate toward the thickest ])art causes tliem 

 to se})arate at the thinnest point, and finally to form oblate 

 spheroids of nebulous matter, which iiltimately condense 

 into sjjheres. 



Kip:. 4. The jilaiiet Saturn, i^howinp; rinjxs, and size as compared with the earth. 



Let US illustrate this by supposing that Ave have a grind- 

 stone, on which, while rotating, we pour a him of water. J f 

 we revolve it fast enough the water will fly off, but we ma\' 

 revolve it -just fast enough to cause the centrifugal and cen- 

 trip(>tal forces to balance. Then if we could make the stone 

 €onti-act in size, the layer of water would be left suspended 

 in the air as a ring surrounding the revolving grindstone. 

 In tlie case of the revolving nebula, the contraction of the 

 imier s])here of nebulous matter assists in the sei)aration of 



