So/cr (1)1(1 I'hi iicfii CI/ Kraliiti 



59 



of matter separates off ;iii(l is left sxispended around the con- 

 tracting nucleus. Other rings form in the same way, until 

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

 tracted into a si)here. ]>ut these rings arc not everywhere 

 of equal thickness, and the tendency of their constituent 

 particles to gr;ivit:ite toward the thickest ]);irt causes them 

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

 s})heroids of nebulous matter, which idtimately condense 

 into spheres. 



T"ip:. 4. The jilanet Saturn, showintr rinj^s, and size as compared with the earth. 



Let us illustrate this by supposing that we have a grind- 

 stone, on which, whih; rotating, we pour a film of water. If 

 we revolve it fast enough the water will fly off, but we may 

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

 tripetal forces to balance. Then if we could make the stone 

 <*.onf ract in size, the layer of water would ])e left suspended 

 in the air as a ring surrounding the revolving gi'indstone. 

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

 inner spliere of nebulous matter assists in the separation of 



