THE WHIRLING FIRE MIST. 215 



its rate of rotation is accelerated. This is one of the neces- 

 sary laws of matter. A rotating sphere of tenuous matter 

 undergoes some flattening at the poles ; as the velocity of rota- 

 tion increases, the polar flattening increases; the equatorial 

 protuberance increases. The earth is equatorially protuberant 

 because it rotates. 



When a body rotates on its axis, the parts around the 

 equator experience a tendency to fly off, which is greater than 

 such tendency on other parts of the surface. A rapidly rotat- 

 ing grindstone throws off the water. An emery wheel rotating 

 too rapidly for its strength flies asunder, in consequence of 

 excess of the flying-off or centrifugal tendency. The centrif- 

 ugal tendency is stronger than the cohesion of the parts. If 

 the earth were to rotate seventeen times as rapidly as it does, 

 bodies at the equator would have no weight. In the rotating 

 nebula which we are considering, the centrifugal tendency of 

 the equatorial parts diminishes their weight, and the undimin- 

 ished weight of the polar parts presses the equatorial out 

 in a bulge. 



Meantime the nebula contracts and the rate of rotation 

 continues to be accelerated. What must result under this 

 tendency of things? Evidently the time will arrive when 

 parts on the equator will have acquired a tendency to fly off 

 just equal to the attraction by which they had been held in 

 their places. If contraction still continues, as it must in a 

 cooling mass, the peripheral parts, balanced between equal 

 centrifugal and centripetal forces, will not move either toward 

 the center or from the center. What should make them? 

 Those parts will remain where they are, and the parts within 

 will withdraw from the equatorial parts. That is, a ring will 

 be disengaged not thrown off. The ring will retain the rota- 

 tion which it had, and the residual mass will continue to cool 

 and accelerate its rotation within the ring. 



What will happen to the ring? Perhaps you have seen 

 the ring of white smoke resulting from the explosion of a soap 

 bubble inflated with phosphureted hydrogen ; what happened 

 to that? It floated as a ring till external disturbances caused 



