LIFE IN THE PAST 153 



the one inside it and separated from the next by an 

 area nearly as wide as the ring itself. 



With such material in the heavens to guide him, La 

 Place suggested that the sun had once been an enor- 

 mous fire mist scattered over an area billions of miles 

 in diameter. This gaseous material, by the attraction 

 of its particles for each other, began to condense and 

 contract. When the plug is pulled from a washbasin 

 the particles of water, in moving toward the center, 

 in order to get out of the basin, invariably set up a 

 rotary motion. As the particles of this diffused 

 nebula began to gather together they, too, gave to the 

 mass a rotary movement. This grew more and more 

 rapid, with greater contraction, until the particles on 

 the outer edge of the rotating mass had just so much 

 speed that the least bit more would make them tend 

 to fly off as mud would fly from a revolving wheel. 

 When this point was reached there was a balance of 

 forces which made the outermost portion remain as 

 a ring while the rest contracted away from it, leaving 

 it behind. 



It was La Place's idea that this process had re- 

 peated itself, and ring after ring had been left behind. 

 Finally the sun condensed and grew into a ball, oc- 

 cupying the center of the system. At varying dis- 

 tances from it were to be found either rings or planets 

 which had been formed out of such rings. For La 



