PLANETARY EVOLUTION 



simply an elaborate corollary from the theory 

 of nebular genesis, is fully confirmed by ob- 

 servation in the cases of Saturn, Jupiter, Mars, 

 and the Moon, — the only planets whose sur- 

 faces have been studied with any considerable 

 success. According to the nebular hypothesis, 

 Jupiter and Saturn ought to be prodigiously 

 hot ; and so they appear to be when carefully 

 examined. The tremendous atmospheric dis- 

 turbances observed upon both these planets are 

 such as cannot well be explained by the com- 

 paratively sluggish action of the sun's radiance 

 upon such distant orbs. The atmosphere of 

 Jupiter is laden with masses of cloud, whether 

 composed solely of water or not, whose cubic 

 contents far exceed those of all the oceans on 

 the earth. The trade-winds, due to the swift 

 rotation of the planet, gather these enormous 

 masses into belts parallel with its equator. 

 Storms and typhoons are incessantly raging in 

 this vapour-laden atmosphere ; and the forces 

 at work there are so stupendous that dense 

 cloud-belts, thousands of miles in width, are 

 often formed in a single hour. This state of 

 things is not like that which is now witnessed 

 upon the earth's surface ; it is more like the 

 state of things observed upon the sun, where 

 tornadoes continually occur, in which the earth, 

 if it were there, would be whirled along like a 

 leaf in an equinoctial gale. A similar state of 

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