SECT, ix.] EOTATION OF THE PLANETS. 75 



to the perfection of the whole, a coincidence so remarkable 

 cannot be accidental. And, as the revolutions of the planets 

 and satellites are also from west to east, it is evident that both 

 must have arisen from the primitive cause which determined 

 the planetary motions. Indeed, La Place has computed the 

 probability to be as four millions to one that all the motions 

 of the planets, both of rotation and revolution, were at once 

 imparted by an original common cause, but of which we 

 know neither the nature nor the epoch. 



The larger planets rotate in shorter periods than the 

 smaller planets and the earth. Their compression is conse- 

 quently greater, and the action of the sun and of their sa- 

 tellites occasions a nutation in their axes and a precession of 

 their equinoxes (N. 144) similar to that which obtains in the 

 terrestrial spheroid, from the attraction of the sun and moon 

 on the prominent matter at the equator. Jupiter revolves in 

 less than ten hours about an axis at right angles to certain 

 dark belts or bands, which always cross his equator. This 

 rapid rotation occasions a very great compression in his 

 form. His equatorial axis exceeds his polar axis by 6000 

 miles, whereas the difference in the axes of the earth is only 

 about twenty-six and a half. It is an evident consequence 

 of Kepler's law of the squares of the periodic times of the 

 planets being as the cubes of the major axes of their orbits, 

 that the heavenly bodies move slower the farther they are 

 from the sun. In comparing the periods of the revolutions 

 of Jupiter and Saturn with the times of their rotation, it 

 appears that a year of Jupiter contains nearly ten thousand 

 of his days, and that of Saturn about thirty thousand 

 Saturnian days. 



The appearance of Saturn is unparalleled in the system of 

 the world. He is a spheroid nearly 1000 times larger than 

 the earth, surrounded by a ring even brighter than himself, 

 which always remains suspended in the plane of his equator : 

 and, viewed with a very good telescope, it is found to con- 

 sist of two concentric rings, divided by a dark band. The 



