THE PLANETS. 



121 



In another more perspicuous form the two periods of revo- 

 lution are : 



Mercuiy 87'^- 23'^- 15"^ 47"- 



Venus 224 16 49 7 



Earth 365 ' 6 9 10 -7496 



whence it follows that the period of the tropical revolution, 

 or the length of the solar year, is 365''-24222, or 365d. 5h. 

 48m. 47"* 80 91 ; the length of the solar year is shortened 

 0"'595 in 100 years' on account of the precession of the equi- 

 noxes : 



Mars 1 year, 321'^- 



Jupiter 11 years, 314 



Saturn 29 years, 166 



Uranus 84 years, 5 



Neptune 164 years, 225 



The rotation is most rapid in the case of the exterior planets, 

 which have, at the same time, a longer period of revolution ; 

 slower in the case of the smaller interior planets, which are 

 nearer to the Sun. The periods of revolution of the asteroids 

 between Mars and Jupiter are very various, and will be spoken 

 of in the enumeration of the individual planets. It is there- 

 fore sufficient, in this place, to give a comparative result, and 

 to observe that among the small planets Hygeia has the lon- 

 gest, and Flora the shortest period of revolution. 



8. Inclination of the Planetary Orbits and Axes of Ro- 

 tation. — Next to the masses of the planets, the inclination 

 and eccentricity of their orbits are among the most important 

 elements upon which the disturbances depend. The compar- 

 ison of these, in the order of succession of the interior, small 

 intermediate and exterior planets (from Mercury to Mars, from 

 Flora to Hygeia, from Jupiter to Neptune), presents manifold 

 similarities and contrasts, which lead to considerations as to 

 the formation of these cosmical bodies, and their changes dur 



Vol. IV.— F 



