74 EOTATION OF THE SUN. [SECT. ix. 



SECTION IX. 



Rotation of the Sun and Planets Saturn's Rings Periods of the Rotation 

 of the Moon and other Satellites equal to the Periods of their Revolutions 

 Form of Lunar Spheroid Libration, Aspect, and Constitution of the 

 Moon Rotation of Jupiter's Satellites. 



THE oblate form of several of the planets indicates rotatory 

 motion. This has been confirmed in most cases, by tracing 

 spots on their surface, by which their poles and times of ro- 

 tation have been determined. The rotation of Mercury is 

 unknown, on account of his proximity to the sun ; that of 

 the new planets has not yet been ascertained. The sun re- 

 volves in twenty-five days and ten hours about an axis which 

 is directed towards a point halfway between the pole-star 

 and Lyra, the plane of rotation being inclined by 7 30', or 

 a little more than seven degrees, to the plane of the ecliptic : 

 it may therefore be concluded that the sun's mass is a spheroid, 

 flattened at the poles. From the rotation of the sun, there 

 is every reason to believe that he has a progressive motion in 

 space, although the direction to which he tends is unknown. 

 But, in consequence of the reaction of the planets, he de- 

 scribes a small irregular orbit about the centre of gravity of 

 the system, never deviating from his position by more than 

 twice his own diameter, or a little more than seven times the 

 distance of the moon from the earth. The sun and all his at- 

 tendants rotate from west to east, on axes that remain nearly 

 parallel to themselves (N. 137) in every point of their orbit, 

 and with angular velocities thatare sensibly uniform (N. 138). 

 Although the uniformity in the direction of their rotation is 

 a circumstance hitherto unaccounted for in the economy of 

 nature, yet, from the design and adaptation of every other part 



