SECT. IX. ROTATION OF SUN AND PLANETS. 61 



been ascertained. The sun revolves in twenty-five days 

 and ten hours about an axis which is directed toward a 

 point half-way 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 there- 

 fore 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 progres- 

 sive motion in space, although the direction to which he 

 tends is unknown ; but, in consequence of the reaction 

 of the planets, he describes a small irregular orbit about 

 the center 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 attendants 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 that are 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 adapta- 

 tion of eveiy other part 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, 

 consequently, greater, and the action of the sun and of 

 their satellites 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 at- 

 traction 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 rota- 

 F 



