518 COSMOS. 



face, 76 is lOh. 29m. 17s. Such a great velocity of rotation 

 corresponds to the considerable j&tffcm'ft^. William Herschel 

 estimated it, in 1776, at y^; Bessel, after corresponding 

 observations during a period of more than three years, found 

 that at a mean distance the polar diameter was 15"-381 ; the 

 equatorial diameter 17"'053, consequently a flattening of 

 -j-i-.-g-. 77 The body of the planet has also riband-like stripes, 

 which are however less perceptible, though, at the same time, 

 rather broader than those of Jupiter. The most constant of them 

 is a grey equatorial stripe. Next to this follow several others, 



76 The earliest and careful observations of William Her- 

 schel, in November, 1793, gave for Saturn's period of rota- 

 tion lOh. 16m. 44s. It has been incorrectly attributed to the 

 great philosopher, Immanuel Kant, that he conjectured the 

 period of Saturn's rotation from theoretical considerations in 

 Iris Allgemeinen NaturyescliicJite des Himmels, forty years before 

 Herschel. The number that he gives is 6h. 23m. 53s. He 

 calls his determination " the mathematical calculation of an 

 unknown motion of a heavenly body, which is perhaps the 

 only prediction of that kind in pure Natural Philosophy, 

 and awaits confirmation at a future period." This confirma- 

 tion of his conjecture did not take place at all; observations 

 have shown an error of y of the whole, i. e. of four hours. In 

 the same work it is said respecting the ring of Saturn, " that in 

 the aggregation of particles which constitute it, those of the 

 inner edge complete their revolution in 10 hours, those of 

 the external edge in 15 hours. The first of these ring- 

 numbers is the only one which accidentally comes near the 

 planet's observed period of rotation (10 d. 29m. 17s.). Com- 

 pare Kant, SdmmtllcJw Werke, Th. vi. 1389, pp. 135 and 140. 



77 Laplace (Expos, du Syst. du Monde, p. 43,) estimates the 

 flattening at -^y The .extraordinary deviation of Saturn from 

 the spheroidal figure, according to which William Herschel, 

 after a series of laborious observations made with very diffe- 

 rent telescopes, found the major axis of the planet not in the 

 equator itself, but in a diameter which intersected the equa- 

 torial diameter at an angle of about 45, was not confirmed 

 by Bessel, but found to be incorrect. 



