THE PLANETS. 427 



erroneously, that the difference in size of the meteoric stones 

 which there is a tendency to consider as small planetary 

 bodies, from Vesta, which, according to a measurement by 

 Madler, is 264 geographical miles in diameter, therefore 380 

 miles less than the diameter of Pallas according to Lament, 

 is not greater than the difference between Vesta and the Sun. 

 According to these relations, there must be meteoric stones 

 of 517 feet in diameter. Fire-balls certainly have, while 

 they retain a disc-like appearance, a diameter amounting to 

 2,600 feet. 



The dependence of the flattening at the .poles upon the 

 velocity of rotation, appears most strikingly in the compa- 

 rison of the Earth as a planet of the interior group (Rot. 

 23 h 56'., Flattening -5^9) with the exterior planet Jupiter 

 (Rot. 9 h 55', Flattening, according to Arago, -^y, according to 

 John Herschel T V), and Saturn (Rot. 10 h 29', Flattening^.) 

 But Mars, whose rotation is still 41 minutes slower than 

 the rotation of the Earth, has, even when a much smaller 

 result is assumed than that of William Herschel, very pro- 

 bably a much greater flattening. Does the reason of this 

 anomaly, inasmuch as the figure of the surface of an elliptical 

 spheroid ought to correspond with the velocity of rotation, 

 consist in the difference of the law of the increasing density 

 towards the centre of the superincumbent strata? or in 

 the circumstance that the liquid surface of some planets was 

 solidified before they could assume the figure appertaining to 

 their velocity of rotation ? The important phenomena of the 

 backward motion of the equinoctial points or the apparent 

 advance of the stars (precession), that of nutation (oscillation 

 of the earth's axis), and the variation of the inclination 

 of the ecliptic, depend, as theoretical astronomy proves, 

 upon the configuration. 



The absolute magnitudes of the planets, and their distance 

 from the earth, determine their apparent diameter. We 



