310 SPECIAL RESULTS IN THE URANOLOGICAL 



stones of 517 German feet in diameter: igneous meteors 

 have certainly been seen of 2600 feet in diameter before tlie 

 explosion. 



The connection between the degree of compression at the 

 poles and the velocity of rotation is most strikingly shown 

 by a comparison between the Earth, as a planet of the inner 

 group, and Jupiter and Saturn belonging to the outer group 

 of planets. For the Earth, period of rotation 23 h 56 m , 

 compression -^-g', for Jupiter, period of rotation 9 h 55 m , 

 compression, according to Arago, T l r , according to John 

 Herschel, -yV; for Saturn, period of rotation 10 h 29 m , com- 

 pression -yV But Mars, whose rotation is slower than that 

 of the Earth by 41 minutes, has, even assuming a much 

 smaller result than that adopted by William Herschel, still 

 a probably much greater compression than the Earth. May 

 this anomaly, since the form of the superficies of an elliptic 

 spheroid should correspond to the velocity of rotation, be 

 founded on a different law of increasing density from the 

 surface to the centre in the two planets, or in the possible 

 circumstance of the consolidation of the fluid surface of some 

 planets having taken place before they had assumed the 

 figure corresponding to their velocity of rotation ? On the 

 form of the ellipticity of our planet depend, as theoretical as- 

 tronomy demonstrates, the important phenomena of the retro- 

 gression of the equinoctial points, or the apparent progres- 

 sion of the heavenly bodies, termed the " Precession of the 

 Equinoxes," "Nutation" (libration of the Earth's axis) 

 and the change of the obliquity of the ecliptic. 



The apparent diameters of the planets are determined by 

 their absolute magnitudes, and by their distances from the 

 Earth : the following is the order of arrangement which 



