78 COSMOS. 



even if we adopt the smaller mass, 24 ^ oS , assumed by Lamont ; 

 and notwithstanding the inconsiderable difference of density 

 observed in the innermost planetary group,*' we find both 

 Venus and Mars less dense than the Earth, which lies between 

 them . The time of rotation certainly diminishes with increasing 

 solar distance, but yet it is greater in Mars than in the Earth 

 and in Saturn than in Jupiter. The elliptic orbits of Juno, 

 Pallas, and Mercury, have the greatest degree of eccentricity, 

 and Mars and Venus, which immediately follow each other, 

 have the least. Mercury and Venus exhibit the same con- 

 trasts that may be observed in the four smaller planets, or 

 asteroids, whose paths are so closely interwoven. 



The eccentricities of Juno and Pallas are very nearly iden- 

 tical, and are each three times as great as those of Ceres and 

 Vesta. The same may be said of the inclination of the orbits 

 of the planets towards the plane of projection of the ecliptic, 

 or in the position of their axes of rotation with relation to 

 their orbits, a position on which the relations of climate, 

 seasons of the year, and length of the days depend more than 

 on eccentricity. Those planets that have the most elongated 

 elliptic orbits, as Juno, Pallas, and Mercury, have also, 

 although not to the same degree, their orbits most strongly 

 inclined towards the ecliptic. Pallas has a comet-like incli- 

 nation nearly twenty-six times greater than that of Jupiter, 

 whilst in the little planet Vesta, which is so near Pallas, the 

 angle of inclination scarcely by six times exceeds that of Jupiter. 



n equally irregular succession is observed in the positi9ii of 

 the axes of the few planets (four or five) whose planes of 

 rotation we know with any degree of certainty. It would ap- 

 pear from the position of the satellites of Uranus, two of which, 

 the second and fourth, have been recently observed with cer- 

 tainty, that the axis of this, the outermost of all the planets, is 

 scarcely inclined as much as 11 towards the plane of its orbit, 

 while Saturn is placed between this planet, whose axis almost 



as the densest of all the heavenly bodies; in the Epitome Astron. Co- 

 pern, in vii. libros digesta, 1618-1622, p. 420. Leibnitz also inclined 

 to the opinions of Kepler and Otto von Guericke, that the planets in- 

 crease in volume in proportion to their increase of distance from the Sun. 

 See his letter to the Magdeburg Burgomaster (JMayence, 1671), ia 

 Leibnitz, Deutschen Scliriften, lierausg. von Guliraver, th. i. ?64. 



* On the arrangement of masses, see Encke, in PC hum. Astr. Nadir. 

 1843, Nr. 488, 114. 



