THE PLANETS. 127 



9. Eccentricity of the Planetary Orbits. The form of 

 the elliptical orbits is determined by the greater or less dis- 

 tance of the two foci from the center of the ellipse. This 

 distance, or the eccentricity of the planetary orbits expressed 

 in fractional parts of their half major axes, varies from 0*006 

 in the orbit of Venus (consequently very near the circular 

 form), and 0'076 in that of Ceres, to 0-205 and 0-255 in 

 those of Mercury and Juno. Next in succession to the least 

 eccentric orbits of Venus and Neptune follows that of the 

 Earth, whose eccentricity is now decreasing at the rate of 

 about 0-00004299 in 100 years, while the minor axis in- 

 creases ; then corne the orbits of Uranus, Jupiter, Saturn, 

 Ceres, Egeria, Vesta, and Mars. The most eccentric orbits 

 are those of Juno (0-255), Pallas (0-239), Iris (0-232), Vic- 

 toria (0-217), Mercury (0-205), and Hebe (0-202). The ec- 

 centricity is on the increase in the orbits of some planets, as 

 Mercury, Mars, and Jupiter ; on the decrease in those of 

 others, as Venus, the Earth, Saturn, and Uranus. The fol- 

 lowing table gives the eccentricities of the large planets for 

 the year 1800, according to Hansen. The eccentricities of 

 the fourteen small planets will be given subsequently, to- 

 gether with other elements of their orbits for the middle of 

 the nineteenth century. 



Hist, of the Conquest of Peru, vol. i., p. 126. The Mexicans possessed 

 among their twenty hieroglyphical signs of the days, one held in espe- 

 cial veneration, called Ollintonatiuh, that of the four movements of the 

 Sun, which governed the great cycle, renewed every 524 x 13 years, 

 and referred to the course of the Sun intersecting the solstices and equi- 

 noxes, and hieroglyphically expressed by foot-steps.* In the beautiful- 

 ly-painted illuminated Aztec manuscript, which was formerly preserved 

 in the villa of Cardinal Borgia at Veletri. and from which I derived 

 much important information, there is the remarkable astrological sign 

 of a cross. The day-signs, which are written on the margin by its side, 

 would perfectly represent the passage of the Sun through the zenith of 

 the town of Mexico (Tenochtitlan), the equator, and the solstitial points, 

 if the points (round disks), added to the da.y-signs on account of the 

 periodic series, were equally complete in all three passages of the Sun. 

 (Humboldt, Vues des Cordilieres, pi. xxxvii., No. 8, p. 164. 189, and 237.) 

 The King of Tezcuco, Nezahualpilli (called a fast child, because his fa- 

 ther fasted for a long time previously to the birth of the wished-for 

 son), who was passionately given to astronomical observations, erected 

 a building which Torquemada rather venturously calls an observatory, 

 and the ruins of which he saw. (Monarquia Indiana, lib. ii.. cap. 64.) 

 In the Raccolta di Mendoza, we find a priest represented ( Vues des 

 Cordilieres, pi. Iviii., No. 8, p. 289), who is watching the stars, which 

 is expressed by a dotted line which passes from the observed star to his 

 eye. 



