104 ASTRONOMY. 
moons of Jupiter, the ring and seven satellites of Saturn, the planet 
Uranus « (March 13, 1781, by Elerschel), his six moons also by Herschel, 
Ceres ? (Jan. 1, 1801, by Piazzi), Pallas » (March 28, 1802, by Olbers), 
Juno : (Sept. 1, 1804, by Harding), Vesta s (also by Olbers, March 29, 
1807), Astrea ¢ (Dec. 8, 1845, by Henke), Neptune 4, his ring and moon 
(Sept. 23, 1846, by Galle), and the planet provisionally called Iris (July 1, 
1847, by Henke). The orbits of all these planets and moons, except 
Astrea, Iris, and Neptune, are represented on pl. 7, fig. 5, upon which are 
represented also the orbits of Hal.ey’s Comet 1759, 1835, and of the great 
comet of 1811, as well as that of Encke. The outer circle of the figure repre- 
sents the ecliptic with its division into the 12 signs, and on it are indicated by 
corresponding signs, in what parts to look for the following points :—the 
ascending node, &, of the great comet of 1811; the aphelion of Mars; the 
aphelion of Jupiter; the descending node, ¢3, of Mars; the aphelion of 
Juno; the perihelion of Vesta; the descending nodes of Mars and Venus; 
the aphelion of Saturn; the descending node of Jupiter; the aphelion of 
the Earth; the descending node of Saturn; the aphelion of Pallas and 
Venus ; the descending node of the Comet of 1811, and the aphelion of 
Ceres. In addition to these are given the proportional diameters for the 
Sun, Jupiter, Saturn, and Uranus. 
24. Since the planets move slower in their orbits as their distance from 
the sun is greater, fig. 6, pl. 7, is intended to exhibit the relative velocity of 
these motions. When Mercury, the planet nearest to the sun, has com- 
pleted an entire revolution in 360°, Venus in the same time describes an 
are of 141° 22’, the Earth an arc of 86° 44’, &c. The proportionate velo- 
cities of the recently discovered planet Astraea (between Vesta and Juno) 
and Neptune (almost twice the distance of Uranus from the sun) could not 
well be represented in the figure. Astrea, if introduced into the preceding 
comparison, would describe an arc of about 21°, and Neptune one of about 
20’. From the measurement of these various axes, it results, that Venus 
moves 23, the Earth 4, Mars 8 times slower than Mercury. fig. 7 repre- 
sents the inclinations of all the planetary orbits (except those of Astrea, 
Iris, and Neptune) to the plane of the ecliptic or the earth’s orbit. 
25. We shall now present a tabular view of the most important elements 
of our planetary system, principally with regard to those points which could 
not be represented on p/. 7, without affecting the distinctness of the figures. 
The estimates are given in Iinglish geographical miles, according to the 
most recent observations and calculations. The different values ascribed 
to Neptune may possibly require rectification whenever his elements are 
better known than they can be now. 
