MARS. * 159 



of tlie satellite upon atmospheric pressure, aqueous depositions, 

 and the dispersion of clouds, will be treated of in the last and 

 purely telluric part of the Cosmos. 



Mars. 



The diameter of this planet, notwithstanding its considera- 

 bly greater distance from the Sun, is only 0*5 19 of the Earth's, 

 or 3568 geographical miles. The eccentricity of his orbit is 

 0-0932168, next to Mercury the greatest of all the planetary 

 orbits ; and also on this account, as well as from its proximi- 

 ty to the Earth, the most suitable for Kepler's great discove- 

 ry of the elliptical form of the planetary orbits. His period 

 of rotation^ i^, according to Miidler and Wilhelm Beer, 24h. 

 37m. 23s. His sidereal revolution round the Sun occupies 1 

 year 321d. I7h. 30m. 41s. The inclination ofMars's orbit 

 toward the Earth's equator is 24° 44' 24"; his mass, ^^.^1--^; 

 his density, in comparison to that of the Earth, 0-958. The 

 mass of Mars will be hereafter corrected by means of the dis 

 turbances which he may experience from his influence with 

 the Comet of DeYico, in the same way that the close approach 

 of Encke's Comet was taken advantage of to ascertain the 

 mass of Mercury. 



The flattenmg of Mars, which (singularly enough) the great 

 Konigsberg astronomer permanently doubted, was first recog- 

 nized by William Herschel (1784). With regard to the amount 

 )f the flattening, however, there was long considerable uncer- 



'xbsorbed in the upper strata of our atmosphei'e, where it converts visi- 

 ble clouds into transparent vapor." The phenomenon of the rapid dis- 

 persion of clouds by the full Moon, when they are not extremely dense, 

 is considered by Sir John Herschel " as a meteorological fact, which," 

 he adds, "is confirmed by Humboldt's own experience and the uni- 

 versal belief of the Spanish sailors in the tropical seas of Arherica." — 

 See Report of the Fifteenth Meeting of the British Association for the 

 Advancement of Science, 1846, Notices, p. 5 ; and Outlines, p. 201. 



* Beer and Madler, Beitrdge zur Phys. Kenntniss des Sonnensystems, 

 1841, p. 113, from observations in 1830 and 1832 ; Madler, Astronomie, 

 1849, p. 206. The first considerable improvement in the data for the 

 period of rotation, which Dominique Cassini found 24h, 40m., was the 

 result of laborious observations by William Herschel (between 1777 and 

 1781), which gave24h. 39m. 21-7s. Kunowsky found, in 1821, 24h. 36m. 

 403., very near to Madler's result. Cassini's oldest observation of the 

 rotation of a spot upon Mars (Delambre, Hist, de VAstron. Mod., torn. 

 :i.,p. 694) appears to have been soon after the year 1670; but in the 

 very rare Treatise, Kern, Diss, de Scintitlatione Stellarum, Wittenb., 

 1686, § 8, 1 find that the actual discoverers of the rotations of Mars and 

 Jupiter are stated to have been " Salvator Serra and Father ^gidius 

 Franciscus de Cottignez, astronomex-s of the Collegio Romano." 



