474 COSMOS. 



expressed, as in all cases, in fractional parts of half the 

 major axes, is only 0-00686182. The diameter of this planet 

 is 6,776 geographical miles; the mass -jorVsiT' ^ ne ma terial 

 contents 0*957, and the density 0'94 in comparison to the 

 Earth. 



Of the transits of the two inferior planets first announced by 

 Kepler after the appearance of his Rudolphine tables, that of 

 Venus is of most importance for the theory of the whole 

 planetary system, on account of the determination of the Sun's 

 parallax, and the distance of the Earth from the Sun deduced 

 from the latter. According to Encke's thorough investigation 

 of the transit of Venus in 1769, the Sun's parallax is 8*'57116. 

 (Berliner Jahrbuch for 1852, p. 323.) A new examination 

 of the Sun's parallax has been undertaken since 1849, by 

 command of the Government of the United States, at the 

 suggestion of Professor Gerling of Marburg. The parallax 

 is to be obtained by means of observations of Venus near the 

 eastern and western stationary points, as well as by micro- 

 meter measurements of the differences in the right ascension 

 and declination of well-determined fixed stars in very different 

 latitudes and longitudes. (Schum. Astr. NacJir. No. 599, 

 p. 36o, and No. 613, p. 193.) The astronomical expedi- 

 tion, under the command of the learned Lieutenant Gilliss, 

 has proceeded to Santiago in Chili. 



The rotation of Venus was long subject to great doubt. 

 l)ominique Cassini, 1669, and Jacques Cassini, 1732, found 

 it 23h. 20m., while Bianchini 14 of Home, 1726, assumed the 



from Adams to the Rev. R. Main, on the 7th of September, 

 1846, in the Report of the Royal Astronomical Society, vol. vii. 

 Ko. 9, p. 142. (Compare also Cosmos, vol. ii.-p. 708.) 



M Delambre, Hist, de I Astr on. au dixhuitieme steely 

 pp. 256-258. The result obtained by Bianchini, was sup- 

 ported by Hussey and Haugergues; Hansen also, whose 



