MERCURY. 471 



and partly belong to the Chaldeans; 9 it is certainly astonishing 

 that Copernicus, who had reached his seventieth year, should 

 have lamented, when on his death- bed, that with all his 

 endeavours, he had never seen Mercury. Still the Greeks lf 

 justly characterized this planet by the name of ((ni\^wv) the 

 sparkling, on account of its occasionally very intense light. 

 It presents phases (variable form of the illuminated part of 

 the disc) the same as Venus, and, like the latter, appears to 

 us as a morning and evening star. 



Mercury is, in his mean distance, little more than 32 millions 

 of geographical miles from the Sun, exactly 0*3870938 parts 

 of the mean distance of the Earth from the Sun. On account 

 of the great excentricity of his orbit (0-2056163) the distance 

 of Mercury from the Sun in perihelion is 25 millions, in 

 aphelion 40 millions of miles. He completes his revolution 

 round the Sun in 87 mean terrestrial days and 23h. 15m. 46s. 

 Schroter and Harding have estimated the rotation at 24h. 5m. 

 from the uncertain observation of the form of the southern 

 cusp of the crescent, and from the discovery of a dark streak, 

 which was darkest towards the east. 



According to Bessel's determination on the occasion of the 

 transit of Mercury on May 5, 1832, the true diameter amounts 

 to 2,684 geographical miles, 11 i. e. 0-391 parts of the Earth's 

 diameter. 



' Lalande, in the Mem. de VAcad. des Sciences for 1766, 

 p. 498; Delambre, Histoire de I Astron. ancienne, torn. ii. 

 p. 320. 



10 Cosmos, vol. iv. p. 409. 



11 On the occasion of the transit of Mercury, on the 4th of 

 May, 1832, Madler and William Beer (Beitrage zur phi/s- 

 Kenntniss der himmlischen Korper, 1841, p. 145) found the 

 diameter of Mercury 2,332 miles; but in the edition of the 

 Astronomic of 1849, Madler has given the preference to 

 Bessel's result. 



