MERCURY. 137 



or smaller pores, and, when illuminated, present the appear- 

 ance of red columns of vapor, and clouds of various forms in 

 the third envelope of the Sun. 



Mercury. 



yVTien it is remembered how much the Egyptians* occu- 

 pied themselves with the planet Mercury (Set-Horus), and 

 the Indians with their Buddha, f since the earliest times ; 

 how, under the clear heaven of Western Arabia, the star- 

 worship of the race of the AseditesJ was exclusively directed 

 to Mercury ; and, moreover, that Ptolemy was able, in the 

 19 th book of the Almagest, to make use of fourteen observa- 

 tions of this planet, which reach back to 261 years before 

 our era, and partly belong to the Chaldeans, § it is certainly 

 astonishing that Copernicus, who had reached his seventieth 

 year, should have lamented, when on his death-bed, that with 

 all his endeavors, he had never seen Mercury. Still the 

 Greeksll justly characterized this planet by the name of 

 (ot'lX(j(x>v) the sparkling, on account of its occasionally very 

 intense light. It presents phases (variable form of the illu- 

 minated part of the disk) 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 mill- 

 ions of geographical miles from the Sun, exactly - 3870938 

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

 account of the great eccentricity of its orbit (0'2056163), the 

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

 in aphelion 40 millions of miles. He completes his revolu- 

 tion round the Sun in 87 mean terrestrial days and 23h. 

 15m. 46s. Schroter and Harding have estimated the rota- 

 tion 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 toward the east. 



According to Bessel's determination on the occasion of the 

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

 to 2684 geographical miles,TI i. e., 0-391 parts of the Earth's 

 diameter. 



* Lepsius, Chronologic der JEgypter, th. i., p. 92-96. 



t Cosmos, vol. iv., p. 93, note t, p. 92. t Ibid., vol. ii., p. 221. 



§ Lalande, in the Mini, de V Acad, des Sciences for 1766, p. 498 ; De- 

 lambre, Histoire de V Astron. Ancienne, torn, ii., p. 320. 



|| Cosmos, vol. iv., p. 93. 



II On the occasion of the transit of Mercury on the 4th of May, 1832, 

 Madler and William Beer {Beitrdge zur Phys. Kenntniss der himm- 

 lischen Korper, 1841, p. 145) found the diameter of Mercury 2332 miles ; 



