476 COSMOS. 



both continents. 1 * With the little that we know with cer- 

 tainty of the appearance of the surfaces of the planets near 

 the Sun, Mercury and Venus, and their physical constitution, 

 the phenomenon of an ash-coloured light, sometimes observed 

 in the dark parts, and mentioned by Christian Mayer, William 

 llerschel," and Harding, also remains exceedingly myste- 

 rious. It is not probable that at so great a distance the 

 reflected light of the Earth should produce an ash-coloured 

 illumination upon Venus as upon our Moon. Hitherto .there 

 has been no flattening observed in the discs of the two inferior 

 planets, Mercury and Venus. 



THE EARTH. 



The mean distance of the Earth from the Sun is 12,032 

 times greater than the diameter of the Earth; therefore, 

 82,728,000 geographical miles, uncertain as to about 360,000 

 miles (-aiir)' '^ e period of the sidereal revolution of the 

 Earth round the Sun is 365d. 6h. 9' 10"- 7496. The excen- 

 tricity of the Earth's orbit amounts to 0-01679226 ; its mass 

 is -ay-gVsT > i ts density in relation to water, 5 '44. Bessel's 

 investigation of ten measurements of degrees, gave for the 

 flattening of the Earth, aTV-TTa ^ ne l en g tn of a geographical 

 mile, sixty of which are contained in one equatorial degree, 

 951,807toises, and the equatorial and polar diameters, 6875'6 

 and 6852*4 geographical miles. (Cosmos, vol. i. p. 157, note.) 



w Wilhelm Beer and Madler, Beitrdge zur Physischen 

 Kenntniss der Himmlischen Korper, p. 148. The so-called 

 moon of Venus, which Fontana, Dominique Cassini, and Short 

 declared that they had seen, for which Lambert calculated 

 tables, and which was said to have been seen in the centre of 

 the Sun's disc, full three hours after the egress of Venus, 

 belongs to the astronomical myths of an uncritical age. 



* Philos. Transact. 1795, vol. Ixxxvi. p. 214. 



