TIIE SUN. 361 



In the description of each of the cosmieal bodies, I shall 

 precede whatever consideration of their physical constitution 

 may (except in the case of the Earth) be necessary, by their 

 respective numerical data. The numerical arrangement of 

 these results, is nearly identical with that which was adopted 

 by Hansen,* in his admirable Review of the Solar System^ 

 although I have necessarily made some alterations and addi- 

 tions in the data, from the fact that 1 1 planets and 3 satellites 

 have been discovered since 1837, the year in which H'ansen 

 wrote. 



The mean distance of the centre of the Sun from the 

 Earth is, according to Encke's supplementary correction of 

 the Sun's parallax (Abhandl. der Berl. A/cad. 1835, p. 309), 

 82,728,000 geographical miles, of which 60 go to an equatorial C4* 

 "degree, and of which each one, according to Bessel's inves- . tl> 

 tigation of ten measurements of degrees (Cosmos, vol. i. 

 p. 157), contains exactly 951*807 toises, or 5710-8405 Paris 

 feet, or 6086*76 English feet. 



Light requires for its passage from the Sun to the Earth 

 . e. to traverse the radius of the Earth's orbit, according to 

 Struve's observations of aberration, 8' 17*'78 (Cosmos, \ol. iii. 

 p. J10); whence it follows that the Sun's true position is 

 about 20*-445 in advance of its apparent place. 



The apparent diameter of the Sun, at its mean distance 

 from the Earth, is 32' 1"'8; and therefore only 54*'8 greater 

 than the Moon's disc at its mean distance from us. In the 

 perihelion, when in winter we are nearest to the Sun, the 

 apparent diameter of the latter increases to 32' 34*'6; in the 

 aphelion, when in summer we are farthest from the Sun, its 

 apparent diameter is diminished to 31' 30"*1. 



The Sun's true diameter is 770,800 geographical miles, or 

 more than 112 times greater than that of the Earth. 



* Hansen, in Schumacher's Jahrbuch for 1837, pp. 65-141. 



