362 COSMOS. 



The mass of the Sun is, according to Encke's calculation of 

 Sabine's pendulum formula, 359,551 times that of the Earth, 

 or 355,499 times that of the Earth and Moon together ( Vierte 

 AbhandL iiber den Cometen von Pons in den Schr. der Berl. 

 Akad. 1842, p. 5); whence the density of the Sun is only 

 about ^ (or more accurately 0'252) that of the Earth. 



The volume of the Sun is 600 times greater, and its mass (ac- 

 cording to Galle) 738 times greater than that of all the planets 

 combined. It may assist the mind in conceiving a sensuous 

 image of the magnitude of the Sun, if we remember that if 

 the solar sphere were entirely hollowed out, and the Earth 

 placed in its centre, there would still be room enough for the 

 Moon to describe its orbit, even if the radius of the latter 

 were increased 160,000 geographical miles. 



The Sun rotates on its axis in 25 \ days. The equator 

 inclines about 7 30' towards the ecliptic. According to 

 Laugier's very careful observations (Comptes rendus de 

 I' Acad. des Sciences, torn. xv. 1842, p. 941), the period of 

 rotation is 25 T 3 ^ days (or 25d. 8h. 9m.), and the inclination 

 of the equator 7 9'. 



The conjectures gradually adopted in modern astronomy 

 regarding the physical character of the Sun's surface, are 

 based on long and careful observations of the alterations 

 which take place in the self-luminous disc. The order 

 of succession, and the connection of these alterations (the 

 formation of the Sun-spots, the relation of the deep black 

 nuclei to the surrounding ash-grey penumbra?), have led to 

 the assumption that the body of the Sun itself is almost 

 entirely dark, but surrounded at a considerable distance by a 

 luminous envelope ; that funnel-shaped openings are formed in 

 this envelope, in consequence of the passage of currents from 

 below upwards, and that the black nucleus of the spot is a 

 portion of the dark body of the Sun which is visible through 

 the opening. In order to render this explanation, of which 



