The volume of the Sun is 600 times greater, and its mass
(according 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 remem-
ber that if the solar sphere were entirely hollowed out, and
the Earth placed in its center, 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 in-
clines about 7° 30'. toward the ecliptic. According to Lau-
gier's very careful observations {Comptes Rendus de I' Acad,
des Sciences, torn. xv.,'1842,'p. 941),'the period of rotation
is 25yW days' (or 25d. 8h. 9m.), and the inclination of the
equator 7° 9'.
The conjectures gradually adopted in modern astronomy re-
garding 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 disk. 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 surround-
ing ash-gray penumbrse), 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 fun-
nel-shaped openings are formed in this envelope, in conse-
quence of the passage of currents from below upward, 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 oi
der to render this explanation, of which we here only bviefl^



62 COSMOS.
