of 32' 12".6, or a little more than half a degree. Three
hundred and sixty such suns, laid side by side, would span the
celestial arch from east to west with a half circle of light. Two
lines drawn from our earth at the angle mentioned would be 860,000
miles apart at the distance of 92,500,000 miles. This, then, is
the diameter of the visible and measurable part of the sun. It
would require one hundred and eight globes like the earth in a line
to measure the sun's diameter, and three hundred and thirty-nine,
to be strung like the beads of a necklace, to encircle his waist.
The sun has a volume equal to 1,245,000 earths, but being only
one-quarter as dense, it has a mass of only 326,800 earths. It
has seven hundred times the mass of all the planets, asteroids,
and satellites put together. Thus it is able to control them all
by its greater power of attraction.

Concerning the condition of the surface of the sun many opinions
are held. That it is hot beyond all estimate is indubitable. Whether
solid or gaseous we are not sure. Opinions differ: some incline to
the first theory, others to the second; some deem the sun composed
of solid particles, floating in gas so condensed [Page 90] by
pressure and attraction as to shine like a solid. It has no sensible
changes of general level, but has prodigious activity in spots.
These spots have been the objects of earnest and almost hourly study
on the part of such men as Secchi, Lockyer, Faye, Young, and others,
for years. But it is a long way off to study an object. No telescope
brings it nearer than 200,000 miles. Theory after theory has been
advanced, each one satisfactory in some points, none in all. The
facts about the spots are these: They are most abundant on the two
sides of the equator. They are gregarious, depressed below the
surface, of vast extent, black in the centre, usually surrounded by
a region of partial darkness, beyond which is excessive light. They
have motion of their own over the surface--motion rotating about an
axis, upward and downward about the edges. They change their
apparent shape as the sun carries them across its disk by axial
revolution, being narrow as they present their edges to us, and
rounder as we look perpendicularly into them (Fig. 35).

[Illustration: Fig. 35.--Change in Spots as rotated across the Disk,
showing Cavities.]

These spots are also very variable in number, sometimes there being
none for nearly two hundred days, and again whole