all
though very brilliant disk, is solely on account of its distance. Its
apparent dimensions by no means reveal its majestic proportions to us.

When observed with astronomical instruments, or photographed, we
discover that its surface is not smooth, as might be supposed, but
granulated, presenting a number of luminous points dispersed over a
more somber background. These granulations are somewhat like the pores
of a fruit, _e.g._, a fine orange, the color of which recalls the hue of
the Sun when it sinks in the evening, and prepares to plunge us into
darkness. At times these pores open under the influence of disturbances
that arise upon the solar surface, and give birth to a Sun-Spot. For
centuries scientists and lay people alike refused to admit the existence
of these spots, regarding them as so many blemishes upon the King of the
Heavens. Was not the Sun the emblem of inviolable purity? To find any
defect in him were to do him grievous injury. Since the orb of day was
incorruptible, those who threw doubt on his immaculate splendor were
fools and idiots. And so when Scheiner, one of the first who studied the
solar spots with the telescope, published the result of his experiments
in 1610, no one would believe his statements.

Yet, from the observations of Galileo and other astronomers, it became
necessary to accept the evidence, and stranger still to recognize that
it is by these very spots that we are enabled to study the physical
constitution of the Sun.

They are generally rounded or oval in shape, and exhibit two distinct
parts; first, the central portion, which is black, and is called the
_nucleus_, or _umbra_; second, a clearer region, half shaded, which has
received the name of _penumbra_. These parts are sharply defined in
outline; the penumbra is gray, the nucleus looks black in relation to
the dazzling brilliancy of the solar surface; but as a matter of fact it
radiates a light 2,000 times superior in intensity to that of the full
moon.

[Illustration: FIG. 29.--Direct photograph of the Sun.]

Some idea of the aspect of these spots may be obtained from the
accompanying reproduction of a photograph of the Sun (taken September 8,
1898, at the author's observatory at Juvisy), and from the detailed
drawing of the large spot that broke out some days later (September 13),
crossed by a bridge, and furrowed with flames. As a rule, the spots
undergo rapid transformations.

[Illustration: FIG. 30.--Telescopic a