ss-lines seen on the disc are in no way connected with the Sun, but
belong to the telescope through which the photograph was taken.

(Page 134)]

Sun spots are, as a rule, some thousands of miles across. The umbra of
a good-sized spot could indeed engulf at once many bodies the size of
our earth.

Sun spots do not usually appear singly, but in groups. The total area of
a group of this kind may be of immense extent; even so great as to cover
the one-hundredth part of the whole surface of the sun. Very large
spots, when such are present, may be seen without any telescope; either
through a piece of smoked glass, or merely with the naked eye when the
air is misty, or the sun low on the horizon.

The umbra of a spot is not actually dark. It only appears so in contrast
with the brilliant photosphere around.

Spots form, grow to a large size in comparatively short periods of time,
and then quickly disappear. They seem to shrink away as a consequence of
the photosphere closing in upon them.

That the sun is rotating upon an axis, is shown by the continual change
of position of all spots in one constant direction across his disc. The
time in which a spot is carried completely round depends, however, upon
the position which it occupies upon the sun's surface. A spot situated
near the equator of the sun goes round once in about twenty-five days.
The further a spot is situated from this equator, the longer it takes.
About twenty-seven days is the time taken by a spot situated midway
between the equator and the solar poles. Spots occur to the north of
the sun's equator, as well as to the south; though, since regular
observations have been made--that is to say, during the past fifty years
or so--they appear to have broken out a little more frequently in the
southern parts.

From these considerations it will be seen that the sun does not rotate
as the earth does, but that different portions appear to move at
different speeds. Whether in the neighbourhood of the solar poles the
time of rotation exceeds twenty-seven days we are unable to ascertain,
for spots are not seen in those regions. No explanation has yet been
given of this peculiar rotation; and the most we can say on the subject
is that the sun is not by any means a solid body.

_Faculae_ (Latin, little torches) are brilliant patches which appear here
and there upon the sun's surface, and are in some way associated with
spots. Their displacement, too, across the solar f