[Illustration: Fig. 11.--The Sun, photographed on September 22, 1870.]

To the unaided eye the sun appears to be a flat circle. If, however, it
be examined with the telescope, taking care of course to interpose a
piece of dark-coloured glass, or to employ some similar precaution to
screen the eye from injury, it will then be perceived that the sun is
not a flat surface, but a veritable glowing globe.

The first question which we must attempt to answer enquires whether the
glowing matter which forms the globe is a solid mass, or, if not solid,
which is it, liquid or gaseous? At the first glance we might think that
the sun cannot be fluid, and we might naturally imagine that it was a
solid ball of some white-hot substance. But this view is not correct;
for we can show that the sun is certainly not a solid body in so far at
least as its superficial parts are concerned.

A general view of the sun as shown by a telescope of moderate dimensions
may be seen in Fig. 11, which is taken from a photograph obtained by Mr.
Rutherford at New York on the 22nd of September, 1870. It is at once
seen that the surface of the luminary is by no means of uniform texture
or brightness. It may rather be described as granulated or mottled. This
appearance is due to the luminous clouds which float suspended in a
somewhat less luminous layer of gas. It is needless to say that these
solar clouds are very different from the clouds which we know so well in
our own atmosphere. Terrestrial clouds are, of course, formed from
minute drops of water, while the clouds at the surface of the sun are
composed of drops of one or more chemical elements at an exceedingly
high temperature.

The granulated appearance of the solar surface is beautifully shown in
the remarkable photographs on a large scale which M. Janssen, of Meudon,
has succeeded in obtaining during the last twenty years. We are enabled
to reproduce one of them in Fig. 12. It will be observed that the
interstices between the luminous dots are of a greyish tint, the general
effect (as remarked by Professor Young) being much like that of rough
drawing paper seen from a little distance. We often notice places over
the surface of such a plate where the definition seems to be
unsatisfactory. These are not, however, the blemishes that might at
first be supposed. They arise neither from casual imperfections of the
photographic plate nor from accidents during the development; they
plainly owe their