dry. The ashen colour
is the result of our atmosphere being laden with watery vapour, and is
similar to what we see at sunset when rain is about. Lastly, when the
air around the earth is thickly charged with cloud, no light at all can
pass; and on such occasions the moon disappears altogether for the time
being from the night sky.

_Eclipses of the Sun_, otherwise known as Solar Eclipses, are divided
into _Total_, _Partial_, and _Annular_. A total eclipse of the sun takes
place when the moon comes between the sun and the earth, in such a
manner that it cuts off the sunlight _entirely_ for the time being from
a _portion_ of the earth's surface. A person situated in the region in
question will, therefore, at that moment find the sun temporarily
blotted out from his view by the body of the moon. Since the moon is a
very much smaller body than the sun, and also very much the nearer to us
of the two, it will readily be understood that the portion of the earth
from which the sun is seen thus totally eclipsed will be of small
extent. In places not very distant from this region, the moon will
appear so much shifted in the sky that the sun will be seen only
partially eclipsed. The moon being in constant movement round the earth,
the portion of the earth's surface from which an eclipse is seen as
total will be always a comparatively narrow band lying roughly from west
to east. This band, known as the _track of totality_, can, at the
utmost, never be more than about 165 miles in width, and as a rule is
very much less. For about 2000 miles on either side of it the sun is
seen partially eclipsed. Outside these limits no eclipse of any kind is
visible, as from such regions the moon is not seen to come in the way of
the sun (see Fig. 4 (i.), p. 67).

It may occur to the reader that eclipses can also take place in the
course of which the positions, where the eclipse would ordinarily be
seen as total, will lie outside the surface of the earth. Such an
eclipse is thus not dignified with the name of total eclipse, but is
called a partial eclipse, because from the earth's surface the sun is
only seen _partly eclipsed at the utmost_ (see Fig. 4 (ii.), p. 67).

[Illustration: (i.) Total Eclipse of the Sun.]

[Illustration: (ii.) Partial Eclipse of the Sun.

FIG. 4.--Total and Partial Eclipses of the Sun. From the position A the
Sun cannot be seen, as it is entirely blotted out by the Moon. From B it
is seen partially blotted out, becaus