ver the corresponding hemisphere with their light. Six months later
this same hemisphere is in winter, and the opposite hemisphere is in its
turn presented to the Sun. June 21 is the summer solstice for the
northern hemisphere, and is at the same time winter for the southern
pole. Six months later, on December 21, we have winter, while the
southern hemisphere is completely exposed to the Sun. Between these two
epochs, when the radiant orb shines exactly upon the equator, that is on
March 21, we have the spring equinox, that delicious flowering season
when all nature is enchanting and enchanted; on September 21 we have the
autumn equinox, melancholy, but not devoid of charm.

The terrestrial sphere has been divided into different zones, with which
the different climates are in relation:

1. The tropical zone, which extends 23 deg. 27' from one part to the other
of the equator. This is the hottest region. It is limited by the circle
of the tropics.

2. The temperate zones, which extend from 23 deg. 27' to 66 deg. 23' of
latitude, and where the Sun sets every day.

3. The glacial zones, drawn round the poles, at 66 deg. 33' latitude, where
the Sun remains constantly above or below the horizon for several days,
or even several months. These glacial zones are limited by the polar
circles.

We must add that the _axis_ of the Earth is a straight line that is
supposed to pass through the center of the globe and come out at two
diametrically opposite points called the _poles_. The diurnal rotation
of the Earth is effected round this axis.

The name _equator_ is given to a great circle situated between the two
poles, at equal distance, which divides the globe into two hemispheres.
The equator is divided into 360 parts or degrees, by other circles that
go from one pole to the other. These are the _longitudes_ or meridians
(see Fig. 62). The distance between the equator and the pole is divided
into larger or smaller circles, which have received the name of
_latitudes_, 90 degrees are reckoned on the one side and the other of
the equator, in the direction of the North and South poles,
respectively. The longitudes are reckoned from some point either to East
or West: the latitudes are reckoned North and South, from the equator.
In going from East to West, or inversely, the longitude changes, but in
passing from North to South of any spot, it is the latitude that alters.

[Illustration: FIG. 62.--The divisions of the globe. Long