each side of the
equator. Every place has its twelve hours' darkness and light at
each revolution. But at C--the axis of the earth always preserving
the same direction--the northern pole is shrouded in continual
gloom. Every place [Page 105] north of the equator gets more
darkness than light, and hence winter.

The varying inclination of the axes of the different planets gives
a wonderful variety to their seasons. The sun is always nearly
over the equator of Jupiter, and every place has nearly its five
hours day and five hours night. The seasons of Earth, Mars, and
Saturn are so much alike, except in length, that no comment is
necessary. The ice-fields at either pole of Mars are observed to
enlarge and contract, according as it is winter or summer there.
Saturn's seasons are each seven and a half years long. The alternate
darkness and light at the poles is fifteen years long.

But the seasons of Venus present the greatest anomaly, if its assigned
inclination of axis (75 deg.) can be relied on as correct, which is
doubtful. Its tropic zone extends nearly to the pole, and at the
same time the winter at the other pole reaches the equator. The
short period of this planet causes it to present the south pole to
the sun only one hundred and twelve days after it has been scorching
the one at the north. This gives two winters, springs, summers, and
autumns to the equator in two hundred and twenty-five days.

If each whirling world should leave behind it a trail of light to
mark its orbit, and our perceptions of form were sufficiently acute,
we should see that these curves of light are not exact circles, but
a little flattened into an ellipse, with the sun always in one
of the foci. Hence each planet is nearer to the sun at one part
of its orbit than another; that point is called the perihelion,
and the farthest point aphelion. This eccentricity of orbit, or
distance of the sun from the centre, is very small. [Page 106] In
the case of Venus it is only .007 of the whole, and in no instance
is it more than .2, viz., that of Mercury. This makes the sun appear
twice as large, bright, and hot as seen and felt on Mercury at its
perihelion than at its aphelion. The earth is 3,236,000 miles nearer
to the sun in our winter than summer. Hence the summer in the
southern hemisphere is more intolerable than in the northern. But
this eccentricity is steadily diminishing at a uniform rate, by
reason of the perturbing influence of the other