orbit seventy-five degrees, so that the arctic circle comes
within fifteen degrees of the equator, and the tropics also
extend to latitude seventy-five degrees, or within fifteen
degrees of the poles, producing great extremes of heat and cold.

"Venus is made still more difficult of habitation by the fact
that she rotates on her axis in the same time that she revolves
about the sun, in the same way that the moon does about the
earth, so that one side must be perpetually frozen while the
other is parched.

"In Uranus we see the axis tilted still further, so that the
arctic circle descends to the equator. The most varied climate
must therefore prevail during its year, whose length exceeds
eighty-one of ours.

The axis of Mars is inclined about twenty-eight and two thirds
degrees to the plane of its orbit; consequently its seasons must
be very similar to ours, the extremes of heat and cold being
somewhat greater.

"In Jupiter we have an illustration of a planet whose axis is
almost at right angles to the plane of its orbit, being inclined
but about a degree and a half. The hypothetical inhabitants of
this majestic planet must therefore have perpetual summer at the
equator, eternal winter at the poles, and in the temperate
regions everlasting spring. On account of the straightness of
the axis, however, even the polar inhabitants--if there are
any--are not oppressed by a six months' night, for all except
those at the VERY pole have a sunrise and a sunset every ten