A Journey in Other Worlds [6]
the
other more obliquely. This wabbling, like that of a top, is the
sole cause of the seasons; since, owing to the eccentricity of
our orbit, the earth is actually fifteen hundred thousand miles
nearer the sun during our winter, in the northern hemisphere,
than in summer. That there is no limit to a planet's
inclination, and that inclination is not essential, we have
astronomical proof. Venus's axis is inclined to the plane of her
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
hours--the exact day being nine hours, fifty five minutes, and
twenty-eight seconds. The warmth of the tropics is also tempered
by the high winds that must result from the rapid whirl on its
axis, every object at the equator being carried around by this at
the rate of 27,600 miles an hour, or over three thousand miles
farther than the earth's equator moves in twenty-four hours.
"The inclination of the axis of our own planet has also
frequently considerably exceeded that of Mars, and again has been
but little greater than Jupiter's at least, this is by all odds
the most reasonable explanation of the numerous Glacial periods
through which our globe has passed, and of the recurring mild
spells, probably lasting thousands of years, in which elephants,
mastodons, and other semi-tropical vertebrates roamed in Siberia,
some of which died so recently that their flesh, preserved by the
cold, has been devoured by the dogs of modern explorers.
"It is not to be supposed that the inclining of the axes of
Jupiter, Venus, the Earth, and the other planets, is now fixed;
in some cases it is known to be changing. As long ago as 1890,
Major-Gen. A. W. Drayson, of the British Army, showed, in a work
entitled Untrodden Ground in Astronomy and Geology, that, as a
result of the second rotation of the earth, the inclination of
its axis was changing, it having been 23@ 28' 23" on January 1,
1750, 23@ 27' 55.3" on January 1, 1800, and 23@ 27' 30.9" on
January 1, 1850; and by calculation one hundred and ten years ago
showed that in 1900 (one hundred years ago) it would be 23@ 27'
08.8". This natural straightening is, of course, going on, and
we are merely about to anticipate it. When this improvement was
mooted, all agreed that the EXTREMES of heat and cold could well
be spared. 'Balance those of summer against those of winter by
partially straightening the axis; reduce the inclination from
twenty-three degrees, thirty minutes, to about fifteen degrees,
but let us stop there,' many said. Before we had gone far,
however, we found it would be best to make the work complete.
other more obliquely. This wabbling, like that of a top, is the
sole cause of the seasons; since, owing to the eccentricity of
our orbit, the earth is actually fifteen hundred thousand miles
nearer the sun during our winter, in the northern hemisphere,
than in summer. That there is no limit to a planet's
inclination, and that inclination is not essential, we have
astronomical proof. Venus's axis is inclined to the plane of her
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
hours--the exact day being nine hours, fifty five minutes, and
twenty-eight seconds. The warmth of the tropics is also tempered
by the high winds that must result from the rapid whirl on its
axis, every object at the equator being carried around by this at
the rate of 27,600 miles an hour, or over three thousand miles
farther than the earth's equator moves in twenty-four hours.
"The inclination of the axis of our own planet has also
frequently considerably exceeded that of Mars, and again has been
but little greater than Jupiter's at least, this is by all odds
the most reasonable explanation of the numerous Glacial periods
through which our globe has passed, and of the recurring mild
spells, probably lasting thousands of years, in which elephants,
mastodons, and other semi-tropical vertebrates roamed in Siberia,
some of which died so recently that their flesh, preserved by the
cold, has been devoured by the dogs of modern explorers.
"It is not to be supposed that the inclining of the axes of
Jupiter, Venus, the Earth, and the other planets, is now fixed;
in some cases it is known to be changing. As long ago as 1890,
Major-Gen. A. W. Drayson, of the British Army, showed, in a work
entitled Untrodden Ground in Astronomy and Geology, that, as a
result of the second rotation of the earth, the inclination of
its axis was changing, it having been 23@ 28' 23" on January 1,
1750, 23@ 27' 55.3" on January 1, 1800, and 23@ 27' 30.9" on
January 1, 1850; and by calculation one hundred and ten years ago
showed that in 1900 (one hundred years ago) it would be 23@ 27'
08.8". This natural straightening is, of course, going on, and
we are merely about to anticipate it. When this improvement was
mooted, all agreed that the EXTREMES of heat and cold could well
be spared. 'Balance those of summer against those of winter by
partially straightening the axis; reduce the inclination from
twenty-three degrees, thirty minutes, to about fifteen degrees,
but let us stop there,' many said. Before we had gone far,
however, we found it would be best to make the work complete.