A Journey in Other Worlds [38]
of its ice-caps
only by the fact that its oceans cover but one fourth of its
surface instead of three quarters, as on the earth, and there is
consequently a smaller evaporation and rain and snow-fall."
They were too much interested to think of sleeping that night,
and so, after dining comfortably returned to their observatory.
When within four million miles of Mars the Callisto began to
swerve perceptibly, its curve, as when near the moon beginning
with a spiral. They swung on unconcernedly, however, knowing
they could check their approach at any time. Soon Mars appeared
to have a diameter ten times as great as that of the moon, and
promised shortly to occupy almost one side of their sky.
"We must be on the lookout for the satellites," said Cortlandt;
"a collision with either would be worse than a wreck on a desert
island."
They therefore turned their glasses in the direction of the
satellites.
"Until Prof. Hall, at Washington, discovered the two satellites
in 1877," he continued, "Mars was supposed to be without moons.
The outer one, Deimos, is but six miles in diameter, and revolves
about its primary in thirty hours and eighteen minutes, at a
distance of fourteen thousand six hundred miles. As it takes but
little longer to complete a revolution than Mars does to rotate
on its axis, it remains in the Martial sky one hundred and
thirty-two hours between rising and setting, passing through all
the phases from new moon to full and back again four times; that
is, it swings four times around Mars before going below the
horizon. It is one of the smallest bodies discovered with a
telescope. The inner one, Phobos, is considerably larger, having
a diameter of about twenty miles. It is but twenty-seven hundred
miles from Mars's surface, and completes its revolution in seven
hours and thirty-eight minutes, which is shorter than any other
known period, Jupiter's nearest moon being the next, with eleven
hours and fifty- nine minutes. It thus revolves in less than a
third of the time Mars takes to rotate, and must consequently
rise in the west and set in the east, as it is continually
running ahead of the surface of the planet, though the sun and
all the other stars rise and set on Mars in the same way as on
the earth."
When about fifteen thousand miles from Mars, they sighted Deimos
directly ahead, and saw that they should pass on its left--i. e.,
behind--for it was moving across them. The sun poured directly
upon it, making it appear full and showing all its features.
There were small unevennesses on the surface, apparently seventy
or a hundred feet high, which were the nearest approach to
mountains, and they ran in ridges or chains. There were also
unmistakable signs of volcanic action, the craters being large
compared with the size of the planet, but shallow. They saw no
signs of water, and the blackness of the shadows convinced them
there was no air. They secured two instantaneous photographs of
the little satellite as the Callisto swept by, and resumed their
inspection of Mars. They noticed red and brownish patches on the
peaks that had that morning turned white, from which they
concluded that the show had begun to melt under the warm spring
sun. This strengthened the belief they had already formed, that
on account of its twenty-seven and a half degrees inclination the
changes in temperature on Mars must be great and sudden. So
interested were they with this, that they did not at first see a
large and bright body moving rapidly on a course that converged
with theirs.
"We must be ready to repel boarders," said Bearwarden, observing
it for the first time and fixing his glass upon it. "That must
be Phobos."
Not ten miles off they beheld Mars's inner moon, and though their
own speed caused them to overtake and rush by it like a
whirlwind, the satellite's rapid motion in its orbit, in a course
temporarily almost parallel with theirs, served to give them a
chance the better to examine it. Here the mountain ranges were
only by the fact that its oceans cover but one fourth of its
surface instead of three quarters, as on the earth, and there is
consequently a smaller evaporation and rain and snow-fall."
They were too much interested to think of sleeping that night,
and so, after dining comfortably returned to their observatory.
When within four million miles of Mars the Callisto began to
swerve perceptibly, its curve, as when near the moon beginning
with a spiral. They swung on unconcernedly, however, knowing
they could check their approach at any time. Soon Mars appeared
to have a diameter ten times as great as that of the moon, and
promised shortly to occupy almost one side of their sky.
"We must be on the lookout for the satellites," said Cortlandt;
"a collision with either would be worse than a wreck on a desert
island."
They therefore turned their glasses in the direction of the
satellites.
"Until Prof. Hall, at Washington, discovered the two satellites
in 1877," he continued, "Mars was supposed to be without moons.
The outer one, Deimos, is but six miles in diameter, and revolves
about its primary in thirty hours and eighteen minutes, at a
distance of fourteen thousand six hundred miles. As it takes but
little longer to complete a revolution than Mars does to rotate
on its axis, it remains in the Martial sky one hundred and
thirty-two hours between rising and setting, passing through all
the phases from new moon to full and back again four times; that
is, it swings four times around Mars before going below the
horizon. It is one of the smallest bodies discovered with a
telescope. The inner one, Phobos, is considerably larger, having
a diameter of about twenty miles. It is but twenty-seven hundred
miles from Mars's surface, and completes its revolution in seven
hours and thirty-eight minutes, which is shorter than any other
known period, Jupiter's nearest moon being the next, with eleven
hours and fifty- nine minutes. It thus revolves in less than a
third of the time Mars takes to rotate, and must consequently
rise in the west and set in the east, as it is continually
running ahead of the surface of the planet, though the sun and
all the other stars rise and set on Mars in the same way as on
the earth."
When about fifteen thousand miles from Mars, they sighted Deimos
directly ahead, and saw that they should pass on its left--i. e.,
behind--for it was moving across them. The sun poured directly
upon it, making it appear full and showing all its features.
There were small unevennesses on the surface, apparently seventy
or a hundred feet high, which were the nearest approach to
mountains, and they ran in ridges or chains. There were also
unmistakable signs of volcanic action, the craters being large
compared with the size of the planet, but shallow. They saw no
signs of water, and the blackness of the shadows convinced them
there was no air. They secured two instantaneous photographs of
the little satellite as the Callisto swept by, and resumed their
inspection of Mars. They noticed red and brownish patches on the
peaks that had that morning turned white, from which they
concluded that the show had begun to melt under the warm spring
sun. This strengthened the belief they had already formed, that
on account of its twenty-seven and a half degrees inclination the
changes in temperature on Mars must be great and sudden. So
interested were they with this, that they did not at first see a
large and bright body moving rapidly on a course that converged
with theirs.
"We must be ready to repel boarders," said Bearwarden, observing
it for the first time and fixing his glass upon it. "That must
be Phobos."
Not ten miles off they beheld Mars's inner moon, and though their
own speed caused them to overtake and rush by it like a
whirlwind, the satellite's rapid motion in its orbit, in a course
temporarily almost parallel with theirs, served to give them a
chance the better to examine it. Here the mountain ranges were