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
considerably more conspicuous than on Deimos, and there were
boulders and loose stones upon their slopes, which looked as if
there might at some time have been frost and water on its
surface; but it was all dry now, neither was there any air. The
evidences of volcanic action were also plainly visible, while a
noticeable flattening at the poles showed that the little body
had once rotated rapidly on its axis, though whether it did so
still they had not time to ascertain. When abreast of it they
were less than two miles distant, and they secured several
instantaneous impressions, which they put aside to develop later.