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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 lefti。 e。；
behindfor 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
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。
As the radius of Phobos's circle was far shorter than that of the
parabolic curve they were making； it began to draw away； and was
rapidly left behind。 Applying the full apergetic force to Mars
and the larger moon； they shot away like an arrow； having had
their speed increased by the planet's attraction while
approaching it； and subsequently by repulsion。
〃Either of those；〃 said Bearwarden； looking back at the little
satellites； 〃would be a nice yacht for a man to explore space on。
He would also； of course； need a sun to warm him； if he wished to
go beyond this system； but that would not have to be a large
affairin fact； it might be smaller than the planet； and could
revolve about it like a moon。〃
〃Though a sun of that size；〃 replied Cortlandt； 〃might retain its
heat for the time you wished to use it； the planet part would be
nothing like as comfortable as what we have here； for it would be
very difficult to get enough air…pressure to breathe on so small
a body； since； with its slight gravitation…pull； to secure
fifteen pounds to the square inch； or anything like it； the
atmosphere would have to extend thousands of miles into space； so
that on a cloudy day you would be in darkness。 It would be
better； therefore； to have such a sun as you describe and
accompany it in a yacht or private car like this； well stocked
with oxygen and provisions。 When passing through meteoric swarms
or masses of solid matter； collision with which is the most
serious risk we run； the car could follow behind its sun instead
of revolving around it； and be kept from falling into it by
partially reversing the attraction。 As the gravitation of so
small a sun would be slight； counteracting it for even a
considerable time would take but little from the batteries。〃
〃There are known to be several unclaimed masses；〃 added Ayrault；
〃with diameters of a few hundred yards； revolving about the earth
inside the orbit of the moon。 If in some way two of these could
be brought into sufficiently violent collision； they would become
luminous and answer very well； the increase in bulk as a result
of the consolidation； and the subsequent heat； about serving to
bring them to the required size。 Whenever this sun showed spots
and indications of cooling； it could be made to collide with the
solid head of some comet； or small asteroid； till its temperature
was again right； while if； as a result of these accretions； it
became unwieldy； it could be caused to rotate with sufficient
rapidity on its axis to split； and we should have two suns
instead of one。〃
〃Bravo！〃 said Bearwarden。 〃There is no limit to what can be
done。 The idea of our present trip would have seemed more
chimerical to people a hundred years ago than this new scheme
appears now。〃
Thus they sat and talked； or studied maps and star… charts； or
the stars themselves； while the hours quickly passed and they
shot through space。 They had now a straight stretch of over
three hundred million miles； and had to cross the orbits of
innumerable asteroids on the way。 The apparent size of the sun
had by this time considerably decreased； and the interior of the
Callisto was no longer uncomfortably warm。 They divided the day
into twenty…four hours from force of habit； and drew the shades
tightly during what they considered night； while Bearwarden
distinguished himself as a cook。
CHAPTER III。
HEAVENLY BODIES。
The following day； while in their observatory； they saw something
not many miles ahead。 They watched it for hours； and in fact all
day； but notwithstanding their tremendous speed they came but
little nearer。
〃They say a stern chase is a long one；〃 said Bearwarden； but that
beats anything I have ever seen。〃
After a while； however； they found they WERE nearer； the time
taken having been in part due to the deceptive distance； which
was greater than they supposed。
〃A comet！〃 exclaimed Cortlandt excitedly。 〃We shall really be
able to examine it near。〃
〃It's going in our direction；〃 said Ayrault； 〃and at almost
exactly our speed。〃
While the sun shone full upon it they brought their camera into
play； and again succeeded in photographing a heavenly body at
close range。 The nucleus or head was of course turned towards
the sun； while the tail； which they could see faintly； preceded
it； as the comet was receding towards the cold and dark depths of
space。 The head was only a few miles in diameter； for it was a
small comet； and was composed of grains and masses of stone and
meteoric iron。 Many of the grains were no larger than peas or
mustard…seeds； no mass was more than four feet in diameter； and
all of them had very irregular shapes。 The space between the
particles was never less than one hundred times their masses。
〃We can move about within it；〃 said Ayrault； as the Callisto
entered the aggregation of particles； and moved slowly forward
among them。
The windows in the dome； being made of toughened glass； set
somewhat slantingly so as to deflect anything touching them； and
having； moreover； the pressure of the inside air to sustain them；
were fairly safe； while the windows in the sides and base were
but little exposed。 Whenever a large mass seemed dangerously
near the glass； they applied an apergetic shock to it and sent it
kiting among its fellows。 At these times the Callisto recoiled
slightly also； the resulting motion in either being in inverse
ratio to its weight。 There was constant and incessant movement
among the individual fragm