Never before had the travellers observed the stars and planets under such favourable conditions. No air or clouds intervened, and as the Callisto did not revolve on its axis there was no necessity for changing the direction of the glasses. After an hour of this interesting work, however, as it was already late at the longitude they had left on earth, and as they knew they had many days in space before them, they prepared to go to bed. When ready, they had only to pull down the shades; for, as apergy was not applied to them, but only to the Callisto, they still looked upon the floor as down, and closed the heavy curtains to have night or darkness. They found that the side of the Callisto turned constantly towards the sun was becoming very warm, the double-toughened glass windows making it like a greenhouse; but they consoled themselves with the thought that the sun's power on them was hourly becoming less, and they felt sure the double walls and thick upholstery would protect them almost anywhere within the solar system from the intense cold of space.
"We could easily have arranged," said Ayrault, for night and day on alternate sides of the Callisto by having strips of metal arranged spirally on the outside as on the end of an arrow. These would have started us turning as slowly as we like, since we passed through the atmosphere at a comparatively low rate of speed."
"I am afraid," said Cortlandt, "the motion, however slow, would have made us dizzy. It would be confusing to see the heavens turning about us, and it would interfere with using the glasses."
The base and one side of the Callisto had constant sunshine, while the other side and the dome were in the blackest night. This dome, on account of its shape, sky windows, and the completeness with which it could be isolated, was an ideal observatory, and there was seldom a time during their waking hours for the rest of the journey when it was not occupied by one, two, or all the observers.
"There is something marvellous," said Cortlandt, "about the condition of space. Its absolute cold is appalling, apparently because there is nothing to absorb heat; yet we find the base of this material projectile uncomfortably warm, though, should we expose a thermometer in the shade in front, we know it would show a temperature of three hundred to four hundred degrees below zero--were the instrument capable of recording it."
Artificial darkness having been obtained, the travellers were soon asleep, Bearwarden's dreams being regaled with thoughts of his company's triumph; Ayrault's, naturally, with visions of Sylvia; while Cortlandt frequently started up, thinking he had already made some great astronomical discovery.
About 9 A. M., according to seventy-fifth meridian time, the explorers awoke feeling greatly refreshed. The tank in which the liquefied oxygen was kept automatically gave off its gas so evenly that the air remained normal, while the lime contained in cups absorbed the carbon dioxide as fast as they exhaled it. They had darkened those windows through which the sun was actually pouring, for, on account of the emptiness of the surrounding ether and consequent absence of diffusion of light, nothing but the inky blackness of space and the bright stars looked in at the rest. On raising the shades they got an idea of their speed. A small crescent, smaller than the familiar moon, accompanied by one still tinier, was all that could be seen of the earth and its satellite.
"We must," said Bearwarden, "be moving at the rate of nearly a million miles an hour, from the way we have travelled."
"We must be doing fully a million," replied Cortlandt, "for by this time we are pretty well in motion, having got a tremendous start when so near the moon, with it and the earth in line."
By steering straight for Jupiter, instead of for the place it would occupy ten days later, they knew they would swing past, for the giant planet, being in rapid motion, would advance; but they did not object to this, since it would give them a chance to examine their new world in case they wished to do so before alighting; while, if they preferred to land at once, they could easily change their course by means of the moons, the fourth, from which their car was named, being the one that they knew would be of most use. Their tremendous speed showed them they should have time for exploration on their arrival, and that they would reach their destination sooner than they had expected. The apergetic force being applied, as we have seen, only to the Callisto, just as power in starting is exerted on a carriage or railway car and only through it to the passengers, Ayrault and his companions had no unusual sensation except loss of weight, for, when they were so far from the earth, its attraction was very slight, and no other planet was near enough to take its place. After breakfast, wishing to reach the dome, and realizing that it would be unnecessary to climb, each in turn gave a slight spring and was obliged to put up his hands to avoid striking the roof. In the cool quiet of the dark dome it was difficult to believe that only twenty feet away the sun was shining with such intensity upon the metal base as to make it too hot on the inside to touch without gloves.
The first thing that attracted their attention was the size and brilliance of Mars. Although this red planet was over forty million miles from the earth when they started, they calculated that it was less than thirty million miles from them now, or five millions nearer than it had ever been to them before. This reduction in distance, and the clearness of the void through which they saw it, made it a splendid sight, its disk showing clearly. From hour to hour its size and brightness increased, till towards evening it looked like a small, full moon, the sun shining squarely upon it. They calculated that on the course they were moving they should pass about nine hundred thousand miles to the right or behind it, since it was moving towards their left. They were interested to see what effect the mass of Mars would have on the Callisto, and saw here a chance of still further increasing their speed. Notwithstanding its tremendous rate, they expected to see the Callisto swerve from its straight line and move towards Mars, whose orbital speed of nine hundred miles a minute they thought would take it out of the Callisto's way, so that no actual collision would occur even if their air-ship were left to her own devices.
Towards evening they noticed through their glasses that several apparently island peaks in the southern hemisphere, which was turned towards them, became white, from which they concluded that a snow-storm was in progress. The south polar region was also markedly glaciated, though the icecap was not as extensive as either of those at the poles of the earth.
"As the Martian winters must be fully as severe as ours," said Cortlandt, "on account of their length, the planet's distance from the sun, and the twenty-seven and a half degrees inclination of its axis, we can account for the smallness 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 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 affair--in 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.