"Had we not better move on?" said Bearwarden, and accordingly they went toward the woods they had first seen. Finding a firm strip of land between the forest and an arm of the sea, they gently grounded the Callisto, and not being altogether sure how the atmosphere of their new abode would suit terrestrial lungs, or what its pressure to the square inch might be, they cautiously opened a port-hole a crack, retaining their hold upon it with its screw. Instantly there was a rush and a whistling sound as of escaping steam, while in a few moments their barometer stood at thirty-six inches, whereupon they closed the opening.
"I fancy," said Dr. Cortlandt, "we had better wait now till we become accustomed to this pressure. I do not believe it will go much higher, for the window made but little resistance when we shut it."
Finding they were not inconvenienced by a pressure but little greater than that of a deep coal-mine, they again opened the port, whereupon their barometer showed a further rise to forty-two, and then remained stationary. Finding also that the chemical composition of the air suited them, and that they had no difficulty in breathing, the pressure being the same as that sustained by a diver in fourteen feet of water, they opened a door and emerged. They knew fairly well what to expect, and were not disturbed by their new conditions. Though they had apparently gained a good deal in weight as a result of their ethereal journey, this did not incommode them; for though Jupiter's volume is thirteen hundred times that of the earth, on account of its lesser specific gravity, it has but three hundred times the mass--i. e., it would weigh but three hundred times as much. Further, although a cubic foot of water or anything else weighs 2.5 as much as on earth, objects near the equator, on account of Jupiter's rapid rotation, weigh one fifth less than they do at the poles, by reason of the centrifugal force. Influenced by this fact, and also because they were 483,000,000 miles from the sun, instead of 92,000,000 as on earth, they had steered for the northern limit of Jupiter's tropics. And, in addition to this, they could easily apply the apergetic power in any degree to themselves when beyond the limits of the Callisto, and so be attracted to any extent, from twice the pull they receive from gravitation on earth to almost nothing.
Bearwarden and Ayrault shouldered their rifles, while Dr. Cortlandt took a repeating shot-gun with No. 4 shot, and, having also some hunting-knives and a sextant, all three set out in a northwesterly direction. The ground was rather soft, and a warm vapor seemed to rise from it. To the east the sky was veiled by dense clouds of smoke from the towering volcanoes, while on their left the forest seemed to extend without limit. Clumps of huge ferns were scattered about, and the ground was covered with curious tracks.
"Jupiter is evidently passing through a Carboniferous or Devonian period such as existed on earth, though, if consistent with its size, it should be on a vastly larger scale," said the doctor. "I never believed in the theory," he continued, "that the larger the planet the smaller should be its inhabitants, and always considered it a makeshift, put forward in the absence of definite knowledge, the idea being apparently that the weight of very large creatures would be too great for their strength. Of the fact that mastodons and creatures far larger than any now living on earth existed there, we have absolute proof, though gravitation must have been practically the same then as now."
Just here they came upon a number of huge bones, evidently the remains of some saurian, and many times the size of a grown crocodile. On passing a growth of most luxuriant vegetation, they saw a half-dozen sacklike objects, and drawing nearer noticed that the tops began to swell, and at the same time became lighter in colour. Just as the doctor was about to investigate one of them with his duck-shot, the enormously inflated tops of the creatures collapsed with a loud report, and the entire group soared away. When about to alight, forty yards off, they distended membranous folds in the manner of wings, which checked their descent, and on touching the ground remained where they were without rebound.
"We expected to find all kinds of reptiles and birds," exclaimed the doctor. "But I do not know how we should class those creatures. They seem to have pneumatic feet and legs, for their motion was certainly not produced like that of frogs."
When the party came up with them the heads again began to swell.
"I will perforate the air-chamber of one," said Col. Bearwarden, withdrawing the explosive cartridge from the barrel of his rifle and substituting one with a solid ball. "This will doubtless disable one so that we can examine it."
Just as they were about to rise, he shot the largest through the neck. All but the wounded one, soared off, while Bearwarden, Ayrault, and Cortlandt approached to examine it more closely.