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.