Later they saw several smaller spots drifting eastward, but concluded that any seaworthy ship might pass safely through them, for, though they were hurricanes of great violence, the waves were small.
"There would be less danger," said Bearwarden, "of shipping seas here than there is on earth; the principal risk to travellers would be that of being blown from the deck. On account of the air's weight in connection with its velocity, this would necessitate some precaution."
The next object of interest was the great red spot. It proved, as Cortlandt had predicted, to be a continent, with at that time no special colour, though they easily recognized it by comparing its outlines with those of the spot in the map. Its length, as they already knew, was twenty-seven thousand miles, and its breadth about eight thousand miles, so that it contained more square miles than the entire surface of the earth, land and water included.
"It is clear," said Cortlandt, "that at some season of Jupiter's long year a change takes place that affects the colour of the leaves--some drought or prolonged norther; for it is obvious that that is the simplest explanation. In like manner we may expect that at some times more white spots will move across the ocean than at others."
"On account of the size of these continents and oceans," said Bearwarden, "it is easy to believe that many climatic conditions may prevail here that can scarcely exist on earth. But what a magnificent world to develop, with its great rivers, lakes, and mountains showing at even this distance, and what natural resources must be lying there dormant, awaiting our call! This constantly recurs to my mind. The subjugation and thorough opening up of this red spot continent will probably supply more interesting problems than straightening the axis of the earth."
"At our next visit," replied Ayrault, "when we have established regular interplanetary lines of travel, we may have an opportunity to examine it more closely." Then they again attracted the nearest moon beyond which they had swung, increased the repulsion on Jupiter, and soared away towards Saturn.
"We have a striking illustration of Jupiter's enormous mass," said Cortlandt, as the apparent diameter of the mighty planet rapidly decreased, "in the fact that notwithstanding its numerous moons, it still rotates so rapidly. We know that the earth's days were formerly but half or a quarter as long as now, having lasted but six or eight hours. The explanation of the elongation is simple: the earth rotates in about twenty-four hours, while the moon encircles it but once in nearly twenty-eight days, so that our satellite is continually drawing the oceans backward against its motion. These tidal brakes acting through the friction of the water on the bottom, its unequal pressure, and the impact of the waves on the shore, are continually retarding its rotation, so that the day is a fraction of a second longer now than it was in the time of Caesar. This same action is of course taking place in Jupiter and the great planets, in this case there being five moons at work. Our moon, we know, rotates on its axis but once while it revolves about the earth, this being no doubt due to its own comparative smallness and the great attraction of the earth, which must have produced tremendous tides before the lunar oceans disappeared from its surface."
In crossing the orbits of the satellites, they passed near Ganymede, Jupiter's largest moon.
"This," said Cortlandt, "was discovered by Galileo in 1610. It is three thousand four hundred and eighty miles in diameter, while our moon is but two thousand one hundred and sixty, revolves at a distance of six hundred and seventy-eight thousand three hundred miles from Jupiter, completes its revolution in seven days and four hours, and has a specific gravity of 1.87."
In passing, they observed that Ganymede possessed an atmosphere, and continents and oceans of large area. "Here," said Bearwarden, "we have a body with a diameter about five hundred miles greater than the planet Mercury. Its size, light specific gravity, atmosphere, and oceans seem to indicate that it is less advanced than that planet, yet you think Jupiter has had a longer separate existence than the planets nearer the sun?"