"At how many degrees is the temperature of the interplanetary space estimated?" asked M'Nicholl.
"Some time ago," replied Barbican, "this temperature was considered to be very low indeed—millions and millions of degrees below zero. But Fourrier of Auxerre, a distinguished member of the Académie des Sciences, whose Mémoires on the temperature of the Planetary spaces appeared about 1827, reduced these figures to considerably diminished proportions. According to his careful estimation, the temperature of space is not much lower than 70 or 80 degrees Fahr. below zero."
"No more?" asked Ardan.
"No more," answered Barbican, "though I must acknowledge we have only his word for it, as the Mémoire in which he had recorded all the elements of that important determination, has been lost somewhere, and is no longer to be found."
"I don't attach the slightest importance to his, or to any man's words, unless they are sustained by reliable evidence," exclaimed M'Nicholl. "Besides, if I'm not very much mistaken, Pouillet—another countryman of yours, Ardan, and an Academician as well as Fourrier—esteems the temperature of interplanetary spaces to be at least 256° Fahr. below zero. This we can easily verify for ourselves this moment by actual experiment."
"Not just now exactly," observed Barbican, "for the solar rays, striking our Projectile directly, would give us a very elevated instead of a very low temperature. But once arrived at the Moon, during those nights fifteen days long, which each of her faces experiences alternately, we shall have plenty of time to make an experiment with every condition in our favor. To be sure, our Satellite is at present moving in a vacuum."
"A vacuum?" asked Ardan; "a perfect vacuum?"
"Well, a perfect vacuum as far as air is concerned."
"But is the air replaced by nothing?"
"Oh yes," replied Barbican. "By ether."
"Ah, ether! and what, pray, is ether?"
"Ether, friend Michael, is an elastic gas consisting of imponderable atoms, which, as we are told by works on molecular physics, are, in proportion to their size, as far apart as the celestial bodies are from each other in space. This distance is less than the 1/3000000 x 1/1000', or the one trillionth of a foot. The vibrations of the molecules of this ether produce the sensations of light and heat, by making 430 trillions of undulations per second, each undulation being hardly more than the one ten-millionth of an inch in width."
"Trillions per second! ten-millionths of an inch in width!" cried Ardan. "These oscillations have been very neatly counted and ticketed, and checked off! Ah, friend Barbican," continued the Frenchman, shaking his head, "these numbers are just tremendous guesses, frightening the ear but revealing nothing to the intelligence."
"To get ideas, however, we must calculate—"
"No, no!" interrupted Ardan: "not calculate, but compare. A trillion tells you nothing—Comparison, everything. For instance, you say, the volume of Uranus is 76 times greater than the Earth's; Saturn's 900 times greater; Jupiter's 1300 times greater; the Sun's 1300 thousand times greater—You may tell me all that till I'm tired hearing it, and I shall still be almost as ignorant as ever. For my part I prefer to be told one of those simple comparisons that I find in the old almanacs: The Sun is a globe two feet in diameter; Jupiter, a good sized orange; Saturn, a smaller orange; Neptune, a plum; Uranus, a good sized cherry; the Earth, a pea; Venus, also a pea but somewhat smaller; Mars, a large pin's head; Mercury, a mustard seed; Juno, Ceres, Vesta, Pallas, and the other asteroids so many grains of sand. Be told something like that, and you have got at least the tail of an idea!"
This learned burst of Ardan's had the natural effect of making his hearers forget what they had been arguing about, and they therefore proceeded at once to dispose of Satellite's body. It was a simple matter enough—no more than to fling it out of the Projectile into space, just as the sailors get rid of a dead body by throwing it into the sea. Only in this operation they had to act, as Barbican recommended, with the utmost care and dispatch, so as to lose as little as possible of the internal air, which, by its great elasticity, would violently strive to escape. The bolts of the floor-light, which was more than a foot in diameter, were carefully unscrewed, while Ardan, a good deal affected, prepared to launch his dog's body into space. The glass, worked by a powerful lever which enabled it to overcome the pressure of the enclosed air, turned quickly on its hinges, and poor Satellite was dropped out. The whole operation was so well managed that very little air escaped, and ever afterwards Barbican employed the same means to rid the Projectile of all the litter and other useless matter by which it was occasionally encumbered.
The evening of this third of December wore away without further incident. As soon as Barbican had announced that the Projectile was still winging its way, though with retarded velocity, towards the lunar disc, the travellers quietly retired to rest.
Chapter VI.
Instructive Conversation.
On the fourth of December, the Projectile chronometers marked five o'clock in the morning, just as the travellers woke up from a pleasant slumber. They had now been 54 hours on their journey. As to lapse of time, they had passed not much more than half of the number of hours during which their trip was to last; but, as to lapse of space, they had already accomplished very nearly the seven-tenths of their passage. This difference between time and distance was due to the regular retardation of their velocity.
They looked at the earth through the floor-light, but it was little more than visible—a black spot drowned in the solar rays. No longer any sign of a crescent, no longer any sign of ashy light. Next day, towards midnight, the Earth was to be new, at the precise moment when the Moon was to be full. Overhead, they could see the Queen of Night coming nearer and nearer to the line followed by the Projectile, and evidently approaching the point where both should meet at the appointed moment. All around, the black vault of heaven was dotted with luminous points which seemed to move somewhat, though, of course, in their extreme distance their relative size underwent no change. The Sun and the stars looked exactly as they had appeared when observed from the Earth. The Moon indeed had become considerably enlarged in size, but the travellers' telescopes were still too weak to enable them to make any important observation regarding the nature of her surface, or that might determine her topographical or geological features.
Naturally, therefore, the time slipped away in endless conversation. The Moon, of course, was the chief topic. Each one contributed his share of peculiar information, or peculiar ignorance, as the case might be. Barbican and M'Nicholl always treated the subject gravely, as became learned scientists, but Ardan preferred to look on things with the eye of fancy. The Projectile, its situation, its direction, the incidents possible to occur, the precautions necessary to take in order to break the fall on the Moon's surface—these and many other subjects furnished endless food for constant debate and inexhaustible conjectures.
For instance, at breakfast that morning, a question of Ardan's regarding the Projectile drew from Barbican an answer curious enough to be reported.
"Suppose, on the night that we were shot up from Stony Hill," said Ardan, "suppose the Projectile had encountered some obstacle powerful enough to stop it—what would be the consequence of the sudden halt?"
"But," replied Barbican, "I don't understand what obstacle it could have met powerful enough to stop it."
"Suppose