hot, which they assuredly would become if friction was allowed to obstruct the motion. You understand, don't you?"
"Don't I though?" replied Ardan, apparently in earnest. "Let me show you how thoroughly. When I have been running hard and long, I feel myself perspiring like a bull and hot as a furnace. Why am I then forced to stop? Simply because my motion has been transformed into heat! Of course, I understand all about it!"
Barbican smiled a moment at this comical illustration of his theory and then went on:
"Accordingly, in case of a collision it would have been all over instantly with our Projectile. You have seen what becomes of the bullet that strikes the iron target. It is flattened out of all shape; sometimes it is even melted into a thin film. Its motion has been turned into heat. Therefore, I maintain that if our Projectile had struck that bolide, its velocity, suddenly checked, would have given rise to a heat capable of completely volatilizing it in less than a second."
"Not a doubt of it!" said the Captain. "President," he added after a moment, "haven't they calculated what would be the result, if the Earth were suddenly brought to a stand-still in her journey, through her orbit?"
"It has been calculated," answered Barbican, "that in such a case so much heat would be developed as would instantly reduce her to vapor."
"Hm!" exclaimed Ardan; "a remarkably simple way for putting an end to the world!"
"And supposing the Earth to fall into the Sun?" asked the Captain.
"Such a fall," answered Barbican, "according to the calculations of Tyndall and Thomson, would develop an amount of heat equal to that produced by sixteen hundred globes of burning coal, each globe equal in size to the earth itself. Furthermore such a fall would supply the Sun with at least as much heat as he expends in a hundred years!"
"A hundred years! Good! Nothing like accuracy!" cried Ardan. "Such infallible calculators as Messrs. Tyndall and Thomson I can easily excuse for any airs they may give themselves. They must be of an order much higher than that of ordinary mortals like us!"
"I would not answer myself for the accuracy of such intricate problems," quietly observed Barbican; "but there is no doubt whatever regarding one fact: motion suddenly interrupted always develops heat. And this has given rise to another theory regarding the maintenance of the Sun's temperature at a constant point. An incessant rain of bolides falling on his surface compensates sufficiently for the heat that he is continually giving forth. It has been calculated—"
"Good Lord deliver us!" cried Ardan, putting his hands to his ears: "here comes Tyndall and Thomson again!"
—"It has been calculated," continued Barbican, not heeding the interruption, "that the shock of every bolide drawn to the Sun's surface by gravity, must produce there an amount of heat equal to that of the combustion of four thousand blocks of coal, each the same size as the falling bolide."
"I'll wager another cent that our bold savants calculated the heat of the Sun himself," cried Ardan, with an incredulous laugh.
"That is precisely what they have done," answered Barbican referring to his memorandum book; "the heat emitted by the Sun," he continued, "is exactly that which would be produced by the combustion of a layer of coal enveloping the Sun's surface, like an atmosphere, 17 miles in thickness."
"Well done! and such heat would be capable of—?"
"Of melting in an hour a stratum of ice 2400 feet thick, or, according to another calculation, of raising a globe of ice-cold water, 3 times the size of our Earth, to the boiling point in an hour."
"Why not calculate the exact fraction of a second it would take to cook a couple of eggs?" laughed Ardan. "I should as soon believe in one calculation as in the other.—But—by the by—why does not such extreme heat cook us all up like so many beefsteaks?"
"For two very good and sufficient reasons," answered Barbican. "In the first place, the terrestrial atmosphere absorbs the 4/10 of the solar heat. In the second, the quantity of solar heat intercepted by the Earth is only about the two billionth part of all that is radiated."
"How fortunate to have such a handy thing as an atmosphere around us," cried the Frenchman; "it not only enables us to breathe, but it actually keeps us from sizzling up like griskins."
"Yes," said the Captain, "but unfortunately we can't say so much for the Moon."
"Oh pshaw!" cried Ardan, always full of confidence. "It's all right there too! The Moon is either inhabited or she is not. If she is, the inhabitants must breathe. If she is not, there must be oxygen enough left for we, us and co., even if we should have to go after it to the bottom of the ravines, where, by its gravity, it must have accumulated! So much the better! we shall not have to climb those thundering mountains!"
So saying, he jumped up and began to gaze with considerable interest on the lunar disc, which just then was glittering with dazzling brightness.
"By Jove!" he exclaimed at length; "it must be pretty hot up there!"
"I should think so," observed the Captain; "especially when you remember that the day up there lasts 360 hours!"
"Yes," observed Barbican, "but remember on the other hand that the nights are just as long, and, as the heat escapes by radiation, the mean temperature cannot be much greater than that of interplanetary space."
"A high old place for living in!" cried Ardan. "No matter! I wish we were there now! Wouldn't it be jolly, dear boys, to have old Mother Earth for our Moon, to see her always on our sky, never rising, never setting, never undergoing any change except from New Earth to Last Quarter! Would not it be fun to trace the shape of our great Oceans and Continents, and to say: 'there is the Mediterranean! there is China! there is the gulf of Mexico! there is the white line of the Rocky Mountains where old Marston is watching for us with his big telescope!' Then we should see every line, and brightness, and shadow fade away by degrees, as she came nearer and nearer to the Sun, until at last she sat completely lost in his dazzling rays! But—by the way—Barbican, are there any eclipses in the Moon?"
"O yes; solar eclipses" replied Barbican, "must always occur whenever the centres of the three heavenly bodies are in the same line, the Earth occupying the middle place. However, such eclipses must always be annular, as the Earth, projected like a screen on the solar disc, allows more than half of the Sun to be still visible."
"How is that?" asked M'Nicholl, "no total eclipses in the Moon? Surely the cone of the Earth's shadow must extend far enough to envelop her surface?"
"It does reach her, in one sense," replied Barbican, "but it does not in another. Remember the great refraction of the solar rays that must be produced by the Earth's atmosphere. It is easy to show that this refraction prevents the Sun from ever being totally invisible. See here!" he continued, pulling out his tablets, "Let a represent the horizontal parallax, and b the half of the Sun's apparent diameter—"
"Ouch!" cried the Frenchman, making a wry face, "here comes Mr. x square riding to the mischief on a pair of double zeros again! Talk English, or Yankee, or Dutch, or Greek, and I'm your man! Even a little Arabic I can digest! But hang me, if I can endure your Algebra!"
"Well then, talking Yankee," replied Barbican with a smile, "the mean distance of the Moon from the Earth being sixty terrestrial radii, the length of the conic shadow, in consequence of atmospheric refraction, is reduced to less than forty-two radii. Consequently, at the moment of an eclipse, the Moon is far beyond the reach of the real shadow, so that she can see not only the border rays
