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With the help of Boeer and Moedler's Mappa Selenographica, the travelers were able at once to recognize that portion of the disc enclosed within the field of their glasses.

"What are we looking at, at this moment?" asked Michel.

"At the northern part of the `Sea of Clouds,'" answered Barbicane. "We are too far off to recognize its nature. Are these plains composed of arid sand, as the first astronomer maintained? Or are they nothing but immense forests, according to M. Warren de la Rue's opinion, who gives the moon an atmosphere, though a very low and a very dense one? That we shall know by and by. We must affirm nothing until we are in a position to do so."

This "Sea of Clouds" is rather doubtfully marked out upon the maps. It is supposed that these vast plains are strewn with blocks of lava from the neighboring volcanoes on its right, Ptolemy, Purbach, Arzachel. But the projectile was advancing, and sensibly nearing it. Soon there appeared the heights which bound this sea at this northern limit. Before them rose a mountain radiant with beauty, the top of which seemed lost in an eruption of solar rays.

"That is--?" asked Michel.

"Copernicus," replied Barbicane.

"Let us see Copernicus."

This mount, situated in 9@ north latitude and 20@ east longitude, rose to a height of 10,600 feet above the surface of the moon. It is quite visible from the earth; and astronomers can study it with ease, particularly during the phase between the last quarter and the new moon, because then the shadows are thrown lengthways from east to west, allowing them to measure the heights.

This Copernicus forms the most important of the radiating system, situated in the southern hemisphere, according to Tycho Brahe. It rises isolated like a gigantic lighthouse on that portion of the "Sea of Clouds," which is bounded by the "Sea of Tempests," thus lighting by its splendid rays two oceans at a time. It was a sight without an equal, those long luminous trains, so dazzling in the full moon, and which, passing the boundary chain on the north, extends to the "Sea of Rains." At one o'clock of the terrestrial morning, the projectile, like a balloon borne into space, overlooked the top of this superb mount. Barbicane could recognize perfectly its chief features. Copernicus is comprised in the series of ringed mountains of the first order, in the division of great circles. Like Kepler and Aristarchus, which overlook the "Ocean of Tempests," sometimes it appeared like a brilliant point through the cloudy light, and was taken for a volcano in activity. But it is only an extinct one-- like all on that side of the moon. Its circumference showed a diameter of about twenty-two leagues. The glasses discovered traces of stratification produced by successive eruptions, and the neighborhood was strewn with volcanic remains which still choked some of the craters.

"There exist," said Barbicane, "several kinds of circles on the surface of the moon, and it is easy to see that Copernicus belongs to the radiating class. If we were nearer, we should see the cones bristling on the inside, which in former times were so many fiery mouths. A curious arrangement, and one without an exception on the lunar disc, is that the interior surface of these circles is the reverse of the exterior, and contrary to the form taken by terrestrial craters. It follows, then, that the general curve of the bottom of these circles gives a sphere of a smaller diameter than that of the moon."