The “Mare Imbrium” lay before the eyes of the travellers like an immense depression of which the details were not very distinct.  Near them on the left rose Mount Lambert, the altitude of which is estimated at 1,813 metres, and farther on, upon the borders of the Ocean of Tempests, in north lat. 23 deg. and east long. 29 deg., rose the shining mountain of Euler.  This mountain, which rises only 1,815 metres above the lunar surface, has been the object of an interesting work by the astronomer Schroeter.  This savant, trying to find out the origin of the lunar mountains, asked himself whether the volume of the crater always looked equal to the volume of the ramparts that formed it.  Now this he found to be generally the case, and he hence concluded that a single eruption of volcanic matter had sufficed to form these ramparts, for successive eruptions would have destroyed the connection.  Mount Euler alone was an exception to this general law, and it must have taken several successive eruptions to form it, for the volume of its cavity is double that of its inclosure.

All these hypotheses were allowable to terrestrial observers whose instruments were incomplete; but Barbicane was no longer contented to accept them, and seeing that his projectile drew regularly nearer the lunar disc he did not despair of ultimately reaching it, or at least of finding out the secrets of its formation.

CHAPTER XIII.

LUNAR LANDSCAPES.

At half-past two in the morning the bullet was over the 30th lunar parallel at an effective distance of 1,000 kilometres, reduced by the optical instruments to ten.  It still seemed impossible that it could reach any point on the disc.  Its movement of translation, relatively slow, was inexplicable to President Barbicane.  At that distance from the moon it ought to have been fast in order to maintain it against the power of attraction.  The reason of that phenomenon was also inexplicable; besides, time was wanting to seek for the cause.  The reliefs on the lunar surface flew beneath their eyes, and they did not want to lose a single detail.

The disc appeared through the telescopes at a distance of two and a half leagues.  If an aeronaut were taken up that distance from the earth, what would he distinguish upon its surface?  No one can tell, as the highest ascensions have not exceeded 8,000 metres.

The following, however, is an exact description of what Barbicane and his companions saw from that height:—­

Large patches of different colours appeared on the disc.  Selenographers do not agree about their nature.  They are quite distinct from each other.  Julius Schmidt is of opinion that if the terrestrial oceans were dried up, a Selenite observer could only tell the difference between the terrestrial oceans and continental plains by patches of colour as distinctly varied as those which a terrestrial observer sees upon the moon.  According to him, the colour common to the vast plains, known under the name of “seas,” is dark grey, intermingled with green and brown.  Some of the large craters are coloured in the same way.