It was half-past twelve at night.  Barbicane then estimated his distance at 1,400 kilometres, a distance rather greater than the length of the lunar radius, and which must diminish as he drew nearer the North Pole.  The projectile was then not at the altitude of the equator, but on the tenth parallel, and from that latitude carefully observed on the map as far as the Pole, Barbicane and his two companions were able to watch the moon under the most favourable circumstances.

In fact, by using telescopes, this distance of 1,400 kilometres was reduced to fourteen miles, or four and a-half leagues.  The telescope of the Rocky Mountains brought the moon still nearer, but the terrestrial atmosphere singularly lessened its optical power.  Thus Barbicane, in his projectile, by looking through his glass, could already perceive certain details almost imperceptible to observers on the earth.

“My friends,” then said the president in a grave voice, “I do not know where we are going, nor whether we shall ever see the terrestrial globe again.  Nevertheless, let us do our work as if one day it would be of use to our fellow-creatures.  Let us keep our minds free from all preoccupation.  We are astronomers.  This bullet is the Cambridge Observatory transported into space.  Let us make our observations.”

That said, the work was begun with extreme precision, and it faithfully reproduced the different aspects of the moon at the variable distances which the projectile reached in relation to that orb.

Whilst the bullet was at the altitude of the 10th north parallel it seemed to follow the 20th degree of east longitude.

Here may be placed an important remark on the subject of the map which they used for their observations.  In the selenographic maps, where, on account of the reversal of objects by the telescope, the south is at the top and the north at the bottom, it seems natural that the east should be on the left and the west on the right.  However, it is not so.  If the map were turned upside down, and showed the moon as she appears, the east would be left and the west right, the inverse of the terrestrial maps.  The reason of this anomaly is the following:—­Observers situated in the northern hemisphere—­in Europe, for example—­perceive the moon in the south from them.  When they look at her they turn their backs to the north, the opposite position they take when looking at a terrestrial map.  Their backs being turned to the north, they have the east to the left and the west to the right.  For observers in the southern hemisphere—­in Patagonia, for example—­the west of the moon would be on their left and the east on their right, for the south would be behind them.

Such is the reason for the apparent reversal of these two cardinal points, and this must be remembered whilst following the observations of President Barbicane.

Helped by the Mappa Selenographica of Boeer and Moedler, the travellers could, without hesitating, survey that portion of the disc in the field of their telescopes.