ect."

"I can see what troubles you," answered Barbican, "but I can also see
that one moment's reflection would have put an end to your perplexity.
On ordinary maps of the Earth's surface when the north is the top, the
right hand must be the east, the left hand the west, and so on. That is
simply because we look _down_ from _above_. And such a map seen through
a lens will appear reversed in all respects. But in looking at the Moon,
that is _up_ from _down_, we change our position so far that our right
hand points west and our left east. Consequently, in our reversed map,
though the north becomes south, the right remains east, and--"

"Enough said! I see it at a glance! Thank you, Barbican. Why did not
they make you a professor of astronomy? Your hint will save me a world
of trouble."[C]

Aided by the _Mappa Selenographica_, the travellers could easily
recognize the different portions of the Moon over which they were now
moving. An occasional glance at our reduction of this map, given as a
frontispiece, will enable the gentle reader to follow the travellers on
the line in which they moved and to understand the remarks and
observations in which they occasionally indulged.

"Where are we now?" asked Ardan.

"Over the northern shores of the _Mare Nubium_," replied Barbican. "But
we are still too far off to see with any certainty what they are like.
What is the _Mare_ itself? A sea, according to the early astronomers? a
plain of solid sand, according to later authority? or an immense forest,
according to De la Rue of London, so far the Moon's most successful
photographer? This gentleman's authority, Ardan, would have given you
decided support in your famous dispute with the Captain at the meeting
near Tampa, for he says very decidedly that the Moon has an atmosphere,
very low to be sure but very dense. This, however, we must find out for
ourselves; and in the meantime let us affirm nothing until we have good
grounds for positive assertion."

_Mare Nubium_, though not very clearly outlined on the maps, is easily
recognized by lying directly east of the regions about the centre. It
would appear as if this vast plain were sprinkled with immense lava
blocks shot forth from the great volcanoes on the right, _Ptolemaeus_,
_Alphonse_, _Alpetragius_ and _Arzachel_. But the Projectile advanced so
rapidly that these mountains soon disappeared, and the travellers were
not long before they could distinguish the great peaks that cl