Chapter 12 - Page 2

are now astronomers. We see now what no mortal eye has ever gazed on
before. This Projectile is simply a work room of the great Cambridge
Observatory lifted into space. Let us take observations!"

With these words, he set to work with a renewed ardor, in which his
companions fully participated. The consequence was that they soon had
several of the outline maps covered with the best sketches they could
make of the Moon's various aspects thus presented under such favorable
circumstances. They could now remark not only that they were passing the
tenth degree of north latitude, but that the Projectile followed almost
directly the twentieth degree of east longitude.

"One thing always puzzled me when examining maps of the Moon," observed
Ardan, "and I can't say that I see it yet as clearly as if I had thought
over the matter. It is this. I could understand, when looking through a
lens at an object, why we get only its reversed image--a simple law of
optics explains _that_. Therefore, in a map of the Moon, as the bottom
means the north and the top the south, why does not the right mean the
west and the left the east? I suppose I could have made this out by a
little thought, but thinking, that is reflection, not being my forte, it
is the last thing I ever care to do. Barbican, throw me a word or two on
the subject."

"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