over 20,000 feet above the surrounding plains.

Langrenus [1] was the first to do serious work on selenography, and
named the lunar features after eminent men. Riccioli also made lunar
charts. In 1692 Cassini made a chart of the full moon. Since then we
have the charts of Schroter, Beer and Madler (1837), and of Schmidt,
of Athens (1878); and, above all, the photographic atlas by Loewy and
Puiseux.

The details of the moon's surface require for their discussion a whole
book, like that of Neison or the one by Nasmyth and Carpenter. Here a
few words must suffice. Mountain ranges like our Andes or Himalayas
are rare. Instead of that, we see an immense number of circular
cavities, with rugged edges and flat interior, often with a cone in
the centre, reminding one of instantaneous photographs of the splash
of a drop of water falling into a pool. Many of these are fifty or
sixty miles across, some more. They are generally spoken of as
resembling craters of volcanoes, active or extinct, on the earth. But
some of those who have most fully studied the shapes of craters deny
altogether their resemblance to the circular objects on the moon.
These so-called craters, in many parts, are seen to be closely
grouped, especially in the snow-white parts of the moon. But there are
great smooth dark spaces, like the clear black ice on a pond, more
free from craters, to which the equally inappropriate name of seas has
been given. The most conspicuous crater, _Tycho_, is near the south
pole. At full moon there are seen to radiate from Tycho numerous
streaks of light, or "rays," cutting through all the mountain
formations, and extending over fully half the lunar disc, like the
star-shaped cracks made on a sheet of ice by a blow. Similar cracks
radiate from other large craters. It must be mentioned that these