d, that it has often been seen on the dark side just after new
moon, and has thus given rise to marvellous stories of active lunar
volcanoes. To the south-east lies another smaller crater, Herodotus,
north of which is a narrow, deep valley, nowhere more than 2-1/2 miles
broad, which makes a remarkable zigzag. It is one of the largest of the
lunar "clefts."

13. _Grimaldi_ calls for notice as the darkest object of its size in the
moon. Under very exceptional circumstances it has been seen with the
naked eye, and as its area has been estimated at nearly 14,000 square
miles, it gives an idea of how little unaided vision can discern in the
moon; it must, however, be added that we always see Grimaldi
considerably foreshortened.

14. The great crater _Gassendi_ has been very frequently mapped on
account of its elaborate system of "clefts." At its northern end it
communicates with a smaller but much deeper crater, that is often filled
with black shadow after the whole floor of Gassendi has been
illuminated.

15. _Schickard_ is one of the largest walled plains on the moon, about
134 miles in breadth. Within its vast expanse Maedler detected 23 minor
craters. With regard to this object Chacornac pointed out that, owing to
the curvature of the surface of the moon, a spectator at the centre of
the floor "would think himself in a boundless desert," because the
surrounding wall, although in one place nearly 10,000 feet high, would
lie entirely beneath his horizon.

16. Close to the foregoing is _Wargentin_. There can be little doubt
that this is really a huge crater almost filled with congealed lava, as
there is scarcely any fall towards the interior.

17. _Clavius._--Near the 60th parallel of lunar south latitude lies
this enormous enclosure, the area of which is not less than 16,500
square miles. Both in its interior and on its walls are many peaks and
secondary craters. The telescopic view of a sunrise upon the surface of
Clavius is truly said by Maedler to be indescribably magnificent. One of
the peaks rises to a height of 24,000 feet above the bottom of one of
the included craters. Maedler even expressed the opinion that in this
wild neighbourhood there are craters so profound that no ray of sunlight
ever penetrated their lowest depths, while, as if in compensation, there
are peaks whose summits enjoy a mean day almost twice as long as their
night.

18. If the full moon be viewed through an opera-glass or any small
hand