uminated side of the boundary between light and shade, for then
the features are brought out with exquisite distinctness.

Plate VII.[7] gives an illustration of lunar scenery, the object
represented being known to astronomers by the name of Triesnecker. The
district included is only a very small fraction of the entire surface of
the moon, yet the actual area is very considerable, embracing as it does
many hundreds of square miles. We see in it various ranges of lunar
mountains, while the central object in the picture is one of those
remarkable lunar craters which we meet with so frequently in every lunar
landscape. This crater is about twenty miles in diameter, and it has a
lofty mountain in the centre, the peak of which is just illuminated by
the rising sun in that phase of our satellite which is represented in
the picture.

A typical view of a lunar crater is shown in Plate VIII. This is, no
doubt, a somewhat imaginary sketch. The point of view from which the
artist is supposed to have taken the picture is one quite unattainable
by terrestrial astronomers, yet there can be little doubt that it is a
fair representation of objects on the moon. We should, however,
recollect the scale on which it is drawn. The vast crater must be many
miles across, and the mountain at its centre must be thousands of feet
high. The telescope will, even at its best, only show the moon as well
as we could see it with the unaided eye if it were 250 miles away
instead of being 240,000. We must not, therefore, expect to see any
details on the moon even with the finest telescopes, unless they were
coarse enough to be visible at a distance of 250 miles. England from
such a point of view would only show London as a coloured spot, in
contrast with the general surface of the country.

We return, however, from a somewhat fancy sketch to a more prosaic
examination of what the telescope does actually reveal. Plate IX.
represents the large crater Plato, so well known to everyone who uses a
telescope. The floor of this remarkable object is nearly flat, and the
central mountain, so often seen in other craters, is entirely wanting.
We describe it more fully in the general list of lunar objects.

The mountain peaks on the moon throw long, well-defined shadows,
characterised by a sharpness which we do not find in the shadows of
terrestrial objects. The difference between the two cases arises from
the absence of air from the moon. Our atmosphere diffuses