d on a map,
and a good finder used. We have only to turn the telescope to a few
stars seen in the finder nearly in the place marked in our map, and
presently we shall recognise the one we want by the peculiarity of its
light. What is the lowest power which will exhibit Neptune as a disc I
do not know, but I am certain no observer can mistake him for a fixed
star with a 2-inch aperture and a few minutes' patient scrutiny in
favourable weather.

[Illustration: PLATE VII.]

CHAPTER VII.

HALF-HOURS WITH THE SUN AND MOON.

The moon perhaps is the easiest of all objects of telescopic
observation. A very moderate telescope will show her most striking
features, while each increase of power is repaid by a view of new
details. Yet in one sense the moon is a disappointing object even to the
possessor of a first-class instrument. For the most careful and
persistent scrutiny, carried on for a long series of years, too often
fails to reward the observer by any new discoveries of interest. Our
observer must therefore rather be prepared to enjoy the observation of
recognised features than expect to add by his labours to our knowledge
of the earth's nearest neighbour.

Although the moon is a pleasing and surprising telescopic object when
full, the most interesting views of her features are obtained at other
seasons. If we follow the moon as she waxes or wanes, we see the true
nature of that rough and bleak mountain scenery, which when the moon is
full is partially softened through the want of sharp contrasts of light
and shadow. If we watch, even for half an hour only, the changing form
of the ragged line separating light from darkness on the moon's disc, we
cannot fail to be interested. "The outlying and isolated peak of some
great mountain-chain becomes gradually larger, and is finally merged in
the general luminous surface; great circular spaces, enclosed with rough
and rocky walls many miles in diameter, become apparent; some with flat
and perfectly smooth floors, variegated with streaks; others in which
the flat floor is dotted with numerous pits or covered with broken
fragments of rock. Occasionally a regularly-formed and unusually
symmetrical circular formation makes its appearance; the exterior
surface of the wall bristling with terraces rising gradually from the
plain, the interior one much more steep, and instead of a flat floor,
the inner space is concave or cup-shaped, with a solitary peak rising in
the centr