By means of the telescope, mountain-peaks are distinguished in the
ash-gray light of the larger spots and isolated brightly-shining points
of the moon, even when the disc is already more than half illuminated.
Lambert and Schroter have shown that the extremely variable intensity
of the ash-gray light of the moon depends upon the greater or less
degree of reflection of the sunlight which falls upon the earth,
according as it is reflected from continuous continental masses, full
of sandy deserts, grassy steppes, tropical forests, and barren rocky
ground, or from large ocean surfaces. Lambert made the remarkable
observation (14th of February 1774) of a change of the ash-coloured
moonlight into an olive-green colour bordering upon yellow. “The moon,
which then stood vertically over the Atlantic Ocean, received upon its
right side the green terrestrial light which is reflected towards her
when the sky is clear by the forest districts of South America.”
Plutarch says distinctly, in his remarkable work _On the Face in the
Moon_, that we may suppose the _spots_ to be partly deep chasms and
valleys, partly mountain-peaks, which cast long shadows, like Mount
Athos, whose shadow reaches Lemnos. The spots cover about two-fifths
of the whole disc. In a clear atmosphere, and under favourable
circumstances in the position of the moon, some of the spots are
visible to the naked eye; as the edge of the Apennines, the dark
elevated plain Grimaldus, the enclosed _Mare Crisium_, and Tycho,
crowded round with numerous mountain ridges and craters.
Professor Alexander remarks, that a map of the eastern hemisphere,
taken with the Bay of Bengal in the centre, would bear a striking
resemblance to the face of the moon presented to us. The dark portions
of the moon he considers to be continental elevations, as shown by
measuring the average height of mountains above the dark and the light
portions of the moon.
The surface of the moon can be as distinctly seen by a good telescope
magnifying 1000 times, as it would be if not more than 250 miles
distant.