The ash-gray light with which a part of tue Mooii'd disk
shines when, some days before ol after the new Moon, she
presents only a narrow crescent, illuminated by the Sun, is
earth-light in the Moon, " the reflection of a reflection." The
less the Moon appears illuminated for the Earth, so much the
more is the Earth luminous for the Moon. But our planet
shines upon the Moon with an intensity 13|- times greater
than the Moon upon the Earth ; and this light is sufficiently
bright to become again perceptible to us by a second reflec
tion. By means of the telescope, mountain-peaks are distin-
guished in the ash-gray light of the larger spots and isolated
brightly-shining points, even when the disk is already more
than half illuminated.* These phenomena become particu-
larly striking between the tropics and upon the high mount-
ain-plains of duito and Mexico. .SincL the time of Lambert
and Schroter, the opinion has become prevalent that the ex-
tremely 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 reflect-
ed 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-
colored moonlight into an olive green color, bordering upon
yellow. " The Moon, which then stood vertically over the
Atlantic Ocean, received upon its night side the green terres-
trial light, which is reflected toward her when the sky is clear
by the forest districts of South America. "t

The meteorological condition of our atmosphere modifies
the intensity of the earth-light, which has to traverse the

* Madler, Astroti., § 1 12.
