144 COSMOS!. 



The aah-gray light wi:h which a part of tiie Moon's disk 

 shines when, some days before or after the new Moon, she 

 presents only a narrow crescent, illuminated by the Sun, ig 

 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 w^hen 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. Since 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 w4iich 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 w4ien the sky is clear 

 by the forest districts of South America."! 



The meteorological condition of our atmosphere modifies 

 the intensity of the earth-light, which has to traverse the 



* Madler, Astron., § 112. 



t See Lambert, Siir la Lumiere Cendr^e de la Lune, in the Mim. de 

 VAcad. de Berlin, annie 1773, p. 46 : " La Terre, vue des planetes, pour- 

 ra paraitre d'luie lumiere verdEitre, a peu pres comme Mars uous parait 

 d'uue couleur rougeatre." " The Earth, seen from the planets, may- 

 appear of a green color, much the same as Mars affords to us of a 

 reddish color." We will not, however, on that account, conjecture 

 with this acute man that the planet Mars may be covered with a red 

 vegetation, such as tlje rose-red bushes of Bougainvillaea. (Hum- 

 boldt, Vieios of Nature, p. 334.) " When in Central Europe the Moon, 

 shortly before the neio Moon, stands in the eastern heavens during the 

 morning hour, she receives the eavth-light principally from the large 

 plateau surfaces of Asia and Africa. But if, after the new Moon, it stands 

 during the evening in the west, it can only receive the reflection in less 

 quantities from the narrower American continent, and principally from 

 the wide ocean." — Wilhelm Beer and Madler, Der Mond nach seinen 

 Cntmischen Verhdltnissen, \ 106, p. 152. 



