THE MOON'S LIGHT. 481 



light of the Moon depends upon the greater or less degree of 

 reflection of the sunlight which falls upon the Earth, accord- 

 ing 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, border, 

 ing upon yellow. " The Moon, which then stood vertically 

 over the Atlantic Ocean, received upon its night side the 

 green terrestrial light, which is reflected towards her when 

 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 

 double course from the Earth to the Moon, and from thence 

 to our eye. " Thus when we have better photometric instru- 

 ments at our command we may be able," as Arago remarks, 24 



23 See Lambert, Sur la Lumiere Cendree de la Lune in the 

 Mem. deVAcad. de Berlin, annee 1773, p. 46: "La Terre, 

 vue des planetes, pourra paroitre d'une lumiere verdatre, a 

 peu pres comme Mars nous paroit d'une couleur rougeatre." 

 " The Earth, seen from the planets, may appear of a green 

 colour, much the same as Mars affords to us of a reddish 

 colour." 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 the rose-red bushes of 

 Bougainvillaea. (Humboldt, Views of Nature, p. 334.) 

 " When in central Europe the Moon, shortly before the new 

 Moon, stands in the eastern heavens during the morning 

 hour, she receives the earth-light principally from the large 

 plateau surfaces of Asia and Africa. But if after the neio 

 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 Cosmischen 

 Verhaltnissen, 106, p. 152. 



24 Seance de VAcademie des Sciences, le 5 Aout, 1833, 



