66 Effect of the EartlCs Light upon the Moon. 



looking at a good chart, it may be seen that these remarks re- 

 fer, without doubt, to three annular mountains, viz. Aristarchus, 

 Kepler, and Copernicus, which this distinguished astronomer 

 perceived, as others, and as we have often done, shining in the 

 obscure part with a feeble ash-coloured glimmering light, and 

 exhibiting in the telescope the lustre of a star of the fourth 

 magnitude, as seen by the naked eye. Herschel, it is true, de- 

 signated these under the appellation of volcanos, but simply, as 

 he explicitly declares, because it was necessary to give them 

 some designation, and not at all with the intention of explain- 

 ing the appearances. Bode, Olbers, and Struve, all agree in 

 thinking, that the variations which these luminous appearances 

 present are owing to a difference in the circumstances of illumi- 

 nation and of libration ; and that a burning volcano would not 

 shew itself only in the obscure portion of the moon, when the 

 terrestrial light is sensibly upon it, but in quite different cir- 

 cumstances when that light is in full activity. We may add, 

 that it should shine brightly in proportion as the terrestrial light 

 is less visible, when the surrounding region is more obscure, 

 because real inherent light always appears most strikingly in 

 the absence of all foreign light. 



Schroeter imagined that he could perceive, that the ash- 

 coloured light is more sensible before than after the full moon ; 

 and he conceived that this was owing to the difference of the 

 reflection of the solar light from the earth, according as it was 

 transmitted from the ocean or the continents. When (in Cen- 

 tral Europe) the moon, a little before the change, appears in 

 the morning in the east, the ash-coloured light proceeds princi- 

 pally from the great table-lands of Asia and Africa. When 

 again, towards the evening, she is found in the west at the com- 

 mencement of the first quarter, being confronted with the Ame- 

 rican continent, which is much narrower, and to the ocean, she 

 must then receive much less light. Those observers who are 

 situated within the tropics, and who can in all seasons easily 

 distinguish the ash-coloured light as well before as after the 

 new moon, and still more, those who can examine where the 

 contrast of the oceanic and continental portions is greater than 

 with us, — those, for example, situated at Canton and at Para- 



