500 COSMOS. 



than all the other planets. She sheds her agreeable light 

 upon men, more especially in the primitive forests of the tro- 

 pical world, and the beasts of the forests. 80 The Moon, in 



40 See my Essay upon the Nocturnal Life of Animals in 

 the Primeval Forest, in the Views .of Nature, Bonn's ed. 

 p. 198. Laplace's reflections upon a perpetual moonlight 

 (Exposition du Systeme du Monde, 1824, p. 232) have met 

 with a disproval in the Mem. of Liouville sur un cas particu- 

 lier du problem des Trois Corps. Laplace says : " Quelques 

 partisans des causes finales ont imagine que la Lune a etc 

 donnee a la Terre pour Teclairer pendant les nuits ; dans ce 

 cas, la nature n'aurait point atteint le but qu'elle se serait 

 propose, puisque nous sommes souvent prives a la fois de la 

 lumiere du Soleil et de celle de la Lune. Pour y parvenir, il 

 eut suffi de mettre a 1'origine la Lune en opposition avec le 

 Soleil dans le plan nieme de 1'ecliptique, a une distui.ce egale 

 a la centieme partie de la distance de la Terre au Soleil, et de 

 donner a la Lune et a la Terre des vitesses paralleles et pro- 

 portionnelles a leurs distances a cet astre. Alors la Lune, 

 sans cesse en opposition au Soleil. eut decrit autour de lui 

 une ellipse semblable a celle de la Terre; ces deux astres se 

 seraient succede 1'un a 1'autre sur 1'horizon ; et comme a cette 

 distance la Lune n'eut point ete eclipsee, sa lumiere aurait 

 certainement remplace celle du Soleil." " Several partizans 

 of final causes have imagined that the Moon has been given 

 to the Earth to light it during the night ; in that case, nature 

 would not have attained the object which she had proposed, 

 because we are frequently deprived at the same time of the 

 light of the Sun and Moon. To have attained this end, it 

 would have been sufficient in the beginning to place the Moon 

 in opposition with the Sun, in the same plane of the ecliptic, 

 at a distance equal to the hundredth part of the distance of 

 the Earth from the Sun, and to give to the Moon and the 

 Earth velocities parallel and proportional to their distances 

 from that body. Then the Moon, constantly in opposition to 

 the Sun, would have described an ellipse round it like that of 

 the Earth ; these two bodies would have succeeded each other 

 in the horizon, and as at that distance the Moon would never 

 have been eclipsed, its light would certainly have replaced 



