METEOROLOGY. 151 



of longer duration, on account of the sun's orbit being much 

 inclined to the horizon. In countries lying in the vicinity of 

 50 of latitude, twilight continues until the sun has descended 

 from 15 to 20 below the horizon. 



The moon's light is only the reflected light of the sun, and 

 is estimated to be, when in its greatest intensity, only 

 part as much as the light of that vast luminary. 



