OUTLINES OF NATURAL PHILOSOPHY. 



night, it is nearly a straight line, and the disk a 

 semicircle. The diminution continues, the disk 

 becoming more and more concave to the west, 

 till, about the end of another seven days, it dis- 

 appears altogether. 



After a few days, the moon again appears, 

 like a fine crescent, to the eastward of the sun, 

 with its concavity turned toward the east, and 

 continues to increase on that side till it become 

 entirely full orbed, about -29 days from the time 

 when it was last full. 



The line separating the light and the dark part of the 

 moon is irregular and serrated, and its form va- 

 ries while one is looking at it through the teles- 

 cope : the light, as it advances, touches some 

 points, while they are yet at a distance from the 

 illuminated surface, and while all round them is 

 dark. The light on them spreads, till it be uni- 

 ted to the rest. 



The Moon, when full, is opposite to the Sun : when 

 she disappears, or when it is New Moon, she is in 

 conjunction with the sun : these two aspects of the 

 moon are called the Syzygies. At the time when 

 the moon appears as a semicircle, she is 90 dis- 

 tant from the sun on either side : she is then said 

 to be in the quadratures. 



The moon, during all these changes, advances among 

 the fixed stars, at the rate of 13 10'4 at an ave- 

 rage 



