COMMON THINGS TIME. 



The sun and moon move round the celestial sphere in the same 

 direction from west to east, but the moon moves more than thirteen 

 times faster than the sun, and consequently makes more than 

 thirteen revolutions of the heavens while the sun makes one. 

 The moon is therefore constantly either departing from or 

 approaching to and overtaking the sun. At the moment it over- 

 takes the sun it is said to be in CONJUNCTION, and is called NEW 

 MOON. At the moment it is in the opposite part of the heavens, 

 and when therefore it is 180 removed from the sun, it is in 

 opposition ; and as it then presents its enlightened hemisphere 

 directly towards the earth, it appears with a complete circular 

 disc, and is called FULL MOON. "VVhen it is a quarter of the 

 heavens, or 90, before or behind the sun, it is said to be in the 

 QUARTERS, and appears as an enlightened semicircle, and is call 

 HALF MOON. 



The time which the moon takes to make one complete revolution 

 of the heavens, is called the moon's "period," or "periodic 

 time," and is found by the most exact modern observations to be 



27-32166 days 



expressed in decimals. If expressed in hours, minutes, 

 seconds it is 



9 7 d 7 h 43 m HA S 

 . 10 



The moon's period is unsuitable for a measure of civil time for 



two reasons : first and chiefly because the moment which terminates 

 one period and begins the next, is not marked by any conspicuous 

 and generally observable phenomenon, and can only be ascertained 

 by astronomers ; and secondly, because it is incommensurable with 

 the fundamental chronometric standard, the day, and as will 

 hereafter appear, equally so with the year. For these reasons it 

 has never been adopted as a chronometric unit either for civil or 

 astronomical purposes^ 



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