84 



On the true Measure of a Lunar Cycle. 

 Days. H. M. 

 The new moon difference 6939 8 13 



-6939 18 00 



Moon's motion faster than sun 



First quarter difference 



Moon slower than suu 

 Full moon difference 



i. > IK : Moon slow . . 



Last quarter difference 



Moon fast . . 



New moon fast 

 Last quarter fast 



5 31 



6939 23 24 

 -6939 IS 00 



5 24 



6939 16 47 

 :-6939 18 00 



1 13 



H. M. 



M. un moon slow 5 24 

 First quarter slow 5 31 



Full 



Moon fast 11 00 Moon slow 10 55 



The difference in the aggregate amounts to no more than five 

 minutes in 19 Julian years, or 6939 days, 18 hours, which con- 

 vincingly shovvs that this method of calculating by the lunar 

 quarters, and bringing their variations into the account, is the 

 most correct way of ascertaiin'ng the true mean quantity sought, 



The aggregate sum of the times between the corresponding 

 quarters according to the Ephemeris of ISOl and 1820, stands as 

 follows : 



D. H. M. 

 From O Sept. 1801 to % Sept. 1820 6939 8 13 

 From ]) first quarter to }) first quarter 6939 23 31 

 From O to O 6939 23 24 



From ([ last quarter to ^ last quarter 6939 16 47 



27758 23 55 

 D. H. M. 

 4 X 6939 18 00 = 27759 00 00 



Diff. 5 



Tliis difference in 48 cycles or 912 years amounts to six hours, 

 by which the moon anticipates the sun. Could we proceed in 

 (fje Eame manner in computing the moon's mean quaptity in 



IQO 



