[ 2o6 ] 



precifion ; for if you take the 12th part of the moon's move- 

 ment in longitude or A. R. for 12H. from noon to midnight, 

 or from midnight to the fucceeding noon, you will have the 

 horary motion either in longitude or A. R. that took place at 

 6H. or 18H. For by the method of interpolation, vide article 3928, 

 he afcertained that in fpite of all the irregularities of the lunar 

 motions the 2d differences proceed at a rate that is to all 

 fenfe uniform even for the fpace of 24 hours ; it is evident 

 therefore, that having obtained the horary motion, for 6 or 

 i8Hs. by taking the Vt of the movement for laH. you may 

 then have it for any other hour of that interval by an even 

 proportion. 



As the A. R's. are the only lunar motions we have occa- 

 fion to make ufe of, in this method for the longitude of places, 

 I fliall only conlider the manner of finding the moon's horary 

 motion in A. R. for any required minute of any interval of 

 12, and thence of afcertaining the exad quantity of the A. R. 

 for 12H. that is to be ufed both for the corredion of the in- 

 terval of obferved A. R. between the 2 meridians, and alfo for 

 the corredtion of the efcimate longitude. 



Take out of the Nautical Almanac, or any other good 

 Ephemeris, the two calculated A. R's. immediately preceding, 

 and the two that immediately follow, the hour and minute for 

 which you want to determine the moon's horary motion ; place 



thefe 



