.[ 2o8 3 



Here 30' being the cxcefs of the time for which the rate is re- 

 quired above the laft mid-interval, and i' the variation of the 

 horary motion for 1 2H. fay, 12 : i : : 30' : 2" 30 ', which added to 

 31'. 20' the rate of the horary motion at 6H. gives the horary 

 motion at 6H, 30' = to 31'. 22". 30"'. If we now fuppofe the 

 mid-interval of the moon's paffage over two fucceflive meridians, 

 at each of which the diftance of her enlightened limb from the 

 fame ftar was obferved to have happened at this very time, 

 then to determine the difference of their longitudes from thefe 

 obfervations her whole increafe of A. R. for 12 hours, at the 

 precife rate at which fhe then moved, is required ; and this 

 quantity is had by multiplying the horary motion at 6H. 30' 

 by 12 — thus, 31. 22'. 30". Xi2 = 6°. 16'. 30". 



All that feems now requifite is to add a few words on the 

 meafure of time to be employed in the calculation of the lon- 

 gitude, by this method of comparing the I)'s limb, when on two 

 different meridians, with the fame fixed ftar. 



As the calculations in the Nautical Almanac, of all the lunar 

 motions, are exprefsly declared to be made for the apparent 

 moments of noon and midnight, as deduced immediately from 

 the fun, and as this apparent time, about the 20th of December, 

 varies 30" in a day from M. O time, it is evident that the change 

 of the 3)'s A. R. for 12H. at that time, as given in the Nau- 

 tical Almanac, is in fad, the change for 12H. o' 15" of M. © T. 

 In this cafe therefore the A. R. gained in 15", fhould be de- 



duded 



