By the Moon's Travis. g^ 



Brought over 12*^ 36"" z6'6^ 

 On a meridian ((3 *) far to the wcflward 

 the tranfit of the moon's firft limb was ob- 

 ferved the fame day, and being reduced to 

 the centre, its right afcenfion was - 12 47 56*7 



II 30-1 



Increafe of right afcenfion between A 

 and - - ~ - 



The increafe of the moon's right afcenfion 

 in twelve hours apparent time per the Nauti- 

 cal Almanac was - - _ o 25 3t 



The increafe of the fun's in the fame time o i 49'55 



Difference - - - o 24 ^S'SS 



And 12 hours minus this difference is = ii*" 35*" 46-65'; 

 therefore. As 26"" 3' : ii'> ^^"^ 46-65' : : ii"" 30-1' to 5'' 7*" 

 12% the corredt difference of longitude between A and 0. 



By reducing the three terms to feconds, and ufing loga- 

 rithms, the operation is much fhortened. 



In a book published by Mr. Mackay on longitude about 

 fifteen or fixteen years ago, there is a rule given, and alfo an 

 example, for finding the difference of longitude at land from 

 the tranfits of the moon, but no demonftration. The rule, 

 when diverted of its high-founding enunciation, runs thus : 



As the increafe of the moon's right afcenfion in twelve 

 hours apparent time : is to 180' : :, fo is anv other obferved 

 increafe between two meridians : to their difference of longi- 

 tude. It follows from this, that the moon as well as tlie 

 fun would, in twelve hours apparent time, pafs over an arc 

 of 180^, although the apparent motion of the moon to the 

 weft ward in tvi'elve hours, or 180' of fpace, be lefs than that 

 of the fun by fix or feven degrees; and fo much error would 

 this method produce, if the two places differed about 180'' 

 in longitude. 



The above example, wrought according to Mackay's rule, 

 would come out thus : 



As 26'"3' : 12'' : : li"> 30-1' to - 5'' 17"" 53-7» 

 But the correal difference as above is - 5 7 12 



Error - - o 10 41-7 

 which amoLmts to more than 2;-°, or 150 miles, in a differ- 

 ence of longitude little exceeding five hours. 



A place ncir Port-Royal, Id Jamaica, 

 loindtj 



t By interpolation jC™ yd?''; but the frailion of the fecond v/as not 



II a Mr. 



