100 Longitude determined 



Mr. Edward Pigott adopts the very fame rule for deter- 

 mining the difi'erence of longitude between Greenwich and 

 York, and ftates the refult in the Philofophical Tranfa£licms 

 for 1786, p. 417. 



Mr. Vince has inferted this rule and example in his Trea- 

 tife of Praftical Allrononiy ; but we have to regret that they 

 were not accompanied with a ftrii;^ demonftraticn. 



The Rev. Mr. Wolladon, in the appendix to his Fafciculus 

 Aftrononiicus, publiflied two or three years ago, has given 

 a rule, without dcnionftration or example, for findmg the 

 dift'crence of lono;itude from the moon's tranlits, which pro- 

 duces the fame error as Mackay's and Pigott's, although 

 worded differently from theirs. Mr. Wollafton makes the 

 firft term of his proportion apparent, and the third mean 

 time; this renders the refult erroneous. Since the motion 

 of the fun, moon, and planets are computed for apparent 

 time, and given fo in the Nautical Almanac, mean time is 

 not at all requifite for refoKing the dift'crence of longitude 

 either at fea or at land. We ihall therefore endeavour to 

 apply Mr. WoUafton's rule, according to its literal meaning, 

 for finding: the difference of longitude from the above ob- 

 lervations. 



The right afcenfion of the moon's centre on the meridian 

 of Greenwich being known, we can eafily deduce the mean 

 and apparent time correfponding to it; and in like manner 

 the mean and apparent time at the dillant meridian (8*. The 

 apparent and mean time of the tranfits of the moon's centre 

 over the meridians of A and (3, when Ilriftly computed, were 

 as follows : Apparent Time-. Mean Time. 



At A - ~ ii"* 26'" 47-81' ii*' 28" 33*5* 



Ate - - II 37 29*5 II 39 "'4 



Time later at e than at A o 10 41 '69 o 10 37*9 



From the increafe of the 

 moon's right alcenfion in 

 twelve hours - - 26 3 



Subtraft the increafe of ■ 



the fun's right afcenfion in 

 that time > - i 49-55 



The- moon's retardation 

 in twelve hours - - 24 13*3^ 



■' Mean time, however, at B. before its longitude be known, is not a 

 fair poftulatum. The method above dcmonftrated docs not require it. 



G. L. 

 Then, 



