i 



[ 195 ] 



ful application of it by Mr. E. Pigott, then of York, in de- 

 ducing the difference of longitude of his obfervatory from that 

 of Greenwich. Both he and Mr. E. Pigott, to whom indeed 

 we principally owe the advantages that may, and moft pro- 

 bably will accrue to geography from this method, befides 

 flating the general proportion, mention, that when the moon's 

 rate is irregular attention fhould be paid to that circumftance; 

 and Mr. Vince further adds, that the accuracy of the refult 

 will be greater, if we allow for the difference of the increafe 

 of the moon's A. R. in the intervals of the paffages of the 

 two meridians over the moon and ftar, for that the obferved 

 difference is not accurately the true difference, when the two 

 meridians pafs the ftar. 



As the fixed ftar is the permanent and immutable term of 

 the comparifon for both meridians, Mr. Vince very juftly 

 refers the difference of A. R. that is to be determined to the 

 adual moment under each meridian, that thefe meridians apply 

 to the ftar and not to the moon's enlightened limb. The 

 queftion then, in its moft fimple and accurate form is, when 

 the meridians fucceflivcly apply to the fame ftar, what is 

 i/ien the precife difference of the A. R. of the moon's enlight- 

 ened limb from that of the ftar for each meridian ? 



To elucidate this point — Let us fuppofe the paffages to be 

 obferved by a clock, moving fydereal time, and the meridian 

 applies firft to the moon's enlightened limb ; its A. R. is then 



Bb 2 denoted 



