And LONGITUDE of ABERDEEN. 141 



much more to be depended on than thofe inferred from the ob- 

 fei'vations of the third and fourth fateliites, I have therefore re- 

 jected the obfervations of the two lafl. This I was inchned to 

 do, partly from the difagreernent of the refults of the corre- 

 fponding obfervations of thefe two fateliites, and partly upon 

 account of the fmallnefs of the number of correfponding obfer- 

 vations. Indeed, as thefe two fateliites take a confiderable time 

 to immerge into, and emerge out of the fliadow of Jupiter, and 

 as the flate of the atmofphere, at the times of obfervation at 

 Greenwich and Aberdeen, may be very different, and as powers 

 will be applied to the telefcopes according to the flate of the . 

 atmofphere, it is not wonderful, that there lliould be a con- 

 fiderable difference between the refults of the adlual obfer- 

 vations ; and hence the propriety of reje<5ling the obfervations * 

 of the third and fourth fatellite will be obvious ; efpecially in the 

 cafe when the correfponding obfervations are very few, and the 

 number of immerfions unequal to that of the emerfions. The 

 longitude of this place, as deduced from the comparifon of the 

 ad^ual obfervations of the firft and fecond fateliites of Jupiter^ 

 made here and at Greenwich, feems to be lefs than the truth, or, 

 at leaft, lefs than what I had been accuftomed to flate it ; but 

 the near agreement of the final refults of each of thefe fateliites 

 is really furprifing. 



Of all the other obfervations which I have compared, I have 

 fent you only two, as being the mofl to be relied on, namely, a 

 folaf eclipfe, and an occultation, befides a lunar eclipfe, which I . 

 had publiflied formerly in my T^reatife on the Longitude^ and 

 which is not far from being a mean between the refults of the 

 other obfervations. I had, indeed, only one other occultation, 

 of which the obfervations at Greenwich and Aberdeen were 

 complete, namely, that of /3 >? of 15th Odober 1790 ; my 

 other obfervations of that kind, being either incomplete, or ha- 

 ving no correfponding obfervations at Greenwich. 



I 



