Jnd LONGITUDE of JBERDEEN. 141 



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

 fervations of the third and fourth latellites, I have therefore re- , 

 jeded the obfervations of the two laft. Tlijs I was incUned to , 

 do, partly from the difagreement of the i-efuks of the corre- 

 fponding obfervations of thefe two fatelhtes, and partly upon 

 account of the fmallnefs of the number of correfponding obfer- 

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

 to immerge into, and emerge out of the fhadow 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 tliere lliould be a con- 

 fiderable difference between the refults of the adtvial obfer- 

 vations ; and hence the propriety of rejecfling 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 

 adual obfervations of the firft and fecond fateilites of Jupiter^ 

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

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

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

 is really furprifing. 



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

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

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

 had publiflied formerly in my Treati/e 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 w of 15th Oiftober 1790 ; my 

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

 ving no correfponding obfervations at Green-wich. 



I 



