i6o DETERMINJtlON of the LJTITUDE 



Determination of the Longitude of the Obfervatory at Aber- 

 deen by a Chronometer, conftrudled by Mr Arnold of Lon- 

 don*. 



The chronometer was fet to mean folar time at Greenwich, 

 1 6th June 1788, and loft 7 ".5 in eleven days. It was fent to 

 Aberdeen by fea ; and being compared with the Obfervatory 

 clock, 15th July, it was found to be 7' 26'.6 faft, and was lofmg 

 6*.'4 daily : It is hence probable that the motion of the fliip had 

 altered its rate. Now, fuppofmg this alteration to have com- 

 menced when the fhip left London, which was on the 8th of 

 July, its error at that time, for the meridian of Greenwich, 

 would therefore be if^.o ; from this time, till 15th July, it loft 

 4^".8, (=:6'''. 4 X 7,) its rate being fuppofed uniform. Hence its 

 error, for the meridian of Greenwich, 15th July at noon, was 

 — 59'''. 8. But its error, for the meridian of the Obfervatory at 

 Aberdeen, at the fame time, was + 7' 2 6*. 6. Hence the longi- 

 tude of Aberdeen, in time, is 8' 26''''.4 weft. 



This laft method of afcertaining the longitude of Aberdeen, 

 although it agrees very well with the former, yet it is not to 

 be fo much depended on, as there are fome fuppofitions intro- 

 duced which may be objedled to. 



From a comparifon of the preceding refults, it may be prefu- 

 med, that the longitude of this place, in time, is probably not lefs 

 than 8' 18*, as deduced from the obfervations of the eclipfes of 

 the firft and fecond fatellites of Jupiter, nor greater than 8' 36'', 

 as inferred from the folar eclipfe of 3d June 1788. The diflFe- 

 rence between thefe limits is only 1 8" in time ; which in this 

 latitude does not amount to two miles and an half. Upon ac- 

 count of the near agreement of the refults of the folar eclipfe 

 and occultation, as well as from other obfervations, I am led to 



i :-^A?r : believe 



* e Hi t . i I 



I I 



» See Theory and Praflice. of finding tiie Longitude, &c. vol. I- p. 3q8. 



