THE SOURCE OF THE NILE. 161 



(almoft infurmountable) in diftinguilliing the diviilon of 

 the penumbra. 



There certainly is one error very apparent, in meafuring 

 the bafe betwixt Syene and Alexandria ; that is, they were 

 not (as fuppofed) under the fame meridian ; for though, to 

 my very great concern afterwards, I had no opportunity of 

 fixing the longitude at this firft vifit to Syene, as 1 had done 

 the latitude, yet on my return, in the year 1772, from an 

 cclipfe of the firft fatellite of Jupiter, I found its longitude to 

 be 33 30'; and the longitude of Alexandria, being 30 iG' y'\ 

 there is 3 14' that Syene is to the eaftward of the meridian 

 of Alexandria, or fo far from their being under the fame 

 meridian as fuppofed. 



It is impomble to fix the time of the building of Syene ; 

 upon the mofl critical examination of its hieroglyphics and 

 proportions, I fhould imagine it to have been founded fome 

 time after Thebes, but before Dendera, Luxor, or Carnac. 



It would be no lefs curious to know, whether the well, 

 which Eratolthenes made ufe of for one of the terms of the 

 geodcfique bafe, and his arch of the meridian, between 

 Alexandria and Syene, was coeval with the building of that 

 city, or whether it was made for the experiment. I fhould 

 be inclined to think the former was the cafe ; and the pla- 

 cing this city firft, then the well under the tropic, were with 

 a view of afcertaining the length of the folar year. In fliort, 

 this point, fo material to be fettled, was the conftant objec> 

 of attention of the firft aftronomers, and this was the ufe of 

 the dial of Ofimandyas ; this inquiry was the occafion of the 

 number of obelifks raifed in every ancient city in Egypt. 



Vol. I. X We 



