and Longitude of the Observatory on the Cation Hill. 261 



to connect the dome of the Observatory with the flagstaff in 

 Leith Fort, (which was known to be nearly due North,) by 

 means of angles taken at each extremity of the base. Now 

 since the latitude of the flagstaff is known with considerable 

 precision, from the observations of Captain Kater and M. Biot, 

 whose pendulum observations were made in its vicinity, it 

 follows that the latitude of the observatory, — if the requisite 

 accuracy be observed in the connecting observations, which 

 since the distance is inconsiderable do not require very fine 

 instruments, — will also become known with a hke precision. 



The latitude of Leith Fort is, by Capt. Kater, 55° 58' 41" N. 



by M. Biot, 55 58 37 



Mean of these 55 58 39 N. 

 DifF. of latitude by the above observations \ i 19 S 



trigonometrically J 



Latitude of the Observatory 55 57 20 N. 



I was considerably surprised at the difference between this 

 and the preceding result 55° 57' 27"-4, derived from the Tri- 

 gonometrical Survey, and was unable to attribute it to any 

 cause. Having suspected that it was owing to my supposing 

 in this case the earth to be a sphere instead of a spheroid, 

 I recomputed the whole with the reduced latitudes, without 

 making much difference in the longitude, but with an increase 

 of latitude of about 4-". In short, the resulting latitude was 

 55° 5T 31" N., and the longitude 12"' 39'-8 W. 



From observations made by Captain Stokes, R.N., and my- 

 selfi with a good sextant by Trough ton, it came out by the 



sun to the south 55° 57' 28" N. 



And by the pole-star to the north 55 57 12 N. 



Mean by both 55 57 20 N. 



This coinciding so exactly with that from Leith Fort, seemed 

 to be a confirmation of it, and also a proof of the errors to 

 which sextants made even by the best artists are liable, as has 

 also been shown by Capt. Foster, R.N., in Capt.Sabine's book, 

 page 408. 



I had also in the beginning of the year 1826, found it by a 



small circle to be 55° 57' 21 "-6 N. 



Andby one ofTroughton's reflecting circles55 57 19 '3 N. 



Mean of these is 55 57 20^ N. 



From a consideration of all these circumstances, I was in- 

 clined with some confidence to adopt 55° 57' 20" N. to be 

 the true latitude within a second or two, though I could not 



account 



