344 Mr Galbraith on Trigonometrical Surveying 



ject, are omitted. The following are the results of all my ob- 

 servations for latitude computed in this manner. 



1 = 



Latitude of light, 56 1 59.62 



Colonel Colby's results from Kellio Law observations, 56 1 59.00 



Difference, 



0.62 



In the first six series of observations the star was bisected as accurately as 

 possible, but in the two last the wire was made a tangent to the star. 



In the seventh the star was apparently above the wire, or really below it, 

 and the latitude came out, .... 56° 1' 55".2 



In the eighth apparently below, . . . 56 2 5 .3 



Making the mean, 56 2 .25 



Difference, 10 .1 



Half difference, or half the thickness of the wire, 5 .05 



Which, applied to each of the observations, brought out the results of 

 seventh and eighth above. 



Mechain, as stated in the " Base du Systeme Metrique, 

 torn, ii." p. 393, always supposed the thickness of the wires of 

 the telescope belonging to his repeating circle to be G", though 

 Delambre found the thickness of his to be 8", 10'', or 12". 

 The thickness of the wires of my telescope, however, ought to 

 have been greater, unless they be finer, since it is less power- 

 ful than theirs. 



To conclude, in the Calton Hill Observations, volume i. 

 Introduction, page xxxviii., the latitude of the Observatory is 

 stated at 55° 57' 23".2 N., which, combined with the bearing 

 of Inchkeith, page xii. and known distance 30272 feet, gives 

 56° 2' 5''.8 N. for the latitude of Inchkeith Lighthouse, ex- 

 ceeding Colonel Colby's by 6".8, and mine by 6".2. To what 



