340 Mr Galbraith on Trigonometrical Surveying 



great precision. In making the usual deductions of latitudes 

 geodetically for other points connected with these, what ought 

 our surveyors to do ? In my opinion, an inquiry ought to be 

 instituted to discover whether one or both of these places are 

 likely, from their geological position, to be affected by the 

 irregularities of local attraction. If so, from the sudden fall 

 of the ground north of the Calton towards Leith, with the 

 Firth of Forth following in succession, the Calton is likely to 

 be more affected than Kellie Law, situated nearly in the 

 centre of the east nenk of Fife, 



From these considerations, it occurred to me that Inch- 

 keith would probably be a good point to test the accuracy of 

 these views. I therefore applied to the Ordnance Map Office 

 for their results, which, with the permission of Colonel Colby, 

 were readily granted me, while my friend Mr Stevenson very 

 kindly gave me an introduction to the principal light-keeper, 

 to allow me such accommodation as the lighthouse afforded. 

 I am consequently under great obligations to both these gen- 

 tlemen for giving every facility to me in their power, to 

 enable me, as far as possible, with the instrument which I 

 possessed, to examine this curious anomaly. 



1 had, during some years past, determined the latitude of 

 my own residence to be 55° 56' 57".89 N. from some hundreds 

 of observations by the same circle I was now about to use. 

 By a trigonometrical operation compared with, and checked 

 by, the results in Professor Wallace's Treatise on Geometri- 

 cal Theorems and Formulas, lately published, page 140, I re- 

 duced this latitude to the Observatory, by adding 25".67 to 

 it, which gives 55° 57' 23".56 N. for the latitude of the Ob- 

 servatory, exceeding Professor Henderson's result by a small 

 fraction of a second only. This circle, then, gives results, when 

 the observations are very numerous, that accord with those of 

 the mural circle when employed in its vicinity, and the ques- 

 tion with me was, Would it likewise do so at Inchkeith, where 

 it is probable local attraction would be insensible ? For this 

 purpose, I resided on the island a few days, during which I 

 made several observations on the heights in the vicinity of 

 Edinburgh, already partly given in the preceding portion of 

 this paper, as well as some on the latitude, but I have chiefly 



