GEOGRAPHICAL POSITIONS. 16 



NOTES. 



1. Edinburgh. — The geographic position of the Astronomical Observatory on the 

 Calton Hill, was given by the Ordnance Survey, ui 1816, as longitude 3° 10' 54" W. But 

 this result appears to have been affected by a singular cause, which demonstrates the 

 refinement to which these operations have been carried. It was afterwards found that 

 the attraction of the mass of Arthur's Seat (a hill to tlie southward of it) had drawn the 

 plumb-lme (or zenith sector) towards it, and thus produced an error of several seconds in 

 the calculation. This error was established in 1839, by Professor Henderson, who made 

 the. longitude 3° 10' 45". Some interesting experiments were made on this curious point, 

 during the late Ordnance Survey, by which, not only the effect of mountainous masses on 

 surveying operations was ascertained, but also the density of the earth was established. 



Since the completion of the triangulation of the Ordnance Sm-vey, a new principle for 

 ascertaining the difference of longitude has come into operation. The extension of the 

 electric telegraph has placed Greenwich Observatory in direct connection with most other 

 important Observatories ; and in April, 1857, a series of instantaneous signals was trans- 

 mitted between it and Edinburgh, under the direction, at the latter place, of Professor 

 Piazzi Smyth, the worthy son of the excellent Admiral Smyth, well known to all sailors. 

 The results of these experiments placed its longitude at 12™ 43-048^ in time, or 3° 10' 45-72" 

 in arc, confirming Mr. Henderson's previous result. It is now, however, considered to 

 be in long. 3° 10' 54". 



2. Orkneys, &c. — The Orkney Islands were originally surveyed by the elder Mackenzie. 

 Murdoch Mackenzie, F.K.S., was the first surveyor of our coasts, who conducted his 

 operations on right principles. His first work, Orcndia, or the Orkney IsUnuh, ivith j)art 

 of Lewis, was done at his own expense, and was published in 1750. Its accuracy is great, 

 and its utility is still unequalled. He was afterwards employed by the king in surveying 

 the coasts of Ireland, &c. Later in life his works were attacked, most unjustly, by 

 Dr. Anderson, which called forth suitable replies and justification from John Clark, in 

 1785. This work may be said to have commenced the Admiralty Surveys. 



3. West of Scotland, and the He'brides. — Up to a recent date the charts of the 

 whole of this portion of our shores remained nearly in the same state that they were left 

 by Murdoch Mackenaie. Notwithstanding their imperfections, however, statistics have 

 shown that no great detriment to navigation arose from their so-called " disgraceful " 

 condition, an epithet which took twenty-five years of organized surveying parties, and 

 ^250,000, to remove. 



We may here add that they were examined, and partially surveyed, by Captain Joseph 

 Huddart, whose charts were long of good service. Captain Huddart also surveyed a great 

 portion of the St. George's Ch&miel at the expense of the predecessors of the publisher 

 of this work. 



The Variation of the Comi>«IS on tlie Coasts of Scotlsuid k now decreasing at il.c rate 

 *v( about 9' per annum. 



