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 maps, the publication of which was, however, suspended during the continuance of the war. In 1811 appeared the third volume of 'Trigonometrical Survey of England—An Account of the Trigonometrical Survey extending over the period 1800-1809. By Lieut.-colonel Mudge, Royal Artillery, and Capt. Colby, Royal Engineers,' the first two volumes of the work containing accounts of the previous surveys reprinted from 'Philosophical Transactions.' Meanwhile, in July 1809, Colonel Mudge had been appointed lieutenant governor of the Royal Military Academy, Woolwich, and Colby became the chief executive officer of the survey.

In 1813 it was decided to extend the measurement of the meridional line between Dunnose and the mouth of the Tees into Scotland, in combination with a mineralogical survey entrusted to Dr. McCulloch. In that and the following year Colby and his chief assistant, James Gardner, were busily engaged in selecting stations in the south-west of Scotland, and observing from them with the great theodolite belonging to the survey. The Waterloo year brought extra work at the Tower map office, and the Scottish observations, completing the connection between Cumberland, Isle of Man, part of the north coast of Ireland and the south-west of Scotland as far as Ayr, were carried out by Gardner, but in 1816-17 Colby was again in the field carrying the triangulation round the eastern coast towards the Orkneys and Shetland, and in the latter year, in conjunction with Gardner, measured the base-line of Belhelvie Links, near Aberdeen, the only base-line in Scotland. He was also engaged in observations in Shetland with M. Biot, who had been deputed by the French Institute to make pendulum and other observations there in connection with the prolongation of the arc of the meridian, the measurement of which had been carried from the Balearic Isles, through France, to Dunkirk. Unfortunately, owing to petty causes, which have been discussed at some length by Colby's biographer (, Mem. of Colby, pp. 73-84), there was an utter want of harmony between the two observers. Colby, however, afterwards accompanied General Mudge to Dunkirk, and took part in the observations made, in conjunction with MM. Biot and Arago, with Ramsden's sector, which was set up in Dunkirk arsenal. In 1819 Colby was again engaged in Scotland, the season's work commencing, early in May, on Corrie Habbie, Banff, and ending in Caithness at the end of September. One of his subalterns, the late Lieutenant-colonel Dawson, has left some reminiscences of Colby's extraordinary activity and of the arduous character of the survey duties in the highlands (ib. pp. 131-53). During the summer, when exploring the eastern side of Inverness, Ross, and Caithness, and the mainland of Orkney, with a party of artillerymen, and afterwards the western sides of Ross and Skye with a fresh party, Colby traversed on foot 1,099 miles in forty-five consecutive days, including Sundays and other rest days, besides scaling many heights, as in the Coolin range in Skye, the ascent of which involved some mountaineering skill. While thus employed in Scotland Colby was made LL.D. of the university of Aberdeen and F.R.S. Edinburgh.

Early in 1820 General Mudge died, and the Duke of Wellington, then master-general of the ordnance, after consulting Sir Joseph Banks and other scientific authorities, appointed Colby to succeed him at the head of the survey (Mem. of Colby, pp. 106-7). On 13 April 1820 Colby became a fellow of the Royal Society of London. Later in the same year Lord Melville nominated him to a seat on the board of longitude, which he retained until the board was dissolved by act of parliament in 1828. He also became an associate and afterwards an honorary member of the Institution of Civil Engineers, in the proceedings of which he always continued to manifest active interest. Living constantly in London, then the headquarters of the survey, and possessing, in addition to his pay, moderate private means, he was a most untiring worker in the cause of science. His name appears among the proprietors of the London Institute, in Finsbury Circus, as early as 1818. He was one of the founders of the Royal Astronomical Society, and with Colonel Mark Beaufoy, Dr. Olinthus Gregory, Troughton, the mathematical instrument maker, and one or two more fellows of the Royal Society, was charged with the task of framing rules and regulations for its government. He was also one of the early members of the Athenaeum Club. After General Mudge's death there was a cessation of the mountain work of the survey; but in 1821 Colby was employed in making observations in Orkney and Shetland, and on the two lone islets of Faira and Foula; and in 1821-3 he was deputed by the Royal Society, in conjunction with Captain H. Kater, late of 12th foot, an Indian geodesist of great experience, to cooperate with MM. Arago and Matthieu, acting on behalf of the French Institute, in verifying the observations made forty years previously for connecting the observations of Greenwich and Paris. The results are given in 'Philosophical Transactions,' 1828. To facilitate the observations across the Channel