Captain Colby's activity and kindliness of disposition were not less apparent in camp than on the station-hunts. He would assist in erecting houses to "shelter the soldiers ; and occasionally join with the men iu a game of quoits, or in putting the stone or crowbar, and was a warm promoter of their feast at the close of each trigonometrical season." He was quite indifferent as to personal fame, but not so as to making known the merits of his officers, and he at times permitted them to publish portions of the work in their own names rather as principals than assistants. His command over his temper was perfect ; but he disliked to be disturbed by curious visitors when busy with observations for which he had long waited the opportunity. Once, while encamped on Slieve Donard in Ireland, the summit of Sea Fell in Cumberland became visible at the distance of 111 miles, and after many trials the instrument was brought to bear upon it. "Colby was on the point of successfully finishing his observation, which would have been a geodesical triumph, as including the longest side of a triangle ever attempted, when an officer on entering the observatory accidentally struck his elbow, and threw the telescope off the object. A momentary ejaculation of anger escaped his lips, but though he could not agaiu succeed, and the object was therefore lost, he never afterwards alluded to the subject." He was one of the party that accompanied Hint on his trip to Shetland in 1817, compliance with the wishes of the French government, one of their savants was permitted to observe on the line of the English arc A coolness however arose between Biot and Colby, and while the latter, undeterred by fog or storm, made his observations with the sector on the rock of Balta, the former carried on his pen dulum observations on the island of Uist; and Colby afterwards assisted in connecting the French with the English triangulation by the observations across the straits of Dover. [131or.] Iu ]S20 Captain Colby was elected a Fellow of tho Royal Society ; he took an active part in establishing the Astronomical Society; and General Mudge having died, he was appointed his successor as super intendent of the Survey, and in the Board of Longitude. In 1821 he was promoted to the rank of major, and in 1824 he undertook the survey of Ireland. In this work the usual mode of proceeding was modified : the survey was made dependent on actual measuremeuts with the chain, with a trigonometrical point fixed for every 400 acres; and the whole series of opemtione was so ably combined that one portion became a check on the other, and the utmost accuracy was arrived at, although the number of persons employed .exceeded two thousand, mostly from the native peasantry. A change was also made in the publication : the sheets were engraved on a scale of six inches to the mile, all the principal farms, fields, and inclosures being repre sented, so that the maps have ever since been regarded by the govern ment, land-proprietors, and surveyors, as authentic plans of all the estates in the country. Poor-law boundaries, townlands, land
improvements, engineering works, and the Irish census, have all been based upon them. They are comprised in 1939 sheets.
In 1825 Major Colby became lieutenant-colonel, and in that year he obtained the Duke of Wellington's sanction for raising and training three companies of sappers and miners to aid in the Irish survey, as the want of really efficient assistants was felt at first as a serious hindrance to the progress of the work. In the course of the operations Colby measured a base-line of eight miles, on the south shore of Lough Foyle, with 'compensation-bars' which be had himself invented. He had carried on'a series of experiments on the heating and cooling of metal rods, and he succeeded in constructing a bar of brass and iron in combination, the extremities of which remained always the same distance apart whatever might be the temperature. Such is the exactitude obtained with this apparatus that it has since been used in measuring a base of eight miles at the Cape of Good Hope, in the re-measurement of the English bases, and in those required for the great arc of the meridian in India.
In 1838 Colonel Colby resumed the triangulation of Scotland, which had been suspended; and from this date up to his promotion to the grade of major-general in 1846, when by the regulations of the service his connection with the survey ceased, he continued his usual active and energetic superintendence of the various operations. He brought the engraving of the English maps to an excellence never before achieved. The seconds of latitude and longitude were marked on the margins, and be co-operated with Sir Henry De la Bache in introducing the geological facts and features which have since become so important a part of the survey. He took the necessary measures for a series of tidal observations round the coast of Ireland, for the purpose of establishing a true datum level : "the most important series of tide observations," says the astronomer-royal, " that has ever been made." Through all his scientific career General Colby never sacrificed duty to selfish considerations ; and his rare administrative abilities, and sound judgment combined with high principle, enabled him to accomplish well all that he undertook. He had resources ready for every emergency, and the hardy perseverance that triumphed over all obstacles. He died at Liverpool on the 9th of October 1852, leaving a widow and seven children. He was a fellow of the chief scientific societies of London, Edinburgh, and Dublin; LL.D. of Aberdeen, and a knight of Denmark.
(Prof. Papers Roy. Eng. ; Proc. Roy. Soc.; Monthly Not. A stron. Soc.)