« PreviousContinue »
tended over the south of Scotland, but it was done roughly and with imperfect instruments, and the results were never published. Thus it was, however, that practical experience in the art of surveying happened to be possessed in a high degree by military officers, and that, when survey operations on a grander scale and for higher purposes were resolved upon, military officers were naturally called upon to superintend them. A project for a general survey of the country was formed in 1763, but fell aside, to be renewed in 1783. In this year a representation was made from France to our Government, of the advantages which the science of astronomy would derive from the connection, through trigonometrical measurements, of the Observatories of Greenwich and Paris, and the exact determination of their latitudes and longitudes. The French had by this time carried a series of triangles from Paris to Calais, and what they proposed was that the English should carry a similar series from Greenwich to Dover, when the two might be connected by observations from both sides of the channel. The scheme was approved of by George III., and the English Survey begun by the measurement of an initial base-line at Hounslow Heath by General Roy—the foundation of the triangulation since effected of Great Britain. While, then, the officers who, from the first, superintended the geodesical operations in Great Britain belonged to the Engineers, and had been trained to the work in the interests of war, it is yet true that the British Survey, of which the measurement of Hounslow base was truly the commencement, had its origin in philosophical operations conducted in the interests of science, and directed mainly to the determination of the figure of the earth. The measures employed in measuring the Hounslow
base were Ramsden's steel chain, 100 feet long; Riga pine wood rods, 20 feet long; and glass rods, 20 feet long, enclosed in wooden cases for protection. These measures were, all of them, liable to expansion and contraction from changes of temperature ; while the rods were, moreover, affected by changes of the hygrometer. The rods, it was found, gained 1th of an inch in length after a week of rain ; which on the length of the base would have caused an error of about 45 inches. On the other hand, the chain, while it possessed many good qualities, was attended by not inconsiderable difficulties in the use. The base, however, was as carefully measured as with the instruments it could be, everything being done to prevent or allow for instrumental errors : its length, reduced to the level of the sea, was about 6}th miles. A chain of triangles was then carried from the Hounslow base to Dover, connected with the Greenwich Observatory at one end, and at the other with a base of verification, which was next measured with Ramsden's chain at Romney Marsh. This base was about 5} miles long, and differed only by a few inches from its length as determined by triangulation from the Hounslow base. This completed the operations immediately required for the connection of the Observatories of Greenwich and Paris. But the survey of Great Britain, which from the first had been contemplated, being now resolved upon, the triangulation which had so far been made for purely scientific purposes, formed the basis of the survey of Kent and Middlesex. The Hounslow base was remeasured in 1791, General Roy having died in the previous year; and in 1792, and the two following years, the triangulation was extended southwards to the Isle of Wight. In 1794 a base of verification was measured on Salisbury
Plain with the steel chain, and the triangulation thence continued westward along the whole southern coast, till the triangles embraced Dorset, Devon, Cornwall to the Land's End, and even the Scilly Isles. The work had now assumed the distinct character of a national survey, under the direction of Colonel Mudge. By 1800 the larger triangles had in many districts been filled in, and several counties had been mapped. In 1801 the triangles were carried northwards, and a base measured in North Lincolnshire on Misterton Carr, it being part of the director's plan that a new base, for verification, should be measured every hundred miles. By 1806 the triangles embraced part of North Wales, and a base had been measured on Rhuddlan Marsh, near St Asaph.
While these operations were being carried on, others of a more purely scientific nature were conducted by the officers superintending the survey. The direction of the meridian had been determined at Dunnose and Beachy Head as early as 1794, and calculation made of the length of a degree of a great circle perpendicular to the meridian in latitude 50° 41'; great interest being taken at the time in the question, Whether the length of a degree increased in approaching the equator ? The direction of the meridian had subsequently been traced far northwards, and in 1811 it was determined to prolong the line into Scotland. The French, who had moved the English to begin the work, were urging them on in its prosecution at once by precept and example. A meridian had been traced through France, and extended by Biot and Arago to the southernmost of the Balearic Isles. This arc it was proposed, with the assistance of the British geodesists, to terminate at Yarmouth. On the other hand, it was proposed that the meridional line which had been traced through England should be followed northwards through Scotland to the Shetland Islands. On this being done, the French and English arcs together would stretch over upwards of 20°. These were great conceptions, and the operations for their realisation increased in difficulty the farther northwards they were extended. They not only required great skill in scientific observations, but the employment of immense personal energy. Captain, afterwards Colonel Colby, had by this time been long associated with Colonel Mudge in the survey, and possessed all the qualifications necessary for its delicate but arduous duties.
By the year 1817 the triangulation had been extended as far north as Aberdeen, near which, on the Belhelvie Sands, was measured the only base-line measured in Scotland. The triangles included the whole country northwards from Cumberland, embracing the Isle of Man and part of the coast of Ireland. In 1819, the year in which Drummond and Colby became acquainted, the latter had commenced operations north of Aberdeen, his “ head-quarters” in the beginning of the season being placed on Corrie Habbie, a mountain in Banffshire. The survey officers were by this time a numerous and important body. Besides the staff employed in the work of triangulation and base measurements, there was another employed in filling in the spaces within the larger triangles by a system of smaller ones, and yet another employed as draughtsmen in embodying in maps the results of the measurements and calculations. The permanent head-quarters of the service were established at the Tower in London, where all the necessary offices for the work were provided. During the summer and
autumn months the officers engaged in the measurements were in the field or on the mountain. In winter they were quartered in London, engaged in calculations and in improving the apparatus employed in the
survey. The life of the officers who went “ out" in the surveying season was an exceedingly trying one. a life of hardship and exposure ; of frequent privation and fatigue ; occasionally of hazard and adventure ; a life to try the strongest, and certain to injure the less robust. The duties were twofold-station-hunting, and the work of observation. A country was to be rapidly traversed—for every day in the season was of valueand hill after hill to be ascended till the most eligible for a station of observation was discovered. The station was always on a hill top or mountain peak. The observatory once erected there, the officers made it their home; some of them made expeditions thence for the purpose of erecting flag-staffs on the hills as points for observation ; while others, through all weathers, kept by the theodolite, ready to avail themselves of every able opportunity of observation. There is an admirable account of a surveying season in the Highlands in a letter from Major Dawson to Lieutenant-Colonel Portlock, published in extenso in Portlock’s “Memoir of Colonel Colby.” It was the season of 1819, from which Colby was just returning, when Drummond became acquainted with him. As germane to my present purpose I cannot refrain quoting here some extracts from this letter. In describing Colby's life in one surveying season, it describes the life which Drummond led for several seasons in “station-hunting" and the work of observation on mountains; and is all the more valuable as, during the years when he was leading this sort of