The great triangulation was the first point attended to. “That wonderful specimen of skill, the scaffolding on and around the cross of St. Paul’s, put up in the spring, was the main station for observations. The summits of Primrose and other hills, the towers,” steeples, “and roofs of churches, the parapets or terraces of public buildings or houses,” were made “available as the sites for signal-staffs, visible from each other and from St. Paul’s.”[3] By these observations, “the relative angular positions” of the several points were obtained, from which, as the bases of the work, a detailed survey was made, embracing not only the principal streets and squares, but the minutiæ of alleys and single buildings. Of every street the slope or ascent was ascertained, and also the exact height of every spot above the assumed datum or base-line.[4] The benchmarks to show the permanent points of the survey and levels were cut in stone, or on the most prominent objects, by the sappers, who, though not brought up to that work, became very expert in the use of the mallet and chisel. At least twelve parties with twelve-inch instruments were scattered to the most conspicuous places in the metropolis and its vicinage, to complete the observations; and sergeant James Donelan, with the great three-feet instrument, visited some of the old stations celebrated by the labours of General Roy and other officers, to check the smaller triangles formed by the operation of the twelve-inch instruments. Some of those stations were at Hanger’s Hill near Twyford, Banstead Downs, Severndroog Castle on Shooter’s Hill, &c. The survey, including the city, extended to a distance of eight miles in every direction from St. Paul’s.[5] London was unaccustomed to see soldiers employed in so important a work as the metropolitan survey, and much excitement was caused by their unobtrusive and peaceful operations. The jealousy of a class of surveyors was at once called into angry activity, and under the name of the “Associated Civil Surveyors,” they formed themselves into a body, and opposed by meeting, petition, and remonstrance, the continuance of the sappers on the duty.[6] The Metropolitan Commissioners did the Association the honour calmly to investigate their grievance; but from the lucid and truthful statements of Mr. Edwin Chadwick and others, the continuance of the sappers on the duty was confirmed and justified, not only on the score of competency, but of policy, from the disciplined experience of the men, and the perfection of the Ordnance system of responsibility and resource.[7]