C.—3

2

Triangulation. Referring to previous annual reports, it will be unnecessary to again explain the basis or standard astronomical data which govern this work and enable it to be prosecuted from independent points, wherever wanted, with the certainty of the parts forming an harmonious whole. Could the surveyor have either a new country to himself entirely for a time, or an old country already settled, his plan of procedure would be a comprehensive network of triangulation first and details afterwards, but in the settlement of a country both processes must for a time proceed together, care being taken to keep the tringulation in advance of the settlement survey. This has now been more than accomplished for New Zealand, the triangulation having been extended over all the settled districts, and over many of those yet to be settled. There is now a continuous network of triangulation extending lineally a thousand miles from Mangonui to Stewart Island. There are however still considerable areas on the flanks of this network which await the extension of triangles over them. The operations last year have been principally in the Provincial Districts of Auckland, Taranaki, Westland, Marlborough, Canterbury, and Otago, an area of 5,495 square miles having been included within the sides of triangles. The best test of the general accuracy of a triangulation is the close on a base of verification, or the close of one triangulation on another; any radical error either in the measure of the initial base or in the triangles themselves is sure to be revealed when the work is so checked and verified. The closures last year have been almost in every case very satisfactory. Mr. C. W. Adams' triangulation of the Upper Waimakariri closed to -18 links per mile on the base of verification. Mr. Cussen extended a triangulation across a piece of difficult country between the Bay of Plenty and Tuhirangi Circuits, closing on a side of the major triangulation, 7£ miles long, with an error of 3 - 4 links, or "46 links per mile. This result is gratifying, not only in itself as a part of the year's operations, but is another proof of the excellence of the major triangulation conducted in the Auckland District under Mr. Heale, when Inspector of Native Surveys. In Marlborough District, Mr. A. D. Wilson has extended a network of triangles over a large area of country from Awatere across to the coast-line at Cape Campbell. He is now working up results, and during the next season he will continue the triangulation down the coast-line past the Kaikoura to a close on the triangulation in the Amuri. His observations have diminished the hitherto accepted altitudes of Mount Tapuaenuka, the summit peak of Inland Kaikoura Eange, by 238 feet, his mean height being 9,462 feet, as against 9,700 feet, the height given on the Admiralty Chart. The progress of the trigonometrical surveys is revealing very material errors in the nominal altitudes of many of the principal points : thus, last year, Mount Cook was reported as nearly 1,000 feet lower than the Admiralty determination; and it is now found that Tongariro and the Kaimanawa Range, in the North Island, are nearly 1,000 feet higher than the altitudes hitherto given. These variations are easily accounted for and understood when it is considered that the heights have been obtained in a variety of ways, by different methods, on no definite plan, and often imder circumstances adverse to correct work; indeed, the wonder is they come so near sometimes to the trigonometrical determinations. In Westland, Mr. G. E. Roberts has continued the triangulation of the West Coast; he has now got well down towards Jackson's Bay. The accuracy of this officer's work, and the progress he has made, despite the difficulties of a very rugged bush country and a wet climate, entitle him to the warmest commendation. The coast-line from Milford Sound northward to Earewell Spit was never properly surveyed, the maps of it are simply a patchwork of good and bad work, with the result that the position of many points is very doubtful, and the coastline is distorted at places on the maps to make it fit in. The triangulation will set this right, and the topographical survey, which is carried on simultanously, will give a correct map of the country inland for fifteen or twenty miles. It would be too tedious to mention all the officers who have been engaged in trigonometrical and topographical work, but an acknowledment is due to Messrs. Cussen, Baber, Roberts, and Wilmot for the exposure and hardships they had severally to undergo