Page 2 Advertisements Column 1

Wellington Independent, Volume XXIV, Issue 2806, 6 March 1869, Page 2

Instructions for the Guidance of the Staff of Surveyors under the Provincial Government of Wellington. Survey Office, Wellington, N.Z., November 25, 1868. A uniform system of Surveying essentially requisite for the prosecution of General Surveys. 1. For the economical and efficient prosecution of a general survey it is essentially requisite that a uniform system of operations should be determined and acted upon. Though various systems may be adopted to suit different localities, each having for its object to meet the requirements of population and to combat with the natural difficulties encountered with in the physical features of the country to be operated upon, yet the cost of surveys will be found to be proportionately more expensive the less efficient the system that is adopted. In order, therefore, to perfect the present system of surveying as practised in this Province the strict attention of the officers of the staff is directed to carry out the following instructions which also contain a general outline of the principles employed. Primary object of the Surveys. Chain Surveys liable to great accumulation of error. 2. The division of land into small sections being the chief object of the surveys in this Province, and as the districts may be said to consist generally of hilly and in most cases wooded country it is obvious that to find how many times a certain measure, such as a chain, is contained in a given piece of ground becomes a matter of some difficulty, and that by trusting entirely to chain measures under such circumstances, the accumulation of error must necessarily be great, thus rendering these surveys incapable of union "inter se" or of harmonious combination with other surveys. Triangulation the best method for Surveys of an extended character. 3. Recourse must therefore be had to an accurate system of triangulation over such parts of the country as afford facilities for such a process, thus the wooded districts eventually became incorporated by an external network of triangles, precluding the errors before mentioned being transmitted beyond the precincts of their origin. 4. But even in the prosecution of a trigonometrical survey, which beyond dispute is the only safe basis for operations of an extended character, due regard should be given to the principle of working from " whole to part " and not from " part to "whole"; by the former method any errors become subdivided, but by the latter an undue accumulation becomes promulgated in the extension of the work. The object of Major and Minor Triangulation. 5. Hence arises the necessity of applying two distinct series of trigonometrical operations, viz., the Major Series, embracing a large tract of country in as few triangles as the power of the instrument at command and the natural features of the country will permit, thereby attaining the shortest lines of connection ; and the Minor Series, the triangles of which derive their bases from the Major sides, and are made to be entirely dependent upon them. In turn these Minor sides afford checks to the chain measurements of the Sectional Surveys, and thus a system is initiated by means of which any undue errors become certainly detected, and limits to the intrusion of small unavoidable errors can be assigned. The Major Triangulation, although assimilating in principle, not to be compared with the Great Trigonometrical operations of other countries. 6. It must be clearly understood that the Major Triangulation here spoken of is not of such a character as to be in any ways compared with the "Grand Trigonometrical Surveys of Great Britain or of India". The refinement and care bestowed upon these scientific operations were for the express object of measuring "Arcs of the Meridian" in order to determine the figure and magnitude of the "Earth", a purpose which can only be undertaken by wealthy nations and which would practically be of no service in meeting the wants of a new country, where the primary object is to execute expeditious and economical surveys so as to facilitate the sales of land and the settlement of the country. Cost of Triangulation and statement of errors exhibited in the work. 7. In all National Surveys it is the custom to assign certain limits to the errors committed in the prosecution of the works, and this limit is apportioned according to the amount of accuracy known to be attainable in practice. By assimilating the principles of the Great Trigonometrical works to what is here called the Major Series, but without attempting to attain the same refinement and results, a considerable amount of accuracy is arrived at, and attended only with a moderate expenditure. It has been proved in this Province that the Major Series of triangles, the sides of which averaged from 8 to 10 miles, and executed with an 8-inch Transit Theodolite, exhibited errors less than six inches per mile at a cost of 14 shillings the square mile ; and that the errors of the Minor Series of triangles, averaging from 2½ to 5 mile sides, and performed with ordinary 5 or 6 inch theodolites were less than 2 feet per mile when costing £2 14s. the square mile. As it would be impossible even in a champaign and well favored country to attain such constant accuracy solely by chain measurements, these results may be satisfactorily considered to be far within a limit of error that could safely be assigned.