634
THE NEW ZEALAND GAZETTE.
[No. 30

SCHEDULE.

As witness the hand of His Excellency the Governor, this eighteenth day of May, one thousand eight hundred and eighty-six.

P. A. BUCKLEY.

Survey Regulations under “The Land Act, 1885.”

WM. F. DRUMMOND JERVOIS,
Governor.

IN pursuance and in exercise of the powers and authorities conferred upon me by the fourth section of the “Land Act, 1885,” I, William Francis Drummond Jervois, the Governor of the Colony of New Zealand, do hereby make the following regulations for the purposes of the said Act, namely:—

SETTLEMENT SURVEYS.

MINOR TRIANGULATION.

1. THE surveyor should be provided with a 5in. theodolite, standard steel band, thermometer, prismatic compass, aneroid, and straining apparatus. Survey districts shall each comprise an area of 12½ miles square or thereabout, which are apportioned on the maps of the standard survey of the colony.

2. In triangulating a survey district or a portion thereof, a level piece of ground should be chosen—centrical, or most convenient—for the measurement of a base. The line should be chipped or otherwise prepared, and should be of about 2 miles in length. Before commencing the measurement of the base, a chain’s length should be laid down on the ground by standard steel band—adjusted to 62° Fah.—for reference. The band should be tried on this at the commencement and ending of actual measurements. During measurements temperatures are to be observed (the co-efficient to be used may be ·000006 for each degree) for correction of expansions and contractions of band, which have to be applied in calculations. The steel band when in use is to be held with a tension of 14lb., and the ends marked on flat-boards spiked into the ground. These flat-boards should have a hollow filled with lead, for receiving the end marks made by a sharp instrument. Three boards are used, the last being always carried forward. Measure the base thus: forward and back again, and take the mean. Angles of inclination should be observed, so that a vertical section of the line can be made for reduction to true level. Bases of verification are to be measured in the same way. When for any reason it is inconvenient to prepare the ground, a base line may be measured 2ft. or 3ft. above the surface, the steel band being supported on adjustable stands.

3. Should a major triangulation cover the area to be surveyed, no measured base will be necessary, for the distances of minor trigonometrical stations will be obtained by breaking down the larger triangles.

4. Trigonometrical stations should be, as near as practicable, about 2½ miles apart. To extend the true meridian from the geographical into the settlement survey, one of the geodesical or major trigonometrical stations is to be chosen as origin, the instrument being set on the bearing given in the standard maps. This done, if a theodolite, with three verniers, is being used, three sets of observations are to be taken to each minor trigonometrical station in view; the vernier A of instrument being placed at zero, 40° and 80° of the horizontal limb respectively—thus nine readings will be observed; but if a plain theodolite is being used, four sets of observations are to be made, the vernier A of instrument being placed at zero, 45°, 90°, and 135° respectively—thus eight readings will be observed on different parts of the limb. In each set the instrument should be turned in one direction until the back station is again bisected with the initial reading of the vernier. This done, the next minor trigonometrical station is to be observed in like manner, so as to complete the three angles of each triangle. Points are to be selected so as to have well-conditioned triangles—no angle being less than 30° nor greater than 120°, unless under very exceptional circumstances. As far as practicable, crossing triangles are to be avoided, or one bearing over another bearing; each triangle should appear on the maps distinct from others. When the series of triangles of a minor triangulation extend a greater distance than 20 miles from the base, the first favourable opportunity of measuring a base of verification should be taken. Vertical angles are to be observed between stations with similar care, the datum being taken from the standard maps.

5. The differences of the means of bearings will give the value of the angles of each triangle; these are to be summed up, and the correction noted, one-third of which + or – for calculation is to be applied to each angle. The logarithms should be taken out to seven places, and the angles to seconds. This being completed, and so all the sides and angles known, all stations are to be calculated on the meridian and perpendicular of the initial station of the survey district with the same accuracy, and a table prepared. From this table the skeleton maps are constructed by standard scale and beam compass. The difference of height between two trigonometrical stations is to be obtained from the vertical angles taken at both stations.

6. In executing the survey of an isolated section or of a block, if a base has to be measured, minor triangulation is to be carried from it to the land to be surveyed; but, if the work is to be based on major triangulation already executed, triangles are to be carried thence in the most direct course to such survey, and no more work is to be executed than is necessary for checking the chain measurements.

7. With average care the degree of error in minor triangulation need not exceed 2 links to the mile, so the extreme error allowable, but only in very special cases, is 4 links to the mile; the error in the summation of angles of a triangle need not exceed 30″, and the extreme error allowed in special cases is 60″. All work having error in excess of this will require revisal.

8. Combined with trigonometrical operations, a topographical survey is to be made showing the disposition of natural features and their names, also tracks, ridges, rocks, streams, forests, pas, remarkable objects, natural and artificial, &c.; and a map of the same is to be constructed. For altitudes vertical angles are to be observed to prominent objects, such as peaks, passes, valleys, and confluence of streams. A surveyor with a good eye can make a serviceable sketch-map from his trigonometrical stations, and by theodolite alone, by taking the bearings, cross-bearings, and tangents, with estimated distances of objects; but, if the country be intricate, bearings from intervening positions can be taken where necessary. Prismatic compass and aneroid may be used when the theodolite cannot be had recourse to.

9. Minor trigonometrical stations should be constructed in the following manner: Gas-pipes, 2in. internal diameter, are cut to 2½ft. lengths; these are inserted into cast-metal plates with sockets, secured by an iron pin. The alphabetical letter of the station is to be cut on the upper end of the pipe with a cold-chisel. The pipe thus constructed is sunk in the hole prepared for it to a depth of 2ft. 3in., with the metal plate downwards. The hole is then refilled, and the loose soil firmly beaten down. Round this a circular ditch, 20ft. diameter, 1ft. deep, and 18in. wide, should be dug. On high rocky peaks where a ditch cannot be dug a circle of stones should be made. When in use, the trigonometrical tube should have a pole carrying a black-and-white flag inserted into it and properly stayed; or a light wooden pyramid may be erected over it, with calico tightly tacked or battened to the sides all round for about 3ft. from the top. It is not desirable to build trigonometrical mounds, but in low positions these may be necessary, and of which the surveyor will exercise his own judgment. If mounds be built the exterior rim had better be of stone with earth in the centre. In positions where the nature of the soil may require modifications special directions will be given.

10. The trigonometrical work only is to be mapped on one sheet, which should show trigonometrical stations (two concentric pink circles) with their alphabetical letters and local name, the base line in red, other lines in black, bearings observed from each station (in blue), calculated mean distances (black), the observed angles (in the middle of each triangle) summed up (black). A few of the streams should be shown, so as to localize the trigonometrical stations readily. There should also be a note giving the results of