Page 2 Advertisements Column 2

Wellington Independent, Volume XXIV, Issue 2812, 20 March 1869, Page 2

errors exhibited lie within the limits stated in paragraph 49 they may be apportioned amongst the several distances according to the following rule: as the sum of all the chained distances of the traverse is to the whole error in northing and southing or easting and westing respectively, so is each chained distance to its correction, additive or substractive from the particular northing or southing, easting or westing between the two stations, and then the sum of the meridian distances so corrected will agree with the check data. Cases in which this system of Traverse may be modified. 53. When all the coordinates on the meridian have been referred to some one point on the survey, they afford an easy method for the deduction of the bearing and distance between any two of the points, and thus great facilities are acquired for setting off and running intersecting lines at certain intervals apart, to represent the divisional lines of the several purchases or applications for land. But when the object of the traverses is simply to delineate the course of streams and other features forming what may be termed indefinite boundaries in in order to compute the areas of blocks, but without requiring to base thereon the dimensions of definite boundary lines or of sectional sub-divisions, then the same amount of accuracy is not sought for, and it will only be necessary to plot the traversed stations by the ordinary method of protraction. Standard length of chain to be obtained from the Survey Office, and its uniform length preserved during survey operations. 54. The instrument used for traversing is generally a 4-inch theodolite. The length of the chain used is a subject of primary consideration; the correct standard length as obtained from the Survey Office, must be carefully preserved by laying down blocks to mark this length on the occasion of every shift of camp, and the chain should be tested with this measure after every day's work. The neglect of this precaution causes a vast amount of inconvenience besides making use of a wrong measure, which in itself is a very reprehensible proceeding; and should this measure be constantly varying all efforts to test the accuracy of the work become unavailable notwithstanding the care that may have been bestowed in its execution, and thus the survey is rendered incapable of being harmoniously combined with other surveys. Reduction of lines measured over uneven surfaces to the horizontal measure. 55. The dimensions of all lines are to be given as if measured on the horizontal plane, and the area of land is to be computed on the same basis. The measurements of lines, therefore, over the surface of hills and slopes of various inclinations require to be reduced to the horizontal measure, either by calculation or by the more practical method of holding the chain or part of it at a time as nearly horizontal as may be judged and letting a plum line fall from the elevated end to the surface of the ground. Field Book. 56. The field book is to be paged and indexed, and should be kept in a neat and explanatory manner the reverse case being a sure indication of carelessness and neglect. Memoranda are to be entered in pencil at the time and place of observation, and are not to be entrusted to memory nor noted on slips of paper, as such are liable to become lost, and thereby entailing the necessity of going over the work again. The pencil remarks are to be inked in as soon as practicable, and no erasures are permitted, nor are leaves allowed to be torn from the book. The field book is ruled with a double line down the centre of the pages, between which the chain distances are entered, and commencing at the bottom of the page. The offsets are noted to the right or left of this central column, according as to whether they lay on the right or the left hand of the chain line, and opposite to the distance that they have been measured or estimated from. A circle round a distance thus (1500) denotes the total length of line between two stations, and the commencement of a new line should further be marked by a line drawn across the page. Each traverse station should be numbered, and the bearings observed from them entered on the left hand side of the page. Always write down the backset from which the meridian is derived at each station thus B. B. station 1=221° 40' and whenever the backset of the last station observed from is rejected for that derived from a more reliable source, or otherwise when the bearing as brought up by traverse is to undergo correction by a reset of the instrument upon a bearing known to be a more correct one, the back reading of the last station, as well as the fore reading to the station in advance, should be recorded in order to obtain the requisite data for the correction of the errors committed in observing the bearings up to this point as explained in paragraph 50. If this remark is neglected there will be no evidence forthcoming to prove the constant direction of the meridian throughout the survey. The field book is to be deposited in the Survey Office on the completion of the map. Traverse stations to be permanently marked at certain intervals. 57. Every traverse station should be temporarily pegged during the prosecution of the work, and eventually at intervals averaging 40 chains along the traverse, three of the stations lying in consecutive order should become permanently marked with blocks 4 inches square, and eighteen inches long, but if there is an absence of Trigonometrical points throughout the survey the size of these blocks ought to be increased to six inches square and two feet in length. One of the stations is to be chosen whenever practicable within the view of a Trigonometrical station. These precautions will furnish to a future Surveyor a point of departure, and a correct bearing of the meridian in terms of the survey for commencing additional work without entailing the necessity of re-execu-ting much of the traverse work in order to arrive at such data.