After as many stations as may be thought fit have been determined in the manner just described, and the lengths of the lines (that is, the sides of the triangles) connecting them have been computed, the survey nifty be completed by actual admensurements with the chain, in each triangle eepstrately.
Poles having been set up at the angular points of every triangle, the surveyor and his assistant set out from any one of these points, as n, and proceeding across the ground, measure the whole length of any one line, as B C, leaving pickets in the ground in the direction of the line at or near every place where it crosses a hedge, as at a, a stream, as at 11, a road, or any other object which is to be introduced in the plan. Should it happen that the line n c, or any part of it, coincide with the direction of a road, °Meta, as they are called, are measured perpendicularly to the line, on one or both sides of it, in order to express the distance from the line to the sides of the road, or to the hedges or walls along those sides ; these offsets (which are shown at c, d, and e) should be measured at the end of every chain's length, and particularly at every point in the station line opposite to which there is a remarkable object, as a house, a gate, or merely a bend in the direction of the road. Thus, when the work is laid down en paper, the precise form and breadth of the road will be expressed.
In like manner the other side, A c, of the triangle, is to be measured with the chain ; pickets aro to be left in the ground at or near every place where a stream, as at li, a road, or a hedge crosses the side of the triangle ; and offsets, as at k, 1, in, are to be measured from the station line to and aerate such boundaries as may be nearly parallel to any part of its direction. The like process is to be followed on each side of every triangle; the measured lengths of the sides of each triangle should then be compared with the computed lengths; and if the difference be not considerable, the work may be considered as having been performed with suffioient accuracy ; otherwise the operations must be repeated, in order that the sourer of the error may be detected.
To carry on the work in the interior of any angle, as A n F, the surveyor, where it is possible, measures with the chain the direct dis tance from the pickets in one side of the triangle to the pickets in another side, as air, pq ; and since these pickets are supposed to have been placed near the intersections of boundary-lines (roads, streams, or hedges) with the sides of the triangle, the lines last measured will, at least in part of their length, coincide with or be parallel to some of the boundaries in the interior of the triangle; and the precise figures of such boundaries will be determined as before by offsets from the measured line to all the principal bends. The length of each of these secondary station lines may be obtained by trigonometry, since the line is the base of a secondary triangle of which the two sides arc known, being measured parts of two sides of the principal triangle, and the angle included between those sides has been found by the theodolite; therefore the measured length of this line, on being compared with the computed length, will afford an additional test of the accuracy of the work.
In measuring these secondary lines within each principal triangle, pickets must, as before, be left in the ground in the direction of the line, at or near places, as at r, where hedges, walls, &c., cross the line ; and from one of these pickets, r, to another, as t, lines are afterwards to be measured (these being as much as possible in or near the direc tion of other boundaries), till at length the whole interior of each principal triangle will have been divided into several secondary triangles, all the sides of which have been measured. These sides, by means of the offsets which have been measured from them, deter mine the figures of all the natural and artificial boundaries within the tract of ground.
The situations of the buildings are also determined by offsets from the station lines nearest to them : the ground plans of the more con siderable edifices, as churches and mansions, are measured, and the directions of their fronts With respect to the meridian are ascertained by a compass or otherwise. .