The chain lines in this field-book are the sides of a polygon, and the lengths of all these sides except one, and all its interior angles except the two at the extremities of the unknown side, are given; and these are sufficient for constructing it or for calculating its contents. The first angle 12° 10′ gives the bearing of the first chain line; and as the inclination of each of the successive chain lines to the preceding is given, the bearings of all the rest are given. The direction of the meridian can therefore be drawn through the first station, as it will lie to the left of the first chain line, making with it an angle of 12° 10′, as AN' in the plan. Then any line, NS, on any convenient part of the plan parallel to AN', will be the direction of the meridian. The second chain line lies to the left of the first; and hence the angle of the polygon is here a re-entrant angle, and 360° 156° 15′ — 203° 45'. When any boundary line crosses a chain line, as KL in the plan, an oblique line is drawn on the right and left opposite to the number which denotes the distance of the point of intersection from the station at the beginning of the line. Thus, opposite to 300 and 640, between 04 and 05, oblique lines are drawn for this purpose. When any internal boundary, fence, or other important line, is passed, as at E in DF, a straight line is drawn on both sides of the corresponding distance in the chain line, and when the line is straight to the end, these lines are marked S, as in the field-book opposite to 780, between 0 and 0; and oppo04 site to 725, between 0 and 0; and these two points determine the line. Thus, RS is determined by the points E and H. When an offset is not at right angles, but in another direction, as along a fence, the mark is placed over it, as 100 at 780 between 04 and 05 The plan is given below, and the student is requested to construct it from the field-book, after examining this plan. 46. Construct the plan, and compute the area, of a small farm from the following field-book. Area 71 ac. 2 ro. 28.9 pls. 47. In the following field-book, the expression "in line with fence," with dots... on the left or right of the chain lines, means that the point arrived at in the chain line is in the same line with some straight fence on the left or right, which does not extend so far as the chain line. In the subjoined plan, the continuous lines represent the fences, and the dotted lines represent the lines that are measured, and also the extension of the lines of some of the fences. |