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Writers on this subject are generally very prolix in describing the method in which surveyors take dimensions, use their instruments, &c. But it must be confeffed, that the practice of a few hours in the field is preferable to all the description that can be given. We shall therefore be very brief as to this particular, and shall only point out a method or two by which an irregular field may be measured, its plan delineated on paper, and its contents found.
Let the figure ABCDEF Fig. 1. represent a field, whose plan and area is required.
First, walk over the field, and make the necessary remarks on the ground, and draw an eye-draught, or a representation of the field, as exact as can be done by the light of the
eye. Divide this draught into triangles, rectangles, or trapezias, as the figure of the field directs. Erect poles at the different corners.
Choose any of the corners A for your first station ; provide yourself with a person to lead the chain, and let him have 10 arrows or iron pins in one hand, and the end of the chain int: the other. You take your station ar A, while he advances the length of the chain towards B. Direct him, by waving your hand, to the right or left, till you find him in so straight a line as to intercept the view of the pole B: Then stretch the chain at full length, and let him leave one of the arrows at the far end, as a mark for you to go to. In the mean time let him advance another chain-length towards B, directed to keep in a straight line as above. At the end of the second chain-length let him stick another arrow, and you take up the first and proceed to the next, where you are to stand till the chain is again stretched in the direction AB, and he put down another as a mark; which done, you take up the second, and proceed to the third ; and so on, till you come to B. The number of arrows taken up by you is the number of chain-lengths; and the dif
tance between the last arrow and the pole B is taken in links: Thus, when you arrive at B, you will have 6 arrows; and there are 90 links over which, together with the chain-lengths, you are carefully to mark on the corresponding line in your eyedraught. In like manner, proceed to measure the lines BC, CD, DE, EF, FA, and lastly the diagonals DB, DA, and EA.
Or otherwise, The field may be measured thus :—Step over the straight line DB; and where you imagine the perpendicular Cc will cut it, set up the theodolite, directing the fixed fights in the direction DB, and the index to C: if it cuts the limb of the instrument at an angle of 90°, you have guessed right; but if it does not, go towards B or D till you hit the point, and there fix a pole. In the same manner, find the points b, e, in the diagonal DA, and x in the straight line AF. Then measure BD, Cc, DA, Ee, FA, Ex.
Mark down carefully on the eye-draught the segments into which the perpendiculars cut the lines BD, DA, AF, also the length of the perpendiculars on the corresponding lines.
By either of these methods, the plan of the field may be protracted, and its area truly cast up as follows :-Let ABCDEF be an irregular figure, whose measures and area are required.
Whien the three sides of each triangle are given, the following method is the best for finding the area. The arithme . tical computations being intolerably laborious.
It must be observed, that, in the above example, the dimenfions are set down in links, (as being the best method) and not in chains and decimals of a chain, consequently the area is found in square links, and may be reduced to acres by cutting off five figures towards the right hand for decimals; those remain