পাতা:সূক্ষ্ম কালি কষা.pdf/১৩

A SURVEYOR'S HAND-BOOK. s. INTRO DU(XTJON. A SUMMARY OF RULES FOR CALCULATING AREAs. 1. THE most convenient and accurate method for calculating areas is to divide the field into triangles and taking half the products of the perpendiculars and the bases thereof. Practically fields may not be square or rectangular, in which case, the length into the breadth will give the area. Irregular fields should therefore be divided into convenient triangles and lengths of the bases and the perpendiculars should be measured by a scale on the plan—if not obtainable from the fieldbook—and the sum of half their products will give the required area. There is only another figure, which a surveyor may find in calculating area viz.: a field which is bounded partly by a curve. In such a case, Simpson's Rule might be applied. It is as follows:–Divide the portion of the boundary of the figure which is straight, into any even number of equal parts; at the points of division draw straight lines at right angles to it to the curve. These are called ordinates; add together the first and last ordinates, which are, in this case, nothing, two times the total of other odd ordinates and four times the total of all even ordinates; take one-third of the sum and multiply it by the common distance between the ordinates, But the better course would be to divide this figure also, into as many triangles as possible, till the portions of the curve may be so reduced as to be considered as straight lines, forming a side or sides of approximate triangles. Thus it is found that in calculating areas, two dimensions have always to be found out and dealt with. 2. To find out area in acres, roods and poles. I. When measurement is made by a Gunter's chain of 66 ft. :— (a) If the two dimensions are found to be of one or more full chains, multiply them and divide (if possible) the product by ten ; the result will be acres. If not possible or if there is any remainder, multiply by 4 and divide (if possible) by 10; the result will be rood.