plied by the feet in a four-pole chain, will give the feet and decimals of a foot. Thus, Ch. L. In 17. 21. of two-pole chains, how many feet? To reduce feet and inches to chains and links. Reduce the inches to the decimal of a foot, and annex that to the feet; that divided by the feet in a four-pole chain, will give the four-pole chains and links in the quotient these may be reduced to two-pole chains and links, if required, by prob. 2. Thus, Feet. Inches. In 217. 9 how many two-pole chains? 60 66)217.75(3.29 of four-pole chains, or 197 Ch. L. 655 6. 29. 61 HOW TO TAKE A SURVEY BY THE CHAIN ONLY. PROBLEM I. To survey a piece of ground, by going round it, and the method of taking the angles of the field, by the chain only. Plate VI. fig. 6. Let ABCDEFG be a piece of ground to be surveyed: beginning at the point A, let one chain be laid in a direct line from A, towards G, where let a peg be left, as at c; and again, the like distance from A in a direct line towards B, where another peg is also to be left, as at d: let the distance from d to c be measured, and placed in the field-book, in the second column under the denomination of angles, in a line with station No. 1; and in the same line, under the title of distances, in the third column, let the measure of the line AB in chains and links be inserted. Being now arrived at B, let one chain be laid in a direct line from B towards A, where let a peg be left, as 'at ƒ, and again, the like distance from B in a direct line towards C, where let also another peg be left, as at e; the distance from e to ƒ is to be inserted in the field-book in the second column, under angles, in a line with station No. 2; and in the same line, under the title of distances in the third column, let the measure of the line BC, in chains and links, be inserted: after the same manner we may proceed from C to D, and thence to E; but because the angle at E, viz. FED, is an exterual angle, after having laid one chain from E to h, and to g, the distance from g to his measured, and inserted in the column of angles, in the line with station No. 5. and on the side of the field-book against that station, we make an asterisk, thus *, or any other mark, to signify that to be an external angle, or one measured out of the ground. Proceed we then as before, from E to F, to G and thence to A, measuring the angles and distances, and placing them as before, in the field-book, opposite to their respective stations; so will the field-book be completed in manner following. N. B. After this manner the angles for inaccessible distances may be taken, and the method of constructing or laying them down, as well as the construction of the map, from the following field notes, must be obvious from the method of taking them. The form of the field-book, with the title. A field-book of part of the land of Grange, in the parish of Portmarnock, barony of Coolock, and county of Dublin; being part of the estate of L. P. Esq. let to C. D. farmer. Surveyed January, 30, 1782. Mr. J. D's part of Grange bounds, or is adjacent to the surveyed land from the first to the third station; Mr. L. P's part of Portmarnock bounds it from the third to the fourth station; the strand then is the boundary from thence to the sixth, and from the sixth to the first station, the widow J. G's part of Grange is the boundary. It is absolutely necessary to insert the persons' names, and town-lands, strands, rivers, bogs, rivulets, &c. which bound or circumscribe the land which is surveyed, for these must be expressed in the map. In a survey of a town-land, or estate, it is sufficient to mention only the circumjacent townlands, without the occupiers' names; but when a part only of a town-land is surveyed, then it is necessary to insert the person or persons's names, who hold any particular parcel or parcels, of such town land, as bound the parts surveyed. When an angle is very obtuse, as most in our present figure, are, viz. the angles at A, B, C, E, and G; it will be best to lay a chain from the angular point as at A. on each of the containing sides to c and to d; and any where nearly in the middle of the angle as at e: measuring the distances ce and ed; and these may be placed for the angle in the field-book. Thus, For when an angle is very obtuse, the chord line, as ed, will be nearly equal to the radii Ac and Ad; so if the arc ced be swept, and the chord line ed be laid on it, it will be difficult to determine exactly that point in the arc where ed cuts it: but if the angle be taken in two parts, as ce the arc, and the angle thence may be truly determined and constructed. After the same manner any piece of ground may be surveyed by a two-pole chain. PROBLEM II. To take a survey of a piece of ground from any point within it, from whence all the angles can be seen; by the chain only. |