A complete treatise on practical land-surveying, in seven parts; . consequently, (25 X 4 -f- 2 =) 102 links must be takenfrom A C; hence AB = 2448 links, the line required. Proof.—As 1 : 2550 :: .96005 (the nat. co-sine of 16° 15): links — A B. A Table for reducing hypothenusal to horizontal Lines. Different Altitudes of Hills Links to be subtracted from each Chain measured upon the Surface. Deg. Min. Links. 5 44 h 8 6 1 11 28 2 14 4 3 16 16 4 18 12 5 19 57 6 21 34 7 23 4 8 24 30 9 Deg. Min. j Links. 25 51 10 27 8 11 28 21 12 29 32 13 30 42 14 31 47 15 32 52 16 33 54 17 34 55 18 35~
A complete treatise on practical land-surveying, in seven parts; . consequently, (25 X 4 -f- 2 =) 102 links must be takenfrom A C; hence AB = 2448 links, the line required. Proof.—As 1 : 2550 :: .96005 (the nat. co-sine of 16° 15): links — A B. A Table for reducing hypothenusal to horizontal Lines. Different Altitudes of Hills Links to be subtracted from each Chain measured upon the Surface. Deg. Min. Links. 5 44 h 8 6 1 11 28 2 14 4 3 16 16 4 18 12 5 19 57 6 21 34 7 23 4 8 24 30 9 Deg. Min. j Links. 25 51 10 27 8 11 28 21 12 29 32 13 30 42 14 31 47 15 32 52 16 33 54 17 34 55 18 35~ 54 19 36 52 20 37 49 21 38 44 22 39 39 23 40 32 24 Note.—To construct the above Table, suppose the base A B, in the pre-ceding triangle, to be = , and the hypothenuse A C = 100 ; then, byTrig, as 100 : 1 :: : .995, the nat. co-sine of the angle B A C= 5° 44.—In the same manner, the rest of the angles are obtained, by different opera- third, &c, Part IV.) LAND-SURVEYING, 175 A Quadrant for taking the altitude of Hills, Steeples?> By those who do not wish to incur the expense of a Theo-dolite, a Quadrant may be made of about twelve inches radius,by which the altitude of a hill, steeple, &c. may be taken to atolerable degree of accuracy. The arc A B must be correctly divided into 90 equal partsor degrees ; and numbered from right to left. Upon the radiusA C, must be fixed two brass sights, a and b, through each ofwhich must be made a very fine hole; and from the centre Cmust be suspended a plummet, by a thread of fine silk. 176 land-surveying. (Part IV. Note.—In taking the altitude of an object, the quadrant is commonly heldin the hand ; but it is much better to fix it to a staff, which may be done bymeans of a nail, passing through the quadrant and staff, upon the end ofwhich must be screwed a small nut. To take the Altitude of a Hill with the Quadrant. Upon the top of the hill fix an object, exactly as high asyonr eye will be from the ground, in tak
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