A treatise on land-surveying; comprising the theory developed from five elementary principles; and the practice with the chain alone, the compass, the transit, the theodolite, the plane table, &cIllustrated by four hundred engravings, and a magnetic chart . (179) Across a Talley. When a valley, or low spot, intopvenes between the two ends Fig. lie. of the line, A and Z m the |^-rfigure, a rod held in thelow place, as at B, wouldseldom be high enough tobe seen, from A, to coverthe distant rod at Z. Insuch a case, the surveyor at A should held up a plumb-hne overthe point, at arms length, and pl
A treatise on land-surveying; comprising the theory developed from five elementary principles; and the practice with the chain alone, the compass, the transit, the theodolite, the plane table, &cIllustrated by four hundred engravings, and a magnetic chart . (179) Across a Talley. When a valley, or low spot, intopvenes between the two ends Fig. lie. of the line, A and Z m the |^-rfigure, a rod held in thelow place, as at B, wouldseldom be high enough tobe seen, from A, to coverthe distant rod at Z. Insuch a case, the surveyor at A should held up a plumb-hne overthe point, at arms length, and place nis eye so that the plumb-linecovers the rod at Z. He should then direct the rod held at B tobe moved till it too is covered by the plumb-line. The point B isthen said to be in hne between A and Z. In geometrical lan-guage, B has now been placed in the vertical plane determined bythe vertical plumb-line and the pomt Z. Any number of interme-diate points can thus be interpolated, or placed in line betweenA and Z. (180) Over a hill. Wlien a liill rises between two pouits andprevents one being seen from the other, as m the figure, (the upper Fig. of which shows the hill in Elevation, and the lower part in Plan), two observers, B and C, each holding a rod, may placethemselves on the ridge, in the line between the two points, aanearly as tliey can guess, and so that each can at once see the otherand the pouit beyond him. B looks to Z, and by signals puts 0 CHAP, v.] Obstacles to I^easiirement. Ill in line. C then looks to A, and puts B in line at B. B re-peats his operation from B, putting C at C, and is then himselfmoved to B, and so they alternately line each other, continu-ally approximating to the straight line between A and Z, till they at last find themselves both exactly in it, at W and C. (181) A single person may put himself in hne between twopoints, on the same principle, by laying a straight stick on somesupport, going to each end of it in turn, and making it po
Size: 1895px × 1318px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectsurveying, bookyear18
