. The elements of railroad engineering . ographer first measures the distance of his eye abovethe ground, which is a constant quantity, to be subtracted fromall the rod readings. He then stands at a station and keepsthe rodman at right angles to the line of survey. The rod-man, having reached the end of a slope, i. e., a point, wherethe rate of slope changes, he holds his rod at the point andthe topographer takes the reading with the hand this reading the topographer subtracts the constant,i. e., the height of his eye above the ground. The remain-der is the difference between the el
. The elements of railroad engineering . ographer first measures the distance of his eye abovethe ground, which is a constant quantity, to be subtracted fromall the rod readings. He then stands at a station and keepsthe rodman at right angles to the line of survey. The rod-man, having reached the end of a slope, i. e., a point, wherethe rate of slope changes, he holds his rod at the point andthe topographer takes the reading with the hand this reading the topographer subtracts the constant,i. e., the height of his eye above the ground. The remain-der is the difference between the elevation of the surfacewhere the topographer stands and the surface where the rod-man stands. The tapemen having measured the distancebetween the two points, the rate of slope is determined bydividing the distance measured by the difference in eleva-tion. This method of taking slopes or cross-sections isillustrated in Fig. 296. Let A be Station 156 of a preliminary survey. The topog-rapher stands at A. The rodman goes to the point i>,. Fig. 296. where the slope changes, holding his rod, which measures16 feet in length, at that point. The topographer sightswith his hand level and reads feet on th^rod. From thisreading he mentally subtracts ft., the height of his eye G7G SURVEYING. above the ground. The remainder, ft., is the difference inelevation between the points A and B. Meanwhile, the tape-men find that the horizontal distance from A to ^ is 31 rate of the slope A B is the horizontal distance betweenthe points A and B, .31 ft., divided by , their difference inelevation. The quotient is and the slope is recorded 2 2 — -^. The topographer then moves to the point /), and the rodman goes to C, which is so much lower than B thatwith the rod held on the ground the line of sight will passover the top of the rod. Here the rodman gives a *Mong or high rod. Planting himself firmly at C, he raises therod until the line of sight, from the topographers
Size: 2420px × 1032px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
