. The railroad engineer's practice . water, and a line was stretched from it to the abut-ment. The assistant then took his rodman in a boat, witha rod ten feet long, which was applied successively to theline, beginning at the abutment, a common pin beingthrust through the line at the front end of the rod, towhich the hind end was then held. This measurementwas not in a straight line, because the string sagged. Thiswas corrected by using inversely Weisbachs formula forthe length of a suspension-bridge cable, having the span 2 T^and versin. X = -; the versin. being estimated by holding a level r
. The railroad engineer's practice . water, and a line was stretched from it to the abut-ment. The assistant then took his rodman in a boat, witha rod ten feet long, which was applied successively to theline, beginning at the abutment, a common pin beingthrust through the line at the front end of the rod, towhich the hind end was then held. This measurementwas not in a straight line, because the string sagged. Thiswas corrected by using inversely Weisbachs formula forthe length of a suspension-bridge cable, having the span 2 T^and versin. X = -; the versin. being estimated by holding a level rod at the middle and sighting from oneend to the other, observing where the visual line cut therod. This second measurement, by which the bridge wasbuilt, differed about one foot from the triangulated dis-tance, which was allowed for in the framing of the next example is that of the Delaware River bridge, 91 on the North Pennsylvania Railroad route to New was devised by Mr. D. McN. Stauffer, the engineer in charge. He took advantage of the cold winter weather, when theriver was frozen over, and measured the spans carefully onthe ice, marking the different centres of the piers A, J3, C,etc. He then put iron plugs, one inch in diameter, fourfeet long, on the shore at D, E, F, etc., in line, and atequal distances apart. He set his transit over TJ, sightedon A, and put in a plug on the opposite side of the river atG, similarly 7/was put in on the line -E^ produced ;etc. The piers were built on wooden jilatforms, whichwere floated into place when the ice had disapi:)earcd. Thecentre line having been drawn on each platform, andmarked by a long pin on each side, and a short one withred flannel attached in the centre, a transit at P served toput it in proper line, while one at D, E, I\ etc., success-ively served to correctly place the centres. An unforeseendifficulty arose from boys stealing some of the iron plugs,but the ground being frozen the holes remained, and t
Size: 1874px × 1333px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookcentury1800, bookdecade1880, bookidrailroadengineer00clee
