Land Surveying and Levelling

Land Surveying and Levelling

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 edition. Excerpt: ...and if, for example, the staff reads 2-61, this is booked as a back sight and shows the line of collimation to be at a level of (2-61 plus 137-86) 140-47 ft. above the given datum. Now the contour being 20-47 ft. below this, it is evident that the line of collimation must be lowered in position before a level staff, 14 ft. or 16 ft. long, could be read by the instrument when set up level. A fore sight for the purpose of connecting the levels is taken in such a position that the staff is read near the top, say at 12-85, and the level is re-set in a new position to read near the foot of the staff, say 1-83. Reducing the book we find the level of the point upon which we changed the level of the line of collimation to be 127'62. The position of this point is not recorded in the level book, as it is not required to be indicated upon the plan, but we have by this means fallen from a known level of 137'86 to a known level of 127-62, and have now only to fall 7-62 ft. lower to find the position of a point upon the required contour. Adding 7'62 to 1'83 we obtain 9-45 as the necessary reading upon the staff to give the height required, and this figure is then booked for reference in the intermediate column. If the staff reads less than 9-40 the staffman is told to go to lower ground, whereas if the staff reads more than 9-50, the staffman is told to come to higher ground. Except where extreme precision is required, the divisions indicating hundreds may be disregarded in reading the staff, but it is well to observe them in the Level 'Book for sake of accuracy in connecting the levels. So far as points of equal level are concerned, a reflecting level would serve to fix them approximately, but the most accurate work is secured by the aid of a Dumpy level as...show more

Product details

  • Paperback | 78 pages
  • 189 x 246 x 4mm | 154g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 123649895X
  • 9781236498953