A treatise on levelling, topography, and higher surveying (1876)
Gillespie, W. M. (William Mitchell), 1816-1868, Staley, Cady, b. 1840, ed · New York, D. Appleton and company · leaf 42
e upside down,end for end, and halfway around horizon-tally, and sight again.Half the sum of thetwo readings is thecorrect one, no matterhow much the instrument is out of adjustment (assuming thecollars to be of equal size) ; for the errors then cancel eachother. This is the one used principally in…
Surveying
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![An illustration from Bicknell's village builder. Elevations and plans for cottages, villas, suburban residences, farm houses [etc.] also exterior and interior details for public and private buildings, with approved forms of contracts and specifications. Containing fifty-five plates drawn to scale (1872)](https://img.insideoutlibrary.com/img/200/ia-bicknellsvillage00bick-195-183.webp)