Machinery and processes of the industrial arts, and apparatus of the exact sciences (1869)
Barnard, Frederick A. P. (Frederick Augustus Porter), 1809-1889 · Washington, Govt. print. off. · leaf 614
vation; but the zen-ith and nadir points are foundwith facility. For the nadirpoint resort is had, as usual, toreflection from the surface ofmercury. For the zenith, atrough filled with water, andhaving as a bottom a plate ofglass with parallel surfaces, isplaced over the object end ofthe… … to Dabbadies Theodolite. their accuracy by observing the zenith distance of any object, and alsothat of its image seen by reflection in mercury, and adding the two.The sum should be a semi-circumference. The horizontal circle is ofthe same diameter as the vertical. The movements, both horizontaland…
Machinery · Scientific apparatus and instruments
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