A treatise on surveying, comprising the theory and the practice ; (1887)
Gillespie, W. M. (William Mitchell), 1816-1868, Staley, Cady, 1840- [from old catalog] ed · New York, D. Appleton and company · leaf 121
Fig. 141. … the other end of the sights to be directed to the same object.Suppose that the needle would have pointed to 45° if the line ofsight had passed through the center ; the needle will now pointto 44°, the error being doubled by the reversion, and the truereading being the mean. This does not, however,…
Surveying
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![An illustration from L'optique divisée en trois livres : ou, l'On démontre d'une maniere aisée tout ce qui regarde 1. la propagation & les proprietez de la lumiere. 2. La vision. 3. La figure & la disposition des verres qui servent à la perfefectionner [sic] (1682)](https://img.insideoutlibrary.com/img/200/ia-loptiquedivise00ango-329-36.webp)
