The theory and practice of surveying. Designed for the use of surveyors and engineers generally, but especially for the use of students in engineering (1886)
Johnson, J. B. (John Butler), 1850-1902 · New York, J. Wiley & sons · leaf 365
or vertical pointings will be found indis-pensable. In sighting up or down a shaft theordinary form becomes useless when the lineof sight passes inside the upper plate of theinstrument. A prismatic eye-piece, Fig. 90,will overcome this difficulty for upward sights,but the survey cannot be carried… … Fig. 90.
Surveying
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