A treatise on surveying, comprising the theory and the practice (1906)
Gillespie, William Mitchell, 1816-1868, Staley, Cady, 1840- · New York D. Appleton · leaf 416
swith a hole through the head to support them fromthe top. Where the roof is high, it is difficult toget up to the station to put the string through thehole. If care is taken not to make them too heavy,they can be supported with the device mentioned in Art. 839. Another objection is the additional… … be easily read by lamplight, and that the marking should be verydistinct, on account of the imperfect light available. Again, theinstrument should not be too heavy, as there is often difficult climb-ing to be done over fallenrock and other mine debris.If the instrument be easilydetached from its…
Surveying
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