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 140
and reads to 10 seconds of arc. ADJUSTMENT, USE, AND CARE OF INSTRUMENTS. IO9 There is a mirror M (Fig. 22), called the Index Glass, rigidlyattached to the movable arm MA, which carries a vernierreading on the graduated limb CD. There is another mirror,/, called the Horizon Glass, rigidly attached… … Fig. 22. through the clear portion of the mirror /on through the tele-scope to the eye at E. Also, a ray from an object at O strikesthe mirror M, is reflected to m, and then through the telescopeto E. Through one half of the objective come the rays fromHj and through the other half the rays from O,…
Surveying
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