Herschel, John F. W. (John Frederick William), Sir, 1792-1871 · London : Longman, Rees Orme · leaf 87
ian of the place of observation. Theextremities of the axis are formed into cylindrical pivotsof exactly equal diameters, which rest in notches formedin metallic supports, bedded (in the case of largeinstruments) on strong piers of stone, and suscept-ible of nice adjustment by screws, both in a… … the latter adjustment the axis is brought precisely intothe east and west direction, the criterion of which isfurnished by the observations themselves made withthe instrument, or by a well-denned object/ called ameridian mark, originally determined by such observ-ations, and then, for convenience…
Astronomy
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