Transactions . Octant in Use. into 360°; also the four cardinal lines are marked upon it. Dis a circular writing-table placed under the divided circle andextending concentrically beyond it. E is a bound book, partof the instrument, to which all the other parts, previously de-scribed, are firmly attached. The book wTas intended for writ-ing and drawing. FG represents a tube or telescope, attachedby means of a short axis and appendage to the side of the book. h; REMARKS ON MINE-SURVEYING INSTRUMENTS. A vortical semicircle was also fixed to the underside of the tele-BCOpe, and the vertieal angles
Transactions . Octant in Use. into 360°; also the four cardinal lines are marked upon it. Dis a circular writing-table placed under the divided circle andextending concentrically beyond it. E is a bound book, partof the instrument, to which all the other parts, previously de-scribed, are firmly attached. The book wTas intended for writ-ing and drawing. FG represents a tube or telescope, attachedby means of a short axis and appendage to the side of the book. h; REMARKS ON MINE-SURVEYING INSTRUMENTS. A vortical semicircle was also fixed to the underside of the tele-BCOpe, and the vertieal angles were indicated by swingingpendulums suspended from the short horizontal axis previouslynoted. NQP represents the upper partofthe stand, with jointsfor giving horizontal motion to the instrument. The cylindri-cal part at N appears to have been divided. When in use, thetelescope of this instrument was directed to an object and theindex bar, B, was then moved by hand round the divided circle, Fig. Albrechts Instrument. until the magnetic needle pointed north and south; and thebearing angle of the observed object was then obtained fromthe divided circle. The instrument* shown in Fig. 106f seems to be an im-proved form and probably derived from that of Fig. 145. Inan old English book,! translated from the French, a graph-ometer, or surveying horizontal semicircle, is represented with * Geometric, Forensis, Reinhold, 1781, p. 106 and plate xii. t Raymonds Discussion of Scott, Trans., xxx., 799. X Stones translation of Bion, on Mathematical Instruments, p. 121, 1723. RBMARK8 ON MINE-8URVBYING [NST^UMENTS. II double Bights, the one fixed and the other movable, as in theinstrument of Fig. l(>. bul without vertical motion for eitherof the Bights. The upper telescope of Fig. L06, however, baaa vertical motion, proving thai it is of more recent construc-tion, and approaching towards the simplest form of idea of attaching a vertical arc to the telescope of the in-s
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
