Transactions . ng tangent-screw is nullified, and the carrying-plate, with thetheodolite locked upon it, maybe pushed unhindered along thetable-plate until, say, the vertical hair of the telescope cone-within the field of two illuminated objects placed at the bottomof a shaft below the instrument. When this has been done,the clamp-screw m is made to clamp together the carrying-plateand the upper part of Fig. 15 ; and, by turning the two hori-zontal screws of Fig. 15, the two halves of the elongated plate4 4 are made to clasp the long tangent-screw, or slow-motionscrew, bringing it into action.
Transactions . ng tangent-screw is nullified, and the carrying-plate, with thetheodolite locked upon it, maybe pushed unhindered along thetable-plate until, say, the vertical hair of the telescope cone-within the field of two illuminated objects placed at the bottomof a shaft below the instrument. When this has been done,the clamp-screw m is made to clamp together the carrying-plateand the upper part of Fig. 15 ; and, by turning the two hori-zontal screws of Fig. 15, the two halves of the elongated plate4 4 are made to clasp the long tangent-screw, or slow-motionscrew, bringing it into action. Then the heads .? s are the vertical spider-line of the theodolite is made to bisectthe two illuminated marks at the bottom of the shaft. Whenthis has been effected the screw m, Fig. 13, which is shown 904 AN IMIKOVHD lni;\| n| TRANSIT-THEODOLITE. in the sectiou Fig. is, is turned, clamping tin- plates together; so thai if an attempt were made to move tin- 9Crew-headfl s Sf, no Figs. 13-19. Hoskolds Traversing Stand. effect would be produced upon the vertical spider-line in the tele-scope. But such an act might spoil the threads of the screw. w i MPROVED l OB m OF i i; w-i 1-1 HEODOL] i 1:. Fig, 19 simplv represents the inside of the metal projectionwith a bracket, against the exterior part of which the Bhould<of the Bcrew-head & or tf press, The brack* ts resist the pnBure of the Bcrew-heads. Fig, L6 is the cover for the metallicbox of Fig. 15, and, when placed in position, ensures a smoothmotion to the clasping halves of the rectangular piece of metalinside. The long slow-motion or tangent-sere^ E F1 appears, on thewhole, to be the only mode of securing the maximum travers-ing-distance of the carrying-plate upon a table of comparativelymoderate diameter. It is true and evident that an ordinaryclamp-and-tangent screw might be applied; but, in that iportion of the space in the slit 10 10 would be occupied with? pin and the appendages of the clamp-screw,
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
