11,725. Prinsep, D. G. May 21. Range-finders.-Relates to a method of and apparatus for determining the distances of objects, especially for military and surveying purposes, the object being similar to that described in Specification No. 13,915, A.D. 1892. An instrument having two telescopes, as shown in Fig. 5, or an instrument having a number of mirrors, as shown in Fig. 6, is used, at two observing-points A, B, Fig. 1, in turn. The range B C is determined by taking a point D in a line A D parallel to the line B C, such that the angle C B D is equal to the supplement of the angle C A B, so that B C = (A B)2¸A D. The range is read directly from a suitably graduated tape, having a logarithmic scale, stretched from A to D. The instrument shown in Fig. 5 has a lower telescope a', which is sighted on the distant object C, and an upper telescope a, which is sighted along the base-line and can be turned through an angle of 180‹ or reversed in its V bearing-blocks O1 to enable the back-sight along the line B D to be taken, after the telescopes have been sighted and clamped together at the station A. The instrument can turn as a whole about a vertical axis, and it may be clamped to the tripod stand by a screw e. The telescope supports are fixed to plates c1 adapted to be clamped to plates c by nuts i, engaging bolts secured to bevelled rings f and passing through washer sleeves h1. Tangent screws l engage sleeves j on plates k secured to the telescope supports, backlash being prevented by spring-pressed bolts l1. The bevelled rings fare held concentric by bevelled rings g and discs g'. The bearing-block O1 of the base-line telescope is pivoted to standards O3 and may be turned about its pivots by a pinion and a sector, a screw being provided to clamp it when adjusted. The baseline telescope may be rotated by a worm and a train of wheels. The reflecting-instrument shown in Fig. 6 has two index mirrors r, r1, placed back to back, and two horizon glasses l, s1, placed at angles of 45‹ with the axis of the instrument. The index mirrors are mounted on a pivoted plate t connected by swivelling parts v, v1, and a screw w1 to a second pivoted plate t1. The index mirrors are roughly adjusted and clamped in position by a clamping-screw y and a nut y1, the final adjustment being effected by the tangent screw w1. This instrument is graduated so that, when an observation has been made, the supplement of the angle read on one side can be read on the other side.
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