GB165915A - Improvements in or relating to surveying instruments - Google Patents

Abstract

165,915. Shaw, J. P. March 6, 1920. Theodolites; angle-measuring instruments.-Relates to instruments for the measurements of angles and distances, of the kind comprising a telescope with an extension at right-angles to its axis, this extension having at its outer end a reflector attached to a pivoted lath &c., which reflector co-operates with a fixed reflector within the telescope to produce an image which can be brought into coincidence with a .direct image by turning the lath. The invention consists in the manner of graduating the circles &c. and in the general construction of the instrument. As shown in Figs. 1 and 2, each of the circles of the instrument carries two concentric scales, of equal width, the outer scale E being a scale of tangents whilst the inner scale F is divided equiangularly. Only one quadrant is shown in the Figure. To facilitate the reading by means of a micrometer of fractions of the smaller divisions on the scales, the actual scale markings consist of the diagonal lines connecting opposite ends of successive divisions as shown in Fig. 2. The distance to be subdivided by the micrometer is then the constant width of the scales. The micrometer comprises a microscope - 5 with pointers 6, Fig. 3, mounted so as to be traversed radially across the scales by a differential screw 8, 9 having an evenly divided head 10. The microscope is moved until the pointer intersects the diagonal graduation line on the scale, the traverse for a complete turn of the head 10 being equal to the radial width of the scales. The instrument comprises a telescope 21, Figs. 5 and 7, rotatable in altitude and azimuth and having at right angles to its axis a rigid tube 24 carrying at its outer end H a reflector 23 attached to a pivoted lath 28. The field of the telescope is partly occupied by a. reflector 25 receiving light directed along the tube 24 by the reflector 23 so that two images of an observed object are seen in the eyepiece 20. These images can be brought into coincidence by turning the lath 28, the angle of rotation being read on scales 29 graduated as above described. For levelling the instrument the horizontal circle 36 carries two diametrically opposite pins 52. One of the pins engages in a bracket 44 pivoted at 43 in a channel iron 42 secured to an arm 48. The bracket carries a toothed sector 45, Fig. 9, which can be rotated by a worm 46. The other pin 52 passes into a block 50, Fig. 8, which is pivoted at 51 in a fork 49 which can be adjusted vertically by a screw 53 bearing in an arm 54. The arms 48, 54 may be integral with a ring 56 which can be clamped to the tripod head by screens 57.