Patent GB-190105806-A (GB)
Title: Improvements in or relating to Geodetical Instruments.
Inventor: GRUBB HOWARD
Filed: 1901-03-19
Granted: 1902-03-19
Abstract: 5806. Grubb, Sir H. March 19. Compasses, magnetic; levels; clinometers; rangefinders; surveying-instruments.-Relates to the application to geodetical instruments generally of the sighting-devices described in Specifications Nos. 12,108 and 22,127, A.D. 1900, [Abridgment Class Ordnance &c.], and also of the reflecting- film, of sulphide of lead, described in Specification No. 4420, A.D. 1901. Fig. 3 shows a section of a prismatic compass. The compass card m, of some transparent substance such as celluloid, with an annular scale, is mounted upon a pivot m<1> below a sighting-tube g. The object observed is sighted directly through apertures r, r<1>. The graduations of the card, in the form of clear or white lines on a dark ground, are projected virtually upon the object by the following optical system :-A fiducial and sighting line at h<3> is illuminated by a reflecting-prism c<3>. Above this is mounted a compound reflecting and converging prism o, which with a lens p' parallelizes the light from the sighting-line and the compass scale opposite. The parallel rays fall in succession upon a reflecting-prism s and plate q, and thence enter the eye collinearly with those from the object observed. Parallax is thus avoided. Fig. 5 shows a modification, in which the rays from the object are collineated with those from the scale on the compass card by a reflecting-prism t<3> and plate q. The rays from the sight are collineated by a lens p. In some cases the collineation of the light from the sight is effected by a concave semi-transparent reflecting-surface. A clinometer consisting of a vertical graduated and weighted card combined with the sighting-system is also described. For graphometers, the sighting-system, of either the reflecting or refracting type, is mounted upon a radius bar carrying needles to prick off the direction when determined. Fig. 11 shows a level. The sight h is mounted in a vertical tube g with a collineating lens p above the reflecting-plate q in the sighting-tube a. This tube is made with a hole in the top just below the middle of the level 15, to enable the latter to be seen by reflection in the plate q. In another arrangement, the level is placed in front of the sight. The sighting-system may be made separately, with a dovetail, to fit it, as required, to any one of the instruments already described in combination, it may be, with a telescope. Fig. 26 shows an optical square. The face 30<b> is covered with a film of sulphide of lead which allows of the passage of the direct light 32 and reflects also light at right-angles as shown. The prism may be mounted in a tube in combination with a telescope. The reflecting-film may be mounted separately on a parallel plate. Fig. 30 shows a combination which can be used alternatively as an optical square and a range-finder. The prism 30 is mounted to rotate about the axis of the tube 35. In the position shown, it acts as an optical square. When rotated through two right-angles, it may be used in combination with a sighting-scale h, from the projection of which upon an object of known dimensions the range may be determined. Fig. 33 shows a circumferenter. The sighting-tube 36 is mounted above a compass-box c, the card of which is observed by a mirror 40. To the top of the sighting-tube is secured a box 41, which carries a fixed tube 42 within which rotates a tube 43 carrying a prism 30. Upon the box 41 is mounted a graduated disc 44 carrying a tube 45 fitted at the top with a prism 48. The inner tube 43 is connected to the disc 44 through toothed gearing, so that, when the latter is rotated, the tube 43 rotates through half the angle. By inverting the arrangement; it may be used as a prismatic compass.