207,184. Goerz Optische Anstalt Akt.-Ges., Akciovß Spolecnost K. P. Goerz Opticky ustav, C. P. Nov. 14, 1922, [Convention date]. Range-finders; telescopes.-Apparatus for predetermining mechanically the azimuth angle and the angle of sight of a point moving in a straight line with constant velocity in a horizontal plane at a known height, at a given time after the observation comprises mechanism and a sighting device whereby the angles are indicated on a chart. An observation telescope is mounted to rotate on vertical and horizontal axes intersecting at the point 10. Figs. 1 and 2 and the positions 2, 3, 4 represent positions of the target at known intervals of time. The intersection 5 of the optical axis of the telescope 1 with the horizontal plane 13 for the first of these positions is marked thereon and a ruler 8 is brought into register with the mark and maintained in register during the movement of the target from the position 2 to the position 3. Along the ruler slides a second mark 9 in the form of a stop pin mechanically coupled with the device for longitudinal movement of the ruler 8 so that the relative velocities are proportional to the intervals of time between successive positions of the target. The point 9 thus indicates the position the target will occupy after the lapse of a predetermined interval of time. The straight line 9, 10<1>, Fig. 2, gives the azimuthal direction. The angle of sight is determined from the position of the point 9 with the aid of a marked plate 11, carrying two rulers at right angles and parallel to the edges moving oyer curves on the plate 11. The plate 11 is turned to contact with the pin 9 and the angle of sight read off on the outlet. Curves may also be drawn on the plate 11 to indicate the angle of elevation for guns and the fuse-settings necessary. The interval of time between the points 3, 4 is such that it suffices for serving the gun, for setting the fuse, and for the flight of the projectile. The time of fire is then given from the point of observation. The construction of apparatus for effecting the above operations is indicated in Figs. 3, 4 and 6. In operation, the sight telescope 18 is set to the known height on the scale 61 by the milled head 86 and the ruler 47 is also set to the same height on the curve-plate 42. The telescope 18 is also rotated in azimuth until the target is visible in the eyepiece by turning the head 87. The bracket 16 is then secured to the stand by the screw 17 and the mark 31 on the table 25 is brought into register with the image of the target in the eyepiece. The zero mark 88 is also made coincident with the mark 31, these operations being effected by handles 28, 89, one giving radial displacement and the other rotation about the vertical axis through the telescope. The simultaneous sighting of the target 41 and mark 31 is provided for by the arrangement of a semi-reflecting prism 66 behind the objective 64 of the telescope and an arrangement of lenses 67, 69, 70 in conjunction with prisms, whereby the mark 31 is focused in the eyepiece 65. The centre of the lens 67 is arranged at the intersection of the horizontal and vertical axes of rotation of the telescope. When the target 41 and mark 31 have been brought into coincidence a determined time is arranged during which the target 41 moves away from the mark 31 and a horizontal rotation of the ruler 30 is made so that the edge of the ruler coincides with the image of the target 41, the mark 31 being caused by the handle 93 to follow the target. At the end of the time the edge 46 of the plate 42 is brought into contact with the pin 34, corresponding to the point 9, Fig. 2, which has moved simultaneously with the mark 31, but at an increased rate in accordance with the second predetermined interval of time. The ruler 48 is also brought into contact with the pin 34 so that the intersection 49 of the two rulers will give directly by reading from the curves the elevation as well as the fuse-setting. The azimuth angle is nead off on the circle 44, and the results communicated to the gun, the order to fire being given at the end of the second period of time. To maintain the mark 31 in focus the two lenses 69, 70 are made of equal focal length, one positive and the other negative, the negative lens being moved by rotation of the sleeve 74 from the rod 76 operated by the head 87 when adjusting the sighting-line to maintain the target in the field of view. Alteration of the position of the telescope in accordance with the height of the target also effects an adjustment of the lens 70. For correction for the drift of the projectile the edge 46 of the plate 42 may be curved.