Patent GB-191504651-A (GB)
Title: Improvements in or relating to Sighting Apparatus for Ordnance.
Filed: 1915-03-25
Abstract: 4651. Barr & Stroud, Barr, A., and Stroud, W. March 25. Angle-measuring instruments.-Relates to means for use in determining the lead to be put on a gun when aiming at a moving target, and consists in a device for effecting mechanically the multiplication of angular velocity by range to determine the relative speed of target, whence the lead to be put on the gun may be ascertained. The device comprises essentially members arranged to produce a right-angled triangulation as shown diagrammatically in Fig. 4, the base A 0 being graduated for ranges so that the height of the perpendicular such as a b at a range R may be arranged to indicate the product Ra which constitutes the resultant velocity of target. The device may be used in combination with a special method of sighting, which consists in firing a preliminary shot from a subsidiary gun aimed direct at the target without any deflection correction, not with the intention of hitting the target, but to give a splash, smoke or other indication at an intermediate point in the line of sight at a certain time interval after firing. An observation may be made of the displacement of the target relatively to the splash or other indication, and the relative angular velocity calculated therefrom by means of an instrument as shown in Figs. 5, 6, and 7. The optical device for measuring the azimuthal angle between the target and the splash comprises an eyepiece 4 and parts 1, 2, 3 constituting an ordinary prismatic telescope, in which the upper half of the objective 1 receives an image of the splash or other indication by means of two reflectors 5, 6, one of which, 5, is adjustable about the axis 7 to raise the image of the splash to the level of that of the target. For this purpose a screw 8 with a head graduated according to ranges may be utilized. In the lower half of the objective 1 an image of the target is received from reflectors 10, 11, the reflector 11 being adjustable about a vertical axis 13 to bring the images of target and splash into vertical alinement. The reflector 11 is operated by means of an arm 12 slidably connected at 14 to a lever 19 pivoted at 0. The lever 19 is operated by a screwed spindle 22 actuated by a crank handle 21, a slide block 28 carried by the slotted lever being connected to a nut 24 working on the screw 22. The movement of the lever 19 is thus proportional to the angular displacement observed. Mounted upon a pair of screwed spindles 31, 32 so as to be adjusted thereby is a slide carrier 33, in which a plate 34 formed with a rack a is adapted to slide. At the back of the rack plate 34, is pivoted a slide block 26 by means of which the rack is connected to the slotted lever 19 so as to follow the angular movements thereof. The rack engages and serves to operate a long pinion 35 to which is fixed a wheel 37 co-operating with a fixed pointer 38 and graduated to indicate values of Ra. To use the device the slide carrier is adjusted along the pinion 35 so that its distance from the pivot centre 0 (see also Fig. 4) varies according to the range, this adjustment being effected by means of a crank handle 27, acting through the gears 28, 29, 30 to rotate the screws 31, 32. The crank handle 27 being turned to the position corresponding to the known range, the handle 21 is rotated till the image of the splash is in vertical alinement with the image of the target. Then the position of the wheel 37 in relation to the pointer 38 indicates the value of the product Ra. The multiplying device may be used in conjunction with other optical means for observing the relative angular displacement of target.