220,659. Naamlooze Vennootschap Nederlandsche Instrumenten Cie. Aug. 17, 1923, [Convention date]. Speed indicators ; sighting aerial objects by telescopic and other apparatus.-An aircraft range-finder is mounted to rotate about a vertical as well as an horizontal axis and by its movement to operate mechanism contained in a casing on which it is supported whereby an indication is given of the speed of the aircraft and the change in direction of the projected path of the aircraft during the measuring period. The mechanism is provided with couplings so that the measuring period may be selected independently of the observation period. The speed is indicated by the position of the point of intersection of two wires at right angles which are moved over a disc having on its surface a number of concentric speed circles, and the angle between the line joining this point with the centre of the circles and one of the wires gives the change in the sighting direction during the period of observation. The whole apparatus is mounted on a bed 2 secured to a support 1, and comprises a casing 3 containing mechanism for giving the various indications and having a cover 4 upon which is supported a rangefinder 6, fitted with a telescopic sight 7. In the casing 3 is mounted a spindle 8 parallel to the axis of rotation Y-Y of the rangefinder carrying a drum 9 coupled to a drum 11 on the rangefinder by a band 10, and a lever 12 the zero position of which is parallel to the vertical axis of rotation X-X. The lever 12 is provided with a slot 13 in which slides a block 14 having a pin 15 engaging slots 16, 18 in bars 17, 19 respectively, the bar 17 being moved by the handwheel 23 in accordance with the height of the aircraft and the bar 19 being moved by the handwheel 29 in accordance with the map distance of the aircraft. The rotation of the spindle 28 by the wheel 29 is also transmitted by bevel wheels 30, 31 to a spindle 32, parallel to the spindle 8, operating one member 33 of a friction coupling, by which the shaft 37 is rotated to traverse a wire 43, connected to bands 42, across a plate 81 carrying a number of concentric circles, each corresponding to a definite speed. The movement of the wire 43 is proportional to changes in the map distance of the target. The spindle 32 is also connected by gear wheels 44, 45 to a screwed spindle 46 mounted in the casing 3 parallel to the axis of rotation Y-Y of the rangefinder, and operating a sliding-carrier 47 upon which is mounted a block 49 adjustable at right angles to the spindle 46. Movements of the block 49 relatively to the carrier 47 are transmitted by a rack and sector 50, 51 to bevel gear 52, 53 to rotate a spindle 54 and through a coupling 70, 72 and band 74 a shaft 75 by which a wire 80 is moved across the disc 81 in a direction at right angLes to that of the wire 43. The block 49 is moved as the result of angular displacements of the casing 3 around the axis X-X, by a sector 56 which carries a slotted arm 57 engaging a pin 59 on the block 49. This sector 56 is rotated from a fixed wheel 66 on the bed 2 through a wheel 65, coupling 61, 62 and wheel 60, the. parts being proportional so that the arm 57 turns through the same angle as the casing 3. The initial position of the arm 57 can be set by the milled head 67 outside the casing 3. The three couplings are operated by levers 86 from electromagnets 87 connected in series and controlled bv a contact arc 91, forming part of a stop-watch 89. The length of the arc 91 is arranged so that the magnets are energized and the couplings engaged for the measuring period selected. The apparatus is operated by three observers, one of whom gives the rangefinder the correct lateral defection and attends to the measuring mechanism. The second observer uses the sight 7 and operates the handwheel 29, and the third observer sets the handwheel 23 in accordance with the altitude of the aircraft. To determine the speed of the aircraft, the stop-watch is started and the wires 43, 80 are moved by the mechanism described during the measuring period, and the point of their intersection will move from the zero position to a point over the circle which corresponds to the required speed. The radial position of the point of intersection indicates the change of angle of the sighting direction during the period. To obtain a second observalion the wires 13, 80 are returned to the zero position by the rotation. of milled heads 67, 73.