505,561. Determining course &c. of aircraft. OESTERREICHISCHE UNGARISCHE OPTISCHE ANSTALT C. P. GOERZ GES. Nov. 8, 1937, No. 30655. Convention date, Sept. 15. [Class 97 (i)] The direction of flight of an aerial target is determined from the ground by means of an observation instrument provided with two graticule lines which can be independently rotated about the axis of the observation instrument so that one line can be made to coincide with the image.of a horizontal part, e.g. the wings, of the aeroplane and the other line can be made to coincide with the image of a part, e.g. the fuselage lying in the direction of flight, The rotation of the graticule lines is effected by the rotations of two members, one of which can turn about a vertical axis and the other is mounted in the first member so as to be rotatable therein about a horizontal axis, the arrangement being such that, when the lines have been set, one of the said members is parallel to the course of the aircraft and the other is parallel to the direction of flight. A second observation instrument may be provided, having a graticule so shaped as to enable the speed of the aircraft to be determined if its range is known. The apparatus comprises a base 2 which can be trained by turning a wheel 1 and carries uprights 4 to which is pivoted, for adjustment about the axis 5-5, a support 7 carrying a telescope 8 for determining the course of. an aircraft and a telescope 9 for determining its velocity. The adjustments of the graticules in the telescopes are effected by a gimbal system comprising a slotted ring 10 carrying a tube 22 parallel to the axes of the telescopes and rotatable within the support 7. A toothed wheel 23 at the end of this tube is connected by a chain 24 to a toothed wheel 25 which is mounted in the telescope 8 and carries a glass plate bearing a diametrical graticule line a<4>, Fig. 6. Passing through slots 13 of the ring 10 are the pivots 26 of a stirrup 27, these pivots being journalled in a frame 28 which is rotatable about a vertical axis in the stand 2. The stirrup can be rotated about the pivots 26 by handles 31 either directly, as in Fig. 5, or through gearing 32, Fig. 4. Passing through the tube 22 is a tube 33 having at its inner end a frame 34 embracing the gimbal. centre, and pivoted in this frame at right-angles to the axis of the tube is a pin 35 connecting the prongs of a fork 36 provided with a pivot 37 entering a recess in the stirrup 27. Secured to the pin 35 is a bevel wheel 38 gearing'with a bevel wheel 39 secured to a shaft 40 which passes through the tube 33 and has at its outer end a toothed wheel 46 connected to a wheel 48 in the telescope 9. The wheel 48 carries a glass plate bearing a curved graticule c<4>, Fig. 3. The outer end of the tube 33 carries two toothed wheels 41, 42 respectively connected to wheels 44, 45 in the telescopes 8, 9. The toothed wheels 44, 45 carry glass plates bearing radial graticule marks b<4>, d' which are parallel to each other. In using the instrument to determine the course and direction of flight of an aircraft, the target is aighted in the telescope 8 and the frame 28 and stirrup 27 are adjusted until the graticule lines a<4>, b<4> respectively coincide with the image of the wings and the image of the fuselage, as shown in Fig. 6. The frame 28 is then parallel to the course, and the axis of the pivot 37 is parallel to the direction of flight ; the angular positions of these members can be read on scales 14, 15. For determining the velocity of the target, the instrument is provided with a drum bearing a number of curves 17 corresponding to different target ranges, and having a co-operating scale 16. The drum is rotatable by clockwork controlled by a lever 18. At the moment when the target image occupies the position shown in Fig. 3 in the telescope 9, the clockwork is started and no further adjustments of the instrument are made. The target imago travels along the graticule line d<4> and when it again intersects the curve c' the clockwork. is stopped, the speed of the target then being read on the scale 16 against the appropriate range curve.