5750. Cowey, L. E. April 16. [Cognate Application, 12,887/15.] Sighting-devices for use on aerial vessels.-Relates to sighting-devices for use in bomb-dropping from aircraft to enable the pilot to determine the true vertical through the aircraft, and also the proper bomb-dropping angle, and consists in employing the known principle that when a beam of light is reflected successively from two plane surfaces set at a fixed angle, the reflected beam emerges at an angle to the incident beam which is constant and equal to twice the angle between the surfaces, being therefore independent of any angular or other movement of the surfaces. According to the invention, a beam of light from a distant object, such as the horizon, is reflected from two mirrors so that, when the observer views the reflected image, he knows that he is looking along the vertical or along a line making a predetermined angle with the vertical. To obtain a vertical plane through the aircraft and target, a transverselyarranged pair of mirrors are used to reflect a distant object on one side of the aircraft, and a longitudinally-arranged sight-bar is provided, the reflected image, target, and sight-bar being brought into alinement by the pilot manoeuvring the aircraft; the proper dropping angle is obtained by means of a second pair of mirrors, or two pairs, which give a fixed angle or angles to the vertical, the object employed for observation being at the front or at the rear ; or any known means may be employed for this purpose. As shown in Figs. 1, 2, and 3, the two pairs of mirrors A, A' give the true vertical ; the mirrors B, B<1> give a predetermined angle in the line of flight; the mirrors B', B' are provided for giving a predetermined angle relatively to the reflected beam from the mirrors B, B<1> for measuring speed of flight. The mirrors are mounted on a frame C carried by a bracket D. The mirrors A, A' are carried in a frame a and are inclined to each other at 45‹ so that the horizontal beam from the horizon is reflected through 90‹ into the vertical. The aircraft is manoeuvred until the reflected horizon x is in line with, and midway between, two sighting-bars E. Any means of known-type may be employed to give the right time for releasing the bomb, the following means being described. Two lines of sight in the vertical plane of flight at known angles are used to observe the apparent travel of a stationary object below the aircraft ; the altitude at which the observations are taken, and the interval between the times at which the object is observed to cross the lines are noted ; the speed of flight can then be calculated. The speed and altitude being knuwn, the point or time at which a bomb should be released can be deduced. The two lines of sight necessary are obtained by means of the pairs of mirrors B, B<1>; B<2>, B<3> mounted in carriers b. the pair B, B' having an inclination of 58‹ and a reflected beam at 26‹ to the vertical, while the pair B<2>, B<3> have an inclination of 32‹ and a reflected beam at 26‹ to the vertical, the two reflected beams having an inclination of 52‹ to each other. The pair of mirrors B<2>, B<3> may be dispensed with by mounting the frame C, as shown in Fig. 2, to swing through 180‹ to reverse the direction of the mirrors B, B'. The modification shown in Fig. 4 allows of the use of a distant object such as the edge of a cloud, a clump of trees, &c., instead of the horizon. A plumb-line device comprising a ball F rolling freely in a track f forming an arc of a circle having its centre coincident with a wire E<1> can be observed simultaneously with the image of the reference object. The lower mirror A<3> is fixed and the upper mirror is pivoted at d and controlled by a screw a' and pivoted nut a', so that, with the aid of the plumb-line device, a vertical reflection of the reference object can be obtained. A sighting- line is marked centrally across the mirror A<3> in continuation of the wire E' which, with the ball F and track, is placed a little in front of, or behind, the mirrors A<2>, A<3>. The target must be kept sighted along the wire E', and the image of the reference object along the central line on the lower mirror.