14,379. Fox, H. W. Oct. 11. Sights and methods of sighting.-Relates to apparatus adapted to predict the probable position of an object, such as an aircraft moving in space of three dimensions, at the end of a given period. It is used in conjunction with the range-finder described in Specification 13,213/15, [Class 97 (i), Optical systems &c.], wherein the intersection on a translucent screen of two beams of light moving in synchronism with observing telescopes gives the range. According to this invention, secondary motions are superimposed upon the primary motions as determined by the former invention so as to ascertain the probable position of the object at the end of n seconds. For this purpose the speed of motion of the object light-spot along each of three axes mutually at right angles is measured by a speedometer and communicated to a Wheatstone bridge in terms of an adjustment of length of one of its resistance arms, in order that a motor by which equilibrium is established upon the bridge may communicate a corresponding secondary movement according to the number of seconds n, to the mechanism defining for that axis the corrected position of the object. Fig. 1 shows an apparatus for defining the position of the object, in relation to the horizontal plane, upon a screen a of translucent material below which is a carrier g for a vertical-beam light-projector mounted to be capable of simultaneous movement in two directions at right angles. each movement having a primary component derived directly from the apparatus described in Specification 13,213/15, and a secondary component derived from the Wheatstone bridge. The vertical beam is followed by means of an arm h rotatable about a central axis k, having a radially-movable carrier l for a position pointer m. The speed indicator for each primary movement determines, bv means of its pointer or contact-arm, the magnitude of a resistance R', Fig. 5, placed on a semicircular arc and constituting one of the arms of a bridge, formed by arms R<1>, R<2> chosen according to the number of seconds n, and a fourth rheostat R<4> which is automatically varied by means of a motor M, energized whenever the galvanometer G of the bridge varies from zero reading, and communicating simultaneously a secondary movement to the carrier g in the required direction. The second part of the apparatus, shown in Fig. 4, gives indications of angle of elevation, height, and range, for which purpose a frame 8 is moved vertically upon a support o by a screw 9 rotated from the height element of the apparatus of the prior Specification, and within it a carrier q<1> for a height pointer 11 receives an additional relative motion by means of gearing 4, 5, 6 and a rotary and slidable spindle 7 operated by the Wheatstone bridge apparatus for the secondary height movement. Similarly the position of the radially movable carrier l of the horizontal plane apparatus is reproduced by a carrier q<2> upon a horizontal rail p, so that the inclination of a rack-bar r may vary according to the angle of elevation, while its effective length or range is shown upon a dial indicator driven from a gearing-rotated spindle 14.