7853. Barr & Stroud, Barr, A., and Stroud, W. May 27. Teaching gunnery.-Consists in an instrument for testing and recording the efficiency of range - finder operations. The instrument has means for making an imitation of the optical appearance characteristic of a range-finder, and means for recording the observation upon a strip of paper on a suitably magnified scale. In the construction shown in Figs. 1, 3, and 4, the field of view of a rangefinder of the coincidence type is imitated by a separating line S, Fig. 4, and two vertical rods M1, M2 representing the partial images of a mast M, Fig. 1. One of the rods M2 is movable by means of a working head B and is also connected by suitable gearing to a pencil 8, which moves transversely across a strip of paper 9. The paper can be moved longitudinally step by step by a key 15, Fig. 3, the resulting longitudinal mark recording the position of the movable rod M2 with respect to the fixed rod M'. The rods are not viewed directly, but through a system of lenses, to give a diminished view. The working head B is connected to the movable rod M2 by differential gear, of which one element 3, Fig. 1, can be independently controlled by a handle 19 to provide the equivelent of a moving object the range of which is altering. In modifications, the instrument is adapted for the stereoscopic system of working.
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