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Online Encyclopedia
Originally appearing in Volume V22, Page 889 of the 1911 Encyclopedia Britannica.
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LEFT SEARING A rubber guard is fitted round the eye-pieces. Its functions are to guide the eyes of the observer into the correct position, and to protect them from side light and the distressing effect of wind. It also guards the forehead against the jar occasioned by firing heavy guns. The upper portion of the field presented to the left eye is used as a finder, the lower portion is occupied by the scale upon which the ranges are engraved. The finder is a low-power telescope of large field, to the centre of which the objective is brought. When the telescope is thus correctly aligned, the objective will be seen with the right eye largely magnified, but as two partial images separated by a thin black horizontal line. When coincidence of the images is effected by means of the working head, the range can be 2 The length of tube varies from 3 ft. in the smaller to 9 ft. in the larger instruments. i read off against a pointer from the scale seen with the left eye. For 1 or on different parts of the same objective, and thus inaccuracy in the night use, means are provided for illuminating the scale. The range recorded-range must result. The instruments are expected to give an to lights may be ascertained by the use of the astigmatizer, an optical accuracy of less than device by which a point of light is drawn out into a vertical streak. 2 % at 2000 yds. For A*,ogjectioe A beam of light from the objective falls on each reflector (fig. 2), ranges over that distance, i.e. for usual DOW uFPORT /IMDER OBJECT GLASS SUIMORT WINDOW RE n artillery ranges, it is IRATE WIN ) FRAME EYE PIECE PRIS5S-W SCALE ass desirable to use a ccro OBJECT GLASS CASE >rZn 'redouble base (1oo yds.
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