26,507. Garcia, M. J. Dec. 19. Bearings and courses, determining; longitude instruments.-Relates to apparatus for determining mechanically the hour-angle and the ship's position at sea, and for solving other problems in nautical astronomy such as tracing Sumner lines on a chart, determining the variation of the hour-angle with the latitude and altitude, finding the azimuth, and calculating the ship's position by simultaneous altitudes or two altitudes taken at intervals. In this instrument all the determining lines, angles, &c. are projected on to a plane passing through the meridian of the heavenly body observed, and a single are is used for all the readings, the solution of a problem being determined by the intersection of two circles projected as straight lines on to the plane of the instrument. The body 1 of the instrument has guides 2, 3 for a frame 4, which when adjusted is clamped by a thumb-screw 6 to a slide 5 which can be adjusted slightly by a screw 7. A part 10 slides in the frame 4, and has a number of parallel lines to enable readings to be transferred from the sides of the frame 4 to a rotatory graduated arm 13. This arm and a similar arm 14 have longitudinal slots and end verniers which move over the arc 11. The arms are secured to the arc by a screwed part 16, and can be clamped in position separately by screws 17, 18 arranged as shown in Fig. 2. The lower arm 13 carries two sliding markers 19, 20 to facilitate reading, while the upper arm 14 carries a rule 24 arranged at right-angles to it and adjusted along its length by a rack and pinion 22, Fig. 3. In using the instrument, the equator is represented by the vertical line through the zero of the arc 11. The rule 24 may be replaced by the sighting-device shown in Figs. 4 and 5. This consists of two reflecting prisms 27, 28 adjustable along the arm 14, and a sighting-tube 25 and a mirror. A sight is also provided at the end of the arm 13, and adjustable sights are arranged in guides 8, 9 in the frame 4. In using the instrument to determine the hour-angle from the declination and altitude of a star, and the latitude, the arm 14 is fixed at zero and the arm 13 is fixed at the angle corresponding to the zenith distance along the arc 11. The rule 24 is then adjusted, until it passes through the end of the arm 13, and clamped to the arm 14, which is then turned to the angle corresponding to the declination, as shown diagrammatically in Fig. 11. The ship is somewhere on the rule 24. The arm 13 is then turned to the angle corresponding to the latitude, and one edge of the frame 4 is brought into coincidence with the end of the arm 13. Then the ship will be at the point of intersection b of the edge of the frame with the rule 24. A marker 19 is adjusted at the point where a parallel from the point b meets the arm 13, both arms 13, 14 are turned to zero, and the rule 24 is adjusted until it coincides with the marker 19. The rule 24 will then indicate the hour-angle on the arc 11.