Patent GB-470724-A (GB)
Title: Sextant
IPC: G01C1/10
Filed: 1936-07-06
Abstract: 470,724. Sextants. RINKEL. P. and PLATH, T. C., (trading as PLATH, C., [Firm of]). July 6, 1936, Nos. 18782 and 18783. Convention dates, July 6, 1935 and May 11, 1936. [Class 97 (ii)] An image of an observed object, e.g. a star and a comparison image comprising an inverted image the light for which is first reflected an even number of times, preferably twice, one of the reflections being by a rotary index mirror, and then reflected by a pendulous mirror, are brought into a common line of view by two further reflections at a stationary and a rotary mirror. As shown in Fig. 1, the light for the comparison image is reflected at the rotary index mirror 10, the stationary mirror 9, the mirror 12 which is fixed to the swinging member 13 damped by the magnet 16, and is directed into the telescope 1 by the reflecting faces 7, 6 of the pentagonal prism 5. The light for the main image is reflected into the telescope 1 by the mirrors 9, 10. To facilitate observation the main image may be offset slightly with relation to the comparison image or a Wollaston prism 18 may be provided to give a double main image. In a modification the main and comparison images may be reflected side by side at the mirrors 9, 10 instead of one above the other as in Fig. 1, and the mirrors 9, 10 may be extended and a second telescope provided to enable the natural horizon to be used. As shown in Fig. 9, all the reflections are in the path 44 of the light for the comparison image. The ray 44 is reflected by the mirrors 46, 48 on to the liquid horizon 51 and from thence to the eye at 42 by the mirror 47 and semi-transparent mirror 45. In order to bring the comparison ray 44 and the main ray 43 in to coincidence the mirrors 47, 48 are rotated together. In Fig. 14 the mirror group 47, 48 is replaced by a single mirror 49 and the comparison ray 44 is reflected by the mirrors 46 and 49 on to a mirror 51 secured to a pendulum whose pivot axis 52 coincides with the pivot axis 50 of the mirror 49. From the mirror 51 the comparison ray is reflected a second time by the mirror 49 and in to the telescope at 42 by the mirror 45. The mirrors 45, 49 may be extended and a second telescope provided to enable one eye to observe the altitude scale 57 whilst, the other observes the celestial body. In Fig. 16, the pivotal axis 501 of the mirror 49 is outside the plane of the mirror so that the latter, in addition to the angular movement, is displaced within the casing 60 so that the light always impinges on the same part of the horizon mirror 51 which may be made small. Figs. 19 and 20 show a binocular instrument. The main rays 43 pass directly to the eyepieces 64 via the objectives 65 and reflecting prisms 66. The comparison rays 44 are reflected by the common reflecting base 46 of two erecting prisms 67, 68, by the common reflecting base 49 of two prisms 69, 70, which are rotatable on the axis 50, by the mirrors 51 carried by the pendulous frame 71, a second time by the reflecting surface 49 and into the respective objectives 65 by the reflectors 45. Lateral displacement of the comparison rays 44 is effected by inclining the fixed mirrors 45 and the two parts of the horizon mirror 51 or by replacing each mirror 45 and each part of the mirror 51 by a pair of reflectors fixed at right angles to each other. Fig. 8 shows an arrangement for adjusting a rotary index mirror 33. The mirror 33 is mounted on an arm 34 with an index mark 35 moving over a scale 37 carried by a frame 36 which itself carries an index mark 38 moving over the altitude arc 40.