GB610561A - Improvements in sextant-type instruments - Google Patents

Abstract

610,561. Sextants. DURKEE, W. B. March 7, 1946, No. 7095. Convention date, April 12, 1945. [Class 97 (ii)] In a sextant comprising a telescope for obesrving distant objects and having sighting means associated with the telescope for orientating the instrument on the distant object, the telescope and sighting means are mounted in a support for rotation independently thereof around the optical axis of the telescope and the sighting means include a light deflector adjustable about an axis perpendicular to the optical axis so as to direct light rays from the distant object into a path wherein they may be focused by the telescope. As shown, the support comprises a glass plate 21 which is adapted to be held in the observer's hands and to which is secured a bracket 22. The telescope 27 is mounted to rotate about its own axis in bearings 25, 26 carried by the bracket 22 and projects through a central aperture in the plate 21 so that the eye-piece 28 lies on the observer's side thereof. A graduated circle 39, the hour angle arc, is fixed to the telescope and cooperates with a vernier fixed to the plate 21. A mirror 32, adapted to reflect light from a celestial body into the telescope 27, is carried by a yoke 31, which may be adjusted about an axis 33 in arms 29, 30, fixed to the objective end of the telescope in accordance with the known declination of the celestial body. For this purpose an arm 34 fixed to a trunnion of the yoke 31 carries a vernier 35 adapted to move over a declination scale 36 fixed to the telescope 27. A clamp 38 is provided. A spirit level 41 is carried by an arm 46 which is angularly adjustable about a hub 47 in the bracket 22 and has an extension 48 carrying a vernier 49 co-operating with a latitude scale 44 fixed to the bracket 22. An adjustable mirror 491 is provided to enable the observer to see the level 41. Mirrors 42, 43, adapted to reflect two sections of the horizon into the telescope, are secured to a pivot shaft 52 mounted in an arm 53 fixed to the bracket 22-and are coupled by pulleys 54, 55 and wire 56 to the arm 46 so as to move therewith, but only through half the angle. In use, the telescope axis is parallel to the earth's axis when the arc 39 and verniers 35, 49 are appropriately adjusted and the celestial body and intersection of the horizon sections are aligned with the cross-hairs in the telescope. In a modification, the mirrors 42, 43 are pivotally mounted at the side of the telescope and the light therefrom is reflected into the telescope by a fixed mirror. In a further modification, an image of the spirit level is reflected into the telescope and an additional mirror, similar to the mirror 32, is provided to reflect an image of a second celestial body into the telescope. The additional mirror is adjustable independently in accordance with the declination of the second celestial body about an axis perpendicular to the telescope axis in a frame, which extends from a graduated circle adjustable about the axis of the telescope in accordance with hour angles.