GB589078A - Improvements in and relating to sextants and like angle-measuring instruments - Google Patents

Abstract

589,078. Sextants. LINK, E. A. May 23, 1944, No. 9941. Convention date, Aug. 30, 1943. [Class 97 (ii)] An attachment for a sextant to enable the real horizon to be viewed comprises a housing with an objective lens at one end and an inclined mirror at the other. Fig. 2 shows the sextant described in Specification 556,573, with the bubble level and illuminating unit removed and replaced by the attachment, which is interchangeable with the illuminating unit. The cylindrical housing 38 of the-attachment fits snugly in the socket 36 in the sextant and is positioned by the collar 40 and locating pin 42. Light from the horizon is brought to a focus by the objective 46 and-mirror 50 at the opening 55. The latter occupies the position which would otherwise be occupied by the bubble level and is provided with a pair of parallel thin wires 57. Light from the image of the horizon and from the wires 57 is reflected bv the mirror 56 to the collimating lens 58, which has the same focal length as the objective 46, and then passes through the semi-reflecting index mirror 16 to the eyepiece 59. Alternatively the celestial body may be viewed through the index mirror and the real horizon by reflection in the index mirror.