GB581722A - Improvements in or relating to bubble sextants - Google Patents

Abstract

581,722. Sextants. BAKER, T. Y., HASSELKUS, J. W., and ROSS, Ltd. Jan. 31, 1941, No. 1313. [Class 97 (ii)] The sextant comprises a bubble collimating tube 2, a reflecting prism 7, a transparent parallel plate 4 and an integrating mechanism. The prism 7 is carried by a shaft 6 having an arm which coacts with a scale 12 and constitutes the coarse motion, the scale 12 showing each 10 degrees of altitude. The plate 4 is carried by an arm 5 pivoted on the shaft 6 and having an upstanding arm 13 provided with a cam 14 for coacting with the roller 15 of the integrating mechanism and constituting the fine motion, the plate 4 being operated by a. movement of the roller 15 through a screw 19 and thumb wheel. A trim disc 23 is provided operated by a spring and controlled by escapement gearing 25 ... 30 to give uniform rotation. The roller 15 is mounted on a carriage 18 on the screw 19 and coacts through a planimeter wheel 21 marked in degrees and minutes. The planimeter wheel 21 is driven by friction from the time disc 23 in a direction dependent on whether the wheel is above or below the centre of the time disc and the mean altitude of the star is read from the scale 12 to denote the number of 10 degrees, a window on the carriage 18 to denote unit degrees and the planimeter wheel to denote minutes, the images of the star and the bubble being kept continuously in juxtaposition.