+
-
Roxby's Pendulum Quadrant
The sextant has a polished brass single cross-pattern frame and fittings with two wooden handles on either side of the frame. The limb has rack teeth cut in its underside and the pinion wheel, which is engaging in the rack on the limb, is on the back of the index arm. The sextant has four shades, three red and one green, and three horizon shades, two red and one green. Index-glass adjustment is made by a screw and on the horizon-glass by a capstan screw and a capped capstan screw.
Attached to the sextant is a magnifier on an 80mm swivelling arm as well as a threaded telescope bracket that is non-adjustable. The telescope is 160 mm in length with an inverted image and four cross wires. A second telescope is 81 mm with an erect image. The sight-tube is 81 mm in length with a red shaded eyepiece, an eyepiece without glass, and a spare indicator for the artificial horizon. The sextant is contained in a fitted mahogany box with a brass carrying handle.
The artificial horizon consists of a pendulum attached to the lower part of the instrument frame with an indicator that extends above the pendulum weight, and is visible in front of the horizon glass. The compass bowl (diameter 106 mm) is fitted with a mounting bracket to attach it to the instrument. It has a card stop mechanism and two lubber lines. The paper card (diameter 89 mm) is covered with mica, and has a jewelled pivot cap at the centre. The card is graduated to eight points, and quadrantally in degrees on a silver ring. The needle (106 mm) is a flat bar type attached below the card, floating on a steel pin in a brass mounting.
The instrument has a polished limb with an inlaid silver scale from -5° to 135° by 10 arcminutes, measuring to 116°. The sextant has a silver vernier measuring to 10 arcseconds, with zero at the right.
This instrument has been identified as a sextant, because it measures to 116 degrees and not 135 as indicated on the scale. The iventor, however, identified the object as a quadrant.
Robert Benton Roxby patented the artificial horizon (no. 4695 of 1822).
Attached to the sextant is a magnifier on an 80mm swivelling arm as well as a threaded telescope bracket that is non-adjustable. The telescope is 160 mm in length with an inverted image and four cross wires. A second telescope is 81 mm with an erect image. The sight-tube is 81 mm in length with a red shaded eyepiece, an eyepiece without glass, and a spare indicator for the artificial horizon. The sextant is contained in a fitted mahogany box with a brass carrying handle.
The artificial horizon consists of a pendulum attached to the lower part of the instrument frame with an indicator that extends above the pendulum weight, and is visible in front of the horizon glass. The compass bowl (diameter 106 mm) is fitted with a mounting bracket to attach it to the instrument. It has a card stop mechanism and two lubber lines. The paper card (diameter 89 mm) is covered with mica, and has a jewelled pivot cap at the centre. The card is graduated to eight points, and quadrantally in degrees on a silver ring. The needle (106 mm) is a flat bar type attached below the card, floating on a steel pin in a brass mounting.
The instrument has a polished limb with an inlaid silver scale from -5° to 135° by 10 arcminutes, measuring to 116°. The sextant has a silver vernier measuring to 10 arcseconds, with zero at the right.
This instrument has been identified as a sextant, because it measures to 116 degrees and not 135 as indicated on the scale. The iventor, however, identified the object as a quadrant.
Robert Benton Roxby patented the artificial horizon (no. 4695 of 1822).
For more information about using images from our Collection, please contact RMG Images.
Object Details
| ID: | NAV1355 |
|---|---|
| Collection: | Astronomical and navigational instruments |
| Type: | Sextant with Artificial Horizon |
| Display location: | Not on display |
| Creator: | Unknown |
| Date made: | After 1822 |
| Credit: | National Maritime Museum, Greenwich, London |
| Measurements: | Overall: 145 mm x 220 mm x 285 mm |
| Parts: |
Roxby's Pendulum Quadrant
|