Ebony octant on pillar stand with artificial horizon.

Octant with artificial horizon made by Benjamin Martin, London Octant with artificial horizon made by Benjamin Martin, London Octant with artificial horizon made by Benjamin Martin, London Octant with artificial horizon made by Benjamin Martin, London Octant with artificial horizon made by Benjamin Martin, London Octant with artificial horizon made by Benjamin Martin, London Octant with artificial horizon made by Benjamin Martin, London Ebony octant on pillar stand with artificial horizon. Ebony octant on pillar stand with artificial horizon. Ebony octant on pillar stand with artificial horizon. Ebony octant on pillar stand with artificial horizon.

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Octant with artificial horizon made by Benjamin Martin, London
Science Museum Group
© The Board of Trustees of the Science Museum

Octant with artificial horizon made by Benjamin Martin, London
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Octant with artificial horizon made by Benjamin Martin, London
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Octant with artificial horizon made by Benjamin Martin, London
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Octant with artificial horizon made by Benjamin Martin, London
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Octant with artificial horizon made by Benjamin Martin, London
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Octant with artificial horizon made by Benjamin Martin, London
Science Museum Group Collection
© The Board of Trustees of the Science Museum

Science Museum Group Collection
© The Board of Trustees of the Science Museum

Science Museum Group Collection
© The Board of Trustees of the Science Museum

Science Museum Group Collection
© The Board of Trustees of the Science Museum

Science Museum Group Collection
© The Board of Trustees of the Science Museum

Octant with artificial horizon made by Benjamin Martin, London, 1750-1760. Ebony frame, limb and index arm, the lower part of the arm is of brass; brass fittings and a brass stop for the index arm; an inlaid ivory plate on the crossbar. Signed on the brass section of the index arm: B. Martin Invent London. Inlaid ivory scale from -5° to 95° every 20', measuring to 89°. Ivory vernier to 1', zero at the centre. There is no tangent screw or clamping screw; a brass pressure plate on the back of the index arm holds the arm in place on the limb. Two socket shades (both red). Index-glass adjustment by screw; adjustment of the horizon glass by screws, and by levers, wing nuts and milled clamping screws. The sight vane has two pinholes and a swivelling shutter, it has an ivory lining on the objective side; the back sight vane has one pinhole.

When using the artificial horizon, the octant is mounted by a ball and socket and a wing nut (broken) on a mahogany column with three feet, that are mounted on a second set of three feet with three milled levelling screws. The column can rotate the octant and has a brass indicator arm that moves over a circular silvered brass scale, divided 0°-360° every 1°. There is a compass at the centre of the levelling feet , the paper card is divided in four quadrants of 90° every 1°; a silver scale is divided in the same way, whereby the zeros of the two scales differ by 90°. By the wing nut connection between the octant and the stand, the octant can be placed in a horizontal and in a vertical position. The plumb-line to position the octant vertically, is missing. No box.

Details

Category:
Astronomy
Object Number:
1937-118
Materials:
metal and mahogany
Measurements:
overall (estimate): 780 mm x 460 mm x 460 mm, 5kg
type:
octant and artificial horizon - glass
credit:
Stevens's Auction Rooms Ltd.