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Bubble for Mark IX or IXA Sextant


This item is contained inside a cardboard box with a paper label on the outside. The item is cushioned in brown, layered papery material. The instrument is largely made of metal and painted black. It consists of an arrangement of lenses, with one cylindrical section holding a pair of round lenses creating a small chamber, next to this an angled lens with a slight magnification, and further along a round lens that has two parallel lines etched on the surface. These three are arranged in a row along a metal support. Next to the angled lens, there is a metal plate with a round hole through the centre.

Next to the lens with the parallel lines, there is a cylindrical section with a pointed end sticking out along the same plane as the line of lenses. Underneath this lens, there is a broad cylinder with a rotating plastic knob attached.

Accession Number: 2019.ast.207 (DAA-0082)

Alternative Name:

Primary Materials: Metal: Iron Alloy, Plastic, Glass.


Stamped on the plate that supports the lenses: “25114”

Handwritten on the paper label: “1 Spare bubble
Mark IX or IXA Sextant
Oct 21/69”

Dimensions (cm):

Height = 5.2, Width = 4.5, Length = 12.7.


This object is the “bubble” component for a Mark IX or IXa Bubble sextant, which was designed for use by pilots to identify the position for navigational purposes in circumstances where the viewer may not be horizontal to the horizon. The bubble creates an artificial horizontal horizon.


Fair: The box is in good condition, as is the packaging material. The instrument appears used. In places, the black paint on its surface has been scratched off. The liquid in the bubble chamber appears to have leaked out, and there is a brown dry residue on the exterior of the chamber and on the window.

Associated Instruments:

Manufacturer: U.K. Air Ministry?

Date of Manufacture: c. 1940s-1960s


The bubble was likely acquired alongside the sextants, in the late 1950s or in the 1960s. The label on the box indicates it may have been put in the box on October 21, 1969. This object was likely moved from the David Dunlap Observatory in Richmond Hill in 2008, upon the sale of the observatory. It was stored at the Department of Astronomy and Astrophysics until 2017 when it was moved to a new storage location in McLennan Physical Laboratories.

Additional Information and References:

Historical Notes: