Bubble Sextant Mk IXA


Accession Number: 2019.ast.150


This object is contained in a dark red plastic box with a slanted lid, that is held closed with two metallic clips. There are metallic loops attached to the box that enable the box to be hung in two orientations on hooks a wall. There is a plastic label in a metal surround on the box. There is a paper calibration sheet inside the box.

The instrument itself is roughly the shape of a right-angle triangle, with an eyepiece on the one side through which a bubble is visible. On one side of this blocky triangle there is a plastic tube with an unscrewable cap and a notched wheel. At the front of the triangle there is a large round cylindrical piece on the front of which there is a rotating key and an indicator arrow, and on one side a window with rotating dial indicating numbers. On the other side of the sextant there a number of knobs, indicators and switches. These include: a rotating dial cut with holes of different aperture, a knob named “DEG”, a switch marked “INCREASE” that alters other indicators on the instrument and a flat white plastic section divided into four section on which is written “OBJECT” “START” “FINISH” “ALTITUDE” for recording observations.

The object is cut open on the top along the slanted edge. Visible inside the object there is mounted a rectangular slanted mirror.

On the top of the object there is a metal hook onto which a metal clip is attached. Next to this, there is a circular glass window with a rotating cover which can be slid across the window to close or open it.

Inside the box there is also a cylindrical object wrapped in dark orange paper attached to yellow textile-insulated wiring, a pair of empty tubes of unknown purpose, and padding to protect the instrument.

Primary Materials:

Metal: Iron Alloy, Plastic, Glass, Rubber


On the label on the exterior of the box: “A.M. 6B/218

On a sticky label above this: “AVIATION ELECTRIC LIMITED
REF. NO. 68/133
DATE 19-9-57”

On a paper label: “Ast60c”

On the instrument: “A.M.
REF. No. 6B/218
480112 490621

“SERIAL No 4453/42”

On the cylindrical attachment: “SERIAL No 6572/42”

On the paper calibration sheet tucked inside: “BUBBLE SEXTANT
Ser. No. 4453/42
Date Sept 19, 1957”

Dimensions (cm): Length = 27, Width = 20.5, Height = 24


The Bubble Sextant enables stellar navigation in situations where a standard sextant cannot be used as the horizon may not be level, as in an aircraft. The bubble creates an artificial horizon when the sextant is held correctly.


Very Good: The box of the sextant is in excellent condition, although somewhat dusty. In places, it is scratched, and splattered with paint. The leather handle is in excellent condition. The sextant itself is in very good condition. It has minor damage on the edges of the instrument in the form of places where paint/surfacing has been scratched or chipped off. The recording label is yellowed and slightly warped, pulling away from the screws that hold it in place.

The rubber surround of the eyepiece is still soft and intact. It is not bent.

Manufacturer: U.K. Air Ministry

Date of Manufacture: 1939-1945


The sextant was acquired by the Department of Astronomy or the David Dunlap Observatory sometime after 1957 (when it was last overhauled). 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.