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Bubble Sextant Mk IXA


This object is contained in a dark red plastic box with a slanted lid, that is held closed with two metallic clips. A card label is attached to a leather handle; this is torn in half. The missing part of the label is tucked inside the box, alongside another paper label.

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 (for holding batteries) 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 numnbers. Wires go into this On the other side of the sextant there are 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 a flat white plastic section divided into four section on which is written “OBJECT” “START” “FINISH” “ALTITUDE” for recording observations.

The object is open on the top along the slanted edge. Visible inside the object there is mounted a slanted mirror which diverts light into the instrument.

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

Inside the box there is also a cylindrical object wrapped in orange paper attached to purple textile-insulated wiring, a pair of papery cylinders, padding to protect the instrument, and a piece of paper labelled “CALIBRATION SHEET”. The serial numbers on this sheet do not match that of the box or the instrument.

Accession Number: 2019.ast.149

Alternative Name:

Primary Materials:

Instrument Metal: Iron Alloy, Plastic, Glass,


On a label on the box:
No 7551/42

Scratched into the metal surround of the label: “7355”

On a sticky label above this: “OVERHAULED BY
68/133 AUG 58”

Printed directly on the instrument: “BUBBLE SEXTANT
REF. No 6B/218
SERIAL No 3137/44(V)”

“SERIAL No 3137/44 (V)”

On the red paper of the cylindrical piece inside: “FOR 12V CIRCUIT”

On the torn card label:
“6B Ref. No. 233 Part No. MK1XA
[Manufa]ctured By: A.M. Serial No. 7551/42
Description: Bubble Sextant
Contractor or Unit AVIATION ELECTRIC LTD Order No. 483723
Overhaul Technician 33-57 [Jsit?]
Certified Serviceable G. E. Martin (INSPECTOR)
R.C.A.F. W 11
200M-6-56 (8352)”
And on the reverse of the label”
“ Accordance
Time error
2 min ± 10 seconds
Err of att
± 2 min
Index err0r
(with incr.)
± 2 min

On paper label inside box, handwritten: “NOT FOR SEXTANT IN BOX OF SERIAL #-7551/42”
Printed on label:
Ser. No. 3520/42
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 good condition, although very dusty. In places, it is dented and scratched, although not badly. The leather handle is in fair condition, with a few small tears and cracks on the smooth surface, but otherwise intact. 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 rubber surrounding the eyepiece is still soft and intact. It is bent on the right side, towards the instrument.

Associated Instruments:


Aviation Electric Ltd. for 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 1958 (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.

Additional Information and References:

Information about a similar sextant surviving at the University of Queensland, in Australia can be found <a href=>here</a>.

Historical Notes: