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This instrument is a tall precision chronometer resembling a grandfather clock. The case is wood with a glass fronted door hinged on the right and closed by two locks, with keyholes on the left side of the case. Affixed to the rear of the case there is a metal plate. On the left side of the case there are two cylindrical electrical posts with screw tops; these pass through the case to the interior.

Inside the case, the clock instrument consists of a large silver-coloured metal face with a single hand in the centre; this dial is labeled in minutes, with “60” at the top. Inside the face of the larger dial there are two smaller dials, each with a single central hand. The upper dial measure seconds (0-60) and the lower 24 hours. There is a round hole in the seconds dial, just above where the hand is fixed. Also on the face, there is also a smaller round hole with a square peg in the centre of it. The clock mechanism is located behind the face.

A pendulum hangs below the face. This constists of a large vertical rod with a cylindrical weight fixed to the base. Hanging beside this, although detatched, there is a looped string with a metal pulley hanging loosely off it. Beneath the pendulum rod there is a small arced scale with 0 in the centre, and graduated in tenths on either side, labeled up to 2.

Loose in the base of the case there are two metal tins with blue lids and paper stickers affixed to their lids. Each of these contains a small number of weights. One is labeled “Rm 18” (2012.ast.21.2), the other “Rm 77” (2012.ast.21.3). Also in the case, there is a wooden box with a hinged lid and a key in the front. This is a weight set consisting of different weights (2012.ast.21.4). There is also a cylindrical metal weight loose in the base of the case (2012.ast.21.5).

Accession Number: 2012.ast.21

Alternative Name: Astronomical Chronometer

Primary Materials:

Wood, Glass, Metal: Iron Alloy, Metal: Copper Alloy


On the clock face: – “DENT
“61, STRAND &

On the hour dial face: “58153”

On a metal plaque affixed to the case behind the pendulum rod: “SIDEREAL TIME”

On the paper label on the lid of 2012.ast.21.2: “Weights for
Sidereal Clock
Rm 18”

On the paper label on the lid of 2012.ast.21.3: “Weights for
Sidereal Clock
Rm 77”

On the lid of 2012.ast.21.5: “81”
Engraved on the interior of this box: “L. OERTLING LONDON”

Dimensions (cm): Height = 147.5, Width = 46, Length= 24


Astronomical chronometers are for the very precise measurement of time, used to located and time the position of celestial bodies.


Good: The case of the clock is in good condition, although dusty and dirty on the top. The metal plate affixed to the rear appears to be a modification. There is some label/tape residue on the door and side of the case about half way down. There are small chips and marks on the case, particularly on the corners and sides of the case. The top front left corner of the case is badly chipped and the wooden joins out of alignment.

The clock has been disassembled partly, but the mechanism appears to be present and intact. The string and pulley are hanging loosely in the case. The face is in excellent condition with few very minor marks; however, the serial number appears to be partly worn off.

The weights in the base of the box may not all be related to this instrument.

Associated Instruments:

Manufacturer: Dent, London

Date of Manufacture: c. 1900


This instrument was used at the University of Toronto David Dunlap Observatory in Richmond Hill. Upon its closure and sale in 2009, the chronometer was moved to storage at the Department of Astronomy and Astrophysics at the St George Campus. In 2017, the object was moved to a new storage location in the McLennan Physical Laboratories.

Additional Information and References:

This chronometer appears briefly, alongside others, in the short documentary Universe by director Roman Kroitor and Colin Lon, which was filmed at the David Dunlap Observatory in 1960 and featured Professor Don MacRae operating the 74” telescope. Although in the film the chronometers appear to be wall-mounted and operating, Professor Emeritus John Percy has suggested that they weren’t actively in use in 1960 by astronomers, but instead used as evocative props:
“… I don’t remember the film as to whether these were shown in the basement or actually moved up to be filmed. But in those days they [the clocks] weren’t being used for scientific purposes; by then you had an electric clock that was in the dome. But the thing is that these are so visually stunning that I can imagine that any filmmaker would want to use these simply to represent time.”
John Percy was interviewed on March 11, 2021.

Historical Notes: