Weight-Driven Clock Drive


Accession Number: 2019.ast.138


This object is kept in a pale-coloured wooden box with a blue David Dunlap Observatory label on the top. The instrument inside is basically rectangular, with metal sides and base, and front, top and base clear plastic. On the top of the box there is a round dial on which is written “FAST” and “SLOW”. Visible inside the box is a centrifugal governor with three balls. Below this there is a gear system connected to a ridged wheel around which is wrapped a length of thick metal wire. This end of this wire, coiled into a loop, emerges through a rectangular window cut in the plastic side of the box.

On the left and right of the box there are metallic attachments that connect to the mechanism on the interior. On one side there is a square rod to which a separable two ended handle can be attached to enable the coil inside to be rewound. On the other side of the box, there is a small metal box to which is attached a jointed metallic arm which ends in an open tube; the angle of this box can be adjusted and fixed in place. This appears to be a coupling device to connect the instrument to another instrument such as a telescope.

There is a cylindrical metal piece with a hook on one end which perhaps is intended to to be hooked onto the metal wire to prevent the wire being retracted into the box of the instrument.

Primary Materials:

Metal: Iron Alloy, Metal: Copper Alloy, Plastic: Acrylic


On a sticker stuck to the exterior of the box, to the side of the instrument and to the hooked attachment: “UNIVERSITY OF TORONTO

In white lettering on the plastic on one side of the instrument: “UNITRON”

Dimensions (cm):

Length = 22.4, Width = 12.5, Height = 19.5


This instrument uses weights and a centrifugal governor to mechanically provide highly regulated, very slow rotational energy to drive a telescope to track a point in the sky. This instrument will run for about 15-20 minutes. This probably ran a small Unitron telescope.


Excellent: The instrument is in near-perfect condition. There are some small smudges on the metallic surfaces on the instrument, and white residue on the winding handle face of the box. It may be missing a piece that supports the weight so it falls smoothly. The box is in very good condition, with small scratches and slightly worn corners and edges.

Manufacturer: Unitron

Date of Manufacture: 1951-1992


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:

This website, “Unitron History Project“, assembles some history of the company that made this instrument.