Accession Number: 2014.ast.28


This is a brass instrument standing on a circular base that supports a rotating mirror.

The instrument has a central stand with three adjustable legs. This stand is cut open at the base to reveal a glass disc fixed flat in the base of the stand. Above this, there is a cylindrical stand with a knob enabling the rotating instrument to be fixed in place. Above this, a brass piece holds a circular rotating assembly: this has a central semi-circular piece with a graduated scale around its rim, and a long arm with a u-shaped attachment at the end. This is attached by a rod to a clockwork motor that turns the rotating piece slowly. The clockwork motor has a key to wind it up, and two switches, one that permits shifting between “A” and “R” settings.

Attached to the central stand there is an arm that supports a rectangular mirror. This arm can be lengthened, and rotates smoothly around the stand; the mirror’s angle can be adjusted in any direction via a ball and socket joint. Behind the mirror there is a round knob for adjustments. At one end of the mirror, a long rod emerges; this is intended to be fixed to the arm attached to the rotating clockwork assembly with the u-shaped attachment, but is currently free.

Primary Materials:

Metal: Copper Alloy, Metal: Iron Alloy, Glass


Engraved on the circular base of the instrument: “R. FUESS

Dimensions (cm): Length = 48, Width = 18cm, Height = 31


A heliostat is a biaxial single-mirrored instrument that traces and reflects the rays from a light source toward a predetermined target. Often the device would track the sun’s motions in the sky. A heliostat would be used in stellar spectroscopy and stellar photography, in order to keep the image stationary during very long exposures. During the 19th century it would less commonly be used to provide constant daylighting in art studios.

Turner, G. L’E. 1998. Scientific Instruments, 1500-1900: An Introduction. London: University of California Press, p. 70.


Good: The surface of the instrument is somewhat tarnished and corroded around the base and the knobs attached to the base. The rod emerging from the mirror is also corroded. Many of the upper parts of the instruments are splattered by fine drops of white paint. The mirror is blackened in places around its edges, and has many fine scratches across its surface.

Some small pieces, such as the attachment to connect the mirror to the clockwork-driven arm, are missing. The glass piece in the centre of the stand is cracked across its whole width. The instrument rotates quite freely but some orientations appear jammed.

Manufacturer: R. Fuess, Steglitz, Berlin

Date of Manufacture: 1880s


This instrument was likely acquired for astronomical work at the University of Toronto at the end of the 19th century; alternatively, it was acquired later, as an antique. It was stored at the Department of Astronomy & Astrophysics until 2017, when it was moved to a new storage location in McLennan Physical Laboratories.

Additional Information and References:

Rudolf Fuess was a precision mechanic, inventor, designer and draftsman who lived between 1838 and 1917. His company was famous for manufacturing goniometers (an instrument that measures angles) and microscopes. R. Fuess was not particularly known for producing many heliostats and consequently such devices with his name are rare. Often these optical instruments were well-made yet overly-elaborate.

Harvard University. 2014. CHSI- The Collection of Historical Scientific Instruments: Rudolf Fuess. Accessed February 15, 2014.http://dssmhi1.fas.harvard.edu/emuseumdev/code/eMuseum.asp?lang=EN