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Optical Flat


This instrument is a cylindrical disk-shaped piece of glass about 4cm deep, with a metal rim and casing. Around this rim there are dark marks drawn in pairs at somewhat regular intervals. The metal case and glass appear to be separable. The glass is slightly beveled around the very edge. Fitted beneath the glass is a circular piece of newspaper containing an article on hockey player Gordie Howe.

The object is accompanied by a piece of paper with writing on it.

Accession Number: 2017.ast.42 (DAA-0077)

Alternative Name:

Primary Materials: Glass, Aluminum


None on the object itself.

On the accompanying piece of paper, handwritten in crayon: “This Box Contains 1-8″ optical FLAT. Donated by Dr. R.K. Young July 1960. RK says outside 1/4″ slightly turned down.”

Dimensions (cm): Diameter = 21, Height = 4.


An optical flat is a highly polished flat surface used to measure the flatness of other objects. When the flat is placed in contact against another surface, interference bands from monochromatic light can be examined to determine the flatness of the unknown surface.


Very good. The metallic casing has a few small scratches.

Associated Instruments:

Manufacturer: Unknown

Date of Manufacture: Unknown


According to an accompanying note, the flat was donated to the David Dunlap Observatory or the Department of Astronomy in July 1960 by Reynold K. Young (1886-1977), who was Director of the David Dunlap Observatory from 1935 to 1945.

It was likely transferred from the observatory in the early 2000s, at which point it was stored at the Department of Astronomy and Astrophysics at the University of Toronto. In 2017, it was moved to another storage room at McLennan Physical Laboratories.

Additional Information and References:

The newspaper set behind the glass is an article about hockey player Gordie Howe, described as being in his 14th season with the Detroit Red Wings. Howe was in his 14th season in 1960, the date in which this flat was donated.

Historical Notes: