Hartl Optical Disc

Astronomy

Accession Number: 2019.ast.174

Description:

This object consists of a large disk mounted vertically standing on a stand. The whole apparatus can be rotated horizontally around the stand.

The disk has a deep lip around the rim. Cut in one side of this lip half way up the disk there are seven horizontal slits; the top one of these is covered by a small rectangular piece of black glass, and the bottom-most slit is covered by a rectangular piece of clear transparent glass.

Mounted inside the disk there is a metal panel with a rim graduated in 360 degrees, with 0 degrees opposite one another, and 90 degrees opposite each other. The panel can be rotated by means of a handle on the rear of the disk. Inside the disk, there are four knobs, three in a horizontal row and one directly above (when the lettering on the panel is set upright) the rightmost knob; these can be unscrewed and moved to five additional screw holes in the panel. Printed on the panel between these knobs there are various geometric shapes.

Alternative Name: Optical Disk

Primary Materials: Metal: Iron Alloy, Plastic

Markings:

Printed on the rotating circular panel: “cenco”
“HARTL”
“HARTL OPTICAL DISC
CENTRAL SCIENTIFIC CO.
CHICAGO, U.S.A.
SOLE AUTHORIZED MANUFACTURERS”

In raised lettering on the feet of the stand: “cenco”

On a sticker affixed to the rear of the disc: “CENTRAL SCIENTIFIC DIVISION OF
CENCO INSTRUMENTS CORPORATION
CATALOGUE NO. 85245
cenco”

On a paper sticker affixed to the rear of the disc: “AST50”

On a tag dangling from the rear of the disk: “Central Scientific Co.
CHICAGO
CAT. NO.
85215
LOT NO.
200172L62
SER. NO.
INSPECTOR
[?] P M”

Dimensions (cm): Length = 36.2, Width = 22, Height = 42

Function:

The Hartl Optical Disc demonstrates optical effects. It demonstrates the path of a ray of light (shone through the gaps on the rip of the disc) through acrylic prisms and lenses that can be mounted on and between the knobs screwed into the rotating panel. The change in the angle of rays can be measured against the graduations on the rim of the disc.

Condition:

Good: The disc structure is in good condition, although the screws of the pegs are very rusty. However, all the acrylic lenses and prisms are missing.

Manufacturer: Central Scientific Company (Cenco)

Date of Manufacture: 1930-1950

Provenance:

This object may have been used for demonstrating optical effects at the Department of Astronomy and Astrophysics. At some point, it may have been moved to the David Dunlap Observatory at some point, if it was not always there. In 2008, with the closure and sale of the observatory, the object was stored at Department of Astronomy and Astrophysics until 2017 when it was moved to a new storage location in McLennan Physical Laboratories.