Menu Close

Diffraction Grating


This object consists of a rectangular sheet of glass, in the centre of which there is a small rectangle of a slightly rougher glass; this is the grating. There is a paper label stuck to the glass, it reads: “Thorp’s Transparent Replica of Rowland Metal Diffraction Grating
14515 lines to the inch.”

This piece of glass is set on top of a piece of tissue paper, and a fluffy material, possibly wool or cotton. This is all contained in an open cardboard box.

Accession Number: 2019.ast.140 (DAA-0119)

Alternative Name:

Primary Materials: Glass, Paper, Cardboard


On a paper label stuck to the glass: “Thorp’s Transparent Replica of Rowland Metal Diffraction Grating
14515 lines to the inch.”

Dimensions (cm):

Grating: Length = 6.6, Width = 5, Height = 0.7


Gratings act like prisms to split light into its constituent parts revealing spectroscopic information. This can be analyzed to identify the chemical makeup and other features of the light source and media through which the light is traveling.


Very Good: The glass piece is in excellent condition, although the paper label is yellowed. The cardboard box is somewhat worn around the corners.

Associated Instruments:

Manufacturer: Thomas Thorp

Date of Manufacture: 1900-1910


This object was possibly purchased by the early U of T Department of Physics & Astronomy in the 1900s or 1910s. At some point, it may have been moved to the David Dunlap Observatory. If so, it was probably moved back 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:

<a href=”…..14…93T”>An article written by Thomas Thorp</a> in 1906 describes his method for creating glass diffraction gratings which were similar in quality to Henry Rowland’s metal gratings. (Popular Astronomy, 1906, vol. 14: 93-96)

Historical Notes: