Diffraction Grating


Accession Number: 2009.ph.14


A flat metal disc, one side of which is reflective, with a rectangular grating in the middle; this appears dull and if tilted refracts the light into rainbows. The other side of the disk is dull and dotted with air holes. This metal piece is contained within a purpose-built wooden box which shows evidence of having been screwed shut. There is a paper label affixed to the top of the box.

Alternative Name:

Primary Materials: Metal, Glass


The box has a label which reads: “TO WHOM IT MAY CONCERN: This box contains one diffraction grating which is being sent to Dr. E.F. Burton by Dr. H.G. Gale for trial purposes,” (typewritten); This side up (handwritten, red pencil); 317.5 Centimeter ______” [label torn]; on one edge of the grating is written “TOP”.

On the back of the grating is marked directly into the metal: “Grating No. 129” and “Melt No. 151”.

Dimensions (cm): Height = 2, Diameter = 14.5


Diffraction gratings consist of an array of extremely fine engraved lines on a glass or metal surface. These break light into a spectrum which can be analyzed in order to learn about either the source of the light or a medium through which the light passes.


Fair: The box had been screwed shut, perhaps for transport. Now, only a few screws remain in place; they are rusty. The paper label on the lid is ripped in one corner. The reflective side of the disc is somewhat dulled and corroded; this is especially true of the rectangular grating, which is browned, although it still reflects and splits light with a prism-like effect.

Associated Instruments:


Prof. Henry Gordon Gale and assistants at the Department of Physics at the University of Chicago

Date of Manufacture: 1931-1943


Sent to Dr. E.F. Burton (University of Toronto Department of Physics) by Dr. Henry Gordon Gale at the Department of Physics at the University of Chicago, sometime between 1931 and 1943. It may have been used by Burton.

Additional Information and References:

Crew, H. “Henry Gordon Gale 1874-1943” The Astrophysical Journal, Vol. 97, No. 2 (March 1943) pg 88.

Historical Notes:

H.G. Gale took on the mantle of improving the University of Chicago ruling engine for ruling diffraction gratings in 1931, following Albert Michelson’s death in 1931. According to an obituary (1943) by H. Crew, he “improved the engine by the addition of a ‘work screw’ to drive the heavy carriage, while a ‘precision screw’ of the same nominal pitch drives a superimposed light carriage upon which rests the speculum plate about to be ruled. The irregularity of friction between nut and screw Gale eliminated by immersing both of them in an oil bath.” The author of the obituary also credits “three skilful assistants” Pearson, O’Donnell and Getzholtz. Crew, H. “Henry Gordon Gale 1874-1943” The Astrophysical Journal, Vol. 97, No. 2 (March 1943) pg 88.

It is likely that this grating is one of those made during Gale’s tenure presiding over the ruling engine and Burton’s directorship of the Department of Physics at the University of Toronto, and therefore dates from between 1931-1943 (and most likely dates from before 1939).