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Rolling Parallel Rule


This is a ruler stored in an open wooden box and wrapped in yellow paper. The ruler is rectangular, with beveled ivory edges slowing down the surface on which it is placed. These are graduated in inches, one side subdivided into 1/8″ and the other in to 1/10″. Along the length of the ruler is a long rod with two ridged wheels at each end; this rod is covered with a wooden cover with a small metal knob in the middle. This was once glued in place but has now separated from the ruler. The wheels protrude through the ruler, and permit it to be rolled in one direction only.

Accession Number: 2012.ast.4 (DAA-0103)

Alternative Name:

Primary Materials: Wood, Ivory, Metal: Copper Ivory


Engraved into wood is: “CHAS HEARN ROMAIN BDGS TORONTO”.

Inside the wooden box, stamped: “E. F. FU[????]”

Dimensions (cm):

Length = 2.5, Width = 6.7, Height = 32.2


The ridged wheels of this ruler mean it can be rolled in one direction only, and thus can be used to draw parallel lines. This ruler is used in navigation, cartography, drafting and astronomy.


Poor: The box of the ruler is in good condition. The rest of the ruler is in poor condition. The ivory scale on one side of the ruler has split and there are several cracks on both sides. The cover to the rolling wood has come away from the wood. The brass surfaces are worn. There is a strip of black material that is no longer connected to anything tucked inside the paper.

Associated Instruments:

Manufacturer: Charles Hearn, Toronto

Date of Manufacture: c. 1900


University of Toronto Department of Astronomy and Astrophysics

Additional Information and References:

Entry updated courtesy of information provided by R. A. Rosenfeld, M.A., M.S.L., Archivist, Royal Astronomical Society of Canada.

See also: A Descriptive Treatise on Mathematical Drawing Instruments… (London: the author, 1873), pp. 155-156; Maya Hambly, Les instruments de Dessin 1580-1980, tr. D. Bauthier (Paris[?]: Ars mundi, 1991 [orig. Engl. ed. 1988]), pp. 110 (fig. 103), 113.

Information on Charles Hearn can be found <a href=”>here</a>, at David Pantalony’s “Digital Museum Seminar” pages. [12/02/19]

Historical Notes: