Parallel Rules

Parallel rules help draftsmen, surveyors, cartographers, architects, and navigators draw accurate parallel lines. The instrument comes in two main forms: two rectangular straight edges connected by brass or silver hinges, or a single frame surrounding a roller. The first type was known in Europe by 1600, while Englishman A. George Eckhardt is credited with inventing the second in 1771. The parallel rule was superseded for most uses by the T-square in the 19th century, but navigators continue to use parallel rules in conjunction with gridded charts.

The mathematics collections contain about twenty parallel rules and combination instruments, dating from the late 18th century to the late 20th century and ranging in length from 6 to 24 inches. The objects are made from ebony and other woods, brass, German silver, and plastic. They were manufactured in the United States, England, Italy, and Taiwan. They were used for military surveying, in navigation, in business, in art and technical drawing, and for placing handles on caskets. Several of the objects in this group illustrate innovations added to the basic instrument.

Acknowledgement

The digitization of this group of artifacts was made possible through the generous support of Edward and Diane Straker.

A 14" trapezoidal mahogany frame with metal end pieces covers two mahogany rollers that rotate on metal shafts. A paper label is marked: CARRINGTON'S PATENT PARALLEL RULER, FOR COUNTING HOUSES, &C. The label is decorated with an eagle over a shield with arrows in its claws.
Description
A 14" trapezoidal mahogany frame with metal end pieces covers two mahogany rollers that rotate on metal shafts. A paper label is marked: CARRINGTON'S PATENT PARALLEL RULER, FOR COUNTING HOUSES, &C. The label is decorated with an eagle over a shield with arrows in its claws. The eagle's beak holds a banner marked: E PLURIBUS UNUM.
On April 14, 1832, James Carrington of Wallingford, Conn., patented a parallel ruler that was later manufactured by William Hill of Wallingford. The rollers were raised in order to prevent ink from smearing as the ruler was moved across a drawing. In 1849 the U.S. House of Representatives ordered six dozen of the rulers from R. Farnham, a stationer in Washington, D.C., for $2.30 per dozen. This suggests the rules were used relatively widely for a significant period of time. Before he built a dam and factory in Wallingford around 1830, Carrington was a supervisor and inspector at the Harpers Ferry and Springfield armories.
References: "American Patents," The Repertory of Patent Inventions 15 (1833): 24; "Power, Factories, Invention," in Centennial of Meriden: June 10–16, 1906 (Meriden, Conn.: Journal Publishing Co., 1906), 245; U.S. House of Representatives, Contracts for Stationery, 31st Congress, 1st Session, Miscellaneous, No. 16, December 31, 1849 (Washington, D.C., 1850), 16–17; Hiram Williams Beckwith, History of Montgomery County, Together With Historic Notes on the Wabash Valley (Chicago, 1881), 246; Merritt Roe Smith, Harpers Ferry Armory and the New Technology (Cornell: University Press, 1977), 203, 207, 229.
Location
Currently not on view
date made
mid 19th century
patentee
Carrington, James
ID Number
MA.293320.2818
accession number
293320
catalog number
293320.2818
This clear plastic ruler has two aluminum hinges and small positioning knobs that may be tightened or loosened. The lower left and upper right corners of the blades are marked: 18". The hinges are marked: THE C-THRU RULER CO. (/) BLOOMFIELD, CONN. U.S.A.
Description
This clear plastic ruler has two aluminum hinges and small positioning knobs that may be tightened or loosened. The lower left and upper right corners of the blades are marked: 18". The hinges are marked: THE C-THRU RULER CO. (/) BLOOMFIELD, CONN. U.S.A. Six circular slices of cork on the bottom of the instrument protect the surface on which it is used.
Teacher Jennie Zachs established the C-Thru Ruler Company of Hartford, Conn., in 1939. Although the firm was acquired by Acme United Corporation in 2012, it continues to make drafting tools and drawing instruments, including an aluminum version of this instrument. For other C-Thru products, see 1984.1071.12 and 1988.0807.02.
References: Brian Dowling, "Acme United Acquires Bloomfield's C-Thru Ruler," Hartford Courant, June 11, 2012; "About Us," C-Thru Ruler Company, http://www.cthruruler.com/.
Location
Currently not on view
date made
mid 20th century
maker
C-Thru Ruler Company
ID Number
1990.3130.01
catalog number
1990.3130.01
nonaccession number
1990.3130

Our collection database is a work in progress. We may update this record based on further research and review. Learn more about our approach to sharing our collection online.

If you would like to know how you can use content on this page, see the Smithsonian's Terms of Use. If you need to request an image for publication or other use, please visit Rights and Reproductions.