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 The parallel rule was superseded for most uses by the T-square in the 19th century, but navigators continue to use parallel rules in conjunction with gridded charts.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.

This brass semicircular protractor is divided by single degrees and marked by tens from 10° to 90° to 10°. It is attached with metal screws to a set of brass parallel rules. Brass S-shaped hinges connect the rules to each other.
Description
This brass semicircular protractor is divided by single degrees and marked by tens from 10° to 90° to 10°. It is attached with metal screws to a set of brass parallel rules. Brass S-shaped hinges connect the rules to each other. The bottom left screw on the parallel rules does not attach to the bottom piece. A rectangular brass arm is screwed to the center of the protractor. A thin brass piece screwed to the arm is marked with a small arrow for pointing to the angle markings. The protractor is stored in a wooden case, which also contains a pair of metal dividers (5-1/4" long).
The base of the protractor is signed: L. Dod, Newark. Lebbeus Dod (1739–1816) manufactured mathematical instruments in New Jersey and is credited with inventing the parallel rule protractor. He served as a captain of artillery during the Revolutionary War and made muskets. His three sons, Stephen (1770–1855), Abner (1772–1847), and Daniel (1778–1823), were also noted instrument and clock makers. The family was most associated with Mendham, N.J. (where a historic marker on N.J. Route 24 indicates Dod's house), but Dod is known to have also lived at various times in Newark.
ID number MA.310890 is a similar protractor and parallel rule. Compare also to a Dod instrument owned by the Metropolitan Museum of Art in New York, http://www.metmuseum.org/Collections/search-the-collections/5535.
References: Bethuel Lewis Dodd and John Robertson Burnet, "Biographical Sketch of Lebbeus Dod," in Genealogies of the Male Descendants of Daniel Dod . . . 1646–1863 (Newark, N.J., 1864), 144–147; Alexander Farnham, "More Information About New Jersey Toolmakers," The Tool Shed, no. 120 (February 2002), http://www.craftsofnj.org/Newjerseytools/Alex%20Farnham%20more%20Jeraey%20Tools/Alex%20Farnham.htm; Deborah J. Warner, “Surveyor's Compass,” National Museum of American History Physical Sciences Collection: Surveying and Geodesy, http://americanhistory.si.edu/collections/surveying/object.cfm?recordnumber=747113; Peggy A. Kidwell, "American Parallel Rules: Invention on the Fringes of Industry," Rittenhouse 10, no. 39 (1996): 90–96.
Location
Currently not on view
date made
late 1700s
maker
Dod, Lebbeus
ID Number
1978.2110.06
accession number
1978.2110
catalog number
336732
This 12" clear plastic rolling parallel rule is combined with a scale of inches that is divided to 1/16"; a centimeter scale divided to millimeters; and a protractor divided to 5° and numbered by 30s from 0 to 90 to 0.
Description
This 12" clear plastic rolling parallel rule is combined with a scale of inches that is divided to 1/16"; a centimeter scale divided to millimeters; and a protractor divided to 5° and numbered by 30s from 0 to 90 to 0. Holes in the scales at every 1/2-inch and centimeter help the user align the instrument on a drawing. The holes may also be used with a pencil to produce parallel lines. The instrument is marked with a small centimeter-inch conversion table and the words: MADE IN TAIWAN.
The white roller is also marked with various useful mathematical formulas, a small table of sines and cosines of various angles between 1° and 45°, and comparative centimeter and inch scales that function as a line spacing guide for measuring evenly spaced lines.
The rule appears to be model 1205 of Hua Ching Manufacturing Co., Ltd., which has been making plastic and wooden drafting supplies in Taichung, Taiwan, since 1978. Several firms currently distribute the rule in the United States for a price of about $10.25.
Reference: Hua Ching Manufacturing Co., Ltd., "About Us," http://www.taiwantrade.com.tw/huaching/home/en_US.
Location
Currently not on view
date made
1978–2012
ID Number
2013.0016.01
catalog number
2013.0016.01
accession number
2013.0016

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.