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 The parallel rule was superseded for most uses by the T-square in the 19th century, but navigators continue to use parallel rules in conjunction with gridded charts.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 brass parallel rule has a semicircular protractor attached to the top blade. The protractor is divided to degrees and marked by tens from 10 to 90 to 10.
Description
This brass parallel rule has a semicircular protractor attached to the top blade. The protractor is divided to degrees and marked by tens from 10 to 90 to 10. A movable arm attached to the origin point of the protractor contains a vernier, which was intended to permit the measurement of angles to 5 minutes of accuracy. The hinges connecting the blades of the rule are straight. There is no maker’s mark.
Mathematician James McKenna gave this measuring instrument to the Smithsonian. He reported that an ancestor used it at Bedford, Pa., before 1800. A name, scratched on one of the tools in the set of drawing instruments (310891) that accompanied this protractor, suggests that the ancestor was John A. Stuart, who surveyed a line in Bedford County on Wills Mountain that continues to bear his name.
Compare this instrument to 1978.2110.06.
Reference: 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 18th century
ID Number
MA.310890
catalog number
310890
accession number
131549
This instrument has a wooden handle attached by a large brass thumbscrew to a brass protractor that is divided to single degrees and numbered by tens in both directions from 10 to 170.
Description
This instrument has a wooden handle attached by a large brass thumbscrew to a brass protractor that is divided to single degrees and numbered by tens in both directions from 10 to 170. The protractor is screwed to a rectangular brass piece that slides in a groove in a rectangular wooden guide-piece. The guide-piece has brass clamps and thumbscrews for affixing the instrument on a table. The protractor is also attached by a split nut to a metal screw shaft that runs the width of the instrument. A thumb rest and gear on the left clamp rotates the screw shaft.
A T-square is a technical drawing instrument used by draftsmen primarily as a guide for drawing horizontal lines on a drafting table. In this instrument, the two blades of the T-square are not fixed in a perpendicular position but rather can be rotated to any angle on the protractor. The large thumbscrew can then be used as a handle to move the blades along the screw shaft, allowing the user to draw parallel lines.
Eugene James Towne (1847–after 1900) of North Dana, Mass., received a patent for this device in 1877. He submitted this example with his application as a prototype for the instrument, and the U.S. Patent Office marked it on the bottom: 187330 (/) L.1201.1228. Towne, a cabinetmaker, and J. W. Goodman, who made pianos, billiard table legs, and other wooden items in North Dana, apparently intended to manufacture the device together. However, the instrument likely was not widely adopted.
References: Eugene J. Towne, "Improvement in Parallel Rulers" (U.S. Patent 187,330 issued February 13, 1877); Edwin Eugene Towne, ed., The Descendants of William Towne (Newtonville, Mass., 1901), 284; The Worcester County Directory for 1878–79 (Boston: Briggs & Co., 1878), 41; 1870 and 1900 U.S. Census records.
Location
Currently not on view
date made
1877
maker
Towne, Eugene J.
ID Number
MA.308953
catalog number
308953
accession number
89797

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