Mathematical Treasure: Captain Field's Improved Parallel Rule

Amy Ackerberg-Hastings (University of Maryland University College)

Capt. Field's Improved Parallel Rule

Captain Field's Improved Hinged Parallel Rule, Signed by Henry Hughes & Son, 1923, Smithsonian Institution negative number DOR2012-8041.

Parallel rules are drawing instruments used to make accurate parallel lines on maps, charts, and architectural drawings. In 1854, English captain William Andrew Field (or Feild, ca 1796–1871) modified the hinged form of parallel rules, which had been used in Europe since about 1600, by adding scales for 0° to 180°, like those on a protractor, and compass points. These innovations made it easier for ship navigators to move the rule without losing track of the ship's course.

Henry Hughes & Son of London manufactured metal forms of the rules, several of which were purchased by the U.S. Coast & Geodetic Survey in the early 20th century.

This object and other parallel rulers from the Smithsonian's National Museum of American History are now shown and described at the website

Index of Mathematical Treasures

Index of Mathematical Objects