ProtractorsEngineering & Drafting
By the end of the 18th century, protractors were routinely manufactured by machinery, with the invention of dividing engines, such as Jesse Ramsden's, particularly important for enabling the precise division of a circle into fractions of angles. Makers produced protractors that read minute fractions of angles, particularly when a vernier was added to the instrument.
Mechanics or machinists also used protractors to draw designs for new types of machinery. For instance, there were several forms of limb protractors for draftsmen that both functioned as T-squares and provided angle measurement. Similarly, protractors assisted with the preparation of architectural drawings. The instruments were only displaced by the advent of computer-aided drafting in the late 20th century.
"Protractors - Engineering & Drafting" showing 1 items.
- This semicircular brass protractor is divided by single degrees and marked by tens from 0° to 180° in both the clockwise and counterclockwise directions. The bottom edge is indented so that a pencil or pricker may be placed at the origin point. The protractor bears three marks: POSTS; MADE IN GERMANY; and a fleur-de-lis pointing to the origin. The Frederick W. Post Company, a Chicago mathematical instruments dealer established in 1893, used the type style found on this protractor in the 1920s and 1930s. However, the brass protractor depicted in Post's 1936 catalog is not indented on its lower edge, and it shows an eagle under the maker's mark.
- William J. Ellenberger (1908–2008) donated this object. He studied electrical and mechanical engineering at the George Washington University between 1925 and 1934. He then worked for the Potomac Electric Power Company and the National Bureau of Standards. During World War II, Ellenburger served in the U.S. Army Signal Corps. He was a civilian construction management engineer for the army from 1954 to 1968, when he became a private consultant.
- References: Frederick W. Post Company, Dependable Drawing Materials, 18th ed. (Chicago, 1936), 195; "The G[eorge] W[ashington] Engineering Hall of Fame 2006 Inductees," http://www.seas.gwu.edu/ifaf/hall_of_fame_inductees_2006.php.
- Currently not on view
- date made
- Frederick Post Co.
- ID Number
- accession number
- catalog number
- Data Source
- National Museum of American History, Kenneth E. Behring Center