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 graduated to half-degrees. It is marked by tens from 10° to 170° in both directions, from left to right and from right to left. A brass rectangle with a curved notch has been soldered on at the origin point. The rectangle contains a small hole for locating the vertex of the angle being measured. The base of the protractor bears the maker's mark: W. C. Cox, Devonport. The letters DB are scratched near the maker's mark.
- William Charles Cox, a British instrument maker who worked in Plymouth and Devonport, had his shop in Devonport from 1830 to 1851. He presumably made this protractor during that period. The Smithsonian purchased this instrument in 1959 from the estate of Henry Russell Wray via an auction conducted by Maggs Bros. Ltd. of London.
- Reference: Gloria Clifton, Directory of British Scientific Instrument Makers 1550-1851 (London: National Maritime Museum, 1995), 69–70.
- Currently not on view
- date made
- ca 1840
- Cox, William Charles
- ID Number
- accession number
- catalog number
- Data Source
- National Museum of American History, Kenneth E. Behring Center