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 The parallel rule was superseded for most uses by the T-square in the 19th century, but navigators continue to use parallel rules in conjunction with gridded charts.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.
The digitization of this group of artifacts was made possible through the generous support of Edward and Diane Straker.
"Parallel Rules - Overview" showing 1 items.
- This ten-inch German silver instrument has two rollers connected by a shaft. Both ends have knobs to hold while rolling the parallel rule. Both long edges have centimeter scales, divided to millimeters and numbered by ones from 0 to 24. The instrument is marked: "LA FILOTECNICA" MILANO. A wooden case is lined with dark blue velvet and has ornate brass clasps. The bottom of the case is marked in red pencil: S_301 £ £ £.
- Ignasio Porro (1801–1875) established La Filotecnica in Milan in 1865 to train students to make optical and mathematical instruments. Between 1870 and 1877, one of his apprentices, Angelo Salmoiraghi (1848–1939), purchased the firm and put more emphasis on manufacturing. By 1906 the company was renamed Filotecnica Salmoiraghi.
- References: Paolo Brenni, "Italian Scientific Instrument Makers of the Nineteenth Century and Their Instruments," in Nineteenth-Century Instruments and Their Makers, ed. P. R. de Clercq (Amsterdam: Rodopi B.V., 1985), 196–198; Bill Morris, "A Fine Sextant by Filotecnica Salmoiraghi of Milan," October 5, 2010, The Nautical Sextant, http://sextantbook.com/2010/10/05/a-fine-sextant-by-filotecnica-salmoirhagi-of-milan/.
- Currently not on view
- date made
- ca 1870
- Officina Filotecnica
- ID Number
- catalog number
- accession number
- Data Source
- National Museum of American History, Kenneth E. Behring Center