Squares & TrianglesTriangles
The triangles in the mathematics collections illustrate the products sold by leading American makers of drawing instruments, including Darling, Brown & Sharpe of Providence, R.I.; and Keuffel & Esser of New York City. An American inventor, LeRoy J. Leishman, devised the Arcascope triangle and combination instrument. The objects on this page also show a transition from triangles made from steel, wood, and rubber to triangles made from plastic. The change in materials in the early 20th century has created a problem for preserving these instruments, as celluloid-based plastics are chemically unstable. Several of these objects are deteriorating despite efforts to store them in a controlled environment.
"Squares & Triangles - Triangles" showing 1 items.
- This wooden case of military drafting instruments has leather handles and metal hooks and is lined with black velvet. Wooden and metal pieces inside the case help hold the instruments in place. The set includes a 12" aluminum circular protractor, divided to 1000s of mils and numbered by ones from 1 to 64, with a vernier controlled by a spring. The vernier permits readings to 100 mils of accuracy and is marked: R = 170 m/m. A bar across the center of the protractor has three oval cutouts covered by plastic marked with a hairline that are used to position the instrument. The bar is marked: SALMOIRAGHI (/) MILANO. Black plastic is screwed to the bar on both sides. Both plastic pieces are marked: 3559. They are also marked: MISS-BAK.
- An 18" aluminum scale rule with two positioning knobs is divided along one edge to ten mils and numbered by hundreds of mils from 100 to 11,200. The other edge is divided to half-millimeters and numbered by centimeters from 0 to 39. The rule is marked: SCALA 1:25000. A 5-1/4" aluminum and plastic sight is divided to 1000s of mils and numbered by ones from 1 to 64. An aluminum or German silver beam compass has two points, an additional clamp with two thumbscrews, and a 12-1/4" wooden beam with a notch at the middle.
- The case also holds a black plastic and aluminum joint tightener; a 3-5/8" aluminum triangle divided to millimeters and numbered by tens from 60 to 10 along the x axis and from 10 to 80 along the y axis; 2-7/8" German silver and aluminum beam dividers; a 3-1/8" crayon holder; 6-1/8" aluminum dividers with pen and pencil attachments; a 2-3/4" German silver screwdriver; a 1-1/2" cylindrical aluminum case with seven pencil leads; and an additional pencil attachment for a compass that does not appear to fit either pair of dividers. The large dividers are marked: IAS. At least one piece of the original set is missing.
- 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 1900
- ID Number
- catalog number
- accession number
- Data Source
- National Museum of American History, Kenneth E. Behring Center