La Filotecnica Rolling Parallel Rule

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,
Currently not on view
Object Name
parallel rule in case
parallel rule
date made
ca 1870
Officina Filotecnica
Physical Description
german silver (overall material)
wood (overall material)
fabric (overall material)
overall: 3.8 cm x 27.5 cm x 7.5 cm; 1 1/2 in x 10 13/16 in x 2 15/16 in
place made
Italia: Lombardia, Milan
ID Number
catalog number
accession number
Drafting, Engineering
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Parallel Rules
Data Source
National Museum of American History, Kenneth E. Behring Center


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