Prism Monocular

The eye end of this small optical instrument is engraved “443” and “J. G. Hofmann / rue de Buci 3 / Paris.” The objective end is engraved “J. G. HOFMANN / PARIS.” Inside is a prism assembly that shortened the length of the instrument but maintained its longer focal length. Both prisms are marked, in pencil, “J.G.H.” The objective lens is marked, in pencil, “J.G. Hofmann à Paris 1862.”
Ignazio Porro (1801-1875) was an Italian engineer who moved to Paris in 1842. In 1847 he established an Institut Technomatique et Optique that manufactured optical instruments for surveying work. He designed the prism assembly, as found in this monocular and in later binoculars, around 1850. He returned to Italy around 1861.
Jean Georges Hofmann was a German optician who worked with Porro in Paris. He would later design and make such instruments as spectroscopes and saccharimeters.
Currently not on view
Object Name
date made
ca 1862
Hofmann, Jean Georges
overall: 2 1/2 in x 1 7/8 in x 4 1/4 in; 6.35 cm x 4.7625 cm x 10.795 cm
place made
France: Île-de-France, Paris
ID Number
accession number
catalog number
Science & Mathematics
See more items in
Medicine and Science: Physical Sciences
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Ralph K. Dakin
Additional Media

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