Delure Graphometer

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This graphometer is marked "Delure A Paris" and dates from the early 18th century.The semicircle is graduated to single degrees, numbered clockwise and counterclockwise, and read by diagonal scales at either end of the alidade to 10 minutes.
A graphometer consists of a graduated semicircle with a pair of sight vanes at either end, and a movable alidade with another pair of sights at either end. The form was introduced in Philippe Danfrie, Déclaration de l’usage du graphomètre (Paris, 1597), and was always popular in France. Many graphometers have an inset magnetic compass. Most graphometers are made of brass, but some American ones are made of wood. Some 19th-century graphometers had telescopes rather than open sights. Graphometers were also known as semi circles or semicircumferentors.
Ref: J. A. Bennett, The Divided Circle (Oxford, 1987), pp. 49–50.
Currently not on view
place made
France: Île-de-France, Paris
overall: 9 1/2 in; 24.13 cm
needle: 1 1/2 in; 3.81 cm
overall: 6 3/4 in x 9 3/4 in x 6 3/4 in; 17.145 cm x 24.765 cm x 17.145 cm
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Data Source
National Museum of American History