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This plaster model consists of four roughly spherical parts attached to one another. It represents a surface of constant positive curvature. More specifically, it is a surface of Enneper of elliptic type. The Enneper surface is a minimal surface (a surface of zero mean curvature) that intersects itself.
A paper tag on the model reads: 206. Another tag reads: Fläche von const. posit. Krűmm.-Mass [/] mit einem System ebener Krűmm.-Lin. [/] II. Cycl. Typus [/] Verl. v. L. Brill. 17. Ser. Nr. 3b.
The model was designed for Ludwig Brill by Georg H. L. Sievert in 1886. A student of Alexander Brill in Munich, Sievert spent much of his career teaching mathematics in Nuremberg and Bayreuth.
This example of the model was exhibited at the German Educational Exhibit at the Columbian Exposition, a World’s Fair held in Chicago in 1893. It there was purchased by Wesleyan University in Connecticut, and subsequently was donated to the Smithsonian.
L. Brill, Catalog mathematischer Modelle..., Darmstadt: L. Brill,1892, p. 41, 81.
http://www.math.rug.nl/models/ - This website displays an example of the model sold somewhat later by Brill’s successor, Martin Schilling. Schilling sold this model as Ser. 17, No. 3.
G. Fischer, Mathematical Models,vol. I, p. 83 (Photo #87), vol. 2, pp. 38-39.
Currently not on view
Germany: Hesse, Darmstadt
plaster (overall material)
overall: 8.5 cm x 14.5 cm x 17.5 cm; 3 11/32 in x 5 23/32 in x 6 7/8 in