The German Karl Rohn (1855-1920) intended to become an engineer, but found the mathematical part of his studies at the polytechnic in Darmstadt more intriguing. He studied mathematics with Alexander von Brill and Felix Klein in Munich, and went on to a career as a professor of mathematics in Leipzig and Dresden.
In 1886 and again in 1892, Rohn published sets of string models with the publisher and mathematical model distributor Ludwig Brill. Several models from the first set, Brill’s Series XIII, were exhibited at the Columbian Exposition, a world’s fair held in Chicago in 1893. This is one of them, number 9 in the series. It has a black metal frame and gold strings.
As described in the Brill catalog, the surface consists of a mantle on which there are two pieces of the double curve; the generators are partly real, partly ideal, double secants of the space curve of third order, including four tangents.
Compare 1985.0112.128, MA.211257.122 and MA.304722.29. The last two models are by Richard P. Baker.
L. Brill, Catalog mathematischer Modelle. . ., Darmstadt: L. Brill,1892, pp. 27-28, 69.
An example of the model is shown in the website of the Dresden collection of mathematical models, accessed October 17, 2017. At that time, their copy of this model was described at http://www.math.tu-dresden.de/modellsammlung/karte.php?ID=557.
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