Brill Model of an Elliptic Paraboloid, 1892, Smithsonian Institution negative number NMAH-AHB2017q014188

The Danish-born mathematician Olaus Henrici (1840–1918) studied engineering and then mathematics in Germany, settling in England in 1865. Henrici first worked as an engineer but then taught at University College London and, from 1884, at the Central Institution in South Kensington. At both schools, he arranged space for the construction of mathematical models. In 1873, his interlocking paper model of an elliptic hyperboloid was exhibited at a meeting of mathematicians in Göttingen. Alexander Brill (1842–1935) of Munich attended the meeting and was much impressed. Brill designed a series of such paper models, almost all made up of circular discs and arcs of discs. He apparently first simply displayed these, but by 1888, his brother, the publisher Ludwig Brill, was selling them as “Carton Models.” This was the first of numerous series of mathematical models that L. Brill and his successor Martin Schilling published over the next decades. This example of a model from the series was exhibited at the 1893 World’s Fair in Chicago and then sold to Wesleyan University. Several paper models of second-order surfaces, including this one, are shown at https://americanhistory.si.edu/collections/object-groups/geometric-models-degree-two-paper.