Clebsch left Giessen in 1868 when he was appointed to fill the chair at Göttingen that had been held by Bernhard Riemann who had died in 1866. This changed the research environment at Giessen since Clebsch took his entourage of students with him. However, Paul Gordan remained at Giessen and his interests were similar to those of Brill. In 1869 Brill left Giessen to take up an appointment as a full professor at the TechnischeHochschule in Darmstadt [7]:-
In 1874 he brought out a series of paper models of second order surfaces. These models were inspired by a model of an elliptic paraboloid made from half-circles which the German-educated mathematician OlausHenrici of London had sent to a meeting of mathematicians in Göttingen. Brill's models, which represented surfaces by delicately interlaced circles or quadrilaterals, were not as sturdy as wooden or even plaster models, but cost considerably less.