**Karl Geiser** was a Swiss mathematician who worked in algebraic geometry and minimal sufaces. He organised the first International Mathematical Congress in Zurich.

- Then he spent a further four semesters at the University of Berlin where he was taught by Karl Weierstrass and Leopold Kronecker.
- At Zürich Polytechnikum, Geiser was appointed as an extraordinary professor in 1869, and then in 1873 he was appointed to a full professorship of higher mathematics and synthetic geometry, with special responsibility for teaching mathematics to engineering students and to mathematics students.
- Geiser had a number of famous colleagues at Zürich Polytechnikum, first Georg Frobenius between 1875 and 1892, and then Adolf Hurwitz who filled Frobenius's chair.
- Geiser taught algebraic geometry (his own research topic), differential geometry and invariant theory at Zürich.
- He attended some of Geiser's lectures and towards the end of his life recalled his fascination with Geiser's Infinitesimalgeometrie course.
- In this course Geiser taught the Gaussian theory of surfaces and, in 1912, Einstein had what he described as "the decisive idea" of an analogy between general relativity and Gaussian surfaces.
- Geiser published on algebraic geometry and minimal surfaces.
- It was in large part due to Geiser that when the laboratories were rebuilt in the 1880s and 1890s, theoretical knowledge in scientific experimentation was seen to be an important aspect of good teaching.
- Although Geiser was helped in his career by his relationship with Jakob Steiner, he repaid the debt by editing Steiner's unpublished lecture notes and treatises.
- Using university lectures and posthumous manuscripts of Jacob Steiner) (1867), Construction der Fläche zweiten Grades durch neun Punkte: Nach den hinterlassenen Manuscripten Jacob Steiners dargestellt von Herrn C F Geiser in Zürich Ⓣ(Construction of quadric by nine points: After the posthumous manuscripts of Jacob Steiner presented by Mr C F Geiser in Zurich) (1868), and Zur Erinnerung an Jakob Steiner Ⓣ(In memory of Jakob Steiner) (1874).
- Another important contribution which Geiser made, that was not in the area of research, was to organise the first International Congress of Mathematicians held in Zürich in 1897.
- Geiser was honoured with election as one of the first three honorary members of the Swiss Mathematical Society, elected in session 1911-12.
- Although struck by loss of clear eyesight and temporary blindness which was later partly removed by a surgical operation, Geiser's mind remained active and alert.
- The writer last saw Geiser in the spring of 1929, when he spent a friendly afternoon with him at his home on the lake.

Born 26 February 1843, Langenthal, Bern, Switzerland. Died 7 May 1934, Küsnacht, Zürich, Switzerland.

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Algebra, Geometry, Origin Switzerland

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive