**Georg Sidler** was a Swiss mathematician and astronomer.

- Sidler senior also had a great interest in astronomy and mathematics, having attended lectures in both subjects during his law studies.
- Sidler senior did not publish any scientific papers, but it is likely that he helped spark his son's interest in mathematics and astronomy.
- Let us now return to Georg Sidler junior.
- Sidler attended the Gymnasium in Zürich from 1843-1850, excelling in mathematics and ancient languages.
- In 1852, Sidler moved to Paris to study there for a further two years.
- It was Puiseux's lectures that inspired Sidler's doctoral dissertation Sur les inégalités du moyen mouvement d'Uranus dues à l'action perturbatrice de Neptun Ⓣ(On the inequalities of the mean motion of Uranus due to the disturbing action of Neptune), published after his return from Paris in 1854.
- Ⓣ(On the movements in the solar system and general attraction.) A more succinct version of Sidler's thesis was published as Über die Acceleration des Uranus durch Neptun in Astronomische Nachrichten in 1858.
- After having received his doctorate, Sidler habilitated as Privatdozent at the University of Zürich with a lecture entitled Methode der kleinsten Quadrate Ⓣ(Method of least squares).
- Sidler often went for a walk with Steiner; the two mathematicians stayed in touch for the rest of Steiner's life.
- Encke asked Sidler to calculate the ephemeris of Neptune for the year 1856, to be published in the Berliner Astronomisches Jahrbuch 1856, and allowed him to use the Berlin observatory.
- As a result, Sidler spent many nights in the observatory, observing and mapping recently discovered minor planets.
- Despite this, Sidler retained an interest in astronomy for the rest of his life.
- After his return to Zürich in August 1855, Sidler habilitated at the newly founded Polytechnic.
- After a year in Zürich, Sidler was appointed to a teaching position at the newly founded Kantonsschule (secondary school) in Bern.
- The school had two departments, one specialising in arts and the other one in sciences, but Sidler taught mathematics, and for a few years mechanics, in both departments.
- In addition to his duties at the school, Sidler also lectured at the University of Bern.
- The promotion was proposed by his colleagues, who recognised Sidler's contribution to mathematics and astronomy both at the university and in Switzerland; in particular they highlighted his commitment to the university's observatory.
- Sidler remained a member of the university's academic staff and lectured occasionally even after resigning from his post.
- We note that Sidler had a particular interest in the geometry of triangles and collected books on this topic.
- The University of Zürich renewed Sidler's doctorate in 1904 to mark the 50th anniversary of obtaining it.
- Furthermore, Geiser dedicated his paper Die konjugierten Kernflächen des Pentaeders Ⓣ(The conjugated kernel surfaces of the dodecahedron) and Rudio his paper Die Möndchen des Hippokrates Ⓣ(The Lune of Hippocrates) to Sidler.
- Two years later, Sidler's 50th year in the Bernese educational service was celebrated officially as well, on Graf's instigation.
- Apart from in his teaching positions, Sidler also made a name for himself as a member of the Bernese cantonal Matura Examination Committee (1880-1905) and of the Examination Committee for teachers in higher education.
- At the time, three secondary schools in Bern awarded the Matura (in Bern, Burgdorf and Pruntrut), and Sidler had to examine all pupils in mathematics.
- As examiner, Sidler had to set the problems for the written exam and do all the marking, as well as conduct every oral examination in the canton.
- He comments that Sidler was an excellent examiner, making the pupils work independently and encouraging them to develop their own thoughts.
- As a result of his work as an examiner, Sidler published two papers, Zur Theorie des Kreises Ⓣ(On the theory of the circle) (1902) and Zu den logarithmischen Reihen Ⓣ(On the logarithmic series) (1904).
- In addition, Sidler published a number of papers and talks on astronomical problems and phenomena as well as on problems in analysis and geometry.
- As most Swiss mathematicians of his time, Sidler was a member of the Schweizerische Naturforschende Gesellschaft, and of the societies for natural scientists in Bern and Zürich for most of his life.
- As mentioned above, Sidler was in touch with a number of mathematicians in Zürich.
- Sidler met Steiner during his first stay in Berlin.
- Steiner spent a lot of time with Sidler during his stay in Bern in 1856-1858 and during the subsequent summers.
- He seems to have hoped that Sidler would help him formulate mathematical ideas, but this never came to fruition as Steiner suffered a stroke in 1862 and died half a year later.
- In the 1880s, Sidler donated a tombstone for Steiner's grave that has been rediscovered in the Bernese cemetery by Bützberger and Moser.
- Schläfli was Sidler's colleague at the University of Bern for thirty-five years.
- Whilst he mainly lectured on analytic geometry, infinitesimal calculus, theory of functions and number theory, Sidler primarily gave lectures on theoretical astronomy and synthetic geometry.
- No doubt one can imagine the autodidact Schläfli's interest when he asked Sidler to tell him about the famous lectures in Paris and Berlin, and how valuable Sidler's exemplary lecture notes were to him.
- Sidler introduced his older friend to the theory of spherical harmonics, ...
- and when Schläfli mastered this area through his inventions, Sidler, as a student, looked up to him without envy.
- Although described as lank and bookish, Sidler enjoyed good health throughout his lifetime.
- could ever forget Georg Sidler! Today we live in completely different times than just a few decades ago, and as the times change, so do the faces.
- But according to the whole of his outward appearance, Georg Sidler belonged to the good old times, when we still had characters like Schweizer-Sidler, Mommsen, Weierstrass.

Born 31 August 1831, Zug, Switzerland. Died 9 November 1907, Bern, Switzerland.

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Astronomy, Origin Switzerland

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