Johann Wilhelm Andreas Pfaff (5 December 1774 Stuttgart – 26 June 1835 Erlangen) Director in 1804−1809

Pfaff was born as the third son in the family of Friedrich Burkhard (1738-1817), the leading financial advisor in the Princedom of Württemberg, and Maria Magdalena (1742-1783), the daughter of the local advisor of clerical and court issues. Thanks to the welfare of the family all the three sons could get university education and they devoted their lives to scientific research: Christoph Heinrich (1772-1852) became a professor of chemistry and medicine at Kiel University, Johann Friedrich (1765-1825) a professor of mathematics at Helmstedt University and Johann Wilhelm Andreas a professor of mathematics at the Imperial University of Tartu.

In the years 1791-1796 Johann Wilhelm studied at the famous Württemberg protestant theological seminary, the so-called Tübingen stift. At the graduation examinations passed in 1796 Pfaff occupied the second place in excellence but it was not his ambition to become a pastor. Beside theology he had also studied mathematics and other natural sciences. Thanks to the relations with Christoph Friedrich Pfleiderer (1736-1821), a professor of mathematics and physics at Tübingen University, and the observer of the local observatory Johann Gottlieb Bohneberger (1765-1831), Pfaff became interested also in astronomy.

Johann Wilhelm came to Tartu on recommendation of his elder brother Johann Friedrich who did not take the offered post. Pfaff arrived in Tartu in the spring of 1804. In the autumn of 1804 he married Pauline von Patkul (1779-1816).

In Tartu Pfaff delivered lectures on differential and integral calculation in addition to elementary mathematics and also taught combinations and the theory of probability (1806). He started using stationary astronomical observation instruments (at first in the Lenz’s house, then in the Lamberti’s house) and tried to solve the problem of determining the geographical longitude between Tartu, Riga, Mitavi and Moscow. The most important instruments helping it was the large passage instrument, received in 1807 from the Dollond company, for observing the stars passing through the Tartu meridian.

Pfaff was the centre of a circle of the people interested in astronomy including M. G. Paucker, K. Williams and H. Ch. Schumacher. In addition Pfaff worked out an exact mathematical theory for all the observation instruments thus being ahead of the theoreticians who became recognized later (Fr. W. Bessel, P. A. Hansen). In 1806-1807 he published the first series of astronomical publications in Tartu Astronomiche Beyträge.

Pfaff could not see the completion of the observatory. Because of economic decline he left Tartu in the spring of 1809 for Germany to the Nuremberg Institute of Sciences. In 1807 Pfaff was elected corresponding Member of the Academy of Sciences in St. Petersburg. Later he was dealing with astrology.