Christian Zeller

Julius Christian Johannes Zeller was a German mathematician, born on 24 June 1822 at Mühlhausen am Neckar and died on 31 May 1899 at Cannstatt. He trained in mathematics, geography and theology, and in 1874 he became director of the seminary at Markgröningen and of a girls' orphanage. In 1882 he joined the Société Mathématique de France, and on 16 March 1883 he presented to it a short account of the congruence relation that now carries his name, Zeller's congruence, which gives the day of the week for a given calendar date. His four papers on calendar formulae also treat the date of Easter Sunday for both the Julian and the Gregorian calendars, and he published separately on number theory, including work on Bernoulli numbers and on Euler's recursion formula for sums of divisors. He received the Order of Friedrich, First Class, and the Ritterkreuz of Württemberg, and retired in 1898.