(b. Bernburg, Anhalt, Germany; d. Bernburg, 1599–1608)
The exact dates of Rothmann’s birth and death are not known. He studied theology in Wittenberg and also attended lectures in mathematics and astronomy (maybe under Johann Praetorius). In 1577 William IV of Hesse persuaded Rothmann to come to Kassel as his mathematicus and assist him in his observatory and with the publication of his star catalog. The clocks and other instruments were in the care of Bürgi, an outstanding instrument maker and a competent mathematician. Rothmann and Burgi worked on “prosthaphairesis,” a method for converting multiplication into addition by means of trigonometric functions. Rothmann, who seems to have been a conceited and difficult person, tried to claim priority for the discovery, although the very modest Bürgi probably contributed more.
In 1590 Rothmann visited Tycho Brahe at Hven. He stayed one month and then, instead of returning to Kassel, went back to his native town, where he became occupied with theological controversies. He remained there until his death, which must have occurred between 1599 (when, according to a letter from Tycho to Severin, he was still living) and 1608 (when a notice Bericht von der Tauffe was published in Goslar as posthumous).
Rothmann’s importance derives mainly from his correspondence with Tycho Brahe. Tycho had visited William IV in Kassel in 1575; but they did not communicate again until the comet of 1585, which led to an exchange of letters between Tycho in Hven and William IV and Rothmann in Kassel that lasted for six years. A last letter was written by Rothmann from Bernburg in 1594. This correspondence covered all aspects of contemporary astronomy: instruments and methods of observing, the Copernican system (which Rothmann supported against Tycho’s system), comets, and auroras. These letters were eventually published by Tycho in Tychonis Brahe Dani Epistolarum astronomicarum … (Uraniborg, 1596).
Rothmann did not publish anything himself. According to Rudolf Wolf, his manuscripts are preserved in Kassel and consist of several star catalogs, a description of the Kassel observatory and its instruments, a general work on astronomy, and trigonometric tables.
Willebrord Snell published part of Rothmann’s MSS in his Coeli et siderum in eo errantiun observationes hassiacae (Leiden, 1618).
The contents of the MSS are extensively described by R. Wolf, Astronomische Mittheilungen, 5 , no. 45 (1876–1880). See also his Geschichte der Astronomie (Munich, 1877); and J. L. E. Dreyer, Tycho Brahe, a Picture of Scientific Life and Work in the Sixteenth Century (Edinburgh, 1890; repr. New York, 1963).
Lettie S. Multhauf