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This article sheds light onto life and work of the German land surveyor, cartographer, astronomer, and mechanic Johannes Humelius (1518-1562), paying special attention to the situation of the University of Leipzig in the middle of the 16th century. At this scientific institution, the scholar Humelius--born in the imperial town of Memmingen and highly regarded by the emperor Charles V and by Melanchthon--assumed the main chair of mathematics in 1551, succeeding Georg Joachim Rheticus as professor on this position. Humelius became an intimate friend of the Saxon elector August and laid the foundations of cartography, land surveying and engineering of measurement instruments in the electorate of Saxony. The relations of Humelius to the important professor of Greek and Latin at the Leipzig University, Joachim Camerarius, deepened after his marriage to a daughter of Camerarius' in 1558. Not only with respect to astronomical topics, Camerarius apparently was an important partner for Humelius, who precisely observed the movement of planets and hence, critically opposed Copernican theories. Since Humelius did not publish his scientific results, his fame soon faded in later times. However, two scholars continued his research and reached unforgotten importance: in the area of cartography, his student and assistant Bartholomäus Scultetus, and in the area of astronomy, his indirect student Tycho Brahe. This is an example of the scientific importance of the University of Leipzig in the mid 16th century, and demonstrates its abilitiy to drive scientific momentum.