Fleischer, Johannes

(b. Breslau, Germany [now Wrocław, Poland], 29 March 1539; d. Breslau, 4 March 1593)

optics

Fleischer was born into a well-to-do family and received his education at the Goldberg Gymnasium near Breslau and later at the University of Wittenberg, where he matriculated in 1557. During his first years at Wittenberg, Fleischer studied under Philip Melancthon; he returned to Wittenberg after Melancthon’s death to concentrate on Hebrew, astronomy, and theology, and in 1589 he was awarded the theological doctorate. Fleischer spent 1568–1569 teaching arts and languages at the Goldberg Gymnasium, and beginning in 1572 he was professor in the Gymnasium attached to St. Elizabeth’s Church in Breslau. He also held a series of ecclesiastical posts in Breslau, in St. Maria Magdalena’s Church as well as St. Elizabeth’s.

Fleischer’s only published scientific work is a treatise on the rainbow, which appeared in 1571. This book is remarkable, not for its correct solution to the problem of the rainbow, but for the precision and clarity of its argument, for its emphasis on what occurs in the individual drop of vapor, and for its insistence that both reflection and refraction of solar rays participate in the generation of the rainbow. The essential feature of Fleischer’s explanation is that solar rays are refracted by individual drops as they enter the vapor cloud before being reflected back to the observer’s eye by denser drops more interior to the cloud. The idea is drawn largely from Witelo, whom Fleischer cites repeatedly, although Fleischer has considerably clarified the mechanism of reflection and refraction described by Witelo.

BIBLIOGRAPHY

I. Original Works. See his De iridibus doctrina Aristotelis et Vitellionis (Wittenberg, 1571).

II. Secondary Literature. Fleischer’s life is dealt with briefly in C. G. Jöcher, et al., Allgemeines Gelehrten-Lexicon, I (Leipzig, 1750), col. 636; and Gustav Bauch, Valentin Trazendorf und die Goldberger Schule (Berlin, 1921), pp. 235–237. On Fleischer’s theory of the rainbow, see Carl B. Boyer, The Rainbow: From Myth to Mathematics (New York, 1959), pp. 163–166; and A. G. Kästner, Geschichte der Mathematik, II (Göttingen, 1797), 248–250.

David C. Lindberg