Kepler's Defense of Tycho against Ursus

History of Astronomy: Kepler's Defense of Tycho against Ursus by Edward Rosen, Popular Astronomy, Vol. 54, p.405, 1946. In 1595, the inexperienced Kepler had written a flattering letter to Nicholas Reimers (who called himself Ursus (the bear)), then Imperial Mathematician to Rudolph II, Holy Roman Emperor in Prague. In 1597, Reimers issued his De astronomicis hypothesibus, with its venomous attack on Tycho Brahe. He incorporated Kepler’s letter in it without Kepler’s knowledge or consent, thereby unscrupulously making it appear that in his duel with Tycho he was supported by Kepler. Kepler himself had by now become renowned through publication of his Cosmographic Mystery. Reimers died in mid-August 1600. In October 1600, Kepler, at the request of Tycho, began composing a rebuttal of Reimers works (A Defense of Tycho against Ursus (Apologia Tychonis contra Ursum)), but it remained unpublished by the time of Tycho's death (24. October 1601). In the end, Kepler's Defense of Tycho was found among his unpublished manuscripts by Christian Frisch, who edited Kepler’s collected works, and put it in print for the first time in 1858. More on Kepler at Stanford Encyclopedia of Philosophy.