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Rh after a prolonged illness, but Tycho found other scientific friends at Prague, among whom were Martin Bachazek, Rector of the University, Peter Wok Ursinus of Rosenberg, Baron Johan von Hasenburg (who was an ardent alchemist), and the Jewish chronologist, David Ganz.

As Tycho at Benatky or at Prague had never more than a few assistants at a time, and most of his instruments did not reach him till October or November 1600, the observations made in Bohemia cannot compare in fulness and extent with those made during an equal period of time at Hveen, to which disparity the interruptions caused by Tycho's various removals also contributed. In December 1600, and the first week of January 1601, observations were made in the Emperor Ferdinand's villa, and on the 3rd March the work was resumed in Curtius' house, where Tycho had just become settled. Kepler hardly took an active part in the observations, but he began preparing for the great work to which he afterwards devoted his life. When he arrived at Benatky in February 1600, Mars had just been in opposition to the sun, and a table of the oppositions observed since 1580 had been prepared, and a theory worked out which represented the motion in longitude very well, the remaining errors being only about 2′. On this a table of the mean motion of Mars and the mean motions of the apogee and node for 400 years had been founded (as was done for the sun and moon in the Progymnasmata). But the latitudes and annual parallax at opposition (or the difference between the heliocentric and geocentric longitude) gave trouble, and Longomontanus was just then occupied with this matter.