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124 Bülow, returned to Germany after having carried out its mission to the Danish Court. As the embassy was sent to Dantzig in some royal ships, it was easy for Tycho Brahe to obtain permission for Elias Olsen to make the voyage on one of these. He happened to be keeping the meteorological diary at that time, and continued on the journey to record in it the state of the weather. We learn thus that he started from Copenhagen on the 1st May, reached Dantzig the 10th, and Frauenburg on the 13th. In this quiet little cathedral town Copernicus had lived many years, engaged solely in building up his great astronomical work, and only now and then turning aside from this to assist with his clear mind in the government of the little diocese-principality of Ermland or in the affairs of the chapter of Frauenburg. Elias Olsen remained on this classical spot from the 13th May till the 6th June, and, with a sextant which he had brought with him, he found by meridian altitudes of the sun and stars the latitude to be 54° 22$1⁄4$′, while Copernicus made it 54° 19$1⁄2$′ (the modern value is 54° 21′ 34″). Tycho remarks that the solar declinations of Copernicus are consequently 2$3⁄4$′ in error, which, together with his omission of refraction, was sufficient to explain the shortcomings of his solar theory. We shall afterwards examine this question again when discussing Tycho's labours on the solar theory. While Elias Olsen was at Frauenburg he was requested to determine the latitude of Königsberg, and went there on the 8th June. He found 54° 43′, greatly different from 54° 17′, which Erasmus Reinhold had assumed in the Prutenic tables on the authority of Apianus. On the 28th June Elias left Königsberg