biography hitherto published is that of Gassendi. This writer obtained valuable materials from some of Tycho Brahe's pupils, and from the Danish savant Worm, but he chiefly derived his information from a close scrutiny of Tycho's own writings, never failing to make use of any particulars of a biographical nature which might be recorded in passing by Tycho. In studying Tycho's works, I have repeatedly come across small historical notes in places where nobody would look for such, only to find that Gassendi had already noticed them. In 1745 a biography was published in a Danish journal (Bang's Samlinger, vol. ii.), the contents of which are chiefly taken from Gassendi, but which also contains a few documents of interest. Of far greater importance is a collection of letters, royal decrees, and other documents, published in 1746 by the Danish historian Langebek in the Danske Magazin, vol. ii., which still remains the principal source for Tycho's life. A German translation of this and the memoir in Bang's Samlinger was published in 1756 by Mengel, a bookseller in Copenhagen, who wrote under the high-flown pseudonym Philander von der Weistritz; and as his book has naturally become more generally known than the Danish originals, I have, when quoting these, added references to Weistritz's book. During the present century several Danish historians have brought to light many details bearing on Tycho's life which will be referred to in this volume; and in 1871 a Danish author, F. R. Friis, published a popular biography in which were given various hitherto unpublished particulars, especially of Tycho's beneficiary grants and other endowments. The same writer has also published a number of letters exchanged between Tycho and his relations, and various contemporary astronomers. Of great scientific interest is the correspondence between Tycho and Magini, published and
