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Rh commented by Professor Favaro of Bologna with the care and learning by which the writings of this author are always distinguished. Some other letters from the last years of Tycho's life have recently been published by Professor Burckhardt of Basle. Lastly, we must mention the meteorological diary kept at Uraniborg, which is of great historical value as affording many interesting glimpses of Tycho Brahe's home life. It was published in 1876 by the Royal Danish Society of Science.

Among other publications of importance for the study of Tycho Brahe's life and activity must be mentioned the biography of Kepler, by Frisch, in the last volume of Kepler's Opera Omnia, and several papers by Professor Rudolph Wolf of Zürich on Landgrave Wilhelm of Hesse-Cassel, and his astronomers Rothmann and Bürgi. Though only indirectly bearing on Tycho (of whose merits Professor Wolf on every occasion speaks somewhat slightingly), these valuable papers throw much light on the state of science at the end of the sixteenth century, and will often be found quoted in the following pages.

Having for many years felt specially interested in Tycho Brahe, it appeared to me that it would be a useful undertaking to apply the considerable biographical materials scattered in many different places to the preparation of a biography which should not only narrate the various incidents in the life of the great astronomer in some detail, but also describe his relations with contemporary men of science, and review his scientific labours in their connection with those of previous astronomers. The historical works of Montucla, Bailly, Delambre, and Wolf have indeed treated of the astronomical researches of Tycho Brahe, but as the plans of these valuable works were different from that adopted by me, I believe the scientific part of the present