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Rh many branches of astronomy, and as the current observations continued to reveal imperfections in the values of astronomical constants handed down from antiquity, Tycho was unwilling to finish the book and deprive himself of the power of inserting in it further results of his work. The book was never issued in a complete state in his lifetime; only a very few friends or correspondents received incomplete copies or portions of the book; and after Tycho's death an important section (32 pp.), separately paged, was inserted at the end of the first chapter. When completed, the book numbered more than 900 pages, divided into three parts and a "conclusion;" and it bears many traces of having been both written and printed in the course of many years, succeeding sheets frequently before preceding ones. The first chapter deals with the apparent motion of the sun, the length of the year, the elements of the solar orbit, refraction, and gives tables for the motion of the sun. As there were a few pages to spare (the second chapter having been printed and paged first), Tycho determined to devote them to the lunar theory, though this had nothing to do with the determination of star places, and was not even mentioned in the title of the chapter; and as this subject grew in importance and difficulty, it eventually delayed the publication of the volume considerably. The second chapter describes the methods of determining the places of stars, investigates the amount of precession, and contains Tycho's own catalogue of star places. This finishes the first part of the book, and as we shall examine in our last chapter the various subjects dealt with, we may pass to the second part of Tycho's book, which is devoted to his own observations of the star of 1572.