The principal use of this largest quadrant was the determination of the angle of elevation of the stars within the sixth part of a minute, the collineation being made by means of one of the sights, the parallel horizontal slits in which were aligned with the corresponding parts of the circumference of the cylinder. The altitude was recorded according to the position of the sight attached to the graduated arc. Tycho Brahe had a great reverence for Copernicus, but he did not accept his planetary system; and he felt that advance in astronomy depended on painstaking observation. For over twenty years under the kings of Denmark he had good opportunities for pursuing his investigation. The island of Hven became his property. A thoroughly equipped observatory was provided, including printing-press and workshops for the construction of apparatus. As already implied, capable assistants were at the astronomer's command. In 1598, after having left Denmark, Tycho in a splendid illustrated book (_Astronomiæ Instauratæ Mechanica_) gave an account of this astronomical paradise on the Insula Venusia as he at times called it. The book, prepared for the hands of princes, contains about twenty full-page colored illustrations of astronomical instruments (including, of course, the mural quadrant), of the exterior of the observatory of Uraniborg, etc. The author had a consciousness of his own worth, and deserves the name Tycho the Magnificent. The results that he obtained were not unworthy of the apparatus employed in his observations, and before he died at Prague in 1601, Tycho Brahe had consigned to the worthiest hands the painstaking record of his labors.