What Hipparchus was to the astronomy of the Ancients such was Tycho to the astronomy of the Middle Ages. As such his life merits a brief notice before we proceed to his work. He was born at Knudsthorp, near Helsingborg, in Sweden, in 1546, and went to the University of Copenhagen to prepare to study law; while there he was so struck with the prediction of an eclipse of the sun by the astrological almanacks that he gave all his spare time to the study of astronomy. In 1565 his uncle died and Tycho Brahe fell into possession of one of his uncle’s estates; and as astronomy, or astrology as it was then called, was thought degrading to a man in his position by his friends, who took offence at his pursuits and made themselves very objectionable, he left for a short stay at Wittenberg, then he went to Rostock and afterwards to Augsburg, where he constructed his large quadrant. He returned to his old country in 1571; while there, Frederick II., King of Denmark, requested him to deliver a course of lectures on astronomy and astrology and became his most liberal patron. The King granted to Tycho Brahe for life the island of Huen, lying between Denmark and Sweden, and built there a magnificent observatory and apartments for Tycho, his assistants and servants. The main building was sixty feet square, with observing towers on the north and south, and a library and museum. Tycho called this Uraniberg—the city of the heavens; and he afterwards built a smaller observatory near called by him Sternberg—city of the stars, the former being insufficiently large to contain all his instruments. The following is a list of these instruments as given in Sir David Brewster’s excellent memoir of Brahe, in _Martyrs of Science_:— _In the South and greater Observatory._ 1. A semicircle of solid iron, covered with brass, four cubits radius. 2. A sextant of the same materials and size. 3. A quadrant of one and a half cubits radius, and an azimuth circle of three cubits. 4. Ptolemy’s parallactic rules, covered with brass, four cubits in the side. 5. Another sextant. 6. Another quadrant, like No. 3. [Illustration: FIG. 15.—Portrait of Tycho Brahe (from original painting in the possession of Dr. Crompton, of Manchester). ] 7. Zodiacal armillaries of melted brass, and turned out of the solid, of three cubits in diameter. Near this observatory there was a large clock with one wheel two cubits in diameter, and two smaller ones which, like it, indicated hours, minutes, and seconds. _In the South and lesser Observatory._ 8. An armillary sphere of brass, with a steel meridian, whose diameter was about four cubits. _In the North Observatory._ 9. Brass parallactic rules, which revolved in azimuth above a brass horizon, twelve feet in diameter. 10. A half sextant, of four cubits radius. 11. A steel sextant.