There is to be found in the Mathematical Salon of Dresden a fine example of the work of Christian Heyden (1525-1576), son of a rector of the St. Sebaldus School of Nürnberg. Doppelmayr[310] tells us that after years of study in Leipzig and Wittenberg, he returned to his native city, became interested in making mathematical instruments, and in 1564 he was appointed to a professorship of mathematics in the famous Nürnberg gymnasium. His biographer does not refer to his activity as a globe maker, but tells us that about the year 1570 he constructed for the Emperor Maximilian II a mechanical device for illustrating the movement of the sun and the moon, which instrument, he notes, especially interested the noted Frenchman, Petrus Ramus, who carefully examined it on the occasion of a visit to Nürnberg. The Dresden example of his work (Fig. 67), the only example known, consists of a brass celestial globe encased in a covering of brass, on the surface of which is engraved a terrestrial map. It has a diameter of 72 cm., the whole being furnished with a horizon, a meridian, and an hour circle. This is indeed a choice specimen of a sixteenth-century engraved metal globe, of which we have numerous examples, but it is rather an ornamental piece than one of great scientific value. [Illustration: Fig. 67. Globe of Christian Heyden, 1560.] Doppelmayr likewise gives us a brief biographical note referring to one Johannes Praetorius, a globe maker, born at Joachimsthal in the year 1537.[311] After a considerable period of study, chiefly at Wittenberg, where he turned his attention to the philosophical and mathematical sciences, he took up a residence in Nürnberg in the year 1562. Here he became interested in the construction of mechanical and astronomical instruments, and soon won the favor of the Emperor Maximilian II, which favor he enjoyed to the end of that Emperor’s reign. It was about the year 1576 that he became a professor of mathematics at Altdorf, where he died in the year 1616. Doppelmayr refers to a number of the mathematical and astronomical instruments constructed by him, noting that in the year 1566 he completed two globes of metal richly gilded, each having a diameter of 11¼ inches, that each was furnished with an hour circle, a movable quadrant and semicircles, and that a compass was set in the base of each. We learn also from the same biographer that in the year 1568 he completed a brass astrolabe having a diameter of “one schuh” (foot?), three and one half inches, and that it was supplied with all parts essential to a complete apparatus of its character. We are further informed that shortly after the beginning of his career in Altdorf he undertook the construction of a large celestial globe of wood and paper, having a diameter of four Nürnberg feet, that he was assisted in this work by the artist and draughtsman, Christopher Heinrichs, and that on the surface of the sphere one thousand six hundred and fifty stars were