A second privilege granted by the States General, dated March 9, 1623, as the preceding, gives us the first word concerning another work by Blaeu intended especially for the use of seamen. This work, apparently not issued until the following year, though a copy dated 1624 does not seem now to be known, bears the following title taken from the issue of 1627: “Zeespiegel, Inhoudende een korte Onderwysinghe in de Konst der Zeevaert, en Beschryvinghe der Seen en Kusten van de Oostersche, Noordsche end Westersche Schipvaert. Wt ondervindinghen van veel ervaren Zeevaerders vergadert, en t’ samen ghestelt. Door Willem Jansz. Blaeuw Tot Amsterdam. Ghedruckt by Willem Jansz. Blaeuw, in de vergulde Sonnewyser 1627. Met Privilegie voor thien Jaren”; or, “Mirror of the Sea, containing brief instruction in the art of Navigation, and a description of the seas and coasts of the Eastern, Northern and Western Navigation. Collected and arranged from the experiences of numerous Navigators. By Willem Jansz. Blaeuw, At Amsterdam. Printed by Willem Jansz. Blaeuw, in the gilded Sun-dial, 1627. With a privilege for ten years.” Blaeu figures his declination tables from the years 1624, 1625, 1626 and 1627, on a parallel of the earth from the meridian of the west point of England, since this longitude was most frequently used by the Dutch navigators in sailing the Channel, as well as in sailing the coasts of France, Portugal or Spain. The work is divided into two parts, the first being a short treatise on the art of navigation, and the second a collection of maps or sea charts. We have in this work a striking illustration of the lingering influence of Ptolemy, for he takes as a basis of many of the ideas he presents the work of Ptolemy. The book does not undertake, as Baudet points out, to add to or improve the methods of defining geographical location. It does not undertake to correct what were the known errors in his day. He treats in his first part of the several spheres; he presents what he considers to be acceptable proof that the earth is in the center of the universe, as the stars appear at all times to be of the same size, in whatever part of the heavens they may be; he explains the construction and the use of the cross-staff by means of which the observer determines the altitude of the sun; he points out that in determining latitude by observing the altitude of the Pole Star, 2° 42′ should be taken as the distance from the star to the pole; he discusses the subject of atmospheric refraction, basing his observations on those of Tycho Brahe, which discussion is of special interest since it sets forth the attitude of seamen of that day toward this subject, and the difficulty they had in meeting it by reason of the imperfect instruments with which they made their calculations.