Blaeu’s reference to the declination of the needle in this introduction is of considerable scientific importance and interest. In his day the compass makers found the needle’s declination for Holland to be from about 7° 45′ to about 8° 26′ eastward. They were, therefore, accustomed to lay the compass lily a corresponding number of degrees to the left or westward from the direction in which the needle pointed that this lily might turn to the true north. He found that in the Adriatic the declination of the needle was 0, and that in the Italian compasses the direction of the needle and of the lily agreed. Compass roses on Italian portolan or sailors’ charts, therefore, indicated no declination as the Italian compasses indicated none, and the compass lily simply marked the true meridian. As distances to be sailed in the Mediterranean were not great, latitude, therefore, was not laid down, and longitude was omitted, by reason of the fact that there was no accurate method of determining the same, consequently vessels sailed from port to port directed only by the compass. Blaeu wrote that “since the skies are there [in the Mediterranean] almost always clear, and the land high, and places are not far distant one from another, one losing sight of one part of the coast will be in sight of another part, and the majority make very little use of latitude. The seamen and those who have navigated these parts have not taken into consideration the latitudes, and follow only general direction.” This being Blaeu’s observation, which is practically taken word for word from Barentszoen’s introduction to his “Caertboeck,” one would not, therefore, expect to find either parallels or meridians laid down on his maps. He gives only compass roses and direction for sailing in accord with the Dutch compass. On the maps of Barentszoen, which maps Blaeu closely followed in many respects, the directions for sailing are given in accord with the Dutch and with the Italian compasses. Blaeu could not have followed a better master in plan and purpose, and while not always indicating just what he borrowed, he seems to have been inclined to give adequate praise to the work of his predecessor. It cannot be without interest to cite here a brief word from Barentszoen’s introduction to his “Caertboeck,” as indicating his spirit and method. He says “that not only being urged by my many good friends, but also feeling inclined myself to do so, since I always have been accustomed from my boyhood up to draw as many maps as I found it possible to draw of the countries which I visited, or around which I sailed, giving the seas, the waters and the directions, I have decided to publish certain maps of the sea-coast of the Mediterranean Seas [which I have collected for some years past] into book form, for the use and the benefit of all navigators, and persons interested in navigation. In part, I describe what I myself have seen on my journeys, in part what I have learned