ON

THE USE

OF THIS BOOK.

On the difference between Italian and Dutch sea charts.

Those who come to compare these Descriptions and Charts original: "Pascaerten" of the Mediterranean Sea with the Italian sea charts, will find that they do not correspond with them: but everywhere almost a whole point a compass point is 11.25 degrees differs in their directions. The cause thereof is: that the Italian charts are corrected and made according to Italian compasses: but these Descriptions and charts are set (for the service of our Dutchmen) according to such compasses as are made and used here in Holland, which differ from the Italian by about two-thirds or three-quarters of a point. Which difference arises from the fact that the needles of the Italian compasses are placed exactly under the Fleur-de-lis the north-pointing indicator on the compass card of the compass rose, as can be seen in the first figure here alongside: but on the compasses here in this country, they are placed about two-thirds or three-quarters of a point from the Fleur-de-lis to the east, according to the indication of the second figure.

Two circular compass rose diagrams are stacked vertically. The top diagram shows a compass rose where the magnetic needle (a line with a central lozenge) is aligned exactly with the north-pointing fleur-de-lis. The bottom diagram shows the same compass rose, but the magnetic needle is set at an angle, rotated approximately 3/4 of a compass point to the east of the fleur-de-lis, demonstrating the specific adjustment used for Dutch maritime compasses compared to Italian ones.

From this it arises: that two identical places according to the Italian and Dutch compasses differ by almost a point in their directions: as for example: the southeast corner of Minorca and the northwest corner of Corsica lie differently according to a Dutch compass, exactly northeast and southwest, which is how this our Description is set: but according to an Italian compass, those aforementioned places lie a little more easterly than northeast, and a little more westerly than southwest; that is how the Italian sea charts are made.