Licht der Zee-vaert of Willem Blaeu
Pictures of Linda Timmer for the Grundtvig project. By courtesy of the The Special Collections Department of the University of Amsterdam.
Part of the map of the former “Zuyderzee”, now named “IJsselmeer”. In the cartouche is written that the description, measurement and the sound of the depths are perfectly done in this map. So sailors can trust it. This map is made byorder of the rulers of the city of Medemblik, a town at the Zuyderzee.
Explanation how to work with an astrolabe (left) or cross-staff (right), instruments used for measuring altitudes (navigation)
Another exampel how to measure the altitude. In this figure P is the North Pole, and G the South Pole, E H the equator, A B the Horizon, Z the Zenith and D the Sun. De gemeten hoogte van de zon is 40°(DB). The measured height of the Sun is 40 ° (DB). We have to add 20 ° (ED). The sun is 20 degrees south of the equator (it is autumn or winter). This means that one is located at 60 ° north latitude (40 ° + 20 °).