GEORG MARGGRAFE’s fame has led to several incorrect assumptions. For example, the question has been raised whether he was the maker of a piece of parchment carving representing Vrijburg palace (fig. 119). Although this assumption could immediately be discarded, because Frans Post’s depiction of Vrijburg, published long after MARGGRAFE’s death in 1647, was taken as starting point, this piece of clever craftsmanship still needs our attention. This because MARGGRAFE’s authorship was motivated by the fact that the carving in question was mounted on a paper quire consisting of five sheets, full of astronomical notes written in a seventeenth-century hand (fig. 120).

An article discussing this carving of Vrijburg stated that this manuscript contained ‘astronomical observations’, so our strong interest in this piece of material was raised. However, a close examination by one of us (HJZ) revealed that the manuscript did not contain any observations, but personal notes about the determination of the polar height. The notes refer several times to Hooftstuck 11 (‘Chapter 11’) from a book named the Schatkamer by a certain CORNELIS JANSZ. By this reference undoubtedly is meant De schat-kamer des grooten seevaerts- kunst (The treasury of the great maritime art), published in Amsterdam for the first time in 1621. Its author, CORNELIS JANSZ LASTMAN, was a former skipper from the Dutch island of Vlieland. After returning from his sea voyages, he started a school on navigation in Amsterdam that would become rather well known. Today, only very few copies of of LASTMAN’s Schatkamer have survived, but an online available copy of the book shows that no Chapter 11 refers to the subject discussed in the manuscript. How is this possible? The solution to this riddle is to realize that at the time LASTMAN’s book was so widely used as a manual for Dutch skippers that the name Schatkamer became generic for all Dutch navigational manuals. In later years LASTMAN reworked his book and renamed it into the Beschrijvinghe van de kunst der stuer-luyden (Description of the art of the helmsmen). It is actually this last book that is meant here. It has indeed a chapter discussing the determination of the polar height, or more generally the problem ‘how to find the latitude?’.