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| Gemma Frisius was the first to advocate the clock as a device for measuring the longitude at sea. |
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| Gemma Frisius' method for determining the longitude |
In 1530, the Frisian mathematician Gemma Frisius (1508-1550) published his 'De principiis astronomiae et cosmographiae', an introduction to astronomy and cosmography. This is the earliest known work mentioning the use of portable clocks for determining the longitude at sea. Hailing from Dokkum (Friesland), Frisius was a professor at Louvain University, where he taught Charles V mathematics.
Sources: N. Ottema: Geschiedenis van de uurwerkmakerskunst in Friesland (Leeuwarden/Assen 1948); H. Terpstra: Friesche Sterrekonst ((Franeker 1981); E. Fraiture: Uurwerkmakers en uurwerkmakersnijverheid in Vlaanderen (Leuven 2002)
Illustrations:
1) Frontpage De Principiis Astronomiae...
2) Portrait of Frisius in a study
3) Portrait of Frisius as professor
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