Gemma Frisius

Gemma Frisius (; born Jemme Reinerszoon; December 9, 1508 – May 25, 1555) was a Dutch physician, mathematician, cartographer, philosopher, and instrument maker. He created important globes, improved the mathematical instruments of his day and applied mathematics in new ways to surveying and navigation. Gemma's rings, an astronomical instrument, are named after him. Along with Gerardus Mercator and Abraham Ortelius, Frisius is often considered one of the founders of the Netherlandish school of cartography, and significantly helped lay the foundations for the school's golden age (approximately 1570s–1670s).

Early life and education Frisius was born in Dokkum, Friesland (present-day Netherlands), of poor parents who died when he was young.

He began his studies at the Old University of Leuven in Leuven (present-day Belgium) in 1525, aged about 16, and qualified there as a doctor of medicine in 1536.

Under the guidance of Monachus and with the technical assistance of Van der Heyden, Frisius was involved in the production of globes and mathematical instruments noted for their quality and accuracy. Jean-Baptiste Morin (1583–1656) did not believe that Frisius' method for calculating longitude would work, remarking, "I do not know if the Devil will succeed in making a longitude timekeeper but it is folly for man to try." It took two centuries before John Harrison produced a sufficiently accurate clock.

Frisius created or improved many instruments, including the cross-staff, the astrolabe, and the astronomical rings (also known as "Gemma's rings").

Students His students included Gerardus Mercator (who became his collaborator), Johannes Stadius, John Dee, Andreas Vesalius and Rembert Dodoens.

Death Frisius died in Leuven on 25 May 1555 at the age of 46. According to his son Cornelius, he died from complications of kidney stones, from which he had suffered for at least seven years.

Legacy His oldest son, Cornelius Gemma, edited a posthumous volume of his work and continued to work with Ptolemaic astronomical models.

Frisius Point in the South Shetland Islands in Antarctica is named after Gemma Frisius.

A lunar crater has been named after him.

Works Cosmographia (1529) von Petrus Apianus, annotated by Gemma Frisius De principiis astronomiae et cosmographiae (1530) De usu globi (1530) Libellus de locorum describendorum ratione (1533) Arithmeticae practicae methodus facilis (Antwerp, 1540), and Paris, 1543 available on KU Leuven Special Collections (high quality) De annuli astronomici usu (1540) De radio astronomico et geometrico (1545)

De astrolabio catholico (1556) also available on KU Leuven Special Collections (high quality)