Twenty years later, in ~1553, he was the first to describe how an accurate clock could be used to determine longitude. 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"). His students included Gerardus Mercator (who became his collaborator), Johannes Stadius, John Dee, Andreas Vesalius and Rembert Dodoens. Frisius died in Leuven at the age of 46. According to an account by his son, Cornelius, Gemma died from kidney stones, which he had suffered from for a minimum of 7 years. A lunar crater has been named after him. Gualterus Arsenius, the 16th-century scientific instrument maker, was his nephew. 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) De annuli astronomici usu (1540) De radio astronomico et geometrico (1545) De astrolabio catholico (1556) Honours Frisius Point in the South Shetland Islands in Antarctica is named after Gemma Frisius. See also Triangulation (surveying)#Gemma Frisius Notes Further reading N. Haasbroek: Gemma Frisius, Tycho Brahe and Snellius and their triangulations. Delft 1968. Robert Haardt: The globe of Gemma Frisius. Imago mundi, Bd. 9, 1952. W. Karrow: Mapmakers of the Sixteenth Century and Their Maps. Chicago 1993. G. Kish: Medicina, mensura, mathematica: The Life and Works of Gemma Frisius. Minneapolis 1967, sowie sein Artikel in Dictionary of Scientific Biography A. Pogo: Gemma Frisius, his method of determining longitude. In: Isis. Bd. 22, 1935, S. 469–485. External links Description of the Camera Obscura in 1544 by Frisius Arithmeticae practicae methodus facilis From the John Davis Batchelder Collection in the Rare Book and Special Collection Division at the Library of Congress 1508 births 1555 deaths 16th-century Flemish cartographers 16th-century Dutch cartographers 16th-century Dutch mathematicians 16th-century philosophers Dutch cartographers People from Dokkum Dutch scientific instrument makers Old University of Leuven alumni Academic staff of the Old University of Leuven Early modern Netherlandish cartography