1-158-172 - Oxford Science Archive/Heritage Images

Reiner Gemma Frisius, Dutch astronomer, geographer, cartographer and mathematician, 1539. Gemma Frisius (1508-1555) holding an adjustable ring dial for determining the altitude of the Sun for calendar calculations. He was the first to propose the use of triangulation as a method for locating places and for mapping, and also suggested using portable chronometers to calculate longitude by means of elapsed time. From Cosmographia by Peter Apian. (Antwerp, 1539).