1508-1555

Dutch mathematician and mentor of Gerhard Mercator (1512-1594) who provided the first published illustration of a camera obscura, and who advanced attempts at solving the longitude problem. At that time, navigators were still many years away from finding a means of easily and accurately measuring longitude, a challenge that literally posed a life-and-death problem to sailors at sea. Frisius's De principiis astronomiae cosmographicae (1530) discussed a method for finding longitude using a clock and astrolabe. During the 1530s, he trained Mercator, and in 1545 published De radio astronomico et geometrico, which discusses his observations of a solar eclipse the preceding January. The book included a drawing of the camera obscura, a dark, enclosed chamber that was a forerunner of the modern camera.