GEMMA FRISIUS, REINER

Reiner Gemma Frisius, highly respected as a practicing physician, was a lead­ing theoretical mathematician of his day whose work in practical trigonometry modernized surveying and earned him a name in the field of geography as well. Gemma was born in 1508 in Dokkum, Netherlands; the poverty-stricken district of Friesland in which this small town was located was the source of his nick­name, Frisius, or "the Frieslander." Gemma excelled in his premedical courses at Louvain, the only university of the Low Countries, but it took him eight years instead of the usual six to complete his degree because he was too consumed by his interest in the fields of mathematics and geography to attend to his med­ical studies.

In 1529, while still a student, Gemma revised and published a new edition of one of the standard textbooks of his day, Cosmographicus liber Petri Apiani mathematici.His first original work, Gemma Phrysius de principiis astronomiae et cosmographiae, was published in less than a year and later translated into several languages.

The globes, maps, and astronomical instruments designed by Gemma were renowned throughout Europe, and the income they provided enabled him to marry in 1534. His son and later biographer, Cornelius, was born in 1535; the next year Gemma received his medical degree and began his practice. Gemma's abilities were held in high esteem by Louvain, his alma mater, and sometime between 1536 and 1539 he was appointed to the university's medical faculty.

Two of Gemma's contributions to the earth sciences are particularly note­worthy. The principle of triangulation, a trigonometrically based surveying pro­cedure used to measure inaccessible sites, was first proposed in a chapter he added to the Cosmographicus in 1533. Gemma was also the first to suggest the use of portable clocks for determining longitude at sea, a method that was ex­cellent theoretically but could only be put into practice when a suitable timepiece was invented in the late eighteenth century.

Gemma was also known for mentoring Gerardus Mercator,* who later became the leading mapmaker of his time. Gemma's contemporary, the anatomist An­dreas Vesalius,* spoke of Gemma as "famous as a physician, and as a mathe­matician comparable to but a few."

G. Kish, Medicina, Mensura, Mathematica: The Life and Works of Gemma Frisius, 1508-1555, 1967.