Published in 1524, and subsequently edited and added to by Gemma Frisius under the title of Cosmographia, based the whole science on mathematics and measurement.
Schäner (1515), P. Apianus, Gemma Frisius (1530) and G.
23-79) mentions the gemma Gallaica, a precious stone.
His pupil, Rainer Gemma-Frisius, used it for the observation of the solar eclipse of January 1544 at Louvain, and fully described the methods he adopted for making measurements and drawings of the eclipsed sun, in his De Radio Astronomico et Geometrico (1545).
It is probably during this period that he wrote the Gemma ecclesiastica (discussing disputed points of doctrine, ritual, &c.) and the Vita S.