The Calculations

Dryander, Johann (1500-1560)
Noui annuli astronomici
Marburg: Eucharij Ceruicorni Agrippinatis, 1536.

Despite this book’s mathematical and astronomical subject matter, Johannes Dryander was principally an anatomist and physician, known for his early dissections of the human brain. Just as Dryander was interested in the practice of medicine, he was also interested in the more practical elements of mathematics and astronomy. This is evident from his focus on the instruments of astronomy: astrolabes, astronomical rings, and a volvelle.

Volvelles are constructed by layering several circles on top of each other and fastening them together at the center in such a way that they can still turn. In this case, the largest circle was printed on the page with a woodblock, and the smaller, handwritten circles were fastened on top. By arranging the circles in various configurations, one could make calculations and predictions based on the time of year and the position of the sun and moon.