Hand-colored woodcut Petrus Apianus (1495—1552). Astronomicum caesareum. Ingolstadt: for the author, 1540 Rare Books Division, The New York Public Library Purchased from the Bequest of Alexander Maitland     (228 k)

Until well into the seventeenth century, the determination of appropriate bloodletting sites, of childbirth times, and of the optimum time for the treatment of various ailments required the accurate plotting of planetary conjunctions, eclipses, and other astronomical phenomena. The Astronomicum caesareum provided for this need in a magnificent book that combined elegant typography with exquisite woodcuts and hand-coloring. For this book, Apianus created thirty-five elaborate mechanical devices called volvelles whose multiple disks, pointers, and string allowed the reader to accurately determine the position and movement of the planets and other celestial phenomena.