Sphaera Libellus, 1547
Johannis Sacrobosco's Sphaera is the gem in The Popuplady's collection. In blind-stamped vellum with engraved brass clasps, the book is precious to hold. As was the custom, it is bound with other manuscripts. The Sphaera was published in the 13th century. But despite its being based on the Ptolemaic system [Sun revolves around the Earth], it remained an astronomical text until the 17th century. The 3 volvelles were added to the edition some time in 1538, according to Owen Gingerich, Professor Emeritus of Astronomy and the History of Science at Harvard University. What is especially beautiful about this particular copy is its exquisite marginalia. Previous owners of the book had read it carefully and recorded their thoughts in a minute Latin hand, sometimes with formulae or drawings. Sometimes in red ink! The owners were surely learned scholars.