In this edition of Treasures of the RAS, Librarian Jenny Higham introduces The Sphere by John of Holywood.
Astronomy was widely taught in medieval universities. This textbook from 1485, in the early days of printing, shows that these students developed a sophisticated level of understanding -- they certainly didn't think that the Earth was flat!
The Latin title of the book is Tractatus De Sphaera, which translates as Discussion Of The Sphere. It is also known as De Sphaera Mundi - The Sphere of the World. The author is John of Holywood, also known as Johannes de Sacrobosco.