Breves in sphaeram meditatiunculae

“Short Meditations on the World” is the only work written by the Bartholomaeus Mercator (1540-1568), son of the famous cartographer Gerard Mercator. It is a treatise based on Gerard's lectures on cosmography at the Duisburg gymnasium in the early 1560s. Gerard had asked his son to take over his class because he was too busy working on other projects. Faced with the need of providing course material overnight, Bartholomaeus mainly based himself on what he had learned from his father. Despite his young age (23 years old) and the short notice, Bartholomaeus was able to put together a rational and methodical introduction, that allows us to have a unique insight in what it may have been like to be in class with the Mercators.