 The first topic addressed in the first section are the so-called “quadrivium” (a Latin term meaning “the four ways”) sciences (arithmetic, geometry, astronomy and music): Epistle 1 deals with arithmetic, Epistle 2 with geometry, Epistle 3 with astronomy and Epistle 5 with music. Arithmetic, geometry and music are later approached together in Epistle 6 On proportions. Between these two treatises another one is added, Epistle 4 On geography: ‘ilm al-hay’a (literally “cosmography”) was evidently considered part of astronomy – but Epistles 4 and 5 are copied in an inverted order in some MSS.