This chapter reconstructs Bacon’s account of sound and music while considering his attitude to the sources he had at hand. Bacon adopted the Pythagorean definition of sound, albeit with an important correction: sounds are not, in fact, permanent quantities of the same sort as mathematical beings but rather non-enduring quantities which fit the sensible and physical nature of sound. Accordingly, he agreed with Aristotle in considering music an earthly construct, devoid of super sensible features. This led to a rejection of the idea that the motions of the planets produce heavenly music which cannot be perceived by our ears. In attempting to provide an account of the way sound is transmitted in the medium, Bacon discovered that an analogy between sound and light cannot be maintained. Such analogy was held by both Aristotle (although not by all his Muslim interpreters) and by the “sounding beam” theorists, who adopted the Pythagorean position regarding sound and music. Moreover, Bacon found out that the production, transmission, and reflection of sound cannot be explained by the mechanism of the multiplication of species and thus that sound is unique among the proper sensibles and deserves a separate account. We may consider Bacon’s treatment of sound as a suggestion for a relation between mathematics and physics which was different than both the Pythagorean and Aristotelian approaches: physics can be linked with quantities, however, with quantities that have a particular empirical nature: namely, a non-stable being.