In his wide-ranging and important article on ‘Medieval Concepts of Celestial Influence’ John North surveys various doctrines on celestial influence on sublunar matter from Aristotle to Robert Boyle. When he comes to Hermann of Carinthia, the mid-twelfth century philosopher and translator from Arabic, he characterizes his account as a ‘physical explanation of influence, as we might describe it: sympathetic vibration in the sublunar world’ (North’s emphasis). 1 Given that the rediscovery of the concept of cosmic sympathetic vibration determined some of the Renaissance theories of world harmony central to this volume (such as Ficino’s), I would like in this article, first of all, to determine how accurate it is to describe Hermann’s theory as involving ‘sympathetic vibration’, and then to see what the precedents are, in classical antiquity and in Islam, for such an idea.