Collection of essays focusing on the roles of intermediaries such as brokers and spies, messengers and translators, missionaries and entrepreneurs, in linking different parts of the ever more densely entangled systems of knowledge production and circulation at a key moment in the development of global scientific, commercial and political systems. The period 1770-1820 was decisive for the reformation of imperial projects in the wake of military catastrophe and politico-economic crisis, both in the Atlantic and the Asian/Pacific spheres -- economic and political worlds dominated by complex trade systems and violent contest. This conjuncture also saw the overhaul of networks and institutions of natural knowledge, whether commercial, voluntary or organs of state. Both the industrial and the second scientific revolutions have been dated to this moment. New and decisive relations were forged between different cultures' knowledge carriers. The authors consider knowledge movements of the epoch that escape simple models of metropolitan centre and remote colonial periphery. They question the immutable character of mediators and agents in knowledge communication.