The study concerns a seventeenth-century analogy between the movement of seawaters and the movement of fluids in human body. The ideas of Athanasius Kircher (1602–1680) on the geocosmos, expressed in his Mundus subterraneus (1664–1665) and Iter extaticum II (1657) are compared with the work of his correspondent, the physician from Wroclaw and editor of the first medicine journal, Philipp Jacob Sachs von Lewenheimb (1627–1672), who wrote Oceanus macro-microcosmicus (1664). In this analogy Sachs took into account the latest discoveries of the Danish physician Thomas Bartholin (1616–1680) on the lymphatic system in addition to William Harvey's (1578–1657) experiments on the circulation of blood. These elements make Sachs' treatise an interesting mixture of a undamentally analogical approach with the latest findings of natural philosophy. Both authors use the analogy between the seawaters' movement and the movement of fluids in the human body in different ways, which leads to an analysis of the Aristotelian and Platonic approaches to analogy in their works and the question of the shift from the Renaissance episteme to the modern one.