Carla Rita Palmerino

The Application of Fluid Mechanics to the Study of Planetary Motion in the 17th-Century

As is well known, one question the supporters of the fluid-heaven theory could not escape was: a quo moventur planetae? The answer to this question was often given in metaphorical terms. Some, like Bellarmine, argued that planets move by themselves, like “ the birds of the air and the fish of the water”; others compared them instead to inanimate objects floating in a fluid medium. The second option opened the possibility of using balls floating in a water vessel to simulate planetary motion.

In my paper I shall analyze some attempts in this direction. Among other things, I shall describe: a) an experiment invoked by Galileo in the Saggiatore (1623) and in the Dialogo (1632) to demonstrate the inexistence of the third motion attributed to the Earth by Copernicus; b) a model used by Descartes in his correspondence and in the Principia philosophiae (1644) to illustrate the vortex theory of planetary motion; and c) a hydraulic orrery described by Gassendi in the Epistolae de motu impresso a motore translato (1642). Although similar in their construction, these devices entailed rivaling cosmological views. I shall therefore first try to shed light on the relation between theory and model in the different cases at hand. Secondly, I will examine certain intrinsic difficulties that invariably accompany attempts to apply fluid mechanics to planetary motion.

.................................

Carla Rita Palmerino

Carla Rita Palmerino (Ph.D. University of Florence, 1998) is a research fellow at the Center for Medieval and Renaissance Natural Philosophy at the Radboud University Nijmegen (The Netherlands). Her publications focus mainly on 17th-century theories of matter and motion. She is currently carrying out research on the reception and diffusion of Galileo’s new science of motion in 17th-century Europe.