 Descartes’ vortex theory of planetary motion proved initially to be one of the most influential aspects of Cartesian physics, at least until roughly the mid-eighteenth century. A vortex, for Descartes, is a large circling band of material particles. In essence, Descartes’ vortex theory attempts to explain celestial phenomena, especially the orbits of the planets or the motions of comets, by situating them (usually at rest) in these large circling bands. The entire Cartesian plenum, consequently, is comprised of a network or series of separate, interlocking vortices. In our solar system, for example, the matter within the vortex has formed itself into a set of stratified bands, each lodging a planet, that circle the sun at varying speeds. The minute material particles that form the vortex bands consist of either the atom-sized, globules (secondary matter) or the “indefinitely” small debris (primary matter) left over from the impact and fracture of the larger elements; tertiary matter, in contrast, comprises the large, macroscopic material element (Pr III 48–54). This three-part division of matter, along with the three laws of nature, are responsible for all cosmological phenomena in Descartes’ system, including gravity. As described in Pr III 140, a planet or comet comes to rest in a vortex band when its radially-directed, outward tendency to flee the center of rotation (i.e., centrifugal force; see  Section 6)  is balanced by an equal tendency in the minute elements that comprise the vortex ring. If the planet has either a greater or lesser centrifugal tendency than the small elements in a particular vortex, then it will, respectively, either ascend to the next highest vortex (and possibly reach equilibrium with the particles in that band) or be pushed down to the next lowest vortex—and this latter scenario ultimately supplies Descartes’ explanation of the phenomenon of gravity, or “heaviness”. More specifically, Descartes holds that the minute particles that surround the earth account for terrestrial gravity in this same manner (Pr IV 21–27). As for the creation of the vortex system, Descartes reasons that the conserved quantity of motion imparted to the plenum eventually resulted in the present vortex configuration (Pr III 46). God first partitioned the plenum into equal-sized portions, and then placed these bodies into various circular motions that, ultimately, formed the three elements of matter and the vortex systems (see Figure 3).