Theories of the Medicean Planets Deduced from Physical Causes

only seems to apply to general characteristics, not to the specific measurements of these motions or their methods of operating. Yet, let it suffice that these qualities agree with one another. We will confirm this with greater evidence later, when we demonstrate from physical causes that these rules and instruments of action must necessarily be found in those small planets. For now, let it be more than enough that we have drawn these conclusions from the analogies of the other planets. There should be no distinction between those planets and the Medicean stars The four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto.

On the theories of the common planets, and first concerning the Moon itself.

Chapter II.

It is now established and understood that among the bright bodies spread through the ether, some are luminous, namely the Sun and the other fixed stars. Others are opaque and borrow light from them; these are commonly called planets. These exist in two categories: some are called primary, and others secondary. Those that orbit the Sun are called primary. Those that directly orbit a primary planet are called secondary. Because they are carried along by the power of the primary planet, they must also be turned around the Sun itself. The four Medicean Stars, which are carried directly around the globe of Jupiter, are of this type. The Moon of Saturn referring to Titan, discovered by Christiaan Huygens is of the same kind. All of these, along with the primary planets they circle, are moved through the Zodiac around the Sun.

Furthermore, it is clear that every planet, whether primary or secondary, circles some significant celestial globe that acts as a source of power original: "virtutis fontem", a source of physical force or influence. This source binds and glues them so firmly that they cannot be pulled away from it. Instead, they are forced to follow that body in perpetual and continuous orbits wherever it moves. We see Saturn, Jupiter, Mars, Venus, and Mercury circling the Sun. We see the Medicean stars circling Jupiter and the Huygenian star circling Saturn, just as the Moon revolves around the globe of the Earth.

Furthermore, a common path through the Zodiac for all planets