Theories of the Medicean Planets Deduced from Physical Causes

The motions of the Medicean stars must be similar to the motions of the other planets. Chapter 1.

To properly investigate and explain the theories of the Medicean stars the moons of Jupiter, named by Galileo to honor the Medici family, it would indeed be necessary to have an exact and complete prior knowledge of their motions and their many irregularities. The investigation of these things has not been fully granted to us in the short time since their first discovery was handed down by Galileo Galileo Galilei first observed these moons in 1610, only 56 years before Borelli's book was published. For this reason, further contemplation regarding these motions does not seem possible. Indeed, all our scientific and logical knowledge must arise from the senses and from experiments. But even though this is true, I will nevertheless show that it is possible for us to examine the arrangements and movements of the mentioned Medicean stars.

We can do this with only those few observations that have become known to us so far. In place of those observations we lack, we can use the many well known observations of the other planets. The Jovian stars original: "iouialia sydera", referring to the satellites of Jupiter must generally agree with the other planets in all types of motion. This can be deduced from this first principle and axiom axiomate: a self evident truth that requires no proof: that nature always uses the simplest and easiest means to perform all its tasks. Finally, nature does not take delight in variety or in different ways of operating. Instead, nature always uses the same organs and instruments with constant perseverance and the same method when it produces effects that are similar to one another.

I could say that countless examples of this fact are available. However, it will be enough to consider the structure and actions of animals and plants. In these, nature produces the same natural, vital, and animal operations by using exactly the same organs and movements. Therefore, we never see nature give movement from one place to another to living beings or their parts without those very thin cords which we call muscle fibers.