Physicists Before Galileo
We can see that people were getting key components of the ideas right, but what about some of the math that we take for granted? Those who took a nominalistic approach felt that if motion was related to the space the object was moving in, then mathematical models should be able to predict the outcome of the motion. Sounds like kinematics to me! Those nominalists looked at velocity as a ratio relating itself to space and time. Using that, they could look at motion as a cause and effect scenario, with the cause being some force applied and the effect being the distance traveled (hence where the motion comes in). But though many tried to think about how the resistance to motion might appear here, they did not think it was a physical cause (Wallace 67).
But some didn’t care for the by-the-numbers approach and instead wanted to discuss the “reality” behind the motion, like Paul. But there was even a third group that took an interesting position on both sides, realizing that some good ideas were present with both. John Majors, Jean Dullaert of Ghent, and Juan de Celaya were but a few who tried to look at the pros and cons objectively and develop a hybrid between the two (67-71).
The first to publish such a position was Domingo de Soto. He claimed that not only was there compromise but that many of the differences between the nominalists and the realists were just a language barrier. Motion itself is removed yet related to the object as it stems from a cause and effect scenario. The velocity is a product of the effect, like, for example, a falling object, but can also come from the cause, like a hammer strike. De Soto was also the first to relate the mean speed theorem to the distance an object falls and the time it takes for it to fall (72-3, 91)
With much of this clarified, the focus shifted to how a force causes motion but is not within the object itself. Aristotle had claimed that nature itself was the “cause of motion,” but in 1539, John Philiiponus disagreed. He wrote that “nature is a kind of force that is diffused through bodies, that is formative of them, and that governs them; it is a principle of motion and of rest.” That is, nature was the source of motion and not the cause of motion, a subtle but important distinction. This caused people to ponder the internal nature of force and how it applied to the world (110).
John’s work is just one example of the ideas that were coming out of Collegio Romano at the time. Like Merton College, this institution would see many gifted minds grow and develop new ideas that would expand into many disciplines. In fact, evidence exists for many of their works being in Galileo’s procession, for he references this view on nature without justifying it. We have our possible first direct link to an inspirational source for Galileo (111).
Another one of these authors was Mutio Vitelleschi, who was definitely aware of John’s work and expanded upon it. Nature, Vitelleschi claimed, gives each object its own type of motion from within, a “natural motive power.” This hints at what medieval minds called vis, or an external cause. Now, Vitelleschi went a step further and discussed what happens when a moving object causes other objects to move as well. He attributes this new motion to the original object being an “efficient cause” or an object bringing about changes in objects other than itself (111-2).
Early Theories of Gravity
Content with that explanation, the author went on to talk about “natural motion,” which arises from the object and how it relates to a falling body. He simply states that it falls because of a quality from within it and thus not because of vis nor because of an efficient cause but more of a passive cause, especially if because of an efficient cause. In such instance, he would describe the now falling object as having “violent motion,” which is similar to both vis and an efficient cause, but unlike them, the violent motion doesn’t add anything to the force of the object (112).
Clearly, we can see how the wordiness begins to murk up Vitelleschi’s ideas, and it doesn’t get any better when he moves on to gravity. He figured it was a passive cause but wondered if it had an active component and if it was external or internal. He figured that something akin to iron being attracted to magnets was happening here, where an object contained some force that caused it to respond to gravity. The makeup of the falling object is what made gravity “an instrumental principle of the body’s fall.” But is it an efficient cause? It seemed so because it was bringing about change, but was it changing itself? Was gravity an object? (113)
Vitelleschi needed to become clearer, so he refined his definition of an efficient cause into two types. The first was what we have already discussed (known by the author as proprie efficiens) while the second is when the cause works only on itself, creating the motion (dubbed efficiens per emanationem). With this, Vitelleschi came up with three major theories of gravity. He felt it was:
- “Potency to the substantial form by a generator.”
- “Motion that follows on the form” by the removal of what would normally impede it.
- Motion which leads to a natural state by “the substantial form of the element as the acting principle form from which the motive quality flows.”
They sure did have a way with words, didn't they? (Ibid)
Wallace, William A. Prelude to Galileo. E. Reidel Publishing Co., Netherlands: 1981. Print. 67-73. 91, 110-3.
© 2017 Leonard Kelley
Darquavius on April 20, 2018:
Pretty good writing