Synopsis: Overview of mechanical philosophy, the principle of contact and the concept of vacuums
Opening line: "And some people, maybe it's in the need to write a new dissertation and say something that hasn't been said before. Are trying to get away from the idea that the principle feature or the mechanical philosophy was contact."
Now I'm gonna work a few minutes before I turn to the laws, we'll do the laws the second half. Descartes is an example of what was called the mechanical philosophy. There've been a lot of recent books on the mechanical philosophy, and increasingly people are struggling to try to define exactly what it amounted to.
And some people, maybe it's in the need to write a new dissertation and say something that hasn't been said before. Are trying to get away from the idea that the principle feature or the mechanical philosophy was contact. I'm less concerned about a generic characterization of the mechanical philosophy.
And more concerned with the features that Descartes, Marsenne, Galileo too for that matter and Gassendi jumped on. The key feature that summarizes at the top, all action, all change of state occurs only through the direct contact of one body or aggregate of matter with another. It's like saying no action at a distance, but that is an ambiguous phrase in modern physics, to physicists it means no instantaneous action at a distance.
That's not what they're talking about at all. They mean real contact. And of course the model's a clock. It'd be nice to build a clock that keeps time without anything touching. But we haven't figured out how to do that yet. And that's the picture. Now there are two schools of mechanical philosophy.
Gassendi, and I say following Lucretius. Lucretius's de rerum natura, which is a work on, he called them corpuscles, we think of them as atoms. It's the fundamental work, historically, developing an atomistic picture of the world. Gassendi, very much following Lucretius adopts the core prescularian view, and Boyle follows him and Huygens as well follows Gassendi.
This is a view in which there are vacuums, and even to the extent I'll do it our modern way, the vast majority of the space around us is empty. The total volume filled by the atoms is a very very small fraction, even in the solid, it's a fairly small fraction.
That's the view and now Gassendi has just like Lucretius all these corpuscles running around, bouncing off of one another. And what happens when that's occurring is going to explain everything. That's the Corpuscularian approach. The Plena school denies that there are any vacuums. So that's Descartes. It's also Leibniz.
They just flat say vacuums are impossible. I'll come back to why Descartes says it. Aristotle said it, too, said vacuums are impossible. None of them are saying it on experimental grounds. They're saying it purely on philosophical grounds. It is conceptually impossible for there to be a vacuum. The idea here is to constrain theorizing.
So, picture this versus what little I've told you about Renaissance Nationalism. You're not allowed to postulate or hypothesize any power without specifying a possible mechanism by which it can be affected through contact alone. And that's enough to tell you why they resisted Newton's Principia. Cause he postulated gravity and gave between any two particles of matter in the universe.
And gave you no mechanism of contact by which it can occur. As in fact it's Huygens says, I think I get this almost correct in English. He translated it in English. There is no possible mechanical explanation of particle to particle, gravity. That's not quite what he said, you'll read it later.
So it's a constraint on on theorizing. And it's a very severe constraint that Descartes's gonna run with, big time. Because if whatever change in, let's do it for the orbits. If there's something up there making the orbits circular rather than going off in a straight line, then there's gotta be matter up there we can't see doing it.
We're free to postulate it, because it has to be. That's the kind of gain you get from imposing this restriction. That even when you can't see the contact, it's gotta be there. Therefore, you can postulate. And the rationale, as you can see, otherwise the means through which the power is affected remains beyond our capacity to understand, and it's mysterious.
And the alternative is the pseudo explanations. Why does opium put one to sleep, because of its dormitive power, etc. That's of course Moliere a few years later than this, not very much later than this. I'll bring the learned ladies in appropriately in a couple weeks. Three weeks, thereabouts.
But at any rate, what lies behind it in Descartes' case of course is a benevolent god would not create a world that's beyond our capacity to understand. So he has even a stronger reason to think that if God's created a world in which all the mechanisms are beyond our comprehension That just can't be, okay?
And now the quote. All the properties which we clearly perceive in it are reducible to the sole fact that this is matter. It is divisible and it's parts are moveable. And that it is therefore capable of all the dispositions which we perceive can result from the movement of its parts.
So, everything has to be reduced to movement of matter. And in this case, matter in a world in which there are no vacuums, even locally. That's gonna be important in a moment, vacuum. This got very much more controversial after Descartes. Let's go back though. Why did Aristotle say vacuum's impossible?
Because it can't be that there's nothing can't separate two bodies. There has to be something while there is something, it's not a vacuum, because a vacuum is nothing. Okay, if people know Aristotle's physics better than I do at the present moment, you could say that's a crude summary of Aristotle, but that's the line of argument.
Nothing can't separate two things. Descartes is of course different, he said take away all the properties of any body, one by one on a piece of wax, in the meditations what's left at the end is still extension. Therefore, big therefore, therefore, extension is the essence of matter. Therefore, anything that has extension is matter.
Okay. But therefore, there can't be a void. Because it would have extension. And it therefore is matter. Pure and simple. Now, notice that's a purely conceptual argument against vacuums. In 1644, 45 Torricelli taking an idea from his mentor Galileo, constructs the first barometer. Initially doing it with water down at the ocean showing that water will hold up.
Excuse me a column of water will rise about I think it's about 30 feet. But then he switched to mercury and what we now think of as the 28 inches. What is it, 780 millimeters. Whatever the correct number is. And immediately Torricelli said that the end of a barometer is a vacuum.
And that became very, very contentious. So Paschal to try to prove it did several things. This is a beautiful experiment. You set up the barometer, but with enough of a well in the middle that there’s a collection of fluid there. I'll use the correct account. I'll use Pascal's account.
The weight of the air on this surface is enough to suspend that column of mercury or to put it differently the two are in balance. There's the weight of the air and there's a weight of the column of mercury on the reservoir of mercury in the bottom. And this is just an example of a balance.
Then he pulls the plug on the top and look what happens. This oil rushes down and this becomes a barometer. Now, this particular experiment which I've lifted the diagram out of Westfall's book, because it's particularly nice. What Pascal was proving was not there's a vacuum. He was proving that the barometer works as a balance.
The experiment he did climbing up the mountain with a barometer was one of the things that argued that the vacuum was real. People who opposed this said such things as, and I love this, there's a foeniculum extending down from the top of the tube, pulling the Mercury up.
We just can't see it. Okay. The book I mentioned last week, and the end, Chapin and Schaeffer on Leviathan and the Air Pump. What it's all about is the controversy of whether or not a vacuum is possible. What's so interesting about it is, everybody who was committed to doing any kind of experiment or have any empirical answer to the question whether there's a vacuum were concluding there's a vacuum.
And they did experiment after experiment. And the people who opposed it kept offering philosophic arguments that this can't be the right answer. Okay there was never any empirical evidence offered that there can't be a vacuum. And there was never any philosophic evidence offered that there can be, it was rather that the two were at crossed purposes, rather strikingly in some ways.
It's going to be important in a moment, when we come back from break. Descartes said there's not a vacuum because it makes us in the manner of uuu. It forces us to read him differently from the natural way in which we read him.