Further complications. How the Earth is moved around it's own center and the moon around the Earth? In addition to the great vortex which forms a heaven having the sun at it's center, there are other smaller ones which can compare to those I have often seen in eddies of rivers where they all follow the current of the larger vortex which carries them in naught.
Now, he's right about that. There are vortices inside of vortices. In fact, what turbulence is is lots of vortices inside of vortices. So he's quite correct that if you look carefully behind the abutment of a bridge and see a nice large vortex forming, you will often see smaller vortices in it.
One of these vortices has Jupiter at its center and moves with its four satellites, which revolve around Jupiter. Similarly, the vortex which has the Earth at its center carries the moon around the Earth in the space of a month, while the Earth turns on it's axis in the space of 24 hours.
So the diagram, I have two diagrams. I'll come back to the second one. It's used to explain tides. I'll come back later in the hour to, later in the first half of the class. The one on the right is showing the Earth and the moon with the moon in its orbit, and it's meant to show how as the moon goes around in it's orbit, it's meeting with different levels of resistance effects versus the Earth.
So there's more resistance at, I have to say this carefully, you can't quite balance out the centrifugal effect of the moon at any one spot. It is circulating between two spots in which it is thrown back and forth, so it ends up at a net equilibrium in it's orbit, as he's showing there going around the Earth.
Doesn't have the same use's the pressure field thing. It doesn't meet the same level of resistances to outward tendency as the Earth does. At one point, it gets more the other point in gets less. Where it gets less, it moves back out. Where it get's more, it moves back in.
And that examples why it's going in an orbit. Okay, now the question is, which of two things is happening here? Is the Earth driving the vortex that's carrying the moon, or is the moon's motion going circulating because it's moving from a higher to a lower to a higher to a lower resistance, is it driving the vortex, or what's probably the case, he thought both were.
And it was a combination of the two. But at any rate, the Moon and Jupiter and things like that fall into place in this account. He does remark that the Moon is, has irregular motion because it's not a perfect circle. He keeps coming back to the idea these vortices are not perfect circles and if you look at vortices, they tend toward a circle, but they also have great trouble maintaining a circle.
Now, what's the defense of this? There's a defense before it in a letter to Morin. So let me read that then read the top one. Morin challenged him at the time of the publication of the discourse with his account of refraction in terms of unseen globules. Descartes actually makes the claim he discovered Snell's law from the physics of these globules fitted into a package to one another, and how if you press it to certain points, you're automatically gonna get some displacement, because the globules don't line up exactly along the diagonal of the point you pressed.
I don't know that anybody believes he actually discovered it that way now, but it's possible. The thing is, it's far more likely that he had heard of the law and then worked it out. But regardless, that's what Morin prompted by. To challenge him and I don't have the letter Morin wrote him.
I put the French, which I've never seen this one translated except this one portion, I put Descartes' letter to Morin in French on supplementary material today. But let's read what he says, you say the phenomena of the heavenly movements can be deduced with no less certainty from the assumption that the Earth is stationary, than from the assumption that it moves.
This is because of a prior letter Descartes had made the claim that the movements can't be deduced successfully if the Earth is stationary. You'll see the argument for that in just a moment. I agree readily. You say also that there is a viscous circle in proving effects from a cause and then proving the cause by the same effects.
I agree, but I do not agree that it is circular to explain effects by a cause and then prove the cause by the effects. Because there is a big difference between proving and explaining. I should add also that the word demonstrate can be used to signify either. If it is used according to common usage and not in the technical, philosophical sense.
Finally you say that nothing is easier to fit a cause to, nothing is easier than to fit a cause to an effect. It is true that there are many effects to which it is easy to fit many separate causes, but it is not always so easy to fit a single cause to many different effects, unless it is the true cause which produces it.
So that's gonna be the line, the line that's not entirely false. Most causes have many effects. The way we end up, and I'm speaking as a failure, unless the way we end up determining what among various possible causes is the one that produces all the known effects. Hopefully, there's not more than one of those.
That's why we collect all these clues, every scrap of metal and look at it carefully in the hope that only one possible candidate will pick out the cause of this particular failure. He's got a point. This is the way we do such causal reasoning. A bit about the circularity, it's not totally clear, of course, what he means.
But it looks like what he's saying is, and this is not Newton, folks, but it sure sounds like it the way I'm about to put it, is we arrive at the cause proving it from the phenomenon. But then, as we in effect derive the cause from looking at the phenomenon under certain constraints, but then we test it by seeing all the other things it does.
And if it doesn't do all the other things, we shouldn't be that confident that we've done the derivation. That at least is his defense. Now a comment here, I've already made a version of this comment, I'm gonna make it more extensively now. If we were to do justice to Descartes by my own standards, we would have to spend two or three weeks on him and learn to read him as if we're from inside the text, from inside his own head, or at least how people very close to him read it.
Now to do that, what you need to do is number one, learn most of what his own education was. What he had read, what he knew, things like that. Then you need to dig in to a lot of places other than publications like letters. And finally, you need to look at the genesis of his thought.
To where it got to the. And if you do all that, you can often put together, this is the way this guy was really thinking through all of this. As Tompkins would say, you're recovering the way in which that person conceptualized matters. And that's what Kuhn thought he was best at doing.
Reading a text like this and recovering. He never tried it with Descartes, but somebody who greatly admired his work and Tom came to admire John Schuster's work a great deal too. John Schuster sort of spent his adult life doing for Descartes what I just described. His dissertation, it's a legend, it's two volumes, it's over 500 pages.
It's never been published but it is a legend because he just got into Descartes and figured out how to work things out. So that it was really plausible. It didn't look strange anymore. And that's what Kuhn calls for. It should not look strange. This is a very intelligent person.
He's being read by very intelligent persons. If we can't make it totally sensible that he holds these views, it's our not having read it carefully enough. So I haven't done that. I've never done that for Descartes, I wouldn't try to do it for Descartes. But it also means I'm not presenting him to you properly from that point of view.
Now, I have a simple excuse. The whole point of this course is to enable us to do that with Newton. As we're putting ourselves in a position to do the very thing I just described for Descartes with Newton. And that's my promise in the second semester. You'll be able to read every sentence in the Principia and in principle understand exactly why it's there.
Descartes, I mean Newton's a lot easier than Descartes. He was a clearer thinker and had higher standard. But what I've done is to put one of John Schuster's papers on the vortex theory and it's genesis, and it's tied to Beekman, Steven and other people at the time for you to read if that's what you want to do.
It's in supplementary material. And you can get a better handle on exactly how Descartes thought. The other place you can turn to is my good buddy Dan Garber's book. He sort become the expert on Descartes text. Now he hasn't done exactly what Schuster has done because Dan's not crazy.
And Schuster's not crazy. I got to know him at the memorial of Manford Tom Kuhn where I was, Jed Buchwald and I invited him to the United States from Australia specifically, because Kuhn admired him so much. But he's really very good. I have the highest regard of John Schuster.
But I'm not sure you don't have to be a little crazy to immerse yourself for 45 years in the way Descartes thought scientifically. But I put that on reserve and this afternoon, I decided to put a second paper on Schusters on reserve. It gives a more arconian account on why we ought to take Descartes more seriously as a scientist.
I'm gonna give my own account tonight, but then I decided my own account is very heavily empiricist, and I've not done what Schuster has done, so I'm not at all confident. I'm representing Descartes, I'm instead representing someone like Mursen reading Descartes, and why Mursen would take it seriously.
Any rate, I made my point, I hope. There is a proper way to read texts like this. And it takes real work. What we're doing is the work to be able to read Newton. Okay, and I'm not gonna do it for everybody coming up to Newton because it would take many, many semesters.