Well, there's a comet that shows up going from north to south. I hope I'm right about that, I constantly flipped directions for some odd reason. In November of 1680. And then, starting on December 12th they observe a comet going from south to north. And they follow the one going south to north, Flamsteed follows it til early February, Newton using a telescope is still following it at the end of late February and begging Flamsteed to do further observations of it as it moves away from the Sun.
Flamsteed writes a letter to Haley, this is February 1681 so Haley's 25 years old at the time. I keep trying to drive home to you that Haley was quite an impressive young person. And in it, the core of this letter, I'm gonna read a lot of this out.
The core of this, which you haven't seen, cuz I've put the whole Flamsteed-Newton correspondence on reserve but the letters are very, very long. And I didn't want to trouble you with them because so much of them are arguing about observations and which ones you can trust. But the principle thing Flamsteed is saying is, these were not two comets.
This was one comet that approached the Sun and went back away from the sun. So the principle section. I can see, therefore, that the Sun attracts all the planets. And all like bodies that come within our vortex. The underlining there is Burner Collins. I'm biting my copy of, of the correspondence is, I inherited from him.
More or less according to the different substance of their bodies in nearness or remoteness from him. That it drew the comet. By its northern pole, the line whose motion was at first really inclined from north into the south part of the heavens, but was by this attraction as it drew near to him, the sun, bent the contrary way as if EE were the plain of the ecliptic P the North Pole of the sun.
AD etc. etc. The comet was then to the north of the solar equator and perhaps here the contrary motion of the vortex might help to bear it up from the plane of the ecliptic into the northern latitude. When it came within the compass of the Orbit, that’s our orbit, the annual orbit.
This attraction of the Sun would have drawn it near him in a straight line, had not the lateral resistance of the matter of the vortex moved against it, bent into a curve, as if in the figure of the next page, your page 339 I'm not gonna continue all these details with the individual words.
But individual points. This active repulsion would carry the comet from the sun in a straight line were it not that the cross motion of the vortex Bends it back. Which yet the acquired velocity, in straight of its motion, may compensate and restore, so that the one countervailing the other.
I see no reason why we may not admit it to have run from sun nearby in a straight line. My theory of the motion differs very little from yours, Haley's, but to tell you the truth, I have made no trial by calculation yet. But by a large draft on paper.
In other words he's graphing it. My other affair is not permitting me to bestow so much time as is necessary for this business on it. As for the body of the comet nothing better occurs to my thoughts at present that it may have become some planet belonging formerly to another vortex now etc.
So we got a cartesian picture of what is going on here basically. But with magnetism of the Sun pulling the comet down, deflecting it when it gets too close, sending it back off in a fairly sharp, not literally hairpin, but you'll see in a moment why you'd call it hairpin.
And in fact here you start seeing a hairpin-type drawing on that. Okay that's the proposal. Fair enough people. And remember the prevailing view of comets at this point was that they described great circles. The issue was way out there in the middle of our planet system or inside the moon.
That was the dispute. But even Newton what little attention he had given the comets was mostly tied to that diagram of Rynn's I showed you back when we did astronomy in this period, where Rynn had it as a straight line slightly bent, or allowed to be bent. By the action of the sun.
And Hooke and his book, Cometa, said the same thing. In Cometa he has the planets being governed by traction towards the sun, but he has the comets made of different material less sensitive to that attraction. So that was all consistent with Newton's view. Flamsteed was saying something fairly radical here, Newton's response and notice this is second hand Flamsteed letter to Haley is February 17th 81.
That's just about the end of the time Flamsteed followed it and within just a few days in February Newton is. Going to Flamsteed through Compton, I thank Mr. Flamsteed for his kind mention me in his letters to Mr. Compton, etc. Now let's go on to what Newton has to say.
Starting on the right where I marked it off in the right hand side, the attraction of the Earth by it's gravity will make the bullet tend more and more downward. but it can never make it tend directly downwards, much less verge from east to west. Now this is describing what happens if you throw a bullet which is a lot like that picture that he drew for Hook.
Nor will the motion of the vortex. Relieve the difficulty but, rather, increase it. For that being according to the order of the letters in Mark's alpha beta would make the comment verge from the line GS rather towards the line FQ Then towards H. The only way to relieve this difficult, in my judgement, is dispose the comet to have gone not between the Sun and the Earth, but to fetch the compass around the Sun in this figure.
So instead of it button hooking before it gets to the Sun, he's saying it's going around the Sun. Due to the attraction of the sun. Secondly, though I can easily allow an attractive power in the sun whereby the planets are kept in their courses about here from going away in tangent lines.
Yet, I notice how everybody's just so comfortable with inertia at this point, it's amazing how comfortable they get fast. Yet I am... The less inclined to believe this attraction to be of a magnetic nature because the Sun is a vehemently hot body. And magnetic bodies, when made red hot, lose their virtue.
A red hot lodestone attracts not iron nor any lodestone, a red hot iron. Nor will a lodestone propagate its virtue through a rod of iron, etc. So he's throwing out magnetism as the explanation. But thirdly were the sun a magnet he would act on the comet as a great magnet does on a little one floating in a walnut shell or other little boat or on water.
If the little magnet were forcibly turned about by one's hand and put into a wrong or unagreeable position the great magnet So long as the little one was forcibly detained and that wrong position would repel it but so soon as the little magnet was set at liberty, the great magnet would make it nimbly turn about into an agreeable position and then attract it.
So, we've got the polarity entering in here. And so, the sun, were the comet in the wrong position, would make it turn about quickly into a right one. Et cetera, so he's just giving a series of arguments why Flamsteed has to be wrong. Last one, I am further suspicious of the comets of November and December, which Mr. Flamsteed accounts one and the same, correct were two different ones.
And I find Caccini in a copy of a letter of which Mr. Ellis We don't know who he is by the way, somebody at Cambridge. Showed me is of my mind. If there were but one comet its motion where thrice accelerated and retarded. And I'm not gonna go on from there.
What goes on it this runs several pages and it's talking about data and whether you can trust data. Now what we know happened at this point, I'll come back to this in just a moment. We know now, and it's largely due to the work of Jim Ruffner, who died two years ago.
Just briefly, Ruffner's an interesting guy, he did his dissertation at Indiana in history of science and became the foremost authority on calculating comets in the 17th century. Couldn't get a job as a historian as science became the chief librarian after starting his library. And at Wayne State University did no work in history of science until he retired in the mid 1990s.
I got a call one day from him asking if I would help him resume Work in history of science and then the last 12 years of his life, he produced four major papers tying to comets and I put all four now on supplementary material. But what I'm gonna be saying now comes from him.
What he could do that nobody else could do is go into Newton's manuscripts Find calculations Newton was making, identify what observations he was using, where he got the observations, and what method he was using. Because he was totally adept at doing calculations on comets the way people did them at the time.
And none of the rest of us could do that. I sat with him and I had the manuscripts and he would flip through them. He'd look at a number and say, oh I know what this is. And then you know, it's a page full of numbers. I can do that with Huygens, I can't do that with comets, let me assure you.
So thanks to Jim Ruffner, we now know that in this period Newton was busily trying to calculate this trajectory of this comet, the spring comet. He didn't think there was one. He thought there were two, and there were very few observations of the one in November. So he's looking at the one moving South to North.
He was doing so in a straight line motion. He was doing so in the very manner Rynn had done earlier. And he was having terrible trouble with various things. One was, which observations to trust. Second even when he did his own observations he was referring him to nearby stars.
Whose star chart could he trust? So he gets and starts the new using that star chart. And after awhile gets very frustrated and gets have 1668 book. And starts trying to work from that. But what goes between Flamsteed and Newton here to a very great extent is a set of observations many of which are really lousy, some of which are good.
It is very hard to figure out which ones, even if you can figure out which ones to trust, you now have to figure out how to reduce them to longitude and latitude Remember, we don't know how far away they are. We only know their position relative to stars.
If you don't have very, very good star charts trying to do a trajectory is difficult. And do remember, comets move very, very fast as they go towards the sun. And very, very near straight lines until they get near the sun. At which point they go through a huge curvature.
They didn't know that then, but that's what actually happened. So this is a very tough problem. But the striking thing is Newton is quite committed to vortices at this time, and quite committed to the idea that the sun doesn't do anything significant to comets. Okay? Now how does he fit that with what he did with Hook?
Well there's an obvious thing to say. Universal gravity is very, very far removed at this point. He's got an attractive power toward the Sun and it works on the planets but it's not yet working on comets the same way. And what he's doing for Flamsteed is helping Flamsteed develop the best version of Flamsteed's account.