Listening to the Feynman lectures on CD (the one on electromagentism is quite a challenge on CD 🙂 we got to gravity, and I was rather struck by a historical note he made, concerning the shift from geocentrism to heliocentrism – essentially, the process of working out how the planets really moved, and why.
The first I’ve heard elsewhere: that once you have some idea of momentum, then you realise that the invisible angels you need to push your planets around suddenly change direction: instead of pushing from behind the planets to make them go round in circles, suddenly they are pushing the planets towards the sun. So all of a sudden the idea that the sun might be the source of the invisible angels becomes rather more likely.
And the second was that the person he selects as making the outstanding initial contribution is Tycho Brahe. Feynman phrases it something like this: “and then someone had a great idea… instead of just arguing from first principles about the planets motions, why not measure them carefully to see what they actually did”. This is interesting, because in the versions of the story I know, Brahe is a somewhat minor character: a rich but rather uninspired figure, mechanically making careful observations that he didn’t know what to do with; the big boys of that story are then Copernicus and Kepler, and then Newton. I think Feynman’s view isn’t really historically accurate; but it is a new way to look at the story.