All right, upshot for the night. That's your evidence. We've got the evidence question resolved as to 1651. The last slide here, I just want to mention. What we got tonight are four fundamental principles of local motion that are come out of the third day. They are, in vertical descent you acquire equal increments of speed and equal increments of time.

You acquire the same speed in descending from the same height, regardless of the weight or shape. You acquire the same speed in falling from a given height, whether falling vertically or along a inclined plane. And you acquire a speed in descending from any given height which is just sufficient to raise them to that height.

Those are four of the most fundamental principles of modern physics. You get them in high school physics. The obvious question I pose here at the end, that you will have a chance to come back to is, what's the evidence for all four? And the thing I want to leave you with is take Riccioli's great experiment, it's a wonderful experiment, he reports exact agreement.

Think of yourself as living, not in Bologna having witnessed it, how do you assess it's accuracy? Do you take him at his word? Do you repeat the experiment? Where do you find 300 foot towers, etc? That's the situation they're in. They're getting individual good experiments that are supportive.

But the question of replicating them, the whole community redoing them and verifying them, that's completely hanging. Worse than that, they're not sure what a Roman foot is, Huygens is using Rhenish foot and Mersenne's using Paris feet. By the mid-1650's, the Paris foot becomes the standard. That's a nice step forward, but at this point, they're not even sure how to compare them.

So how can you really do the kind of assessment of evidence that was being done standardly in astronomy? The community is in a different position here entirely. You're depending very heavily on individuals, their truthfulness, in particular the truthfulness in their reporting results.