'And lastly suppose that the Cam flowed always at the same speed, and that our punt matched it. That is what I call a fluxion – a flowing movement along the curve over time. I think you can see that as we rounded the first limb of the S-curve around Jesus College, where the river bends southward, our fluxion in the north-south direction would be steadily changing. At the moment we passed under the Bridge, we'd be pointed northeast, and so we would have a large northwards fluxion. A minute later, when we reached the point just above Jesus College, we'd be going due east, and so our north-south fluxion would be zero. A minute after that, after we'd curved round and drawn alongside Midsummer Commons, we'd be headed southeast, meaning that we would have developed a large southward fluxion – but even that would reduce and tend back towards zero as the stream curved round northwards again towards Stourbridge Fair.'