Chapter 35

There is also this about the tides, which we all know to be true, and which we can see at work any day, but which I defy any man to rationalize: when the tide runs up a narrow river—or, indeed, any river—it will be still running up, say, ten miles from the mouth, when it is running _down_ again, say, five miles from the mouth. What happens in between? Slack water, of course. But _how_ is there slack water? How can the running _down_ be going on at one point and, immediately beyond, the running up, without a divisio…