Tides of Power How the Moon Shapes Life, Law, and Coastlines

Twice a day, in a long funnel of water between New Brunswick and Nova Scotia, the sea performs a trick that seems to break the rules. Boats tied up at a wharf in the afternoon sit on mud by evening, tilted on their keels as if they had been abandoned. Hours later the water is back, rising as high as a five-story building. In the Bay of Fundy, the difference between high tide and low tide can reach about fifty-four feet.

That is a strange number when you consider that on many open coastlines the ocean rises and falls by only a few feet, and in some enclosed seas by only a few inches. The same Moon hangs over all of them. The same Sun is behind it. So why does one stretch of water barely stir while another heaves like a living thing?

The answer connects the deep past of the planet, the spawning of small silver fish on California beaches, the schedules of medieval pilgrims, and the engineers now trying to turn the ocean's pulse into electricity. It also involves a famously brilliant man who got the explanation wrong, and another who got it right.

Let's start with the basic machinery, because everything else grows out of it.