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Monday, June 08, 2020

Review: Tides

Tides is appropriately written by a sailor. The book taught me several things that I didn't know, even though I was taught how to sail in the San Francisco Bay Area, where a tide table consultation is required before leaving the slip --- with currents exceeding 10 knots through the golden gate, a sailboat will not make it in or out of the gate except during slack tide.

Things I didn't know:

  • A tide coming up or down a river is called a bore. The largest tidal bore in the world is in the Qiantang river in China. (The pictures are impressive)
  • I'd long assumed that tides are small in places like the Mediterranean was because of restricted flow through a funnel. This is false. The reason tidal variation is small in certain places (e.g., the Carribean) is because tides actually vary around various centers in the oceans, and the further away you are from the center, the higher the amplitude.
  • The earth itself (not just the ocean) is also affected by the same gravitational forces that creates the tides:  

If the moon can cause such a stir in the ocean, wouldn’t it also affect the solid earth? Do our bodies, made of 70 percent water, have a tide? Yes and no. The earth is as rigid as a steel ball, but it does distort under the gravitational influence of the sun and moon. High tide on the solid earth varies from half a foot to three feet and spreads over such a large distance—about ten thousand miles—that it’s not perceptible. For example, a high spring tide might raise the sidewalks and buildings of New York by a couple of inches. You could never detect this as you walk down Broadway, because everything rises and falls together over a six-hour period (unlike on the coast, where the ocean rises and falls relative to the beach). The tide’s daily squeezing and releasing of the earth has long been known to affect water wells too. A Wisconsin well, about eight hundred miles from the nearest ocean, has a two-inch tide. An inland well in France increases its flow from sixty to ninety gallons an hour during spring tides. (kindle loc 1883)
The book itself is written English-major journalism style. Sometimes I get very impatient with this style, because all sorts of "color" that might be interesting to an English major is uninteresting when I'm in a hurry to learn information. Similarly, I roll my eyes whenever he does something English-major like, for instance, visiting the British Library to examine Newton's manuscript for "Principia" and then writing things like: "The equations didn't mean anything to me." He does this several times in the book, which had me wondering why he was bothering to burn all those fossil fuels getting to those exotic destinations just to throw his hands up at a little bit of math.

All in all, the book was interesting in the concepts and for its visual imagery of some of the places he visited. It probably could have been 50 pages long if he'd just condensed all the technical information into concise, easy to understand form, but I guess that wouldn't get a publisher interested.

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