Water Writes Its Own Autobiography

The tide-gauge at the Nore was finished this afternoon - a float in a stilling well, a pencil bearing on a drum turned by clockwork, so that the water writes its own autobiography without the observer’s hand anywhere in it. I had the apparatus set against the pier head and let it run from noon until the evening ebb, expecting nothing but confirmation of what every almanac asserts: that the rise at this station follows the equilibrium theory with the modest irregularities of a river mouth.

The pencil disagreed. The flood came in as a staircase - three abrupt lifts, each of a few inches, separated by plateaus of several minutes - where the almanac demands a smooth and continuous ascent. I checked the float for fouling, the well for leaks, the pencil for slack in its carrier. Nothing. The water itself, or something moving through it, is stepping.

Here is the temptation I must record and refuse. The temptation is to call these steps an anomaly, file them under local circumstance - the sandbank, the wind, the pilot boats - and keep the theory whole. But an anomaly is a name for a thing we have declined to examine. What the drum has produced this evening is not an anomaly; it is a datum, and the datum has a shape, and the shape has a period. Three steps, roughly equal, within a single flood. If the second flood tomorrow shows the same staircase, we have a pattern. If the pattern holds at Sheerness and fails at Gravesend, we have a boundary - and a boundary is the most instructive thing an instrument can find, because it tells you where your explanation stops.

The equilibrium theory of the tide explains the ocean’s breathing but says nothing about how that breath climbs a riverbed. What we call the tide’s “irregularity” in estuarine waters was, before this afternoon, merely our word for whatever the smooth curve left out. I begin to suspect the smooth curve is the abstraction and the staircase the fact - that the flood does not rise; it accumulates, a bore in miniature, or several bores, arriving in installments.

Tomorrow I run the gauge through two full tides and have a second drum set at Sheerness. If the steps appear there also, the almanac’s curve must be redescribed, not the water corrected. I entered the day believing the instrument would confirm the tables; I end it believing the tables describe an ocean, and I have been measuring a river.