Entry No. 42 · November 1931

Sixty-one arrows

Three winters in a rowboat with a cork float and a chronometer. How the tidal atlas got its drift arrows, and why each one is signed.

A tidal chart can be drawn from a desk. The mathematics of tide and stream were settled by the time Plate IX was begun, and a competent draughtsman could have produced the arrows from published tables in a fortnight. The house did not do this, for a reason the junior partner wrote at the top of the working sheet: the tables predict the water. Sailors need the water itself.

So the surveyors rowed. At slack water they positioned. At full flood they threw a corked float with a tin tail over the side, started a chronometer, and rowed behind it, noting where it went and how fast. Sixty-one times over three winters, in water cold enough to make the pen an instrument of endurance rather than writing.

Each arrow on the finished plate is timed to the minute and initialled by the man who threw the float. This was not sentiment. When two arrows disagreed, the initials settled which observation to trust, and the disagreement itself was engraved as a question mark in the margin. Three question marks survive on the plate. Nobody ever resolved them. The Sound kept its own counsel on those three tides and the house recorded its refusal to explain itself.

The senior partner argued the question marks looked like uncertainty and should go. The engraver, who had not been in the boat, argued they looked like honesty and should stay. The engraver won, which the record notes was the first and last time the argument was put to a vote.

The plate took three winters and one hundred and twenty impressions before the copper showed through the arrows' wear. It has never gone out of print since, though the intervals between restrikes grow longer as the plate thins. The current state is the fifth. The question marks are barely a hair's width deep now. In another twenty years they will be gone, and the plate will have answered the tide's refusal by forgetting it, which is, we think, what the Sound always intended.

Filed in the daybook, 2 November 1931. Plate IX, fifth state, remains in print.