ARCHIVE.

A lump of corroded gears from an ancient shipwreck turned out to be a calculator for the sky. What survives shows how it flagged eclipse months; how much more it once did is partly a modern rebuild.

Over a couple of centuries, the long vowels of English (vowel sounds held for longer than their short partners) moved, and the letters that spelled them mostly stayed put. For the most part the spelling didn't change to follow the sounds, so English spelling that looks wrong is often a record of older speech.

A century ago, a quiet electric car was a perfectly normal way to get around town. Then the job it was good at stopped being the job most drivers wanted done, and a better battery, much later, helped bring it back.

Swap a ship's planks one at a time and every repair looks harmless. Then someone builds a second ship from the old planks, and "the same ship" stops being an easy phrase.

In Renaissance painting contracts, one colour got written up like a precious material: ultramarine, made from a stone mined in what is now Afghanistan. The odd part is that crushing the stone doesn't give you that blue. Getting it out took a strange kneading ritual in wax, resin and lye.