“Second” is Latin for second-small-part — pars minuta secunda; “minute” is the first-small-part. The hour is divided into 60, and those 60s into 60s again, and that number came to us from Babylon, mostly as bookkeeping for the sky. For most of history the second existed only on paper: sundials and water clocks told the time, and a second was something you computed, not something you could hear. The pendulum clock of the 1600s was the first machine that could actually count seconds.

But the Earth is a lousy clock. Tidal friction slows its spin, and by the 1950s the planet was visibly behind the best quartz in the lab. So in 1956 the second was redefined by Earth’s orbit instead — the ephemeris second, a number that took years of astronomical observation to pin down. Then atoms arrived: in 1955 Louis Essen and Jack Parry built the first working caesium clock at the UK National Physical Laboratory, and in 1967 the weights-and-measures conference defined the second as exactly 9,192,631,770 cycles of radiation from a single transition inside a caesium-133 atom.

The number wasn’t pulled from thin air: it was the best measurement of that moment, rounded so the atomic second would land exactly on the astronomical one. And in 2019 the logic quietly flipped — instead of measuring the atom’s frequency in seconds, the frequency is fixed at 9,192,631,770 Hz and the second is derived from it. Same digits, reversed authority.

The Earth keeps a quiet job in the background: atomic clocks vote on what time it is, and the occasional leap second is what we insert when we want clock faces to keep up with the sky. Three definitions, one unbroken length of second — time’s unit left the planet and moved into an atom, and nobody noticed, because they didn’t have to. https://9192631770.com/en/history.html

The & is the oldest letter that never made it into the alphabet. It began in Roman cursive as a ligature — a scribe writing et, the Latin word for "and," so often that he fused the e and the t into a single stroke. The oldest known example is a piece of Pompeii graffiti, so Vesuvius in 79 AD sets a hard upper bound on its age.

The name arrived much later. When the alphabet was recited letter by letter, single letters that were also words were disambiguated with the Latin per se, "by itself": A per se A, I per se I. Our 27th quasi-letter got the same treatment: & per se and — "& by itself is the word and" — and 19th-century children recited it as the last beat of the alphabet. "And per se and" slurried down to ampersand. When the 26 letters won back their ground, the word outlived the letter.

In some italics you can still spot the et tucked inside the shape. A two-thousand-year-old cursive flourish, still doing the same job.