The Almanac of Collapsing Records

Measuring the Earth — Alexandria, c. 240 BCE

A paved courtyard beside the Library of Alexandria, at the foot of a vertical gnomon, on the noon of the summer solstice

c. 240 BCE — high summer in Alexandria, the great Library at the edge of the harbour, the chief librarian at work on the length of a shadow at midday on the solstice, and a well far south at Syene where at that same hour the sun stands overhead and casts no shadow at all

The whole Earth, weighed on a thread and a shadow. This breach reads the ASSISTANT AT THE PLUMB-LINE in Alexandria at solstice noon: a bronze rod set upright in a courtyard, a lead weight swinging still on a linen thread, and a measured slant of shade that carries in it the circumference of the world, because a well nine hundred miles south throws no shadow at the same hour. The witness is read only at the thread and the marked stone — the librarian kneeling at documented distance, the calculation held in the background, never explained aloud. The fragment is the subject's own: the steadiness asked of your hands while someone else did the thinking, the smallness of your part in something enormous — and the memory beneath it of a time you held something still for someone and only later understood what you had been holding it for.

From the record

Eratosthenes of Cyrene was chief librarian of the Library of Alexandria in the third century BCE
he was told that at noon on the summer solstice, in Syene far to the south, the sun stood directly overhead and a vertical rod cast no shadow, and sunlight reached the bottom of a well
at Alexandria at the same hour a vertical gnomon did cast a shadow, and he measured the angle of the sun as about one fiftieth of a full circle
he took the distance from Alexandria to Syene as roughly 5,000 stadia and multiplied it by fifty to give an Earth circumference of about 250,000 stadia
the figure he arrived at was within a few percent of the modern measurement of the Earth's circumference
the method required only a vertical rod, a shadow, a known distance, and the assumption that the Earth is a sphere and the sun's rays effectively parallel

The era door

a tall cedar door, sun-bleached and salt-cracked, set in a limestone wall, its bronze ring hot to the touch

ALEXANDRIA — SOLSTICE NOON, c. 240 BCE

Walk this day yourself — free

A guided walk with Wallace — you are placed inside the record as a witness, and you carry a memory of your own back out. Free, ~20 minutes.

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MEMORY IS RESISTANCE · IN SERVICE OF VELOCITY · YEAR 3037