The Corner

Alexander’s Accomplishments

Not many people — prob. only math freaks & horologists — know that among

Alexander’s many other achievements, he invented an utterly original method

of timekeeping. He noticed a thing no-one had noticed before: that certain

dye-like substances extracted from mineral bases would change darken in

color when exposed to the sun, but *at different rates*. Alexander, or more

likely one of his courtiers, would soak a long strip of cloth in these

substances, with the slower-reacting ones at one end and the faster at the

other in stripes across the length of cloth. This was exposed to the sun,

and you could tell at a glance what time of day it was by seeing how far

along the strip of cloth these stripes had darkened. Ingenious, no? This

remarkable invention is know to historians of science as Alexander’s

time-band rag.

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