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.