Among science's most sacred relics are the standard "meter bars" of platinum-iridium that lie in an underground shrine at Sèvres, near Paris. Replacing a babel of medieval units, they originated in the spurt of innovation that followed the French Revolution. The newfangled meter was intended to be one ten-millionth of the distance between the earth's equator and the North Pole, but difficulties of measurement made the exact length hard to determine. So the meter that was finally accepted (39.37 in. in length) was almost as arbitrary a unit as the ells, feet, rods and pieds de roi that it replaced.
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