Today, we find out how long an inch is. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
Units of measure were fairly
standard in 18th-century England. Henry VIII had
defined the yard as the distance from his nose to
the tip of his outstretched hand. His daughter,
Queen Elizabeth, rather liked the Roman mile -- a
distance of about 5000 English feet. But she wanted
it to be exactly eight English furlongs, so she
standardized it at 5280 feet. Units like these were
the same everywhere in England by the late 1700s.
But in France, measurements were a mess. Every
province had different standards, and that made
scientific discourse very difficult. Finally, in
1791, the French Academy of Science was asked to
set up national standards, and it did so from
scratch. What England did arbitrarily over hundreds
of years, France vowed to do rationally. France
determined to let the immutable laws of nature set
her weights and measures.
At first, they wanted to standardize the length of
a pendulum that would give a one-second swing. But
gravity isn't exactly the same everywhere, so they
gave that up. Instead, they used one ten-millionth
of the distance from the north pole to the equator
as the standard meter. They took the mass of liquid
in a one-centimeter cube as the standard gram, and
so on.
So the metric system was born, and French
scientists gloated over its beauty. Antoine
Lavoisier was anything but detached when he praised
this product of detached science. "Never has
anything more grand and simple, more coherent in
all its parts, issued from the hand of man," he
cried. (Three years later, the not-so-detached
revolutionary government detached Lavoisier's head,
but they kept the metric system for another century
and a half.)
The metric system finally gave way to the
International System of units. The calorie -- the
energy needed to heat a gram of water one degree --
was replaced with the Joule. A Joule is defined in
terms of work, not heat. The Centigrade temperature
scale was shifted a little and renamed after
Celsius.
We're less sure of science's detachment today. We
realize that no system of units will ever be
completely coherent because science itself isn't
complete. Yet we have accepted the brilliance of
the French idea -- the notion that nature itself
should guarantee the consistency of our units.
By the way, do you know how the inch is defined
today? It's not the 12th part of a standard foot.
The inch is defined as precisely 2.54 centimeters.
We quit trying to base length on a dead man's arm.
We abandoned the old English standard -- a long
time ago.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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