Today, we invent the thermometer. 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.
Daniel Fahrenheit, the man
who put thermometry on a solid footing, was born in
the Polish city of Gdansk in 1686. He was only
fifteen when his parents both died from eating
poisonous mushrooms. The city council put the four
younger Fahrenheit children in foster homes. But
they apprenticed Daniel to a merchant, who taught
him bookkeeping and took him off to Amsterdam.
There he found out about thermometers. The
Florentine thermometer had been invented in Italy
some sixty years before. Now it showed up as a
trade item in Amsterdam, and it caught young
Fahrenheit's fancy. So he skipped out on his
apprenticeship and borrowed against his inheritance
to take up thermometer making.
When the city fathers of Gdansk found out, they
arranged to have the 20-year-old Fahrenheit
arrested and shipped off to the East India Company.
So he had to dodge Dutch police until he became a
legal adult at the age of 24. At first he'd simply
been on the run; but he kept traveling -- through
Denmark, Germany, Holland, Sweden, Poland. He
studied and learned.
Ulrich Grigull, who tells Fahrenheit's story,
points out that Florentine thermometer scales were
quite arbitrary. No two were alike. Makers marked
the low point on the scale during the coldest day
in Florence that year. They marked the high point
during the hottest day. Fahrenheit wanted
thermometers to be reproducible. He realized the
trick wasn't using the coldness or hotness of a
particular day or place, but finding materials that
changed at certain temperatures. Isaac Newton had
had the same idea a few years earlier, but he
wasn't a thermometer-maker. His idea stayed in
books.
For seven years Fahrenheit worked out an alcohol
thermometer scale based on three points. He chose
the freezing point of a certain salt-water mixture
for zero. He used the freezing point of water for
32 degrees. And body temperature he called 96
degrees.
Why the funny numbers? He originally used a
twelve-point scale with zero, four, and twelve for
those three benchmarks. Then he put eight
gradations in each large division. That's how he
got that strange 96 number -- it was eight times
twelve. Body temperature is actually a tad higher
than 96, but it was close. Later, Fahrenheit made
mercury thermometers that let him use the boiling
point of water instead of human body temperature
for the high mark.
Fahrenheit was still only 28 when he startled the
world by making a pair of thermometers that both
gave the same readings. No one had ever done that
before. The turning points of inventive genius are
subtle. Fahrenheit made sense of temperature by
seeing temperature scales in abstract terms. He
realized, independently of Newton, that scales
could be wed to universal material properties. But
he also did what Newton failed to do. He built fine
thermometers, and they carried his thinking into
the world.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
