Today, let's look at Fahrenheit's thermometers. 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. When he was 15
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.
And there he found out about thermometers. The
Florentine thermometer, invented in Italy some 60
years before, caught his 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. He dodged
the Dutch police until he became a legal adult at
the age of 24. At first Fahrenheit had gone on the
run; but then he continued traveling -- through
Denmark, Germany, Holland, Sweden, and Poland -- to
learn and study.
Ulrich Grigull, who tells Fahrenheit's story, notes
that Florentine thermometer scales were quite
arbitrary. No two were alike. Makers set the low
point on the scale during the coldest day in
Florence that year and the high point during the
hottest day.
Fahrenheit wanted thermometers to be reproducible.
He realized that the trick was not to use the
coldness or hotness of a particular day or place,
but to find materials that changed at certain
temperatures. Isaac Newton had had the same idea a
few years earlier, but he wasn't a professional
thermometer maker, and he was ignored.
Between 1707 and 1714 Fahrenheit worked out an
alcohol thermometer scale based on three points:
Zero was freezing point of a salt-water mixture, 32
degrees was the freezing point of water, and body
temperature was called 96 degrees. Body temperature
was a little off in this scale, but it was close.
In 1714 he startled the world with a pair of
thermometers that both gave the same readings. No
one had ever managed to do that. Later he made
mercury thermometers that let him use the boiling
point of water instead of the human body
temperature.
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 the scales must be
set by universal material properties. But he also
did what Newton failed to do. He manufactured fine
thermometers that 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.
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