thermometers in 1709 and a temperature scale in 1724
that bears his name today.
When Daniel was 15 years of age, his parents died
of mushroom poisoning. The city council placed the
four younger Fahrenheit children in foster homes and
apprenticed Daniel to a merchant who taught him
bookkeeping. He was sent to Amsterdam around 1714,
where he learned of the Florentine thermometer,
invented in Italy 60 years prior in 1654 by the Grand
Duke of Tuscany, Ferdinand II (1610–70), a member of
the great Medici family. For some unknown reason it
sparked his curiosity, and he decided to make ther-
mometers for a living. He abandoned his bookkeeping
apprenticeship, whereupon Dutch authorities issued
warrants for his arrest. While on the run, he spent sev-
eral years traveling around Europe and meeting scien-
tists, such as Danish astronomer Olaus Romer.
Eventually he came back to Amsterdam in 1717 and
remained in the Netherlands for the rest of his life.
What seems so simple today—having a fixed scale
and fixed points on a thermometer—did not exist for a
long time, since several makers of thermometers used
different types of scales and liquids for measuring. In
1694 Carlo Renaldini, a member of the Academia del
Cimento and professor of philosophy at the University
of Pisa, was the first to suggest taking the boiling and
freezing points of water as the fixed points. The
academy was founded by Prince Leopoldo de’ Medici
and the Grand Duke Ferdinand II in 1657 with the
purpose of examining the natural philosophy of Aristo-
tle. The academy was active sporadically over 10 years
and concluded its work in 1667 with the publication of
the Saggi di Naturali Esperienze.
Unfortunately, Florentine thermometers, or any
thermometers of the time, were not very accurate; no
two thermometers gave the same temperature, since
there was no universal acceptance of liquid type or
agreement on what to use for a scale. Makers of Flo-
rentine thermometers marked the lowest scale as the
coldest day in Florence that year and the highest scale
for the hottest day. Since temperature fluctuations nat-
urally occur over the years, no two thermometers gave
the same temperature. For several years Fahrenheit
experimented with this problem, finally devising an
accurate alcohol thermometer in 1709 and the first
mercury or “quicksilver” thermometer in 1714.
Fahrenheit’s first thermometers, from about 1709
to 1715, contained a column of alcohol that directly
expanded and contracted, based on a design made by
Danish astronomer Olaus Romer in 1708, which
Fahrenheit personally reviewed. Romer used alcohol
(actually wine) as the liquid, but his thermometer had
two fixed reference points. He selected 60 degrees for
the temperature of boiling water and 7^1 / 2 degrees for
melting ice.
Fahrenheit eventually devised a temperature scale
for his alcohol thermometers with three points cali-
brated at 32 degrees for freezing water, 96 degrees for
body temperature (based on the thermometer being in a
healthy man’s mouth or under the armpit), and zero
degrees fixed at the freezing point of ice and salt, which
was believed at that time to be the coldest possible tem-
perature. The scale was etched in 12 major points, with
zero, four, and 12 as the three points and eight gradua-
tions between the major points, giving him a total of
96 points for his scale for body temperature on his
thermometer.
Since his thermometers showed such consistency
between them, mathematician Christian Wolf of Halle,
Prussia, devoted a whole paper in an edition of Acta
Eruditorum,one of the most important scientific jour-
nals of the time, to two of Fahrenheit’s thermometers
that Wolf received in 1714. In 1724 Fahrenheit pub-
lished a paper entitled “Experimenta circa gradum
caloris liquorum nonnullorum ebullientium instituta”
(Experiments done on the degree of heat of a few boil-
ing liquids) in the Royal Society’s publication Philo-
sophical Transactionsand was admitted to the Royal
Society the same year.
Fahrenheit decided to substitute mercury for the
alcohol because its rate of expansion was more con-
stant and could be used over a wider range of tempera-
tures. Fahrenheit, like Isaac Newton before him,
realized that it was more accurate to base the ther-
mometer on a substance that changed consistently
based on temperature, not simply the hottest or coldest
day of the year like the Florentine models. Mercury
also had a much wider temperature range than alcohol.
This was contrary to the common thought at the time,
promoted by Halley as late as 1693, that mercury
could not be used for thermometers due to its low coef-
ficient of expansion.
Fahrenheit later adjusted his temperature scale to
ignore body temperature as a fixed point, bringing the
scale to the freezing and boiling of water alone. When he
died, scientists recalibrated his thermometer so that the106 Fahrenheit, Daniel Gabriel