born in Danzig, Germany (now Gdansk, Poland), in
1686, the oldest of five children. Fahrenheit’s major
contributions lay in the creation of the first accurate
thermometers in 1709 and a temperature scale in 1724
that bears his name today.
When he was 15 years of age, his parents died of
mushroom poisoning. The city council placed the four
younger Fahrenheit orphans 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, invent-
ed in Italy 60 years prior in 1654 by the grand duke of
Tuscany, Ferdinand II (1610–70), a member of the
powerful 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, whereby Dutch authorities issued war-
rants for his arrest. While on the run, he spent several
years traveling around Europe and meeting scientists,
such as Danish astronomer Olaus Roemer. Eventually
he returned 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—was not obvious
in Fahrenheit’s time, when several makers used differ-
ent types of scales and liquids for measuring. In 1694
Carlo Renaldini, a member of the Academia del Cimen-
to 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 acade-
my was founded by Prince Leopoldo de Medici and the
Grand Duke Ferdinand II in 1657 with the purpose of
examining the natural philosophy of Aristotle. 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 low end of the scale
as the coldest day in Florence that year and the high
end of the scale as the hottest day. Because tempera-
ture fluctuations naturally occur over the years, no
two thermometers gave the same temperature. For sev-
eral years Fahrenheit experimented with this problem,
finally devising an accurate alcohol thermometer in
1709 and the first mercury or “quicksilver” ther-
mometer 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 Fahren-
heit personally reviewed. Romer used alcohol (actually
wine) as the liquid, but his thermometer had two fixed
reference points. He selected 60 degrees for the tempera-
ture of boiling water and 7.5 degrees for melting ice.
Fahrenheit eventually devised a temperature scale
for his alcohol thermometers with three points calibrated
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,
believed at the time to be the coldest possible tempera-
ture. The scale was etched in 12 major points (with zero,
four, and 12 as three points) and eight gradations
between the major points, giving him a total of 96 points
for his scale for body temperature on his thermometer.
Because his thermometers showed such consistency
in their measurements, mathematician Christian Wolf
at Halle, Prussia, devoted a whole paper in an edition
of Acta Eruditorum,one of the most important inter-
national journals of the time, on two of Fahrenheit’s
thermometers that were given to him in 1714. From
1682 until it ceased publication in 1731, the Latin Acta
Eruditorum, published monthly in Leipzig and sup-
ported by the duke of Saxony, was one of the most
important international journals. The periodical was
founded by Otto Mencke, professor of morals and
practical philosophy, and mathematician Gottfried Wil-
helm Leibnitz. Written in Latin, the journal covered sci-
ence and social science and was primarily a vehicle for
reviewing books. In 1724 Fahrenheit published a paper,
“Experimenta circa gradum caloris liquorum nonnullo-
rum ebullientium instituta (Experiments done on the
degree of heat of a few boiling liquids), in the Royal
Society’s publication Philosophical Transactions and
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 than that of alcohol and could be used over a
wider range of temperatures. Fahrenheit, like ISAAC
NEWTONbefore him, realized that it was more accurate
to base the thermometer on a substance that changed
consistently based on temperature instead of simply on124 Fahrenheit, Daniel Gabriel