Thermometer Timeline
Who invented the thermometer?
The first recorded thermometer was produced by the Italian, Santorio
Santorio (1561-1636) who was one of a group of Venetian scientists working
at the end of the Sixteenth Century. As with many inventions the thermometer
came about through the work of many scientists and was improved upon
by many others.
1596
Galileo Galilei and the first thermoscope
Galileo Galilei is often claimed to be the inventor of the thermometer.
However the instrument he invented could not strictly be called a thermometer:
to be a thermometer an instrument must measure temperature differences;
Galileo's instrument did not do this, but merely indicated temperature
differences. His instrument should rightly be called a thermoscope.
The Thermoscope
The predecessor to the thermometer, the thermoscope is a thermometer
without a scale; it indicates differences in temperature only ie it
can show if the temperature is higher, lower or the same, but unlike
a thermometer it cannot measure the difference nor can the result be
recorded for future reference. The thermoscope was widely used by a
group of scientists in Venice that included Galileo. It was only a small
step from the thermoscope to the thermometer.
1612
Santorio Santorio - the first thermometer
The Italian, Santorio Santorio (1561-1636) is generally credited with
having applied a scale to an air thermoscope at least as early as 1612
and thus is thought to be the inventor of the thermometer as a temperature
measuring device. Santorio's instrument was an air thermometer. Its
accuracy was poor as the effects of varying air pressure on the thermometer
were not understood at that time.
1654
The first sealed liquid-in-glass thermometer
The sealed liquid-in-glass thermometer, more familiar to us today, was
first produced in 1654 by the Grand Duke of Tuscany, Ferdinand II (1610-1670).
His thermometer had an alcohol filling. Although this was a significant
development his thermometer was inaccurate and there was no standardised
scale in use.
1714
The first mercury thermometer
Gabriel Fahrenheit (1686-1736) was the first person to make a thermometer
using mercury. The more predictable expansion of mercury combined with
improved glassworking techniques led to a much more accurate thermometer.
Fahrenheit - the first Standard Thermometer Scale
Fahrenheit used the newly discovered fixed points to devise the first
standard temperature scale for his thermometer. Fahrenheit divided the
freezing and boiling points of water into 180 degrees. 32 was chosen
as the the figure for the lower fixed point as this produced a scale
that would not fall below zero even when measuring the lowest possible
temperatures that he could produce in his laboratory - a mixture of
ice, salt and water. It is sometimes suggested that Fahrenheit divided
his scale into 100 degrees using blood temperature (incorrectly measured)
and the freezing point of water as fixed points - this is not true.
The Fahrenheit scale is still in use today.
1731
The Réamur Scale
In 1731 the Frenchman, René Antoine Ferchauld de Réamur
(1683-1757) proposed a thermometer scale on which the freezing point
of water was 0° and the boiling point was 80°. The Réamur
scale is not in use today.
1742
The Celsius Scale
In 1742 a Swedish scientist named Anders Celsius (1701-1744) devised
a thermometer scale dividing the freezing and boiling points of water
into 100 degrees. Celsius chose 0 degrees for the boiling point of water,
and 100 degrees for the freezing point. A year later, the Frenchman
Jean Pierre Cristin (1683-1755) inverted the Celsius scale to produce
the Centigrade scale used today (freezing point 0°, boiling point
100°). By international agreement in 1948 Cristin's adapted scale
became known as Celsius and is still in use today.
1848
The Absolute Temperature Scale or Kelvin Scale
In 1848 Sir William Thomson, Baron Kelvin of Largs, Lord Kelvin of Scotland
(1824 - 1907) proposed the absolute temperature scale with zero degrees
being the theoretical lowest temperature possible where molecular motion
ceases. Kelvin defined 1 Kelvin degree as being equal to one Celsius
degree. The Degree Kelvin is the current Standard Unit of temperature
measurement.