Who
invented the thermometer?
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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.
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
Information for Teachers
- Make your own Thermometer
Use the Brannan Classroom
Thermometer Kit to calibrate your own thermometer using the
freezing and boiling points of water or alternatively create your
own temperature scale using your own fixed points.
The kit contains an accurate thermometer set and an uncalibrated
thermometer,
The kit comes complete with teachers' notes.
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