The Thermometer
History of the Thermometer
By Mary
Bellis
Thermometers measure
temperature, by using materials that change in some way when they are heated or
cooled.
In a mercury or alcohol
thermometer, the liquid expands as it is heated and contracts when it is
cooled, so the length of the liquid column is longer or shorter depending on
the temperature.
Modern thermometers are
calibrated in standard temperature units such as Fahrenheit (used in the United
States) or Celsius (used in Canada) and Kelvin (used mostly by scientists).
WHAT IS A THERMOSCOPE?
Before there was the thermometer, there was the earlier and
closely related thermoscope, best described as a thermometer without a scale.
A thermoscope only showed the
differences in temperatures, for example, it could show something was getting
hotter.
However, the thermoscope did
not measure all the data that a thermometer could, for example, an exact
temperature in degrees.
EARLY
HISTORY
Several inventors invented a version of the thermoscope at the
same time.
In 1593, Galileo Galilei invented a rudimentary water
thermoscope, which for the first time, allowed temperature variations to be
measured.
Today, Galileo's invention is
called the Galileo Thermometer, even though by definition it was really a
thermoscope.
It was a container filled
with bulbs of varying mass, each with a temperature marking, the buoyancy of
water changes with temperature, some of the bulbs sink while others float, the
lowest bulb indicated what temperature it was.
In
1612, the Italian inventor Santorio Santorio became the first inventor to put a
numerical scale on his thermoscope.
It was perhaps the first
crude clinical thermometer, as it was designed to be placed in a patient's
mouth for temperature taking.
Both
Galilei's and Santorio's instruments were not very accurate.
In 1654, the first enclosed liquid-in-a-glass thermometer was invented by the
Grand Duke of Tuscany, Ferdinand II.
The Duke used alcohol as his
liquid. However, it was still inaccurate and used no standardized scale.
FAHRENHEIT
SCALE - DANIEL GABRIEL FAHRENHEIT
What can be considered the first modern thermometer, the mercury
thermometer with a standardized scale, was invented by Daniel Gabriel
Fahrenheit in 1714.
Daniel
Gabriel Fahrenheit was the German physicist who invented the alcohol
thermometer in 1709 and the mercury thermometer in 1714.
In 1724, he introduced the
standard temperature scale that bears his name - Fahrenheit Scale - that was
used to record changes in temperature in an accurate fashion.
The
Fahrenheit scale divided the freezing and boiling points of water into 180
degrees.
32°F was the freezing pint of
water and 212°F was the boiling point of water.
0°F was based on the
temperature of an equal mixture of water, ice, and salt.
Fahrenheit based his
temperature scale on the temperature of the human body.
Originally, the human body
temperature was 100° F on the Fahrenheit scale, but it has since been adjusted
to 98.6°F.
CENTIGRADE
SCALE - ANDERS CELSIUS
The Celsius temperature scale is also referred to as the
"centigrade" scale.
Centigrade means "consisting of or divided into 100
degrees".
In 1742, the Celsius
scale was invented by Swedish Astronomer Anders Celsius.
The Celsius scale has
100 degrees between the freezing point (0°C) and boiling point (100°C) of pure
water at sea level air pressure.
The term
"Celsius" was adopted in 1948 by an international conference on
weights and measures.
KELVIN
SCALE - LORD KELVIN
Lord Kelvin took
the whole process one step further with his invention of the Kelvin Scale in
1848.
The Kelvin Scale measures the
ultimate extremes of hot and cold.
Kelvin developed the idea of
absolute temperature, what is called the "Second Law of Thermodynamics,” and
developed the dynamical theory of heat.
In
the 19th century, scientists were researching what was the lowest
temperature possible.
The Kelvin scale uses the
same units as the Celcius scale, but it starts at ABSOLUTE ZERO, the
temperature at which everything including air freezes solid.
Absolute zero is O K, which is - 273°C degrees Celsius.
When
a thermometer was used to measure the temperature of a liquid or of air, the
thermometer was kept in the liquid or air while a temperature reading was being
taken.
Obviously, when you take the
temperature of the human body you can't do the same thing.
The mercury thermometer was
adapted so it could be taken out of the body to read the temperature.
The clinical or medical
thermometer was modified with a sharp bend in its tube that was narrower than
the rest of the tube. This narrow bend kept the temperature reading in place
after you removed the thermometer from the patient by creating a break in the
mercury column.
That is why you shake a
mercury medical thermometer before and after you use it, to reconnect the
mercury and get the thermometer to return to room temperature.
MOUTH
THERMOMETERS
In 1612, the Italian inventor Santorio Santorio invented the
mouth thermometer and perhaps the first crude clinical thermometer.
However, it was both bulky,
inaccurate, and took too long to get a reading.
The
first doctors to routinely take the temperature of their patients were: Hermann
Boerhaave (1668–1738), Gerard L.B. Van Swieten (1700–72) founder of the
Viennese School of Medicine, and Anton De Haen (1704–76).
These doctors found
temperature correlated to the progress of an illness, however, few of their
contemporaries agreed, and the thermometer was not widely used.
FIRST
PRACTICAL MEDICAL THERMOMETER
English physician, Sir Thomas Allbutt (1836–1925) invented the
first practical medical thermometer used for taking the temperature of a
person in 1867.
It was portable, 6 inches in
length and able to record a patient's temperature in 5 min.
EAR
THERMOMETER
Pioneering biodynamicist and flight surgeon with the
Luftwaffe during World War II, Theodore Hannes Benzinger invented the ear
thermometer.
David Phillips invented the
infrared ear thermometer in 1984.
Dr. Jacob Fraden, CEO of
Advanced Monitors Corporation, invented the world's the best-selling ear
thermometer, the Thermoscan® Human Ear Thermometer.
https://www.thoughtco.com/the-history-of-the-thermometer-1992525
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