| How does a thermometer tell the temperature? |
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| ::darkshadows:: (blood@thirsty.net) |
2008/06/09 02:17 |
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From: "::darkshadows::" <blood@thirsty.net>
Newsgroups: alt.fan.rolex
Subject: How does a thermometer tell the temperature?
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Date: Mon, 09 Jun 2008 08:17:04 GMT
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How does a thermometer tell the temperature?
A thermometer measures temperature through a glass tube sealed with
mercury that expands or contracts as the temperature rises or falls.
The tiny size of the bulb and micro-fine size of the tube help the
mercury reach the temperature of what it is measuring very rapidly.
Bulb thermometers follow the simple principle that liquids change
their volumes relative to their temperature. As temperatures rise, the
mercury-filled bulb expands into the capillary tube. Its rate of
expansion is calibrated on the glass scale. Two different scales can
be found on thermometers--the Fahrenheit scale and the Celsius scale.
With the Fahrenheit scale, Daniel Fahrenheit decided that the freezing
and boiling points of water would be separated by 180 degrees and he
pegged freezing water at 32 degrees. So he made a thermometer, stuck
it in freezing water, and marked the level of the mercury on the glass
as 32 degrees. Then he stuck the same thermometer in boiling water and
marked it 212 degrees. He then put 180 evenly spaced marks between
those two points.
In Celsius scale, Anders Celsius decided that the freezing and boiling
points of water would be separated by 100 degrees and he made the
freezing point of water at 100 degrees. (His scale was later inverted,
so the boiling point of water became 100 degrees and the freezing
point became 0 degrees.)
Bulb thermometers are most commonly found in two places--outside on
our porches measuring the temperatures outside or under our tongues
measuring our bodily temperatures.
With the age the technology came the invention of other types of
thermometers. Each different type of thermometer has their own
distinctive means of measuring or controlling temperature. For
instance, bimetallic strip thermometers are extremely effective for
controlling temperatures. Although bulb thermometers are good for
measuring temperature accurately, they are harder to maintain set
temperatures.
While bulb thermometers measure our changing temperatures when we feel
feverish, bimetallic strip thermometers help us bake our favorite
cakes by maintaining a set temperature in ovens. The bimetallic strip
thermometer, because it is made of metal, is good at maintaining the
same temperature for a long period of time.
Recent technology has created new ways to measure temperatures with
electronics. The most common device is known as a thermoresistor (or
thermistor). This sensor changes its resistance with changes in
temperature. A computer or other electronic circuit measures the
resistance and converts it to a temperature, either to display it or
to make decisions about turning something on or off.
The first attempt to make a standard temperature scale was done by
Galen in AD 170. In his medical writings, Galen created a standard
"neutral" temperature consisting of equal quantities of boiling water
and ice. On each side of this "neutral" temperature were four degrees
of heat and four degrees of cold.
The earliest devices that were used to measure temperature were
referred to as thermoscopes. A thermoscope was a glass bulb with a
long tube extending downward into a container of colored water.
Did you know?
In 1610 Galileo supposedly used wine instead of water in thermoscopes.
In 1641, the first sealed thermometer that used liquid rather than air
as the thermometric medium was invented for Ferdinand II, Grand Duke
of Tuscany. His thermometer used a sealed alcohol-in-glass device,
with 50 "degree" marks on its stem but no "fixed point" was used to
zero the scale. These were referred to as "spirit" thermometers.
Robert Hook, Curator of the Royal Society, created in 1664 the
thermometer that eventually became the standard temperature-measuring
instrument of Gresham College and was used by the Royal Society until
1709. (The first intelligible meteorological records used this scale).
Mercury's unique characteristics are perfect for measuring
temperatures for the following reasons:
It has large and uniform expansion abilities,
Its silvery appearance allows for easy reading,
Its ability to remain a liquid over a wide range of temperatures.
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