 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.
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
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.
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