 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 thermometersfollow 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
calibratedon the glass scale. Two different scales can be found on thermometers--the
Fahrenheitscale and the
Celsiusscale.
With the Fahrenheit scale, Daniel Fahrenheit decided that the freezing and boiling points of water would be separated by 180 degrees and he
peggedfreezing 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 thermometersare 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 athermistor. This sensor changes its resistance with changes in temperature. A computer or otherelectronic circuitmeasures theresistanceand converts it to a temperature, either to display it or to make decisions about turning something on or off.
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