# Temperature, Measurement of

From the Eskimo in Alaska to the Nigerian living near the equator, people of various cultures are exposed to variations in temperature. Our early experiences help us to develop the concept of temperature as a measure of how hot or cold something is. Warmth may be associated with a season of the year or an object such as a stove or a fireplace. The measurement of temperature is important to everyday life, providing information about our health and regulating our outdoor activities with accurate weather reports.

## Defining and Measuring Temperature

Temperature is the number assigned to an object to indicate its warmth. The concept of temperature came about because people wanted to quantify and measure differences in warmth. When an object with a higher temperature comes in contact with a cooler object, a transfer of heat occurs until the two objects are the same temperature. When the heat transfer is complete, it can be said that that the two objects are in thermal equilibrium. Temperature can hence be defined as the quantity of warmth that is the same for two or more objects that are in thermal equilibrium. The temperature 0°C, 273.16 K (kelvin), is the point at which ice, water, and water vapor are all present and in thermal equilibrium. This is known as the triple point of water. Absolute zero temperature occurs when the motion of atoms and molecules practically stops, which occurs at 273°C, or 0 K.

Accurate temperature readings are necessary in maintaining meteorological records. Meteorology is the science that deals with the study of weather, which is the condition of the atmosphere at a specific time and place. A meteorologist is a professional who studies and forecasts the weather. The accuracy of weather forecasts is dependent upon collecting data that includes temperature. Air temperature is measured by using a thermometer.

## Evolution of the Thermometer

Thermometers are instruments that are used to measure degrees of heat. Ferdinand II, Grand Duke of Tuscany, used the first sealed alcohol-in-glass thermometer in 1641. Robert Hook used a thermometer containing red dye in alcohol in 1664. Hook's thermometer used water as the fixed freezing point and became the standard thermometer that was used by Gresham College and the Royal Society until 1709.

In 1702, Ole Roemer of Copenhagen developed a thermometer that used a scale with two fixed points: snow and boiling water. This thermometer became a calibrated instrument that contained a visible substance, either mercury or alcohol, that traveled along a narrow passageway in a tube that used two-fixed points on a scale. The passageway through the tube is called a bore. At the bottom of the bore is a bulb that contains the liquid. The thermometer operates on the principle that these fluids expand (swell) when heated and contract (shrink) when cooled. When the liquid is warmed, it expands and moves up the bore, but when the liquid cools, it contracts and moves down the bore in the opposite direction. When a thermometer is placed in contact with an object and reaches thermal equilibrium, we have a quantitative measure for the temperature of the object. For instance, when a thermometer is placed under the arm of an infant, heat is transferred until thermal equilibrium is reached. Thus, when you observe how much the mercury or alcohol has expanded in the bore, you can find the baby's temperature by reading the scale on the thermometer.

Other thermometers besides alcohol and mercury thermometers are metal thermometers, digital thermometers, and strip thermometers. Rather than containing liquid, the metal thermometer uses a strip of metal made up of two different heat-sensitive metals that have been welded together. A thermograph is a metal thermometer that records the temperature continuously all day. However, today's meteorologists use electronic computers rather than thermographs to obtain permanent records. Digital thermometers are highly sensitive and give precise readings on electronic meters. The strip thermometer is a celluloid tape made with heat-sensitive liquid crystal chemicals that react by changing the color of the tape according to the temperature. Strip thermometers are useful in taking the temperature of infants because one only need put the strip on the baby's forehead for a few seconds to obtain an accurate temperature reading.

## Thermometer Scales

The scale on the thermometer tells us how high the liquid is in the thermometer and gives the temperature of whatever is around the bulb. Thus, the thermometer can be used to measure heat in any object including solids, liquids, and gases. The scale on a thermometer is divided equally with divisions called degrees. The most commonly used scales are Fahrenheit (F) and Celsius (C). The Fahrenheit scale (English system of measurement) is used in the United States while the Celsius scale (metric system of measurement) is used by most other countries.

Gabriel Fahrenheit (16851736), a German physicist, developed the Fahrenheit scale, which was first used in 1724. In 1745, Carolus Linnaeus of Sweden described a scale of a hundred steps or centigrade, which became known as the Centigrade scale. In 1948, the term "centigrade" was changed to Celsius. The Celsius scale was named after the Swedish scientist, Anders Celsius (17011744).

The Celsius scale was used to develop the Kelvin scale. William Thomson (18241907), also known as Lord Kelvin, was a British physicist and proposed the Kelvin scale in 1848. The scale is based on the concept that a gas will lose 1/273.16 of its volume for every one-degree drop in Celsius temperature. Thus, the volume would become zero at 273.16 degrees Celsiusa temperature known as absolute zero. Thus, the Kelvin scale is used primarily to measure gases.

Mathematics is used to convert temperatures from one scale to another. To convert from Celsius to Fahrenheit, multiply by 1.8 and add 32 degrees (°F = 1.8°C + 32). To convert from Fahrenheit to Celsius, subtract 32 degrees and divide by 1.8 . To convert from Celsius to Kelvin, simply add 273 degrees to the Celsius temperature (K = °C + 273).

Jacqueline Leonard

## Bibliography

Jones, Edwin R., and Richard L. Childers. Contemporary College Physics, Second Edition. Addison-Wesley Publishing Co., Inc., 1993.

National Council of Teachers of Mathematics. Measurement in School Mathematics: 1976 Yearbook. Reston, VA: NCTM, 1976.

Victor, Edward, and Richard D. Kellough. Science for the Elementary and Middle School, Ninth Edition. Upper Saddle River, NJ: Prentice-Hall, 2000.

Yaros, Ronald A. Weatherschool: Teacher Resource Guide. St. Louis: Yaros Communications, Inc, 1991.

### Internet Resources

Lynds, Beverly T. "About Temperatures." <http://www.unidata.ucar.edu/staff/blynds/tmp.html>.

## WATER AND TEMPERATURE SCALES

Water is the medium that is used as an international standard for determining temperature scales. On the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees. Water freezes at 0 degrees and boils at 100 degrees Celsius.

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