Temperature can be defined as the degree of hotness or coldness of a body or environment. A concept related to the flow of heat from one object or region of space to another. It is a measure of the average energy of the molecules of a body.
Temperature can be denoted by symbol T.
The SI unit of temperature is the kelvin, denoted by symbol K.
Until about 260 years ago temperature measurement was very subjective. For hot metals the color of the glow was a good indicator. For intermediate temperatures, the impact on various materials could be determined.
A thermometer is a device used to measure temperature. Galileo invented the first documented thermometer in about 1592.
It was an air thermometer consisting of a glass bulb with a long tube attached.
The tube was dipped into a cooled liquid and the bulb was warmed, expanding the air inside.
As the air continued to expand, some of it escaped. When the heat was removed, the remaining air contracted causing the liquid
to rise in the tube and indicating a change in temperature. This type of thermometer is sensitive, but is affected by changes in
Ferdinand II, Grand Duke of Tuscany is credited with developing the first thermometer in 1641.
Ferdinand's thermometer used alcohol sealed in glass, which was marked with a temperature scale containing 50 units.
It did not designate a value for zero.
In 1714, Daniel Gabriel Fahrenheit invented both the mercury and the alcohol thermometer.
Fahrenheit's mercury thermometer consists of a capillary tube which after being filled with mercury is heated to expand
the mercury and expel the air from the tube.
The tube is then sealed, leaving the mercury free to expand and contract with temperature changes.
Although the mercury thermometer is not as sensitive as the air thermometer, by being sealed it is not affected by the
atmospheric pressure. Mercury freezes at -39° Celsius, so it cannot be used to measure temperature below this point.
Alcohol, on the other hand, freezes at -113° Celsius, allowing much lower temperatures to be measured.
Fahrenheit further subdivided this range into 96 points, giving his thermometers more resolution and a temperature scale
very close to today's Fahrenheit scale.
Later in the 18th century, Anders Celsius realized that it would be advantageous to use more common calibration references
and to divide the scale into 100 increments instead of 96. He chose to use one hundred degrees as the freezing point and
zero degrees as the boiling point of water. Sensibly the scale was later reversed and the Celsius scale was born.
The Celsius scale is sometimes called the centigrade scale, because it is divided into 100 degrees, cent being a Latin root
In about 1787, French physicist and chemist J. A. C. Charles made an interesting discovery that at 0°C, the volume of gas
at constant pressure drops by 1/273 for every Celsius degree drop in temperature. This seemed to suggest that the gas would
simply disappear if cooled to -273°C, which made no sense. In any case, the gas would most likely become first a liquid
and then a solid long before it reached that temperature.
Lord Kelvin in 1848 gave solution to Charles Theory, he put forward the suggestion that it was molecular translational energy
and not volume that would become zero at -273°C. He went on to establish what came to be known as the Kelvin scale.
The Kelvin scale is based not on the freezing point of water but on absolute zero, the temperature at which molecular motion
comes to a virtual stop. This is -273.15°C (-459.67°F), which in the Kelvin scale.