A measure of the relative warmth of an object or
substance that allows it to be compared to another object or substance
(one is warmer or cooler) or to a standard (so many degrees). Temperature
and heat are not the same: heat is a form of energy, temperature the
effect it produces.
A thermometer is an instrument that absorbs kinetic energy from impacting
atoms and molecules and converts it to a reading against a scale. Three
temperature scales are used. Scientists usually prefer the Kelvin scale,
in which the temperature is written in the unit K (for kelvin), without a
degree sign. The celsius temperature scale is the most widely used
everyday scale; it is sometimes still called the centigrade scale,
because there are 100 of its degrees between the freezing and boiling
points of water. Celsius temperatures are written as ° C. Its name was
officially changed from centigrade in 1948, at the Ninth General
Conference on Weights and Measures. The fahrenheit temperature scale is
more often used in the United States and Britain (where it is being
replaced by the Celsius scale). Its temperatures are written as ° F.
A fourth scale, the réamur temperature scale, is used in very few places
today. It was devised in 1730 by the French physicist and naturalist René
Antoine Ferchault de Réamur (1683–1757). Réamur measured the expansion of
a mixture of water and alcohol as its temperature increased. The liquid
was held in a bulb at the base of a tube, as in any thermometer. When it
was at the freezing point he marked the point it reached on the tube as
zero. He then graduated the remainder of the tube into units, each of
which was equal to one-thousandth of the volume of the liquid in the bulb
and tube when it was at freezing. When the liquid reached boiling point
he found its length had increased to 1,080 units, so it had risen 80
units (or degrees). Consequently his scale ran from 0° R at freezing to
80° R at boiling point. |
