What are Heat and Temperature?

  One might ask what the nature of heat is and how it differs from temperature. We can't say that they are identical since bodies can acquire heat without changing temperature when they melt or evaporate.

Our word temperature comes from the Latin word temperatura which connoted proper measures and like tempero mixture or moderation. One gets the impression that in ancient times heat and it manifestation temperature were considered a form of animism more spiritual than substance. It was something that could be admixed with a body and could pass from one body to another. But modern science has to treat the subject more rationally, objectively and quantitatively.

So one refers to a thermometer a device designed to measure changes produced by heat acquired in a reference body based on the assumption that two bodies at the same temperature are in equilibrium. Two points on the temperature scale are determined by the melting and boiling points of water. Points in between, the degrees of heat, can be determined by the expansion of a gas, liquid or solid which changes with heat content. But how do we know the steps on the scale represent equal amounts of heat change? Note melting and boiling points may have been used in ancient times to mark certain temperatures on a crude scale for the smelting of metals.

The answer to the question of equal steps was aided by the study of gases around 1800 specifically the discovery of Charles's Law, that for all gases the changes in volume with temperature is a constant proportion relative to some standard volume and temperature. Charles's original discovery was forgotten but later rediscovered by Dalton and Gay-Lussac.

In the last half of 19th century the study of the kinetic theory of gases connected the temperature of a gas with the average kinetic energy of the molecules of a gas and the specific heat of a gas, its heat content per standard mass, depends on the number of ways its molecules can move linearly and rotationally. Monoatomic molecules like the ideal gases do not have any rotational motion so the proportional heat is smallest. In theory ideal gases can be used for a thermometer to provide linear temperature scale.

Bibliography

   Boyle - The Mechanical Origin of Heat and Cold (1738)

   Dalton - equal expansion of gases with heat (1801)

   Gay-Lussac - Recherches sur la dilatation des gaz et des vapeurs (1802)

   Young - On the measures and the nature of heat (1807)

   Dalton - A new system of chemical philosophy (1808), on temperature

   Kelland - Theory of Heat (1837), temperature

   Whewell - History of the Inductive Science (1847), Laws of Change Occasioned by Heat

   Maxwell - Motions & Collisions of Perfectly Elastic Spheres (1860), mean v²

   Boltzmann - Lectures on Gas Theory (1896), mean square velocity

   Boltzmann - Vorlesungen über Gastheorie Vol 1 (1896), mean square velocity

   Ames (ed.) - Expansion of gases by heat (1902)