entropy

Heat Heat (h[=e]t), n. [OE. hete, h[ae]te, AS. h[=ae]tu, h[=ae]to, fr. h[=a]t hot; akin to OHG. heizi heat, Dan. hede, Sw. hetta. See {Hot}.] 1. A force in nature which is recognized in various effects, but especially in the phenomena of fusion and evaporation, and which, as manifested in fire, the sun's rays, mechanical action, chemical combination, etc., becomes directly known to us through the sense of feeling. In its nature heat is a mode of motion, being in general a form of molecular disturbance or vibration. It was formerly supposed to be a subtile, imponderable fluid, to which was given the name {caloric}. [1913 Webster]

Note: As affecting the human body, heat produces different sensations, which are called by different names, as heat or sensible heat, warmth, cold, etc., according to its degree or amount relatively to the normal temperature of the body. [1913 Webster]

2. The sensation caused by the force or influence of heat when excessive, or above that which is normal to the human body; the bodily feeling experienced on exposure to fire, the sun's rays, etc.; the reverse of {cold}. [1913 Webster]

3. High temperature, as distinguished from low temperature, or cold; as, the heat of summer and the cold of winter; heat of the skin or body in fever, etc. [1913 Webster]

Else how had the world . . . Avoided pinching cold and scorching heat! --Milton. [1913 Webster]

4. Indication of high temperature; appearance, condition, or color of a body, as indicating its temperature; redness; high color; flush; degree of temperature to which something is heated, as indicated by appearance, condition, or otherwise. [1913 Webster]

It has raised . . . heats in their faces. --Addison. [1913 Webster]

The heats smiths take of their iron are a blood-red heat, a white-flame heat, and a sparkling or welding heat. --Moxon. [1913 Webster]

5. A single complete operation of heating, as at a forge or in a furnace; as, to make a horseshoe in a certain number of heats. [1913 Webster]

6. A violent action unintermitted; a single effort; a single course in a race that consists of two or more courses; as, he won two heats out of three. [1913 Webster]

Many causes . . . for refreshment betwixt the heats. --Dryden. [1913 Webster]

[He] struck off at one heat the matchless tale of ``Tam o' Shanter.'' --J. C. Shairp. [1913 Webster]

7. Utmost violence; rage; vehemence; as, the heat of battle or party. ``The heat of their division.'' --Shak. [1913 Webster]

8. Agitation of mind; inflammation or excitement; exasperation. ``The heat and hurry of his rage.'' --South. [1913 Webster]

9. Animation, as in discourse; ardor; fervency; as, in the heat of argument. [1913 Webster]

With all the strength and heat of eloquence. --Addison. [1913 Webster]

10. (Zo["o]l.) Sexual excitement in animals; readiness for sexual activity; estrus or rut. [1913 Webster +PJC]

11. Fermentation. [1913 Webster]

12. Strong psychological pressure, as in a police investigation; as, when they turned up the heat, he took it on the lam. [slang] [PJC]

{Animal heat}, {Blood heat}, {Capacity for heat}, etc. See under {Animal}, {Blood}, etc.

{Atomic heat} (Chem.), the product obtained by multiplying the atomic weight of any element by its specific heat. The atomic heat of all solid elements is nearly a constant, the mean value being 6.4.

{Dynamical theory of heat}, that theory of heat which assumes it to be, not a peculiar kind of matter, but a peculiar motion of the ultimate particles of matter.

{Heat engine}, any apparatus by which a heated substance, as a heated fluid, is made to perform work by giving motion to mechanism, as a hot-air engine, or a steam engine.

{Heat producers}. (Physiol.) See under {Food}.

{Heat rays}, a term formerly applied to the rays near the red end of the spectrum, whether within or beyond the visible spectrum.

{Heat weight} (Mech.), the product of any quantity of heat by the mechanical equivalent of heat divided by the absolute temperature; -- called also {thermodynamic function}, and {entropy}.

{Mechanical equivalent of heat}. See under {Equivalent}.

{Specific heat of a substance (at any temperature)}, the number of units of heat required to raise the temperature of a unit mass of the substance at that temperature one degree.

{Unit of heat}, the quantity of heat required to raise, by one degree, the temperature of a unit mass of water, initially at a certain standard temperature. The temperature usually employed is that of 0[deg] Centigrade, or 32[deg] Fahrenheit. [1913 Webster]