a. Physics. [f. Gr. ἀδιάβατ-ος not to be passed through (f. ἀ not + διά through + βατός passable, vbl. adj. f. βα-ίν-ειν to go) + -IC.] Impassable (sc. to heat); existing under a constant temperature, i.e., when no heat enters or leaves the substance.
1877. Wormell, Thermodyn., 130. If a substance can expand without gain or loss of heat, and a curve is drawn, such that the abscissa and ordinate of any point respectively represent the volume of a unit of mass, and the corresponding pressure for unit of area, this curve is termed an adiabatic line.
1882. Siemens, in Nature, XXV. 603. Let us suppose that the attenuated matter in space has a temperature of 160° on the absolute scale, and that it is 3000 times more rarified than when it reaches by adiabatic compression the solar photosphere.
