{Isodiabatic lines} or {curves}, a pair of lines or curves
exhibiting, on a diagram of energy, the law of variation
of the pressure and density of a fluid, the one during the
lowering, and the other during the raising, of its
temperature, when the quantity of heat given out by the
fluid during any given stage of the one process is equal
to the quantity received during the corresponding stage of
the other. Such lines are said to be isodiabatic with
respect to each other. Compare {Adiabatic}.