CONVECTION, the transference of a mass of fluid against the force of gravity. If a fluid is heated from below it becomes less dense than the super-incumbent fluid and rises, the latter falling and taking its place. This motion involves an upward transfer of heat and is quite distinct from conduction (see HEAT), whereby the heat is transferred in all directions equally by the vibrations of molecules (for isotropic media, ISOTOPES) and from radiation (see RADIATION, which is transmitted by the ether (q.v.). Convective equilibrium occurs in the atmosphere in temperate regions where a steady circulation of the atmosphere is preserved. It is adiabatic (see THERMODYNAMICS).