The continuous change in composition of a solid-solution mineral in order to maintain a state of equilibrium with a cooling magma. The mineral changes its composition by continuously exchanging cations with the cooling magma in which it floats. The plagioclase feldspar solid-solution mineral series is a good example of a continuous reaction series. During the cooling of a magma, the plagioclase continuously exchanges Ca and Al for Na and Si in order to maintain an equilibrium composition. The principle of continuous reaction was first presented by Norman Bowen in 1928. See also bowen’s reaction principle.