EVOLUTION, in Algebra, the unfolding or opening of a curve, and making it describe an evolute.—The word evolutio is formed of the preposition e, "out;" and volvo, "I roll, or wind;" q. d. an unwinding or unrolling.
The equable evolution of the periphery of a circle, or other curve, is such a gradual approach of the circumference to rectitude, as that its parts do all concur and equally evolve or unbend; so that the same line becomes successively a less arc of a reciprocally greater circle: till at last they change into a straight line. In the Phil. Trans. No 260. a new quadratrix to the circle is found by this means, being the curve described by the equable evolution of its periphery.