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EVOLU'TION, noun [Latin evolutio.] The act of unfolding or unrolling.

1. A series of things unrolled or unfolded; as the evolution of ages.

2. In geometry, the unfolding or opening of a curve, and making it describe an evolvent. 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.

3. In algebra, evolution is the extraction of roots from powers; the reverse of involution.

4. In military tactics, the doubling of ranks or files, wheeling, countermarching or other motion by which the disposition of troops is changed, in order to attack or defend with more advantage, or to occupy a different post.