KINGS

Sfc Scrofula. EVOLUTE (ljs.t. e\oUo, I roll out), in the theory of curve lines, is a curve from which any given curve may be supposed to be formed by the evolution or unlap ping of a thread from a surface having the same curvature as the first curve. For example, let B H E be a model of a plane curve made of a solid material having some thickne ; and let one end of a thread H E C be fastened to a point B on the edge of the model, and applied along its convexity, so as to coincide with it entirely between B and E, the remaining j)ortion E C of the thread forming a straight line touching the curve at E. Suppose, now, the thread to be gradually i' unlapped from the curve B E, keeping it always tight: the extremity C will describe another curve, [s. 438]