(first image is a mirror-image, reversal of fortunes)

Any noncircular curve may be approximated by tangent circle arcs, selecting a center by trial, drawing as much of an arc as will practically coincide with the curve, then changing the center and radius for the next portion, remembering always that if arcs are to be tangent, their centers must lie on the common normal at the point of tangency. — French, Thomas E. A Manual of Engineering Drawing for Students and Draftsmen (New York: McGraw-Hill, 1911) 54


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