Note 6 — CHAP. XVIII. MECHANICAL CONTRIVANCES FOR MODIFYING MOTION.
Reading edition
In a strictly mathematical sense, the path of the point P is a curve, and not a straight line; but in the play given to it in its application to the steam-engine, it moves through a part only of its entire locus, and this part extending equally on each side of a point of inflection, the radius of curvature is infinite, so that in practice the deviation from a straight line, when proper proportions are observed in the rods, is imperceptible.