What is the act of reversing; the causing to move or face in an opposite direction, or to stand or lie in an inverted position; as, the reversal of a rotating wheel; the reversal of objects by a convex lens called?

reversal — The act of reversing; the causing to move or face in an opposite direction, or to stand or lie in an inverted position; as, the reversal of a rotating wheel; the reversal of objects by a convex lens. (Webster's 1913.)