There was once a debate on whether a curveball actually curves or is an optical illusion. In 1949, Ralph B. Lightfoot, an aeronautical engineer at Sikorsky Aircraft, used wind tunnel tests to prove that a curveball curves. On whether a curveball is caused by an illusion, Baseball Hall of Fame pitcher Dizzy Dean has been quoted in a number of variations on this basic premise: "Stand behind a tree 60 feet away, and I will whomp you with an optical illusion!"