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"Ultimately, Lightfoot and other investigators proved that the curve is real. They did so by means of both wind-tunnel tests and high-speed photography. For his part, Lightfoot measured force that causes balls to veer sideways and down. Moreover, he found a striking relationship between those forces and the orientation of a pitched ball's seams as the ball cuts through the air toward a batter.

The results were never published in a scientific journal. But they made it into a 1953 article entitled "The Hell It Don't Curve," which sportswriter Joseph F. Drury wrote for the then-popular magazine American Mercury."

http://www.phschool.com/science/science_news/articles/pitching_science.html