In the 1890s the world of racing was turned on its ear by a young American who rode horses as no professional jockey had ever ridden: Tod Sloan hitched up his stirrups and thrust his weight far forward. Traditionalists laughed at first and dismissed him as a novelty, but as he came to dominate racing on both sides of the Atlantic, his style of riding became widely imitated, and his famous "forward seat" remains universally practiced to this day. Sloan's...