For nearly 150 years, Abraham Lincoln's pocket watch has been rumored to carry a secret message, supposedly written by an Irish immigrant and watchmaker named Jonathan Dillon. Dillon, working in a D.C. watch repair shop in 1861, told family members that he -- by incredible happenstance -- had been repairing Lincoln's watch when news came that Fort Sumter had been attacked in South Carolina. It was the opening salvo of what became the Civil War. Dillon told his children (and, half a century later, a reporter for the New York Times) that he opened the watch's inner workings and scrawled...