...mber, covered by a cloud of Stuart's cavalry before the United States capital, the army crossed the Potomac and advanced to Frederick City, Md. Thence Jackson's corps and portions of the divisions of McLaws and John G. Walker were diverted westward to attack the 12,000 Federal soldiers at Harper's Ferry, and the remainder of Lee's forces marched to Sharpsburg. The army of McClellan, hesitating at firs...