James Ford Rhodes (18481927). History of the Civil War, 18611865 1917.
But fortune turned McClellans way. Lees written order, disclosing the division of the Confederate army and the exact scheme of their march, was sent to three generals, of whom one pinned it securely in an inside pocket, another, Longstreet, memorized it and then chewed it up; whilst the third copy was lost, found by a private soldier of the Union Army and at once taken to McClellan, who showed his elation in his despatch to the President, I have all the plans of the rebels and will catch them in their own trap if my men are equal to the emergency.
McClellan acted with energy but not with the energy that Lee or Jackson would have shown under similar circumstances. He marched his army forward, and on September 14 won the battle of South Mountain, securing a passage over the South Mountain range to the field of Antietam; by this victory he restored the morale of the Union Army and gave heart to the President and people of the North. He did not, however, relieve the Harpers Ferry garrison which fell without a struggle.
A citizen friendly to the Confederate cause had been present when Lees lost order was brought to McClellan; he got an inkling of its importance to the Union Army, made his way through the lines and after nightfall gave the information to a cavalry officer who at once transmitted it to the Confederate commander. Having this knowledge before daylight of September 14, Lee, who was disappointed and concerned at the rapid advance of McClellan, left Hagerstown, disputed the passes of South Mountain and took up a strong position behind Antietam Creek, around the village of Sharpsburg. In the order for the division of the Confederate army, Jackson and the different detachments acting with him for the capture of Harpers Ferry were directed to join the main body of the army after accomplishing