Soon afterward the Federal commander attempted reconnoissances in his turn.  A considerable force of infantry, supported by artillery, crossed the Potomac and advanced to the vicinity of the little village of Leetown, but on the same evening fell back rapidly, doubtless fearful that Lee would interpose a force between them and the river and cut off their retreat.  This was followed by a movement of the Federal cavalry, which crossed at the same spot and advanced up the road leading toward Martinsburg.  These were met and subsequently driven back by Colonel W.H.F.  Lee, son of the general.  A third and more important attempt to reconnoitre took place toward the end of October.  General McClellan then crossed a considerable body of troops both at Shepherdstown and Harper’s Ferry; the columns advanced to Kearneysville and Charlestown respectively, and near the former village a brief engagement took place, without results.  General McClellan, who had come in person as far as Charlestown, then returned with his troops across the Potomac, and further hostilities for the moment ceased.

These reconnoissances were the prelude, however, of an important movement which the Federal authorities had been long urging General McClellan to make.  Although the battle of Sharpsburg had been indecisive in one acceptation of the term, in another it had been entirely decisive.  A drawn battle of the clearest sort, it yet decided the future movements of the opposing armies.  General Lee had invaded Maryland with the design of advancing into Pennsylvania—­the result of Sharpsburg was, that he fell back into Virginia.  General McClellan had marched from Washington with no object but an offensive-defensive campaign to afford the capital protection; he was now enabled to undertake anew the invasion of Virginia.

To the success of such a movement the Federal commander seems rightly to have considered a full and complete equipment of his troops absolutely essential.  He was directed at once, after Sharpsburg, to advance upon Lee.  He replied that it was impossible, neither his men nor his horses had shoes or rations.  New orders came—­General Halleck appearing to regard the difficulties urged by General McClellan as imaginary.  New protests followed, and then new protests and new orders again, until finally a peremptory dispatch came.  This dispatch was, “Cross the Potomac and give battle to the enemy or drive him south,” an order bearing the impress of the terse good sense and rough directness of the Federal President.  This order it was necessary in the end to obey, and General McClellan, having decided in favor of a movement across the Potomac east instead of west of the mountain, proceeded, in the last days of October, to cross his army.  His plan was excellent, and is here set forth in his own words: