On the 3rd of August, General Halleck issued an order to General McClellan, directing him to remove his army from Harrison’s Landing to Acquia creek. This order was received by McClellan on the 4th inst., and though protesting against this change of plan as impolitic and sacrificial, that officer took immediate measures to obey the unwelcome command. To retire under the eyes of a vigilant foe, was not, however, either a safe or an easy task; and it was not until the 14th of August that the general movement of the Army of the Potomac commenced. The occasion was, to the last degree, critical. Lee, as we have seen, had been imperiling the Army of Virginia, under Pope, since the 7th of August. Step by step that commander had yielded ground. The Capital of the Republic was considered to be in jeopardy. Party feeling ran high. Congress was divided. General Pope, on assuming command had issued a very spirited address to his soldiers, giving them the assurance of certain victory, and reflecting, with unmistakable sarcasm, upon McClellan’s campaign. Then came the discomfiture of Pope, which, of course, gave assurance to the partisans of McClellan. The tardiness of the latter in reaching Acquia creek, and reinforcing the army of Pope, was, in some quarters, confidently ascribed to a desire for that general’s defeat. Danger and difficulty of transportation were in some measure the causes of this tardiness. The movement which commenced at Harrison’s Landing on the 14th of August, continued during ten days. On the 24th inst., McClellan’s headquarters were established at Acquia creek. From that point he held frequent communication with General Halleck at Washington, and thence, also, he detached the corps of Generals Franklin and Sumner to cooperate with General Pope—the latter receiving these reinforcements on the 30th of August. At this juncture, McClellan was detached from the remains of his army, and transferred to the command of the defences of Washington. He arrived at the Capital on the 1st of September. On the following day, the Army of Virginia, led by Pope, was ordered to fall back upon the defences of Washington. This it did, closely pursued by the bold and reckless enemy. The rebels disappeared, however, on the following day, and it soon became evident that they were operating in another direction,—that, in fact, they were making up towards Leesburgh, on the south side of the Potomac. On the 7th of September, General Pope having been relieved of his command, General McClellan left Washington, leading an army to oppose whatever movement against that city might be intended by the rebel General Lee. His advance was made along the north bank of the Potomac, his left wing resting upon that river, his right upon the Baltimore and Ohio railroad. General Banks, meanwhile, was left in command of the defences around Washington. On the 8th, the rebels, who had crossed the Potomac into Maryland, were in the vicinity of Frederick, the main body being in