Enemy reported to be advancing from York (Ewell's corps). The First and Eleventh Corps are engaged with Hill's forces. Have ordered General Sickles to push forward.

O. O. HOWARD,

Major-General.

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HDQRS. ARMY OF THE POTOMAC, July 1, 1863-12 m. (Copy received, War Department, 5 p. m.)

General COUCH, Harrisburg:

The enemy are advancing on Gettysburg-Hill, from Cashtown; Ewell, from Heidlersburg. Can you throw a force in Ewell's rear, to threaten him, and at the same time keep your line of retreat open? If you can, do so. GEO. G. MEADE, Major-General.

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CIRCULAR.]

HEADQUARTERS ARMY OF THE POTOMAC, Taneytown, July 1, 1863.

From information received, the commanding general is satisfied that the object of the movement of the army in this direction has been accomplished, viz, the relief of Harrisburg, and the prevention of the enemy's intended invasion of Philadelphia, &c., beyond the Susquehanna. It is no longer his intention to assume the offensive until the enemy's movements or position should render such an operation certain of success. If the enemy assume the offensive, and attack, it is his intention, after holding them in check sufficiently long, to withdraw the trains and other impedimenta; to withdraw the army from its present position, and form line of battle with the left resting in the neighborhood of Middleburg, and the right at Manchester, the general direction being that of Pipe Creek. For this purpose, General Reynolds, in command of the left, will withdraw the force at present at Gettysburg, two corps by the road to Taneytown and Westminster, and, after crossing Pipe Creek, deploy toward Middleburg. The corps at Emmitsburg will be withdrawn, via Mechanicsville, to Middleburg, or, if a more direct route can be found leaving Taneytown to their left, to withdraw direct to Middleburg. General Slocum will assume command of the two corps at Hanover ant Two Taverns, and withdraw them, via Union Mills, deploying one to the right and one to the left, after crossing Pipe Creek, connecting on the left with General Reynolds, and communicating his right to General Sedgwick at Manchester, who will connect with him and form the right. The time for falling back can only be developed by circumstances. Whenever such circumstances arise as would seem to indicate the necessity for falling back and assuming this general line indicated, notice of such movement will be at once communicated to these HEADQUARTERS and to all adjoining corps commanders. The Second Corps now at Taneytown will be held in reserve in the vicinity of Uniontown and Frizellburg, to be thrown to the point of strongest attack, should the enemy make it. In the event of these movements being necessary, the trains and impedimenta will all be sent to the rear of Westminster.