HEADQUARTERS ARMY OF THE POTOMAC.

Washington, September 10, 1862-10.30 p. M.

Brigadier General S. WILLIAMS.

Assistant Adjutant-General, Headquarters near Rockville:

I sent copy of Captain King's order through General Porter and copy of Captain Walker's through Colonel Beckwith. I know that Captain Dandy is colonel of the One hundredth New York, and I hear Peck's division is ordered up. The point is how to reach Captain dandy. Where is he now? Colonel Thomas L. Kane (now brigadier-general of volunteers) reported this morning, and asked me to forward his regards to the general and all the staff. Before General Heintzelman was put in command on the other side it became necessary, in consequence of confusion in orders and troops, as well as in regard to digging and choping, to limit General Abercrombie's responsibility to Forts Marcy and Ethan Allen and their approaches. This I forgot to tellyou until the order about Heintzelman was published, which would have effected the same thing. General Banks wants to give General Abercrombie another regiment as soon as he can. The One hundred and nineteenth New York and Eleventh Vermont have gone to Haskin to-day and are posted near Forts Lincoln and Bunker Hill. The Fifth Maryland arrived after I reported Weber's brigade, and was by order of General Halleck directed to proceed to headquarters without delay and report to General McClellan. I will find out in the morning whether it has gone. A telegram just received from General Porter says that a scouting party passed through Fairfax Court-House, Vienna, Freedom Hill, and Union Church but found no enemy. They were going on to find out about a picket which they heard of near Hunter's Mills and Dranesville. Your telegram of 10 p. M. about Hooker's order just received.

RICHD. B. IRWIN.

Captain, Aide-de-Camp, and Acting Assistant Adjutant-General.

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HEADQUARTERS ARMY OF THE POTOMAC.

Camp near Rockville, September 10, 1862-3.15 a. M.

Major General E. V. SUMNER.

Middlebrook:

GENERAL: General Burnside moves immediately with his command to Ridgeville. The major-general commanding directs that you immediately move one of your corps to Damascus and the other to Clarksburg. The one sent to Damascus must move so as to occupy that place as soon as it shall have been left by Burnside's troops. It is important that this place should be held continously, and that no interval should intervene between the passing of Burnside's troops through it and its occupation by your forces. Franklin is ordered to march at once to Barnesville. Keep in communication with Burnside on your right and Franklin on your left, holding all important points. Send a staff officer to report here as soon as you shall established your new headquarters.

By command of Major-General McClellan:

R. B. MARCY,
Chief of Staff.

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