HEADQUARTERS, Fairfax Court-House, Va., October 18, 1863.

Captain Batterson, Thirteenth New York Cavalry, reports having see about 30 rebel cavalry about 8 miles from here, while on his way in charge of train from Washington to this post, via Annandale. He reported to Colonel Baker's command. A private of same regiment has been captured last evening about 3 miles from here toward Centerville.

MICHAEL CONCORAN,
Brigadier-General.

FAIRFAX COURT-HOUSE, VA., October 18, 1863. (Received 12. 40 p. m.)

Lieutenant-Colonel TAYLOR,

Chief of Staff, and Assistant Adjutant-General:

The following received from Colonel Lowell, at Vienna:

OCTOBER 18.

We have take one of Mosby's men this morning, who says that Mosby, with 275 men, is prowling around below here to take supply trains. It will be well to delay all wagon trains without heavy escort till something more definite is learned about Mosby's movements. If you could post strong infantry pickets at points between here and Fairfax, Mosby might be ambushed on his way back.

C. R. LOWELL, JR.

I will communicate the above to General Buford, commanding cavalry, and General Griffin, commanding corps, now stationed here. I have just learned that a company of our cavalry has been attacked about 3 miles from here toward Alexandria, and the captain captured.

MICHAEL CORCORAN,

Brigadier-General, Commanding.

WAR DEPARTMENT, Washington, October 18, 1863-2 p. m.

Major-General COURCH,

Chambersburg, Pa.:

The enemy has appeared in some force at Charlestown. Your troops will move down in supporting distance of Harper's Ferry, so as to re-enforce Maryland Heights, should the enemy cross the river.

H. W. HALLECK,

General-in-Chief.

HARPER'S FERRY, W. VA., October 18, 1863-11 a. m. (Received 1. 40 p. m.)

Major General H. W. HALLECK,

General-in-Chief:

I will be prepared to defend Harper's Ferry. Imboden this morning surprised Charlestown and dispersed or captured the force stationed there. The field officers all escaped somehow. I have ordered two regiments and my cavalry to ascertain the movements of teh enemy, and whatever Imboden is attempting a raid on the Baltimore and Ohio Railroad. I can furnish infantry by 12 o'clock.

JER. C. SULLIVAN,

Brigadier-General.