FALMOUTH, VA.,

August 12, 1862-12.15 p. m.

Major General H. W. HALLECK:

Is this force for General Pope's assistance to be sent on the north side of the Rapidan or the north side of Rappahannock? One way is short as the other. Will answer your telegraph soon as we decide. Troops from Rappahannock Station can have transportation by railroad to Culpeper and reach General Pope sooner train by going south of the Rappahannock.

A. E. BURNSIDE,

Major-General.

FALMOUTH, VA.,

August 12, 1862-1.45 p. m.

H. W. HALLECK, General-in-Chief:

I have ordered twelve regiments of infantry, four batteries of artillery, and two companies of cavalry, under General Reno, to join General Pope at once. The advance will move at six this evening. They will join him as early as possible without breaking down the men. I think they should move up the north bank of the Rappahannock to Rappahannock Station, from thence by railroad to Culpeper. You will understand that in sending this force I am reducing mine here to the minimum strength, which is one regiment at Fredericksburg, five on this side of the river, and one guards the railroad, with six companies of cavalry. In view of the fact that large amounts of artillery, wagons, and supplies are arriving at Aquia Creek with no infantry, I cannot promise to hold this place and Aquia Creek to a certainty, as I consider the force that we now have here and on this road is not too large to hold Aquia Creek as a base. But we will with the force retained defend the line as long as possible. You best know the importance of this line of operations, and if I am weakening it too much you will have ample time to telegraph me. I am thus elaborate in my dispatch because your telegraph says: "Retain all the force required to protect the bridge and the landing at Aquia Creek." The enemy drove in our pickets a few moments since, but I do not believe they are in front of us in force.

A. E. BURNSIDE,

Major-General.

WAR DEPARTMENT,

Washington, August 12, 1862.

Major-General BURNSIDE, Falmouth, Va.:

Select your own line for the movement, so as to re-enforce General Pope as quickly and safely as possible. The enemy in front of General Pope has fallen back to-day, but it may be a feigned retreat.

H. W. HALLECK,

General-in-Chief.

WINCHESTER, VA., August 12, 1862.

(Received 4.20 p. m.)

Major-General POPE,

Headquarters Army of Virginia:

The enemy's cavalry, some 25 strong, dashed into Front Royal yes-