Hillsborough, if possible, to-night. You will please send a small force of your cavalry with him as far as Leesburg, to look after his trains, and to remain at that place for a day or two after his rear has passed.

A. E. BURNSIDE,

Major-General, Commanding Army of the Potomac.

[Inclosure No. 2.]

HEADQUARTERS ARMY OF THE POTOMAC, December 9, 1862-3.45 a.m.

Major General FRANZ SIGEL, Fairfax Court-House:

By a copy of a dispatch to General Slocum, this moment forwarded to you, you will see that he is ordered to join you. You will, in the mean time, move the main body of the force now under you command to Wolf Run Shoals, keeping your cavalry well out in the direction of New Market and the gaps in the Bull Run Mountains. Have your command ready to move at an hour's notice, with five or six days' rations of bread and small stores, with a good supply of beef cattle. Your cavalry can communicate with those from these headquarters at Dumfries, or in the direction of Stafford Springs and Hartwood. One of your telegraph operators can establish a station at Dumfries at once, or immediately on your arrival at Wolf Run Shoals, from which point, or from Fairfax Station, you can communicate with me by telegraph. You will leave strong guards at Fairfax Station, Fairfax Court-House, and at Union Mills, until the arrival of General Slocum; after which it is hoped that they can be replaced by troops from Washington. Captain Dahlgren will leave to-morrow at 10.45 with special verbal instructions.

Please acknowledge the receipt of this, with any suggestion you may have to make.

Should you deem it advisable to concentrate your main force at Brentsville instead of Wolf Run Shoals, drawing your supplies from Manassas Junction, you are at liberty to do so. It is expected that you quartermaster and commissary will look out for supplies for your two corps until you join the main army.

A. E. BURNSIDE,
Major-General, Commanding Army of the Potomac.

[Inclosure No. 3.]

HEADQUARTERS ARMY OF THE POTOMAC, December 9, 1862-3 a.m.

Major General H. W. SLOCUM,
Commanding Corps, Harper's Ferry:

You will move your corps at once to this place, by way of the pontoon bridge over the Shenandoah, through Hillsborough, Wheatland, Leesburg, Centreville, Wolf Run Shoals, and Dumfries. It would appear that the best road between Leesburg and Centreville is by way of Gum Spring. Upon arriving at Centreville, you will report by an aide-de-camp to General Sigel, who will be at or in the neighborhood of Wolf Run Shoals crossing of the Occoquan, under whose command you will remain, forming part of the grand reserve division of this army. The route ordered for you from Centreville or Wolf Run Shoals may be changed by General Sigel, in accordance with directions from these headquarters.

General Morell has been ordered to replace the garrison at Harper's Ferry, and it is hoped you will be able to reach Hillsborough to-night, and Leesburg to-morrow night, and the neighborhood of Gum Spring on