The rebels in leaving Frederick are reported to have gone on the Hagerstown road. Their force there is reported by a citizen, who was through a few days, to be Jackson's and Longstreet's divisions, each four brigades of five regiments each.

Very respectfully, your obedient servant,

J. D. COX,

Brigadier-General, Commanding.

COOKSVILLE, September 11 [1862]-10.30 a. m.

Major-Genral HOOKER, Commanding Corps:

GENERAL: Captain Beardsley, Sixth New York Cavalry, who is posted here, states that John S. Doll, proprietor of the Eutaw House, Baltimore, passed through this place on his way from Frederick to Baltimore at 1 o'clock last night. He (Doll) states that the main force of the enemy left Frederick yesterday morning for Harrisburg, and that at 1 o'clock yesterday but one division was left at Frederick, and that it was preparing to march. The entire numbers 160,000. Jackson has the advance. He met Lee's and Stuart's cavalry at New Market; about 1,000 men. He also met a squadron, about 1 mile this side of New Market, returning to that place. From information obtained, it is believed that this squadron had been to Hood's Mills, 2 miles from here, on the railroad. We have now a picket at Hood's Miles, and one company of Sixth New York has gone this morning to Ridgeville by this pike. Nothing has been heard of the enemy here this side of New Market since yesterday. Captain Beardsley deems the information of Mr. Doll reliable. He visited Frederick to attend to his family, and was detained at Frederick several days. The railroad bridge over the Monocacy is destroyed. The enemy took the road up the Cumberland Valley.

Very respectfully,

D. C. HOUSTON,

Major of Engineers.

POPLAR HILL-1.15 p. m.

Lieutenant-Colonel RICHMOND:

Just reached here with Reynolds' division this evening. Please read the inclosed [preceding] letter just received. Headquarters will be here to-night.

Very respectfully,

JOSEPH HOOKER,

Major-General, Commanding Corps.

A. E. BURNSIDE.

DAMASCUS [MD.],

September 11, 1862-11.20 p. m.

Major-General HOOKER:

GENERAL: I wish you to communicate with General ReNumbers Have the main body of your corps brought up to within good supporting distance of him at Ridgeville, posting a portion of your corps judiciously in your rear for the purpose of protecting our right flank. General McClellan inform me that the enemy is reported to be in large force between Frederick and Liberty, but there is no confirmation of this. Please throw your cavalry out in that direction to-night in strong force, and ascertain positively if there is any enemy at Liberty or its neighborhood. Send couriers frequently to Ridgeville.

Very respectfully, your obedient servant,

A. E. BURNSIDE,

Major-General,

Per JNumbers G. PARKE,

Chief of Staff.

SEPTEMBER 11, 1862.

Colonel WEBB,

Chief of Staff, Arlington Heights:

COLONEL: My scouts have just returned from Broad Run and Goose Creek. Yesterday there were two brigades at Leesburg; one went to

17 R R-VOL XIX, PT II