Major-General HALLECK:

A courier just arrived with the following from General F. J. Porter:

BRISTOE, August 28, 1862 - 9.30 a. m.

My command will soon be up, and will at once go into position. Hooker drove Ewell some 3 miles, and Pope says McDowell intercepted Longstreet, so that, without a long detour, he cannot join Ewell, Jackson, and A. P. Hill, who are, or supposed to be, at Manassas. Ewell's train, he says, took the road to Gainesville, where McDowell is coming from. We shall be to-day as follows: I on right of railroad, Heintzelman on left, then Reno, then McDowell. He hopes to meet Ewell and push to Manassas to-day, I hope all goes well near Washington. I think there need be no cause of fear for us. I feel as if on my way now, and thus far have kept my command and trains well up. More supplies than I supposed on hand have been brought, but none to spare, but we must make connection soon. I hope for the best. You will hear of us soon by way of Alexandria.

F. J. PORTER,

Major-General.

I send you the above just as received.

A. E. BURNSIDE,

Major-General.

GREENWICH, August 28, 1862 - 1.30 a.m.

General McDOWELL:

GENERAL: I am ordered by General Pope to proceed at the earliest dawn toward Manassas. It is said to be 11 miles from here. General Kearny is here also with a part of his division.

Yours, respectfully,

J. L. RENO,

Major-General.

HEADQUARTERS ARMY OF VIRGINIA,
August 28, 1862. (Received 3.15 p. m.)

General I. McDOWELL, Commanding:

GENERAL: I am directed by the general commanding to say that the enemy has retreated in the direction of Centreville, or the right of that place, form here, and that he wishes you to pursue in that direction.

You had best, perhaps, keep somewhat to the north of Centreville, say in the direction of Plum Valley or Gum Spring. Find out, if possible, by your cavalry were he is. In searching for him with your cavalry you had better mass it and put a battery of artillery with it.

I am, general, very respectfully, your obedient servant,

W. L. ELLIOTT,

Brigadier-General and Chief of Cavalry.

P. S. - Go light, and if you think it desirable send your trains in this direction.

AUGUST 28, 1862 - 10.45 p. m.

General McDOWELL:

GENERAL: From prisoners taken to-night there is no doubt that Jackson's main force is in our immediate front. Our position is not