MEMORANDUM.] HDQRS., CAMP FISHER, November 26, 1861.

Premising that the enemy designs to attack the Evansport batteries by a combined land and river movement, let the first be considered. The attacking column can be regarded as crossing the Occoquan at Colchester, and uniting with a force thrown from Indian Head across the Potomac. With the applies we have seen gathered there this would be matters of no difficulty. Occoquan is 10 or 12 miles from Dumfries, and connected by an excellent road, the old Telegraph road, which crossed in that distance the Neadsco at 6 and Powell's Run at 7 miles from Occoquan. Two miles out of Occoquan the main country road branches out to Brentsville. This from Occoquan to the Nebsco is also an excellent road, and would undoubtedly be used by the enemy as his natural direction for the purpose of turning the left flank of the force supporting Dumfries. It is essential that we shall hold with these roads, especially the latter, by which not only the Evansport batteries but Manassas might be turned. To do this effectually, between the two position on the Neabsco there is a third, which is vital to both. This is at Satowell's farm. The Third Brigade at Dane's farm, the Texas at Kaube's (and little enough there). We must have at least, two regiments to occupy this farm, which is the key-point of the line. A brigade would be better, but perhaps so much is not available. It may reasonably be supposed that the passage of the Occoquan, the march thence ot the Neabsco through a strange country, and the forcing of our positions by overwhelming numbers, would occupy more time than daylight at this season. Notice being given of the crossing by the enemy, we ought reasonably to count on twenty-four hours for General Johnston to move by Bacon road (this supposing the main attack to be here). If the enemy had advanced to attack at Dane's farm by that time, Johnston's attack by the route indicated would fall upon his right and rear, and would unquestionably result in his entire annihilation. It is not, however, well to divide General Johnston's army, for at the same time undoubtedly a heavy demonstration, if not a real attack, will be made in front of Centreville. The gain of twenty-four hours, then, is vital. o insure it, I must have more troops. To take them from the masteries will not do. Those are required to watch the river, and few enough they are, since they are threatened both above and below and by the fleet.

Can no aid be given front the well-drilled regiments occupying the Peninsula of from Borfolk. If Given, it must be given at once. The enemy has one advance. The road from him ot us are in capital condition, and pass over a hard, sandy, gravelly soil; ours for supply or for retreat are almost impassable. It should be remembered I have but two batteries.

W. H. C. WHITING,

Brigadier-General, Commanding.

[Indorsement.]

HEADQUARTERS, CENTREVILLE, November 26, 1861.

Respectfully submitted to the War Department. i earnestly recommend that the re-enforcement asked for by Brigadier-General Withing be sent to him immediately. His force is too small for what it must attempt, and this one is too weak to be further weakened. We must be driven back if the enemy establishes himself near Evansport.

J. E. JOHNSON,
General.