If the enemy should retire by Culpeper and Gordonsville, you will endeavor to hold your force in his front, and harass him day and night, on the march, and in camp, unceasingly. If you cannot cut off from his column large slices, the general desires that you will not fail to take small ones. Let your watchword be Fight, and let all your orders be Fight, Fight, FIGHT; bearing in mind that time is as valuable to the general as the rebel carcasses. It is not in the power of the rebels to oppose you with more than five thousand sabres, and those badly mounted, and, after they leave Culpeper, without forage and rations. Keep them from Richmond, and sooner or later they must fall into our hands. The general desires you to understand that he considers the primary object of your movement the cutting of the enemy's communication with Richmond by the Fredericksburg route, checking his retreat over those lines; and he wishes to make every thing subservient to that object. He desires that you will keep yourself informed of the enemy's whereabouts, and attack him wherever you find him. If, in your operations, an opportunity should present itself for you to detach a force to Charlottesville, which is almost unguarded, and destroy depots of supplies said to be there, or along the line of the Aquia Railroad, in the direction of Richmond, to destroy bridges, etc., or the crossings of the Pamunkey, in the direction of West Point, destroying the ferries, felling trees to prevent or check the crossing, they will all greatly contribute to our complete success. You may rely upon the general's being in communication with you before your supplies are exhausted. Let him hear from you as often as necessary and practicable. A brigade of infantry will march to-morrow morning at eight o'clock for Kelly's Ford, with one battery, and a regiment to the United-States Ford and Banks's Ford, to threaten and hold those places. It devolves upon you, general, to take the initiative in the forward movement of this grand army; and on you and your noble command must depend, in a great measure, the extent and brilliancy of our success. Bear in mind that celerity, audacity, and resolution are every thing in war, and especially is it the case with the command you have, and the enterprise on which you are about to embark. Very respectfully, your obedient servant, S. WILLIAMS, Assistant Adjutant-General.