Two regiments of cavalry have been ordered out and are now on the way to relieve the two regiments of Sumner.

Four thousand infantry and one battery leave Washington at once for Manassas; some 3,000 more will move in one or two days, and soon after some 3,000 additional.

I will order Blenker to march on Strasburg and to report to you for temporary duty, so that, should you find a large force in your front, you can avail yourself of his aid. As soon as possible please direct him on Winchester, thence to report to the Adjutant-General of the Army for orders, but keep him until you are sure what you have in front.

In regard to your own movements the most important thing at present is to throw Jackson well back and then to assume such a position as to enable you to prevent his return. As soon as the railway communications are re-established it will be probably important and advisable to move on Staunton, but this would require secure communications and a force of from 25,000 to 30,000 for active operations. It should also be nearly coincident with my own move on Richmond; at all events not so long before it as to enable the rebels to concentrate on you and then return on me. I fear that you cannot be ready in time, although it may come in very well, with a force less than that I have mentioned, after the main battle near Richmond. When General Sumner leaves Warrenton Junction General Abercrombie will be placed in immediate command of Manassas and Warrenton Junction under your general orders. Please inform me frequently by telegraph and otherwise as to the state of things in your front.

I am, very truly, yours,

GEO. B. McCLELLAN,

Major-General, Commanding.

P. S.- From what I have just learned it would seem that the two regiments of cavalry intended for Warrenton Junction have gone to Harper's Ferry. Of the four additional regiments placed under your orders two should, as promptly as possible, move by the shortest route on Warrenton Junction.

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

GEO. G. McCLELLAN,

Major-General, Commanding.

CITY OF NEW YORK, January 3, 1863.

A true copy.

S. WILLIAMS,

Assistant Adjutant-General.

FORTY-SEVENTH DAY.

COURT-ROOM, COR. FOURTEENTH AND PA. AVENUE,

Washington, D. C., January 19, 1863.

* * * * * *

Lieutenant Colonel DAVIS TILLSON, Maine Artillery, a witness, was recalled.

Question. by General McDOWELL. Were you with General McDowell on the 29th of August last, on the occasion of his march from near Bethlehem Church, with King's and Ricketts' division, up the Sudley Springs road to the battle-field?

Answer. I was.