WASHINGTON, D. C., September 4, 1861.

Major General N. P. BANKS, Commanding, &c., Darnestown, Md.:

SIR: The Commanding General directs me to invite your particular attention to the importance of keeping a careful watch upon the Potomac in from of your position. It is believed, from recent information derived from sources deemed reliable, that the enemy still entertains the design of crossing the river in force at some point above Washington.

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

A. V. COLBURN,

Assistant Adjutant-General.

HEADQUARTERS CORPS OF OBSERVATION,
Poolesville, Md., September 4, 1861.

Major General GEORGE B. MCCLELLAN,

Commanding Army of the Potomac:

GENERAL: Your telegram of this date I have had the honor to receive and its requirements have been complied with so far as making preparations for marching promptly, with two days' provisions cooked.

There are three camps in the immediate vicinity of Leesburg, one apparently large enough for two regiments, the others for one each.

Movements of troops were believed to be heard last night opposite Conrad's Ferry, going west, but I cannot satisfy myself from the reports of the pickets that any considerable body moved.

The Eighth Virginia Regiment now furnishes the pickets opposite ours at Edward Ferry, while Mississippi troops are posted opposite Conrad's.

The troops of this command are in good spirits, and, with the exception of the First Minnesota, in good health. In the latter the measles is increasing the sick report.

Very respectfully, your obedient servant,

CHAS. P. STONE,

Brigadier-General, Commanding.

HEADQUARTERS ARMY OF THE POTOMAC,
Washington, September 5, 1861.

Honorable S. CAMERON, Secretary of War:

SIR: I have most urgently to request that the following-named companies of regular artillery be ordered to report to me with the least possible delay, viz:

Seven of the nine companies of the Third Regiment of Artillery, now stationed on the Pacific coast.

Four of the eight companies now stationed at Fortress Monroe, Va.

The necessity for an increase of the regular artillery force under my command is most pressing.

I have also to request that all the officers belonging to Companies E and H, First Regiment U. S. Artillery, be ordered to join their respective companies without delay. These companies, now mounted as light artillery, have but one officer each on duty with them. In this condition they are not and cannot be efficient.

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

GEO. B. MCCLELLAN,

Major-General, U. S. Army.