HEADQUARTERS ARMY OF THE POTOMAC, April 27, 1862.

Hon. E. M. STANTON,
Secretary of War:

The first parallel essentially finished without accident; are at work upon batteries for the 10-inch mortars. Will commence new gun batteries to-night. Am anxious for the arrival of the expected 20 and 30 pounder Parrotts. The 13-inch mortars and the 200-pounder Parrotts - ten of the first and one of the latter - are safely within the mouth of Wormley's Creek, and will in batteries to-day. No rain to-day. The roads were becoming again. Enemy fired sharply with artillery for a while this morning, but did no harm.

GEO. B. McCLELLAN,

Major-General.

HDQRS. HOOKER'S DIVISION, THIRD ARMY CORPS, Camp Winfield Scott, near Yorktown, Va., April 27, 1862.

Brigadier General S. WILLIAMS,
Adjutant-General, Army of the Potomac:

I have the honor to report that Lieutenant-Colonel Mott, with 1,000 men, held the advance of my front last night, extending from Porter's pickets to the Yorktown road. He reports the exchange of a few shots between his advanced pickets and those of the enemy. One of his men received a slight flesh wound in the leg. One of the rebel pickets delivered himself up soon after daylight this morning and has been sent to the provost-marshal-general. Valuable information can be gotten from him.

Colonel Brewster, commanding the Seventy-third Regiment New York Volunteers, was posted in the vicinity of Batteries Nos.2 and 3. I received instructions yesterday for this regiment to throw out pickets to the left of the Yorktown road as far out as Battery No. 5, and accordingly so instructed the officer on duty. This morning he reports that, instead of that, the general of the trenches directed him to post his reserves farther to the right, and extended a portion of the Fourth Maine and Thirty-seventh New York Regiments to the right of the Yorktown road without his being informed that a change was to be made in the disposition of the troops. Colonel Brewster reports that he heard brisk firing, and that he is of opinion that it was between the two last-names regiments.

My single object in referring to this subject is to impress upon the mind of the major-general commanding the necessity of having a perfect understanding in the disposition for night defense to avoid catastrophe. Nothing is more easy than for troops to mistake friends for enemies in these movements.

As it is required of the general of the trenches to report the operations of the pickets and reserve, is it expected that division commanders shall do the same thing?

Very respectfully,&c.,

JOSEPH HOOKER,

Brigadier-General, Commanding Division.