[Inclosure No. 2.]

AT ALLEN'S FARM, May 5-8 p.m.

GENERAL: Some 30 prisoners have fallen into the hands of my cavalry to-day while it was engaged in feeling about the enemy's right; among them a very intelligent gentleman (Mr. Allen), adjutant of the information I can gather I think I can state the following as very nearly the truth: Johnston is commanding the enemy's forces. He left Williamsburg at 8 o'clock this morning, intending to attack us before our re-enforcements could come up. Longstreet's division is opposite our left. He is jolly to-day - in good spirits. J. E. B.

Stuart commanded the cavalry which General Cooke attacked yesterday, and leaving his brigade this morning he stood on the road and cheered the rebel regiments on. Three more regiments left Williamsburg at 5 p.m. to-day at a double-quick to re-enforce their line here, which shows that there was a presume somewhere. The most intelligent of them say that they have over 50,000 men here, and they express the belief that they cannot be whipped. They know nothing of any other movements of ours. They think our force in front is 120,000. They have suffered considerably to-day.

From the fact that most of these prisoners have strayed from their regiment with the intention of reaching Williamsburg, and have fallen inadvertently into my hands, I believe that there is a communication from our left directly to rear of the enemy's right which could be made by, say, five of our most reliable regiments, followed by two or three batteries with amen and two regiments of cavalry. I don't think the party that undertook their right the right direction or started early enough. I was now with it, but believe they struck into the woods too soon.

We must be ready to-morrow morning early, I think.

Respectfully, yours,

WM. W. AVERELL.

General HEINTZELMAN.

[Addenda.]

HEADQUARTERS THIRD CORPS, ALLEN'S FARM, May 5, 1862-9.30 p.m.

GENERAL: We have been hard pressed by the enemy all day, and nothing but the opportune arrival of General Kearny's division saved us from the loss of some of our artillery and defeat. Cannot you cut a road in front of the enemy's intrenchments by which I can be re-enforced before daylight in the morning, as I fear they will make another effort to drive us back? It will require at least a division for me to hold the position against the force the enemy has to bring against me. General Hooker's division suffered so severely that I do not expect to receive much aid from it. By cutting this road the troops can readily join me without having to make the large circuit by Cheesecake Church. Cannot you also attack him at daylight on his left and in your front? I fear greatly that unless he is strongly pressed I will not be able to maintain my position. May I rely upon your aid to sustain me? Our loss has been heavy, some 500 killed and wounded.

I am, general, very respectfully, your obedient servant,
S. P. HEINTZELMAN,

Brigadier-General, Commanding Third Corps.

General E. V. SUMNER, Commanding,&c., Allen's House.