[Received at the WAR DEPARTMENT, June 18, 1861.]

I am enabled now to give you additional and exact details of the affair near Vienna last evening. A perfectly reliable Union man, residing in Vienna, [and who] was there during the attack, has arrived, bringing with him in patriotic and Christian kindness, the six bodies of our killed who were left behind. I have sent them to Camp Lincoln by the train which has just left for burial. He reports also one wounded man remaining at Vienna, John Volmer of Company G, for whom I have just sent an assistant surgeon and two men with the same gentleman who brought the killed in his wagon, carrying a flag of truce, to be displayed if necessary. When the wounded man arrives I will send him forward by a train to my camp, to be conveyed from there to Georgetown Hospital by ambulance.

The casualties, as I now am able accurately to state them, are as follows:

Dead, 8.- Captain Hazlett's: 1st, George Morrison of Company H, brought in to-day. 2nd, David Mercer of same company, brought off the field to this place, and died here. 3rd, Daniel Sullivan of Captain Bailey's company, G. 4th, Joseph Smith, Company G, brought in to-day. 5th, Philip Strade, Company G. 6th, Thomas Finton, Company G, 7th, Eugene Burke, Company G. 8th, J. R. T. Barnes, Company G, shot in the passenger car that was carried away from us by the engineer, and died on his way to this camp.

Wounded and yet living, 4. - 1st, David Gates, Company G, dangerously. 2nd, B. F. Lanman, Company G, severely, but not dangerously. 3rd, Henry Pigman, Company H, dangerously. (Those three were sent to the hospital this morning.) 4th, John Volmer, Company G, supposed dangerously; yet at Vienna and sent for.

Total killed and wounded, 12. None, I believe are now missing.

From the same reliable source I ascertain that the whole force attacking us was at least 2,000, as follows; South Carolina troops, 800; these had left Fairfax Court-House on Sunday and gone over to the railway; two [hundred] came down yesterday through Hunters Grove. They sent, anticipating our coming to Fairfax Court-House, for 2,000 additional infantry, of whom only from 600 to 1,000 arrived before the attack. The enemy had cavalry numbering it is believed not less than 200, and, in addition to these, was a body of 150 armed picked negroes, who were posted nearest us in a grain field on our left flank, but not observed by us, as they lay flat in the grain and did not fire a gun. The enemy had three pieces of artillery, concealed by the curve of the railway as we passed out of the cut, and more pieces of ordnance-six, our informant believes-arrived on the field, but not in time for action . The three pieces thus placed were fired very rapidly; must have been managed by skillful artillerists; but I cannot learn who was in command of the enemy. Our men picked up and brought away several round and grape shot, besides two or three shells, which did not explode because the cars and upon us as we retired through the woods and along each side of the railway. Its deadliest effect was on Company G, on the third platform car from the front, and on Company H, on the second platform car. Company E, on the foremost car, was not touched. The first firing raked the train diagonally with round shot; the other, before the train came to a full stop, was cross-firing with canister and shells through the hind cars. The pieces were at a distance of about 150 yards, and no muskets or rifles were brought into action.

The rebels must have believed that our number far exceeded the little