The point to which it was intended the regiment should go by train, and establish itself for the twenty-four hours, had been occupied, for the day before, by the Sixty-ninth New York Regiment, under Colonel Hunter, commanding the brigade. The latter regiment had been sent there, on the return of General Tyler from his reconnaissance up the road, as an advance guard and a protection to the road, which had been repaired in anticipation of the demonstration I was to make on the notification of the General-in-Chief in favor of the attack on Harper's Ferry. It is said the attack on the Ohio regiment was made by the South Carolinians. If so, they must have been moved forward from Centreville, where they have been stationed for some time past. This would seem to indicate that the reports of an advance of troops to their posts in front of this position are well founded. I have asked if it would accord with the plans of the General-in-Chief that a movement be made in force in the direction of Vienna, near which the attack was made. I learn from a reliable source that the force at Fairfax Court-House has been increased. Had the attack not been made, I would not suggest this advance at this time; but now that it has, I think it would not be well for us to seem even to withdraw. General Schenck applies for permission to send a flag of truce to Vienna to bury his dead and care for his wounded. I do not think this necessary for either purpose, but think the morale of the troops would be increased it they went over the ground again with arms in their hands. The distance by turnpike from Falls Church to Vienna is about six miles.

General Tyler, who is in advance, sends me word that he sees the country as far as Falls Church. No signs of any movement. He wants no more troops than he has, unless it is intended to hold permanently the position he occupies.

I have the honor to be, very respectfully, your obedient servant,

IRVIN McDOWELL,

Brigadier-General, Commanding.

Lieutenant Colonel E. D. TOWNSEND,

Assistant Adjutant-General, Headquarters Army, Washington.

[Inclosure.]

HEADQUARTERS DEPARTMENT NORTHEASTERN VIRGINIA.

Arlington, June 17, 1861

Brigadier-General SCHENCK, Commanding Ohio Brigade:

SIR: The general commanding directs that you send one of the regiments of your command, on a train of cars, up the Loudoun and Hampshire Railroad to the point where it crosses the wagon-road running from Fort Corcoran, opposite Georgetown, southerly into Virginia.

The regiment, being established at that point, will by suitable patrols, feel the way along the road towards Falls Church and Vienna, moving, however, with caution, and making it a special duty to guard effectually the railroad bridges and to look to the track. The regiment will go supplied for a tour of duty of twenty-four hours, and will move on the arrival at your camp of a train of cars ordered for that purpose, and will relieve all the troops of Colonel Hunter's brigade now guarding the line.

I am, sir, very respectfully, your obedient servant,
JAMES B. FRY,

Assistant Adjutant-General.