Major-General McCLELLAN, Rockville:

The following dispatch has just been received:

DAMASCUS, September 11, 1862-6 a. m.

General BURNSIDE:

With the view of following your instructions, I left yesterday, at 12.30 p. m., and went to Cracklinton, where i had expected a cavalry scout, under Colonel Devin. After waiting until 4 p. m. I received about 100 men, under Colonel Allen, First maine, and learned that Colonel Devin was absent from General Cox's headquarters, and his men and horses unfit for the march. I received, however, and increase of 60 cavalry from General Rodman. Colonel Allen's command had been on march the whole day without forage, and the horses were allowed to feed an hour at the quartermaster's department at Cracklinton. I mention this to show why we did not arrive here until dark, and why the horses could not go farther that night. At this place i found one regiment infantry, under Colonel Ewing, who offered all facilities. The same reports were prevalent here as we heard at your camp, viz, of rebel forces at Hyattstown, Urbana, and New Market, with a large force at Frederick. It was reported that rebel pickets extend on the New Market road to within 4 miles of this place. i suggested to Colonel Ewing that if a rebel picket guard could be captured and brought here, it might afford us valuable information. He agreed with me, and selected a lieutenant and 25 men on this duty, with orders to march through fields, avoiding the roads, try and capture the supposed rebels, and bring them in. They started at 11 p. m., and returned just now. They found no rebel force at the hamlet, 4 miles from Damascus, where their pickets had been the night before and up to 11 a. m. yesterday, when they left, saying they would return, but did not. There had been 6 or 8 of them. The lieutenant then went 1 1/2 miles still farther, and at 4 a. m. heard drums beating, supposed 1 1/2 miles a still farther on, probably near Morena, or, perhaps, a mile this side. At the hamlet, 4 miles from here, called Kemptown, and about as large as this place, six or eight houses, the lieutenant took two citizens of that place and brought them to me. They report some 1,200 cavalry came to New Market last Saturday, and these were distributed north and south between Liberty and Hyattstown. No other kind of force in immediate vicinity than cavalry. When asked how many rebels entered Maryland, under Jackson, they say from 100,000 to 150,000, but these numbers are rumors.

Colonel Ewing will occupy the forks of the road, 2 miles from here, to enable me to go with all the cavalry escort to Ridgeville, and then, if rebels are there on the roads toward New Market, on returning I will forward you another report, having reserved a fresh horse for the purpose. The section of cavalry arrived last night. The roads, as far as I have gone, are good, with fields and open timber and good water at intervals.

R. S. WILLIAMSON,

Captain Topographical Engineers.

A. E. BURNSIDE,

Major-General.

HEADQUARTERS RIGHT WING,
September 11, 1862-8 p. m.

(Received Washington, D. C., September 12-1.55 a. m.

General GEORGE B. McCLELLAN:

The following has just been received:

HEADQUARTERS KANAWHA DIVISION,
Ridgeville, September 11, [1862]-5.30 p. m.

CAPTAIN: I have the honor to report that an Irishman, named Michael Kingsley, has just come into my camp from Fredericktown, which place he says he left at 11 a. m. to-day. He reports that place evacuated by the rebels except pickets. That there is no force but cavalry pickets of small numbers anywhere on the road between Frederick and Ridgeville; saw only 30 or 40 cavalry at New Market. He dodged their pickets through the woods. His report is confirmed by several partial accounts received by me from citizens in the neighborhood, and I think it reliable. He lives in Baltimore, and has been working near Harper's Ferry. The reports of force in direction of New London and Liberty are somewhat vague, and I am trying to obtain something more definite. I do not incline to believe there is much force in our front.