...vision of men at Poolesville, with a battery on the hills occupied by Gen. Banks last year, after Ball's Bluff, would render such an attempt a dangerous experiment. Poolesville, Point of Rocks, and Harper's Ferry are all strongly guarded, while a large body of troops are being massed at Baltimore, as I am told, to be held as a reserve, for the purpose of resisting the capture or the invasion of Maryland, or t...