October 26th. The fall campaign opened with the usual accompaniment of rainy weather. The general supposition is, that we are to march through the Loudon Valley, seizing the several gaps in advance, and occupy Pope’s old lines along the Rapidan and Rappahannock. The Twelfth corps is to remain and hold Harper’s Ferry, while the cavalry, or some part of it, is in advance at Cumberland. Harper’s Ferry will remain the base of supplies until we reach the ancient Manassas railroad, when it is to be used again. So we shall be exactly in the same position as before the second Bull Run campaign. We understand the present advance has been ordered peremptorily by the President, who is disgusted with McClellan’s torpidity, and is bound to make him take the offensive. Report says Lee’s army has been greatly reinforced, and is in excellent condition again. The season is so late it is not likely we shall accomplish much. Mais, nous verrons! Troops have been crossing the pontoon bridge all day long, and to-morrow we expect the Second corps to cross.