PHILADELPHIA, Friday, Aug. 30.

The Baltimore American has the following reliable intelligence regarding the division of Gen. ROSECRANS, obtained from a well-known citizen of Baltimore, who returned yesterday from North-Western Virginia. The name of this gentleman has been freely used in Baltimore for the last few days, as having written a letter declaring that there had been a great battle, in which Gen. ROSECRANS was defeated. The gentleman says that up to the afternoon of the 27th inst., Gen. ROSECRANS was not only alive and well, but was quietly transacting his important functions at his head-quarters. No information whatever was understood to have been received at head-quarters. News of the affair of Col. TYLER, near Summerville, had been received, but no other action beyond an occasional contact of pickets or scouts. Although it was not known exactly where the forces of Gen. ROSECRANS were posted, or their numbers, it was evident that the General was under no special alarm in regard to them.

It is said that his scouts had reported that the main body of the Confederate forces, believed to be commanded by Gen. LEE, and from seven to eight thousand strong, was encamped on a large plain, within four or six miles only of the encampment of Capt. REYNOLDS, who is supposed to have with him the largest portion of Gen. ROSECRANS' troops. It was believed that no attack would be made by either of the Southern forces commanded by Gen. LEE or Gen. WISE, unless they could find a strolling detachment to encounter, as in the case of Col. TYLER, of the Seventh Ohio Regiment, near Summerville.

Various accounts are given of the forces of Gens. LEE, WISE and FLOYD, but no accurate information seems to be possessed, outside of Gen. ROSECRANS' own staff. Opinions differ very much among military men and others in Western Virginia, as to the probabilities of anything like a general engagement between the respective armies in that quarter. Every confidence seems to be reposed in the ability of Gen. ROSECRANS to maintain himself against any forces likely to be spared to attack him. He has excellent aids and officers to support him, who have, doubtless, helped him in providing an effective Army.