On Sunday, September 7, the Army of the Potomac took the field for the campaign in Maryland.

On Monday, September 1, it had become evident to the generals commanding near Centreville that the enemy were passing the right of menace the crossings of the Upper Potomac. Under orders from Major Fen. N. P. Banks, First Lieutenant W. W. Rowley, chief signal officer of the party serving with the Eleventh (Twelfth) Army Corps, started on the afternoon of that day from near Manassas with a party consisting of Captain L. R. Fortescue, Lieuts. B. N. Miner, and E. A. Briggs, acting signal officers, to reach, if possible, the summit of the Catoctin Mountains, near the Potomac, prior to the arrival there of the enemy, and to thence report their movements to General Banks.

Arriving on the Potomac, Captain Fortescue was ordered by Lieutenant Rowley to Maryland Heights, whence there is an extensive view of the Shenandoah and Pleasant Valleys. Lieutenant Briggs was stationed at Poolesville to receive communications by signals from Sugar Loaf Mountain, and to thence transmit them by electric telegraph to Washington, while Lieutenant Miner established a station upon the summit of that peak. The range of vision from this point is unequaled by that from any other in Maryland. It includes several prominent fords of the Potomac, the approaches to them in Virginia, and much of the country into which an army passing those fords would move. Lieutenant Miner occupied the summit of Sugar Loaf Mountain on the 3rd of September. The position was opposed to an attack, but was courageously held by the officer, who thence reported the advance of the enemy and the direction taken by their trains in the vicinity of Leesburg, their approach to the river, their crossing the Potomac near the Monocacy, and the commencement of their movement into Maryland. He was last seen to send a message announcing the near approach of the enemy, and to then furl his flags as if to leave the station. There is unofficial information that he left the summit of the mountain, encountered and captured when near its base a courier with dispatches, by the enemy's cavalry. It seems probable that the first official information of the enemy's cavalry at that place. The enemy at once occupied the mountain with infantry and artillery, and held it as a signal station.

On Saturday evening, September 6, signal officers from our army occupied stations on Seneca Ridge and near Great Falls, the line of stations thus reaching from Seneca Ridge to Fairfax Seminary, near Alexandria.

On Sunday, September 7, the signal party of the Army of the Potomac, under the immediate charge of Captain B. F. Fisher, under whose supervision the stations of observation near Washington had been established, left their camp at Hall's Hill, Va.

On Monday, September 8, the party were reported for duty at the headquarters of the army at Rockville, Md. On Tuesday, September 9, Wednesday, September 10, and Thursday, September 11, signal officers took part in the operations of the advance of the army at Poolesville and near Sugar Loaf Mountain. At the latter place communication was maintained between General Franklin at Barnesville and General Hancock at the foot of the mountain, while preparations were making to occupy it. On Thursday, September 11, at about 3 p.m., the mountain