Sent report of observation to chief signal officer.

September 20, opened communication with signal officers on Thoroughfare Mountain. Sent four reports of observation to chief signal officer.

September 21, sent three reports of observation to chief signal officer; also some important intercepted rebel dispatches.

September 22, discovered early in the morning an important movement of enemy's cavalry, which I reported to chief signal officer at 10.30 a.m. Received and transmitted some messages; also reports of intercepted dispatches taken during the day.

September 23, important movement of our and enemy's cavalry noticed and reported to chief. Read and transmitted fifteen messages to-day.

September 24, reported enemy's cavalry and infantry returning from Liberty, and other important movements of the enemy during the day. Intercepted some important reports from rebel signal stations of our movements and sent came to chief. Received and transmitted ten messages.

September 25, some very important dispatches intercepted, giving disposition of enemy's forces, &c.

September 26, observation was of but little importance other than a review of the rebel cavalry, with the exception of General Fitz. Lee's division. Received and transmitted six messages.

September 27, observations show no change in enemy's position, which I reported to chief. Received and transmitted five messages.

September 28, important dispatches were intercepted from rebel signal stations and forwarded to chief. Three messages.

September 29, three messages.

September 30, discovered a change in enemy's cavalry this a.m., which I reported to chief. Fifteen messages.

The within is respectfully submitted.

Your obedient servant,

D. E. CASTLE,

Captain, and Acting Signal Officer.

No. 3. Report of Colonel Horace B. Sargent, First Massachusetts Cavalry, commanding detachment First Brigade, Second Cavalry Division, of skirmish (15th) at Rapidan Station.

CAMP NEAR SLAUGHTER MOUNTAIN,

September 15, 1863.

CAPTAIN: I have the honor to report that in accordance with verbal orders from Colonel McIntosh, commanding brigade, I took command of a reconnaissance toward Rapidan Station about 12 m., for the purpose of determining the presence of infantry on the other side of the river, and the general position of the enemy.

My force was as follows: Sixth Ohio Cavalry, Lieutenant-Colonel Stedman, 165 men and 11 officers; First Rhode Island Cavalry, Colonel Thompson, 170 men and 13 officers; First Massachusetts Cavalry, Captain Sargent, 228 men and 12 officers; total, 563 men and 36 officers.