remained all night in Pleasant Valley and was of no service, save in transmitting a few messages from the cavalry command to headquarters.

General Howe this day assumed command, with headquarters at Sandy Hook, and at 8 p. m. the whole detachment was moved to the east of Maryland Heights, for the purpose of operating between Maryland Heights and the Catoctin range, whither the enemy were moving.

I had intended to open a station on the morning of the 9th on the Catocin Mountain, leaving Lieutenant Kennedy on the heights. During the night, however, our forces under Colonel Mulligan fell back and reported the enemy crossing at Point of Rocks. General Howe sent for me early on the morning of the 9th and requested me to remain on the heights to discover if the enemy were crossing at the point indicated. He also directed my detachment to remain at Sandy Hook prepared to move, as he did not consider it safe to attempt to reach the Catoctin range. I reported continually that no force was crossing at Point of Rocks, or had crossed, that the main body of the enemy were at or near Frederick. This information was fully and completely confirmed at 8 p. m. by scouts who returned from Middletown and reported the engagement between Generals Wallace and Early at Monocacy Junction.

Our services this day show the utility of a signal party in determining the movements of an enemy in a country well adapted to signaling. For twelve hours our reports were directly opposed to all others. All evidence but ours represented the enemy at Point of Rocks, and yet they were found to be exactly where our observations and reports located them. I do not claim that our operations this day were more important than previous days, but they most certainly increased the confidence of the general commanding in our accuracy and utility.

At 12 m. on the morning of the 10th, after the enemy were found to be in the vicinity of Frederick, General Howe gave me permission to establish a station on the Catoctin Mountain, as I had intended on the previous day. At daylight I sent the following dispatch:

5.30 A. M.

GENERAL: The enemy's forces have left Frederick and are now all across the Monocacy River, save a rear guard of 200 cavalry. They are moving on the Georgetown pike. General Wallace is retreating on the same road. They are either marching on Washington or Baltimore, or are retreating toward Edwards Ferry.

THAYER,

Lieutenant, Signal Officer, Catoctin Mountain.

Lieutenant-Colonel Blakely, who superseded General Stahel, came by station at 8 a. m. this day, and requested me to go on with the advance. I, therefore, abandoned the station, and moved with the advance cavalry through Frederick and across the Monocacy. At Urban, four miles beyond the latter river, Colonel Blakely at 4 p. m. sent to General Howe his first dispatch. It embraced no further information, and was the same in substance as my dispatch of 5.30. I found that it was impossible from this point to communicate with Maryland Heights, and I, therefore, thought it best to return with my detachment to Sandy Hook. I reported to General Howe at 11 p. m. this day. The general requested me to sent out a