POHICK CHURCH, March 6, 1862.

Brigadier General R. B. MARCY,

Chief of Staff, Army of the Potomac:

GENERAL: I ascended at 5 this p.m. and remained up until 6 o"clock. It was calm and clear, and many of the enemy's camps were visible, and the smoke ascending straight gave a good idea of the enemy's position.

There are more smokes than usual at Fairfax Station, and a line of picket smokes extending southeast from there and nearly forming a junction with our lines running toward Springfield Station.

Heavy smokes (besides those seen in the morning) at Dumfries, Brentsville, Bradley's and Manassas. General Heintzelman was here at 2 o"clock and went up twice.

I am greatly in need of that map that I spoke about yesterday to enable me to name place and distance more correctly. The one I have is small and inaccurate.

Very respectfully, your obedient servant,

T. S. C. LOWE,

Chief Aeronaut.

POHICK CHURCH, March 6, 1862.

Captain E. SEAVER,

In Charge of Balloon, Budd's Ferry, Md.:

I saw your balloon up this morning, but not this p.m. If to- morrow morning is calm I shall ascend at 7 o"clock, or the first favorable spell. Do the same at your place, with one of your signal officers, that I may see if signals may be used at this distance.

T. S. C. LOWE,

Chief Aeronaut.

On the 7th General Berry, of General Heintzelman's command, ascended several times and discovered the evacuation of the Occoquan, which he reported to the latter officer. This was the first indication of the retirement of the enemy from Manassas.

I was personally absent in Washington, preparing a balloon to be taken to a point near Fairfax Court-House to watch for the evacuation, as it was somewhat expected, but for want of transportation I was unable to reach Fairfax until the 10th. To show with what esteem the commanding general held the operations of the aeronautic department, the following orders are submitted, which embrace all the items of interest up to the 1st of April, and it is believed that they indicate an appreciation of my services after an experience of the previous seven months:

WASHINGTON, D. C., March 12, 1862.

Mr. T. S. C. LOWE,

Aeronaut, Army of the Potomac:

SIR: You will make arrangements without delay to send to Fortress Monroe, Va., a balloon with all the requisite apparatus and materials for inflating it and making ascensions, and an aeronaut to manage the same.

By order of Major-General McClellan:

J. N. MACOMB,

Lieutenant-Colonel, Aide-de-Camp, in Charge of Balloons.

HALL'S HILL, March 8, 1862.

Professor LOWE,

National Hotel, Washington:

I am authorized by General McClellan to call upon you for the balloon and inflating apparatus from Poolesville, and will be glad to have it here at as early an hour as possible, to take an observation a short distance in advance, where it will be well protected. Please reply what hour you will send it, as I desire to take an advantage of clear and calm wearther. I wish the balloon but a few hours.

F. J. PORTER,

Brigadier-General.