comments is received. If, with a full knowledge of all the circumstances, you consider it preferable to crush the enemy at Petersville before undertaking the movement I have direct, youare at liberty to do so, but you will readily perceive that no slight advantage should for a moment interfer with the decisive results I propose to gain. I cannot too strongly impress upon you the absolute necessityof informing me every hour during the day of your movements, and frequently during the night. Force your colonesel to prevent straggling, and bring every available man into action. I think the force you have is, with good mangement, sufficient for the end in view. If you differ widely from me, and being on the spot you know better than I do the circumstances of the case, inform me at once, and I will do my best to re-enforce you. Inform me at the same time how many more troops you think you should have. Until 5 a. M. to-morrow general headquarters will be at this place. At that hour they will move upon the main road to Hagerstown.

I am, general, very respectfully, your obedient servant,

GEO. B. McCLELLAN,

Major-Generall, Commanding.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC.

Frederick, September 13, 1862-11.45 p. M.

Major-General BURNSIDE:

The rebel cavalry is reported to have been seen about 5 p. M. to-day, five or six miles from Frederick, on the Emmitsburg turnpike. The major-general commanding directs you to send out on this road five or six miles one regiment of cavalry and a section of artillery to ascertain as to the truth of this report. Should no cavalry appear to be in the neighborhood, the force detached by you will join the main body of your command on the National road.

Respectfully, your obedient servant,
R. B. MARCY,

Chief of Staff.

[19.]

HEADQUARTERS ARMY OF THE POTOMAC.

Camp near Frederick, September 13, 1862-3.35 p. M.

Brigadier General J. D. COX.

Commanding Division:

GENERAL: General McClellan directs me to say that it was the intention for you to proceed direct to Middletown, and desires that you will march to that place and support General Pleasonton. Pick up Rodney [Rodman], if you should find him, and take him with you to Middletown.

Very respectfully, yours,
R. B. MARCY,

Chief of Staff.

[19.]

HEADQUARTERS NINTH CORPS,
Frederick, Md., September 13, 1862.

Brigadier General O. B. WILLCOX,

Commanding First Division, Ninth Army Corps:

GENERAL: Major-General Reno instructs me to direct you to put your column in motion for Middletown; also detail one company of