HEADQUARTERS SECOND BRIGADE,
Baton Rouge, La., August 2, 1862

John Mahan [Mann?], with a pass from General Butler, dated July 22, for Vicskburg, and who left New Orleans July 25 and arrived at Ponchatoula and Camp Moore Monday, July 28, having proceeded up the Jackson Railroad as far as Jackson, arrived here by the way of Summit, Liberty and Bayou Sara this morning at 10 o'clock. He says he saw Breckinridge's force of six full regiments and fourteen guns at Camp Moore and Ponchatoula Monday, July 28, and that their purpose is to attack this place; says they may be expected on the rear of Baton Rouge at this time or at any time in the next day or two.

Mahan also reports that the rebels have field guns and beef cattle at the mouth of Red River. They intend crossing to the east bank of the Mississippi to-night or to-morrow morning, and I have sent him with a note to Captain Porter, U. S. Navy, commanding the flotilla here, at the same time advising Porter of Mahan's statement regarding Breckinridge's movement on this place, to put the gunboats designed to flank us on their guard.

If Mahan be a true man and a true observer there is to be an attack here or at New Orleans; if at New Orleans, a demonstration here.

Respectfully, your obedient servant,

T. WILLIAMS,

Brigadier-General, Volunteers.

Captain R. S. DAVIS,

Assistant Adjutant-General.

P. S. - I shall send Mahan down by the first opportunity to headquarters. I hope the rebels have as many sick as I have. Perhaps (let us hope at least) that a battle may to our sick exert all the effects of the best tonic of the pharmacopoeia.

T. W.,

Brigadier-General.

P. S. - Two additional gunboats are desirable. The Arkansas may come to co-operate with the rebel land force, and also the Music and the Webb; the latter is said to be rather formidable, carrying eight guns.

Why not send up the sloop Oneida? Preble is here. Who is to command her-the Oneida and a gunboat?

HEADQUARTERS DEPARTMENT OF THE GULF,

New Orleans, August 3, 1862

Brigadier-General WILLIAMS,

Commanding at Baton Rouge:

GENERAL: I received your note by the hand of John Mann [Mahan?], who was in my confidential service. While his information may be relied upon as correct, yet all the inferences may not be which he draws. The truth is this, as I gather it from various sources: On the 25th of July I sent 500 men on an expedition around the lake at Mandeville and Madisonville. The movement was delayed forty-eight hours, and in that time word was sent to the enemy that it was to go out. There upon Breckinridge was telegraphed, down to Camp Moore, with four regiments to proceed to Madisonville, but it so happened that Colonel McMillan on the same day sent out to the Amite River a reconnoiter-