DEPARTMENT OF STATE, Washington, September 18, 1861.

R. MINTURN, Jr., Esq., New York.

SIR: Your letter of the 14th instant requesting a passport for the Reverend Mr. Mercer and others to proceed to New Orleans has been received. You cannot doubt my disposition to comply with any reasonable request of yours, but a rule has for some time past been in force pursuant to which such request are invariably refused. It must be allowed, however, that if any exceptions were allowable the case of the Reverend Mr. Mercer would afford strong grounds therefor.

I am, sir, your obedient servant,

WILLIAM H. SEWARD.

CUSTOM-HOUSE, COLLECTOR'S OFFICE,

New York, September 18, 1861.

Honorable S. P. CHASE.

SIR: Mansfield Lovell, a native of Washington, D. C., aged about forty, formerly a captain U. S. artillery, resigned and joined General Quitman in his filibustering expedition against Cuba, was acting street commissioner of this city until Friday last (13th isntant); recently left this city and has gone probably by way of Canada to the rebels. He is an accomplished military man and would be of great service to the rebels. Mr. Gustavus W. Smith, the street commisioner, who was of the U. S. Engineer Corps, left the Army at the same time and for the same purpose as Lowell; is a first cousin of John C. Breckinridge and a warm friend and co-operator of his; left the city some months ago on account of his health and is still absent. Both Smith and Lovell are strong sympathizers with the rebels, and it is presumed are aiding them in all practicable ways.

I get the above from Colonel Craven, the chief engineer and president of the Croton Aqueduct Board, who thinks that Breckinridge ought to be arrested at once. He, Colonel C., was last fall a Breckinridge man, but was then, is now and always was and always will be an uncompromising Union man and friend to the Government. He is a Southern man by birth, and has relatives in the rebel army. He has also two brothers in the U. S. Navy, one in command of the flotila in the Potomac, and the other commands the Crusader. Colonel C. 's opinions are entitled to great respect on account of his character and his knowledge of certain men.

By the way he informs me that Mark Mount, the keeper of Conover Beacon in Raritan Bay has received intimation of a removal. If there are no objections to his official conduct there are political and prudential reason for his retention.

I am, truly, yours,

HIRAM BARNEY.

HEADQUARTERS ARMY OF THE POTOMAC,
Washington, September 18, 1861.

Major General JOHN A. DIX, U. S. Army, Baltimore, Md.:

I am directed by Major-General McClellan * * * to say that he wishes you to make any arrest that you may consider necessary even if you have not direct authority from the Government. The general