Intelligence from the Mexican Boundary Commission has been received to the 31st of August, on which day they were at Indianola, Texas. There was some sickness among the members of the corps, but every thing looked promising.—Hon. WILLIAM DUER, member of Congress from the Oswego District, New York, has declined a re-election, in a letter in which he vindicates the bills passed by Congress, and earnestly urges his constituents not to encourage or permit any further agitation among them of questions connected with slavery. Hon. E.G. SPAULDING, from the Erie District, and Hon. GEORGE ASHMUN, of Massachusetts, also decline a re-election.—Captain AMMIN BEY, of the Turkish Navy, arrived at New York on the 13th, in the United States ship Erie, being sent out by his Government as special Commissioner to collect information and make personal observations of the character, resources, and condition of the United States. He is a gentleman of ability, education, and experience and has been employed by his Government on various confidential missions. He was the secret agent of Turkey on the frontiers of Hungary during the recent struggle of that gallant people with Austria and Russia. He has been warmly received here, and enjoys every facility for prosecuting the objects of his mission. Congress has appropriated $10,000 toward defraying the expenses of his mission.—Hon. A.H.H. STUART, of Virginia, has been appointed Secretary of the Interior, to fill the vacancy caused by the resignation of Mr. M’KENNAN. He has accepted the appointment and entered upon the duties of the office. Mr. M’KENNAN resigned on finding, from an experience of a day, that his health was not adequate to the performance of the duties of the place. Mr. STUART has been a member of Congress, where he was universally recognized as a man of ability, assiduity, and character.—Mr. CONRAD, of Louisiana, on accepting the office of Secretary of War, addressed a letter to his constituents, explaining and justifying the course he had taken in Congress. He said that opinions on the subject of the extension of slavery might be classified as follows: 1. There are those who seek, through the direct agency of the Federal Government, to introduce slavery into this territory. 2. Those who wish, by the same means, to prevent this introduction. 3. Those who resist any interference with the question by the Federal Government, and would leave to the inhabitants of the country the exclusive right to decide it. He claims to belong to the latter class. The Union, he says, is too great a blessing to be staked upon any game of hazard, and the prolongation of the controversy upon the subject of slavery, he deems in itself a calamity “It alarms the South and agitates the North; it alienates each from the other, and augments the number and influence of those who wage an endless war against slavery, and whom this discussion has raised to a political importance which, without it, they never could have attained.”—Dr.