The exploring expedition sailed from Norfolk on the 19th of August last, and information has been received of its safe arrival at the island of Madeira. The best spirit animates the officers and crews, and there is every reason to anticipate from its efforts results beneficial to commerce and honorable to the nation. It will also be seen that no reduction of the force now in commission is contemplated. The unsettled state of a portion of South America renders it indispensable that our commerce should receive protection in that quarter; the vast and increasing interests embarked in the trade of the Indian and China seas, in the whale fisheries of the Pacific Ocean, and in the Gulf of Mexico require equal attention to their safety, and a small squadron may be employed to great advantage on our Atlantic coast in meeting sudden demands for the reenforcement of other stations, in aiding merchant vessels in distress, in affording active service to an additional number of officers, and in visiting the different ports of the United States, an accurate knowledge of which is obviously of the highest importance. The attention of Congress is respectfully called to that portion of the report recommending an increase in the number of smaller vessels, and to other suggestions contained in that document. The rapid increase and wide expansion of our commerce, which is every day seeking new avenues of profitable adventure; the absolute necessity of a naval force for its protection precisely in the degree of its extension; a due regard to the national rights and honor; the recollection of its former exploits, and the anticipation of its future triumphs whenever opportunity presents itself, which we may rightfully indulge from the experience of the past--all seem to point to the Navy as a most efficient arm of our national defense and a proper object of legislative encouragement. The progress and condition of the Post-Office Department will be seen by reference to the report of the Postmaster-General. The extent of post-roads covered by mail contracts is stated to be 134,818 miles, and the annual transportation upon them 34,580,202 miles. The number of post-offices in the United States is 12,553, and rapidly increasing. The gross revenue for the year ending on the 30th day of June last was $4,262,145; the accruing expenditures, $4,680,068; excess of expenditures, $417,923. This has been made up out of the surplus previously on hand. The cash on hand on the 1st instant was $314,068. The revenue for the year ending June 30, 1838, was $161,540 more than that for the year ending June 30, 1837. The expenditures of the Department had been graduated upon the anticipation of a largely increased revenue. A moderate curtailment of mail service consequently became necessary, and has been effected, to shield the Department against the danger of embarrassment. Its revenue is now improving, and it will soon resume its onward course in the march of improvement.