In the West Indies and the Gulf of Mexico our naval force has been augmented by the addition of several small vessels provided for by the "act authorizing an additional naval force for the suppression of piracy," passed by Congress at their last session. That armament has been eminently successful in the accomplishment of its object. The piracies by which our commerce in the neighborhood of the island of Cuba had been afflicted have been repressed and the confidence of our merchants in a great measure restored.

The patriotic zeal and enterprise of Commodore Porter, to whom the command of the expedition was confided, has been fully seconded by the officers and men under his command. And in reflecting with high satisfaction on the honorable manner in which they have sustained the reputation of their country and its Navy, the sentiment is alloyed only by a concern that in the fulfillment of that arduous service the diseases incident to the season and to the climate in which it was discharged have deprived the nation of many useful lives, and among them of several officers of great promise.

In the month of August a very malignant fever made its appearance at Thompsons Island, which threatened the destruction of our station there. Many perished, and the commanding officer was severely attacked. Uncertain as to his fate and knowing that most of the medical officers had been rendered incapable of discharging their duties, it was thought expedient to send to that post an officer of rank and experience, with several skillful surgeons, to ascertain the origin of the fever and the probability of its recurrence there in future seasons; to furnish every assistance to those who were suffering, and, if practicable, to avoid the necessity of abandoning so important a station. Commodore Rodgers, with a promptitude which did him honor, cheerfully accepted that trust, and has discharged it in the manner anticipated from his skill and patriotism. Before his arrival Commodore Porter, with the greater part of the squadron, had removed from the island and returned to the United States in consequence of the prevailing sickness. Much useful information has, however, been obtained as to the state of the island and great relief afforded to those who had been necessarily left there.

Although our expedition, cooperating with an invigorated administration of the government of the island of Cuba, and with the corresponding active exertions of a British naval force in the same seas, have almost entirely destroyed the unlicensed piracies from that island, the success of our exertions has not been equally effectual to suppress the same crime, under other pretenses and colors, in the neighboring island of Porto Rico. They have been committed there under the abusive issue of Spanish commissions. At an early period of the present year remonstrances were made to the governor of that island, by an agent who was sent for the purpose, against those outrages on the peaceful commerce of the United States, of which many had occurred. That officer, professing his own want of authority to make satisfaction for our just complaints, answered only by a reference of them to the Government of Spain. The minister of the United States to that court was specially instructed to urge the necessity of the immediate and effectual interposition of that Government, directing restitution and indemnity for wrongs already committed and interdicting the repetition of them. The minister, as has been seen, was debarred access to the Spanish Government, and in the meantime several new cases of flagrant outrage have occurred, and citizens of the United States in the island of Porto Rico have suffered, and others been threatened with assassination for asserting their unquestionable rights even before the lawful tribunals of the country.

The usual orders have been given to all our public ships to seize American vessels engaged in the slave trade and bring them in for adjudication, and I have the gratification to state that not one so employed has been discovered, and there is good reason to believe that our flag is now seldom, if at all, disgraced by that traffic. It is a source of great satisfaction that we are always enabled to recur to the conduct of our Navy with pride and commendation. As a means of national defense it enjoys the public confidence, and is steadily assuming additional importance. It is submitted whether a more efficient and equally economical organization of it might not in several respects be effected. It is supposed that higher grades than now exist by law would be useful. They would afford well-merited rewards to those who have long and faithfully served their country, present the best incentives to good conduct, and the best means of insuring a proper discipline; destroy the inequality in that respect between military and naval services, and relieve our officers from many inconveniences and mortifications which occur when our vessels meet those of other nations, ours being the only service in which such grades do not exist.

A report of the Postmaster-General, which accompanies this communication, will shew the present state of the Post-Office Department and its general operations for some years past.

There is established by law 88,600 miles of post-roads, on which the mail is now transported 85,700 miles, and contracts have been made for its transportation on all the established routes, with one or two exceptions. There are 5,240 post-offices in the Union, and as many postmasters. The gross amount of postage which accrued from the 1st July, 1822, to the 1st July, 1823, was $1,114,345.12. During the same period the expenditures of the Post-Office Department amounted to $1,169,885.51, and consisted of the following items, viz: Compensation to postmasters, $353,995.98; incidental expenses, $30,866.37; transportation of the mail, $784,600.08; payments into the Treasury, $423.08. On the 1st of July last there was due to the Department from postmasters $135,245.28; from late postmasters and contractors, $256,749.31; making a total amount of balances due to the Department of $391,994.59. These balances embrace all delinquencies of postmasters and contractors which have taken place since the organization of the Department. There was due by the Department to contractors on the 1st of July last $26,548.64.

The transportation of the mail within five years past has been greatly extended, and the expenditures of the Department proportionably increased. Although the postage which has accrued within the last three years has fallen short of the expenditures $262,821.46, it appears that collections have been made from the outstanding balances to meet the principal part of the current demands.

It is estimated that not more than $250,000 of the above balances can be collected, and that a considerable part of this sum can only be realized by a resort to legal process. Some improvement in the receipts for postage is expected. A prompt attention to the collection of moneys received by postmasters, it is believed, will enable the Department to continue its operations without aid from the Treasury, unless the expenditures shall be increased by the establishment of new mail routes.

A revision of some parts of the post-office law may be necessary; and it is submitted whether it would not be proper to provide for the appointment of postmasters, where the compensation exceeds a certain amount, by nomination to the Senate, as other officers of the General Government are appointed.