WASHINGTON, March 12, 1822.

To the Senate and House of Representatives of the United States:

I lay before the Senate the copy of a supplementary report, made by William Lambert, in relation to the longitude of the Capitol from Greenwich, in pursuance of a joint resolution of the two Houses of Congress of the 3d of March, 1821, and I subjoin an extract from the letter of Mr. Lambert submitting that report. JAMES MONROE.

WASHINGTON, March 26, 1822.

To the Senate and House of Representatives of the United States:

Congress having suspended the appropriation, at the last session, for the fortification at Dauphine Island, in consequence of a doubt which was entertained of the propriety of that position, the further prosecution of the work was suspended, and an order given, as intimated in the message of the 3d of December, to the Board of Engineers and Naval Commissioners to examine that part of the coast, and particularly that position, as also the position at Mobile Point, with which it is connected, and to report their opinion thereon, which has been done, and which report is herewith communicated.

By this report it appears to be still the opinion of the Board that the construction of works at both these positions is of great importance to the defense of New Orleans and of all that portion of our Union which is connected with and dependent on the Mississippi and on the other waters which empty into the Gulf of Mexico between that river and Cape Florida. That the subject may be fully before Congress, I transmit also a copy of the former report of the Board, being that on which the work was undertaken and has been in part executed. Approving as I do the opinion of the Board, I consider it my duty to state the reasons on which I adopted the first report, especially as they were in part suggested by the occurrences of the late war.

The policy which induced Congress to decide on and provide for the defense of the coast immediately after the war was founded on the marked events of that interesting epoch. The vast body of men which it was found necessary to call into the field through the whole extent of our maritime frontier, and the number who perished by exposure, with the immense expenditure of money and waste of property which followed, were to be traced in an eminent degree to the defenseless condition of the coast. It was to mitigate these evils in future wars, and even for the higher purpose of preventing war itself, that the decision was formed to make the coast, so far as it might be practicable, impregnable, and that the measures necessary to that great object have been pursued with so much zeal since.

It is known that no part of our Union is more exposed to invasion by the numerous avenues leading to it, or more defenseless by the thinness of the neighboring population, or offers a greater temptation to invasion, either as a permanent acquisition or as a prize to the cupidity of grasping invaders from the immense amount of produce deposited there, than the city of New Orleans. It is known also that the seizure of no part of our Union could affect so deeply and vitally the immediate interests of so many States and of so many of our fellow-citizens, comprising all that extensive territory and numerous population which are connected with and dependent on the Mississippi, as the seizure of that city. Strong works, well posted, were therefore deemed absolutely necessary for its protection.

It is not, however, by the Mississippi only, or the waters which communicate directly with or approach nearest to New Orleans, that the town is assailable. It will be recollected that in the late war the public solicitude was excited not so much by the danger which menaced it in those directions as by the apprehension that, while a feint might be made there, the main force, landing either in the bay of Mobile or other waters between that bay and the Rigolets, would be thrown above the town in the rear of the army which had been collected there for its defense. Full confidence was entertained that that gallant army, led by the gallant and able chief who commanded it, would repel any attack to which it might be exposed in front. But had such a force been thrown above the town, and a position taken on the banks of the river, the disadvantage to which our troops would have been subjected, attacked in front and rear as they might have been, may easily be conceived. As their supplies would have been cut off, they could not long have remained in the city, and, withdrawing from it, it must have fallen immediately into the hands of the force below. In ascending the river to attack the force above, the attack must have been made to great disadvantage, since it must have been on such ground and at such time as the enemy preferred. These considerations shew that defenses other than such as are immediately connected with the city are of great importance to its safety.

An attempt to seize New Orleans and the lower part of the Mississippi will be made only by a great power or a combination of several powers, with a strong naval and land force, the latter of which must be brought in transports which may sail in shallow water. If the defenses around New Orleans are well posted and of sufficient strength to repel any attack which may be made on them, the city can be assailed only by a land force, which must pass in the direction above suggested, between the Rigolets and the bay of Mobile. It becomes, therefore, an object of high importance to present such an obstacle to such an attempt as would defeat it should it be made. Fortifications are useful for the defense of posts, to prevent the approach to cities and the passage of rivers; but as works their effect can not be felt beyond the reach of their cannon. They are formidable in other respects by the body of men within them, which may be removed. and applied to other purposes.

Between the Rigolets and the bay of Mobile there is a chain of islands, at the extremity of which is Dauphine Island, which forms, with Mobile Point, from which it is distant about 34 miles, the entrance into the bay of Mobile, which leads through that part of the State of Alabama to the towns of Mobile and Blakeley. The distance between Dauphine Island and the Rigolets is 90 miles. The principal islands between them are Massacre, Horn, Ship, and Cat islands, near to which there is anchorage for large ships of war. The first object is to prevent the landing of any force for the purposes above stated between the Rigolets and the bay of Mobile; the second, to defeat that force in case it should be landed. When the distance from one point to the other is considered, it is believed that it would be impossible to establish works so near to each other as to prevent the landing of such a force. Its defeat, therefore, should be effectually provided for. If the arrangement should be such as to make that result evident, it ought to be fairly concluded that the attempt would not be made, and thus we should accomplish in the best mode possible and with the least expense the complete security of this important part of our Union, the great object of our system of defense for the whole.

There are some other views of this subject which it is thought will merit particular attention in deciding the point in question. Not being able to establish a chain of posts, at least for the present, along the whole coast from the Rigolets to Dauphine Island, or on all the islands between them, at which point shall we begin? Should an attack on the city be anticipated, it can not be doubted that an adequate force would immediately be ordered there for its defense. If the enemy should despair of making an impression on the works near the town, it may be presumed that they would promptly decide to make the attempt in the manner and in the line above suggested between the Rigolets and the bay of Mobile. It will be obvious that the nearer the fortification is erected to the Rigolets with a view to this object, should it be on Cat or Ship Island, for example, the wider would the passage be left open between that work and the bay of Mobile for such an enterprise. The main army, being drawn to New Orleans, would be ready to meet such an attempt near the Rigolets or at any other point not distant from the city. It is probable, therefore, that the enemy, profiting of a fair wind, would make his attempt at the greatest distance compatible with his object from that point, and at the bay of Mobile should there not be works there of sufficient strength to prevent it. Should, however, strong works be erected there, such as were sufficient not only for their own defense against any attack which might be made on them, but to hold a force connected with that which might be drawn from the neighboring country, capable of cooperating with the force at the city, and which would doubtless be ordered to those works in the event of war, it would be dangerous for the invading force to land anywhere between the Rigolets and the bay of Mobile and to pass toward the Mississippi above the city, lest such a body might be thrown in its rear as to cut off its retreat. These considerations show the great advantage of establishing at the mouth of the bay of Mobile very strong works, such as would be adequate to all the purposes suggested.

If fortifications were necessary only to protect our country and cities against the entry of large ships of war into our bays and rivers, they would be of little use for the defense of New Orleans, since that city can not be approached so near, either by the Mississippi or in any other direction, by such vessels for them to make an attack on it. In the Gulf, within our limits west of Florida, which had been acquired since these works were decided on and commenced, there is no bay or river into which large ships of war can enter. As a defense, therefore, against an attack from such vessels extensive works would be altogether unnecessary either at Mobile Point or at Dauphine Island, since sloops of war only can navigate the deepest channel. But it is not for that purpose alone that these works are intended. It is to provide also against a formidable invasion, both by land and sea, the object of which may be to shake the foundation of our system. Should such small works be erected, and such an invasion take place, they would be sure to fall at once into the hands of the invaders and to be turned against us.

Whether the acquisition of Florida may be considered as affording an inducement to make any change in the position or strength of these works is a circumstance which also merits attention. From the view which I have taken of the subject I am of opinion that it should not. The defense of New Orleans and of the river Mississippi against a powerful invasion being one of the great objects of such extensive works, that object world be essentially abandoned if they should be established eastward of the bay of Mobile, since the force to be collected in them would be placed at too great a distance to allow the cooperation necessary for those purposes between it and that at the city; in addition to which, it may be observed that by carrying them to Pensacola or farther to the east that bay would fall immediately, in case of such invasion, into the hands of the enemy, whereby such cooperation would be rendered utterly impossible, and the State of Alabama would also be left wholly unprotected.

With a view to such formidable invasion, of which we should never lose sight, and of the great objects to which it would be directed, I think that very strong works at some point within the Gulf of Mexico will be found indispensable. I think also that those works ought to be established at the bay of Mobile-one at Mobile Point and the other on Dauphine Island-whereby the enemy would be excluded and the complete command of that bay, with all the advantages attending it, be secured to ourselves. In the case of such invasion, it will, it is presumed, be deemed necessary to collect at some point other than at New Orleans a strong force, capable of moving in any direction and affording aid to any part which may be attacked; and, in my judgment, no position presents so many advantages as a point of rendezvous for such force as the mouth of that bay. The fortification at the Rigolets will defend the entrance by one passage into Lake Pontchartrain, and also into Pearl River, which empties into the Gulf at that point. Between the Rigolets and Mobile Bay there are but two inlets which deserve the name, those of St. Louis and Pascagola, the entrance into which is too shallow even for the smallest vessels; and from the Rigolets to Mobile Bay the whole coast is equally shallow, affording the depth of a few feet of water only. Cat Island, which is nearest the Rigolets, is about 71⁄2 miles distant from the coast and 30 from the Rigolets. Ship Island is distant about 10 miles from Cat Island and 12 from the coast. Between these islands and the coast the water is very shallow.

As to the precise depth of water in approaching those islands from the Gulf, the report of the topographical engineers not having yet been received, it is impossible to speak with precision; but admitting it to be such as for frigates and even ships of the line to enter, the anchorage at both is unsafe, being much exposed to northwest winds. Along the coast, therefore, there is no motive for such strong works on our partno town to guard, no inlet into the country to defend-and if placed on the islands and the entrance to them is such as to admit large ships of war, distant as they are from the coast, it would be more easy for the enemy to assail them with effect.

The position, however, at Mobile Bay is essentially different. That bay takes its name from the Mobile River, which is formed by the junction of the Alabama and Tombigbee, which extend each about 300 miles into the interior, approaching at their head waters near the Tennessee River. If the enemy possessed its mouth, and fortified Mobile Point and Dauphine Island, being superior at sea it would be very difficult for us to dispossess him of either, even of Mobile Point; and holding that position, Pensacola would soon fall, as without incurring great expense in the construction of works there it would present but a feeble resistance to a strong force in its rear. If we had a work at Mobile Point only, the enemy might take Dauphine Island, which would afford him great aid in attacking the point, and enable him, even should we succeed in repelling the attack, to render us great mischief there and throughout the whole Gulf. In every view which can be taken of the subject it appears indispensable for us to command the entrance into Mobile Bay, and that decision being taken, I think the considerations which favor the occupation of Dauphine Island by a strong work are conclusive. It is proper to observe that after the repulse before New Orleans in the late war the British forces took possession of Dauphine Island and held it till the peace. Under neither of the reports of the Board of Engineers and Naval Commissioners could any but sloops of war enter the bay or the anchorage between Dauphine and Pelican islands. Both reports give to that anchorage 18 feet at low water and 20% at high. The only difference between