DEAR SIR,--Your letters of July 31st and August 5th were received yesterday. The ground taken in conformity with the Act of Congress, of considering as public enemies British armed vessels in or entering our waters, gives us the benefit of a system of rules, sanctioned by the practice of nations in a state of war, and consequently enabling us with certainty and satisfaction to solve the different cases which may occur in the present state of things. With these rules most officers are acquainted, and especially those old enough to have borne a part in the revolutionary war. 1. As to the enemy within our waters, intercourse, according to the usages of war, can only be by flag; and the ceremonies respecting that are usually a matter of arrangement between the adverse officers commanding in the neighborhood of each other. If no arrangement is agreed on, still the right of sending a flag is inherent in each party, whose discretion will direct him to address it to the proper adverse authority; as otherwise it would be subject to delay or rejection. Letters addressed by flag to persons in authority with the adverse power, may be sent sealed, and should be delivered. But, if to others, or to their own friends happening to be within the limits of the adversary, they must be open. If innocent in the judgment of the receiving officer, courtesy requires their delivery; if otherwise, they may be destroyed or returned by him; but in a case of only suspended amity, as ours, they should be returned. Letters sent from the interdicted vessels to their consul in Norfolk must be open; and the propriety of delivering them judged of by our officer, tempering his judgment however with liberality and urbanity. Those to their minister plenipotentiary here, sealed or unsealed, should be sent to the Secretary of State without any delay. As to the demand of fugitive slaves, it was the custom during the late war, for the owner to apply to our commander for a flag, and to go himself with that, to exhibit his claim and receive the fugitive. And with respect to Americans detained on board their ships, the application should be still, as heretofore, made through the Secretary of State, to whose proper documents are to be furnished. But without waiting for his application, the British officer, knowing them to be Americans and freemen, cannot but feel it a duty to restore them to their liberty on their own demand.