DEAR SIR,--I have been lately visited by a Mr. Miralla, a native of Buenos Ayres, but resident in Cuba for the last seven or eight years; a person of intelligence, of much information, and frankly communicative. I believe, indeed, he is known to you. I availed myself of the opportunity of learning what was the state of public sentiment in Cuba as to their future course. He says they would be satisfied to remain as they are; but all are sensible that that cannot be; that whenever circumstances shall render a separation from Spain necessary, a perfect independence would be their choice, provided they could see a certainty of protection; but that, without that prospect, they would be divided in opinion between an incorporation with Mexico, and with the United States.--Columbia being too remote for prompt support. The considerations in favor of Mexico are that the Havana would be the emporium for all the produce of that immense and wealthy country, and of course, the medium of all its commerce; that having no ports on its eastern coast, Cuba would become the depôt of its naval stores and strength, and, in effect, would, in a great measure, have the sinews of the government in its hands. That in favor of the United States is the fact that three-fourths of the exportations from Havana come to the United States, that they are a settled government, the power which can most promptly succor them, rising to an eminence promising future security; and of which they would make a member of the sovereignty, while as to England, they would be only a colony, subordinated to her interest, and that there is not a man in the island who would not resist her to the bitterest extremity. Of this last sentiment I had not the least idea at the date of my late letters to you. I had supposed an English interest there quite as strong as that of the United States, and therefore, that, to avoid war, and keep the island open to our own commerce, it would be best to join that power in mutually guaranteeing its independence. But if there is no danger of its falling into the possession of England, I must retract an opinion founded on an error of fact. We are surely under no obligation to give her, gratis, an interest which she has not; and the whole inhabitants being averse to her, and the climate mortal to strangers, its continued military occupation by her would be impracticable. It is better then to lie still in readiness to receive that interesting incorporation when solicited by herself. For, certainly, her addition to our confederacy is exactly what is wanting to round our power as a nation to the point of its utmost interest.