A letter from the commanding officer of the British division was received, dated April 15th, containing information to the following effect: that he had the pleasure of receiving the intelligence, which the commander of the Perry had kindly sent him by the lieutenant, informing him that a report had been circulated, that the American brigantine Louisa Beaton, which vessel was lying at Ambriz, in company with the British and American cruisers, on the 7th instant, had shipped a cargo of negroes. He had observed the Louisa Beaton weigh from Ambriz on the evening of the 12th instant, and pass close to the stern of the Perry, with her colors flying; and at sunset she was observed by him, close in with the land. He also sighted her next morning, and continued to see her until the evening, apparently working in-shore to the southward. As the wind had been exceedingly light all night, he thought it possible that the steamer might overtake her, and accordingly proposed to the lieutenant of the Perry to accompany him, and watch the proceedings of the vessel, in case they should discover her. The lieutenant having acceded to this proposal, he steamed to the westward for nearly forty miles, but saw nothing of her; and was of opinion, that the report affecting the character of the Louisa Beaton was not _then_ correct, and that when intelligence next arrived from Loanda, she would be found to have reached that place. But he believed it very probable that she had been disposed of by sale, in consequence of the slave-dealers not having been successful, as they had effected the embarkation of only two cargoes of negroes that year (1850), and therefore all the vessels that could be procured, no matter at what expense, would be eagerly sought after. But, as he had heard that there was no water at Ambriz, he had supposed it possible that arrangements were making for the Louisa Beaton’s cargo to be discharged at Loanda; whence, after having procured the necessary articles and fitments required, she would probably return to Ambriz for the negroes. He remarked that this would be no new occurrence, as many American vessels had been disposed of in a similar manner, and escaped with cargoes of Africans, since he had been stationed on the coast. Had no American man-of-war been present on the 12th instant, when the Louisa Beaton left Ambriz, he should have considered it his duty (from there having been observed, whilst in company with her on the 7th instant, a large quantity of plank, sufficient for a slave-deck, on her upper deck, together with water-casks, which would have created suspicion) to have visited her, and satisfied himself that her nationality had not been changed, by _sale_, at Ambriz; not taking it for granted, that the flag displayed by any vessel is a sufficient evidence of her nationality.