The inclosed letter, above referred to, stated that American seamen were often enticed on board of slavers, without knowing their real character until it was too late to leave them. And that the owner of a lodging-house in Rio, where two or three sailors were boarding, offered, on one occasion, to get them a ship bound to the United States, which, at the time, was loading at Vittoria--a harbor to the northward of Cape Frio. They agreed to ship; and, after receiving their advance, proceeded in a small steamer outside the harbor of Rio, when they were transferred to a schooner, in company with a number of Brazilians; and, in a few days, reached Vittoria. On joining the slaver, which was named “Pilot,” they discovered her true character, but were not allowed to go on shore; and were promised, on their arrival in Africa, a good reward, with the option of returning in the vessel, or having their passage found in another. It was affirmed that these men had never seen the American consul; and the crew-list, register and other papers, were forgeries. Also that the owner of the Pilot was a Brazilian, and esteemed one of the richest men in the empire. Two slave-steamers were owned by him; and it was said that he had boasted that not a week passed that he had not had a full cargo of slaves landed on the coast. He then owned seven or eight vessels, sailing under the American flag, which he had bought in Rio, and whose papers were all forgeries. One of the vessels belonging to the rich Brazil merchant, and sailing alternately under the American and Brazilian flag, had made nine clear voyages; and on the last voyage, before she was captured, the American captain had landed at Ambriz, with part of his crew, his flag and papers; and then the vessel shipped one thousand slaves. An American was the consignee of these vessels, bearing his country’s flag. He obtained for them masters, crews, flag and papers; and received for his agency a percentage on all slaves landed from the vessels. During the month when the Pilot was equipped at Vittoria, two other slavers were also fitting out for the slave-trade, under the American flag; viz., the “Casco” and the “Snow.” The former was afterwards captured, with four hundred and fifty slaves, by the English steamer “Pluto;” the other entered the harbor of Rio under Brazilian colors, having landed her slaves outside.