Factories or agencies are maintained on the African coast, where the vessels obtain their living freight. The captains seldom go on shore except for purpose of observation. Each vessel generally takes with her from New York a Spaniard to transact the business. The complement being obtained, it only remains to get away and beyond the cruisers. The action of the Federal government, some years since, in relation to the visitation of vessels, has been effectual in impairing the energy of the British squadron, which has been maintained on the coast of Africa, pursuant to the treaty of Washington. As for the American squadron, it never co-operated heartily in the matter of suppressing the slave-trade; and the vessels were generally absent for the purpose of obtaining coal, or for repairs, whenever there was opportunity of making a capture. But the capitalists of New York do not depend entirely upon these precautions. Their vessels are occasionally taken; and then the men on board must be protected, or they will disclose everything. Not only are appliances used to make an examination result in a discharge, but a corps of attorneys is kept under pay to defend those who fall within the clutches of the law. The impunity which has attended these men is notorious. CAPTAIN LATHAM. Some time ago the brig Cora was captured at sea and brought by a prize crew to the port of New York. Her commander, Captain Latham, was incarcerated in Eldridge-street jail. Hendrickson, the mate, was, however, permitted to communicate to his friends on shore, who procured a boat, pulled quietly to the side of the brig, received him on board, and took him ashore. His clothing and other property were conveyed to the office of the marshal, and he was not only permitted to go and take them away, but to visit his acquaintances in Eldridge-street jail. It was an easy matter to arrest him, but the marshal remarked to an associate that he did not care how the man made his money.