On the 17th of May, the Perry took final leave of St. Paul de Loanda, leaving a letter addressed to the commander of any U. S. cruiser on the coast, and receiving from the British commissioner, a letter expressing his views on the subject of the slave-trade, and of the agencies in operation for its suppression. After cruising a day or two off Ambriz, she bid adieu to the south African coast, and made all sail for the island of St. Helena. The letter addressed to the commander of any U. S. cruiser, was to the following purport: “Nothing has occurred to interrupt the cordial and harmonious co-operation with the British men-of-war, during the present cruise on the southern coast. “The agent of the American House at Loanda asserts, that the presence of our cruisers has had a salutary effect upon his interests. Formerly there were many vexatious detentions in the clearance of vessels, prohibitions of visiting vessels, &c., which are now removed. Having no consul on the coast, he says that the interests of the House are liable to be jeopardized on frivolous pretexts, in case that a man-of-war is known to be withdrawn for any length of time.” The letter of Sir George Jackson, the commissioner, received on leaving Loanda, says: “I have the honor to acknowledge the receipt of your letter of the 7th instant, in which, referring to my official position and long residence here, you request my opinion on the past and present state of the slave-trade, and of the measures respectively adopted for its suppression. “From the time I left your magnificent and interesting country, I have been mostly engaged as H. M. commissioner in the mixed courts at Sierra Leone, Rio de Janeiro, and for the last five years nearly, at this place; but in all that long period, the present is the first occasion when I could have answered your inquiry with any satisfaction. When you did me the honor of calling upon me, on your first arrival here, in March, 1850, I welcomed you with those feelings of pleasure, which the recollection of kindnesses received in your country will ever excite in my breast at the sight of an American; but I was far from anticipating those benefits, in a public point of view, in a cause in which we both take so deep an interest, which, I am happy to say, have resulted from your appearance, and that of other vessels of the U.S. Navy, on this coast, which soon followed you. During the four years preceding your arrival, I did not see, and scarcely heard of one single American officer on this station. The Marion and the Boxer did, indeed, if I recollect right, anchor once or twice in this harbor, but they made no stay in these parts. What was the consequence?