There devolves on me the painful duty of reporting to you a wanton act of aggression on this ship by the United States war screw-steamer _San Jacinto_, carrying a broadside of seven guns, and a shell pivot-gun of heavy calibre on the forecastle, which took place on the 8th instant, in the Bahama Channel, abreast of the Paredon lighthouse. The _Trent_ left Havana at 8 a.m. on the 7th instant, with Her Majesty’s mails for England, having on board a large freight of specie, as well as numerous passengers, amongst whom were Messrs. Mason and Slidell, the former accredited with a special mission from the Confederate States to the Government of Great Britain, and the latter to the French Government, with their respective secretaries, Messrs. McFarland and Eustis. Shortly after noon, on the 8th, a steamer, having the appearance of a man-of-war, but not showing colours, was observed ahead, hove to; we immediately hoisted our ensign at the peak, but it was not responded to until, on nearing her, at 1.15 p.m., she fired a round shot from her pivot-gun across our bows, and showed American colours. Our engines were immediately slowed, and we were still approaching her, when she discharged a shell from her pivot-gun immediately across our bows, exploding half a cable’s length ahead of us. We then stopped, when an officer with an armed guard of marines boarded us and demanded a list of passengers, which demand being refused, the officer said that he had orders to arrest Messrs. Mason, Slidell, McFarland, and Eustis, and that he had sure information of their being passengers in the _Trent_. Declining to satisfy him whether such persons were on board or not, Mr. Slidell stepped forward, and announced that the four persons he had named were then standing before him, under British protection, and that if they were taken on board the _San Jacinto_, they must be taken _vi et armis_; the commander of the _Trent_ and myself at the same time protesting against this illegal act, this act of piracy, carried out by brute force, as we had no means of resisting the aggression, the _San Jacinto_ being at the time on our port beam, about 200 yards off, her ship’s company at quarters, ports open, and tompions out. Sufficient time being given for such necessaries as they might require being sent to them, these gentlemen were forcibly taken out of the ship, and then a further demand was made that the commander of the _Trent_ should go on board the _San Jacinto_, but as he expressed his determination not to go, unless forcibly compelled likewise, this latter demand was not carried into execution. At 3.40 we parted company, and proceeded on our way to St. Thomas, on our arrival at which place I shall deliver to the Consul duplicates of this letter to Lord Lyons, Sir Alexander Milne, Commodore Dunlop, and the Consul-General at Havana. I have, etc., (Signed) RICHARD WILLIAMS, _Commander, R.N._