Mr. Justice GRIER.

. The .collision, which is the subject of inquiry in this suit, took place, in the narrows, inBoston -harbor, bétwee.n Lovell’s island and Gallup island.

The libellants are oivners of the schooner Empire, and the appellants of the ship Marcellus, The schooner was' going out, the ship coming into Boston harbor. They were sailing in opposite courses, through a channel of about three hundred and sixty feet.

The libellants charge in their libel, that the- collision was wholly attributable to the carelessness and' negligence of those in the ship. They.allege that the wind, just before and at' the time of the collision, was south-southw'est; that the schooner wassailing on the western side.of the channel,’close-hauled on the’wind, with her starboard 'tacks aboard, and with all or 'nearly, all her -sails set; that she was steering- southeast' by south; working up to the wind, • in order to give the ship as muqh room as possible; that .the ship was sailing up the channel at great speed and with the wind free, so that she' might have passed thé schooner on the larboard side without-difficulty; that as the'ship approached towards the point of danger, the schooner hailed her to keep off; that the hail Was answered frond the ship, requiring the schoonei’.to luff, which was impossible, as she was already- close to the wind ;• that the schooner did not change her-course, .but that.the ship,'imm¿diately after she. hailed the schooner, luffed, and instantly ran into the schooner, and presently both vessels drifted to the leeward shore.

*417 In their answer, the respondents admit that the collision occurred at the time specified in. the libel, and that the ship was running free on her larboard tack,- but allege that the collision took place on the easterly side of the channel, and that every possible precaution was taken by the ship, by hailing and otherwise, to prevent the .vessels from coming in contact. Their, theory is, that it was occasioned entirely through the fault and mismanagement of those in charge of the schooner, and accordingly allege that' the wind at the time of the collision was southwest; that the ship between six and seven o’clock was sailing along the leeward edge of the channel, hugging the shore as close as it was possible for her to do with safety; that while so passing, the schooner was discovered some distance ahead coming, down the harbor with a free wind, and appearing at first to be going to the windward of the ship, ar. she should and might easily have done, but that she afterwards changed her course as if going to the leeward, and when sh^ had approachéd within á short distance of the ship, luffed across her bows, resulting in a violent collision, sinking the schooner and damaging-the'hull, rigging, and spars of the ship,, for which they pray they may be allowed.

The only question proposed by these pleadings is one oF fact. In this, as in all other cases of the kind, there is great discrepancy and conflict in the testimony of the witnesses, as to'every averment in the pleadings. "We have had occasion to remark more than once, that, when both courts below have concurred in the decision of questions of fact under such circumstances, parties ought not to expect this' court to reverse such a decree, merely by raising a doubt founded on the number or credibility of witnesses. The appellant in such case has all. presumptions against him, and the burthen of proof cast on him tp prove affirmatively some mistake made -by the judge below, in the law or in the evidence. It will not do to show that on one theory, supported by some witnesses, a different decree might have been rendered, provided there be sufficient’ evidence to be found on the record to establish the one that was rendered.

When the wind is southwest, it is the general rule that ves *418 seis going out shall keep to the windward side of the channel, and the vessels coming in the leeward. The witnesses, who could know best, testify, that throughout the passage down the narrows the schooner was kept close to the wind, and was not suffered to fall off, and did not luff at all. Others may have formed erroneous judgments. But if their testimony be untrue, they .must have wilfully perverted the' truth. It is a com7 mon mistake to attribute the motion of one of two passing bodies to the other. Calculations of time and distance, resting on-the loose recollections of witnesses, can seldom be relied upon with much confidence.- The collision took place in the evening, when it was not quite dark, The testimony of three of the ship’s crew concurs with that of witnesses on the schooner, in establishing the state of facts as alleged in the-libel;

.The' pilot of the. ship hád observed the approach of the schooner, and directed the mate to go forward and-see- how .she was standing. Tie did so;.:and observing that the scliooper was heading to windward of the ship, he responded to-the-order: “all right, she. is going to windward;’’-but in a short time was ..heard to say : “luff, hard-down, hard7down, luff,” which were the first words'heard by the man at-the .wheel; the pilot repeated the'words, “hard-down, luff.” The wheel was let down, or nearly so, when' the order was changed to “hard-up;” but before this last order could have any effect, the collision took place.

Another, of the'ship’s crew- gives a similar account, with some difference: that the mate'of the ship called out to the schooner “to luff;” and repeating the command to them, “you must luff" heave her hard-down.” During this colloquy, the ship . luffed, as the witness supposed, in consequence of the pilot.having made the mistake, of supposing the mate’s order “to. luff” was directed to. him.-

The collision was attributed by some on the ship to the fact, that, the mate “bothered” the pilot. This testimony,- on the -part of the-crew of the ship,. corroborates, that of the officers, and crew of the schotíhér. 'Without any .further attempt-to vindicate the correctness of the decree, .by a minute comparison of the testimony, it is sufficient to say, that the weight of *419 the testimony is on the side of the charges in the libel, and supports the decree of the court below, which is therefore affirmed.