the movement by which a vessel is wafted along the surface of the water, by the action of the wind upon her sails.

When a ship changes her state of rest into that of motion, as in advancing out of a harbour, or from her station at anchor, she acquires her motion very gradually, as a body which arrives not at a certain velocity till after an infinite repetition of the action of its weight.

The first impression of the wind greatly affects the velocity, because the resistance of the water might destroy it; since the velocity being but small at first, the resistance of the water which depends on it will be very feeble; but as the ship increases her motion, the force of the wind on the sails will be diminished; whereas, on the contrary, the resistance of the water on the bow will accumulate in proportion to the velocity with which the vessel advances. Thus the repetition of the degrees of force, which the action of the sail adds to the motion of the ship, is perpetually decreasing; whilst, on the contrary, the new degrees added to the effort of resistance on the bow are always augmenting. The velocity is then accelerated in proportion as the quantity added is greater than that which is subtracted; but when the two powers become equal; when the impression of the wind on the sails has lost so much of its force, as only to act in proportion to the opposite impulse of resistance on the bow, the ship will then acquire no additional velocity, but continue to sail with a constant uniform motion. The great weight of the ship may indeed prevent her from acquiring her greatest velocity; but when she has attained it, she will advance by her own intrinsic motion, without gaining any new degree of velocity, or lessening what she has acquired. She moves then by her own proper force in vacuo, without being afterwards subject either to the effort of the wind on the sails, or to the resistance of the water on the bow. If at any time the impulsion of the water on the bow should destroy any part of the velocity, the effort of the wind on the sails will revive it, so that the motion will continue the same. It must, however, be observed, that this state will only subsist when these two powers act upon each other in direct opposition; otherwise they will mutually destroy one another. The whole theory of working ships depends on this counter action, and the perfect equality which should subsist between the effort of the wind and the impulsion of the water.

The effect of sailing is produced by a judicious arrangement of the sails to the direction of the wind. Accordingly the various modes of sailing are derived from the different degrees and situations of the wind with regard to the course of the vessel. See Seaman-ship. To illustrate this observation by examples, the plan of a number of ships proceeding on various courses is represented by fig. 3, which exhibits the 32 points of the compass, of which C is the centre; the direction of the wind, which is northerly, being expressed by the arrow.

It has been observed in the article Close-Hauled, that a ship in that situation will fail nearly within five points of the wind. Thus the ships B and y are close-hauled; the former being on the larboard-tack, steering E. N. E. and the latter on the starboard-tack, failing W. N. W. with their yards a braced obliquely, as suitable to that manner of failing. The line of battle on the larboard-tack would accordingly be expressed by CB, and on the starboard by C y.

When a ship is neither close-hauled, nor steering afore the wind, she is in general said to be sailing large. The relation of the wind to her course is precisely determined by the number of points between the latter and the course close-hauled. Thus the ships c and x have the wind one point large, the former steering E. b N. and the latter W. b N. The yards remain almost in the same position as in B and y; the bowlines and sheets of the sails being only a little slackened.

The ships d and u have the wind two points large, the one steering east and the other west. In this manner of sailing, however, the wind is more particularly said to be upon the beam, as being at right angles with the keel, and coinciding with the position of the ship's beams. The yards are now more across the ship, the bowlines are cast off, and the sheets more relaxed; so that the effort of the wind being applied nearer to the line of the ship's course, her velocity is greatly augmented.

In e and t the ships have the wind three points large, or one point abaft the beam, the course of the former being E. b S. and that of the latter W. b S. The sheets are still more flowing, the angle which the yards make with the keel further diminished, and the course accelerated in proportion.

The ships f and j, the first of which steers E. S. E. and the second W. S. W. have the wind four points large, or two points abaft the beam. In g and r the wind is five points large, or three points abaft the beam, the former failing S. E. b E. and the latter S. W. b W. In both these situations the sheets are still farther slackened, and the yards laid yet more athwart the ship's length, in proportion as the wind approaches the quarter.

The ships h and q, steering S. E. and S. W. have the wind fix points large, or more properly on the quarter; which is considered as the most favourable manner of sailing, because all the sails co-operate to increase the ship's velocity; whereas, when the wind is right aft, as in the ship m, it is evident that the wind in its passage to the foremost sails will be intercepted by those which are farther aft. When the wind is on the quarter, the fore-tack is brought to the cat-head; and the main-tack being cast off, the weather-clue of the main-sail is hoisted up to the yard, in order to let the wind pass freely to the fore-fall; and the yards are disposed so as to make an angle of about two points, or nearly 22°, with the keel.

The ships i and p, of which the former fails S. E. b S. and the latter S. W. b S. are said to have the wind three points on the larboard or starboard quarter: and those expressed by k and o, two points; as steering S. S. E. and S. S. W. in both which positions the yards make nearly an angle of 16°, or about a point and a half, with the ship's length.

When the wind is one point on the quarter, as in the ships l and n, whose courses are S. b E. and S. b W. the situation of the yards and sails is very little different from the last mentioned; the angle which they make with the keel being somewhat less than a point, and the staysails being rendered of very little service. The ship m sails right afore the wind, or with the wind right aft. In this position the yards are laid at right angles with the ship's length: the staysails being entirely useless, are hauled down; and the main-fall is drawn up in the brails, that the fore-fall may operate; a measure which considerably facilitates the steerage, or effort of the helm. As the wind is then intercepted by the main-top-fall and main-top-gallant-fall, in its passage to the fore-top-fall and fore-top-gallant-fall, these latter are by consequence entirely becalmed; and might therefore be furled, to prevent their being fretted by flapping against the mast, but that their effort contributes greatly to prevent the ship from broaching-to, when she deviates from her course to the right or left thereof.

Thus all the different methods of sailing may be divided into four, viz. close-hauled, large, quartering, and afore the wind; all which relate to the direction of the wind with regard to the ship's course, and the arrangement of the sails.