mentioned sails of the foremast, without any considerable loss.

29. In consequence of this stealing of the wind by one sail from another, a ship will sail faster with a side wind than with a direct one. For with a side wind all the sails may be crowded; because they all turn their sides to one another, without one standing in the way of the other, or stealing the wind from it.

30. With a side wind likewise the sails are stretched tighter against the wind, which somewhat compresses it, and impels it to that part where it ought to blow; whereby it receives some additional strength. The most favourable wind however is that which blows half way between a fore wind and a side one.

31. The mainsail of the bowsprit can scarcely ever be useless; for, as it collects all the wind that blows. everywhere round the sides of the ship and beneath the other sails, it does not suffer from being robbed.

32. In the motion of winds in ships, both impulse and direction are regarded. But direction by the rudder does not much belong to the present inquiry, except so far as it is connected with the motion of winds in the sails.

Transition.

As the motion of impulse is greatest at the head, so the motion of direction is greatest at the stern. And therefore the mainsail of the mizenmast contributes most thereto, and supplies an auxiliary power to the rudder.

33. The mariner's compass being divided into thirtytwo points, and each semicircle containing sixteen, a vessel may sail straight forward (without tacking, as is

usual when the winds are directly contrary), even though of these sixteen points ten are opposite, and only six favourable; but this navigation greatly depends on the mainsail of the mizenmast. For the points of the wind which are contrary to the ship's course, being the stronger and beyond the control of the helm alone, would turn the other sails together with the ship itself into the contrary direction; did not this sail, being tightly stretched, act the other way, and by favouring and strengthening the motion of the helm, turn and bring round the head of the vessel to its right course.

34. All wind in the sails somewhat weighs down and sinks the ship; and this the more, as the wind comes more from above. And this is the reason why in heavy storms they first lower the yards, and furl the topsails; and then, if it is necessary they take down all the rest, cut down the masts themselves, and throw overboard their cargo, guns, &c., to lighten the ship, that she may float and follow the motion of the waves.

35. With a fresh and favourable breeze, a merchant vessel may sail 120 Italian miles in twenty-four hours, by means of this motion of the winds; and some packet boats called caravels, built entirely for speed, will accomplish a still greater distance. When the winds are directly contrary, they have this last but feeble resource to make some way; which is, they proceed sideways, according as the wind will permit, out of their course, and then by an angular movement they bear up again into it; and continuing this mode of progression (which is slower than that of the serpent, for serpents make folds, whereas they make angles), they will perhaps contrive to make 15 miles in twenty-four hours.

Major Observations.

1. The motion of winds in the sails of vessels has three principal heads and fountains of impulse, from whence it springs. From these likewise we may derive rules for increasing and strengthening it.

2. The first source is from the quantity of wind received. For no one doubts that much wind contributes more than little; and therefore a quantity of wind must be carefully procured. This we shall do, if like prudent stewards we are economical and guard against robbery. Therefore, as far as possible, take care that no wind is lost, wasted, or stolen.

3. The wind blows either above the ship's sides, or below them as far as the level of the sea. And as provident men are very careful even about the smallest matters (for there is no one who does not care for the larger ones); so we must first observe these lower winds, though indisputably they are less powerful than the higher ones.

4. With regard to the winds that play chiefly about the sides and under the sails of ships, it is clearly the business of the mainsail of the bowsprit, which is bent low and slanting, to catch them, and so prevent any loss or waste of wind. And this is both a help in itself, and yet it does not hinder the winds which supply the other sails. On this point I do not see how human industry can improve; unless perhaps the same kind of low sails were to be used as feathers or wings from the centre of the ship; two on each side, when the wind blows straight from behind.

5. With regard to the prevention of robbery of the foresails by the backsails, in sailing straight before the

wind (for with a side wind all sails co-operate), I do not see what human care can do; unless it be to make a kind of ladder of sails; in which the sails of the mizenmast should hang lowest, those of the mainmast next, and those of the foremast highest. For in this way one sail would not hinder but rather assist another, by passing on and transmitting the wind. Let these observations then suffice for the first fountain of impulse.

6. The second fountain of impulse springs from the manner in which the wind strikes the sail. For if by reason of the contraction of the wind the blow be sharp and quick, the motion will be greater; but if it be dull and feeble, the motion will be less.

7. And in relation to this, it is of very great importance that the sails should only have a moderate swell and extension. For if they be stretched tight, they act like a wall to repel the wind; if they be slack, they make the impulse feeble.

8. With regard to this, in some things human industry has acquitted itself well, though rather by accident than by judgment. For in a side wind they draw in as much as possible the part of the sail opposite to the wind; and thereby they drive the wind to that part where it ought to blow. This indeed they do intentionally. But another effect (which perhaps they do not see) is, that the wind is more contracted and makes the impulse sharper.

9. I do not see what human industry can add to this part; unless it be to alter the shape of the sails, and make some of them to swell, not spherically but in the shape of a spur or triangle with a yard or pole in the vertical angle; so that the wind may be contracted

more to a point and the external air may be cut more powerfully. And this angle in my opinion ought not to be acute, but like a triangle with the vertex cut off to make it wide. Nor do I know what advantage there might be in having a sail within a sail; that is, in inserting in the middle of a large sail a kind of purse, not altogether slack of simple canvass, but with ribs of wood, so as to catch the wind in the middle of the sail and draw it to a point.

10. The third fountain of impulse depends on the place where the percussion is made, and is of two kinds. For the impulse is stronger and easier at the fore part of the vessel than at the hinder; and from the upper part of the masts and sails than from the lower.

11. Neither has this escaped the industry of man; for both in sailing before the wind they put the greatest stress on the sails of the foremast, and in calms they do not neglect to spread their top-gallantsails. Nor can I think at present of any further improvement open to human industry in this point; unless it be, in the first case, to put in two or three foremasts, (the centre one upright, the others inclined) with sails hanging forward; and in the second case to broaden the top-gallantsails of the foremast, and make them less pointed than usual. But in both cases there should be great care not to sink the ship too much.

The Motion of Winds in other Machines of Human Invention.

1. There is nothing very intricate in the motion of windmills, but yet it is not generally well demonstrated or explained. The sails stand right opposite the wind that is blowing; one side however turning more to the