_B._ It is not one or two little clouds, but many and great ones that do it. Besides, when the air is driven into places already covered, it cannot but be much the swifter for the narrowness of the passage. _A._ Why does the south wind more often than any other bring rain with it? _B._ Where the sun hath most power, and where the seas are greatest, that is in the south, there is most water in the air; which a south wind can only bring to us. But I have seen great showers of rain sometimes also when the wind hath been north, but it was in summer, and came first, I think, from the south or west, and was brought back from the north. _A._ I have seen at sea very great waves when there was no wind at all. What was it then that troubled the water? _B._ But had you not wind enough presently after? _A._ We had a storm within a little more than a quarter of an hour after. _B._ That storm was then coming and had moved the water before it. But the wind you could not perceive, for it came downwards with the descending of the clouds, and pressing the water bounded above your sail till it came very near. And that was it that made you think there was no wind at all. _A._ How comes it to pass that a ship should go against the wind which moves it, even almost point blank, as if it were not driven but drawn? _B._ You are to know first, that what body soever is carried against another body, whether perpendicularly or obliquely, it drives it in a perpendicular to the superficies it lighteth on. As for example, a bullet shot against a flat wall, maketh the stone, or other matter it hits, to retire in a perpendicular to that flat; or, if the wall be round, towards the centre, that is to say, perpendicularly. For if the way of the motion be oblique to the wall, the motion is compounded of two motions, one parallel to the wall, and the other perpendicular. By the former whereof the bullet is carried along the wall side, by the other it approacheth to it. Now the former of these motions can have no effect upon it; all the battery is from the motion perpendicular, in which it approacheth, and therefore the part it hits must also retire perpendicularly. If it were not so, a bullet with the same swiftness would execute as much obliquely shot, as perpendicularly, which you know it does not. _A._ How do you apply this to a ship? _B._ Let A B be the ship, the head of it A. If the wind blow just from A towards B, it is true the ship cannot go forward howsoever the sail be set. Let C D be perpendicular to the ship, and let the sail E C be never so little oblique to it, and F C perpendicular to E C, and then you see the ship will gain the space D F to the headward. _A._ It will so; but when it is very near to the wind it will go forward very slowly, and make more way with her side to the leeward.