CHAPTER VI.. Problems of Rain, Wind, and Other Weather.

PROBLEMS OF RAIN, WIND, AND OTHER WEATHER.

A. What is the original cause of rain? And how is it generated?

B. The motion of the air (such as I have described to you already) tending to the disunion of the parts of the air, must needs cause a continual endeavour (there being no possibility of vacuum) of whatsoever fluid parts there are upon the face of the earth and sea, to supply the place which would else be empty. This makes the water, and also very small and loose parts of the earth and sea to rise, and mingle themselves with the air, and to become mist and clouds. Of which the greatest quantity arise there, where there is most water, namely, from the large parts of the ocean; which are the South Sea, the Indian Sea, and the sea that divided Europe and Africa from America; over which the sun for the greatest part of the year is perpendicular, and consequently raiseth a greater quantity of water; which afterwards gathered into clouds, falls down in rain.

A. If the sun can thus draw up the water, though but in small drops, why can it not as easily hold it up?

B. It is likely it would also hold them up, if they did not grow greater by meeting together, nor were carried away by the air towards the poles.

A. What makes them gather together?

B. It is not improbable that they are carried against hills, and there stopt till more overtake them. And when they are carried towards the North or South where the force of the sun is more oblique and thereby weaker, they descend gently by their own weight. And because they tend all to the centre of the earth, they must needs be united in their way for want of room, and so grow bigger. And then it rains.

A. What is the reason it rains so seldom, but snows so often upon very high mountains?

B. Because, perhaps, when the water is drawn up higher than the highest mountains, where the course of the air between the equator and the poles is free from stoppage, the stream of the air freezeth it into snow. And it is in those places only where the hills shelter it from that stream, that it falls in rain.

A. Why is there so little rain in Egypt, and yet so much in other parts nearer the equinoxial, as to make the Nile overflow the country?

B. The cause of the falling of rain I told you was the stopping, and consequently the collection of clouds about great mountains, especially when the sun is near the equinoxial, and thereby draws up the water more potently, and from greater seas. If you consider therefore that the mountains in which are the springs of Nile, lie near the equinoxial and are exceedingly great, and near the Indian Sea, you will not think it strange there should be great store of snow. This as it melts makes the rain of Nile to rise, which in April and May going on toward Egypt arrive there about the time of the solstice, and overflow the country.

A. Why should not the Nile then overflow that country twice a year, for it comes twice a-year to the equinoxial.

B. From the autumnal equinox, the sun goeth on toward the southern tropic, and therefore cannot dissolve the snow on that side of the hills that looks towards Egypt.

A. But then there ought to be such another inundation southward.

B. No doubt but there is a greater descent of water there in their summer than at other times, as there must be wheresoever there is much snow melted. But what should that inundate, unless it should overflow the sea that comes close to the foot of those mountains? And for the cause why it seldom rains in Egypt, it may be this, that there are no very high hills near it to collect the clouds. The mountains whence Nile riseth being near two thousand miles off. The nearest on one side are the mountains of Nubia, and on the other side Sina and the mountains of Arabia.

A. Whence think you proceed the winds?

B. From the motion, I think, especially of the clouds, partly also from whatsoever is moved in the air.

A. It is manifest that the clouds are moved by the winds; so that there were winds before any clouds could be moved. Therefore I think you make the effect before the cause.

B. If nothing could move a cloud but wind, your objection were good. But you allow a cloud to descend by its own weight. But when it so descends, it must needs move the air before it, even to the earth, and the earth again repel it, and so make lateral winds every way, which will carry forward other clouds if there be any in their way, but not the cloud that made them. The vapour of the water rising into clouds, must needs also, as they rise, raise a wind.

A. I grant it. But how can the slow motion of a cloud make so swift a wind as it does?

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.

B. It will indeed go slower in the proportion of the line A E to the line C E. But the ship will not go so fast as you think sideward: one cause is the force of that wind which lights on the side of the ship itself; the other is the bellying of the sail; for the former, it is not much, because the ship does not easily put from her the water with her side; and bellying of the sail gives some little hold for the wind to drive the ship astern.

A. For the motion sideward I agree with you; but I had thought the bellying of the sail had made the ship go faster.

B. But it does not; only in a fore wind it hinders least.

A. By this reason a broad thin board should make the best sail.

B. You may easily foresee the great incommodities of such a sail. But I have seen tried in little what such a wind can do in such a case. For I have seen a board set upon four truckles, with a staff set up in the midst of it for a mast, and another very thin and broad board fastened to that staff in the stead of a sail, and so set as to receive the wind very obliquely, I mean so as to be within a point of the compass directly opposite to it, and so placed upon a reasonable smooth pavement where the wind blew somewhat strongly. The event was first, that it stood doubting whether it should stir at all or no, but that was not long, and then it ran a-head extreme swiftly, till it was overthrown by a rub.

A. Before you leave the ship, tell me how it comes about that so small a thing as a rudder can so easily turn the greatest ship.

B. It is not the rudder only, there must also be a stream to do it; you shall never turn a ship with a rudder in a standing pool, nor in a natural current. You must make a stream from head to stern, either with oars or with sails; when you have made such a stream, the turning of the rudder obliquely holds the water from passing freely, and the ship or boat cannot go on directly, but as the rudder inclines to the stern, so will the ship turn; but this is too well known to insist upon. You have observed that the rudders of the greatest ships are not very broad, but go deep into the water, whereas western barges, though but small vessels, have their rudders much broader, which argues that the holding of water from passing is the true office of a rudder; and therefore to a ship that draws much water the rudder is made deep accordingly; and in barges that draw little water, the rudders being less deep, must so much the more be extended in breadth.

A. What makes snow?

B. The same cause which, speaking of hardness, I supposed for the cause of ice. For the stream of air proceeding from that both the earth and the sun cast off the air, consequently maketh a stream of air from the equinoxial towards the poles, passing amongst the clouds, shaving those small drops of water whereof the clouds consist, and congeals them as they do the water of the sea, or of a river. And these small frozen drops are that which we call snow.

A. But then how are great drops frozen into hailstones, and that especially (as we see they are) in summer?

B. It is especially in summer, and hot weather, that the drops of water which make the clouds, are great enough; but it is then also that clouds are sooner and more plentifully carried up. And therefore the current of the air strengthened between the earth and the clouds, becomes more swift; and thereby freezeth the drops of water, not in the cloud itself, but as they are falling. Nor does it freeze them thoroughly, the time of their falling not permitting it, but gives them only a thin coat of ice; as is manifest by their sudden dissolving.

A. Why are not sometimes also whole clouds when pregnant and ready to drop, frozen into one piece of ice?

B. I believe they are so whensoever it thunders.

A. But upon what ground do you believe it?

B. From the manner or kind of noise they make, namely a crack; which I see not how it can possibly be made by water or any other soft bodies whatsoever.

A. Yes, the powder they call aurum fulminans, when thoroughly warm, gives just such another crack as thunder.

B. But why may not every small grain of that aurum fulminans by itself be heard, though a heap of them together be soft, as is any heap of sand. Salts of all sorts are of the nature of ice. But gold is dissolved into aurum fulminans by nitre and other salts. And the least grain of it gives a little crack in the fire by itself. And therefore when they are so warmed by degrees, the crack cannot choose but be very great.

A. But before it be aurum fulminans they use to wash away the salt (which they call dulcifying it), and then they dry it gently by degrees.

B. That is, they exhale the pure water that is left in the powder, and leave the salt behind to harden with drying. Other powder made of salts without any gold in them will give a crack as great as aurum fulminans. A very great chemist of our times hath written, that salt of tartar, saltpetre, and a little brimstone ground together into a powder, and dried, a few grains of that powder will be made by the fire to give as great a clap as a musket.

A. Methinks it were worth your trial to see what effect a quart or a pint of aurum fulminans would produce, being put into a great gun made strong enough on purpose, and the breech of the gun set in hot cinders, so as to heat by degrees, till the powder fly.

B. I pray you try it yourself; I cannot spare so much money.

A. What is it that breaketh the clouds when they are frozen?

B. In very hot weather the sun raiseth from the sea and all moist places abundance of water, and to a great height. And whilst this water hangs over us in clouds, or is again descending, it raiseth other clouds, and it happens very often that they press the air between them, and squeeze it through the clouds themselves very violently; which as it passes shaves and hardens them in the manner declared.

A. That has already been granted; my question is what breaks them?

B. I must here take in one supposition more.

A. Then your basin, it seems, holds not all you have need of.

B. It may for all this, for the supposition I add is no more but this; that what internal motion I ascribe to the earth, and the other concrete parts of the world, is to be supposed also in every of their parts how small soever; for what reason is there to think, in case the whole earth have in truth the motion I have ascribed to it, that one part of it taken away, the remaining part should lose that motion. If you break a loadstone, both parts will retain their virtue, though weakened according to the diminution of their quantity; I suppose therefore in every small part of the earth the same kind of motion, which I have supposed in the whole: and so I recede not yet from my basin.

A. Let it be supposed, and withal, that abundance of earth, (which I see you aim at), be drawn up together with the water. What then?

B. Then if many pregnant clouds, some ascending and some descending meet together, and make concavities between, and by the pressing out of the air, as I have said before, become ice; those atoms, as I may call them, of earth will, by the straining of the air through the water of the clouds, be left behind, and remain in the cavities of the clouds, and be more in number than for the proportion of the air therein. Therefore for want of liberty they must needs justle one another, and become, as they are more and more straightened of room, more and more swift, and consequently at last break the ice suddenly and violently, now in one place, and by and by in another; and make thereby so many claps of thunder, and so many flashes of lightning. For the air recoiling upon our eyes, is that which maketh those flashes to our fancy.

A. But I have seen lightning in a very clear evening, when there has been neither thunder nor clouds.

B. Yes, in a clear evening; because the clouds and the rain were below the horizon, perhaps forty or fifty miles off; so that you could not see the clouds nor hear the thunder.

A. If the clouds be indeed frozen into ice, I shall not wonder if they be sometimes also so situated, as, like looking-glasses, to make us see sometimes three or more suns by refraction and reflection.

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