cupies a larger space. But here we must assume two things. First, that a drop of water turned into air (whatever stories they may tell of the decimal proportion of the elements) requires at least a hundred times more space than before; and secondly, that a little new air in motion, when superadded to the old, stirs and puts the whole in motion. And this may be seen by the draught from a pair of bellows or a crack in the window, which will set the air of the whole room in motion, as the flame of the candles will directly show.

24. As dews and mists are generated in the lower air, without being turned into clouds or penetrating into the middle region; so it is with many of the winds.

25. There is a continual breeze playing on seas and waters, which is only a slight wind newly generated.

26. The rainbow, which is the lowest of the meteors and generated nearest the earth, when it does not appear entire, but broken and only with the ends visible, is resolved into winds, as much if not more than into rain.

27. It has been observed that in countries which are divided and separated by the interposition of mountains some winds that are common on one side of the range do not reach the other. This manifestly shows that they are generated below the tops of those mountains.

28. There is an infinite variety of winds, which blow in clear weather, and even in countries where it never rains, that are generated where they blow, without ever having been clouds or reaching to the middle region of the air.

Indirect Phenomena.

Any one who knows how easily vapour is resolved into air, how great is the quantity of vapours, and how much greater space a drop of water occupies when turned into air than it did before (as has been mentioned above), and how little compression the air bears, will feel certain that winds must be generated everywhere, from the surface of the earth to the highest parts of the atmosphere. For a large quantity of vapour, when it begins to expand, cannot possibly rise to the middle region of the air without surcharging the air and producing disturbance on the way.

1 Gilbert, Phys. iv. 1.

With reference

to the 9th Article of Inquiry. Transition.

Accidental Generations of Winds.

Accidental generations of winds are those which do not produce or create an impulsive motion, but either excite it by compression, or drive it back by repercussion, or roll and agitate it by curves. And this is effected by external causes, and the position of contiguous bodies.

1. There is more agitation of the air and sensation of winds in places where there are low hills surrounded by vallies with a higher range of hills beyond, than either on mountains or plains.

2. Winds and draughts are felt in towns where there is any wide place with narrow outlets or passages, and at the corners of streets.

3. Ventilation is produced or arises naturally in houses, where there is a thorough draught, the air going in at one side and out at the other. But it is done more effectually, if the air enters from different sides, meets in angles, and has a common outlet at the meeting-place. Arched and circular dining rooms are cooler likewise, because the air which is stirred in them is reflected in all directions. Curved porticoes are better than straight ones; for a wind in a straight line, though it is not confined but has a free outlet, yet does not make the air so unequal, voluminous, and undulatory, as the meeting in angles, the windings about and collections in a round space, and the like.

4. After great storms at sea the accidental wind lasts for a time after the original wind has settled. And this is caused by the collision and percussion of the air from the undulation of the waves.

5. In gardens the wind is commonly found to be repelled by walls, buildings, and mounds; so that one would think it blew in a contrary direction to that in which it really blows.

6. If one side of a country is surrounded by hills, and a wind blow for a long time from the plain to the hills, this wind being repelled by the hills is either condensed into rain, if it be a moist wind, or changed into a contrary wind, which however is of no long continuance.

7. In weathering headlands sailors often experience a change of wind.

With refer

ence to the 10th Article

Transition.

Extraordinary Winds and Sudden Gusts.

Some writers give opinions and reasons touching of Inquiry. extraordinary winds, as hurricanes or storms, whirlwinds, typhoons, and siroccos; but they give no description of the thing itself, which certainly is to be sought from journals and scattered history.

1. Sudden gusts never come in a clear sky, but only when it is cloudy and with rain; so that there is rightly thought to be an eruption, with a discharge of the wind and a concussion of the water.

2. Those storms attended with cloud and fog, called "belluæ," which rise up like pillars, are very violent and dangerous

at sea.

3. The greater typhoons, which extend over some considerable space and carry things up into the air along with them, seldom occur; but the lesser and as it were playful eddies and whirlwinds are common.

4. All storms, typhoons, and greater whirlwinds, have a manifest motion of precipitation or vibration downwards, more than the other winds. And hence they appear to rush like torrents, and to flow down as in channels, and to be then repelled by the earth.

5. It sometimes happens that in meadows haycocks are carried up into the air, and then spread abroad like a cover over the field. Again, bundles of pea-straw, sheafs of corn, and linen hung out to dry, are lifted as high as the tops of trees or above the tops of houses by whirlwinds; and all this is done without any great force or violence of wind.

6. Sometimes these very slight and partial whirlwinds take place even on a clear day; so that a person riding may see dust or straws caught up and whirled round near him without feeling much wind. This is doubtless caused by contrary breezes mutually repelling one another, and making a circulation of air by the concussion.

7. It is certain that there are some blasts which leave behind them on plants manifest traces of burning and scorching. But the sirocco, which is an invisible lightning and a burning air without flame, is referred to the inquiry on lightning.

Things Contributing to Winds, that is, the Original; for of Accidental Winds it has been inquired above.

With reference

to the 11th,

12th, 18th, 14th,

and 15th Articles of Inquiry. Transition.

The ancients have given a very confused and uncertain account of the winds and their causes, and mostly not true. But no wonder that those who do not look close do not see clearly. They talk as if wind were something else, different from air in motion; and as if exhalations generated and composed the whole body of winds; and as if the matter of winds were only a hot and dry exhalation'; and as if the origin of the motion of winds were only an expulsion and repercussion from the cold of the middle region; all which things are mere arbitrary and imaginary suppositions. But yet from these threads, which are indeed but cobwebs, they weave large webs, Whereas in reality every impulse of the air is a wind; exhalations mixed with the air contribute more to the motion, than to the matter of the winds; moist vapours are by a well proportioned heat turned into wind more easily than dry exhalations; and many winds, besides those which are driven down and repelled from above, are generated in the lower region of the air, and exhale from the earth. Let us observe what is the language of the things themselves.

1. I have mentioned in the article on general winds, that the natural rotation of the air, without any other external cause, generates a perceptible wind within the tropics, where the air revolves in larger circles.

2. Next to the natural motion of the air, before inquiring concerning the sun, which is the principal parent of the winds, we must observe whether anything be due to the moon and other stars, upon clear experimental evidence.

3. Great and violent winds arise some hours before an eclipse of the moon; so that if the moon is eclipsed at midnight, there are winds the evening before; but if in the morning, there are winds at midnight.

4. Acosta observes that in Peru, which is a very windy country, there is most wind at the full moon.2

Injunction.

It would be well worth observing, what effect the motions and changes of the moon have upon the winds, for they certainly influence the waters. For instance, whether the winds like the tides are not somewhat higher at the full and new moon, than in the quarters. For though it may be a convenient theory, that the moon has dominion over the waters, and the sun and stars over the air; yet it is certain that water and air are very homogeneous bodies, and that next to the sun, the moon has the greatest power in every thing here below.

5. Greater winds are observed to blow about the time of the conjunctions of planets.

6. Winds and stormy weather are frequent at the rising of Orion; but we should observe whether this does not proceed from the rising of that constellation at a time of year most generative of winds; so that it would be rather a concomitant than a cause. And a similar doubt might justly be raised respecting the rains at the rising of the Hyades and Pleiades, or the storms at the rising of Arcturus. And so much with regard to the moon and stars.

7. The sun doubtless is the primary efficient of many winds, as by its heat it operates upon two kinds of matter; namely, the body of the air, and vapours or exhalations.

8. The sun, when powerful, expands air, though pure and entirely unmixed, perhaps as much as one-third, which is no trifling difference. From this simple expansion therefore some wind must arise in the sun's paths, especially during great heats; and that rather two or three hours after sunrise than at daybreak.

9. In Europe, the nights are more sultry; in Peru, the three first hours of the morning 2; both from the same cause, namely, the cessation of winds and breezes at those hours.

10. In a water thermometer dilated air depresses the water as with a blast; but in a glass filled only with air and capped with a bladder the dilatation of the air blows out the bladder perceptibly, like a wind.

11. I made an experiment of this kind of wind in a round tower that was completely shut up on every side. A chafing dish of coals thoroughly ignited so that there might be no

1 Arist. Problem. De Ventis, 14.

Acosta, Hist. des Indes, ii. 13.