7. It is likewise everywhere observed that waters somewhat rise and swell before storms.

8. The thin subterraneous air which escapes at different spots is not perceived on land till it is collected into wind, by reason of the porous nature of the earth. But when it rises from below the waters it is perceived immediately from a certain swelling of the waters, by reason of their continuity.

9. It has been before observed that hollow and cavernous districts have their attendant winds; so that these would certainly appear to have their local origins from the earth.

10. On large rocky mountains the winds are found to blow both sooner (that is, before they are perceptible in the vallies), and more frequently (that is when there is a calm in the vallies); but all mountains and rocks are cavernous.

1

11. Gilbert observes that in Derbyshire in England, a mountainous and rocky district, there are such strong eruptions of winds from some caverns, that articles of dress or rags thrown into them are blown back again with great violence, and carried up a great height into the air.

12. At Aber Barry on the Severn in Wales, there is a rocky cliff filled with holes, to which if a man apply his ear he will hear various sounds and murmurs of subterranean blasts.

Indirect Phenomenon.

Acosta has observed with respect to the towns of Plata and Potosi in Peru, which do not lie far apart from one another, and are both situated on high and mountainous ground, so that there is no difference in this point; that nevertheless the temperature of Potosi is cold and wintry, while that of Plata is mild and spring-like.' This may perhaps be owing to the silver mines near Potosi; which proves that there are vents for hot and cold blasts from the earth.

13. If the earth be the original source of cold, as Parmenides maintained (an opinion not to be despised, seeing that cold and density are closely united) 3; it is not less probable that warm exhalations should be thrown up from the central cold of the earth, than that they should be thrown down from the cold of the upper air.

14. It is said by some of the ancients that there are certain

The Latin has Denbigh; but the true reading is preserved in Gilbert: Derbiæ. 2 Acosta, Hist. des Indes, ii. 13. 3 Arist. Metaph. i. 5.

wells in Dalmatia and the country of Cyrene, into which if a stone be thrown, storms will soon arise; as if the stone broke through some covering in a place where the winds were confined.

menon.

Indirect Pheno- Etna and many other mountains vomit forth flames; and it is probable that air may break out in the same way, especially being expanded and set in motion by subterranean heat.

15. Upon earthquakes, certain foreign and noxious winds are observed to blow, both before and after the shock; just as a light smoke is commonly emitted before and after great conflagrations.

Admonition. Air confined in the earth is forced out by many causes. Sometimes a badly cemented mass of earth falls into a hollow; sometimes the waters ingulf themselves in the earth; sometimes the air is expanded by subterranean fires and requires greater space; sometimes the earth, which was before firm and vaulted, is reduced to ashes by internal fire, and being no longer able to support itself falls in. And there are many other similar causes.

So much then for the inquiry concerning the first local origin of the winds, namely, from under the earth. I come now to the second origin; namely, from on high, or from what is called the middle region of the air.

Admonition. Let no one misinterpret my words into a denial that the other winds may likewise be generated from vapours both of land and sea. But this I have mentioned is the first kind of winds which spring from the earth as winds ready formed.

16. It has been observed that woods begin to rustle before winds are manifestly perceived 2; whence it is conjectured that wind descends from above. This is likewise remarked on mountains (as I have mentioned before), but the cause is less certain by reason of the hollows therein.

17. The shooting and twinkling of stars foretels wind from that quarter where the shooting is seen 3; which shows that the air is disturbed above, before the motion reaches us.

18. The clearing of the sky and dispersing of the clouds

Pliny, ii. 44.

Arist, Prob. xxvi. 25.; and Cf. Pliny, xviii. 80.

2 Ibid. xviii. 86.

foreshadow winds, before they are felt on the earth; which likeprove that winds commence above.

wise

19. Before the rising of a wind, the lesser stars are not visible, even on a clear night'; the air apparently being condensed, and made less transparent by the matter which is afterwards turned into winds.

20. Halos round the moon, a blood-red sunset, a red moon on her fourth rising, and many other prognostics of winds derived from above (whereof I will treat in their proper place), indicate that the matter of winds is there commenced and prepared.

21. In these phenomena you may remark the difference already mentioned between the two ways whereby winds are generated above; namely, before and after the collection of vapours into cloud. For the prognostics from halos and the colours of the sun and moon have some cloudy matter; but the shooting and obscuration of the smaller stars take place in a clear sky.

22. When wind proceeds from a formed cloud, the cloud is either totally dissipated and turned into wind; or it is divided partly into rain, and partly into wind; or it is rent asunder, and the wind bursts forth as in a storm.

23. Many indirect phenomena may be observed in nature of the repercussion by cold. Wherefore, since the cold in the middle region of the air is plainly very intense, it is evident that vapours cannot for the most part penetrate those regions, but must be either congealed or hurled back again. And this was the opinion of the ancients, which in this instance is sound.

The third local origin of winds is in the case of those which are generated in the lower air; to which likewise I give the name of swellings or overcharges of the air. It is a thing very common and familiar, but yet hitherto passed over in silence.

Speculation. The generation of those winds which are stirred in the lower air is nothing more mysterious than this. The air newly created from water and rarified and resolved vapours, being united to the former air, can no longer be confined within the same limits as before, but swells and rolls onwards and oc

1 Pliny, ubi surpà.

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.