8. Quicksilver contains a flatulent and expansive spirit, so that (as some maintain) it resembles gunpowder, and a little of it mixed with gunpowder makes the powder stronger. Chemists also say that gold, in certain preparations of it, makes dangerous explosions, almost like thunder. But of these things I have no experience.

A Major Observation.

The motion of winds is in most respects seen in the motions of water, as in a mirror.'

Great winds are inundations of the air, the resemblance of which we see in inundations of the waters; both arising from an increase of quantity.

Waters either descend from above or spring from the earth; and so some winds are driven from above, some rise from below.

Sometimes there are contrary motions in rivers, the tide flowing one way, the stream of the river the other; and yet there is only one motion, because the course of the tide prevails. And so, when contrary winds blow, the greater subdues the less.

In currents of the sea and of some rivers, it sometimes happens that the stream at the top of the water moves in a contrary direction to that below. And so in the air, when contrary winds blow together, one flies above the other.

There are cataracts of rain confined in a narrow space; so are there whirlwinds.

Waters, if disturbed, have an undulating besides a progressive motion; at one time rising into ridges, at another descending into furrows. And this likewise happens to the winds, except that they have not the motion of gravity.

There are also other resemblances, which may be observed from the things already inquired.

Transition.

Provisional Rules respecting the Winds.

Rules are either particular or general; but here both kinds are provisional. For as yet I do not pronounce certainly upon anything. Particular rules may be drawn or expressed from almost every article; certain general ones, but only a few, I shall myself select, and subjoin.

Cf. Aristot. Problems, xxvi. 38., and Meteorol. i. 13.

1. Wind is merely air in motion: nothing besides: air put in motion either by simple impulsion, or by the mixture of vapours. 2. Winds arising from the simple impulsion of the air are produced in four ways; namely, by the natural motion of the air, by the expansion of the air in the path of the sun, by the contraction of the air from sudden cold, or by the compression of the air from external bodies.

There may also be a fifth way; namely, by the agitation and concussion of the air from the stars; but let matters of this kind be passed in silence for the present, or only listened to with suspicion.

3. The principal cause of winds produced by the mixture of vapours is the overcharging of the air by the air newly created from vapours; for thereby the bulk of the air is increased and requires more room.

4. A small increase in the quantity of air causes a great swell in every part of the atmosphere; so that this new air from the resolution of vapours contributes more to the motion than to the matter; but the great body of wind is composed of the former air. Nor does the new air drive the old air before it, as if they were separate bodies; but both being mixed together require greater room.

5. Any other concurrent principle of motion, besides the surcharge of the air, acts as an accessory to strengthen and increase the chief one. And this is the reason why high stormy winds seldom rise from the simple surcharge of the air.

6. There are four accessories to the surcharge of the air; namely, exhalation from below, precipitation from what is called the middle region of the air, dispersion from the formation of a cloud, and mobility and acrimony of the exhalation itself.

7. The motion of the wind is almost always lateral. That created by the simple surcharge of the air is so from the very first; that caused by exhalations from the earth or repercussion from above becomes so soon after; unless the eruption, precipitation, or recoil, are extremely violent.

8. The air will submit to some compression before it is conscious of being overcharged, and before it impels the air contiguous to it. This will account for all winds being somewhat more condensed than air at rest.

9. Winds are allayed in five ways; namely, by the meeting, incorporation, elevation, transportation, or deficiency of vapours.

10. The gathering of vapours, and in fact of the air itself into rain, is caused in four ways; namely, by the excess of quantity, or the condensation by cold, or the compulsion of contrary winds, or the repercussion from obstacles.

11. Both vapours and exhalations are the matter of winds. Rain is never generated from exhalations, but winds most frequently proceed from vapours. There is however this dif ference; that winds generated from vapours more easily incorporate themselves with the pure air, are sooner calmed, and are not so stubborn as those arising from exhalations.

12. The modification and different conditions of heat have as much to do with the generation of winds, as have the quantity or conditions of matter.

13. The sun's heat, in the generation of winds, should have just power enough to raise them; neither so abundant as to collect them into rain, nor so scanty as entirely to scatter and disperse them.

14. Winds blow from the direction of their nurseries. When however these nurseries are situated in different quarters, different winds generally blow together, till the stronger either overpowers the weaker, or turns it into its own current.

15. Winds are generated everywhere, from the surface of the earth to the cold region of the air; but the common winds are generated close at hand, the stronger winds above.

16. Countries where the attendant winds are warm are hotter, and countries where these winds are cool are colder, than in proportion to their climate.

A Map or Table of Human Requirements with reference to the Winds; or Desiderata with their Approximations.

Desideratum. 1. A better method of ordering and disposing the sails of ships, so as to make more way with less wind; a thing very useful in shortening sea voyages, and saving expense.

Approximation. No approximation has been hitherto invented which in practice should exactly correspond to this requirement. But for this consult the major observations on the 26th article.

Desideratum. 2. A method of constructing windmills with sails, so as to grind more with less wind; a thing likewise useful and lucrative.

Approximation. Consult on this point our experiments in reply

to the 27th article, where the thing appears to be almost

done.

Desideratum.

3. A method of foreknowing the risings, fallings, and times of winds; a thing useful in navigation and agriculture, but especially so in selecting the times for naval engage

ments.

Approximation. Many things have been remarked in the inquiry which bear upon this subject, but especially the reply to the 32nd article. Now however that the cause of the winds is explained, the more diligent observations of posterity (if it shall care at all about these things) will discover more certain prognostics.

Desideratum. 4. A method of prognosticating and forming an opinion upon other things by means of the winds; for instance, whether in any part of the sea there are continents or islands, or whether the sea is open; a thing of use in new and unknown navigations.

Approximation. The observation about the periodical winds, which Columbus appears to have used, is an approximation to this.

Desideratum. 5. A method likewise of foretelling, every year, whether corn and fruit will be abundant or scarce; a thing useful and lucrative in speculative sales and purchases; of which an instance is related in the case of Thales when he bought up the olives.1

Approximation. Some observations under the 29th article of inquiry, on malignant or tearing winds, and the times when they are prejudicial, bear upon this point.

Desideratum. 6. A method likewise of foretelling the diseases and epidemics for every year; a thing useful to the reputation of physicians, if such things could be predicted; as also for the causes and cures of diseases, with some other matters of busi

ness.

Approximation. Some observations on the 30th article of inquiry have likewise reference to this question.

Admonition. For predictions from the winds concerning crops, fruits, and diseases, consult the Histories of Agriculture and Medicines.

Desideratum. 7. A method of raising and allaying winds.
Approximation. There are some superstitious and magical cere-

Diog. Laert. i. 26.

200

TRANSLATION OF THE "HISTORIA VENTORUM."

monies connected with this subject, which do not appear worthy to be received into a serious and exact natural history. Nor does any approximation at present occur to me. It will however be of service thereto, to inspect and inquire thoroughly into the nature of the air; to see if there be anything which, on being communicated in a small quantity to the air, can excite and multiply the motion of dilatation or contraction in the body of the air. For if this could be done, the raising and calming of the winds would naturally follow; like Pliny's experiment, if it be true, of throwing vinegar against the whirlwind.' Another method might be, by letting out subterranean winds wherever a great quantity was collected, as is told of the well in Dalmatia. But it is difficult to discover these places of confinement. Desideratum. 8. Methods of performing many amusing and

wonderful experiments by the motion of the winds.

Approximation. Such questions I have no time to consider. The approximation is the common games which depend on the wind; and, no question, many pleasant things of this kind, both with regard to sound and motion, may be invented.

1 Pliny, ii. 49.