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there are contrary motions, one motion of the tide, another of the river's course; and yet but a single motion takes place; that of the tide becoming predominant: so, likewise, when contrary winds blow, the greater subdues the less. 4. As it sometimes happens in currents of the sea, and certain rivers, that the water a-top moves in a contrary direction to that below; so, likewise, in the air, when contrary winds blow, together, the one flies over the other. 5. As there are cataracts of rain falling within a narrow compass; so there are, in like manner, narrow eddies of wind, or whirlwinds. 6. As waters, when disturbed, will have an undulation, besides their progressive motion; so likewise have the winds. And besides these, there are other correspondences between them, derivable from the present enquiry.

SECT. XVI.

IMPERFECT AXIOMS; OR VARIABLE CANONS, FORMED UPON THE PRECEDING ENQUIRY.

TRANSITION.

CANONS, or axioms, are either particular or general; but both of them with us are variable or improveable: for we dare not yet pronounce upon any thing. As to particular axioms, they

may be deduced and collected from almost every article; but we shall here subjoin a few of the general ones, that we have ourselves drawn out.*

AXIOM I. Wind is nothing more than air put into motion, either by a simple impulse, or the admixture of vapours.

II. Winds are produced by the simple impulse of the air, four ways; viz. 1. by the natural motion of the air; 2. by the expansion of the air in the path of the sun; 3. the contraction of the air by sudden cold; and, 4. by the compression of the air from external bodies.

There may possibly be a fifth way; viz. by the agitation and concussion of the air from the stars but operations of this kind should not be mentioned yet;† or else should be but sparingly received.

III. The principal cause of winds, produced by the admixture of vapours, is, the air's being over-loaded by the air newly formed from vapours; whence the bulk of the air increases, and requires more room.

IV. A small, fresh supply of air may cause a great swell, every way, in the atmosphere; so that

*See Novum Organum, Part ii. Aph. V.

+ 'Till better known and discovered; or till natural philosophy itself is farther advanced.

this new air, from the resolution of vapours, contributes more to the motion than the matter: but the great body of the wind consists of the former air. And the new air does not drive the old air before it, as if they were separate bodies; but both being mixed together, they require a larger space.

V. When there is another principle of motion besides the surcharge of the air; this proves an accessory, that increases and strengthens the principal: whence it is, that great and boisterous winds seldom arise from a bare surcharge of the air.

VI. There are four accessories to the surcharge of the air; viz. 1. Subterraneal expirations; 2. precipitation from that called the middle region of the air; 3. dissipation of formed clouds; and, 4. mobility and acrimony of the exhalation itself.

VII. The motion of the wind is almost constantly lateral: that which proceeds from the simple surcharge of the air, is so from the first; and that which proceeds from subterraneous expirations, or repercussion from above, becomes so soon after; unless when the eruption, precipitation, or reverberation, are exceedingly violent.

VIII. Air will sustain some compressure before it becomes sensible of being over-loaded, or before it will impel the air contiguous to it;

whence it is, that all winds are somewhat more dense than air at rest.

IX. Winds are allayed five ways, viz. 1. when the vapours come together, 2. incorporate, 3. sublime, 4. transport, or 5. spend themselves.

X. Vapours come together, or the atmosphere forms itself into rain, four ways, viz. 1. by being oppressed with quantity, 2. condensed by cold, 3. by contrary winds driving the vapours together, and 4. by reverberating obstacles.

XI. Both vapours and exhalations afford matter of winds: for though rain never proceeds from exhalations, yet winds may frequently proceed from vapours. But there is this difference, that the winds made from vapours more easily incorporate with pure air, become sooner appeased, and prove not so stubborn, as those from exhalations.

XII. The modification and different states of heat, have as great an effect in the production of winds, as the quantity or conditions of the matter.

XIII. In the generation of winds, the sun's heat should be so proportionate as to excite them; but not so plentifully as to make them collect, into rain; nor yet so sparingly as to make them totally disperse and dissipate.

XIV. Winds blow from the quarters of their nurseries: and when these nurseries are differ

ently seated, different winds generally blow together; but the stronger either subdues the weaker, or turns it into its own current.

XV. Winds are generated all the way up, from the surface of the earth to the cold region of the air: but those that blow oftenest, are generated near hand, and the stronger above.

XVI. The countries which have their servingwinds warm, are hotter, and those that have them cool, are colder, than in proportion to the climate.

SECT. XVII.

▲ TABLE OF PARTICULARS MORE IMMEDIATELY SERVICEABLE TO MANKIND: OR DESIDERATA WITH THEIR APPROXIMATIONS; DRAWN FROM

THE PRECEDING ENQUIRY.

DESIDERATUM. I. A method of forming and disposing the sails of ships, so as with a less wind to make more way: a thing of great use for shortening voyages, and lessening their expence.

No discovery has hitherto been made to answer this desideratum precisely in practice; but consult the larger observations under Sect. XIII.

II. To construct wind-mills, and their sails, so as that they may perform more work with less wind: which also is a matter of advantage.

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