Bucket of Water; and as foon as they fall to the Bottom, you will fee fome Bubbles of the Air that followed 'em rifing up from the Bottom to the Top of the Water; infomuch, that many times if the Bullets defcend from a greater Heighth, and confequently with more Swiftnefs, the Bubbles will even be as large as the Bullets.

The fame has been obferv'd in the Force of the Wind, which fome have felt to their Harm, upon a Cannon-Ball's paffing very near them, yet with out touching them.

'Tis the like Sort of Wind, as fome think, that is excited by the rufhing of great Hail-ftones, as they fwiftly defcend.

SECT. XXX. The Fourth Experiment; Efferves

cence's.

IV. WE fee a Wind likewife generated by mixing together two Effervefcent Matters, and caufing them to ferment; and it is the fame thing, whether both of them be Liquid, or one of them be a Solid Body.

Accordingly, if you throw Filings of Iron or Steel into Spirit of Salt-petre, or into Aquafortis; or if you mix with the Spirit of Sulphur, Sea Salt, Copperas, or any other Acid Spirit, an Alcaline Liquor, fuch as Spirit of Sal-Armoniac impregnated with Potafh, or Spirit of Hartfhorn, Salt of Tartar, or Potafh itself diffolved in Water, they will produce a Fermentation with great Violence, and exhale a Stream of Air and Vapours out of the Mouth of the Glafs or Veffel that you put them in; of the Force of which Fermentation or Ebullition you will be the more fenfible, if you ftop the Mouth of the Glafs for a little space, whilft they are working together; but you must not keep it fhut too long, for unless the Glafs be very ftrong, VOL II.

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it will burst in pieces as if Gun-Powder were kind led in it.

We do not here enquire after what manner the Wind is thus produced, being fufficient to our Purpose, that a Wind can be fo made; and that fuch an Effervefcence may be produced among the like Particles, even in the Air itself, has been in fome fort proved above in §. XIX. about Fogs.

SECT. XXXI. The Fifth Experiment, by burning Sulphureous Bodies and Salt-petre together.

V. SOME Naturalifts are wont to add to thefe Winds, the very violent and turbulent Protrufion of the Air and Smoak that has been obferved by the mixing of Salt-petre with fome Sulphureous Matters, and touching them only with a little Fire.

After this manner, we fhall fee an Inftance of it in mingling Antimony with Salt-petre, or (if we fear any danger from the Smoak arifing from this Mixture) by mixing powder'd Salt of Tartar with the like quantity of Salt-petre, and then setting it on Fire with a live Coal, or red hot Iron, espe cially if you burn these Matters inclofed in a Veffel, out of which their Smoak may have a Paffage thro' a Tube, as the Chymifts do upon certain Occafions: for then you will fee with how much Force and Swiftnefs there will be a Wind and Stream of Air produced.

Some fuppofe that the Hurricanes are generated in this manner, by the inflaming of fome fuch Matters in the Earth. Firft, Becaufe of the great Force and Violence of them, which muft proceed from a very great Velocity of the Air-Stream, which upon this occafion is very remarkable. Secondly, Because they do not laft long, and commonly not above 7 or 8 Hours. Thirdly, Because they are obferv'd to rule for the most Part in cer

tain Places only. Fourthly, Because (as we see in the aforefaid Burning Matters) the Streams of Smoak diffuse themselves on all fides, and fo the Wind blows from all the Points of the Compass. Fifthly, Becaufe Earthquakes are often felt at the fame time in the adjacent Places, and Dead Fishes, found floating in thofe Parts of the Sea that are nearest.

Now, that these Fires produced by Salt-petre and Sulphur, tho' kindled under the bottom of the Sea, are not extinguished by its Waters; and that the Smoak thereof forces its way upwards thro' the fame, may be easily accounted for by the Fire-works, that perform their Operations even in the Water; where they will remain a great while, without being extinguished, and from whence Men may fee the Smoak of them afcend. The fame thing will appear as plainly, by kindling a little Squib or Serpent, as they call it, and throwing it into a Glass full of Water, where you will perfectly fee the Squib burning out, and all the Smoak of it rifing thro' the Water, infomuch, that if any Fifh were there, 'tis likely they would all dye.

Whether this be the true or only the probable Cause of thofe dreadful Winds, which they call Hurricanes, we fhall not enquire any farther here. SECT. XXXII. The Sixth Experiment, she wing, that the Elaftick Power of the Air being augmented, produces Winds.

BESIDES the foremention'd Caufes of the Production of Winds, the Great and Principal Property of the Air does ftill furnifh us with another; which, tho' unknown 'till of late Years, is yet efteem'd by many, and with great Appearance of Truth, in this Age, for one of the Caufes of Winds. This has been fhewn before in the particular Account which we have given of the Elaftick Power Dda

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of the Air; by which it continually endeavouring to dilate itfelf towards every Part where it does not meet with a fufficient Refiftance, breaks forth with a great and swift Stream; infomuch, that when we take away the Balance of Force, by rendering one of the two adjacent Airs ftronger, or t'other weaker, the strongest always expands itself towards the weakest, and by protruding or driving it forwards, caufes that Motion which we call Wind.

VI. The Particles of the Air prefs upon one another in a Wind-Gun; by which means their Elafticity is augmented; and we may fee that it will drive out a Bullet, notwithstanding the Refi stance of the common and external Air, with fuch Velocity as is now well known to the Amazement of many.

After the fame manner, if you blow Air strongly into a little Bottle with a narrow Mouth, and give it room to flow back again, you will find that it will rufh out from thence with great Swiftnefs, tho' it was a long time in blowing in, only because it is strongly compreffed within that narrow Space. Now whether certain Sorts of very violent Winds do fuddenly exert themselves like Gufts and Blafts, after the fame manner, because two other more gentle Winds driving before them all the Vapours and Clouds in the Air, and blowing them against each other, do comprefs the interjacent Air, and dispose it so as to break out with a great Swiftnefs, for want of a fufficient Refiftance, we fhall leave the further Enquiry to fuch as think it worth their while, and may meet with Opportunities of making it.

SECT.

SECT. XXXIII. The Seventh Experiment; the Diminution or Weakning of the Air will produce the Jame Effect.

VII. Now, as we have fhewn from hence with how great a Velocity the Air can be protruded as it becomes stronger in its Elaftick Faculty, it being thicker and clofer compreffed in the fame Place; the fame Velocity does likewife exert itfelf when the Balance of the Refifting Air only is taken away either in whole or in Part, by diminishing the Quantity thereof in any Place.

Thus we fee when a Vacuum is made by exhäufting the Air, the common Strength of the external Air forces in with very great Swiftnefs. Several Experiments proving fuch a strong Blaft, have been alreadyquoted upon the Subject of Respiration.

Those who defire to see more Proofs may confult the Machines of Meffieurs Guerike and Papin, (Philofoph. Tranfa&t. Numb. 121.) with which in the prefence of the Royal Society of London, the fame Force and Noife was in a manner produced by the rufhing of the Air into a Vacuum, as is ufually made by the compreffed Air in a Gun, being let out.

However, if those that have neither an AirPump, nor fuch Machines as these at hand, are defirous to make this Experiment, namely, that the Air forces it felf like a violent Wind into a place where the internal Air is either much diminish'd, or has very little Elafticity in it: Let them take a Glass Bottle, first putting a little Water into it, and tying a wet Bladder over the Mouth of it; fo that turning it upfide down, there may be about the Quantity of two Fingers breadth of Water in the Neck of it; then turning the Bottle right again, that the Water may defcend to the Bottom of it, and the Neck remain empty: Let them make a little Hole in

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