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the middle of the Bladder, with a Pin or Needle, and through the fame fuck out the Air from the Glafs, as ftrongly as they can for several times ftopping the Hole at every turn with the Finger, that no Air may get in again.

;.

When this is done as well as it can be, let the Bottle be inverted again, fo that the Water may run into the Neck, and upon the Bladder stopp'd with the Finger; upon the removing of which Finger, the External Air, like a Wind will rufh into the Bottle thro' the Hole of the Bladder and the Water lying upon it, and rife up to the Top, where the Internal Air had been diminish'd and weaken'd by Suction.

Now, if according to the Calculations of Mathematicians, the Air, which forces it felf into a Vacuum, moves with fo much Velocity, as to advance 1305 Foot in a Pulfe or Second of a Minute (See Philofophical Tranfactions.) And according to the Obfervation of the accurate Mr. Mariotte, it is very difficult to withstand, or advance against a Wind that moves 24 Foot in a Second; and that another, that runs 32 Foot in the fame time, produces fuch a Storm, as is capable of tearing up Trees and overturning Houses: (See his Difcourfe du Movement des Eaux, p. 67, and 78. See likewife the faid Treatife lately done into English, by the Ingenious Dr. Defaguliers.) What Havock and Destruction of every thing might we not expect from the terrible Force of a Wind, which being above 40 times as fwift, would, fuppofing it to act upon the fame Bodies, exert 40 times as much Strength as the aforementioned Storm; especially, if that Air which furrounds the whole Globe fhould have the Opportunity of displaying its Elaftic Power upon any great Space that were almoft or altogether empty of Air? Now, whether fuch a thing

may

may be supposed to have ever happen'd, and whether Winds have been protruded after the like manner in the open Air, we fhall not here enquire

But this however may be plainly inferr'd from. what has been faid, that the Preffure of the Air being enabled to exert itself with its utmoft Force, would, by its exceeding Swiftnefs, produce most dreadful Effects; deftroying every thing upon the Face of the Earth, in a very little Space of Time, as has been already fhewn in Contemplation XVII. by an Experiment of the Air's Breaking a Glafs, tho' the fame was far from being exhaufted of all its Air.

SECT. XXXIV. The Eighth Experiment; of producing Wind by Cold.

VIII. WE have feen that the above-mention'd Motion of the Air or Wind was produced, by diminifhing the Quantity or Strength of the Air. But befides this, there is another Cafe in which, tho' the Quantity of the Air be not diminished, yet the Elaftick Faculty thereof is weaken'd; namely, when one Air is only colder than another, which in every thing befides may be like to the First: By which means alfo a Wind is generated when the lefs Cold, and therefore ftronger Air expands itself, and preffes upon the more cold and confequently weaker Air.

Many Experiments proving the fame, are well known to the Naturalifts; and the Operation of the Thermometers, which are moved by Rarefa&tion and Condenfation of Air, do frequently fhew the fame.

But to give a very eafie Proof hereof, you may try the following Experiment: Bind a wet Bladder upon the Mouth CD, of a Glafs Bottle FGCD, Tab. XIV. Fig. 6.) after having pour'd fo much Dd4 Water

Water into it, as will not quite fill the Neck K C, when the Bottle is inverted. Then take a Second Bladder HKL I, cutting off the Neck of it in fuch a manner, that the Orifice H I, may be very large; then having made a Hole in it at K L, the Neck KLCD, will thereby go thro', and the Bladder at KL must be tied or twisted very clofe about it. After which, throwing in a handful of Salt, and one or two handful of Snow into the Bladder H1KL, upon the globular Part of the Bottle FG KL, ftir the fame together with a Stick or Spoon; when, as it is well known, the Snow will begin to melt, and the Air in the Bottle, which is encompaffed with this Mixture, will become very cold; and the Water itself, if it were higher in the Neck of the Bottle than KL, would eafily be frozen, which might embarrass the Experiment, and for that reason, the Water ought not to be higher than A B, or below the Bladder KL. Now that the Air in the globular Part of the Bottle FGKI, is weaken'd in its Elaftick Faculty by this Cold; and that the External Air, which is not fo cold, being enabled to act upon it, will expand it felf with greater Force, and produce a Wind, blowing upon the colder and weaker Air at P, may appear by pricking the Bladder CD with a great Pin at E; whereupon one may fee the Air forced through the Water ABCD, that is in the Neck of the Bottle with a remarkable Velocity, like a Wind, up to the Globular Part F G K L.

This Experiment having been likewife tried in the great Froft upon the 12th of January, 1709; 'twas obferv'd, that as cold as the Air was then, yet by this Mixture, and by the greater Cold, it loft fill more, of its Elaftick Power; and the External Air being ftronger, rufhing like a Wind thitherwards, fhewed that a great Quantity of Air may be squeez'd together in a cold Place. That which

might probably be infer'd from this Operation of the Cold upon the Air, concerning Winds, fhall be treated of in fome manner hereafter.

SECT. XXXV. The Ninth Experiment; Of Wind produced by Warmth.

IX. THE Operation of Warmth is directly contrary to the foregoing, dilating the Air with greater Force, thereby producing a Current of Wind towards all the Places, where it meets with no Resistance.

This might likewife be fhewn by the Thermometers, in which the Warmth expands the Air; but to reprefent it to those that have no Thermometers at hand; Set again a Bottle, in which there is nothing but Air, with the Mouth turned downwards upon a Plate or Difh, upon which you must pour as much Water as may rife juft above the Brim of the Mouth of the faid Bottle, and thereby prevent any Communication between the External and Internal Air. Now if you hold a Burning-Coal, and move it round the Globular Part of the Glass upwards and downwards, so as to warm the Air within it, you will fee that the rarified Air rufhing out in little Bubbles between the Bottle and the Plate, will produce a foft and gentle Wind.

If you have a mind to fee this Experiment confirmed with a ftronger Blast, you must apply a more fudden and violent Heat thereto; as may be eafily done, if you make use of a Bottle encompaffed with a Bladder (Tab. XIV. Fig. 6.) and leaving it open at C D, fet it down upon a Plate, with Water, then pour hot Water upon the bottom of the Bottle F G, and all round it, with some Care leaft it burft; this increased Heat will produce a fwift Current of Air or Wind, made by the Air, which rushes out as it is expanded. SECT.

SECT. XXXVI. The Tenth Experiment; Wind produced by the Sufpenfion or Ceflation of Warmth.

X. BUT forafmuch as by the driving out of the Air by Warmth, the fame is diminished in the Bottle, and therefore, when the Warmth that had driven it out ceases, the Expanfive Faculty will become weaker than it was before, whilft there was a greater quantity of Air in the Glass, and whaft it had a Communication with the furrounding Air. It will therefore follow, that the Exter nal Air (having the fame degree of Cold or Heat with that which was included in the Bottle, and was diminished in its Quantity by the foregoing Warmth,) will pass more ftrongly that way, and fo crowd itself into the Bottle with a returning Wind. One that underftands Hydroftaercks, might demonftrate the fame in the preceding Experiments; forafmuch as the Air within the Bottle lofing its greater Heat, the Water will rife up into the Neck of the faid Bottle from the Plate, by the Preffure of the External Air: But as this is writ for the fake of the Ignorant, to make them even fee the aforefaid returning Wind, put into a Bottle again as much Water as will fill the Neck when it is inverted, thereby to render vifible, as above, the Discharge of the faid Wind thro' the Water; then hold the Bottle for a while over the Steams of boiling Water, to the end, that the fudden Heat may not burft it, and finally put it into the boiling Water itself, till it be very hot, and the Air rushes out by the Mouth of it, which is open, as is done above in §. XXV; then take a warm wet Bladder, and tie it as close as you can upon the Mouth of the Bottle, and invert it fo, that the included Water may lie upon the Bladder; then fet it by, for a little while in the fame pofture, till the

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