the Air with a Property of conveying to the Instruments of Smelling, all those Exhalations which we endeavour to discover and enjoy by the help of that Senfe?.

SECT. XXXV. Air is the Caufe of Sounds.

BUT that which fhews in the plaineft manner the Obligations of the Thankfulness we lye under to the Great Creator, is that those wonderful Inftruments of Hearing, notwithstanding the most wise and artful Contrivance thereof, would have been implanted in Mankind and all other Living Creatures in vain, and without any manner of Advantage, unless the Air by its Motion had been endowed with a Power of producing Sounds: For how miferable all Men would have been without Sounds, and confequently without Hearing, has been already proved in our Contemplation upon the Senses.

SE CT. XXXVI, and XXXVII. Several Experiments to prove the Production of Sounds by the Air.

It is not now our purpose to enquire here what kind of Motion, or what Parts of the Air produce Sound: This feems to be certain, that it is a Motion of the Air's Elaftick Particles; for upon exhausting these Elaftick Parts of Air fuddenly from the Glafs Globe A (Tab. XIII. Fig. 4.) and upon their protruding one another towards the space of the empty Pump, we could obferve a Sound or Noife, which, when the Receiver was full of Air, and the Spring of the Air more ftrongly dilated, that is to fay,at the beginning of it, is loudeft, but upon evacuating the Receiver, and confequently upon weakening the faid Spring, or perhaps alfo,

upon

upon leffening the number of the mov❜d Parts, the Sound is gradually diminished.

Thus we find by hanging a little Bell within the Receiver,and pumping the Air out, the Sound of the Bell becomes much weaker. A Striking-Watch fhut up in the Receiver of an Air Pump, and faften'd to a String, is not heard fo plain as when it is out of the Bell; but upon exhaufting the Air, the Sound was fo much and fo fenfibly diminifhed, that it could fcarce be heard at all. But as far as I could ever yet learn, no body has been able to exhaust the Air fo far, as that the Sound of a Clock or Bell fhould not be heard at all; unless it were only Mr. Huygens, who in his Traitté de la Lumiere, p. 10. informs us, that he placed a Clock upon Feathers or Cotton, to the end that its tremulous Motion might not be communicated to the Glass in which it ftood.

>

And it is likewife obferved, that a Place in which the Elaftick Power of the Air is much weaken'd, or made a Vacuum in the middle of the common Air, and an opportunity afforded to the faid Air, to be pufh'd in from all Parts thitherwards by its Elaftick Force, fo that its Parts ftrike against one another, a great Noife is caufed thereby; for if you put the two Brafs Hemifpheres which are commonly made ufe of by thofe that ufe Air Pumps, upon one another, and ftopping them very clofe, pump the Air out of 'em, and fo make the hollow Space therein to contain but very little Air, and that much weaken'd too; and if then thofe Hemifpheres, or Half Globes, be fuddenly drown asunder by a great Weight, and thereby an opportunity given to the Parts of the External Air to ftrike against each other, we fhall find a Noife produced thereby, like the discharge of a Gun.

The

The fame has been likewife remarked above, in the breaking of the Glafs (Tab. XIII. Fig. 3.) by the swift forcing in of the Air into the Brafs Veffel ABCD, out of which at K, there was fome Part of its Air exhaufted, and confequently the Elafticity of the remaining Part was weaken'd in Proportion. As it also happen'd, when instead of fuch a Brass Veffel, an octangular Half-Pint Bottle was placed upon the Mouth Q, of the Brass Plate H I, and a little Air exhaufted from the fame; whereupon the Glafs Bottle burften into fmall Pieces with a loud Report by the Preffure of the External Air: To prevent any Danger from thence, the best way will be to cover the Bottle with a Bladder faften'd about the Neck thereof.

SECT. XXXVIII. Convictions from the foregoing Obfervations.

We shall not here enquire farther what probable Conclufions may be deduced from these and other Experiments, concerning Bodies yielding Sounds by the particular Motion of the Parts of the Air; but this may be fafely affirmed, that without Air, little or no Sound would refult from the Motions of Bodies. Now can they that know the neceffity thereof, maintain fuch a fort of Philofophy, as teaches that the Faculty with which the Air is endowed, of conveying Sounds and Smells to our Ears and Noftrils, is only owing to Chance, without any View of being ferviceable to Mankind ?

SBCT. XXXIX. The Ufe of Air in Pumps."

BESIDES all thefe wonderful Ufes and Services daily render'd by the Air to fuch as inhabit this

Earth,

Earth, a great many more might be mention'd: And ought not then every Body that has any Senfe of Generofity, acknowledge how much he is bound to give thanks, when he, without contributing any thing thereto on his own Part, finds himself furrounded with fo vaft a Force and Preffure of the Air, which he can make ufe of according to his own Pleasure, in fo many Occafions for his Conveniency, and to avoid being troublesome to himfelf or others?

Every one who knows, that Pumps, Syringes and Fountains, and fuch like Hydraulick Inftruments, are only render'd ufeful by the Preffure, that is by the Gravitating and Expanfive Power of the Air, which, by the Art of Man, has been applied thereto, will be fully convinced of the Truth of this Propofition,

And those who are ignorant of it, may confider the Spout or Syringe, A BC, Tab. III. Fig. 3. (of which mention has been made above in Contemplation VII. §. XI.) as a Barrel of a Pump ftanding in the Water DCE; in which Pump, as has been there fhewn, no Water will ever afcend, tho' you fhould draw the Pifton F upwards, unlefs the Air G do gravitate upon the Water D E. Now that a Pump on this occafion may be look'd upon as a kind of Syringe, is known to every Body.

SECT. XL. The Air hinders fermenting Liquors from flying out of the Veffels that contain them.

THAT there are fo many fermenting Liquors, fuch as Beer, Wines, &c. working in themfelves, ufed by feveral Nations for their Pleasure, Refreshment, and other Ends, we ought thankfully to confefs to be owing to the Goodness of our Creator; who, by placing the Air upon this Globe, and endowing it with a Gravitating and Elaftick Faculty,

Faculty, caufes thofe Liquors to ftay and remain within their Veffels, which, without fuch a Pref fure of the Air, they would burft to pieces, or run all out of the Mouth thereof. They that have a mind to make a Trial of it, let them take a Glafs of our common Beer, that has done working, and is fome Days old; let them place it in the Receiver of an Air-Pump, and exhaufting the Air, they will presently fee it rife and froth, and run over the Brims of the Glafs like Bottled Beer: but by letting in a little Air again, it will presently fubfide, and ceafe frothing and working.

To take no notice, that unless the Preffure of the Air did put a stop to fuch Working, the Drink would immediately lofe both its Strength and Agreeablenefs, as every body knows that has tafted Beer after fuch working in the Air-Pump, whereby it is rendered as flat and infipid, as if it had stood a great while expofed to the open Air.

The good Wives ought likewife to be informed, that without this Preffure of the Air, no boiling Water wou'd ftay in their Pots and Kettles. They that doubt thereof, let them fet a little Tea-cup full of hot Water under the Receiver of an AirPump, then draw off he gravitating Air, and they will find that the Water will run over and dilate itself almost like Gun-powder that is set on Fire.

SECT. XLI. Refraction and Twilight, or Break of Day.

Now as most of the Effects we have already mention'd concerning the Air, are produced by the Gravity and Elafticity thereof; altho' towards the Refpiration of living Creatures, towards fertilizing the Earth, and perhaps too towards the Nourishment of Plants, and other Matters which are brought to pafs by the Air, there feem likewife

to