( 5 V)

Having prepared a Barrel carrying a Lcad os two Ounces, the Experimentwas shewn betöre the Ppyal Society , and the Effect was found very Conside-rable, the Force being üttle less than that os the Hfind-Gun by Cempreßon ;

•the (ame Experiment being afterwards repeated with a Longer Barrel, hwa,found that the Length in this way os Sbooting was very little, is any Ad-vantage.

XII. My Way os Computing the Velocity os the Air, (which I thinlc isT^ rtiofinBetter than the Trial made by the Royal Academy at Paris) is Grounded up-

. 4 rri. r Kujbci t Htf

on this Ilydrcsiatical Principic, 1 nat Ltqttors bave a Strength ro Aß:n.i äs a n vxbuttfhA

Iligb as their Source is ; and although the RcßjLuicc os the Medium does al- Kfs,,Vcr >ways hinder Jetts d’Eau in the Open Air srom reaching quite so High, never- ^theless the Liquor at its firff Spouting out, bath the necessary Swift ness tocome to that Hei«Ist.

Prop. I.] From this Principle may be casily deduced this Proposition,

That, es two Differing Liquors driven by tbc fame Prejsurc , that which is inSpccic Lighter muß Ascend Higher than that which is Ileavicr, and their Hcigbtswill bc Bcciprocaüy in the [ame Pensen ns their Specificis Gravities arc.

Prop. II.] From the foregoing Propefition another rrmy easily be Deduced,viq. That, of Differing Liquors bearing tbc fame Prejsurc, tbofe that are Lighterin Spccic muß acquire a greater Swift ness, and their Dijfering Vclocities are todie another * as the Reots es the Specificis Gravides es the said Liquors. ' KeciprocAly,

For we have scen, Prop. I. That the Hcigbts to be Attained are * in the * Rf dprocAiy.fame Reasbn as the Specificis Gravities ; Now Gal/il.ius, Hugenius , and others,have Dcmonstrated, That the Vclocities of Bodies are to one another, as theSquarc Pools of the Hcigbts to which they may Ascend : and so in this occa- . R ec ;proc*itj.hon they are also * as the Ppots os the Specificis Gravities.

Is theresore we would know what is the Vclccity of the Air being drivenby any degree of Pressure whatsoever, we ought but to sind what would bethe Vclccity of H'ater urtder the fame Pressure : and theil take the Squarc Pqctsof the Specificis Gravities os tliefe two Tiquors ; becaule as much as theSqfiare Rpot of the Specificis Gravity of H’ater , doth exceed the Squarc fioot otthe Specificis Gravity of the Air j so much in Proportion will the Vclccity ofAir exceed the Vclccity of H’ater. For Exampie , When I would Computewhat ilmuld be the Swiftness of a Bullet fliot by my Pneumaticis Engine, Ifhould sirlt Compute what was the Velocity of the Air it seif that drove theBullet : I did theresore take notice, that in this Occalion the Air bears aPressure much about the kirne as that ot H 'ater when its Spung is ax FootHigh. Nowsoch H’ater would fpotit out with a sufficient Velocity to ascendFoot Perpendicular, and theresore according to the Rules and Obfervations ofGalllUus, Haltey, and others, such Water bath «sie Vclccity of 45- Foot in aSecond. It remains theresore hüt to know the Proportion of the Gravity ofthe Air ro that of H’ater and we have found ic not to be always the farno ;hecauso the Heighr, the Heat, and the Moiffure, of the Anncjphcrc, are Va-riable : nevertheless, v.x may (by in general, that the Reason bet wem theSpecificis Gravities of H’a'cr and Air 15 much about 840 to I. Taking thenVol. I. Ffff their