into the Veffel D, which is then affixed to the Scale B, and immerfed into the Veffel of Water; then put Weights into the Scale B'till there be a juft Equipoife. Now from its Weight in Air, fubduct its Weight in Water, and with the Remainder, divide the Weight in Air, the Quotient will be the Ratio of its fpecifick Gravity; and thus the Ratio's or Proportion of the fpecifick Grávities of feveral Bodies may be found..

A. As to the Manner of weighing thofe Bodies, it feems pretty easy to be apprehended from the Figure; but as to computing the Ratios, believe I could better under

stand that by Example.

B. Why then I will give you one : Suppofe you take a Piece of Lead and a Piece of Ivory, each weighing 60 Grains in Air, but weighing them feparately in Water, you find their Weights therein to be 54 and 29; now the Deficiency of these Weights are 5, and 3; by each of thefe Numbers divide 60, the Weight in Air, the Quotients will be 14 and 1 nearly: Therefore the Ratio or Proportion of the Weight of Lead to that of Ivory, is as 11 to 13; that is, Lead is almoft 7 Times heavier than Ivory.

A. Sir, I perfectly apprehend you now, and thank you pray do you eftimate the fpecifick Gravities of Liquids after the fame? Manner?

B. They

Of the fpecifick Gravities of Fluids. 231

B. They are estimated thus: Take a Piece of Lead, which fuppofe to weigh 455 Grains; then the fame weighed in Oil of Vitriol will be found no more than 379, and in common Water 414 Grains. The Diminution in the firft Cafe is 76, in the latter 41 Grains; now divide 455 by 76 and 41, and you will have the Quotient 6 and II very nearly: Wherefore the Gravity of common Water is to the Oil of Vitriol as I to 6; that is, almost as heavy again: Do you understand me?

A. Yes, Sir, very well: I only wish I had fuch a Pair of Scales as are fit for this Purpose; for then I fhould take a deal of Pleasure in making thofe Kinds of Experi

ments.

B. Sir, you may eafily acquire a Pair; and 'till then, I can lend you a Synopfis of an Estimate of the fpecifick Gravity of various Solids and Liquids, which I have taken from Dr. Quinfey, if you think it worth your

Perúfal.

A. Sir, I am very much obliged to you for fo extraordinary a Piece of philofophical Curiofity: And, pray, have you nothing very remarkable to be obferved from the foregoing Laws of the Preffure of Fluids?

B. Yes, more than I can here exemplify to you; however that you may be fomewhat the wifer for them, learn their Ufe in

Q4

the

4

the following Inftance: Suppofe AB (Fig. XXXVI) a Cistern or Tube filled with Water always even to the Brim, as at S; now let there be any Number of Holes DECFG made through the fame, the Water spouting through each of them, will fall to an horizontal Distance, which is double to the Distances of thofe Holes from the Periphery of a Circle AKB, defcribed about the Length of the Tube, as a Diameter.

A. If this be the Cafe, I eafily perceive why, in the Scheme, the Water spouting from the middle Hole C, falls fartheft from the Tube; for according to you, the Diftance BQ, to which it falls, is equal to twice CK, that is, equal to the Height of the Tube AB; and as this CK is the fartheft Distance from the Circle, the Double thereof BQ muft needs be greater than the Double of any other Distance, and therefore its Water spouts the fartheft.

B. You take the Reafon of the Thing very well ; you may also farther observe, that from two Holes EF, equally diftant above and below the central Hole C, the Water will spout to an equal Distance BP, the Double of EL or FI, which are equal Distances from the Circle: Alfo the Water from G will fpout to O, which is double the Distance GH; and the Water from D will spout to N; for BN is double the Diftance DM from the Circle.

A. I