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Hydrostatics.

Gravity, it could have no Force to dis-place any Particles of the Fluid, and sinktherein.

XV. If any heavy Body F, lighter than anequal Bulk of the Fluid, be placed on its Sur-face , it will Jink or descend therein , till it hasremoved or displaced so much of the Fluidwhose Weight is equal to that of the Body;For then the Pressure upwards and down-wards on the under Surface of the Body isequal; and consequently the Body will bethere quiescent, or in Fquilibrio with theFluid. Hence the whole Solid is to the im-mersed Fart , as the Specific Gravity of theFluid to that of the Solid (LVIII).

XVI. If

ii. Again ; because B : b :: A s : a S, it appearsthat the Bulk. or Magnitude of Bodies will be as theAbsolute Weights directly, and Specific Gravities in-versely. Or the Magnitude of any Body is had bydividing its Absolute Weight by its Specific Gravity,jpl. 5 CIV. (LVIII) i. This Cafe is not strictly true but in Va-

Fig. 12. cuo ; for in the Air such a Body maybe consider’d asfustain’d in two Mediums, viz. Air and Water ; in oneof which it will sink or descend, and in the other rife.And therefore to represent the true State of this Matteruniversally, we must raise a general Theorem in theManner following: Let AB CD be a Vessel filledfirst with an heavy Fluid to the Level E F, and fromthence with a lighter Fluid to A B. Suppose the So-lid X sustain’d by those two Fluids; let the Part in theheavier be call’d A, and that in the lighter B ; and letthe Specific Gravities of the heavier and lighter Fluidsbe as a and b.

2. Then since the Part A displaces a Bulk of theFluid equal to A, the Absolute Weight of that Bulk ofFluid will be A a, (by Annot. LVII. Art. io.) and for

the