222 OF FLOATATION AND THE SPECIFIC GRAVITY OF BODIES. 



these two pressures are equal and opposite to one another, and must 

 therefore be in a state of equilibrium, in which case, the body will 

 remain at rest. 



Hence, the truth of the inference is manifest with respect to a 

 vertical pressure ; but it is equally true in reference to a motion 

 horizontally and obliquely; for the horizontal pressures are obviously 

 equal to one another, and they are in opposite directions; therefore, 

 they are in equilibrio with one another, and no motion can take place. 



And again, with regard to the oblique pressure, it is evidently 

 compounded of a vertical and horizontal one ; but we have just 

 demonstrated that these are equal and opposite; consequently, the 

 body can have no oblique motion, it must therefore remain at rest in 

 any place and in any position. 



If the specific gravity of the immersed body be greater than that of 

 the fluid, the pressure downwards will exceed the pressure upwards ; 

 consequently, the weight of the body will overcome the resistance of 

 the fluid under it, and it will therefore sink to the bottom. 



But if the specific gravity of the body be less than that of the fluid, 

 the pressure upwards will exceed the pressure downwards ; therefore, 

 the buoyant principle will overcome the weight of the solid, and it 

 will rise to the surface of the fluid. 



246. INF. 2. If a solid body be immersed in a fluid, and the whole 

 mass be in a state of equilibrium : 



The pressure upwards against the base of the body, is 

 equal to the weight of a quantity of fluid of equal magnitude, 

 together with the weight of the superincumbent fluid. 



247. INF. 3. If a solid body be placed in a fluid of greater or less 

 specific gravity than itself : 



The difference between the pressures downwards and up- 

 ivards is equal to the difference between the weight of the 

 solid and that of an equal bulk of the fluid. 



248. INF. 4. Heavy bodies when placed in fluids have a twofold 

 gravity, the one true and absolute, the other apparent or relative. 



Absolute gravity is the force with which bodies tend 

 downwards. 



By reason of this force, all sorts of fluid bodies gravitate in their 

 proper places, and their several weights, when taken conjointly, 

 compose the weight of the whole ; for the whole is possessed of 

 weight, as may be experienced in vessels full of liquor. 



