CHAPTER II. 



EQUILIBRIUM OF FLOATING BODIES. SPECIFIC 

 GRAVITY. 



24. Upward Pressure, Buoyant Effort. To find 

 the resultant pressure of a liquid on the surface of a 

 solid either wholly or partially immersed. 



Let ABCD be a solid floating in a liquid whose upper 

 surface is EF. Imagine this solid removed, and the space 

 it occupied filled with the liquid, and suppose this liquid to 

 be solidified. It is clear that the result- 

 ant pressure upon this solidified liquid 

 will be the same as upon the original 

 solid. But this solidified mass is at rest 

 under the action of its own weight and 

 the pressure of the surrounding liquid ; 

 and, as its own weight acts vertically 

 downward through its centre of gravity, 

 the resultant pressure of the surrounding liquid must be 

 equal to the weight of the solidified mass, and must act ver- 

 tically upwards in a line passing through its centre of 

 gravity. 



The above reasoning is equally applicable to the case of a 

 body immersed in elastic fluid. 



Therefore, if a solid be either wJwlly or partially im- 

 mersed in a fluid, it loses as much of its weight as is 

 to the iccight of the fluid it displaces.* 



Fig. 21 



* The discovery of this principle is due to Archimedes. (Goodeve, p. 190 ; Gal- 

 braith, p. 49.) 



