308 Hydrostatics. 



the value of this addition a/, by the surface of the section made 

 at the water's edge (estimated in square feet), multiplied by the 

 weight of a cubic foot of water. 



When a vessel is sheathed, the bulk of the hull is aug- 

 mented by a quantity, the method of calculating which has 

 Gal.l22.been made known. The effect, therefore, is the same, as if the 

 cargo were diminished by the following quantity, namely, the 

 weight of a mass of water equal to the augmentation of the hull, 

 minus the weight of the materials which compose the sheathing. 

 Accordingly, it may easily be determined how much less or more 

 the vessel would sink. 



425. The weight of a body remaining the same, its bulk may 

 be enlarged at pleasure, by forming it so as to inclose a space. 

 There is no substance therefore so heavy that it may not be 

 made to float. 



426. Since, when the weight of a body is diminished with- 

 out changing its bulk, it must elevate itself with an effort which 

 can be counterbalanced only by a weight equal to that which 

 has been taken from it, it will be seen that this upward pressure 

 of water may be advantageously employed in raising large mas- 

 ses ; in drawing up vessels, for example, from the bottom of bays 

 and rivers, by attaching them to other vessels, floating above, 

 and deeply laden with stones or water, afterward to be thrown 

 overboard. 



Specific Gravities. 



427. In general, if S be the specific gravity of a floating 

 body, or, which is the same thing, the weight in ounces of a 

 cubic foot of this body,t the matter being supposed to be uni- 

 formly distributed, b its bulk, S' the specific gravity of the fluid, 



t Water is the unit to which we refer all substances, except the 

 gases, in estimating their specific gravities. It is immaterial what 

 bulk be used for this purpose, or whether any particular bulk, 

 provided the two in question be equal. A cubic foot of any sub- 



