172 OUTLINES OF NATURAL PHILOSOPHY. 



The pressure in the narrow tube may be produced, 

 not merely by the addition of a little water, but by 

 the application of any kind of force, such as the 

 working of a piston, &c. If the bottom or lid be 

 made moveable, the pressure on either may be 

 brought to bear on one point of an external body, 

 and may then produce an enormous compression, 

 as is very successfully done in the engine known by 

 the name of BE AMAH'S Press. 



This property of fluids may therefore be said to fur* 

 nish a SEVENTH MECHANICAL POWER. 



. A body immersed into a fluid is pressed 

 upwards by a force equal to the weight of the 

 fluid it displaces, and the direction of that force 

 passes through the centre of gravity of the part 

 immersed. 



The proposition holds, whether a body sink in a fluid 

 or float on its surface. 



When a body floats, the weight of the water displa- 

 ced is equal to the weight of the body. 



253. The difference between the absolute weight 

 of a body, and its weight when entirely immersed 

 in a fluid, is the same with the weight of a quan- 

 tity of the fluid equal in bulk to the body, 



If W be the weight of a body in vactio, (which we 



may suppose to be nearly the same with its weight 



in air), and if W be its weight in water, W W 



3 is 



