188 THE PRINCIPLE OF ARCIIBIEDES. 



fore less than that upon the lower surface by the weigh 

 of the liquid column abed. This difference bet we 

 the pressure on the lower and upper surface of an im- 

 mersed body constitutes a force which urges th 

 body upwards, and which is called the buoyan 

 of the liquid; the buoyancy is equal to the weig 

 of the volume of the liquid, which is of the sa 

 magnitude as the immersed body. This principle, 

 which by reasoning has been established to hold good 

 for a body of regular form, holds equally good f< 

 bodies of any form, as may be proved by experimen 

 The buoyancy being a force acting upwards, in a dir 

 tion opposite to that in which gravity acts, causes an 

 immersed body to appear lighter than it is: A body (/??- 

 mersed in a liquid loses a part of its weight equal to the 

 weight of the displaced liquid. 



This law is called, after its discoverer, the Principle of 

 Archimedes. 



At the right-hand extremity of the beam of tffi 

 balance the short scale-pan is suspended, and to it 

 fixed, by means of a thin thread, a somewhat larg 

 body, for instance, a pebble weighing a few hundred 

 grammes; weights are placed in the scale-pan on the 

 left, until the whole is in equilibrium. The stone is now 

 immersed in water contained in the vessel which was 

 used for the determination of specific gravity (fig. 

 40, p. 40), and the displaced liquid is received in 

 another vessel. At the moment when the stone dips 

 into the water, the equilibrium of the balance is de- 

 stroyed, and weights must either be taken away from 

 the left-hand scale-pan, or placed in the right-hand 

 one, in order to restore the equilibrium, as represented 



