HYDROSTATICS. 179 



. A body may be so constituted, that in 

 every position the centres of gravity of the whole, 

 and of the part immersed, are in the same vertical 

 line, and in such a body the equilibrium cannot 

 be disturbed by any force which only tends to 

 make it revolve on an axis. 



A homogeneous sphere is a body of this kind, and so 

 also is a cylinder floating with its axis horizontal. 

 These have no tendency to maintain one position 

 more than another, and their equilibrium is called 

 the equilibrium of indifference. 



263. Some floating bodies, when their equili- 

 brium is disturbed, return to their position after a 

 few oscillations backwards and forwards. Others, 

 when their equilibrium is ever so little disturbed, 

 do not resume their former position, but revolve 

 on their centres of gravity, till they come into 

 another position, when they are again in equili- 

 bria. 



The equilibrium in the first case is said to be stable, 

 in the latter case to be unstable. In this last case, 

 the bodies are said to overset. 



264. When a floating body is made to revolve 

 from the position of equilibrium, if the line of 

 support (that is, the vertical through the centre 

 of gravity of the immersed part) move so as to be 

 on the same side of the line of pressure (or the 



M 2 vertical 



