ships' sail-caerying power and steadiness. 143 
With a wholly submerged body equilibrium happens when 
centre of gravity of displacing body is in the perpendicular of 
the centre of gravity of the fluid displaced. This centre termed 
the "centre of buoyancy," is the centre of support. 
Mode of calculating the position of a centre of gravity, or find- 
ing it by experiment. 
"When the centre of gravity of the mass is perpendicularly above 
the centre of buoyancy the equilibrium is unstable ; when below, 
it is stable. Measure of force of stability. 
With a body floating at the surface a new condition arises, 
under which stable equilibrium may subsist, though the centre of 
gravity be above the centre of buoyancy. 
This explained by the change of position imposed on the centre 
of support when the body is inclined, the surface of flotation 
giving increased displacement and support to the depressed side, 
diminished displacement and support to the elevated side. Mode 
of calculating the result of this condition. 
Analogy of body resting on rockers, as a cradle, where, though 
inclination shifts centre of gravity to one side of the original point 
of support, the rocker supplies a new point of support shifted still far- 
ther in the same direction, thus securing return to original position. 
The horizontal distance between the "vertical," drawn through 
the centres of gravity and support, measures the "righting force," 
or, as it is termed, "righting couple," or the "moment of sta- 
bility." Explanation of the terms "couple" and "moment." 
The compound condition thus arising is expressible in terms of 
an "effectual" or "virtual" point of support, termed the "meta- 
centre ;" a point in or belonging to the body such that, if used as 
a point of suspension for the body when removed from the water, 
it will give to the body the same tendency to become upright, as 
when afloat. The body is in neutral equilibrium if its centre of 
gravity be brought to its metacentre; and will be in unstable or in 
stable equilibrium, according as the centre of gravity be above or 
below the metacentre. 
Simplest case of metacentre, that of a cylinder or other body 
turned in a lathe ; where the metacentre is plainly in the axis of 
the body. 
Mode of determining position of metacentre for other bodies. 
Character of its gradual changes of position for bodies of less 
regular form when the inclination is increased. 
T 2 
