144 JOUENAL OF THE PLYMOUTH INSTITUTION. 
These changes expressed by what is termed the metacentric 
curve." 
Corresponding form of rockers" to give equivalent stability. 
Popular error which attributes to this or that vessel the property 
that, while going easily to some considerable angle of inclination, 
great force is required to incline her farther. 
Conditions under which such result is possible, involve abnormal 
form. 
Opposite condition more common, as a consequence of submersion 
of edge of deck, or emersion of turn of bilge. "Low free board" 
and its consequence. 
Eeasons why greater stiffness is practically required and useful 
in small vessels than in large. 
In large vessels sufficient stiffness attainable with centre of 
gravity relatively elevated. 
Height of centre of gravity in large ships practically necessary 
with a view to steadiness in a sea-way — low centre causing great 
unsteadiness. 
General problem of oscillation of floating body. 
General analogy of ship afloat to pendulum. 
''Period" of ship's oscillation depends partly on height of 
metacentre above centre of gravity, partly on lateral distribution 
of weights. 
Character of oscillations when artificially initiated in still water. 
Their gradual extinction by friction and keel resistance. 
Oscillations in a sea-way partly dependent on nature of wave 
motion. 
Wave-motion implies translatory motion of particles, as well as 
slope of surface, and the slope corresponds with the translatory 
motion, so that the slope is virtually level to a body floating on it. 
Those who stand on a raft must stand square to the raft to avoid 
falling — deceptive estimate of wave- elevation consequent on this. 
Old experiment of saucer whirled overhead without spilling 
the water. The surface would carry a stable floating body with 
mast upright to the water surface even while inverted. 
Anatomy of wave, and law of wave slope — ''period" of wave. 
General condition that ship afloat always seeks to place its mast 
square to wave surface. 
Character of consequent oscillations of ship depends on steepness 
of wave, and ratio of " wave period" to "ship's period." 
