Withy. — On the Stability of Ships. 657 



a ship which may be considered at all analogous to a base it 

 is the water-level section, and an increase of its area adds 

 to stability. The form of the bottom, it is true, has its influ- 

 ence on stability, but flatness of bottom in a sea-going vessel 

 tends to reduce it. The method of a ship when floating is in 

 this respect entirely in contrast with that of a body resting on 

 the ground. 



The analogy appears when we consider the case of the 

 body out of water when suspended from a point. The law of 

 its stability in these circumstances is that its centre of gravity 

 will hang perpendicularly below the point of suspension. Let 

 us make use of a model to illustrate this analogy. It will be 

 observed that I have in anticipation found its centre of 

 gravity, and have screwed opj)Osite to the spot a small eye by 

 which to hang it up. A short definition of the term " centre 

 of gravity " may be given as follows: It is that point from 

 which if the body be conceived to be suspended it will remain 

 in equilibrium in any position. This model cannot be hung 

 from the actual point, because it is within its own substance ; 

 but by the law of suspension the centre of gravity must be 

 somewhere in the vertical line below the eye. The model 

 hangs horizontally lengthwise, and the deck hangs vertically, 

 so that the centre of gravity must be at the point at which the 

 perpendicular would cut the half-breadth line. This experi- 

 ment serves to show that we can by this means identify the 

 point in the fore-and-aft, vertical, and athwartship directions. 

 That the model freely chooses its present position is shown by 

 its prompt return to it if disturbed. I will now place it in the 

 water and you will see that it descends, as before stated, until 

 it arrives at a position of equilibrium. If I depress it at either 

 end it rises again directly the pressure is removed. The 

 analogy consists in the fact that the body has a preference for 

 this exact position just as it had for another when suspended. 

 Why is this ? May it not be reasonably inferred that when 

 floating there is an invisible but equally definite point of suspen- 

 sion to that which was provided by the hook upon which I 

 placed it just now ? Is it not equally reasonable to suppose 

 that it obeys the same law, and will not remain at rest until 

 its centre of gravity falls into a vertical line passing down- 

 wards from this invisible point of suspension ? This is the 

 fact of the case, and the point of support is that at which the 

 upward pressure of the water culminates. If this is not quite 

 evident let us demonstrate it by supposing that these two 

 points are not so situated, but that the upward pressure is 

 acting perpendicularly a little way from the centre of gravity. 

 It will follow from this supposition that we have the weight 

 pressing down in one line and the buoyancy up through 

 another, not in the same lateral position. Under these circum- 

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