656 Transactions. — Miscellaneous 



displaces exactly its own weight of w^ater. This means that 

 it occupies a space from which it has expelled as much water 

 as would weigh exactly the same as itself. It is therefore 

 only necessary to calculate the bulk of that portion of the float- 

 ing body which is below the surface of the water, and then to 

 ascertain the weight of an equal bulk of water, in order to lind 

 out what must be the total weight of the body when immersed 

 to the given draught. 



We may vary the statement of this principle as follows : 

 A ship placed in water will descend until she reaches a state 

 of equilibrium, or to such a point that the downward pressure 

 of her weight is exactly balanced by the upward pressure of 

 the water. This fact is entirely unaffected by the depth of 

 the water in which she floats or by the extent of surface 

 around the ship. 



The pressure of the water is constant at every point which 

 is at an equal distance below the surface, and it increases in 

 the same ratio as the depth increases. That the extent of 

 surface has nothing to do with the pressure may be seen by 

 the case of a vessel lying at one side of a dock with, say, 1ft. 

 of water between herself and the wall, while there are 500ft. 

 on the off side. She has no tendency to fall towards the quay. 

 Of the increasing density of water as the depth increases, and 

 of the friction upon the surface of a ship when moving, I 

 intend to take no notice, but shall consider the water as exert- 

 ing an equal pressure at every point of the ship's surface 

 below the water-line, and in direction at right angles to every 

 point of such surface. It will always be assumed that we 

 are dealing with still water. 



To be able to deal with the effects of this pressure we must 

 find out a point through which it acts, or at w4iich it all 

 culminates, and then we shall be able to examine its action in 

 giving stability to bodies floating therein. 



At this stage, then, w^e begin to deal with the stability 

 problem. And in the first place let us consider a contrast and 

 an analogy between a body out of water and the same body 

 floating. 



On land, or on any fixed and solid surface, it is the base 

 upon which the body rests which affords it stability. The law 

 of its stability is that a perpendicular from the centre of 

 gravity must fall within the base. The further it falls within, 

 the greater the stability. Consequently, an increase in the 

 area of the base all round the perpendicular adds to the 

 stability. But a knowledge of the latter fact often leads to 

 misconception as to the stability of a ship, it being frequently 

 asserted that " such a ship will be stifi' enough because she 

 has a good flat bottom to stand upon." There could be no- 

 thing more erroneous than this idea. If there is any part of 



