660 Transactions. — Miscellaneous. 



Let Uo next suppose that we could freeze the water which 

 had been introduced into the cavity, and that we could then 

 lift out the mass and handle it without its melting; it is 

 evident that it would represent in bulk, ni form, and in weight 

 the water displaced by the ship. It would then be possible, 

 if we could balance this mass in different positions, to ascer- 

 tain the location of its centre of gravity. This point would be 

 the one which I have alluded to as the centre of buoyancy. 



Let us perform in another way the equivalent of the sup- 

 posed operation. I have here a model of the under- water 

 portion of H.M.S. " Captain," representing just such a mass of 

 ice as that supposed above. It is a homogeneous piece of pine, 

 and has a small eye inserted in one side, opposite to its centre 

 of gravity ; and you will observe, when it is suspended, that 

 its longitudinal centre-line lies horizontally, while its flat 

 surface, representing the water-level, hangs vertically. It 

 follows, as before shown, that the centre of gravity must be 

 at the intersection of the longitudinal centre-line with a per- 

 TDendicular drawn from the point of suspension. 



Of course, in actual practice the foregoing freezing experi- 

 ments are impossible, and the knowledge desired is therefore 

 obtained by calculation from the vessel's lines and sections. 

 The model before you, however, agrees exactly with the calcu- 

 lations made for the " Captain," and therefore shows that the 

 freezing supposition was safe as an illustration. 



Having now explained the nature of the centre of bttoy- 

 ancy, we may proceed further with our subject. We shall 

 find that it will simplify the consideration of tliis question, 

 and materially assist us as we go forward, if we always clearly 

 separate the question of stability, in our minds, into two 

 parts — namely, that of the ship pressing downwards in the 

 first place, and that of the water pressing or buoying upwards 

 in the second place. 



With this proviso, I will ask you to consider what changes 

 are effected by careening a vessel from the upright position. 

 Let us look first at that of the ship pressing downwards. It 

 will be necessary to assume that no considerable part of her 

 fittings or lading shall break away and fall to leeward when 

 she is careened. It is then obvious that the fact of her being 

 careened can have made no alteration in the position of her 

 centre of gravity. Indeed, if everything held in its place she 

 might be turned completely over without any alteration taking 

 place in its position. We therefore see that, so far as the 

 action of the ship is concerned, there is no difference caused 

 by careening. She will continue to press downwards with 

 the same energy as before, and through the same point — 

 namely, her centre of gravity. 



We may now pass to the second part — namely, that of the 



