658 Transactions. — Miscellaneous. 



stances there can be no equilibrium, and the body, therefore, 

 cannot remain at rest. This being so, the weight of the body 

 must force it to descend in the water at one end until a 

 sufficient movement has been made to change the buoyancy 

 conditions enough to bring the two pressures into the same 

 line. From the fact that no such movement did take place it 

 is evident that the two forces were already in opposition, and 

 had established an equilibrium. This proves that our two 

 suppositions were correct, and that the body obeys the same 

 law in water as when suspended. 



It can be shown, however, by experiment. If a small 

 weight is placed on one end of the model it at once sinks a 

 little deeper at that end. By sinking deeper it has gamed a 

 little more buoyancy there, and evidently just enough to 

 counterbalance the additional weight placed upon it, seeing 

 that it soon comes to rest in the new position . It did this be- 

 cause its centre of gravity had been disturbed, and therefore 

 the perpendicular from it fell a little outside the former line of 

 upward pressure. The result of this gain of buoyancy at one 

 end was to cause the culminating point of upward pressure to 

 follow in the same direction until the two forces were again 

 directly opposed to each other vertically. This culminating 

 point will hereafter be spoken of as the " ujetacentre." 



Before leaving this portion of the subject it may be as well 

 to say a few words upon the meaning of the term " centre of 

 gravity." The words mean centre of weight, but they must be 

 understood to stand for centre of moment of weight. The 

 term would be complete if we had to deal with a plain bar of 

 metal, or a plank of the same sectional area throughout. The 

 centre of gravity of such bodies would be at the half-length, 

 and if they were divided at this point the two halves would be 

 equal in weight. In addition to being of the same sectional 

 area throughout they are homogeneous in substance. But a 

 ship possesses neither of these peculiarities, and it is found 

 that neither is her centre of gravity at the centre of her length, 

 nor would her two parts, supposing her to be divided at this 

 point, equal each other in weight. Supposing that this model 

 was made quite solid and of a homogeneous piece of wood, 

 and that it was sawn across at its centre of gravity, it is not 

 at all likely that the two portions would be equal in weight. 

 The reason is that she is not equal in sectional area through- 

 out her length. I think you will see this clearly if you con- 

 sider the case of a ship lying at the wharf loaded. Let her 

 centre of gravity in the fore-and-aft direction be ascertained 

 and marked on her side. Let it be assumed, if she was 

 divided at this point, that the two parts would be equal in 

 weight, on the supposition that the centre of weight must be 

 at the centre of gravity. In order to show that this need not 



