Withy. — 0?i the Stability of Ships. 655 



The sad fatalities allnded to have greatly increased the 

 number of those who have studied the principles governing the 

 stability of ships, and scarcely a year of the last ten has passed 

 without one or more papers being read before the Institution 

 of Naval Architects. The principal value of these has been 

 that they have introduced various methods by which the cal- 

 culations can be greatly shortened, and their application thus 

 rendered more generally possible. My object in reading this 

 paper is not to explain the detailed calculations, but to en- 

 deavour to popularise a knowledge of the principles of stability 

 by stripping the subject of its technicalities, and by making 

 free use of simple and familiar models and diagrams. 



As a preliminary to these explanations it will be desirable 

 to distinguish between two terms — "steadiness" and "sta- 

 bility " — which are sometimes confounded. A ship which rolls 

 considerably is an unsteady ship ; but it does not follow 

 that she possesses a small amount of stability. Quite the 

 contrary may be the case, and, if her rolling is short and quick, 

 it is very probably caused by having too much. The explana- 

 tion of this apparent contradiction is that a stable vessel does 

 not endeavour to stand upright, but to place herself at right 

 angles to the surface of the water in which she is for the 

 moment floating. If she happens to be amongst waves this 

 tendency leads to a continual change of position ; if she is in 

 smooth water, and acted upon by a beam wind, she endeavours 

 for the same reason to place herself at right angles to the sur- 

 face of the water, which, being horizontal in this case, would 

 be the upright position. Seafaring men know well that quick 

 rolling is promoted by the stowage of heavy weights low down 

 in the hold, but they will readily see that this operation, by 

 lowering the centre of gravity, has increased the stability. On 

 the other hand, very long rolling with slow recovery probably 

 indicates a deficiency of stability. " Steadiness" is the quality 

 of resistance in a ship to the tendency of waves to make her 

 roll from side to side, while stability is the quality of re- 

 sistance 10 the force of the wind (or of some force outside of 

 and above the water) which tends to make her incline to one 

 side, or, as sailors term it, to " take a list." Steadiness is 

 most desirable in a war-ship, to enable her to take good aim 

 with her guns ; and in a passenger-vessel adds greatly to the 

 comfort of passengers. x\t the same time, all vessels should, 

 for the sake of safety, not only possess a fair amount of stability 

 at snail angles, but should have a power of recovery from the 

 very considerable inclination produced by sudden squalls. 

 This quality also stands them in good stead when their cargoes 

 have been badly shifted by stress of weather. 



As another preliminary it will be necessary to define " the 

 law of flotation." It may be stated thus : Any floating body 



