Withy. — On the Stability of Ships. 675 



to get at we are able to deduce from them the required infor- 

 mation — viz., that the centre of gravity must be at a given 

 spot ; otherwise the result of the application of the known 

 powder could not have been precisely what it was. 



The device made use of is to put on board and move a 

 know^n weight through a measured distance across the vessel, 

 and to note its effect as shown by the change produced in the 

 vessel's inclination. The ship must be in smooth water, and 

 there must be no wind. She must be moored at each end 

 only ; the ropes must be attached at the centre-line, and must 

 not be hauled too taut. Everything must be in its sea-going 

 position, and only enough men to shift the weights must re- 

 main on board ; those who stay must, when any measurement 

 is being taken, range themselves in the same position on each 

 occasion. These precautions are for the purpose of preventing 

 any force operating to careen the vessel except that of the 

 weights to be moved. 



Square cast-iron weights with hand-hole and bar are very 

 handy as the power to be used for careening. They should be 

 stacked u-p in rectangular form as near to the bulwarks amid- 

 ship as possible. A board must be fixed up and down in the 

 hatchway, and a plummet or pendulum attached to it for re- 

 cording the angle of heel. "When all is ready, and the men 

 are at their station, the observer notes the exact position. 

 The weights are then carried across the deck and stacked up . 

 as far from their former position as possible. The exact dis- 

 tance between the centres of the two positions is taken. This, 

 when multiplied by the weight moved, will give the moment 

 of the power applied. The men return to their station, and 

 the observer notes the change of inclination. This ends the 

 experiment ; the draught of water at each end of the ship is 

 carefully taken and drawn across the sections on the drawings. 

 The draughtsman now calculates the buoyancy, centre of 

 buoyancy, and metacentre at the given draught when upright, 

 and carefully ascertains the moments of the solids of immer- 

 sion and emersion for the inclination produced by the power 

 applied. From these facts he deduces the metacentric height 

 necessary to account for the change of inclination, and, setting 

 it down, from the metacentre obtains the position of the centre 

 of gravity of ship and w^eights combined. The weights used 

 for careening are finally allowed for, and then he knows the 

 position of the centre of gravity of the ship alone. The 

 operation all through is certainly a great triumph of ingenuity, 

 skill, and accuracy. 



This method could be applied to a loaded ship if desired, 

 or, after making the above experiment, a prediction of the con- 

 dition of such a ship if loaded with any homogeneous cargo 

 could be made by calculating her contents of holds and their 



