fjgO PHILOSOPHICAL TRANSACTIONS. [aNNO 17q6. 



quired, in both cases, to ascertain these points. When the angles of inclination 

 are very small, to find the ship's stability, it is necessary to measure the successive 

 ordinates or breadths of the ship on a level with the water's surface ; and when 

 the angles of heeling are not limited, but are considered as being of any magni- 

 tude, the requisite mensurations are indeed more troublesome, but are not liable 

 to more errors in execution than in the former case, when the angles are limited 

 to tliose which are evanescent. 



The theorems for measuring the stability of ships, which are founded on 

 assuming the angles of inclination from the position of equilibrium evanescent, 

 explain, in the most satisfactory manner, the principles on which the stability of 

 ships, when heeled to small angles of inclination, is founded ; they also ascertain 

 when ships or other bodies float on the water permanently in a given position of 

 equilibrium, or overset. But this can scarcely ever be an object of inquiry in re- 

 spect ol ships, which are always constructed so as to float upright, even before 

 any ballast or lading has been added to them. 



Mons. Romme, in his valuable work, on naval architecture, intltled L'Art de 

 la Marine, published at Paris in the year 1787, informs his readers (p. 106), 

 that the French ship of the line of 74 guns, called Le Scipion, was first fitted 

 for sea at Rochfort in the year 1779' As soon as the ship was floated in deep 

 water, a suspicion arose that she wanted stability: to ascertain this point the 

 guns were run out on one side, and drawn in at the other ; in consequence, the 

 ship heeled 13 inches, probably meaning at the greatest measure on the side of 

 the vessel : by adding the weight of the men brought to the same side, the 

 depth of heeling increased to 24 inches. This being a degree of instability, 

 which was deemed too great to be admitted in a ship of war, the ship was ordered 

 into port, that some remedy might be applied to the defect which had been dis- 

 covered. M. Romme proceeds to relate, that a difference of opinion prevailed 

 among the engineers respecting the cause of this imperfection in the ship, and 

 the remedies by which it might be corrected. The chief engineer, who was sent 

 from Paris to Rochfort to direct what measures ought to be adopted on this oc- 

 casion, and for rectifying the like fault in two other ships of war, L'Hercule and 

 Le Pluton, was of opinion, that the stability of the ship Le Scipion would be 

 sufficiently increased by altering the quality and disposition of the ballast. The 

 original ballast of the Scipio had been 84 tons of iron and 100 tons of stone ; 

 according to the new arrangement of the chief engineer, the ballast was com- 

 posed of IQB tons of iron and 122 tons of stone. But as a ship of war does not 

 admit of any alteration in the total displacement or immersed volume, to com- 

 pensate for the additional weight of ballast, amounting to 130 tons, the quantity 

 of water with which the ship had been supplied was diminished by the weight of 

 136 tons. This alteration must necessarily have the effect of lowering the centre 



