This may be made clearer by illustration. On Figs. 14 and 15, which show in outline a vessel’s midship section, the vessel being inclined to a small angle, =G= represents the centre of gravity of vessel, and =B= the centre of buoyancy. The water line =W.L.= corresponding to the upright position, in the inclined position becomes =W_{1}.L_{1}.=, and the centre of buoyancy =B= shifts out on the immersed side of the vessel to =B_{1}=. Assuming in the case of Fig. 14 that some external force not involving any shifting of the centre of gravity has produced the inclination, then the weight of the vessel acts downwards through =G=, and the buoyancy of her displacement acts upwards through =B_{1}=, as indicated by the arrows passing through these points. The combined effect of these forces, in this case, is to rotate the vessel towards the upright, _i.e._, it forms a “righting couple.” Fig. 15 illustrates a case of the opposite kind. The angle of inclination may be supposed to be greater than in Fig. 14, and the centre of gravity =G= is much higher in the vessel. The vertical through =B_{1}= is to the left instead of to the right of the vertical through =G=. The effect of the forces in this case is to rotate the vessel in the direction of inclining her still further, and to capsize her—_i.e._, it forms an “upsetting couple.” A line at =G=, therefore (Fig. 14), taken at right angles to the new vertical line, gives the distance which corresponds to the righting arm (=G= =Z=). A similar line at =G= (Fig. 15) represents the upsetting arm. The lengths of these arms when multiplied into the displacement, gives the “moments” at the respective degrees of inclination. The “curve of stability” for a vessel is simply a graphic representation of these arms or moments. When calculated for the various degrees of inclination, they are set off as ordinates along a base line—the righting arms or moments above, and the upsetting arms or moments below, the line—at distances corresponding to the number of degrees in the respective inclinations. A curve drawn through the extremities of these ordinates is the curve of stability.