in naval affairs, may be defined the vertical vibration which the length of a ship makes about her centre of gravity; or the movement by which she plunges her head and after-part alternately into the hollow of the sea. This motion may proceed from two causes; the waves which agitate the vessel, and the wind upon the sails, which makes her stoop to every blast. The one depends absolutely upon the agitation of the sea, and is not susceptible of inquiry; the other is occasioned by the inclination of the masts, and may be submitted to certain established maxims.