Naval Architecture and Ship Building 121 



that the word "metacenter" is derived from the Greek work meta, 

 Hmit or goal, and the word center, meaning the Hmit of the position of 

 the center of gravity. 



The position of the metacenter depends upon the geometrical form 

 and dimensions of the ship. Perhaps a homely illustration may clarify 

 this conception of the metacenter which appears to be a mystery to many 

 laymen. Suppose you take an ordinary rocking chair with a circular 

 rocker, (rocking chairs are not made with circular rockers as a rule, but 

 they are sufficiently near the circular for the purposes of my illustration). 

 The rocker is rather flat and the center of its circle is well above the seat 

 of the rocker and even above the arms. So ordinarily the center of the 

 curvature of the circular rocker is above the center of gravity of the chair 

 and the latter is above the center of gravity of the chair and the latter 

 stays upright. The flatter the rocker and hence the higher the center of 

 the circle, the stiffer the rocker is. If, however, one takes a table and 

 secures it on the seat of the chair so that the plane of the table is above 

 the center of curvature of the rocker, and then proceeds to pile weight 

 upon the table, it is only a question of time when the center of gravity of 

 the combination will rise above the center of the rocker circle, in which 

 case the chair will promptly capsize. Before loading the combination 

 with top weight, the chair if tilted will oscillate quickly and sharply. 

 As we pile on weight, the period of oscillation will increase with 

 decrease of metacentric height, and the period will increase indefinitely 

 as we approach a metacentric height of zero, the motion of oscillation 

 becoming more and moire sluggish. 



After Bouger developed the conception of mathematical methods for 

 calculating the position of the metacenter of a ship, Atwood, an English- 

 man, carried the matter further by calculating the righting moment or 

 righting tendency whic,h would tend to bring the vessel upright if twisted 

 over in smooth water. For many years the metacentric conception, 

 which applies only to initial conditions, appears to have been sufficient 

 for practical purposes. About fifty years ago, however, there was a 

 marine disaster which brought home very strqngly to naval architects 

 the fact that t^ere was another factor involved in stability. You may 

 recall that in the Qvil War the United States built a number of monitvors 

 as developed by Ericsson, the monitor being essentially an armored 

 vessel with a very low freeboard and carrying its guns in turrets on a 

 deck not more than two or three feet above the water. The Ericsson 

 monitor was purely a steamer, being without sail power. A distinguished 

 English officer. Captain Cowper Coles, took up with enthusiasm the 

 monitor idea, and as a result of his campaign there was built in England 

 a large low freeboard vessel of the monitor type, called the Captain, 



