and their Action on Floating Bodies. 87 



broadside on one of these waves with such force as caused 

 the cargo, consisting for the greater part of sugar, to settle 

 bodily on the port side. Ascending the next undulation, the 

 loosened mass settled with still greater violence on the star- 

 board side and was again thrown over to the port side, 

 where it remained during the voyage, the vessel retaining a 

 port list of about 15*^. All this may be said to have taken 

 place during the passage of one wave. 



17. To arrive at the nature and extent of the wave forces 

 affecting a floating body, it is necessary to investigate 

 the theoretical motions of such a body. For this purpose, 

 suppose the body to be of perfect buoyancy, that is , a body 

 which, its magnitude being inconsiderable with respect to 

 that of the wave, possesses equal mobility with the particles 

 of water on which it rests, so that it accompanies the 

 particles in their motion. This it can only do, if absolutely 

 inconsiderable, but we may suppose a very small object, 

 such as a cork for instance, to approximate towards the 

 motion of a particle of water. From the laws thus deduced, 

 we shall be able to obtain modified views with respect to 

 floating bodies of imperfect buoyancy, that is, of bodies 

 which, being large with respect to the wave, possess unequal 

 mobility with the particles of liquid on which they rest, 

 and which therefore move relatively to them. 



IS. The direction of the force of buoyancy is always at 

 rio-ht ano-les to the nearest surface of the water, whether 

 that surface be horizontal, as in the case of smooth water, 

 oblique, as in a descending stream, or variable, as in waves.*' 



Thusjetf^i^r. 2, plate 1) e /represent the surface of smooth 

 horizontal water, B a floating body in it. Now, the water 

 pressing upon all sides of the body, as shown by the arrows, 

 the lateral pressures on the sides c i and d k counteract each 

 other, and the upward force of buoyancy is counteracted by 

 and is equal to the weight of B. JBut, suppose the water 

 became a descending stream whose inclined surface is ct 6 ; 

 the lateral pressures are now m i and nh ; take p i equal to 

 n k, then the preponderating lateral pressure m p will turn 



* The wording of Archimedes' law, viz. : "that if a solid body be either 

 wholly or partially immersed in a liquid, it is pressed upwards with a force 

 which is equal to the weight of the liquid displaced, and whose point of 

 application is the centre of gravity of the displaced liquid" is incorrect, if 

 by upward is meant veitically upward. A cork, for instance, imuiersed in 

 a wave, will proceed to the nearest point in the wave surface, not necessarily 

 in a vertical direction. 



