88 LAWRENCE HARGRAVE. 



The wave is the power stored in the water by the wind acting 

 at a distance from the locality where we use it. The propeller is 

 made to act on the water in the trough of the sea where the 

 particles are oscillating towards the wind ; and the deeper the 

 propeller is below the crest of the waves the less movement the 

 particles of water have in that portion of their orbits where they 

 are moving in the direction that the wind is blowing. 



The wind friction is insignificant if we remove the complication 

 of obstructions usually opposed to it. The skin resistance increases 

 as the square of the velocity, and is the principal factor in deter- 

 mining the speed of the vessel. 



It is perhaps unnecessary to point out that there is but one 

 moving part. That when the plane-propeller is doing its best 

 work, the vessel rises and falls without pitching and scending. 

 That no spars are carried. No engine and coal space is required, 

 and the captain and cook constitute the crew. 



The rising and falling on an even keel may seem paradoxical, 

 but it is nevertheless true. Suppose the vessel to be in the trough 

 of the sea with the plane-propeller to windward ; as the wave 

 reaches the centre of buoyancy of the forebody the vessel tries to 

 pitch but the tendency is resisted by the plane-propeller Actuated 

 by the weight of the afterbody. When the crest of the wave 

 reaches the centre of buoyancy of the afterbody, the vessel tries 

 to scend, but is prevented by the weight of the forebody acting 

 on the propeller. When the crest of the wave is under the fore- 

 body the apparatus is a first order lever, and a third order lever 

 when the crest is under the afterbody. 



