HYDRAULICS. 



are more agreeable to theory than those that con- 

 cern resistance. VINCE has found by experiment, 

 that the force of the percussion of a fluid on an 

 oblique plane, varies nearly as the sine of the incli- 

 nation of the plane ; but their resistance to a plane 

 moving in a fluid, is not subject to any law that ad- 

 mits of a simple expression. Encyc. Britan. 3d edit. 

 Article Hydrodynamics, p. 763. 



SECT. IV. 



UNDULATION OF FLUIDS, OR THE FORMATION OF 

 WAVES. ' 



301. WHEN the surface of water is unequally 

 pressed on, in parts contiguous to one another, the 

 columns most pressed on are shortened, and sink 

 beneath the natural level of the surface, while 

 those that are least pressed on are lengthened, and 

 rise above that level. 



As soon as the former columns have sunk to a 

 certain depth, and the latter have risen to a certain 

 height, their motions are reversed, and continue 

 so, till the columns that were at first most depres- 

 sed have become most elevated, and those that 



O 2 were 



