gg MR RUSSELL'S RESEARCHES IN HYDRODYNAMICS. 



genesis and motion of such waves, and the natm-e of their interference witli the 

 resistance of the tiiiid. 



Section III. On the Laws which Regulate the Genesis and Propagation of The 



Progi-essive Wave which is created hy the Motion of a Floating Body. 



It is very necessary that The Wave be carefully distinguished from certain 

 elevations on the surface of a fluid which may liliewise be inckided under the ge- 

 neric title of Wave, as observers who do not make this discrimination will be led 

 into great confusion. I have observed at least four species of Wave, — ^the Ripple 

 or Dentate Wave,— the Oscillatory Wave,— the Surge Wave,— and " The Wave" 

 "par excellence," the solitaiy, progressive, great wave of equilibrium of the fluid. 

 In regai-d also to the vessel, I have obsei-ved several waves. The Great Primary 

 Wave of Displacement, — ^the Secondary Wave of Unequal Displacement, — the 

 Great Posterior Wave of Replacement, — and the Secondary Waves of Replace- 

 ment. It is the Great Prmiary Wave of Displacement which alone belongs to the 

 species of the wave Avhich I am now to examine. 



The wave has been generated in two ways. By the addition of a solid to a 

 limited portion of quiescent fluid, and by the addition of a given quantity of fluid. 

 A loaded vessel being suddenly drawn with considerable force towards the mouth 

 of a narrow channel, sends forward the displaced water into it in the form of the 

 wave. A vessel being in the course of its motion made to vary suddenly, either 

 made to move more rapidly or more slowly, or suddenly stopped, will send for- 

 ward a sensible wave ; and at all times, in smooth Avater, when moving with a 

 velocity less than that of the wave, there wiU be perceived a series of waves pre- 

 ceding the vessel. If, also, there be made, by means of a sluice or otherwise, a 

 sudden and considerable addition to the waters of a limited channel, the elevation 

 ■svill be transferred along the surface in the form of the wave. 



It was found that the mode of the genesis of the wave, whether by a large 

 or small vessel, by a long or short vessel, by a shai-p or obtuse vessel, by a deep or 

 a shallow vessel, whether by the addition of a quantity of water in one manner or 

 in another manner, that the mode of genesis did not in any way, except in mag- 

 nitude, as a great or small wave, produce any modification of form or velocity in 

 the resulting wave. It was remarkable, also, that the velocity of the motion of 

 the generating body did not in any way affect the velocity of the resulting wave, 

 a wave, for example, of 8 miles an hour being produced aUke from bodies moved 

 at the rate of 2, 5, 6, and 12 miles an hour. 



A very simple and early observation convinced me that the A^elocity of the 

 propagation of the wave was owing chiefly to the depth of the fluid. After having 

 propagated a given wave that had a velocity of 8 miles an hour, it was traced to 



