72 



MR RUSSELL'S RESEARCHES IN HYDRODYNAMICS. 



Although this experiment does not give accurate measures of force due to 

 various velocities, it shews simply what was intended, the manner in which the 

 force of horses is exerted to " overcome the wave" (as it is called). The following 

 Table is made up of very correct experiments, continued through considerable 

 spaces, upon the same basin of fluid, and with the vessel which is named the 

 Raith in Part III., the weight of the vessel and load being = 10,239 lbs. 17th 

 October 1834. 



The resistance here is gi-eater at G miles an hour behind the wave, than at 9 miles 

 an hour upon it ; and the resistance at lOf miles, is little more than at SA mUes 

 an hour. 



It is easy to see how the wave influences the resistance in the cases where the 

 vessel has been raised upon it, and is drawn along at precisely the same velocity ; 

 but it is perhaps not quite so clear at first sight what are the phenomena which 

 accompany velocities that are greater than that due to the wave, because, in that 

 case, the vessel would leave the wave behind. But it should be observed, that a 

 new wave is fonned at every successive instant by the motion of the vessel 

 through the water, whatever be the velocity of its motion ; for the displaced fluid 

 thrown aside at the bow, generates a series of waves, which move with a less ve- 

 locity than the vessel, and faU back to a position behind the bow. The displaced 

 fluid, which, in the case of motion with a less velocity than that of the wave, 

 passed foi-ward before the vessel, causing an extensive accumulation, cannot now 

 pass forward with a velocity greater than that due to the depth and to the Avave, 

 and is therefore left behind, to fill up the vacuity which will remain when the 

 stem of the vessel shall have passed on. The displaced fluid is therefore pushed 

 aside by the bow of the vessel, and forms lateral accumulations on both sides 

 of it, in the form of a continuous wave, upon the ridge of which the centre of 

 the vessel is sustained in a position of station of stable equilibrium. The buoy- 

 ant force of this ridge is the cause of the diminished anterior section of resist- 

 ance. 



