350 



REPORT — 1844. 



The horizontal translation of water particles in tlie negative wave presents 

 considerable resemblance to the corresponding phsenomenon in the positive 

 wave. All the particles of water in a given vertical plane move simultane- 

 ously with equal velocities backwards in the opposite direction to the trans- 

 mission, and repose in their new planes, at the end of the translation ; with 

 this modification, however, that this state of repose is much disturbed near 

 the surface by those secondary waves which follow the negative wave, but 

 which do not sensibly agitate the particles considerably removed from the 

 surface. (See Plate LII. fig. 9.) The path is the ellipse of the positive wave 

 inverted. 



The following measures may be useful. In a rectangular channel ■!■ inches 

 deep in repose and 8 inches wide, a volume of 72 cubic inches is withdrawn ; 

 the depth of the negative wave below the plane of repose is gths of an inch deep, 

 the translation throughout the lower half-depth is 2^ inches, and diminishes 

 from the half-depths upwards, settling finally at the surface at If inch from 

 the original position of the superficial particle. 



The form of surface of the anterior half of the negative wave resembles 

 closely the posterior half of a positive wave of equal depth, but the posterior 

 half of the negative wave passes off into the anterior form of a secondary 

 wave which follows it. 



After translation the superficial particles continue to oscillate, as shown in 

 Plate LII. figs. 9, 10, in the manner hereafter to be described, as a phaenomenon 

 of the train of secondary waves. 



The characteristics of this species of wave of the first order are, — 



(1.) That it is negative or wholly belo\v the level of repose. 



