78 MR RUSSELL'S RESEARCHES IN HYDRODYNAMICS. 



served by a gentleman, who was surprised by the phenomenon, although unable 

 to account for it, " The steam-boat Trenton, on the Delaware, in the United States, 

 by passing over shallow portions with a high velocity, carries with it a body of 

 water sufficient to float her over portions on which she would not have been float- 

 ed if at rest." The body of water was of course the wave, the velocity of the 

 vessel being above 13 miles an hour. 



The navigation of the River Clyde presents excellent examples of the effect 

 of the motion of the wave, and affords ample opportunity for the application of 

 the principles developed in the preceding portions of the paper. 



The wealth of an enterprising commercial community has enabled engineers 

 to convert one of the worst rivers for navigation into a good, although as yet only 

 shallow, channel. When the tide leaves the river, there are not more than six or 

 seven feet of water in many parts of the channel, the wave having a velocity of 

 about 9 miles an hour. Any observer looking attentively from the deck of a 

 vessel on the sloping bank of the river, will see delineated there very distinctly 

 the anterior wave preceding the bow of the vessel, the posterior depression, called 

 by sailors " the suction of the vessel," and the stem surge, as delineated in Plate II. 

 Fig.l, rushing along the bank with fury into the vacuity. It is invariably neces- 

 sary for vessels of considerable size to lower their velocity very much in such 

 places, to prevent their grounding in the depression of the wave. When two 

 vessels pass each other this effect is much more sensible, as at the instant when 

 the waves coincide, their elevation is equal to the sum of both, and when the de- 

 pressions coincide, the hollow is equal to the sum of both ; hence, although both 

 may have floated previously, at the instant of passing either may take the ground, 

 or both. It has on this account been found necessary to enact, that at low- water 

 vessels before passing each other shaU diminish their velocity. But if a velocity 

 greater than the wave, such as 11 or 12 miles an hour, could be attained, there 

 would no longer be any danger of grounding, or of lessening the speed, and thus 

 the navigation be materially improved. Another very curious fact I have also 

 observed on the Clyde, namely, that a vessel of greater power and velocity pass- 

 ing one of less power and velocity, wiU take the less powerful along with her in 

 the depression, the more rapid sending forward the wave before the bow of the 

 slower vessel, so as to obviate the immersion of the bow, and give her the impetus 

 of the stern surge. It is further evident, that in a river so shaUow as the Clyde, 

 velocities of 7, 8, or 9 miles an hour behind the wave are very disadvantageous ; 

 whereas, if a vessel could be started over the wave, her progress would be so 

 greatly facilitated, as to enable her with the same force to reach velocities of 12 or 

 13 miles an hour, when the stern surge would cease, and the danger of taking the 

 ground cease along with it. 



In shallow rivers, where the water is in motion, very singular phenomena 



