396 ON THE FRICTION AND 



tides may be carried away by means of the increased velocity, and 

 the bed of the river may be deepened. 



Where a river bends in a considerable degree, it is generally re. 

 marked that the velocity of the water is greater near the concave 

 than the convex bide of the flexure, that is, at the greatest distance 

 from the centre of its curvature. This effect is probably occasioned 

 by the centrifugal force, which accumulates the water on that side; 

 so that the banks are undermined, and the channel is deepened by 

 its friction. Some authors have been led to expect that the velocity 

 would be greater nearest to the convex bank, because the inclina- 

 tion of the surface must be a little greater there : but the efiect of 

 the accelerating force, in any short distance., is inconsiderable, 

 and it is more than compensated by the want of depth. It may 

 easily be understood, that all angles and flexures must diminish the 

 general velocity of the river's motion, and the more as they are 

 the more abrupt. 



It has sometimes been imagined, that because the pressure of 

 fluids is propagated equally in all directions, their motions ought 

 also to diverge in a similar manner ; but this opinion is 1>\ no means 

 tvell founded, even with respect to those particles which receive their 

 motions in an unlimited reservoir from the impulse of a stream 

 which enters it. An experiment, which sets this fact in a clear 

 point of view > . was made long ago by ilauksbee. He produced 

 a very rapid current of air, by means of a vessel, into which 

 three or four times as much air as it naturally contained had been 

 condensed by means of a syringe, and causing the current to pass 

 through a small box, in which the bason of a barometer was placed, 

 the mercury was depressed more than two inches in consequence 

 of the rarefaction which the current produced in the air of the 

 box. 



Professor Venturi has also made several experiments of a similar 

 nature on the motion of water : he observes that not only the water 

 in contact with a stream is drawn along by it, but that the air in 

 the neighbourhood of a jet is also made to partake of its motion. 

 When the mouth of a pipe, through which a stream of water is dis- 

 charged, is introduced into a vessel a little below the, surface of the 

 water which it contains, and is allowed to escape by ascending an 

 inclined surface placed opposite to the pipe, and leading over the 



