HYDROKINETICS. 153 



the wheel B and the outer case D. This collar, called a register 

 gate, may be turned about its axis by the action of a pinion, P, 

 upon teeth placed upon the circumference of C. By means of the 

 register gate, the size of the chute may be reduced and the amount 

 of water used thus diminished. The water passages, to and from 

 the wheel, should be of such a size that the velocity of the water 

 running through them shall not exceed one and a half feet per 

 second. 



266. Lateral Pressure of Running Water. 



If water could flow through a pipe unimpeded (v = 8.02 

 V h)> there would be no lateral pressure. But as the 

 velocity is lessened by friction and other causes, this lateral 

 pressure begins to be felt ; when the velocity is destroyed, 

 lateral pressure has its full force again. Thus, a pipe is 

 less likely to burst when carrying running water than when 

 filled with water at rest. 



267. Bursting Pressure. If a current of water 

 flowing in a pipe be suddenly stopped, much of its mo- 

 mentum will be changed to lateral or bursting pressure. 

 This takes place whenever the faucet of a water-pipe is 

 suddenly closed. Plumbers frequently leave the ends of 

 such pipes in a vertical position so that a quantity of air 

 may be confined between the closed end of the pipe and 

 the water below. This air by its elasticity acts as a pad or 

 cushion, thus lessening the suddenness* of the shock and 

 preventing accidents. 



(a.) This principle is practically applied in the " hydraulic ram," 

 a contrivance by which the impulse of running water when sud- 

 denly checked may be used to raise a part of the water through a 

 vertical distance greater than the head. 



EXERCISES. 



1. A stream of water issues from an orifice at the bottom of a 

 vessel containing water 169 feet deep. Give the velocity of the 

 stream ? 



