148 HTDROKINETICS. 



256. Volume Discharged under a Constant 

 Head. To find the volume discharged in a given 

 tune under a constant head, multiply the area of 

 the orifice by the velocity, and this product by the 

 number of seconds. 



(a.) Suppose that as soon as the water escapes it freezes and re- 

 tains the form and size given it by the aperture. It will then be 

 evident that the water escaping in one second will form a prism 

 whose section will be the area of the orifice and whose length will be 

 the same as the velocity of the jet. The product of these dimensions 

 will give the volume of the imaginary prism, one of which is formed 

 every second. Care must be had that the velocity and the dimen- 

 sions of the orifice are of the same denomination. The theoretical 

 result computed as above directed, will exceed the amount actually 

 discharged. Why ? (See Appendix E.) 



257. The Flow of Liquids through Hori- 

 zontal Pipes. When liquids from a reservoir are 

 made to flow through pipes of considerable length, the 

 discharge is far less than that due to the head. 

 This is chiefly owing to the friction of the liquid particles 

 against the sides of the pipe. A horizontal inch-pipe 200 

 feet long will not discharge much, if any, more than a 

 quarter as much water as a very short pipe of the same 

 size, the head heing the same. Frequent and abrupt 

 bends in the pipe retard the flow, and must be provided for 

 by an increase in the size of the pipe, or an increase of 

 pressure. 



258. The Flow of Rivers. The friction of a 

 stream against its solid bed fortunately retards the velocity 

 of the water. Otherwise the velocity of the current at 

 the mouth of a river, whose head is elevated 1000 feet 

 above its mouth, would be about 170 miles per hour. 

 Such a current would be disastrous beyond description- 



